USOO6936486B2 (12) United States Patent (10) Patent No.: US 6,936,486 B2 Cheng et al. 45) Date of Patent: Aug. 30,9 2005

(54) LOW VOLTAGE MULTI-JUNCTION (56) References Cited YESTIAL CAVITY SURFACE EMITTING U.S. PATENT DOCUMENTS 5,404,373 A * 4/1995 Cheng ...... 372/50 (75) Inventors: Julian Cheng, San Jose, CA (US); 5,747,366 A * 5/1998 Brillouet et al...... 438/44 Chan-Long Shieh, Paradise Valley, AZ 5,757.836 A * 5/1998 Jiang et al...... 372/96 (US); Guoli Liu. Camarillo, CA (US); 6,014,400 A * 1/2000 Kobayashi ...... 372/96 s s s 6,208.680 B1 * 3/2001 Chirovsky et al...... 372/96 Methal Nene Ranana Murty, 6,393,038 B1 * 5/2002 Raymond et al...... 372/50 oodland Hills, CA (US) 6,542,530 B1 * 4/2003 Shieh et al...... 372/46 6,628,685 B1 * 9/2003 Shieh ...... 372/45 (73) Assignee: JDSU Uniphase Corporation, San 6,642,070 B2 * 11/2003 Jiang et al...... 438/22 Jose, CA (US) 2002/0O30198 A1 3/2002 Coman et al...... 257/103 (*) Notice: Subject to any disclaimer, the term of this * cited by examiner patent is extended or adjusted under 35 Primary Examiner Kevin M. Picardat U.S.C. 154(b) by 134 days. (74) Attorney, Agent, or Firm-Parsons & Goltry; Robert A. Parsons; Michael W. Goltry (21) Appl. No.: 10/299,387 (57) ABSTRACT (22) Filed: Nov. 19, 2002 An optical device with a wavelength of operation, the device (65) Prior PublicationO O Data COmoriSingprising a lightligh emittingitting regiregion Whichhich emitsemitS lighlight at theh wavelength of operation, the light emitting region including US 2004/0095978 A1 May 20, 2004 an active region and a contact region of a first conductivity 7 type and a Second conductivity type wherein the light 8. ------4382, so emittingitting region isIS positionedDOSIt Oned Withinwithi an Opticalptical gaigain caVItity which includes a mirror and an opposed mirror and a 438/42 Substrate Solder bonded using a bonding layer to at least one (58) Field of Search ...... 438/22, 31, 39, of the mirror and the opposed mirror. 438/41, 42, 44, 46, 47; 372/43, 44, 45, 46, 50, 96 31 Claims, 9 Drawing Sheets

U.S. Patent Aug. 30, 2005 Sheet 1 of 9 US 6,936,486 B2

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65 60 DC 64 62 RF Q- 2 63 66 32,34 44 33,35 F.G. 6 61 U.S. Patent Aug. 30, 2005 Sheet 5 of 9 US 6,936,486 B2

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U.S. Patent Aug. 30, 2005 Sheet 9 of 9 US 6,936,486 B2

US 6,936,486 B2 1 2 LOW VOLTAGE MULTI-JUNCTION long wavelength vertical cavity Surface emitting laser which VERTICAL CAVITY SURFACE EMITTING operates at lower power. LASER It is another object of the present invention to provide a new and improved method of fabricating an electrically pumped long wavelength vertical cavity Surface emitting FIELD OF THE INVENTION laser which has improved light emission properties. This invention relates to lasers. It is another object of the present invention to provide a new and improved method of fabricating an electrically More particularly, the present invention relates to Semi pumped long wavelength vertical cavity Surface emitting conductor lasers that generate relatively long wavelengths. laser which generates leSS heat. BACKGROUND OF THE INVENTION It is still another object of the present invention to provide a new method of improving the temperature performance of Vertical cavity Surface emitting lasers (hereinafter an electrically pumped long wavelength vertical cavity referred to as “VCSEL’s”) have become the dominant light Surface emitting laser which has a reduced temperature Source for optical transmitters used in Short-reach local area 15 dependence. networks and Storage area network applications, in which a multi-mode optical fiber is used for data transmission. SUMMARY OF THE INVENTION VCSEL's are low cost micro-cavity devices with high To achieve the objects and advantages Specified above Speed, low drive current and low power dissipation, with and others, a method of fabricating a multi-junction vertical desirable beam properties that significantly simplify their cavity Surface emitting laser with a wavelength of operation optical packaging and testing. In order to extend the appli is disclosed. The method comprises the Steps of providing a cation of VCSEL's to optical networks with a longer reach, first Substrate onto which at least one light emitting region e.g., in Metropolitan Area Networks that are based on is epitaxially grown. In the preferred embodiment, the first Single-mode optical fibers, a long wavelength VCSEL is substrate includes indium phosphide (InP). However, it will needed that can emit Sufficiently high Single mode output 25 be understood that the first Substrate can include other power in the 1.3 um to 1.5 um wavelength range. materials which can be lattice matched to Subsequent layers The Simultaneous requirement of high power and Single grown thereon. mode lasing operation create an inherent contradiction in the The light emitting region includes an active region with a VCSEL design. Whereas high power requires a large effec plurality of quantum Structure layers which Substantially tive gain Volume, Single mode operation mandates a Smaller emit light at the wavelength of operation. In the preferred active area that is typically less than 5 um in croSS Section. embodiment, each adjacent quantum Structure layer in the This contradiction may be resolved by increasing the lon active region is spaced apart by a distance approximately gitudinal extent of the gain Volume while restricting its equal to an integer multiple of one-half the wavelength of lateral area, but in practice this approach is limited by the operation. diffusion lengths of the injected electrical carriers, which 35 limit the thickness of the gain Volume. This, along with the Further, each light emitting region is separated from each Stronger temperature dependence of the lasing mode and the adjacent light emitting region by alternate contact regions of gain peak at longer wavelengths, has effectively limited the a first conductivity type and a Second conductivity type So maximum single mode output power of a long wavelength that each light emitting region can be electrically biased in 40 parallel. In the preferred embodiment, the first conductivity VCSEL to 1 mW or less before the onset of thermal type is opposite in conductivity to the Second conductivity roll-over. type Such that each at least one light emitting region is The use of multiple quantum well Stacks arranged in a Sandwiched between contact regions of opposite conductiv resonant gain configuration (with the quantum wells located ity types (i.e. n-type and p-type regions to form a pn at the anti-nodes) can greatly increase the gain volume and 45 junction). total optical of the VCSEL, but in practice this is limited by A first Stack of alternate layers of a first material and a carrier diffusion to a single MOW stack. One approach for Second material is epitaxially grown on the light emitting circumventing the carrier diffusion limit is to electrically region wherein the first Stack of alternate layerS form a cascade Successive pnjunctions formed by embedding indi distributed Bragg reflector (hereinafter referred to as vidual gain regions (MOW Stacks) between p-doped and 50 "DBR"). A second substrate is bonded to the first stack of n-doped contact layers. The Successive pn junctions are alternate layers and the first Substrate is removed by lapping electrically “shorted” and thus serially connected by means or a Similar technique to Substantially expose the light of Esaki tunnel junctions connecting neighboring p-doped emitting region. In the preferred embodiment, the Second and n-doped contact layers. While this approach can result substrate includes indium phosphide (InP). However, it will in a higher optical output and differential slope efficiencies 55 be understood that the Second Substrate can include other that exceed 100%, its principal drawback is the additive materials with Suitable thermally conductive properties Such nature of the junction Voltages, which require the use of high as gallium arsenide (GaAs), Silicon (Si), or the like. The Voltage drivers that are not readily available at high modu Second Substrate can be bonded using a bonding layer of a lation Speeds. Solder material, for example, or another Suitable material It would be highly advantageous, therefore, to remedy the 60 with the desired properties for adhesion. In Some foregoing and other deficiencies inherent in the prior art. embodiments, the bonding layer can include a window to Accordingly, it is an object of the present invention to allow a Substantial light emission through the Second Sub provide a new and improved method of fabricating an Strate. electrically pumped long wavelength vertical cavity Surface A Second Stack of alternate layers of a third material and emitting laser. 65 a fourth material is epitaxially grown on the at least one light It is an object of the present invention to provide a new emitting region to form a DBR. In the preferred and improved method of fabricating an electrically pumped embodiment, the third and fourth materials include a high US 6,936,486 B2 3 4 index of refraction material, Such as magnesium fluoride embodiment, we are illustrating a Single light emitting (MgF) and Zinc Selenide (ZnSe), respectively, to form a region 23 for Simplicity and ease of discussion. In the dielectric DBR. However, the first, second third, and fourth preferred embodiment, Substrate 26 includes indium phos material layers can include other materials, Such as alloys of phide (InP). However, it will be understood that substrate 26 AlGaAs, silicon oxide (SiO), titanium oxide (TiO), or the 5 can include other materials, Such as gallium areSenide like. Further, the first, second third, and fourth material (GaAs) or the like, which can be lattice matched with layers each have a thickneSS approximately equal to one Subsequent layerS grown thereon. quarter of the wavelength of operation. Light emitting region 23 includes an active region 21 with a plurality of quantum Structure layerS 22 with a band gap BRIEF DESCRIPTION OF THE DRAWINGS wavelength wherein each quantum Structure layer 22 Sub The foregoing and further and more Specific objects and Stantially emits light at the wavelength of operation. In the advantages of the instant invention will become readily preferred embodiment, the wavelength of operation is in a apparent to those skilled in the art from the following range given approximately from 1.2 um to 1.6 um which is detailed description of a preferred embodiment thereof taken typically used in optical communication applications, Such in conjunction with the following drawings: 15 as fiber optical networks. However, it will be understood that FIG. 1 is a sectional view of a step in the fabrication of other wavelength ranges may be Suitable for a given appli a Single junction vertical cavity Surface emitting laser in cation. accordance with the present invention; In the preferred embodiment, active region 21 is Sand wiched between a cladding layer 18 and a cladding layer 24. FIG. 2 is a sectional view of a step in the fabrication of It will be understood that while cladding layers 18 and 24 are the Single junction vertical cavity Surface emitting laser in illustrated as including a single material layer, layers 18 and accordance with the present invention; 24 can each include more than one layer. Further, in the FIG. 3 is a sectional view of another step in the fabrication preferred embodiment, cladding layers 18 and 24 include of the Single junction vertical cavity Surface emitting laser in indium phosphide wherein cladding layer 18 is lightly doped accordance with the present invention; 25 n-type and cladding layer 24 is lightly doped p-type. FIG. 4 is a sectional view of still another step in the However, it will be understood that layers 18 and 24 can fabrication of the Single junction vertical cavity Surface include other Suitable cladding materials with various dop emitting laser in accordance with the present invention; ing configurations. FIG. 5 is a sectional view of a step in the fabrication of In the preferred embodiment, quantum Structure layerS 22 the Single junction vertical cavity Surface emitting laser in include quantum wells. However, it will be understood that accordance with the present invention; layers 22 can include other device structures, such as quan FIG. 6 is a circuit Schematic of an electro-optic circuit of tum dots or similar device Structures with Suitable light the Single junction vertical cavity Surface emitting laser emission properties. In the preferred embodiment, each connected to electronic modulation circuitry in accordance 35 adjacent quantum Structure layer 22 in active region 21 is with the present invention. Spaced apart by a distance 11 chosen Such that quantum FIG. 7 is a sectional view of a step in the fabrication of Structures layerS 22 are Substantially at an anti-node of an a multi-junction vertical cavity Surface emitting laser in optical field in VCSEL 5 (i.e. distance 11 is approximately accordance with the present invention; equal to one half the wavelength of operation or integer multiples thereof). FIG. 8 is a circuit schematic of an electrooptic circuit of 40 the multi-junction vertical cavity Surface emitting laser Further, adjacent quantum Structure layerS 22 are sepa connected to electronic modulation circuitry in accordance rated by a barrier layer 20 as illustrated such that a barrier with the present invention; layer 20a is positioned adjacent to cladding layer 24 and a FIG. 9 is a sectional view of another embodiment of a barrier layer 20b is positioned adjacent to cladding layer 18. 45 In the preferred embodiment, an energy gap wavelength of multi-junction VCSEL in accordance with the present inven each barrier layer 20 is Smaller than the energy gap wave tion; length of each quantum Structure layer 22. Further, in the FIG. 10 is a sectional view of yet another embodiment of preferred embodiment, quantum Structure layerS 22 and a multi-junction VCSEL in accordance with the present barrier layers 20 include alloys of AlGainAS (i.e. InAlAs, invention; and 50 InGaAs, etc.). However, it will be understood that quantum FIG. 11 is a sectional view of still another embodiment of structure layers 22 and barrier layers 20 can include other a multi-junction VCSEL in accordance with the present Suitable light emitting materials and barrier materials, invention. respectively. DETAILED DESCRIPTION OF THE It will be understood that in Some embodiments, barrier 55 layer 20a positioned adjacent to cladding layer 24 can PREFERRED EMBODIMENT include a sufficiently low electron affinity material in order Turn now to FIG. 1 which illustrates a step in the to provide improved electron confinement for active region fabrication of a single junction vertical cavity Surface emit 21. Further, in some embodiments, barrier layer 20b adja ting laser 5 with a wavelength of operation in accordance cent to cladding layer 18 can include a Sufficiently high with the present invention. It will be understood that we are 60 ionization potential material to provide improved hole con illustrating a single VCSEL 5 although generally a plurality finement. The addition of barrier layers 20a and 20b pro of VCSEL's are deposited or grown in blanket layers over vides a higher energy barrier against carrier leakage and an entire wafer so that a large number of VCSEL's are carrier loSS, and improves a high temperature performance fabricated Simultaneously. of VCSEL 5. The method of fabricating single junction VCSEL 5 65 A contact region 19 is positioned on light emitting region includes providing a Substrate 26 onto which at least one 23 adjacent to cladding layer 18. In the preferred light emitting region 23 is epitaxially grown. In this embodiment, contact region 19 includes highly n-type doped US 6,936,486 B2 S 6 indium phosphide (InP). However, it will be understood that implant damage, whose energy States favor the compensa contact region 19 can include other Suitable contact mate tion of cladding region 24. It will be understood that a rials. Further, contact region 19 is illustrated as including a Similar implant region could be created within cladding Single layer for Simplicity and illustrative purposes. layer 18 and adjacent to light path channel 49. However, it will be understood that contact region 19 can Index guide regions 30 and 31 are used to improve a include multiple conductive layers. single-mode output power of single junction VCSEL 5 by increasing the lateral croSS-Section of the gain region while A metamorphic DBR region 16 is epitaxially grown on preserving Single-mode lasing operation by means of mode contact region 19. In the preferred embodiment, metamor Selection measures (mode control) that preferentially phic DBR region 16 includes alternate layers of an AlAS enhance a modal gain of one mode through indeX guiding, layer 15 and a GaAs layer 17. However, it will be understood or alternatively SuppreSS the other competing higher order that layers 15 and 17 can include other suitable reflective modes through higher reflection loSS. By allowing the materials that are Stacked alternately between a high and a actively pumped area to increase while Suppressing the low index of refraction. Further, in the preferred competing modes that emerge through Surface relief embodiment, each layer 15 and 17 has a thickness 74 patterning, higher Single-mode output power is achieved approximately equal to one quarter of the wavelength of 15 through a reduced current density, which leads to lower operation to provide a desired reflective property. Metamor Self-heating and reduced gain Saturation. phic DBR region 16 behaves as a heat Spreading region. The Turn now to FIG. 3 which illustrates another step in the higher thermal conductivity of binary compounds in meta fabrication of single junction VCSEL 5. In FIG.3 and in the morphic DBR region 16 provides a lower thermal resistance preferred embodiment, a dielectric DBR region 28 is posi and better high temperature performance for Single junction tioned on light emitting region 23 and adjacent to cladding VCSEL 5. region 24 by using a dielectric lift-off proceSS. However, it A substrate 10 is bonded to metamorphic DBR region 16. will be understood that dielectric DBR region 28 can be In the preferred embodiment, substrate 10 includes indium deposited using other deposition techniques well know to phosphide (InP). However, it will be understood that Sub those skilled in the art. In the preferred embodiment, dielec Strate 10 can include other Suitable Substrate materials, Such 25 tric DBR region 28 includes alternate layers of a silicon as gallium arsenide (GaAs), Silicon (Si), or other Suitable oxide (SiO) layer 25 and a titanium oxide (TiO) layer 27 Supporting materials with a desired property for thermal wherein each layer 25 and 27 has thickness 74 approxi conductivity, such as a heatsink or the like. Substrate 10 can mately equal to one quarter of the wavelength of operation be bonded to region 16 using techniques well known to those to obtain a desired reflective property. skilled in the art. In the preferred embodiment, Substrate 10 However, it will be understood that layers 25 and 27 can is bonded to region 16 using a bonding layer 12 which include other Suitable dielectric materials of alternate layers includes a Solder material Such as gold/silicon (Au?Si), of a high dielectric constant material and a low dielectric gold/tin (Au/Sn), gold/germanium (AuCe), or the like. In the constant material, Such as alternate layers of magnesium preferred embodiment, bonding layer 12 includes a window 35 fluoride (MgF) and zinc selenide (ZnSe). Further, it will be 14 to allow light emission from light emitting region 23 as understood that the use of a dielectric DBR region in this will be discussed separately. embodiment is for illustrative purposes only. For example Turn now to FIG. 2 which illustrates another step in the DBR region 28 could include alternate layers of aluminum fabrication of single junction VCSEL 5. In FIG. 2, Substrate arsenide (AIAS) and gallium arsenide (GaAs) and be similar 26 is substantially removed to expose a surface 46 of light 40 in structure to metamorphic DBR region 16. emitting region 23 by any technique well known to those Turn now to FIG. 4 which illustrates another step in the skilled in the art, Such as lapping or the like. Further, in the fabrication of single junction VCSEL 5. In FIG. 4, light preferred embodiment an implant region 36 and 37 are emitting region 23 and dielectric DBR region 28 are etched formed within cladding layer 24 and aligned Such that an through contact region 19 to form a mesa 47 and expose a electrically conductive channel is formed which Substan 45 surface 70 and a surface 71. Further, dielectric DBR region tially overlaps the light path channel 49 that extends through 28 is etched through light emitting region 23 to form a mesa light emitting region 23, metamorphic DBR region 16, and 48 and expose a surface 72 and 73. substrate 10, as will be discussed separately. In the preferred Turn now to FIG. 5 which illustrates another step in the embodiment, an indeX guide region 30 and 31 are positioned fabrication of single junction VCSEL 5. In FIG. 5, an within cladding layer 24 adjacent to Surface 46 and aligned 50 electrical contact 35 and 33 are deposited on surface 70 and with window 14 and light path channel 49. Index guide 71, respectively. It will be understood that electrical contacts regions 30 and 31 can include, for example, a trench. 33 and 35 can include gold (Au), platinum (Pt), silver (Ag), Implant regions 36 and 37 are used to substantially or the like. Further, it will be understood that while contact confine an electrical current to light path channel 49 to layerS 33 and 35 are illustrated as including a single layer, improve a single mode lasing operation. Hence, ion implan 55 layers 33 and 35 could include multiple conductive layers of tation is used to bombard Some of the Surrounding cladding conductive materials. layer 24 in order to create a region of higher resistivity, and, In the preferred embodiment, a contact layer 42 and 43 are thereby channel a Substantial amount of the electrical current epitaxially deposited on Surfaces 72 and 73, respectively. In into the relatively more conductive light path channel 49. the preferred embodiment, contact layers 42 and 43 include However, it will be understood that implant regions 36 and 60 highly p-type doped InGaAs. However, it will be understood 37 and index guide regions 30 and 31 are optional, but that layers 42 and 43 can include other suitable conductive included in the preferred embodiment for illustrative pur materials. Further, an electrical contact 34 is positioned on pOSes. contact layer 42 and an electrical contact 32 is positioned on The implanted ions may consist of Singly-charged protons contact layer 43 to form a pnjunction 44 between electrical (H), Singley-charged helium ions (He), doubly-charged 65 contacts 70 and/or 71 and electrical contacts 32 and/or 34 as helium ions (He"), or the like. The higher resistivity illustrated wherein pn junction 44 emits light 38 and light substantially results from the deep levels created by the 39. US 6,936,486 B2 7 8 It will be understood that electrical contacts 32 and 34 can layer 17" wherein each layer 15' and 17" has a thickness 74 include gold (Au), platinum (Pt), Silver (Ag), or the like. It approximately equal to one quarter of the wavelength of will also be understood that in the preferred embodiment, operation to obtain a desired reflective property. However, it layers 42, 43, and 24 are p-type doped and layers 19 and 18 will be understood that layers 15' and 17" can include other are n-type doped for illustrative purposes and that other Suitable reflective materials that are Stacked alternately doping configurations are possible. For example, layerS 42, between a high and a low index of refraction. Metamorphic 43, and 24 could be n-type doped and layers 19 and 18 could DBR region 16' behaves as a heat spreading region. The be p-type doped wherein a polarity of pn junction 44 is higher thermal conductivity of binary compounds in meta reversed. morphic DBR region 16' provide a lower thermal resistance Turn now to FIG. 6 which illustrates an electrooptic and better high temperature performance for multifunction circuit 60 of single junction VCSEL 5 connected to elec tronic modulation circuitry. In circuit 60, electrical contacts VCSEL 7. 33 and 35 (See FIG. 5) are electrically connected to an A contact region 77' is positioned on metamorphic DBR electrical power return 61. Further, electrical contacts 32 and region 16'. In the preferred embodiment, contact region 77 34 (See FIG. 5) are electrically connected to a terminal of a includes highly n-type doped InP. However, it will be resistor 66. An opposed terminal of resistor 66 is electrically 15 understood that contact region 77' can include other suitable connected to a terminal of a capacitor 62 and a terminal of contact materials. Further, contact region 77' is illustrated as an inductor 64, as in a "bias tee'. An opposed terminal of including a Single layer for Simplicity and illustrative pur capacitor 62 is electrically connected to an RF power Source poses. However, it will be understood that contact region 77 63. An opposed terminal of inductor 64 is electrically can include multiple conductive layers. connected to a DC power source 65. It will be understood A light emitting region 53' is positioned on contact layer that electrooptic circuit 60 could be formed as an integrated 77". Light emitting region 53' includes active region 29" with circuit or could include a combination of integrated and a plurality of quantum Structure layerS 52' with a band gap discrete electronic components. wavelength wherein each quantum Structure layer 52 Sub In circuit 60, DC power source 65 biases pn junction 44 Stantially emits light at the wavelength of operation. In the with a DC voltage. Inductor 64 provides an electrical short 25 preferred embodiment, the wavelength of operation is in a for DC Signals and a high impedance to RF signals. Resistor range given approximately from 1.2 um to 1.6 um which is 66 added in series with diode 44 behaves as a current limiter typically used in optical communication applications, Such or an impedance matching element, and capacitor 62 isolates as fiber optical networks. However, it will be understood that RF power source 63 from a DC current. RF power source 63 other wavelength ranges may be Suitable for a given appli provides an RF voltage which modulates pn junction 44. cation. It is highly desirable to form a plurality of light emitting In the preferred embodiment, active region 29" is sand regions 23 to enhance light emission. Further, it is desirable wiched between a cladding layer 55' and a cladding layer to increase light emission without dramatically increasing 54. It will be understood that while cladding layers 54" and power consumption and the generation of heat. To accom 35 55' are illustrated as including a single material layer, layers plish these objects, a multi-junction VCSEL is formed in 54 and 55' can each include more than one layer. Further, in which light emitting regions are biased in a parallel manner the preferred embodiment, cladding layers 54" and 55 in order to achieve low bias Voltage operation and minimal include indium phosphide wherein cladding layer 54 is heat generation. lightly doped n-type and cladding layer 55' is lightly doped Turn now to FIG. 7 which illustrates a multijunction 40 p-type. However, it will be understood that layers 54 and 55 VCSEL 7" with a wavelength of operation configured to can include other Suitable cladding materials with various allow improved light emission with lower power consump doping configurations. tion. It will be understood that multijunction VCSEL 7 is In the preferred embodiment, quantum Structure layerS 52 fabricated using Similar Steps in the fabrication Sequence for include quantum wells. However, it will be understood that single junction VCSEL 5 (i.e. substrate bonding, substrate 45 layerS 52 can include other device Structures, Such as removal, etc.). However, we are illustrating the final device quantum dots or Similar device Structures with Suitable light structure in FIG. 7 for simplicity and ease of discussion. emission properties. In the preferred embodiment, each Further, multijunction VCSEL 7 includes two active regions adjacent quantum Structure layer 52 in active region 29" is for simplicity and ease of discussion. However, it will be Spaced apart by a distance 11" chosen Such that quantum understood that multijunction VCSEL 7' can include more 50 Structures layerS 52' are Substantially at an anti-node of an than two light emitting regions electrically connected in optical field in VCSEL 5 (i.e. distance 11' is approximately parallel. equal to one half the wavelength of operation or integer Multijunction VCSEL 7 includes a substrate 10'. In the multiples thereof). preferred embodiment, substrate 10' includes indium phos Further, adjacent quantum Structure layerS 52' are sepa phide (InP). However, it will be understood that substrate 10' 55 rated by a barrier layer 50' as illustrated such that a barrier can include other Suitable Substrate materials, Such as gal layer 50a and 50'b is positioned adjacent to cladding layers lium arsenide (GaAs), Silicon (Si), or other Suitable Support 55' and 54, respectively. In the preferred embodiment, an ing materials with the desired properties for thermal energy gap wavelength of each barrier layer 50' is Smaller conductivity, Such as a heatsink or the like. In the preferred than the energy gap wavelength of each quantum Structure embodiment, substrate 10' is bonded to region 16' using a 60 layer 52. Further, in the preferred embodiment, quantum bonding layer 12" which includes Solder Such as gold/silicon structure layers 52 and barrier layers 50' include alloys of (Au/Si), gold/tin (Au/Sn), gold/germanium (Au/Ge), or the AlGainAS (i.e. InAIAS, InCaAs, etc.). However, it will be like. Bonding layer 12' includes a window 14 to allow light understood that quantum Structure layerS 52 and barrier emission from an active regions 21' and 29' as will be layers 50' can include other suitable light emitting materials discussed Separately. 65 and barrier materials, respectively. In the preferred embodiment, metamorphic DBR region It will be understood that in Some embodiments, barrier 16' includes alternate layers of an AlAs layer 15' and a GaAs layer 50'a positioned adjacent to cladding layer 55' can US 6,936,486 B2 10 include a sufficiently low electron affinity material in order finement. The addition of barrier layers 20'a and 20'b to provide improved electron confinement for active region provides a higher energy barrier against carrier leakage and 29". Further, in some embodiments, barrier layer 50'b adja carrier loSS, and improves a high temperature performance cent to cladding layer 54 can include a Sufficiently high of VCSEL 7. ionization potential material to provide improved hole con In the preferred embodiment, a dielectric DBR region 28 finement. The addition of barrier layers 50'a and 50'b is positioned on light emitting region 23' and adjacent to provides a higher energy barrier against carrier leakage and cladding region 24' by using a dielectric lift-off process. carrier loSS, and improves a high temperature performance However, it will be understood that dielectric DBR region of VCSEL 5. 28' can be deposited using other deposition techniques well known to those skilled in the art. In the preferred A contact region 19" is positioned on light emitting region embodiment, dielectric DBR region 28 includes alternate 53'. Contact region 19 includes a contact layer 40" posi layers of a silicon oxide (SiO) layer 25' and a titanium oxide tioned on cladding layer 54 and a contact layer 41' posi (TiO) layer 27 wherein each layer 25' and 27 has thickness tioned on contact layer 40'. However, it will be understood 74 approximately equal to one quarter of the wavelength of that contact region 19' can include a number of layers greater operation to obtain a desired reflective property. than one with various doping configurations. In the preferred 15 However, it will be understood that layers 25' and 27' can embodiment, contact layer 40' includes p-type doped indium include other Suitable dielectric materials which alternate phosphide (InP) and contact layer 41' includes p-type doped between a high dielectric constant material and a low aluminum gallium indium arsenide (AlGanAS) wherein the dielectric constant material, Such as alternate layers of doping concentration of contact layer 41' is Substantially magnesium fluoride (MgF) and Zinc Selenide (ZnSe). greater than the doping concentration of contact layer 40'. Further, it will be understood that the use of a dielectric DBR Alight emitting region 23' is positioned on contact region region in this embodiment is for illustrative purposes only. 19'. Light emitting region 23' includes active region 21' with For example DBR region 28 could include alternate layers a plurality of quantum Structure layerS 22' with a band gap of aluminum arsenide (AIAS) and gallium arsenide (GaAs) wavelength wherein each quantum Structure layer 22" Sub 25 and be is similar in Structure to metamorphic DBR region Stantially emits light at the wavelength of operation. 16'. In the preferred embodiment, active region 21" is Sand An implant region 36' and 37" are formed within cladding wiched between a cladding layer 18" and a cladding layer layer 24' and an implant region 56' and 57 are formed within 24'. It will be understood that while cladding layers 18' and cladding layer 55' and aligned Such that a light path channel 24' are illustrated as including a single material layer, layers 49' extends through dielectric DBR region 28", light emitting 18" and 24' can each include more than one layer. Further, in region 23", light emitting region 53', metamorphic DBR the preferred embodiment, cladding layers 18' and 24 region 16', and Substrate 10", as will be discussed separately. include indium phosphide wherein cladding layer 18' is An index guide region 30' and 31' are positioned within lightly doped n-type and cladding layer 24' is lightly doped cladding layer 24' adjacent to a Surface 46' and aligned with p-type. However, it will be understood that layers 18' and 24 35 window 14' and light path channel 49'. Index guide regions can include other Suitable cladding materials with various 30' and 31' can include, for example, a trench. Further, it will doping configurations. be understood that implant regions similar to regions 36', In the preferred embodiment, quantum Structure layerS 22' 37, 56', and 57 can be formed within cladding layers 54 include quantum wells. However, it will be understood that and/or 18'. However, the formation of implant regions layerS 22' can include other device Structures, Such as 40 within cladding layers 24' and 55' is for illustrative purposes quantum dots or Similar device Structures with Suitable light only. emission properties. In the preferred embodiment, each Implant regions 36', 37, 56', and 57" are used to confine adjacent quantum Structure layer 22' in active region 21' is an electrical current to light path channel 49' to improve a Spaced apart by distance 11' chosen Such that quantum Single mode lasing operation. Hence, ion implantation is Structure layerS 22' are Substantially at an anti-node of an 45 used to bombard Some of the Surrounding cladding layerS 24 optical field in VCSEL 7" (i.e. distance 11' is approximately and 55' in order to create a region of higher resistivity, and, equal to one half the wavelength of operation or integer thereby channel most of the electrical current into the multiples thereof). relatively more conductive light path channel 49'. The Further, adjacent quantum Structure layerS 22' are sepa implanted ions may consist of Singly-charged protons (H), rated by a barrier layer 20' as illustrated such that a barrier 50 Singly-charged or doubly-charged helium ions (He" or layer 20a is positioned adjacent to cladding layer 24' and a He"), or the like. The higher resistivity substantially results barrier layer 20b is positioned adjacent to cladding layer 18'. from the deep levels created by the implant damage, whose In the preferred embodiment, an energy gap wavelength of energy States favor the compensation of cladding layerS 24 each barrier layer 20' is Smaller than the energy gap wave and 55'. length of each quantum Structure layer 22". Further, in the 55 Index guide regions 30' and 31' are used to improve a preferred embodiment, quantum Structure layerS 22' and single-mode output power of single junction VCSEL 7" by barrier layers 20' include AlGainAS. However, it will be increasing the lateral croSS-Section of the gain region while understood that quantum Structure layerS 22' and barrier preserving Single-mode lasing operation by means of mode layers 20" can include alloys of AlGainAS or other suitable Selection measures (mode control) that preferentially light emitting materials and barrier materials, respectively. 60 enhance the modal gain of one mode through indeX guiding, It will be understood that in Some embodiments, barrier or alternatively SuppreSS the other competing higher order layer 20'a positioned adjacent to cladding layer 24' can nodes through a higher reflection loSS. include a sufficiently low electron affinity material in order By allowing the actively pumped area to increase while to provide improved electron confinement for active region Suppressing the competing modes that emerge through Sur 21". Further, in some embodiments, barrier layer 20'b adja 65 face relief patterning, higher Single-mode output power is cent to cladding layer 18" can include a Sufficiently high achieved through a reduced current density, which leads to ionization potential material to provide improved hole con lower Self-heating and reduced gain Saturation. US 6,936,486 B2 11 12 In the preferred embodiment, dielectric DBR region 28' is An opposed terminal of capacitor 96' is electrically con etched through light emitting region 23' to form a mesa 48 nected to an RF power source 98". An opposed terminal of and expose a surface 72" and 73". Further, in the preferred resistor 93' is electrically connected to electrical contacts 32 embodiment, light emitting region 23' is etched through and/or 34 (See FIG. 7) of multijunction VCSEL 7". Further, contact region 19' emitting region 53' to form a mesa 47" and a DC power return 88" is electrically connected to electrical expose a surface 70' and 71". In the preferred embodiment, contact 33' and/or 35' (See FIG. 7). light emitting region 53' is etched through contact region 77 Electrical contacts 58' and/or 59 (See FIG. 7) of multi to form a mesa 51" and expose a surface 75" and 76'. junction VCSEL 7" are electrically connected to a terminal of In the preferred embodiment, an electrical contact 58' and a resistor 85". An opposed terminal of resistor 85" is electri 59' are positioned on Surfaces 76' and 75", respectively. It cally connected to a terminal of an inductor 84 and a will be understood that electrical contacts 58' and 59' can terminal of a capacitor 90'. An opposed terminal of inductor include gold (Au), platinum (Pt), Silver (Ag), or the like. 84 is electrically connected to a DC power input 86' and an Further, it will be understood that contact layers 58' and 59 opposed terminal of capacitor 90' is electrically connected to are illustrated as including a Single layer, but layerS 58' and an RF power return 82". 59' could include multiple conductive layers of a conductive 15 In electrooptic circuit 80', DC power source 86' biases pn material. junction 45" with a DC voltage and DC power source 94' In the preferred embodiment, an electrical contact 35' and biases pnjunction 44 with a DC voltage. Inductors 84 and 33' are positioned on surfaces 70' and 71", respectively. It 92 provide an electrical short for DC signals and a high will be understood that electrical contacts 33' and 35' can impedance for RF signals, while capacitors 90' and 96 include gold (Au), platinum (Pt), Silver (Ag), or the like. isolate RF power return 82" and RF power source 98", Further, it will be understood that contact layers 33' and 35' respectively, from a DC current. Resistors 93' and 85 are are illustrated as including a Single layer, but layerS 33' and added as current limiters and also for impedance matching 35' could include multiple conductive layers of a conductive when needed. RF power source 98' provides an RF voltage material. which modulates pn junction 44'. In the preferred embodiment, contact layers 42" and 43' 25 Turning back to FIG. 7, active regions 21" and 29' are are epitaxially deposited on Surfaces 72" and 73', respec positioned within a resonance cavity 81' defined by meta tively. In the preferred embodiment, contact layers 42" and morphic DBR mirror 16' and dielectric DBR mirror 28'. 43' include highly p-type doped InCaAs. However, it will be Active regions 21' and 29' are located at the antinodes of the understood that layers 42" and 43' can include other suitable optical field within resonance cavity 81' and emit light conductive materials. Further, an electrical contact 34" is coherently, wherein each active region 21" and 29' contrib positioned on contact layer 42 and an electrical contact 32" utes substantially to the overall optical gain of VCSEL 7". is positioned on contact layer 43' to form a pn junction 44 PN junctions 44' and 45" are connected serially but are between electrical contacts 33' and/or 35' and electrical biased in parallel. Each pnjunction 44' and 45" is biased by contacts 32' and/or 34 as illustrated. Further, a pn junction DC bias 94' and 86", respectively, to produce an optical gain 45" is formed between electrical contacts 33' and/or 35' and 35 that combines coherently to bias VCSEL 7 in close prox electrical contacts 58' and/or 59'. imity to a lasing threshold. RF signal 98" supplies a modu It will be understood that electrical contacts 32' and 34' lation Signal to junction 44, which functions as a "gain can include gold (Au), platinum (Pt), Silver (Ag), or the like. lever” that modulates the gain of VCSEL 7" above threshold and produces a modulated optical output. Further, it will be understood that in the preferred 40 embodiment, layers 42" and 43' are n-type doped, region 19 In order to increase the power output of multifunction is p-type doped, and layer 49" is n-type doped for illustrative VCSEL 7", pnjunctions 44' and 45" are optically cascaded purposes and that other doping configurations are possible. within common optical resonance cavity 81' defined by For example, layerS 42" and 43' could be p-type doped, layer metamorphic DBR region 16' and dielectric DBR region 28". 19' could be n-type doped, and layer 49' could be p-type 45 Placing quantum Structure layerS 22' and 52" at the peaks doped wherein a polarity of pn junctions 44' and 45" is (anti-nodes) of the optical field causes the optical gains of reversed. active regions 21" and 29' to be coherently coupled, thereby In the preferred embodiment, active regions 21' and 29 increasing the Overall gain of the cavity and increasing the are optically cascaded in a resonant configuration to increase power output. the overall optical-gain and to achieve high optical output 50 In the preferred embodiment, active regions 21" and 29 power. However, pn junctions 44' and 45" are electrically are placed at different antinodes within the same resonance biased in parallel to minimize the Voltage required to operate cavity, and each gain Section is electrically biased individu multijunction VCSEL 7", as will be discussed presently. ally within pn junction 44' and 45", respectively. In the Further, in the preferred embodiment, light path channel 49' preferred embodiment, pn junctions 44' and 45" are biased is defined Such that a current path through active region 53' 55 not in Serial, but in parallel by Sharing a common p" is Substantially equal to a current path through active region electrode (i.e. contact region 19"). 23' such that each active region 23' and 53' emits a substan In this three-terminal configuration, both pnjunctions 44 tially equal amount of light. It will be understood that a and 45" are independently forward-biased by different cur current path can be adjusted by changing the properties and rents through Separate current paths, whose Sum constitutes positioning of implant regions 36', 37, 56', or 57, as well as 60 the total drive current. The forward-biased voltages of pn index guides 30 and 31. junctions 44' and 45" are each comparable to that of a Single Turn now to FIG. 8 which illustrates an electrooptic pnjunction. Each current contributes a lower optical gain to circuit 80' of multijunction VCSEL 7" connected to elec the shared resonance cavity, while the collective optical gain tronic modulation circuitry. A DC power input 94 is elec determines the threshold lasing condition of the cavity. trically connected to a terminal of an inductor 92". An 65 In the preferred embodiment of multijunction VCSEL 7", opposed terminal of inductor 92 is electrically connected to pn junction 45" is subjected only to a DC bias, while pn a terminal of a capacitor 96' and a terminal of a resistor 93'. junction 44 (which is substantially similar in area) is sub US 6,936,486 B2 13 14 jected to both a DC bias and a RF modulation current for include two active regions for Simplicity and ease of dis high-Speed operation. In this manner both pn junctions 44 cussion. However, it will be understood that multifunction and 45" are subjected to lower voltage biases and lower VCSEL's 6' and 9' can include more than two light emitting current injection levels, and are, thus, leSS prone to gain regions electrically connected in parallel. Saturation. In the preferred embodiment, the undercutting is facili Turn now to FIG. 9 which illustrates another embodiment tated by dry etching a pattern of narrow trenches 184 of a multijunction VCSEL 8". It will be understood that through light emitting regions 23' and 53'. An undercut multijunction VCSEL 8 is fabricated using similar steps in trench 185' can then be formed in active region 21" and/or the fabrication sequence for multijunction VCSEL 7" (i.e. active region 29 (See FIG. 10). Undercut trench 185' can Substrate bonding, Substrate removal, etc.) and includes also be formed in at least one of cladding region 55", 54, 18", Similar layers. However, we are illustrating the final device and 24" (See FIG. 11). Further, in some embodiments, structure in FIG. 9 for simplicity and ease of discussion. implant region 184' and implant region 183' can be formed Further, multifunction VCSEL8' includes two active regions proximate to trench 184', as illustrated in FIGS. 10 and 11, for simplicity and ease of discussion. However, it will be to provide further carrier confinement. understood that multifunction VCSEL 8" can include more 15 While the steps of the fabrication methods have been than two light emitting regions electrically connected in described, and will be claimed, in a specific order, it will be parallel. clear to those skilled in the art that various StepS and In this embodiment, metamorphic DBR 16' is patterned procedures may be performed in a different order. It is into a self-enclosed etched trench 187" with a Surface 188' intended, therefore, that the Specific order described or which provides direct electrical access to contact region 77 claimed for the various fabrication Steps does not in any was and also provides improved carrier confinement, as will be limit the invention and any variations in order that Still come discussed presently. In the preferred embodiment, etched within the scope of the invention are intended to be covered trench 187" also allows cladding region 54 (or cladding in the claims. region 55') to be ion implanted through bottom surface 188' Various changes and modifications to the embodiments in a direction 182. Substantially opposite to an ion implant in 25 herein chosen for purposes of illustration will readily occur a direction 186' in cladding region 24. In the preferred to those skilled in the art. To the extent that Such modifica embodiment, the ions implanted in direction 186" form tions and variations do not depart from the Spirit of the implant regions 36' and 37" in cladding region 24' and the invention, they are intended to be included within the Scope ions implanted in direction 182 form implant regions 56 thereof which is assessed only by a fair interpretation of the and 57" in contact region 54'. This allows light emitting following claims. regions 23' and 53' to be implanted independently without Having fully described the invention in such clear and Substantially damaging contact region 19'. concise terms as to enable those skilled in the art to In the preferred embodiment, after ion implantation and understand and practice the Same, the invention claimed is: annealing, a base metal layer 183' is deposited over meta 1. A method of fabricating an optical device with a morphic DBR 16'. In the preferred embodiment, base metal 35 wavelength of operation, the method comprising the Steps layer 183' is used as a Seed layer for electroplating a contact of: layer 180' that has a substantially planarized bottom surface providing a first Substrate; 189'. It will be understood that layers 183' and 189' can epitaxially growing a light emitting region which emits include gold (Au), platinum (Pt), or the like. Further, it will light at the wavelength of operation, the light emitting be understood that base metal layer 181' and contact layer 40 region being positioned on the first Substrate wherein 180' can be deposited using other deposition techniques well the light emitting region includes an active region and known to those skilled in the art. In the preferred a contact region of a first conductivity type and a embodiment, contact layer 180' is then bonded to substrate Second conductivity type Such that the light emitting 10' by using bonding layer 12'. 45 region is Sandwiched between contact regions of oppo Multijunction VCSEL 8" has a lower spreading resistance Site conductivity types; which is Substantially obtained through improved current epitaxially growing a first Stack of alternate layers of a confinement by forming trench 187" within metamorphic first material with a first index of refraction and a DBR 16'. The lower spreading resistance is also improved Second material with a Second index of refraction by forming implant regions 56" and 57" in cladding region 54 50 positioned on the light emitting region wherein the first and implant regions 36' and 37" in cladding region 24 index of refraction is substantially different from the without Substantially damaging contact region 19'. These Second index of refraction So that the first Stack of improvements allow the current to be Substantially injected alternate layers forms a first mirror; through contact region 77' toward contact layers 42 and 43' Solder bonding a Second Substrate to the first Stack of and minimizes a lateral current spreading. 55 alternate layers, An alternative means to ion implantation for current removing the first Substrate to Substantially expose the confinement is to Selectively undercut active regions 21" and light emitting region; and 29' to form a current aperture in a multijunction VCSEL 6', epitaxially growing a Second Stack of alternate layers of a as illustrated in FIG. 10, or to selectively undercut a portion third material with a third index of refraction and a of cladding regions 24, 18, 54", or 55' in a multifunction 60 fourth material with a fourth index of refraction posi VCSEL 9', as illustrated in FIG. 11. It will be understood that tioned on the light emitting region wherein the third multifunction VCSEL's 6' and 9" are fabricated using similar index of refraction is substantially different from the steps in the fabrication sequence for multijunction VCSEL 7 fourth index of refraction so that the second stack of (i.e. Substrate bonding, Substrate removal, etc.) and include alternate layers forms a Second mirror. Similar layers. However, we are illustrating the final device 65 2. A method as claimed in claim 1 wherein the Step of structure in FIGS. 10 and 11 for simplicity and ease of epitaxially growing the light emitting region further includes discussion. Further, multifunction VCSEL's 6' and 9 the Step of forming the active region Such that the active US 6,936,486 B2 15 16 region is positioned between a first cladding region and a 15. A method as claimed in claim 1 wherein the wave Second cladding region. length of operation is within a range given approximately 3. A method as claimed in claim 1 wherein the first from 1.2 um to 1.6 um. substrate includes at least one of indium phosphide (InP) and 16. A method as claimed in claim 1 wherein the step of another Suitable Substrate material which is lattice matched Solder bonding includes using a bonding layer which to Subsequent layerS grown thereon. includes at least one of gold/silicon (Au?Si), gold/tin (Au/ 4. A method as claimed in claim 1 wherein the Second Sn), gold/germanium (Au/Ge), or another Suitable Solder Substrate includes at least one of indium phosphide (InP), material with a desired property for adhesion. gallium arsenide (GaAs), Silicon (Si), and another Suitable 17. A method as claimed in claim 16 wherein the bonding substrate material which has suitable thermally conductive layer includes a window to allow Substantial light emission and Supporting properties. through the Second Substrate. 5. A method as claimed in claim 1 wherein at least one of 18. A method as claimed in claim 1 wherein at least one the first and Second Stack of alternate layers include an alloy contact region of at least one of the first and Second of AlGaAS and wherein each layer of the first, Second, third, conductivity type includes at least two layers of the same and fourth material has a thickneSS approximately equal to 15 conductivity type and a Substantially different doping con one quarter of the wavelength of operation. centration. 6. A method as claimed in claim 1 wherein at least one of 19. A method as claimed in claim 2 further including the the first and Second Stack of alternate layers include alternate Step of etching a trench through the light emitting region to layers of silicon oxide (SiO) and titanium oxide (TiO) and provide Substantial current confinement. wherein each layer in the alternate layerS has a thickneSS 20. A method as claimed in claim 19 further including the approximately equal to one quarter of the wavelength of Step of forming an undercut trench adjacent to the trench and operation. Substantially extending into at least one of the active region, 7. A method as claimed in claim 1 wherein at least one of the first cladding region, and the Second cladding region to the first and Second Stack of alternate layers include alternate provide Substantial current confinement. layers of magnesium fluoride (MgF) and Zinc Selenide 25 21. A method of fabricating a multijunction laser with a (ZnSe) and wherein each layer in the alternate layerS has a wavelength of operation, the method comprising the Steps thickneSS approximately equal to one quarter of the wave of: length of operation. providing a first Substrate; 8. A method as claimed in claim 2 wherein the active epitaxially growing a light emitting region which emits region includes a plurality of quantum Structures with a light at the wavelength of operation, the light emitting bandgap wavelength Substantially equal to the wavelength region being positioned on the first Substrate wherein of operation, wherein each of the plurality of quantum the light emitting region includes a plurality of active Structures includes at least one of quantum wells, quantum regions with a plurality of quantum Structure layers dots, and another similar quantum Structure which enhances each Sandwiched between cladding regions and light emission. 35 wherein each of the plurality of active regions is 9. A method as claimed in claim 8 wherein each quantum Separated by alternate contact regions of a first con Structure of the plurality of quantum Structures is positioned ductivity type and a Second conductivity type wherein between quantum barrier layers wherein each quantum the first conductivity type is opposite in conductivity to barrier layer has a bandgap wavelength Smaller than the the Second conductivity type, bandgap wavelength of the quantum Structures. 40 10. A method as claimed in claim 9 wherein each adjacent epitaxially growing a first Stack of alternate layers of a quantum Structure of the plurality of quantum Structures in first material with a first index of refraction and a the active region is spaced apart Such that constructive Second material with a Second index of refraction interference occurs between each adjacent quantum Struc positioned on the light emitting region wherein the first ture. 45 index of refraction is substantially different from the 11. A method as claimed in claim 8 wherein each quantum Second index of refraction So that the first Stack of Structure contains one or more barrier layers including alloys alternate layers forms a first mirror; of InAlAs to provide improved carrier confinement for the Solder bonding a Second Substrate to the first Stack of double heterostructure junction. alternate layers, 12. A method as claimed in claim 1 wherein at least one 50 removing the first Substrate to Substantially expose the at of the first and Second Stack of alternate layers include alloys least one light emitting region; and of AlGaAS which are continuously graded in composition to epitaxially growing a Second Stack of alternate layers of a form continuously graded heterointerfaces. third material with a third index of refraction and a 13. A method as claimed in claim 2 wherein a portion of fourth material with a fourth index of refraction posi at least one of the first and Second cladding regions is 55 tioned on the light emitting region wherein the third isolation implanted with at least one of hydrogen ions (H), index of refraction is substantially different from the helium ions (He" or He"), and another suitable ion to form fourth index of refraction so that the second stack of a light path channel which extends form the first Stack of alternate layers forms a Second mirror. alternate layers to the Second Stack of alternate layers. 22. A method as claimed in claim 21 wherein at least one 14. A method as claimed in claim 2 wherein the step of 60 of the first and Second Stack of alternate layers include epitaxially growing the light emitting region includes the alternate layers of silicon oxide (SiO) and titanium oxide Step of forming the cladding region adjacent to the Second (TiO) and wherein each layer in the alternate layers has a Stack of alternate layers with a plurality of indeX guide thickness approximately equal to one quarter of the wave regions to form a light path channel which extends from the length of operation. first Stack of alternate layers to the Second Stack of alternate 65 23. A method as claimed in claim 21 wherein at least one layers, wherein the at least one indeX guide region is of the first and Second Stack of alternate layers include positioned adjacent to the Second Stack of alternate layers. alternate layers of magnesium fluoride (MgF) and Zinc US 6,936,486 B2 17 18 Selenide (ZnSe) and wherein each layer in the alternate includes a plurality of active regions wherein each of layerS has a thickness approximately equal to one quarter of the plurality of active regions is Separated by alternate the wavelength of operation. contact regions of a first conductivity type and a Second 24. A method as claimed in claim 21 wherein each conductivity type; quantum Structure layer is positioned between a quantum barrier layer wherein each quantum barrier layer has a forming a Suitable electrical contact to each alternate bandgap wavelength Smaller than a bandgap wavelength of contact region of the first and Second conductivity the quantum Structure layers. types, 25. A method as claimed in claim 21 wherein the step of electrically connecting a direct current power Source and Solder bonding includes using a bonding layer which one of an alternating current power Source and an includes at least one of gold/silicon (Au?Si), gold/tin (Au/ alternating current power return to each contact region Sn), gold/germanium (Au/Ge), or another Suitable Solder of the first conductivity type, and material with a desired property for adhesion. electrically connecting a direct current power return to 26. A method as claimed in claim 21 wherein each each contact region of the Second conductivity type. adjacent active region in the plurality of active regions 15 29. A method as claimed in claim 28 wherein at least one includes a Substantially equal current path Such that each contact region includes at least two layers of the same active region emits a Substantially equal amount of light. conductivity type and Substantially different doping concen 27. A method as claimed in claim 21 wherein each contact trations. region in the alternate contact regions includes a Substan 30. A method as claimed in claim 28 wherein each tially equal current path between each adjacent contact adjacent active region in the plurality of active regions region. includes a Substantially equal current path Such that each 28. A method of modulating a multifunction laser with a active region emits a Substantially equal amount of light. wavelength of operation, the method comprising the Steps 31. A method as claimed in claim 28 wherein each contact of: region in the alternate contact regions includes a Substan epitaxially growing a light emitting region positioned 25 tially equal current path between each adjacent contact within an optical gain cavity which includes a mirror region. and an opposed mirror, wherein the light emitting region emits light at the wavelength of operation and UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION

PATENT NO. : 6,936,486 B2 Page 1 of 1 DATED : August 30, 2005 INVENTOR(S) : Cheng et al.

It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:

Column 18 Line 22, “multifunction' should read -- multijunction --.

Signed and Sealed this Fourteenth Day of March, 2006 WDJ

JON W. DUDAS Director of the United States Patent and Trademark Office