(12) United States Patent (10) Patent No.: US 7,813,396 B2 Feng Et Al

USOO781.3396 B2

(12) United States Patent (10) Patent No.: US 7,813,396 B2 Feng et al. (45) Date of Patent: Oct. 12, 2010

(54) TRANSISTOR LASER DEVICES AND 5,892,784. A 4/1999 Tan et al...... 372.43 METHODS 6,526,082 B 1 2/2003 Corzine et al...... 372/46.01 7,091,082 B2 8/2006 Feng et al...... 438,235 (75) Inventors: Milton Feng, Champaign, IL (US); Nick 7,244.997 B2 7/2007 Appelbaum et al...... 257/425 Holonyak, Jr., Urbana, IL (US); Gabriel 7.286,583 B2 10/2007 Feng et al...... 372.30 Walter, Champaign, IL (US); HanWui 7.354,780 B2 4/2008 Feng et al...... 438/20 Then, Urbana, IL (US) s 7,535,034 B2 * 5/2009 Walter et al...... 257/197 (73) Assignee: The Board of Trustees of the (Continued) University of Illinois, Urbana, IL (US) FOREIGN PATENT DOCUMENTS (*) Notice: Subject to any disclaimer, the term of this JP 09-074246 3, 1997 patent is extended or adjusted under 35

(21) Appl. No.: 12/384,772 OTHER PUBLICATIONS (22) Filed: Apr. 8, 2009 Ryzhil, Heterostructure laser transistors controlled by resonant tunneling electron extraction.” Semicond. Sci. Technol., vol. 12, pp. (65) Prior Publication Data 431-438, (1997).* US 2010/0085995 A1 Apr. 8, 2010 (Continued) O O Primary Examiner Minsun Harvey Related U.S. Application Data Assistant Examiner Michael Carter (63) Continuation-in-part of application No. 12/287,697. (74) Attorney, Agent, or Firm—Martin Novack filed on Oct. 10, 2008. 57 ABSTRACT (60) Provisional application No. 60/998,645, filed on Oct. (57) filed12, 2007on SSisional appl1cauonlication No.No 61/206.324s-1 is A method for producing -light 0 emission from a semiconductor • 1-1 s device includes the following steps: providing a semiconduc (51) Int. Cl. tor base region disposed between a semiconductor emitter HOIS 5/34 (2006.01) region and a semiconductor collector region that forms a HOIS 5/062 (2006.01) tunnel junction adjacent the base region; providing, in the (52) U.S. Cl 372/43.01372/44.O1 base region, a region exhibiting quantum size effects; provid ir grgr. e V-3 ing an emitter terminal, a base terminal, and a collector ter (58) Field of Classification Search ...... 29. minal respectively coupled with the emitter region, the base See application file for complete search histo region, and the collector region; and applying electrical sig pp p ry. nals with respect to the emitter terminal, the base terminal and (56) References Cited the collector terminal to produce light emission from the base region. U.S. PATENT DOCUMENTS 5,550,854 A 8, 1996 Chen et al...... 372/45.01 22 Claims, 8 Drawing Sheets

US 7,813,396 B2 Page 2

U.S. PATENT DOCUMENTS Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. 2001/0050934 Al 12/2001 Choquette et al...... 372/43 Phys. Lett. 88,063509 (2006). 2002fOO37022 A1 3/2002 Fukagai ...... 372/46 Collector Current Map Of Gain And Stimulated Recombination On 2002/0131464 A1 9, 2002 Sirbu et al...... 372/45 The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, 2005, OO40432 A1 2/2005 Feng et al...... 257,198 N. Holonyak, Jr., A. James and G. Walter; Appl. Phys. Lett 88, 2005.0054172 A1 3/2005 Feng et al...... 438/313 143508 (2006). 2008/0240173 Al 10/2008 Holonyak et al...... 372/9 Collector Breakdown. In The Heterojunction Bipolar Transistor Laser, G. Walter, A. James, N. Holonyak, Jr., M. Feng, and R. Chan FOREIGN PATENT DOCUMENTS Appl. Phys. Lett. 88, 232105 (2006). High-speed (/splges 1 GHz) Electrical And Optical Adding, Mixing, WO WO97,20353 6, 1997 And Processing Of Square-Wave Signals With A Transistor Laser, WO WO99/O5726 2, 1999 Milton Feng. N. Holonyak, Jr.; R. Chan; A. James; and G. Walter; WO WO2005/020287 3, 2005 Photonics Technology Letters, IEEE vol. 18 Issue: 11; Jun. 2006 pp. WO WO2006/093883 9, 2006 1240-1242. Graded-Base InGaN/GaN Heterojunction Bipolar Light-Emitting OTHER PUBLICATIONS Transistors, B. F. Chu-Kung et al., Appl. Phys. Lett. 89, 082108 (2006). Light-Emitting Transistor: Light Emission From InGaP/GaAs Carrier LifeTime and Modulation Bandwidth Of A Quantum Well Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and AIGaAs/InGaP/GaAs/InGaAs Transistor Laser, M. Feng, N. W. Hafez, Appl. Phys. Lett. 84, 151 (2004). Holonyak, Jr., A. James, K. Cimino, G. Walter, and R. Chan; Appl. Quantum-Well-Base Heterojunction Bipolar Light-Emitting Tran Phys. Lett. 89, 113504 (2006). sistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84. Chirp In A Transitor Laser: Franz-Keldysh Reduction Of The 1952 (2004). Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and Type-II GaAsSb. InPHeterojunction Bipolar Light-Emitting Transis M. Feng. Appl. Phys. Lett. 90,091 109 (207). tor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Photon-Assisted Breadkdown, Negative Resistance, And Switching Appl. Phys. Lett. 84,4792 (2004). In A Quantum-Well Transistor Laser; A. James, G. Walter, M. Feng, Laser Operation Of A Heterojunction Bipolar Light-Emitting Tran and N. Holonyak, Jr., Appl. Phys. Lett. 90, 152109 (2007). sistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Franz-Keldysh Photon-Assisted Voltage-Operated Switching Of A Lett. 85,4768 (2004). Transistor Laser; James, A.; Holonyak, N. Feng, M.; Walter, G., Microwave Operation And Modulation Of A Transistor Laser, R. Photonics Technology Letters, IEEE Volumn; 19 issue:9 May 1, Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86. 2007, pp. 680-682. 1311 14 (2005). Experimental Determination Of The EffectiveMinority Carrier Life Room Temperature Continuous Wave Operation Of A Heterojunc time In The Operation Of A Quantum-Well n-p-n. Heterojunction tion Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, Biopolar Light-Emigging Transistor Of Varying Base Quantum-Well and R. Chan, Appl. Phys. Lett. 87, 131103 (2005). Design And doping; H.W. Then, M. Feng, N. Holonyak, Jr., and Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. C.H.Wu, Appl. Phys. Lett. 91, 033505 (2007). Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. Charge Control Analysis. Of Transistor Laser Operation; M. Feng, N. Dupuis, Appl. Phys. Lett. 88, 012108 (2006). Holonyak, Jr., H.W. Then, and G. Walter; Appl. Phys. 91, 053501 The Transistor Laser, N. Holonyak, MFeng, Spectrum, IEEEvol.43, (2007). Issue 2, Feb. 2006. * cited by examiner U.S. Patent Oct. 12, 2010 Sheet 1 of 8 US 7,813,396 B2

Moteriol ond Thickness Dopont Concentration C m3 0.05 um, n-In 1900.05P 0.10 urn, int-GoAs S 5E-18 Upper Cladding Loyers

110. Emmitter Loyer 0.02 urn, pt-GOAS C 5E-18 120, 0.01 urn, pt-GOAS C 5E-18 Bose 0.01 pm, pt-GOA C 5E-18 0.05 pm, pt-GCAS C 1E-19

125 QW-Bose region 12O \ Bose 121 135 0.01 plm, pt-A01000090AS C 6E-19 13O Tunnel Junction 0.04 pm, int-GaAs Si 7E-8 0.05 p.m., n-Alo4060060AS S SE-18 Bottom Clodding 0.40 p.m, int-A695Co005As S SE- 18 Loyers 0.025 p.m., n-A8000020As St 3E-18 0.05 plm, n -A 40GGO 50AS S SE-18 0.012 um, n-Inga 5P 5E-17 0.50 m, int-GaAs S. 5E-18 0.04 p.m, i-In 496.005P

0.50 am, i-GOAS SI-GOAS Substrate FIG. 1 U.S. Patent Oct. 12, 2010 Sheet 2 of 8 US 7,813,396 B2

In015GooB5As QW

30 Collector I-V Chorocteristics, 20 C (a) Tunnel Junction Tl AIB =4 mA

g 2O "Knee"

s IIH =56mA 10

0. 2.0 U.S. Patent Oct. 12, 2010 Sheet 3 of 8 US 7,813,396 B2

2 LI-V, AIB =4 mA, 20°C -(a) TJ Tronsistor Loser -(b) I-V of Comparison TL

O, 6

0, 4.

Photons 131 outside the

I I I Photons Cf fkT t inside the Weak collector junction field waveguide Weak collector junction field in the presence of an optical field R.C.: QW Recombination Center Available empty states to accept a tunneling electron

FIG. 5 U.S. Patent Oct. 12, 2010 Sheet 4 of 8 US 7,813,396 B2

-5F------Sase-- -10- ...... a - as a ...No. : –20-(a) Current Modulation-...- fR ...f3dB

Frequency (GHz) FIG. 6

In05GooB5As QW El - lz- hWOW U.S. Patent Oct. 12, 2010 Sheet 5 of 8 US 7,813,396 B2

1S O Tunnel Junction Transistor Loser, 20C g O 1. (a) Lineority Characteristics, IB-80 mA -30 NM3-20) TN 5

9.5 -40 Fundomental Tones: fi f2 S E e -90 2f -f2 f f2 22-f & -60 3rd Order IMD: 2f1-f2, 2t2-f es Modulation Frequency t 5 O (D) VCE=0.8V -80 s 0.5 0.6 0.9 2 y -30

VCE(V) S. g E. Y d

S e-soO "EvenOO fier."elec S JS S S-30 S. f=2.39 GHz 8 -60 -60 f2-f=1 MHz s O 0.2 0.4 0.6 0.8 1.0 -90 2f1-f2 f1 f2 22-f DC Optical Output per Focet (mW) Modulation Frequency FIG. 8 U.S. Patent Oct. 12, 2010 Sheet 6 of 8 US 7,813,396 B2

(a) Common-Emitter

(b) Common-Base

T-TL TJ-TL U.S. Patent Oct. 12, 2010 Sheet 7 of 8 US 7,813,396 B2

(o) Common-Emitter

(b) Common-Base TJ-TL

U.S. Patent Oct. 12, 2010 Sheet 8 of 8 US 7,813,396 B2

Three-Port Signal Mixing with TJ-Tl () () () BE-input f=200 GHz (d) CE-input -201 GHz (e) 80 mA () = 0.8 Y

8 O 12 14 16 18 20 22 frequency (GHz)

605 6065

OOO 10,05 10,10 95 200 12.05 12.10

s 14.00 4.05 4.10 15.95 600 1605 16.10 1795 1800 1805 18.10 Frequency (GHz) Frequency (GHz) Frequency (GHz)

US 7,813,396 B2 1. 2 TRANSISTOR LASER DEVICES AND G. Walter, Appl. Phys. Lett. 88,063509 (2006); and Collector METHODS Current Map Of Gain And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. PRIORITY CLAIMS Chan, N. Holonyak, Jr., A. James, and G. Walter, Appl. Phys. 5 Lett. 88, 14508 (2006); Collector Breakdown. In The Hetero This is a continuation-in-part of copending U.S. patent junction Bipolar Transistor Laser, G. Walter, A. James, N. application Ser. No. 12/287,697, filed Oct. 10, 2008, which Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 88, claims priority from U.S. Provisional Patent Application Ser. 232105 (2006); High-Speed (/splges/1 GHz) Electrical And No. 60/998,645, filed Oct. 12, 2007. Also, priority is claimed Optical Adding, Mixing, And Processing Of Square-Wave from U.S. Provisional Patent Application Ser. No. 61/206, 10 Signals With A Transistor Laser, M. Feng, N. Holonyak, Jr., 324, filed Jan. 29, 2009. R. Chan, A. James, and G. Walter, Photonics Technology Letters, IEEE Volume: 18 Issue: 11 (2006); Graded-Base FIELD OF THE INVENTION InGaN/GaN Heterojunction Bipolar Light-Emitting Transis tors, B. F. Chu-Kung et al., Appl. Phys. Lett. 89, 082108 This invention relates to methods and devices for produc 15 (2006); Carrier Lifetime And Modulation Bandwidth Of A ing light emission and laser emission in response to electrical Quantum Well AlGaAs/InGaP/GaAs/InGaAs Transistor signals. The invention also relates to methods for producing Laser, M. Feng, N. Holonyak, Jr., A. James, K. Cimino, G. light emission and laser emission from semiconductor tran Walter, and R. Chan, Appl. Phys. Lett. 89, 113504 (2006): sistor devices, including such emission that can be controlled Chirp In A Transistor Laser, Franz-Keldysh Reduction of The with very fast response time. Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and M. Feng, Appl. Phys. Lett. 90,091 109 (2007); Pho BACKGROUND OF THE INVENTION ton-Assisted Breakdown, Negative Resistance, And Switch ing In A Quantum-Well Transistor Laser, A.James, G. Walter, A part of the background hereoflies in the development of M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 90, 152109 wide bandgap semiconductors to achieve high minority car 25 (2007); Franz-Keldysh Photon-Assisted Voltage-Operated rier injection efficiency in a device known as a heterojunction Switching of a Transistor Laser, A. James, N. Holonyak, M. bipolar transistor (HBT). These transistor devices are capable Feng, and G. Walter, Photonics Technology Letters, IEEE of operation at extremely high speeds. For example, InP Volume: 19 Issue: 9 (2007); Experimental Determination Of HBTs have, in recent years, been demonstrated to exhibit The Effective Minority Carrier Lifetime In The Operation Of operation at speeds above 500 GHz. 30 A Quantum-Well n-p-n Heterojunction Bipolar Light-Emit Another part of the background hereof lies in the develop ting Transistor Of Varying Base Quantum-Well Design And ment of heterojunction bipolar transistors which operate as Doping; H. W. Then, M. Feng, N. Holonyak, Jr., and C. H. light-emitting transistors and laser transistors. Reference can Wu, Appl. Phys. Lett. 91, 033505 (2007); Charge Control be made for example, to U.S. Pat. Nos. 7,091,082, 7.286,583 Analysis Of Transistor Laser Operation, M. Feng, N. Holo and 7.354,780, and to the following: U.S. patent application 35 nyak, Jr., H. W. Then, and G. Walter, Appl. Phys. Lett. 91, Ser. No. 10/646,457, filed Aug. 22, 2003: U.S. patent appli 053501 (2007); Optical Bandwidth Enhancement By Opera cation Ser. No. 1 1/364,893, filed Feb. 27, 2006; and U.S. tion And Modulation Of The First Excited State Of A Tran patent application Ser. No. 1 1/805,859, filed May 24, 2007: sistor Laser, H.W. Then, M. Feng, and N. Holonyak, Jr., Appl. PCT International Patent Publication Number WO/2005/ Phys. Lett. 91, 183505 (2007); Modulation Of High Current 020287, published Mar. 3, 2005, and PCT International 40 Gain (BD49) Light-Emitting InGaN/GaN Heterojunction Patent Publication Number WO/2006/006879 published Bipolar Transistors, B. F. Chu-Kung, C. H. Wu, G. Walter, M. Aug. 9, 2006; all the foregoing being assigned to the same Feng, N. Holonyak, Jr., T. Chung, J.-H. Ryou, and R. D. assignee as the present Application. Reference can also be Dupuis, Appl. Phys. Lett. 91,232114 (2007); Collector Char made to the following publications: Light-Emitting Transis acteristics And The Differential Optical Gain Of A Quantum tor: Light Emission From InGaP/GaAs Heterojunction Bipo 45 Well Transistor Laser, H. W. Then, G. Walter, M. Feng, and N. lar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Holonyak, Jr., Appl. Phys. Lett. 91,243508 (2007), Transistor Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Het Laser With Emission Wavelength at 1544 nm, F. Dixon, M. erojunction Bipolar Light-Emitting Transistor, M. Feng, N. Feng, N. Holonyak, Jr., Yong Huang, X. B. Zhang, J. H. Ryou, Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 and R. D. Dupuis, Appl. Phys. Lett. 93, 021111 (2008). (2004); Type-II GaAsSb/InP Heterojunction Bipolar Light 50 Fundamental to the transistor is the base and base current. Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, This is evident at once from the original transistor of Bardeen G. Walter, and R. Chan, Appl. Phys. Lett. 84, 4792 (2004); and Brattain (J. Bardeen and W. H. Brattain, Phys. Rev. 74, Laser Operation Of A Heterojunction Bipolar Light-Emitting 230 (1948)), the point contact transistor with only, and Transistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, uniquely, the base region semiconductor material. The base Appl. Phys. Lett.85,4768 (2004); Microwave Operation And 55 current (I) separates the low impedance input, the minority Modulation Of A Transistor Laser, R. Chan, M. Feng, N. “emitter current (I), from the high impedance output, the Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, 131114 “collector current (I), thus yielding a “transfer resistor” (2005); Room Temperature Continuous Wave Operation OfA (I+I, +I-0, B-gain II/II, B210, II, I-0). If now, Heterojunction Bipolar Transistor Laser, M. Feng, N. Holo over 60 years later, one considers the highest speed transistor nyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 60 (see W. Snodgrass, B. R. Wu, K.Y. Cheng, and M. Feng, IEEE 131103 (2005); Visible Spectrum Light-Emitting Transistors, Intl. Electron Devices Meeting (IEDM), pp. 663-666 (2007)), F. Dixon, R. Chan, G. Walter, N. Holonyak, Jr., M. Feng, X. B. the n-p-n heterojunction bipolar transistor (HBT), which Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 88, operates at Small size and high current density, there is 012108 (2006): The Transistor Laser, N. Holonyak and M enough base current (and recombination) in a small enough Feng, Spectrum, IEEE Volume 43, Issue 2, February 2006; 65 Volume, say, of 'good' geometry, to change spontaneous Signal Mixing. In A Multiple Input Transistor Laser Near recombination into stimulated recombination. This can be the Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A.James, and basis of a transistor laser (TL) (see G. Walter, N. Holonyak, US 7,813,396 B2 3 4 Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85,4768 (2004)), adjacent the base region includes: providing an emitter region particularly if quantum wells are inserted into the base region that comprises an n-type layer, providing a base region that to control the recombination (trading-off electrical gain B for comprises a plurality of p-- layers; and providing a collector optical gain) and if moreover, the base region, adapted to be region that comprises an n+ layer adjacent a p-- layer of the a resonator, is afforded adequate Q. As has been shown (see A. 5 base region to form said tunnel junction. James, N. Holonyak, Jr., M. Feng, and G. Walter, IEEE Pho A form of the invention is directed to a three terminal tonics Technol. Lett. Vol. 19, 680 (2007)), the recombination semiconductor device for producing light emission in optical signal, via internal Franz-Keldysh (FK) absorption response to electrical signals, comprising: a semiconductor (see C. M. Wolfe, N. Holonyak, Jr., and G. E. Stillman, base region disposed between a semiconductor emitter region Physical Properties of Semiconductors, Prentice Hall, Engle- 10 and a semiconductor collector region that forms a tunnel wood Cliffs, N.J., pp. 219–220 (1989)), causes voltage-de junction adjacent the base region; the base region having a pendent breakdown and negative resistance in the TL collec region therein exhibiting quantum size effects; and an emitter tor characteristics (see A. James, G. Walter, M. Feng, and N. terminal, a base terminal, and a collector terminal respec Holonyak, Jr., Appl. Phys. Lett. 90, 152109 (2007)). Other tively coupled with the emitter region, the base region and the characteristics, properties, and applications of transistor 15 collector region; whereby application of said electrical sig lasers and light emitting transistors are described in detail in nals with respect to the emitter, base, and collector terminals, the above-referenced publications and patent documents. causes light emission from the base region. An optical reso It is among the objectives of the present invention to nant cavity encloses at least a portion of the base region, and improve on the efficiency and flexibility of operation of tran the light emission comprises laser emission. In an embodi sistor lasers and their applications. 2O ment of this form of the invention, the emitter region com prises an n-type layer, the base region comprises a plurality of SUMMARY OF THE INVENTION p+ layers; and the collector region comprises an n+ layer adjacent a p-- layer of the base region to form the tunnel In the parent Application hereof, U.S. patent application junction. Ser. No. 12/287,697, filed Oct. 10, 2008, there is disclosed, 25 In a further form of the invention, a method is set forth for interalia, a two-terminal tunneljunction laser with a collector producing laser emission modulated with mixed signals rep tunnel junction; that is, an n-p-n tunnel junction laser with resentative of a first RF input comprising an input current and electrical contacts on the emitter and collector layers. In the a second RF input comprising an input Voltage, including the disclosure hereof, there is set forth, interalia, a three-terminal following steps: providing a semiconductor base region dis transistor laser and method in which a collector tunnel junc- 30 posed between a semiconductor emitter region and a semi tion is used to great advantage. conductor collector region that forms a tunnel junction adja A form of the invention is directed to a method for produc cent the base region; providing, in the base region, a region ing light emission from a semiconductor device, including the exhibiting quantum size effects; providing an optical resonant following steps: providing a semiconductor base region dis cavity enclosing at least a portion of the base region; provid posed between a semiconductor emitter region and a semi- 35 ing an emitter terminal, a base terminal, and a collector ter conductor collector region that forms a tunnel junction adja minal respectively coupled with the emitter region, the base cent the base region; providing, in the base region, a region region, and the collector region; and applying electrical sig exhibiting quantum size effects; providing an emitter termi nals with respect to the emitter terminal, the base terminal and nal, a base terminal, and a collector terminal respectively the collector terminal to produce said laser emission from the coupled with the emitter region, the base region, and the 40 base region, said applying of electrical signals including collector region; and applying electrical signals with respect application of the first RF input to the base terminal, and said to the emitter terminal, the base terminal and the collector applying of said electrical signals further including reverse terminal to produce light emission from the base region. biasing of the tunnel junction and application of the second In embodiments of this form of the invention the step of RF input across the collector terminal with respect to another providing, in the base region, a region exhibiting quantum 45 of the terminals. In an embodiment of this form of the inven size effects, can comprise, for example, providing a quantum tion, the optical output includes mixed multiples of the fre well in the base region and/or a layer of quantum dots in the quencies of said first and second input signals. In one embodi base region. A plurality of quantum size regions can also be ment, said another of said terminals comprises the emitter employed. A preferred embodiment of this form of the inven terminal, and in another embodiment, said another of said tion further comprises the step of providing an optical reso- 50 terminals comprises the base terminal. nant cavity enclosing at least a portion of the base region. The As will be described further, in three-terminal form, in cavity is partially transmissive, and the light emission com transistor configuration, minority electrons are Supplied by prises laser emission. In an embodiment of this form of the the emitter via forward bias injection, and the holes for elec invention, the step of applying said electrical signals includes tron-hole recombinations at the quantum-well (QW) are sup reverse biasing the tunnel junction, whereby electrons 55 plied by the usual base terminal ohmic current, I, as well as injected into the base region, via the emitter, recombine, in the by collector tunneling, I, +I, Because I can be supplied base region, with holes generated by the tunneljunction con independent of the base-collector bias Voltage, it can Sustain tributing to the laser emission. Also in this embodiment, the a certain photon density in the resonator cavity (proportional step of applying said electrical signals includes providing to I), which can then be employed to assist in collector input current to the base terminal to obtain further carrier 60 tunneling, hence the term "photon-assisted tunneling'. recombination in the base region, also contributing to the Therefore, the three-terminal form makes possible a way to laser emission. The carrier recombining, in the base region, is establish the initial photon density (via I) that consequently Substantially aided by the region exhibiting quantum size leads to the enhancement of laser operation by efficiently effects. In a preferred embodiment of this form of the inven delivering holes to the recombination center (QW and tion, the step of providing a semiconductor base region dis- 65 waveguided region) by photon-assisted tunneling. These posed between a semiconductor emitter region and a semi holes need only traverse a relatively short vertical distance conductor collector region that forms a tunnel junction (for example, ~30 nm) compared to the much larger lateral US 7,813,396 B2 5 6 distances (for example, ~5um) traversed (via relaxation) by a absorption). The LI-V of the comparison TL (b) shows simi hole Supplied by I (with attendant large ohmic loss). lar behavior occurring gradually only at higher V21.6 V. Among the advantages of the methods and devices hereof FIG. 5 is a schematic device cross-section illustrating the (which are sometimes referred to by Applicant as “tunnel various processes shown in FIG. 2. The band diagram below junction transistor laser' (TJ-TL) methods and devices), are the device shows the base quantum well and tunnel junction. the following: (a) The collector tunnel junction re-supplies FIG. 6 shows the modulation characteristics of a common holes to the base region at greater efficiencies, which is advan emitter TJ-TL biased in: (a) region 1 of FIG. 3 with I-90 tageous for design of lasers with low threshold and high mA, V-0.52 V, and BE RF-input current modulation; (b) external quantum efficiency. (b) The collector tunnel junc region 2 with I-90 mA, V-1.08 V, and CE RF-input tions sensitivity to third terminal voltage control enables a 10 Voltage modulation. The optical outputs are equal in both direct Voltage-controlled modulation capability in addition to CaSCS. a direct current modulation capability. (c) Direct Voltage FIG. 7 is a schematic band diagram illustrating the internal modulation of a tunneljunction transistor laser can produce a feedback loop of a TJ-TL involving photon-assisted tunnel high extinction ratio with low Voltage Swing due to its rela ing at the collector junction. Photon signals are “detected tively strong coupling and close proximity (for example, ~30 15 and converted into hole currents that are channeled back into nm) to the photon generation center (quantum-well). (d) the base region. Direct Voltage modulation of a tunneljunction transistor laser FIG. 8 shows (a) the magnitude of the fundamental signal results in low photon coupling loss because the tunnel junc (fi, f.) and the 3" order intermodulation products (2f-f. tion is an integral part of the device. (It is formed as part of the 2f-f) as device bias Voltage V is varied, and (b) depen collector and its design.) In contrast, existing monolithic dence of the intermodulation distortion-to-signal ratio on the Solutions involving separate lasers and external modulators optical output per facet. (all hooked together) Suffer coupling losses and manufactur FIG. 9 shows the TJ-TL in (a) common-emitter, (b) com ingyield issues due to difficulty in material growth and align mon-base, and (c) common-collector configurations for the ment. (e) The ability to operate in both current and voltage conversion of an electrical input to simultaneous optical and modulation circuit formats allows signal mixing employing 25 electrical outputs. two input electrical ports. (f) The collector junction enables FIG. 10 shows an equivalent circuit model of the TJ-TL an improved internal base signal feedback loop involving showing the collector tunneling process represented by a photon-assisted tunneling. This offers an internal mechanism nonlinear resistor, r, in parallel with the extrinsic base-col for more efficient implementation of feedback circuit strate lector capacitance, Cace. In common-emitter configura gies because of the minimal loss of signal strength. In existing 30 tion, r, routes RF (hole) currents more efficiently to the QW feedback implementations involving two-terminal diode recombination center, and away from the extrinsic Cece, lasers, the photon signal is subject to an external photodetec path, thus improving the RF signal isolation between the BE tor, and then converted to an electrical signal before it is fed and CE-ports. back into the laser input. It involves many components and FIG. 11 shows a TJ-TL in (a) common-emitter, (b) com incurs large coupling and conversion losses. (g) The collector 35 mon-base, and (c) common-collector configurations for sig tunnel junction adds a new dimension to design of input nal mixing and conversion of two electrical inputs to an impedance matching. (h) The collector tunnel junction optical output. improves isolation between the two electrical ports, and is FIG. 12 shows signal mixing with a TJ-TL in the configu advantageous for alleviating isolation issues in large devices. ration shown in FIG. 11a, producing an optical output with Good isolation between the ports is beneficial for signal pro 40 harmonics, mf+nf. The Smaller diagrams (a) through (e) cessing, such as for signal mixing utilizing the two ports as show frequency components in further detail around the har inputs. monic peaks labeled with corresponding letters. Further features and advantages of the invention will become more readily apparent from the following detailed DETAILED DESCRIPTION description when taken in conjunction with the accompany 45 ing drawings. As described further hereinbelow, high p+ and n+ tunnel junction doping are employed at the collector of a transistor laser (TL) to enable the laser operation to be more effectively BRIEF DESCRIPTION OF THE DRAWINGS controlled by changes in bias (voltage), which makes possible 50 a direct Voltage modulation circuit format in addition to the FIG. 1 is a diagram, not to scale, of the layer structure of a usual direct current modulation. The collector tunnel junc tunneljunction transistor laser (TJ-TL) in accordance with an tion, as used herein, is a major source of hole re-supply to the exemplary embodiment of the invention. base, and to recombination, complementing and competing FIG. 2 is a schematic band diagram of a TJ-TL of the type with the usual base current I. As will be demonstrated, the represented in FIG. 1, shown with a generic resonator cavity. 55 collector tunneljunction leads to a sensitive region, a Voltage FIG. 3 shows the collector I-V characteristics of (a) a dependent “sweet spot”, in the laser operation. The tunnel TJ-TL in accordance with an embodiment hereof, and (b) a junction can be used to enhance transistor laser operation and comparison transistor laser (TL) without a collector tunnel simultaneously it can be quenched by photon-assisted (FK) junction. Below the “knee' voltages, the transistors are biased tunneling, thus adding significantly to TL flexibility and use. in Saturation. The tunneling process is evident from the slope 60 The n-InCap/p"-GaAs/n-GaAs tunnel junction HBT of the collector current, I, VS emitter-collector Voltage bias, layer structure of an example hereof, and a comparison n-In V (0.4-1.6 V), which otherwise would be “flat” as in the GaP/p"-GaAs/n-GaAs HBT structure without a collector collector I-V of the (b) comparison TL. tunnel junction, are grown on a GaAs substrate by MOCVD. FIG. 4 shows the dependence of optical output of the TJ-TL The detailed tunnel junction HBT structure is shown in FIG. (of FIGS. 1 and 2) on V, indicating the enhancement 65 1. It includes: a 40 nm InooGaos Pemitter 110, Si-doped to (V<0.8 V) and quenching (V20.8 V) of the laser output 3x10'7 cm; an 85 nm GaAs base 120 (with p" and transition by Franz-Keldysh (FK) photon-assisted tunneling (photon layers as shown), C-doped to 1x10" cm; a single undoped US 7,813,396 B2 7 8 15 nm Inos Gaoss AS base-region quantum well 125 at wave carrier injection (I, I-0). However, under stronger reverse length, us980 nm, and a 40 nm n+ GaAs collector 130, biased collector junction field (region 2 of FIG. 4), the optical Si-doped to 7x10" cm. (As seen, in this example, the tun output is reduced and Subsequently quenched by Franz nel junction, labeled 135, comprises the n+ collector forming Keldysh absorption. The collector tunnel junction, as a con a tunnel junction adjacent the p-- base; i.e., in this case the 5 sequence, enables the laser output to be controlled effectively (n+) (p+) tunnel junction comprises collector layer 130 and by the use of a third terminal control voltage. This enables the layer 121 of the base region 120. It will be understood that this TJ-TL to be directly modulated via the usual current control corresponds to calling the adjacent layers 130-121 the “col (ÖI, ÖI) as well as now Voltage control (ÖV, ÖV). lector.) Conventional upper and bottom cladding, contact Despite relying on only the bulk FK effect, the proximity of layers, etch stop layers, etc. are as shown in FIG. 1. The 10 the collector tunnel junction to the photon generation center comparison HBTTL structure is essentially identical to the (QW), and the strong coupling of the tunneling process to the tunnel junction HBT structure except its collector is a 60 nm cavity optical field, the result is a sensitive response of the GaAs layer, Si-doped to 2x10' cm (not directly tunneling stimulated optical field to Voltage control, resulting in a high as-grown, as-doped). The fabrication techniques for this extinction ratio (ER), or “on-off ratio. In FIG.3 the laser can example are of the type disclosed in M. Feng, N. Holonyak, 15 be switched, for example, from a high output of 800 uW to a Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 low output of 30 uW (I-80 mA), achieving an ER of 15 dB (2005) and in M. Feng, N. Holonyak, Jr., A. James, K. over a change in V (third terminal control) of only 0.8V. A Cimino, G. Walter, and R. Chan, Appl. Phys. Lett. 89, 113504 low Voltage-Swing with a high ER is especially advantageous (2006), incorporated herein by reference. As described for making highly efficient, low power Voltage-controlled therein, the various transistor contacts are realized by top lightwave modulators. down metallization on ledges, steps, or apertures processed FIG. 6 shows the modulation characteristics of a common by photolithography and etching down to the relevant expi emitter TJ-TL at two different biases. The biases are chosen taxial layers of the TL crystal. For convenience in cleaving So as to maintain the same photon densities in each case. A and heat sinking, the metallized wafer is lapped to a thickness resonance-constrained modulation response with photon of ~70 Lum. Experimental samples with 6 um emitter mesa 25 carrier relaxation oscillation at frequency f is obtained with widths (reduced to a 4.5um active width by edgewise oxida the BC junction forward biased in FIGS. 6 (a) and (b). In this tion of one of the top AlGaAs layers) and with 3 um wide base mode of operation, the TJ-TL is biased in saturation (i.e., two contacts at 5 um spacings from the emitter edges are cleaved forward biased p-n junctions) as is identified in the regime normal to the emitter stripes to form Fabry-Perot end facets before the “knee of the I-V characteristics of FIG. 3 and with 400 um spacings. 30 operating region (1) of FIG. 4. However, when operated in the It will be understood that while an edge-emitting laser is forward-active mode (region 2 of FIG. 4), the modulation utilized for the examples hereof, other resonant cavity con response is free of resonance, extending the usable bandwidth figurations, such as a vertical cavity configuration, can alter to its greater 3 dB bandwidth, f, . The "tilt” in the base natively be fabricated using, for example, upper and lower charge population, imposed by the boundary condition at the reflecting layers such as DBRs. 35 reverse-biased BC junction, removes the (Saturated) charge FIG. 2 shows the schematic band diagram of the n-p-n “pile-up”, and together with the voltage-controlled photon tunneljunction transistor laser (TJ-TL), biased as shown, and absorption (FK tunneling) at the collector, contributes to the with the key physical processes labeled. The resonator cavity relatively “flat” response (b) of FIG. 6. The performance of reflectors are represented by the shaded squares. The emitter, the TJ-TL employed for the present example is still limited by base, and collector regions are labeled E. B. and C, respec 40 its large geometry and its prototypical layer structure, result tively. It is the emitter current (minority current in the base) ing in undesirable parasitic delay elements. with the junction in forward bias. It is the re-supply of holes It is noted that the photon-assisted tunneling in a TJ-TL by the usual base ohmic contact; I is the re-supply to the forms a mechanism for internal base signal feedback as base of holes by the FK photon-assisted tunneling; I repre shown in FIG. 7. The photon generated from base recombi sents the re-supply to the base of holes via the direct tunneling 45 nation is absorbed or detected by a tunneling electron from of electrons; and I, is the usual minority carriers current that base to collector. This result in a feedback signal that is do not recombine in the base and are collected. The collector proportional to the photon output and in the form of a hole current I, consists of the usual transport component across current re-supplied back into the base. The holes that are fed the base I, the Franz-Keldysh portion I, and the direct back to the base raise the electrical potential of the base, tunnel junction current I, or, 50 which in turn, increases the base-emitter potential difference, causing more minority electrons to be injected into the base Ic-I+I, +It. (1) from the emitter. This is unique to the triode. The feedback signal has a phase that depends on the delay time between the The base recombination current, I, is expressed as the Sum photon signal “detected at the collector junction and the of the hole components, or, 55 resultant change in the base-emitter potential, as well as the relative phase between base-emitter and base-collector volt IBIB+1-1+1-1. (2) age. The delay time and phase relationships may thus be FIG. 3 shows the collector I-V characteristics of (a) the modified by changing the layer structure design (e.g., by TJ-TL, and (b) the comparison TL of lesser collector doping varying the distance between the QW and the collector tunnel and no tunnel junction. The forward-active mode of the TJ 60 junction) as well as by external circuit elements (e.g., load, TL operation (i.e., the base-collector junction in reverse bias) Z) and three-terminal circuit configurations (e.g., common is indicated by the collector current, I, being nearly constant emitter, common-base, or common-collector). FIG. 8 shows (i.e., “flat”) despite further increase in V beyond the “knee” the third order intermodulation outputs of a common-emitter voltages of 0.4 V (I-56 mA) to 0.8 V (I-80 mA). The TJ-TL, and its dependence on bias voltage, V. While the effects of collector tunneling (FIG. 3a) are evident from the 65 signal strength of the fundamental “tones' at f and f, remain upward slope in the collector current, I, VS V, that other unchanged, the strength of the feedback signal depends on the wise would be photon gain established by emitter and base cavity photon density and the collector junction field strength US 7,813,396 B2 10 (bias Voltage, V). The capability to internally generate photon-assisted tunneling at the collector junction provides feedback signals of magnitude governed by a third terminal an internal feedback loop that can potentially be employed for Voltage control can lead to more efficient implementation of an efficient variety of circuit applications involving feedback feedback strategies for reduction of distortions in both the signals. The collector tunnel junction offers improved isola electrical and optical outputs of the transistor laser. tion between the two electrical ports, and convenience in the Moreover, in transistor form, the collector tunnel junction design and choice of input-signal impedance matching adds a new dimension to the design and choice of input opportunities, hence, making it advantageous for applications impedance matching for maximum power transfer. When in signal processing. compared to the comparison TL, the effective input imped The invention claimed is: ance "looking into the CE-input port is not necessarily large 10 1. A method for producing light emission from a semicon when the BC junction is reverse-biased, because the collector ductor device, comprising the steps of: tunnel junction provides, in effect, a low-resistance (tunnel) providing a semiconductor base region disposed between a path for current flow (Iz and I.1). For the common-emitter semiconductor emitter region and a semiconductor col TJ-TL (common-collector and common-base configurations lector region that forms a tunnel junction adjacent said are also possible, see FIG.9 for the various possible configu 15 base region; rations), microwave S-parameter measurements yield imped providing, in said base region, a region exhibiting quantum ances of magnitude 3-692 for the BE-input port, and 25-302 size effects; for the CE-input port. The higher CE-input port impedance is providing an emitter terminal, a base terminal, and a col more Suited for signal matching (50S2 standard) and Voltage lector terminal respectively coupled with said emitter controlled modulation. This is a major advantage (and oppor region, said base region, and said collector region; and tunity for application) of the three-terminal TL compared to a applying electrical signals with respect to said emitter ter two-terminal device. minal, said base terminal and said collector terminal to The collector tunnel junction also provides improved iso produce said light emission from said base region. lation between the two electrical ports, overcoming the 2. The method as defined by claim 1, wherein said step of effects of any signal “shunts’ between the two ports, created 25 providing, in said base region, a region exhibiting quantum for instance, by an extrinsic base-collector capacitance, Cec size effects, comprises providing a quantum well in said base ext in a common-emitter transistor. FIG. 10 shows a schematic region. circuit equivalent model of the TJ-TL. E. B., and C respec 3. The method as defined by claim 1, wherein said step of tively represent emitter, base, and collector. The resistors r providing, in said base region, a region exhibiting quantum and r, respectively represent the base resistance and collector 30 size effects, comprises providing a layer of quantum dots in resistance, C represents the base-emitter junction capaci said base region. tance, I, represents an active current dependent current source 4. The method as defined by claim 1, further comprising the (IfL), D represents the extrinsic collector junction pn step of providing an optical cavity enclosing at least a portion diode, D represents the intrinsic emitter junction pn diode, of said base region, said light emission comprising laser emis and D represents the intrinsic collector junction pn diode. 35 Sion. Collector tunneling is represented as a non-linear resistor, r. 5. The method as defined by claim 4, wherein said step of The resistance, r, in parallel with Cece provides a low applying said electrical signals includes reverse biasing said resistance path for routing current flows away from Cece tunnel junction; whereby electrons injected into the base and directing them towards the relevant recombination center region, via the emitter region, recombine, in the base region, (i.e., electrical-to-optical conversion). The common-emitter 40 with holes generated by the tunnel junction, contributing to TJ-TL employed in the present example gives two-port said laser emission. transconductances, ly, (li/y,l,o), that are 10 dB less 6. The method as defined by claim 5, wherein said step of compared to the comparison TL, while maintaining Isl, applying said electrical signals includes providing input cur (=IV./V, IV," o) of less than-20 dB over frequencies rang rent to said base terminal to obtain further carrier recombina ing from 0.050 to 20 GHz. The RF isolation between the two 45 tion in said base region, also contributing to said laser emis ports is advantageous for multiple-RF-input signal-process Sion. ing applications such as signal mixing. To demonstrate this, 7. The method as defined by claim 6, wherein said recom the TJ-TL is employed in a common-emitter, dual-input con bining, in said base region, is Substantially aided by said figuration, as shown in FIG.11(a). A single tone at frequency, region exhibiting quantum size effects. f=2.00 GHz is provided at the BE-port of the TJ-TL, while 50 8. The method as defined by claim 1, wherein said step of another single tone at frequency, f=2.01 GHz is provided at providing a semiconductor base region disposed between a the CE-port. The choice off and f, are made for the conve semiconductor emitter region and a semiconductor collector nience of later identifying and enumerating the various har region that forms a tunnel junction adjacent said base region monics that are present in the output optical signal. The mix includes: providing an emitter region that comprises an ing of both tones produces detectable harmonics as high as the 55 n-type layer, providing a base region that comprises a plural 11' order, with the highest harmonic (the present experimen ity of p-- layers; and providing a collector region that com tal apparatus has a 3 dB bandwidth limited to 20 GHz) being prises an n+ layer adjacent a p-- layer of said base region to 9f,+2f=22.09 GHz (FIG. 12). form said tunnel junction. The foregoing has demonstrated, interalia, a three-termi 9. The method as defined by claim 4, wherein said step of nal tunnel junction transistor laser with a sensitive third ter 60 providing a semiconductor base region disposed between a minal Voltage control for its optical output. In addition to the semiconductor emitter region and a semiconductor collector usual direct current modulation capability, the collector tun region that forms a tunnel junction adjacent said base region nel junction enables a direct Voltage-controlled absorption includes: providing an emitter region that comprises an modulation of the TJ-TL using collector photon-assisted n-type layer, providing a base region that comprises a plural (FK) tunneling. A relatively “flat, resonance-free response 65 ity of p-- layers; and providing a collector region that com with, advantageously, a comparatively larger usable band prises an n+ layer adjacent a p-- layer of said base region to widthis obtained with the TJ-TL in forward-active mode. The form said tunnel junction. US 7,813,396 B2 11 12 10. The method as defined by claim 9, further comprising 18. The device as defined by claim 16, wherein said emitter providing n-type cladding layers on said emitter layer and region comprises an n-type layer, said base region comprises n-type cladding layers on said collector layer. a plurality of p-layers; and said collector region comprises an 11. The method as defined by claim 1, wherein said step of n+layer adjacent a p-- layer of said base region to form said providing semiconductor emitter, base, and collector regions 5 tunnel junction. comprises providing said regions as III-V semiconductor 19. A method for producing laser emission modulated with materials. mixed signals representative of a first RF input comprising an 12. The method as defined by claim 9, wherein said step of input current and a second RF input comprising an input providing semiconductor emitter, base, and collector regions Voltage, comprising the steps of: comprises providing said regions as III-V semiconductor 10 providing a semiconductor base region disposed between a materials. semiconductor emitter region and a semiconductor col 13. A three terminal semiconductor device for producing lector region that forms a tunnel junction adjacent said light emission in response to electrical signals, comprising: base region; a semiconductor base region disposed between a semicon providing, in said base region, a region exhibiting quantum ductor emitter region and a semiconductor collector 15 size effects; region that forms a tunnel junction adjacent said base region; providing an optical cavity enclosing at least a portion of said base region having a region therein exhibiting quan said base region; tum size effects; providing an emitter terminal, a base terminal, and a col an emitter terminal, a base terminal, and a collector termi lector terminal respectively coupled with said emitter nal respectively coupled with said emitter region, said region, said base region, and said collector region; and base region and said collector region; applying electrical signals with respect to said emitter ter whereby application of said electrical signals with respect minal, said base terminal and said collector terminal to produce said laser emission from said base region, said to said emitter, base, and collector terminals, causes applying of electrical signals including application of light emission from said base region. 25 14. The device as defined by claim 13, wherein said region said first RF input to said base terminal, and said apply exhibiting quantum size effects comprises a quantum well. ing of said electrical signals further including reverse 15. The device as defined by claim 13, wherein said region biasing of said tunnel junction and application of said exhibiting quantum size effect comprises a layer of quantum second RF input across said collector terminal with dots. 30 respect to another of said terminals. 16. The device as defined by claim 13, further comprising 20. The method as defined by claim 19, wherein said opti an optical cavity enclosing at least a portion of said base cal output includes mixed multiples of the frequencies of said region, and wherein said light emission comprises laser emis first and second input signals. Sion. 21. The method as defined by claim 19, wherein said 17. The device as defined by claim 13, wherein said emitter 35 another of said terminals comprises said emitter terminal. region comprises an n-type layer, said base region comprises 22. The method as defined by claim 19, wherein said a plurality of p--layers; and said collector region comprises an another of said terminals comprises said base terminal. n+layer adjacent a p-- layer of said base region to form said tunnel junction.