US007711015B2
(12) Unlted States Patent (10) Patent N0.2 US 7,711,015 B2 Holonyak, Jr. et al. (45) Date of Patent: May 4, 2010
(54) METHOD FOR CONTROLLING OPERATION 4,845,535 A 7/1989 Yamanishi et a1...... 315/172 OF LIGHT EMITTING TRANSISTORS AND 4,958,208 A 9/1990 Tanaka ...... 357/34 LASER TRANSISTORS 5,003,366 A 3/1991 Mishima et al. 357/34 5,239,550 A 8/1993 Jain ...... 372/45 75 _ . _ 5,293,050 A 3/1994 Chapple-Sokolet al...... 257/17 ( ) Inventors‘ H‘irlonyagilh" UrbanIaL’ IL gs)’ 5,334,854 A 8/1994 Ono et al...... 257/13 1 0,“ eng’ ampalgn’ (U )’ 5,389,804 A 2/1995 Yokoyama et al. 257/197 Gabnelwalter, Urbana> IL (Us) 5,399,880 A 3/1995 Chand ...... 257/21 _ 5,414,273 A 5/1995 Shimura et al...... 257/17 (73) Asslgneei Th1? Board 0fTr_l1st_ees of The 5,588,015 A 12/1996 Yang ...... 372/45012 Unlverslty 0f 111111018, Urbana, IL (US) 5,684,308 A 11/1997 Lovejoy etal...... 257/184 5,723,872 A 3/1998 Seabaugh et al...... 257/25 ( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 (Continued) USC‘ 1540’) by 240 days‘ FOREIGN PATENT DOCUMENTS (21) APP1- NO-I 11/805359 JP 61231788 10/1986 (22) Filed: May 24, 2007 (Continued) (65) Prior Publication Data OTHER PUBLICATIONS Us Zoos/0240173 A1 Oct 2’ 2008 Light-Emitting Transistor: Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and Related US. Application Data W‘ Hafez’ Appl' Phys‘ Lett‘ 84’ 151 (2004)‘ (60) Provisional application No. 60/921,425, ?led on Apr. (Continued) 2’ 2007' Primary ExamineriDung T Nguyen (51) Int- Cl‘ (74) Attorney, Agent, or FzrmiMartm Novack H01S 3/113 (2006.01) (57) ABSTRACT (52) US. Cl...... 372/11; 372/1; 372/30; _ _ _ 372/3 8'03 A method for controlling operation of a transistor includes the (58) Fleld of Classl?catlon Search ...... 372/11, following Steps: providing a bipolar transistor having emitter’ _ _ _ 372/1’ 30 base and collector regions; applying electrical signals to the See aPPhCaUOn ?le for Complete Search hlstory- transistor to produce light emission from the transistor; (56) References Cited effecting photon-assisted tunneling of carriers in the transis tor With self-generated photons of the light emission, and U.S. PATENT DOCUMENTS controlling operation of the transistor by controlling the pho ton-assisted tunneling. 2,569,347 A 9/1951 Shockley 4,485,391 A 11/1984 Poulain et al...... 357/19 4,710,936 A 12/1987 Shibata et a1...... 372/45 29 Claims, 11 Drawing Sheets
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US. PATENT DOCUMENTS P. Grossman, and J. Choma, Jr., “Large Signal Modeling of HBT’s Including Self-Heating and Transit Time Effects” IEEE Transactions 5,780,880 A 7/1998 Enquist ...... 257/197 On Microwave Theory And Techniques, vol. 40, No. 3, Mar. 1992. 5,796,714 A 8/1998 Chino et al. 372/50 Y. Mori, J. Shibata,Y. Sasai, H. SeriZawa, and T. Kajiwar, “Operation 6,337,494 B1 1/2002 Ryum et al. . 257/197 Principle Of The InGaAsP/InP Laser Transistor”, Appl. Phys. Lett. 6,479,844 B2 11/2002 Taylor ...... 257/192 47(7), Oct. 1, 1985. 6,737,684 B1 5/2004 Takagiet al. 257/194 J. Genoe, C. Van Hoof, K. Fobelets, R. Mertens, and G. Borghs, “pnp 6,974,969 B2 12/2005 Taylor ...... 257/24 Resonant Tunneling Light Emitting Transistor” Appl. Phys. Lett. 62 7,091,082 B2 8/2006 Feng et al. .. . 438/235 (9), Aug. 31, 1992. 7,286,583 B2 10/2007 Feng et al. 372/30 P. Berger, N. Chand, and N. Dutta, “An AlGaAs Double-Heterojunc 2002/0030195 A1 3/2002 Yoshiiet al. . 257/101 tion Bipolar Transistor Grown By Molecular-Beam Epitaxy”, Appl. 2005/0040387 A1* 2/2005 Feng et al...... 257/14 2005/0040432 A1 2/2005 Feng et al. 257/198 Phys. Lett. 59 (9), Aug. 26, 1991. 2005/0054172 A1 3/2005 Feng et al. 438/313 E. Zanoni, L. Vendrame, and P Pavan, “Hot-Electron 2006/0208290 A1 9/2006 Feng et al. 257/292 Electroluminescence in AlGaAs/GaAs Heterojunction Bipolar Tran 2007/0201523 A1 8/2007 Walter et a1. 372/43 sistors”, Appl. Phys. Lett. 62 (4), Jan. 25, 1993. 2009/0115346 A1* 5/2009 Walter et a1...... 315/291 M. Harris, B. Wagner, S. Halpern and M. Dobbs, “Full Two-Dimen sional Electroluminescent (EL) Analysis of GaAs/AlGaAs HBTs”, FOREIGN PATENT DOCUMENTS IEEE 99CH36296. 37th Annual International Reliability Physics Symposium, San Diego., California, 1999. JP 2007067023 3/2007 K. Wang, P. Asbeck, M. Chang, G. Sullivan, and D. Millar, WO WO2005/020287 3/2005 “Noninterfering Optical Method Of HBT Circuit Evaluation”, Elec WO WO2006/093883 8/2006 tronics Letters, vol. 25 No. 17, Aug. 17, 1989. J. Bardeen and W.H. Brattain, “The Transistor, A Semi-conductor OTHER PUBLICATIONS Triode,” Physical Review 74, (1948). W. Shockley, “The Theory of p-n Junctions in Semiconductors and Quantum-Well-Base Heterojunction Bipolar Light-Emitting Tran p-n Junction Transistors,” Bell System Technology Journal 28, 435 sistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 489 (1949). 1952 (2004). Type-II GaAsSb/InP Heterojunction Bipolar Li ght-Emitting Transis R.N. Hall, G.E. Fenner, J.D. Kingsley, T.J. Soltys, and R0. Carlson, tor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, “Coherent Light Emission From GaAs Junctions,” Phys. Rev. Lett., Appl. Phys. Lett. 84, 4792 (2004). vol. 9. pp. 366-368, Nov. 1, 1962. Laser Operation Of A Heterojunction Bipolar Light-Emitting Tran M.I. Nathan, W.P. Dumke, G. Burns, F.H. Dill, Jr., and G. Lasher, sistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. “Stimulated Emission of Radiation From GaAs p-n Junction,” Appl. Lett. 85, 4768 (2004). Phys. Lett., vol. 1, pp. 62-64. Nov. 1962. Microwave Operation And Modulation Of A Transistor Laser, R. N. Holonyak, Jr. and SF. Bevacqua, “Coherent (Visible) Light Emis Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, sion From GaAs l_XPX Junctions,” Appl. Phys. Lett., vol. 1, pp. 82-83, 131114 (2005). Dec. 1962. Room Temperature Continuous Wave Operation Of A Heterojunc TM. Quist, R.H. Rediker, R.J. Keyes, W.E. Krag, B. Lax, A.L. tion Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, McWhorter, and H.J. Zeiger, “Semiconductor Maser of GaAs,” Appl. and R. Chan, Appl. Phys. Lett. 87, 131103 (2005). Phys. Lett., vol. 1. pp. 91-92, Nov. 1962. Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. H. Kroemer, “Theory Of A Wide-Gap Emitter For Transistors,” Pro Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. ceedings ofthe IRE 45, 1535-1537 (1957). Dupuis, Appl. Phys. Lett. 88, 012108 (2006). W. HafeZ, J.W. Lai and M. Feng, “InP/InGaAs SHBTs with 75 nm The Transistor Laser, N. Holonyak, M Feng, Spectrum, IEEE vol. 43, Collector and fr>500 GHZ”, Electronic Letters, vol. 39, No. 20, Oct. Issue 2, Feb. 2006. 2003. Signal Mixing In A Multiple Input Transistor Laser Near Threshold, W. HafeZ, J.W. Lai, and M. Feng “Record fT and fT + fMAX Perfor M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. mance of InP/InGaAs Single Heterojunction Bipolar Transistors,” Phys. Lett. 88, 063509 (2006). Electronics Letters, May 2003. Collector Current Map Of Gain And Stimulated Recombination On W. HafeZ, J .W. Lai, and M. Feng. “Sub-micron InP/InGaAs Single The Base Quantum Well Transitions Of A Transistor Laser, R. Chan ,N. Holonyak, Jr. ,A. James , G. Walter, Appl. Phys. Lett. 88, 143508 Heterojunction Bipolar Transistors With fT of 377 GHZ,” IEEE Elec (2006). tron Device Letters, May 2003. Collector Breakdown In The Heterojunction Bipolar Transistor laser, W. HafeZ, J .W. Lai and M. Feng, “Vertical scaling of 0.25 um Emitter G. Walter, A. James, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. InP/InGaAs Single Heterojunction Bipolar Transistors With fTof 452 Physics Lett. 88, 232105 (2006). GHZ,” IEEE Electron Devices Letters, Jul. 2003. High-Speed (Z1 GHZ) Electrical and Optical Adding, Mixing, and P. Enquist, A. Paolella, A.S. Morris, F.E. Reed, L. DeBarros, A.J. Processing of Square-Wave SignalsWith aTransistor Laser, M. Feng, Tessmer, and J .A. Hutchby, “Performance Evaluation Of Heterojunc N. Holonyak, Jr., R. Chan, A. James, and G. Walter, IEEE Photonics tion Bipolar Transistors Designed For High Optical Gain”, Research Technology Lett., vol. 18, No. 11, Jun. 1, 2006. Triangle Institute, Research Triangle Park, NC, ARL, Research Graded-Base InGaN/GaN Heterojunction Bipolar Light-Emitting Laboratory, Ft. Monmouth, NJ, Applied Research and Technology, Transistors, B.F. Chu-Kung, M. Feng, G. Walter, and J. Holonyak, Jr. Wake Forest, NC, , IEEE, pp. 278-287, 1995. et al., Appl. Physics Lett. 89, 082108 (2006). Yukihiko Arai, Masaaki Sakuta, Hiroshi Takano, Takashi Usikubo, Carrier Lifetime And Modulation Bandwidth of A Quantum Well RyoZo Furukawa, and Masao Kobayashi, “Optical Devices From AlGaAs/InGaP/GaAs/InGaAs Transistor Laser, M. Feng, N. AlGaAs-GaAs HBTs Heavily Doped With Amphoteric Si”, IEEE Holonyak, Jr., A. James, K. Cimino, G. Walter, and R. Chan, Appl. Transactoins On Electron Devices, pp. 632-638, V0. 42. No. 4, Apr. Phys. Lett 89, 113504 (2006). 1995. Chirp In A Transistor laser: FranZ-Keldysh Reduction of The G.W. Taylor, R.S. Mand, J .G. Simmons, andA.Y. Cho, “LedistoriA Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and Three-Terminal Double Heterostructure Optoelectronic Switch”, M. Feng, App. Phys. Lett. 90, 091109 (2007). Appl. Phys. Lett. 50 (6), Feb. 9, 1987. S. L. Miller and J. J. Ebers, Bell Syst. Tech. J. 34, 883 (1955). N. Holonyak “Quantum-Well And Superlattice Lasers: Fundamental J. L. Moll, M. Tanenbaum, J. M. Goldey, andN. Holonyak, Proc. IRE Effects” pp. 1-18, in “The Physics of Submicron Structures”, Plenum 44, 1174 (1956). Press, 1984. US 7,711,015 B2 Page 3
V. RyZhii, M. Willander, M. RyZhii and I. Khmyrova, M. Feng, N. Holonyak, Jr. and W. HafeZ, “Light-Emitting “Heterostructure Laser-Transistors Controlled By Resonant-Tunnel Transistor: : Light Emission From InGaP/GaAs Heterojunction ling Electron Extraction”, Semicond. Sci. Technol. 12 (1997) 431 Bipolar Transistors”, Appl. Phys. Lett. 84, 151, Jan. 5, 2004. 438. J. Shibata, Y. Mori, Y. Sasai, N. Hase, H. SeriZawa, and T. Kahwara “Fundamental Characteristics Of An InGaAsP/InP Laser Transistor”, V. RyZhi and I. Khmyrova, “Bistability Effect in Laser-Transistor Electronic Letters, vol. 21, p. 98, 1985. Resonant-Tunneling Structure” Solid-State Electronics vol. 37 Nos. F. Jain, C. Chung, R. LaComb and M. Gokhale, “Resonant Tunneling 4-6 pp. 1259-1262, 1994. Transistor Lasers: ANew Approach To Obtain Multi-State Switching R. Bhat, W.-P. Hong, C. Caneau, M. A. KoZa, C.-K. Nguyen, and S. And Bistable Operation”, International Journal Of Infrared And Mil Goswami, “InP/GaAsSb/InP And lnP/GaAsSb/InGaAsP Double limeter Waves, Springer, Dordrecht, NL, vol. 14, No. 6, pp. 1311 Heterojunction Bipolar Transistors With A Carbon-Doped Base 1322, Jun. 1993. Grown By Organometallic Chemical Vapor Deposition” Appl. Phys. Chun-Xia Du, Farice Duteil, Goran Hansson, and Wei-Xin Ni, “Si/ Lett. 68, 985 (1996). SiGe/ Si: Er: O Light-Emitting Transistors Prepared By Differential Molecular-Beam Epitaxy”, App. Phys. Letts., vol. 78, No. 12, Mar. T. McDermott, E. R. Gertner, S. Pittman, C. W. Seabury, and M. F. 19, 2001. Chang, “Growth And Doping Of GaAsSb Via Metalorganic Chemi J. Hu et al., “Type II Photoluminescence And Conduction Band cal Vapor Deposition For InP Heterojunction Bipolar Transistors” Offsets of GaAsSb/InGaAs and GaAsSb/InP Heterostructures Appl. Phys. Lett. 58, 1386 (1996). Grown By Metalorganic Vapor Phase Epitaxy” Applied Physics Let Dvorak, C. R. Bolognesi, O. J. Pitts, and S. P. Watkins, “300 GHZ ters, 73(19) Nov. 1998. InP/GaAsSb/InP Double HBTs With High Current Capability And Y. Yamashita et al., “Pseudomorphic In0_52Al0_48As/In0_7Ga0_3As BVCEO 5 6V” IEEE Elec. Dev. Lett. 22, 361 (2001). HEMTs With an Ultrahigh fT of 562 GHZ”, IEEE Electron Device V. de Walle, “Band Lineups And Deformation Potentials In The Lett. 23 (10), 573-575 (2002). Model-Solid Theory” Physical Review B 39, 1871 (1989). * cited by examiner US. Patent May 4, 2010 Sheet 1 0111 US 7,711,015 B2
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"101M611 US 7,711,015 B2 1 2 METHOD FOR CONTROLLING OPERATION trum Light-Emitting Transistors, F. Dixon, R. Chan, G. OF LIGHT EMITTING TRANSISTORS AND Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, LASER TRANSISTORS and R. D. Dupuis, Appl. Phys. Lett. 88, 012108 (2006); The Transistor Laser, N. Holonyak, M Feng, Spectrum, IEEE RELATED APPLICATION Volume 43, Issue 2, February 2006; Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Priority is claimed from US. Provisional Patent Applica Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. Phys. tion No. 60/921,425, ?led Apr. 2, 2007, and said US. Provi Lett. 88, 063509 (2006); and Collector Current Map Of Gain sional Patent Application is incorporated herein by reference. And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, N. Holonyak, Jr., GOVERNMENT RIGHTS A. James, G. Walter, Appl. Phys. Lett. Some history Will next be summariZed as part of the back The present invention Was made With government support, ground hereof. Employing both electrons and holes, intrinsi and the government has certain rights in the invention. cally bipolar, the transistor operates by injecting minority carriers into the base (B) at the emitter (E, current I E), recom FIELD OF THE INVENTION bining some of the carriers in the base (I B:[1—(X]IE), and transporting the remainder (ICIGIE, 0<0t§ 1, I E+I B+IC:0) to This invention relates to controlling operation of transis the higher impedance collector (C), thus forming a “transfer tors, especially heterojunction bipolar transistors that can resistor” (obviously the 1947 bipolar active device dubbed the operate as light-emitting transistors and laser transistors. 20 “transistor”, (see J. Bardeen and W. H. Brattain, Phys. Rev. 74, 230, 1948), the historic prototype and still relevant). In BACKGROUND OF THE INVENTION contrast to the emitter-to-collector carrier (current) transfer fraction ot, the transistor common-emitter gain [3 can be quite A part of the background hereof lies in the development of large, and is [3EIC/IB:0t/[1—0t]. Just from its geometry, a light emitters based on direct bandgap semiconductors such 25 simple n-type “slab” of Ge (only a semiconductor base “slab” as III-V semiconductors. Such devices, including light emit and a point contact input and outputisee J. Bardeen et al., ting diodes and laser diodes, are in Widespread commercial supra), it can be see at once Why Bardeen designated the use. emitter current as I E, the base current 13, and the collector Another part of the background hereof lies in the develop current IC (I E, I B, IC). It can be recogniZed immediately, from ment of Wide bandgap semiconductors to achieve high minor 30 the all-base Ge “slab” (see, again, Bardeen et al., supra), that ity carrier injection ef?ciency in a device knoWn as a hetero the “magic” of the transistor is intrinsically in the base. And, junction bipolar transistor (HBT). These transistor devices it is the base that potentially offers more, as demonstrated, for are capable of operation at extremely high speeds. For example, by the direct-gap, high-speed, high-current-density example, InP HBTs have, in recent years, been demonstrated (IC¢~106 A/cm2) heterojunction bipolar transistor (HBT) (see, to exhibit operation at speeds above 500 GHZ. 35 e.g., M. Feng, N. Holonyak, Jr., and W. HafeZ, Appl. Phys. Another part of the background hereof lies in the develop Lett. 84, 151 (2004); M. Feng, N. Holonyak, Jr., and R. Chan, ment of heterojunction bipolar transistors Which operate as Appl. Phys. Lett. 84, 1952 (2004)), a direct descendant of the light-emitting transistors and laser transistors. Reference can Bardeen and Brattain transistor, and realiZe the base although be made for example, to US. Pat. No. 7,091,082 and to the thin (10-100 nm), has room for more layering (bandgap and following: US. patent application Ser. No. 10/646,457, ?led 40 doping) and can be modi?ed. At the high current density of Aug. 22, 2003; US. patent application Ser. No. 10/861,320, the high-speed direct-gap HBT, and thus a high enough base ?led Jun. 4, 2004; US. patent application Ser. No. 11/068, current to be interesting (even With [3~100), it has been dem 561, ?led Feb. 28, 2005; US. patent application Ser. No. onstrated that signi?cant recombination radiation can be 11/1 75,995, ?led Jul. 6, 2005; and US. patent application Ser. expected (see, again, e.g., M. Feng, N. Holonyak, Jr., and W. No. 11/364,893, ?led Feb. 27, 2006; PCT International Patent 45 HafeZ, Appl. Phys. Lett. 84, 151 (2004); M. Feng, N. Holo Publication Number WO/2005/020287, published Mar. 3, nyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004)). In 2005, and PCT International Patent Publication Number fact, employing quantum Wells (QWs) and cavity re?ection, it WO/2006/006879 published Aug. 9, 2006; all the foregoing has been demonstrated that it is possible to re-invent the base being assigned to the same assignee as the present Applica region and its mechanics (its carrier recombination and trans tion. Reference can also be made, for example, to the folloW 50 port fraction), reduce the [3 gain (from ~100 to ~10), and ing publications: Light-Emitting Transistor: Light Emission achieve stimulated recombination, i.e., realiZe a transistor From InGaP/GaAs Heterojunction Bipolar Transistors, M. laser (see, eg G. Walter, N. Holonyak, Jr., M. Feng, and R. Feng, N. Holonyak, Jr., and W. HafeZ, Appl. Phys. Lett. 84, Chan, Appl. Phys. Lett. 85, 4768 (2004); M. Feng, N. Holo 151 (2004); Quantum-Well-Base Heterojunction Bipolar nyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. 55 131103 (2005)). This resulted in a unique transistor in form Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-II GaAsSb/InP and operation, as Well as a unique three-terminal laser. Heterojunction Bipolar Light-Emitting Transistor, M. Feng, It is among the objects of the present invention to provide N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Appl. improved techniques for operation of light emitting transis Phys. Lett. 84, 4792 (2004); Laser Operation Of A Hetero tors and laser transistors or transistor lasers. (The terms laser junction Bipolar Light-Emitting Transistor, G. Walter, N. 60 transistors and transistor lasers are used interchangeably Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85, throughout.) 4768 (2004); MicroWave Operation And Modulation Of A Transistor Laser, R. Chan, M. Feng, N. Holonyak, Jr., and G. SUMMARY OF THE INVENTION Walter, Appl. Phys. Lett. 86, 131114 (2005); Room Tempera ture Continuous Wave Operation Of A Heterojunction Bipo 65 In a transistor laser, beyond a certain threshold base recom lar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, and bination current I BIIth (see the upper left-hand corner of the R. Chan, Appl. Phys. Lett. 87, 131103 (2005); Visible Spec IC—VCE characteristics of FIG. 9), stimulated recombination US 7,711,015 B2 3 4 causes compression in the collector IC—VCE characteristics carriers in said transistor With self-generated photons of said and reduction in the gain [3 ([3s?m<[3spon) (see eg M. Feng, N. laser emission, and controlling said laser emission from said Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, transistor by controlling said photon-assisted tunneling. In an 131103 (2005)). As described further hereinbeloW, in the embodiment of this form of the invention, at least the base region of stimulated emission (I B>Ith, [3s?m<[3spon) much region of said transistor is disposed Within said cavity, and more structure is evident in the IC—VCE characteristics oWing said step of applying electrical signals to said transistor to to the sensitivity to QW band?lling, state change, spectral produce laser emission comprises effecting stimulated emis change (coherent/incoherent, or i/c), mode-hopping (c/c), sion from said base region. Again, the controlling of photon change in optical ?eld strength, and the effect of photon assisted tunneling can comprise attenuating and/or enhancing assisted collector tunneling. If the base region cavity Q (e.g., photon-assisting tunneling. In an embodiment of this form of a relatively long narroW device) is spoiled, the IC—VCE char the invention, the step of controlling said photon assisted acteristics revert to those of normal transistor behavior tunneling includes applying a control signal voltage to said (BStZ-MQBSPM) (see eg R. Chan, M. Feng, N. Holonyak, Jr.,A. transistor to render the collector junction of the transistor James, G. Walter, Appl. Phys. Lett. 88, 143508 (2006)), con more absorptive to said self-generated photons of said laser ?rming the basis of the transistor laser and hoW it employs emission. Also, in an embodiment of this form of the inven carrier transport (EQC) and QW-enhanced base recombina tion, the step of applying said control signal voltage com tion. prises applying an increase in emitter-collector voltage to said In accordance With as aspect of the present invention, transistor to render the collector junction more absorptive to operation of a bipolar transistor, Which in many applications said self-generated photons of said light emission. In a form hereof Will be a light-emitting bipolar transistor or laser tran 20 of this embodiment, the step of applying an increase in emit sistor, is controlled by effecting photon-assisted tunneling of ter-collector voltage is continued to implement sWitching carriers in the transistor, using photons generated by the tran from coherent to spontaneous emission. Also in a form of this sistor itself (“self-generated photons), and controlling the embodiment the step of applying an increase in emitter-col photon-assisted tunneling. Techniques can be employed, for lector voltage is continued to implement a state of sWitching example, for attenuating and/or enhancing the photon-as 25 from higher to loWer optical output. sisted tunneling, depending on the application. Further features and advantages of the invention Will In a form of the invention, a method is set forth for con trolling operation of a transistor, include the folloWing steps: become more readily apparent from the folloWing detailed description When taken in conjunction With the accompany providing a bipolar transistor having emitter, base and collec ing draWings. tor regions; applying electrical signals to the transistor to 30 produce light emission from the transistor; effecting photon assisted tunneling of carriers in the transistor With self-gen BRIEF DESCRIPTION OF THE DRAWINGS erated photons of said light emission, and controlling opera tion of the transistor by controlling said photon-assisted FIG. 1 is a simpli?ed cross-sectional diagram, not to scale, tunneling. The controlling of photon-assisted tunneling can 35 of a light-emitting transistor or laser transistor, as described in comprise attenuating and/or enhancing photon-assisted tun referenced PCT International Patent Application Publica neling. In an embodiment of this form of the invention, the tions. step of controlling said photon-assisted tunneling includes FIG. 2 is a simpli?ed schematic diagram of a three port applying a control signal voltage to the transistor to render the light-emitting transistor device as disclosed in the referenced collector junction of the transistor more absorptive to said 40 PCT International Patent Application Publication WO/2005/ self-generated photons of said light emission. Also in an 020287. embodiment hereof, the step of applying said control signal FIG. 3 illustrates re?ectors used in a bipolar transistor laser voltage comprises applying an increase in emitter-collector device as disclosed in the referenced PCT International Patent voltage to said transistor to render the collector junction more Application Publication WO/2005/020287. absorptive to said self-generated photons of said light emis 45 FIG. 4 shoWs a picture of a transistor laser in operation at 3 sion. In a form of this embodiment, the step of applying an GHZ, captured using a CCD camera. increase in emitter-collector voltage is continued to imple ment a state of discontinuous sWitching from higher to loWer FIG. 5 is a diagram, not to scale, of the epitaxial layer emitter-collector voltage at higher collector current. Also in a structure of a type of device that can be utiliZed in practicing embodiments of the invention. form of this embodiment, the step of applying an increase in 50 emitter-collector voltage is implemented at substantially con FIG. 6, Which includes diagrams 6(a), 6(b) and 6(0), shoWs stant base current. band diagrams that illustrate different states of operation of a In a disclosed embodiment of the invention, the step of laser transistor, including photon-assisted tunneling. The dia providing a bipolar transistor having emitter, base, and col gram of FIG. 6(a) shoWs a transistor laser con?guration With lector regions comprises providing a heterojunction bipolar 55 a QW p-type base and an intrinsic collector and n-type sub transistor having a base region thickness in the range of about collector forming a p-i-n junction (base-collector junction). 10 to 100 nm. In a preferred form of this embodiment, the step The diagram of FIG. 6(b) shoWs electron-hole pairs recom of providing a bipolar transistor having emitter, base, and bining in the quantum Well (QW), emitting photons With collector regions includes providing a base region that exhib energy smaller than the bandgap of the collector. When no its quantum siZe effects. 60 reverse bias is applied, the photons are minimally absorbed In accordance With a further form of the invention, a (transmitted). FIG. 6(c) shoWs that When a large enough ?eld method is set forth for producing controlled laser emission, (reverse bias) is applied across the depletion region, the pho including the folloWing steps: providing a bipolar transistor tons are absorbed With FranZ-Keldysh-effect assistance (pho having emitter, base and collector regions; disposing at least ton-assisted tunneling). The larger the ?eld, the higher the a portion of said transistor in an optical cavity; applying 65 absorption coef?cient. electrical signals to said transistor to produce laser emission FIG. 7 is a chart shoWing the epitaxial layers of a transistor from said transistor; effecting photon-assisted tunneling of laser device used in examples hereof. US 7,711,015 B2 5 6 FIG. 8 is a schematic diagram of an example of a circuit also described in the referenced PCT Published International that can be used to operate a laser transistor in accordance Patent Applications, and as illustrated in FIG. 2, a third port, with embodiments hereof. namely an optical output port, is provided, and is based on FIG. 9 shows collector IC—VCE characteristics of a transis (recombination-radiation) emission from the base layer of the tor laser with 6 um wide emitter and 450 um Fabry-Perot HBT light emitter. For the HBT of FIG. 1 operated, for cavity length operating at 150 C. Breakdown and discontinu example, with a common emitter con?guration, when an ous switching is observed for (X—>1 ((FAIC/AIE, IE+I 3+ electrical signal is applied to the input port (Port 1), there 10:0), from higher to lower voltage and higher current, which results simultaneously an electrical output with signal ampli (VCE) is lower at higher base current 15 The left-hand inset ?cation at Port 2 and optical output with signal modulation of shows the laser spectrum in the lower bias (V CE) gain-com light emission at Port 3. pression region (lower [3:0t/[1—a]) at base current 13:50 mA. As further described in the referenced PCT International The diagram in the upper right inset shows the tunneling Patent Application Publications WO/2005/020287 and process of photon generation and regeneration at the collector WO/2006/093883, FIG. 3 illustrates the three terminal light and nearby quantum well leading to 0t—>1 and breakdown. emitting HBT, 910, in a lateral cavity, represented at 920, for FIG. 10 shows a curve-tracer plot of the 15:2 mA IC—VCE operation, for example, as a lateral gain guided laser. The characteristic of FIG. 9 showing in detail the (X—>1 breakdown lateral cavity may be de?ned, for example, by cleaved edges behavior and in the second panel the light intensity corre on or near the light emitting region. As further described in the sponding to points (a), (b), (c) and (d) of the I-V trace. The referenced PCT Published Patent Applications, and as will be light intensity from (a) to (b) agrees with AICIAIEIALW. understood throughout the present application, vertical cavity FIG. 11 shows the spectral curves corresponding to the data 20 laser con?gurations can also be employed. points of the second panel of FIG. 10. The normaliZed spec As also described in the referenced PCT International tral curves (a) and (c) of the inset, with higher and lower Patent Application Publications WO/2005/020287 and intensity compared, show little change in form. WO/2006/093883, stimulated emission can be employed to FIG. 12 shows a curve-tracerplot (left panel) of the IC—VCE advantage in the base layer of a bipolar transistor (eg a characteristics of a transistor laser with 6 um wide emitter and 25 bipolar junction transistor (BJT) or a heterojunction bipolar 450 um Fabry-Perot cavity length operating at —50° C. In the transistor (HBT), in order to enhance the speed of the tran negative resistance region at 15:40 mA, between points (b) sistor. Spontaneous emission recombination lifetime is a fun and (c), the recombination radiation changes from coherent to damental limitation of bipolar transistor speed. The base layer spontaneous and decreases in amplitude as shown by the (a), of a bipolar transistor is adapted to enhance stimulated emis (b), (c) spectral curves on the right. 30 sion (or stimulated recombination) to the detriment of spon taneous emission, thereby reducing recombination lifetime DETAILED DESCRIPTION and increasing transistor speed. At least one layer exhibiting quantum siZe effects, preferably a quantum well or a layer of FIG. 1 illustrates a light emitting transistor device of a type quantum dots, preferably undoped or lightly doped, is pro described in PCT International Patent Application Publica 35 vided in the base layer of a bipolar transistor. Preferably, at tion WO/2005/020287 and in PCT International PatentAppli least a portion of the base layer containing the at least one cation Publication WO/2006/093883, both of these PCT Pub layer exhibiting quantum siZe effects, is highly doped, and of lished International Patent Applications being incorporated a wider bandgap material than said at least one layer. The at herein by reference. A substrate 105 has the following layers least one quantum well, or, for example, layer of quantum disposed thereon: subcollector 110, n-type GaAs collector 40 dots, within the higher gap highly doped material, enhances 130, 600 Angstrom p+ compositionally graded InGaAs base stimulated recombination and reduces radiative recombina 140, n-type InGaP emitter 150, and cap layer 160.Also shown tion lifetime. A two-dimensional electron gas (“2-DEG”) are collector metalliZation (or electrode) 115, base metalliZa enhances carrier concentration in the quantum well or quan tion 145, and emitter metalliZation 165. Collector lead 117, tum dot layer, thereby improving mobility in the base region. base lead 147, and emitter lead 167 are also shown. As 45 Improvement in base resistance permits reduction in base described in the referenced PCT Published International thickness, with attendant reduction of base transport time. Patent Applications, for conventional PN junction diode These advantages in speed are applicable in high speed bipo operation, the recombination process is based on both an lar transistors in which light emission is utiliZed, and/or in electron injected from the n-side and a hole injected from the high speed bipolar transistors in which light emission is not p-side, which in a bimolecular recombination process can be 50 utiliZed. In light emitting bipolar transistor devices, for limited in speed. In the case of HBT light emission (as rep example heterojunction bipolar transistors of direct bandgap resented in FIG. 1 as light emission from base region 140) the materials, the use of one or more layers exhibiting quantum base “hole” concentration is so high that when an electron is siZe effects can also be advantageous in enhancing light emis injected into the base, it recombines (bimolecular) rapidly. sion and customiZing the emission wavelength characteristics The base current merely re-supplies holes via relaxation to 55 of the devices. Doped or highly doped quantum siZe regions neutraliZe charge imbalance. can also be utiliZed. As is also described in the referenced PCT International FIG. 4 shows a picture of a transistor laser in operation, as Patent Application Publications WO/2005/020287 and described in detail in the above-referenced PCT International WO/2006/093883, in typical transistor operation, one of the Patent Application Publication WO/2006/093883. In FIG. 4, three terminals of a transistor is common to both the input and the transistor laser, operating at 3 GHZ, is photographed using output circuits. This leads to familiar con?gurations known as a CCD camera. The light emission from the front Fabry-Perot common emitter (CE), common base (CB), and common facet was coupled (upward in FIG. 4) into an optical ?ber. collector (CC). The common terminal (often ground refer FIG. 5 shows the general epitaxial layers of a type of device ence) can be paired with one or the other of the two remaining that can be utiliZed in practicing embodiments and techniques terminals. Each pair is called a port, and two pairs for any 65 hereof, and which can be modi?ed to implement other con?gurations are called a two-port network. The two ports embodiments and techniques hereof. In the simpli?ed device are usually identi?ed as an input port and as an output port. As diagram of FIG. 5, a substrate, which may be doped or US 7,711,015 B2 7 8 undoped, is represented at 505, and has the following layers cally or lightly doped collector region of the transistor. In disposed thereon. A lower cladding layer, which is n-type in embodiments hereof, the collector region is an important this example (it being understood, throughout, that, where section of the optical waveguide region of the transistor laser suitable, devices of opposite conductivity type can be where it is strongly coupled to the optical ?eld maximum. In employed), is represented at 510. Then, an n-type sub-collec a form hereof, the photon-assisted tunneling absorption is tor contact layer is represented at 515, and an intrinsic or controlled under either common-emitter or common-base lightly doped n-type collector layer is represented at 520. transistor bias conditions. Next, a p-type base region, which preferably exhibits quan The band diagrams (a), (b), and (c) of FIG. 6 illustrate how tum siZe effects (eg by virtue of its own dimensions and/or photon-assisted tunneling is used to advantage in embodi by inclusion of one or more quantum well(s) and/or layer(s) ments hereof. The diagram of FIG. 6(a) shows a transistor of quantum dots and/or quantum wires), is represented at 530. laser con?guration with a p-type base having a quantum well Disposed thereon are n-type emitter 550, n-type upper clad and an intrinsic collector and n-type sub-collector forming a ding 570, and an n-type emitter contact layer, represented at p-i-n junction (base-collector junction). There is no applied 580. Contacts and leads for application of signals are applied bias voltage. The diagram 6(b) shows the situation with to the sub-collector contact layer 515, the base layer 530, and VCE