US20080089368A1 - Semiconductor laser devices and methods - Google Patents
Semiconductor laser devices and methods Download PDFInfo
- Publication number
- US20080089368A1 US20080089368A1 US11/974,323 US97432307A US2008089368A1 US 20080089368 A1 US20080089368 A1 US 20080089368A1 US 97432307 A US97432307 A US 97432307A US 2008089368 A1 US2008089368 A1 US 2008089368A1
- Authority
- US
- United States
- Prior art keywords
- base
- excitation signal
- pulse width
- frequency
- collector
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims abstract description 41
- 239000004065 semiconductor Substances 0.000 title claims abstract description 13
- 230000003287 optical effect Effects 0.000 claims abstract description 46
- 230000005284 excitation Effects 0.000 claims abstract description 29
- 230000002269 spontaneous effect Effects 0.000 claims abstract description 29
- 239000000463 material Substances 0.000 claims abstract description 10
- 230000008878 coupling Effects 0.000 claims abstract description 8
- 238000010168 coupling process Methods 0.000 claims abstract description 8
- 238000005859 coupling reaction Methods 0.000 claims abstract description 8
- 238000004519 manufacturing process Methods 0.000 claims abstract description 5
- 230000007423 decrease Effects 0.000 claims description 10
- 230000001965 increasing effect Effects 0.000 claims description 7
- 230000006798 recombination Effects 0.000 description 40
- 238000005215 recombination Methods 0.000 description 40
- 230000008569 process Effects 0.000 description 18
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 15
- 229920002120 photoresistant polymer Polymers 0.000 description 13
- 238000001228 spectrum Methods 0.000 description 13
- 239000000523 sample Substances 0.000 description 11
- 239000013078 crystal Substances 0.000 description 10
- 229910000530 Gallium indium arsenide Inorganic materials 0.000 description 8
- 238000005259 measurement Methods 0.000 description 7
- 230000001681 protective effect Effects 0.000 description 7
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000000969 carrier Substances 0.000 description 4
- 238000005253 cladding Methods 0.000 description 4
- 239000002096 quantum dot Substances 0.000 description 4
- 230000005855 radiation Effects 0.000 description 4
- 230000002441 reversible effect Effects 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 239000002019 doping agent Substances 0.000 description 3
- 230000001747 exhibiting effect Effects 0.000 description 3
- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 description 3
- 238000001465 metallisation Methods 0.000 description 3
- 230000007935 neutral effect Effects 0.000 description 3
- 230000005476 size effect Effects 0.000 description 3
- 230000003595 spectral effect Effects 0.000 description 3
- 229910017401 Au—Ge Inorganic materials 0.000 description 2
- 229910018885 Pt—Au Inorganic materials 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 238000005530 etching Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 229910001092 metal group alloy Inorganic materials 0.000 description 2
- 238000000059 patterning Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 238000001039 wet etching Methods 0.000 description 2
- 229910000980 Aluminium gallium arsenide Inorganic materials 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 238000005513 bias potential Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910000041 hydrogen chloride Inorganic materials 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 239000000700 radioactive tracer Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 230000005533 two-dimensional electron gas Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/0004—Devices characterised by their operation
- H01L33/0008—Devices characterised by their operation having p-n or hi-lo junctions
- H01L33/0016—Devices characterised by their operation having p-n or hi-lo junctions having at least two p-n junctions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/06203—Transistor-type lasers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/08—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
- H01S5/0422—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0618—Details on the linewidth enhancement parameter alpha
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/06226—Modulation at ultra-high frequencies
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/068—Stabilisation of laser output parameters
- H01S5/06812—Stabilisation of laser output parameters by monitoring or fixing the threshold current or other specific points of the L-I or V-I characteristics
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
- H01S5/3054—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure p-doping
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/3211—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34313—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer having only As as V-compound, e.g. AlGaAs, InGaAs
Definitions
- This invention relates to semiconductor laser devices and methods, and also to a laser transistor and techniques for enhancing high speed optical signal generation.
- HBT heterojunction bipolar transistor
- Another aspect of the prior copending applications involves employing stimulated emission to advantage in the base layer of a bipolar transistor (e.g. a bipolar junction transistor (BJT) or a heterojunction bipolar transistor (HBT), in order to enhance the speed of the transistor.
- a bipolar transistor e.g. a bipolar junction transistor (BJT) or a heterojunction bipolar transistor (HBT)
- BJT bipolar junction transistor
- HBT heterojunction bipolar transistor
- the base layer of a bipolar transistor is adapted to enhance stimulated emission (or stimulated recombination) to the detriment of spontaneous emission, thereby reducing recombination lifetime and increasing transistor speed.
- At least one layer exhibiting quantum size effects preferably a quantum well or a layer of quantum dots, preferably undoped or lightly doped, is provided in the base layer of a bipolar transistor. At least a portion of the base layer containing the at least one layer exhibiting quantum size effects, is highly doped, and of a wider bandgap material than the at least one layer.
- the at least one quantum well, or layer of quantum dots, within the higher gap highly doped material enhances stimulated recombination and reduces radiative recombination lifetime.
- a two-dimensional electron gas (“2-DEG”) enhances carrier concentration in the quantum well or quantum dot layer, thereby improving mobility in the base region.
- Improvement in base resistance permits reduction in base thickness, with attendant reduction of base transport time.
- these advantages in speed are applicable in high speed bipolar transistors in which light emission is utilized, and/or in high speed bipolar transistors in which light emission is not utilized.
- the use of one or more layers exhibiting quantum size effects can also be advantageous in enhancing light emission and customizing the emission wavelength characteristics of the devices.
- a semiconductor laser including: a heterojunction bipolar transistor structure comprising collector, base, and emitter of direct bandgap semiconductor materials; an optical resonant cavity enclosing at least a portion of the transistor structure; and means for coupling electrical signals with the collector, base, and emitter regions to cause laser emission from the device.
- a plurality of spaced apart quantum size regions e.g. quantum wells and/or quantum dots
- the base region can be provided with several spaced apart quantum size regions of different thicknesses, with the thicknesses of the quantum size regions being graded from thickest near the collector to thinnest near the emitter.
- An injected electron is captured in a smaller well, tunnels into the next bigger well, and then the next bigger well, and so forth, until, at the biggest well closest to the collector, it tunnels to and relaxes to the lowest state of the biggest well and recombines.
- the arrangement of wells encourages carrier transport unidirectionally from emitter toward collector. Maximum recombination and light are derived from the biggest well as near as possible to the collector, which is an advantageous position, such as for optical cavity reasons. Carriers diffuse “downhill” in energy; i.e., toward the thicker wells. The asymmetry in well size provides improved directionality and speed of carrier transport. In a light emitting HBT, light emission and device speed are both enhanced.
- a device and technique are set forth for high speed optical signal generation with an enhanced signal to noise ratio and control of “on” and “off” time durations utilizing the stimulated emission process for the “on” state and spontaneous emission process for the “off” state.
- the operating point and excitation of the transistor laser are selected to obtain cycles that each have an “on” portion of stimulated emission (laser optical output, and electrical signal output) and an “off” portion of spontaneous emission (without sensible optical output, and electrical noise).
- a method is set forth in accordance with an embodiment of the invention for producing controllable light pulses, including the following steps: providing a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials; providing an optical resonant cavity enclosing at least a portion of the transistor structure; and coupling electrical signals with respect to said collector, base, and emitter regions, to switch back and forth between a stimulated emission mode that produces output laser pulses and a spontaneous emission mode.
- the electrical signals include an AC excitation signal, and part of each excitation signal cycle is operative to produce stimulated emission, and another part of each excitation signal cycle is operative to produce spontaneous emission.
- the frequency of the excitation signal controls the frequency of the output laser pulses and the relative amplitude of the excitation signal controls the pulse width of the output laser pulses.
- the AC excitation signal is provided at a frequency of at least about 1 GHz, and the pulse width of the output laser pulses is controlled to be less than about 100 picoseconds.
- FIG. 1 is a simplified cross-sectional diagram, not to scale, of a light emitting transistor as described in a referenced copending Application.
- FIG. 2 shows, on the left, a diagram, not to scale, of the epitaxial layers of a crystal used for making a heterojunction bipolar light-emitting transistor (HBLET) in accordance with an embodiment of the invention and which can be used in practicing embodiments of the method of the invention, and, on the right, a corresponding band diagram.
- HBLET heterojunction bipolar light-emitting transistor
- FIG. 3 shows, on the left, a processed, metallized, and cleaved HBLET laser (top view) as made using the crystal of FIG. 2 and, on the right, an image of the operating device obtained with a video CCD detector.
- FIG. 4 shows the transistor I-V curves of another HBLET laser with ⁇ 260 ⁇ m spacing between the Fabry-Perot facets.
- FIG. 5 shows, in quasi-continuous operation (88% duty cycle at 60 Hz), the recombination radiation spectra of the HBLET device of FIG. 3 , but with slightly increased voltage bias V CE to increase the reverse bias on the base-collector junction.
- FIG. 6 shows the transistor I C versus V CE family of curves (at 213 K) of a 450 ⁇ m HBLET of another device in accordance with an embodiment of the invention and which can be used in practicing embodiments of the method of the invention.
- FIG. 9 shows a picture of the transistor laser in operation at 3 GHz, captured using a CCD camera.
- FIG. 10 shows, in traces (a), (b) and (c), respectively, the input signal modulated at 3 GHz, and the corresponding electrical and optical outputs.
- FIG. 11 shows the output collector I-V characteristics of an HBLET.
- I bth 0.744 mA
- the optical recombination process yields spontaneous emission (low optical output).
- the optical recombination process is stimulated (higher optical output power).
- the current gain beta increases (spontaneous emission), and the beta decreases when laser operation of the HBLET starts, since the recombination process for stimulated emission become “faster”.
- FIGS. 13 ( a ), 13 ( b ), 13 ( c ), and 13 ( d ) show, respectively, the input voltage, output voltage, optical output, and optical power spectrum for a laser transistor device operated in a stimulated emission mode.
- FIGS. 14 ( a ), 14 ( b ), and 14 ( c ), show, respectively, the input voltage, optical output, and optical power spectrum for a laser transistor device operated in a spontaneous emission mode.
- FIGS. 15 ( a ), 15 ( b ), 15 ( c ), and 15 ( d ) show, respectively, the input voltage, output voltage, optical output, and optical power spectrum for a laser transistor device operated in a near-threshold mode.
- FIG. 16 is a schematic diagram of an example of a circuit that can be used to operate a light emitting transistor in accordance with an embodiment of the invention.
- FIG. 17 shows output collector I-V characteristics of an HBLET, and signals that result when operated at different operating points.
- FIG. 18 shows the electrical output for operation at each of the different operating points.
- FIG. 19 shows the optical output for operation at each of the different operating points.
- FIG. 1 illustrates a device as set forth in the above-referenced copending application Ser. No. 10/646,457.
- a substrate 105 has the following layers disposed thereon: subcollector 110 , collector 130 , base 140 , emitter 150 , and cap layer 160 . Also shown are collector metallization (or electrode) 115 , base metallization 145 , and emitter metallization 165 . Collector lead 117 , base lead 147 , and emitter lead 167 are also shown.
- the base layer 140 comprises 600 Angstrom thick p+ carbon-doped compositionally graded InGaAs (1.4% In)
- p 4.5 ⁇ 10 19 cm 3
- the recombination process is based on both an electron injected from the n-side and a hole injected from the p-side, which in a bimolecular recombination process can be limited in speed.
- the base “hole” concentration is so high that when an electron is injected into the base, it recombines (bimolecular) rapidly.
- the base current merely re-supplies holes via relaxation to neutralize charge imbalance.
- the base current can be classified into seven components, namely: (1) hole injection into the emitter region (i Bp ); (2) surface recombination current in the exposed extrinsic base region (i Bsurf ); (3) base ohmic contact recombination current (i Bcont ); (4) space charge recombination current (i Bscr ); (5) bulk base non-radiative recombination current due to the Hall-Shockley-Reed process (HSR) (i BHSR ); (6) bulk base Auger recombination current (i BAug ); and (7) bulk base radiative recombination current (i Brad ).
- HSR Hall-Shockley-Reed process
- the surface recombination current can be reduced significantly.
- the base current and recombination lifetime can be approximated as primarily bulk HSR recombination, the Auger process, and radiative recombination.
- the light emission intensity ⁇ I in the base is proportional to i Brad and is related to the minority carrier electron with the majority hole over the intrinsic carrier concentration, (np ⁇ n i 2 ), in the neutral base region and the rate of radiative recombination process, B, set forth in Equation (3) below, where the hole concentration can be approximated as equal to base dopant concentration, N B .
- the base recombination lifetime can be less than half of the total response delay time.
- the optical recombination process in the base should be at least two times faster than the speed of the HBT. In other words, HBT speed, which can be extremely fast, is limiting.
- a device and data are set forth showing laser operation of an InGaP—GaAs—InGaAs heterojunction bipolar light-emitting transistor (HBLET) with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the p-type base region.
- HBLET heterojunction bipolar light-emitting transistor
- GaAs substrate 210 with a GaAs substrate 210 , a 4000 ⁇ n-type heavily doped GaAs buffer layer 215 , followed by a 600 ⁇ n-type Al 0.40 Ga 0.60 As layer 220 , a 3500 ⁇ n-type Al 0.98 Ga 0.02 As layer 222 , and a 400 ⁇ n-type Al 0.40 Ga 0.60 As layer 224 forming the bottom cladding layers.
- a 400 ⁇ n-type sub-collector layer 230 is followed by a 200 ⁇ In 0.49 Ga 0.51 P etch stop layer (not shown), a 650 ⁇ undoped GaAs collector layer 240 , and a 940 ⁇ p-type GaAs base layer 250 (the active layer), which includes also (in the base region) a 120 ⁇ InGaAs QW (designed for ⁇ 980 nm).
- the epitaxial HBLET laser structure was completed with the growth of the upper cladding layers, which included a 1200 ⁇ n-type In 0.49 Ga 0.51 P wide-gap emitter layer 260 , a 300 ⁇ n-type Al 0.70 Ga 0.30 As oxidation buffer layer 270 , a 3500 ⁇ n-type Al 0.98 Ga 0.02 As oxidizable layer 275 (see J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, Appl. Phys. Lett. 57, 2844 (1990)), and a 1000 ⁇ n-type Al 0.40 Ga 0.60 As layer 280 . Finally, the HBLET laser structure was capped with a 1000 ⁇ heavily doped n-type GaAs contact layer 290 .
- the HBLET laser fabrication was performed by first patterning 6 ⁇ m protective SiN 4 stripes on the crystal. The top n-type Al 0.98 Ga 0.02 As oxidizable layer was then exposed by wet etching (1:8:160 H 2 O 2 :H 2 SO 4 :H 2 O) to form a ⁇ 6 ⁇ m emitter mesa. Next, a wide 150 ⁇ m protective photoresist (PR) stripe was placed over the emitter mesa and the unprotected Al 0.98 Ga 0.02 As layer was completely removed (1:4:80 H 2 O 2 :H 2 SO 4 :H 2 O), revealing the In 0.49 Ga 0.51 P wide-gap emitter layer.
- PR photoresist
- the protective PR stripe was then removed and the sample was oxidized for 7.5 min at 425° C. in a furnace supplied with N 2 +H 2 O, resulting in a ⁇ 1.0 ⁇ m lateral oxidation which formed ⁇ 4 ⁇ m oxide-defined apertures in the 6 ⁇ m emitter mesa (see, again, J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, supra (1990); S. A. Maranowski, A. R. Sugg, E. I. Chen, and N. Holonyak, Jr., Appl. Phys. Lett. 63, 1660 (1993)).
- the samples were annealed (in N 2 ) at 430° C. for 7 minutes to reactivate p-dopants before the protective SiN 4 was removed by plasma (CF 4 ) etching.
- a 100 ⁇ m PR window was formed over the emitter mesa and oxide layer, and Au—Ge/Au was deposited over the sample to form metal contact.
- the Photoresist (PR) lift-off of the photoresist (PR) to remove excess metal
- the In 0.49 Ga 0.51 P layer was removed using a wet etch (4:1 HCl:H 2 O), exposing the p-type GaAs base layer.
- An 80 ⁇ m wide PR window was then patterned ⁇ 15 ⁇ m away from the emitter mesa edge, and Ti—Pt—Au was evaporated for contact to the base. Another lift-off process was then performed to remove excess base contact metal.
- a 150 ⁇ m PR window was then patterned ⁇ 6 ⁇ m away from the base contact.
- the GaAs base and collector layers were removed using a selective etch (4:1 C 6 H 8 O 7 :H 2 O 2 ), and the In 0.49 Ga 0.51 P etch-stop layer was removed by a wet etch (16:15 HCl:H 2 O), exposing the heavily doped n-type GaAs sub-collector layer.
- Au—Ge/Au metal alloy was evaporated over the sample for contact to the exposed sub-collector layer, and another lift-off process was performed to remove excess metal.
- the sample was then lapped to a thickness of ⁇ 75 ⁇ m and the contacts annealed.
- the HBLET samples were cleaved normal to the emitter stripes to form Fabry-Perot facets, and the substrate side of the crystal was alloyed onto Cu heat sinks coated with In.
- a processed, metallized, and cleaved HBLET laser (top view) is shown on the left in FIG. 3 .
- the contact probes on the emitter (E), base (B), and collector (C) are shown schematically resembling the actual probes (E PRB , B PRB , and C PRB ) on the operating device at the right.
- the image on the right was obtained with a video CCD detector and shows (h ⁇ ) the device laser beam (photons) scattered from a Cu platform located slightly lower than the laser crystal, which, as shown, has a ⁇ 200 ⁇ m spacing between the cleaved Fabry-Perot facets.
- the transistor I-V curves of another HBLET laser with ⁇ 260 ⁇ m spacing between the Fabry-Perot facets are shown in FIG. 4 .
- Light versus V CE measurements (I b constant, data not shown) indicate that radiative recombination improves as V CE increases and then decreases at the onset of reverse breakdown.
- ⁇ t is the average (carrier) base transit time (which is almost the same below and above threshold) and ⁇ n is the average electron lifetime in the base
- the electron lifetime is reduced by a factor of 2.6 because of the stimulated recombination of the carriers collected in the 120- ⁇ QW.
- the QW operates as a unique pseudo-collector (see E. A. Rezek, H. Shichijo, B. A. Vojak, and N. Holonyak, Jr., Appl. Phys. Lett. 31, 534 (1977)), and can be adjusted to govern the base recombination and thus both the optical output and transistor gain ( ⁇ ).
- FIG. 5 shows, in quasi-continuous operation (88% duty cycle at 60 Hz), the recombination radiation spectra of the HBLET device of FIG. 3 , but with slightly increased voltage bias V CE to increase the reverse bias on the base-collector junction.
- I b 6 mA
- the HBLET recombination radiation exhibits a peak wavelength of 954 nm and a spectral width of ⁇ 280 ⁇ .
- a heterojunction bipolar light emitting transistor having certain features, can support stimulated recombination and laser operation.
- a three-port transistor laser having certain features, exhibits microwave operation and optical modulation.
- the epitaxial layers of the crystal used for the HBLET laser include of a 100 ⁇ n-type heavily doped GaAs buffer layer, followed by a 630 ⁇ n-type Al 0.40 Ga 0.60 As layer, a 4000 ⁇ n-type Al 0.98 Ga 0.02 As layer, and a 250 ⁇ n-type Al 0.40 Ga 0.60 As layer forming the bottom cladding layers.
- a 300 ⁇ n-type sub-collector layer followed by a 150 ⁇ In 0.49 Ga 0.51 P etch stop layer, a 600 ⁇ undoped GaAs collector layer, and a 850 ⁇ p-type GaAs base layer, which includes also (in the base region) a 120 ⁇ InGaAs QW (designed for ⁇ 980 nm).
- the epitaxial HBLET laser structure is completed with the growth of the upper cladding layers, which include a 600 ⁇ n-type In 0.49 Ga 0.51 P wide-gap emitter layer, a 50 ⁇ n-type GaAs buffer layer, a 200 ⁇ n-type Al 0.35 Ga 0.65 As oxidation buffer layer, a 200 ⁇ n-type Al 0.80 Ga 0.20 As oxidation buffer layer, a 4000 ⁇ n-type Al 0.95 Ga 0.05 As oxidizable layer, a 300 ⁇ n-type Al 0.80 Ga 0.20 As layer, and a 500 ⁇ n-type Al 0.35 Ga 0.65 As layer. Finally, the HBLET laser structure is capped with a 1000 ⁇ heavily doped n-type GaAs contact layer.
- the HBLET laser fabrication was performed by first patterning 8 ⁇ m protective SiN 4 stripes on the crystal. The top n-type Al 0.98 Ga 0.02 As oxidizable layer was then exposed by wet etching (1:8:160 H 2 O 2 :H 2 SO 4 :H 2 O) to form a ⁇ 6 ⁇ m emitter mesa. Next, 10 ⁇ m and 50 ⁇ m (40 ⁇ m apart) photoresist (PR) windows were formed with the emitter mesa placed between the two windows and ⁇ 5 ⁇ m away from the 10 ⁇ m window.
- PR photoresist
- the samples were annealed (in N 2 ) at 430° C. for 6.5 minutes to reactivate p-dopants before the protective SiN 4 is removed by plasma (CF 4 ) etching.
- the remaining InGaP emitter was selectively etched using HCl.
- the base-collector contact layers were then exposed by a selective wet etch (4:1 C 6 H 8 O 7 :H 2 O 2 ) for GaAs and InGaAs, and HCl for In 0.49 Ga 0.51 P.
- a 50 ⁇ m PR window was formed over the 10 ⁇ m base contact window and the oxidized Al 0.98 Ga 0.02 As layer.
- a 1 ⁇ m thick Pd—Pt—Au p-type ohmic contact was deposited on top of the partially exposed base layer to form the base metal contact (followed by a lift-off process).
- 30 ⁇ m and 50 ⁇ m (5 ⁇ m apart) PR windows were opened for the emitter and collector metal contact deposition, and 1 ⁇ m thick n-type contact AuGe—Ni—Au metal alloy was deposited on the crystal and another lift-off process was performed to remove excess metal.
- the sample was then lapped to a thickness of ⁇ 100 ⁇ m and annealed.
- the HBLET samples were cleaved normal to the emitter stripes to form Fabry-Perot facets, and the substrate side of the crystal was alloyed onto Cu heat sinks coated with indium.
- the transistor I C versus V CE family of curves (at 213 K) of a 450 ⁇ m HBLET of this embodiment is shown in FIG. 6 .
- a novel technique is used for determining the threshold current of a transistor laser that is based on the electrical gain of the transistor. This eliminates the need to have an additional external feedback system (photodetector) to verify that the device is operating as a laser.
- This method of threshold current measurement is verified by comparison with standard light versus intensity (L-I) measurements (data not shown) and from visual observation of the laser diffraction pattern using an infrared CCD camera. It is consistent also with spectral narrowing.
- the input voltage waveform is generated using a clock signal from an HP70841A pattern generator which has a maximum clock signal of 3 GHz.
- the small output power of the transistor laser was attributed to weak fiber coupling. Additional free space measurements have yielded powers at least 8 times greater.
- FIG. 9 A picture of the transistor laser in operation at 3 GHz, captured using a CCD camera, is shown in FIG. 9 .
- the light emission from the front Fabry-Perot facet was coupled (upward in FIG. 9 ) into the optical fiber, which was connected directly into the input of the optical spectrum analyzer.
- a signal generator, a wideband detector, a power meter and a digital oscilloscope were used for the three-port (electrical input, electrical output and optical output) direct modulation characterization of the transistor laser.
- a cold station equipped with a pair of 40 GHz ground-signal microwave probes was used to enable measurements at 213 K.
- the input voltage waveform was generated using a clock signal from the HP70841A pattern generator (maximum clock signal of 3 GHz), and the electrical output collector-emitter voltage waveform was measured using a 20 GHz digital sampling oscilloscope.
- the complementary output of the input waveform clock signal was measured at a second separate channel of the oscilloscope.
- the output of the transistor laser was coupled into a multimode fiber probe with a core diameter of 25 ⁇ m.
- the laser signal was fed into a high-speed (10 Gb/s) wideband (400 to 1700 nm) InGaAs detector.
- the detector output voltage, base input voltage, and collector output voltage were all displayed simultaneously on a four channel sampling oscilloscope.
- the input signal modulated at 3 GHz (top trace) and the corresponding electrical and optical outputs are shown in FIGS. 10 ( a ), (b) and (c), respectively.
- the optical output waveform was not observed, making evident, in contrast, that stimulated emission defines a much stronger laser output signal.
- a device and technique are set forth for high speed optical signal generation with an enhanced signal to noise ratio and control of “on” and “off” time durations utilizing the stimulated emission process for the “on” state and spontaneous emission process for the “off” state.
- the operating point and excitation of the transistor laser are selected to obtain cycles that each have an “on” portion of stimulated emission (laser optical output, and electrical signal output) and an “off” portion of spontaneous emission (without optical output, and electrical noise).
- FIG. 11 The transistor I-V curves of an HBLET laser with ⁇ 450 ⁇ m spacing between the Fabry-Perot facets are shown in FIG. 11 .
- an HBLET transistor laser has an important feature in the I-V curves in the transition from spontaneous emission to stimulated emission.
- the current gain beta increases (spontaneous emission), and the beta decreases when laser operation of the HBLET starts, since the recombination process for stimulated emission become “faster”.
- the electrical input and output, and the optical output as shown in graphs 13 ( a ), 13 ( b ), and 13 ( c ), respectively, of FIG. 11 are similar to the corresponding graphs 10 ( a ), 10 ( b ) and 10 ( c ) of FIG. 10 for a similar device, and the graph 13 ( d ) of the laser power spectrum is similar to the corresponding graph of FIG. 8 for the similar device.
- the graphs of FIG. 14 show results for the spontaneous emission mode (i.e., with the input consistently at a level below the threshold for stimulated emission), the graph 14 ( a ) showing the sinusoidal electrical input, the graph 14 ( b ) showing the optical signal output, which is seen to be background noise characteristic of spontaneous emission, and the graph 14 ( c ) showing the optical output power spectrum of the spontaneous emission mode.
- the graphs of FIG. 15 show results for the near-threshold mode (i.e., with each cycle of the sinusoidal input signal having an “on” portion during which the base current exceeds the threshold for stimulated emission, and an “off” portion during which the base current is below the threshold for stimulated emission).
- the graphs 15 ( a ) and 15 ( b ) again show, respectively, the electrical input and output signals.
- the graph 15 ( c ) shows the optical output, which is seen to have a stimulated emission laser pulse (during the part of the cycle when the base threshold current is exceeded) and spontaneous emission (during the part of the cycle when the base threshold current is not exceeded).
- the laser pulses for the 3 GHz input signal (which, it is evident, can be readily exceeded, within the capability of the present device, with better test equipment), have a half-power pulse width of less than about 100 picoseconds.
- the pulse width can be advantageously controlled.
- the graph 15 ( d ) shows the optical output power spectrum for this case.
- FIG. 16 is a diagram of an example of a circuit that can be used to operate the light emitting transistor (LET) 1610 , under various conditions, including conditions employed in examples of embodiments hereof.
- a controllable oscillator 1615 is coupled to the base terminal of the LET via a bias tee 1620
- the middle branch of the bias tee 1620 is coupled to a controllable bias voltage V BE .
- the emitter terminal is coupled to ground reference potential and the collector terminal is coupled, via a bias tee 1640 , to a variable load resistor 1660 .
- the middle branch of the bias tee 1640 is coupled to controllable bias potential V CE .
- the graph of FIG. 17 which also illustrates exemplary electrical input (above the graph), electrical output (below the graph), and optical output (on the right side of the graph), shows how three different output DC bias conditions can be used to generate optical outputs with controllable pulse widths.
- FIGS. 19 and 20 respectively show the three electrical and optical outputs, for the three respective operating points, plotted together.
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Nanotechnology (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Crystallography & Structural Chemistry (AREA)
- Biophysics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Bipolar Transistors (AREA)
- Semiconductor Lasers (AREA)
Abstract
A method for producing controllable light pulses includes the following steps: providing a heterojunction bipolar transistor structure including collector, base, and emitter regions of semiconductor materials; providing an optical resonant cavity enclosing at least a portion of the transistor structure; and coupling electrical signals with respect to the collector, base, and emitter regions, to switch back and forth between a stimulated emission mode that produces output laser pulses and a spontaneous emission mode. In a form of the method, the electrical signals include an AC excitation signal, and part of each excitation signal cycle is operative to produce stimulated emission, and another part of each excitation signal cycle is operative to produce spontaneous emission.
Description
- The present application is a continuation-in-part of U.S. patent application Ser. No. 10/861,103, filed Jun. 4, 2004 (which is, in turn, a continuation-in-part of U.S. patent application Ser. No. 10/656,457, filed Aug. 22, 2003), and the present application is also a continuation-in-part of U.S. patent application Ser. No. 10/861,320, filed Jun. 4, 2004 (which is, in turn, a continuation-in-part of U.S. patent application Ser. No. 10/656,457, filed Aug. 22, 2003).
- This invention was made with Government support under Contract Number HR0011-04-1-0034 awarded by the Defense Advanced Research Projects Agency (DARPA). The Government has certain rights in the invention.
- This invention relates to semiconductor laser devices and methods, and also to a laser transistor and techniques for enhancing high speed optical signal generation.
- A part of the background hereof lies in the development of light emitters based on direct bandgap semiconductors such as III-V semiconductors. Such devices, including light emitting diodes and laser diodes, are in widespread commercial use.
- Another part of the background hereof lies in the development of wide bandgap semiconductors to achieve high minority carrier injection efficiency in a device known as a heterojunction bipolar transistor (HBT), which was first proposed in 1948 (see e.g. U.S. Pat. No. 2,569,376; see also H. Kroemer, “Theory Of A Wide-Gap Emitter For Transistors” Proceedings Of The IRE, 45, 1535-1544 (1957)). These transistor devices are capable of operation at extremely high speeds. An InP HBT has recently been demonstrated to exhibit operation at a speed above 500 GHz (see W. Hafez, J. W. Lai, and M. Feng, Elec Lett. 39, 1475 (October 2003).
- The art had contained an objective of light emission in a heterojunction bipolar transistor, and a theoretical striving for a laser transistor. However, for various reasons, an operational laser transistor has not heretofore been reported, and the achievement of same is one of the objectives hereof. Also, control of a laser transistor, to achieve advantageous high speed optical signals, is among the further objectives hereof.
- In the prior copending U.S. patent application Ser. Nos. 10/646,457, 10/861,103, and 10/861,320 (hereinafter, collectively, “the prior copending applications”), all assigned to the same assignee as the present Application, there is disclosed a direct bandgap heterojunction transistor that exhibits light emission from the base layer. Modulation of the base current produces modulated light emission. [As used herein, “light” means optical radiation that can be within or outside the visible range.] The prior copending applications also disclose three port operation of a light emitting HBT. Both spontaneous light emission and electrical signal output are modulated by a signal applied to the base of the HBT.
- Another aspect of the prior copending applications involves employing stimulated emission to advantage in the base layer of a bipolar transistor (e.g. a bipolar junction transistor (BJT) or a heterojunction bipolar transistor (HBT), in order to enhance the speed of the transistor. Spontaneous emission recombination lifetime is a fundamental limitation of bipolar transistor speed. In an embodiment of the prior copending applications, the base layer of a bipolar transistor is adapted to enhance stimulated emission (or stimulated recombination) to the detriment of spontaneous emission, thereby reducing recombination lifetime and increasing transistor speed. In a form of this embodiment, at least one layer exhibiting quantum size effects, preferably a quantum well or a layer of quantum dots, preferably undoped or lightly doped, is provided in the base layer of a bipolar transistor. At least a portion of the base layer containing the at least one layer exhibiting quantum size effects, is highly doped, and of a wider bandgap material than the at least one layer. The at least one quantum well, or layer of quantum dots, within the higher gap highly doped material, enhances stimulated recombination and reduces radiative recombination lifetime. A two-dimensional electron gas (“2-DEG”) enhances carrier concentration in the quantum well or quantum dot layer, thereby improving mobility in the base region. Improvement in base resistance permits reduction in base thickness, with attendant reduction of base transport time. As described in the prior copending applications, these advantages in speed are applicable in high speed bipolar transistors in which light emission is utilized, and/or in high speed bipolar transistors in which light emission is not utilized. In light emitting bipolar transistor devices, for example heterojunction bipolar transistors of direct bandgap materials, the use of one or more layers exhibiting quantum size effects can also be advantageous in enhancing light emission and customizing the emission wavelength characteristics of the devices.
- In a further embodiment disclosed in the prior copending applications, a semiconductor laser is set forth, including: a heterojunction bipolar transistor structure comprising collector, base, and emitter of direct bandgap semiconductor materials; an optical resonant cavity enclosing at least a portion of the transistor structure; and means for coupling electrical signals with the collector, base, and emitter regions to cause laser emission from the device.
- In another embodiment disclosed in the prior copending applications, a plurality of spaced apart quantum size regions (e.g. quantum wells and/or quantum dots) having different thicknesses are provided in the base region of a bipolar transistor and are used to advantageously promote carrier transport unidirectionally through the base region. As an example, the base region can be provided with several spaced apart quantum size regions of different thicknesses, with the thicknesses of the quantum size regions being graded from thickest near the collector to thinnest near the emitter. An injected electron is captured in a smaller well, tunnels into the next bigger well, and then the next bigger well, and so forth, until, at the biggest well closest to the collector, it tunnels to and relaxes to the lowest state of the biggest well and recombines. The arrangement of wells encourages carrier transport unidirectionally from emitter toward collector. Maximum recombination and light are derived from the biggest well as near as possible to the collector, which is an advantageous position, such as for optical cavity reasons. Carriers diffuse “downhill” in energy; i.e., toward the thicker wells. The asymmetry in well size provides improved directionality and speed of carrier transport. In a light emitting HBT, light emission and device speed are both enhanced.
- In accordance with an embodiment of the invention, a device and technique are set forth for high speed optical signal generation with an enhanced signal to noise ratio and control of “on” and “off” time durations utilizing the stimulated emission process for the “on” state and spontaneous emission process for the “off” state. The operating point and excitation of the transistor laser are selected to obtain cycles that each have an “on” portion of stimulated emission (laser optical output, and electrical signal output) and an “off” portion of spontaneous emission (without sensible optical output, and electrical noise).
- A method is set forth in accordance with an embodiment of the invention for producing controllable light pulses, including the following steps: providing a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials; providing an optical resonant cavity enclosing at least a portion of the transistor structure; and coupling electrical signals with respect to said collector, base, and emitter regions, to switch back and forth between a stimulated emission mode that produces output laser pulses and a spontaneous emission mode. In a preferred embodiment, the electrical signals include an AC excitation signal, and part of each excitation signal cycle is operative to produce stimulated emission, and another part of each excitation signal cycle is operative to produce spontaneous emission. In this embodiment, during said part of the cycle, the current in the base region exceeds the stimulated emission threshold of the device, and during said other part of the cycle, the current in the base region does not exceed said threshold. Also in this embodiment, the frequency of the excitation signal controls the frequency of the output laser pulses and the relative amplitude of the excitation signal controls the pulse width of the output laser pulses. In a form of this embodiment, the AC excitation signal is provided at a frequency of at least about 1 GHz, and the pulse width of the output laser pulses is controlled to be less than about 100 picoseconds.
- Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
-
FIG. 1 is a simplified cross-sectional diagram, not to scale, of a light emitting transistor as described in a referenced copending Application. -
FIG. 2 shows, on the left, a diagram, not to scale, of the epitaxial layers of a crystal used for making a heterojunction bipolar light-emitting transistor (HBLET) in accordance with an embodiment of the invention and which can be used in practicing embodiments of the method of the invention, and, on the right, a corresponding band diagram. -
FIG. 3 , shows, on the left, a processed, metallized, and cleaved HBLET laser (top view) as made using the crystal ofFIG. 2 and, on the right, an image of the operating device obtained with a video CCD detector. -
FIG. 4 shows the transistor I-V curves of another HBLET laser with ˜260 μm spacing between the Fabry-Perot facets. -
FIG. 5 shows, in quasi-continuous operation (88% duty cycle at 60 Hz), the recombination radiation spectra of the HBLET device ofFIG. 3 , but with slightly increased voltage bias VCE to increase the reverse bias on the base-collector junction. -
FIG. 6 shows the transistor IC versus VCE family of curves (at 213 K) of a 450 μm HBLET of another device in accordance with an embodiment of the invention and which can be used in practicing embodiments of the method of the invention. -
FIG. 7 shows, in the curves (a) and (b), respectively, the small signal current gain βac=ΔIC/ΔIB and current gain βdc=IC/IB for VCB=0 for the device whose IC curves are shown inFIG. 6 . -
FIG. 8 shows (at 213 K) the laser operation (curve (a)) and spontaneous spectrum (curve (b)) power spectra of the transistor laser biased at VCE=2 V and operating at 3 GHz. -
FIG. 9 shows a picture of the transistor laser in operation at 3 GHz, captured using a CCD camera. -
FIG. 10 shows, in traces (a), (b) and (c), respectively, the input signal modulated at 3 GHz, and the corresponding electrical and optical outputs. -
FIG. 11 shows the output collector I-V characteristics of an HBLET. For the base current below laser threshold Ibth=0.744 mA, the optical recombination process yields spontaneous emission (low optical output). For base current above laser threshold the optical recombination process is stimulated (higher optical output power). -
FIG. 12 shows a Gummel plot of base current and collector current with Vce=Vbe and Vbc=0V. The current gain beta increases (spontaneous emission), and the beta decreases when laser operation of the HBLET starts, since the recombination process for stimulated emission become “faster”. - FIGS. 13(a), 13(b), 13(c), and 13(d) show, respectively, the input voltage, output voltage, optical output, and optical power spectrum for a laser transistor device operated in a stimulated emission mode.
- FIGS. 14(a), 14(b), and 14(c), show, respectively, the input voltage, optical output, and optical power spectrum for a laser transistor device operated in a spontaneous emission mode.
- FIGS. 15(a), 15(b), 15(c), and 15(d) show, respectively, the input voltage, output voltage, optical output, and optical power spectrum for a laser transistor device operated in a near-threshold mode.
-
FIG. 16 is a schematic diagram of an example of a circuit that can be used to operate a light emitting transistor in accordance with an embodiment of the invention. -
FIG. 17 shows output collector I-V characteristics of an HBLET, and signals that result when operated at different operating points. -
FIG. 18 shows the electrical output for operation at each of the different operating points. -
FIG. 19 shows the optical output for operation at each of the different operating points. -
FIG. 1 illustrates a device as set forth in the above-referenced copending application Ser. No. 10/646,457. Asubstrate 105 has the following layers disposed thereon:subcollector 110,collector 130,base 140,emitter 150, andcap layer 160. Also shown are collector metallization (or electrode) 115,base metallization 145, andemitter metallization 165.Collector lead 117,base lead 147, and emitter lead 167 are also shown. As described in the referenced copending Application, thecollector layer 130 comprises 3000 Angstrom thick n-type GaAs, n=2×1016 cm−3, thebase layer 140 comprises 600 Angstrom thick p+ carbon-doped compositionally graded InGaAs (1.4% In), p=4.5×1019 cm3, theemitter layer 150 comprises 800 Angstrom thick n-type InGaP, n=5×1017 cm−3, and the cap layer comprises 1000 Angstrom thick n+ InGaAs, n=3×1019 cm3. - As described in the referenced copending Application, for conventional PN junction diode operation, the recombination process is based on both an electron injected from the n-side and a hole injected from the p-side, which in a bimolecular recombination process can be limited in speed. In the case of HBT light emission, the base “hole” concentration is so high that when an electron is injected into the base, it recombines (bimolecular) rapidly. The base current merely re-supplies holes via relaxation to neutralize charge imbalance. For a heterojunction bipolar transistor (HBT), the base current can be classified into seven components, namely: (1) hole injection into the emitter region (iBp); (2) surface recombination current in the exposed extrinsic base region (iBsurf); (3) base ohmic contact recombination current (iBcont); (4) space charge recombination current (iBscr); (5) bulk base non-radiative recombination current due to the Hall-Shockley-Reed process (HSR) (iBHSR); (6) bulk base Auger recombination current (iBAug); and (7) bulk base radiative recombination current (iBrad). For a relatively efficient HBT with ledge passivation on any exposed base region, the surface recombination current can be reduced significantly. Hence, the base current and recombination lifetime can be approximated as primarily bulk HSR recombination, the Auger process, and radiative recombination. The base current expressed in the following equation (1) is then related to excess minority carriers, Δn, in the neutral base region, the emitter area, AE, the charge, q, and the base recombination lifetime, τn as
i B =i BHSR +i BAUG +i Brad =qA E Δn/τ n (1)
The overall base recombination lifetime, τn, is related to the separate recombination components of Hall-Shockley-Read, τHSR, Auger, τAUG, and radiative recombination, τrad, as
τn=(1/τHSR+1/τAUG+1/τrad)−1 (2) - As further described in the referenced copending Application, the light emission intensity ΔI in the base is proportional to iBrad and is related to the minority carrier electron with the majority hole over the intrinsic carrier concentration, (np−ni 2), in the neutral base region and the rate of radiative recombination process, B, set forth in Equation (3) below, where the hole concentration can be approximated as equal to base dopant concentration, NB. The radiative base current expressed in equation (3) is then related to excess minority carriers, Δn, in the neutral base region, and the base recombination lifetime, τrad as
i Brad =qA E B(np−n i 2)=qA E Bnp=qA E Δn(BN B)=qA E Δn/τ rad (3) - For a high speed HBT, it is easy to predict that the base recombination lifetime can be less than half of the total response delay time. Hence, the optical recombination process in the base should be at least two times faster than the speed of the HBT. In other words, HBT speed, which can be extremely fast, is limiting.
- In a first illustrated embodiment, a device and data are set forth showing laser operation of an InGaP—GaAs—InGaAs heterojunction bipolar light-emitting transistor (HBLET) with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the p-type base region. The epitaxial layers of the crystal used for the HBLET laser are shown schematically in
FIG. 2 , with aGaAs substrate 210, a 4000 Å n-type heavily dopedGaAs buffer layer 215, followed by a 600 Å n-type Al0.40Ga0.60Aslayer 220, a 3500 Å n-type Al0.98Ga0.02Aslayer 222, and a 400 Å n-type Al0.40Ga0.60Aslayer 224 forming the bottom cladding layers. These layers are followed by a 400 Å n-type sub-collector layer 230, then a 200 Å In0.49Ga0.51P etch stop layer (not shown), a 650 Å undopedGaAs collector layer 240, and a 940 Å p-type GaAs base layer 250 (the active layer), which includes also (in the base region) a 120 Å InGaAs QW (designed for λ≈980 nm). The epitaxial HBLET laser structure was completed with the growth of the upper cladding layers, which included a 1200 Å n-type In0.49Ga0.51P wide-gap emitter layer 260, a 300 Å n-type Al0.70Ga0.30Asoxidation buffer layer 270, a 3500 Å n-type Al0.98Ga0.02As oxidizable layer 275 (see J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, Appl. Phys. Lett. 57, 2844 (1990)), and a 1000 Å n-type Al0.40Ga0.60Aslayer 280. Finally, the HBLET laser structure was capped with a 1000 Å heavily doped n-typeGaAs contact layer 290. - The HBLET laser fabrication was performed by
first patterning 6 μm protective SiN4 stripes on the crystal. The top n-type Al0.98Ga0.02As oxidizable layer was then exposed by wet etching (1:8:160 H2O2:H2SO4:H2O) to form a ˜6 μm emitter mesa. Next, a wide 150 μm protective photoresist (PR) stripe was placed over the emitter mesa and the unprotected Al0.98Ga0.02As layer was completely removed (1:4:80 H2O2:H2SO4:H2O), revealing the In0.49Ga0.51P wide-gap emitter layer. The protective PR stripe was then removed and the sample was oxidized for 7.5 min at 425° C. in a furnace supplied with N2+H2O, resulting in a ˜1.0 μm lateral oxidation which formed ˜4 μm oxide-defined apertures in the 6 μm emitter mesa (see, again, J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, supra (1990); S. A. Maranowski, A. R. Sugg, E. I. Chen, and N. Holonyak, Jr., Appl. Phys. Lett. 63, 1660 (1993)). The samples were annealed (in N2) at 430° C. for 7 minutes to reactivate p-dopants before the protective SiN4 was removed by plasma (CF4) etching. A 100 μm PR window was formed over the emitter mesa and oxide layer, and Au—Ge/Au was deposited over the sample to form metal contact. After lift-off of the photoresist (PR) to remove excess metal, the In0.49Ga0.51P layer was removed using a wet etch (4:1 HCl:H2O), exposing the p-type GaAs base layer. An 80 μm wide PR window was then patterned ˜15 μm away from the emitter mesa edge, and Ti—Pt—Au was evaporated for contact to the base. Another lift-off process was then performed to remove excess base contact metal. A 150 μm PR window was then patterned ˜6 μm away from the base contact. The GaAs base and collector layers were removed using a selective etch (4:1 C6H8O7:H2O2), and the In0.49Ga0.51P etch-stop layer was removed by a wet etch (16:15 HCl:H2O), exposing the heavily doped n-type GaAs sub-collector layer. Au—Ge/Au metal alloy was evaporated over the sample for contact to the exposed sub-collector layer, and another lift-off process was performed to remove excess metal. The sample was then lapped to a thickness of −75 μm and the contacts annealed. The HBLET samples were cleaved normal to the emitter stripes to form Fabry-Perot facets, and the substrate side of the crystal was alloyed onto Cu heat sinks coated with In. - A processed, metallized, and cleaved HBLET laser (top view) is shown on the left in
FIG. 3 . The contact probes on the emitter (E), base (B), and collector (C) are shown schematically resembling the actual probes (EPRB, BPRB, and CPRB) on the operating device at the right. The image on the right was obtained with a video CCD detector and shows (hν) the device laser beam (photons) scattered from a Cu platform located slightly lower than the laser crystal, which, as shown, has a −200 μm spacing between the cleaved Fabry-Perot facets. Current and bias voltage (common emitter operation) were provided using a Tektronix Model 370 high resolution curve tracer connected to the HBLET by the three probes labeled EPRB, BPRB, and CPRB inFIG. 3 . The HBLET laser was operated ˜200 K in a dry N2 environment. - The transistor I-V curves of another HBLET laser with ˜260 μm spacing between the Fabry-Perot facets are shown in
FIG. 4 . As the base current, Ib, is increased in 2 mA intervals from 0 to 8 mA, the usual increase of differential current gain is observed, β=ΔIc/ΔIb, in this case from β˜2 at lower current to 6.5 at higher current. Light versus VCE measurements (Ib constant, data not shown) indicate that radiative recombination improves as VCE increases and then decreases at the onset of reverse breakdown. Near Ib=8 mA, and as VCE is increased, however, stimulated recombination (stimulated emission) becomes significant, and the HBLET operates both as a laser and a transistor but with a distinct decrease in the current gain β. Beyond threshold, Ib equal to or greater than Ith˜8 mA, the differential gain β decreases from 6.5 to a nearly constant value of 2.5 (α=β/(β+1)=Ic/Ie=0.71). Since β can be approximated as the simple ratio τn/τt (see B. G. Streetman and S. Banerjee, Solid State Electronic Devices, 5th ed. (Pearson, N.J., 2004), p. 328), where τt is the average (carrier) base transit time (which is almost the same below and above threshold) and τn is the average electron lifetime in the base, the electron lifetime is reduced by a factor of 2.6 because of the stimulated recombination of the carriers collected in the 120-Å QW. The QW operates as a unique pseudo-collector (see E. A. Rezek, H. Shichijo, B. A. Vojak, and N. Holonyak, Jr., Appl. Phys. Lett. 31, 534 (1977)), and can be adjusted to govern the base recombination and thus both the optical output and transistor gain (β). It can be noted for comparison that at room temperature there was observed (data not shown) a differential current gain β of 10 at Ib=2 mA and 30 at 8 mA (or current transfer ratio, α=Ix/Ie of 0.91 and 0.96). -
FIG. 5 shows, in quasi-continuous operation (88% duty cycle at 60 Hz), the recombination radiation spectra of the HBLET device ofFIG. 3 , but with slightly increased voltage bias VCE to increase the reverse bias on the base-collector junction. At (a) Ib=6 mA, the HBLET recombination radiation exhibits a peak wavelength of 954 nm and a spectral width of ˜280 Å. At (b) Ib=8 mA, the onset of stimulated emission can be seen with distinct spectral narrowing and mode development. At (c) Ib=10 mA the laser modes are fully developed (λ=958 nm), clearly indicating transistor laser operation, which is evident also inFIG. 3 . It can be noted that the 200 μm long HBLET laser ofFIG. 3 (right side) was operated with pulsed base current (1% duty cycle at 1 MHz) to prevent saturation of the Si-CCD viewing camera. - The described results demonstrate that an HBLET, suitably modified with a resonator cavity and a recombination QW (or QWs) in the p-type base (a pseudo-collector, a second collector), can be operated simultaneously as a laser and transistor with gain β=ΔIc/ΔIb>1. At laser threshold the transistor gain decreases sharply, but still supports three-port operation (electrical input, electrical output, and optical output).
- In the description of the foregoing embodiment, it is shown that a heterojunction bipolar light emitting transistor (HBLET) having certain features, can support stimulated recombination and laser operation. In the following further embodiment, a three-port transistor laser, having certain features, exhibits microwave operation and optical modulation. In this embodiment, the epitaxial layers of the crystal used for the HBLET laser include of a 100 Å n-type heavily doped GaAs buffer layer, followed by a 630 Å n-type Al0.40Ga0.60As layer, a 4000 Å n-type Al0.98Ga0.02As layer, and a 250 Å n-type Al0.40Ga0.60As layer forming the bottom cladding layers. These layers are followed by a 300 Å n-type sub-collector layer, then a 150 Å In0.49Ga0.51P etch stop layer, a 600 Å undoped GaAs collector layer, and a 850 Å p-type GaAs base layer, which includes also (in the base region) a 120 Å InGaAs QW (designed for λ≈980 nm). The epitaxial HBLET laser structure is completed with the growth of the upper cladding layers, which include a 600 Å n-type In0.49Ga0.51P wide-gap emitter layer, a 50 Å n-type GaAs buffer layer, a 200 Å n-type Al0.35Ga0.65As oxidation buffer layer, a 200 Å n-type Al0.80Ga0.20As oxidation buffer layer, a 4000 Å n-type Al0.95Ga0.05As oxidizable layer, a 300 Å n-type Al0.80Ga0.20As layer, and a 500 Å n-type Al0.35Ga0.65As layer. Finally, the HBLET laser structure is capped with a 1000 Å heavily doped n-type GaAs contact layer.
- The HBLET laser fabrication was performed by
first patterning 8 μm protective SiN4 stripes on the crystal. The top n-type Al0.98Ga0.02As oxidizable layer was then exposed by wet etching (1:8:160 H2O2:H2SO4:H2O) to form a ˜6 μm emitter mesa. Next, 10 μm and 50 μm (40 μm apart) photoresist (PR) windows were formed with the emitter mesa placed between the two windows and ˜5 μm away from the 10 μm window. The unprotected Al0.98Ga0.02As layer was then completely removed (1:4:80 H2O2:H2SO4:H2O), revealing the In0.49Ga0.51P wide-gap emitter layer. The protective PR stripe was dissolved and the sample was oxidized for 6.5 min at 425° C. in a furnace supplied with N2+H2O, resulting in ˜1.0 μm lateral oxidation which forms ˜4 μm oxide-defined apertures in the 6 μm emitter mesa. (Again, see J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, Appl. Phys. Lett. 57, 2844 (1990); S. A. Maranowski, A. R. Sugg, E. I. Chen, and N. Holonyak, Jr., Appl. Phys. Lett. 63, 1660 (1993)). The samples were annealed (in N2) at 430° C. for 6.5 minutes to reactivate p-dopants before the protective SiN4 is removed by plasma (CF4) etching. The remaining InGaP emitter was selectively etched using HCl. The base-collector contact layers were then exposed by a selective wet etch (4:1 C6H8O7:H2O2) for GaAs and InGaAs, and HCl for In0.49Ga0.51P. Then, a 50 μm PR window was formed over the 10 μm base contact window and the oxidized Al0.98Ga0.02As layer. A 1 μm thick Pd—Pt—Au p-type ohmic contact was deposited on top of the partially exposed base layer to form the base metal contact (followed by a lift-off process). Next, 30 μm and 50 μm (5 μm apart) PR windows were opened for the emitter and collector metal contact deposition, and 1 μm thick n-type contact AuGe—Ni—Au metal alloy was deposited on the crystal and another lift-off process was performed to remove excess metal. The sample was then lapped to a thickness of ˜100 μm and annealed. The HBLET samples were cleaved normal to the emitter stripes to form Fabry-Perot facets, and the substrate side of the crystal was alloyed onto Cu heat sinks coated with indium. - The transistor IC versus VCE family of curves (at 213 K) of a 450 μm HBLET of this embodiment is shown in
FIG. 6 . As the base current IB is increased in 2.5 mA intervals from 0 to 15 mA, the current gain (βdc=IC/IB) increases to −5.65 for IB≦Ith and then decreases to −4.5 for IB≧Ith. At IB=7.5 mA one observes inFIG. 6 a negative slope in the differential or small signal γ (γac=ΔIc/ΔIB) associated with a transistor in laser operation, as described in conjunction with the previous embodiment. The transistor's VBE curve is superimposed on the family of IC versus VCE curves to indicate the zero base-collector bias point, the boundary VCB=0. FromFIG. 6 and by observing the gain characteristic, it can be seen that the transistor operates as a laser over a wide range of VCE (beyond VCB=0). Light versus base current measurements (data not shown) indicate small variation in laser light intensity when the transistor operates in the saturation mode (constant IC), and decreases at high reverse bias and the onset of heating. - A novel technique is used for determining the threshold current of a transistor laser that is based on the electrical gain of the transistor. This eliminates the need to have an additional external feedback system (photodetector) to verify that the device is operating as a laser. The small signal current gain βac=ΔIC/ΔIB and current gain βdc=IC/IB for VCB=0 are shown by curves (a) and (b) of
FIG. 7 . From curve (a) it can be observed that the small signal gain increases as IB increases and decreases sharply at the onset of stimulated emission, or for amplified spontaneous emission (IB=6.7 mA, βac=8.6). The peak of curve (b) inFIG. 7 can be defined as the threshold current of the transistor laser (IB=Ith=7.4 mA). The transistor laser operation is fully developed when βac reaches a minimum (βac=3.7) at IB≈7.9 mA. This method of threshold current measurement is verified by comparison with standard light versus intensity (L-I) measurements (data not shown) and from visual observation of the laser diffraction pattern using an infrared CCD camera. It is consistent also with spectral narrowing. -
FIG. 8 shows (at 213 K) the laser operation (curve (a)) and spontaneous spectrum (curve (b)) of the transistor laser of the present embodiment biased at VCE=2 V and operating at 3 GHz. The input voltage waveform is generated using a clock signal from an HP70841A pattern generator which has a maximum clock signal of 3 GHz. The output measurements were made using an HP70951 B optical spectrum analyzer. A maximum power level of −63.4 dBm was measured at λ=966.5 nm for the spontaneous emission, and for laser operation a power output of −21.44 dBm (λ=964.4 nm). The small output power of the transistor laser was attributed to weak fiber coupling. Additional free space measurements have yielded powers at least 8 times greater. A picture of the transistor laser in operation at 3 GHz, captured using a CCD camera, is shown inFIG. 9 . The light emission from the front Fabry-Perot facet was coupled (upward inFIG. 9 ) into the optical fiber, which was connected directly into the input of the optical spectrum analyzer. - A signal generator, a wideband detector, a power meter and a digital oscilloscope were used for the three-port (electrical input, electrical output and optical output) direct modulation characterization of the transistor laser. A cold station equipped with a pair of 40 GHz ground-signal microwave probes was used to enable measurements at 213 K. The HBLET, with ˜450 μm spacing between the Fabry-Perot facets, was biased in the normal operating mode (VCE=2 V and IB=9 mA), and a small signal sinusoidal voltage waveform with a peak-to-peak amplitude of 0.75 V was supplied to the base (input port) of the device. The input voltage waveform was generated using a clock signal from the HP70841A pattern generator (maximum clock signal of 3 GHz), and the electrical output collector-emitter voltage waveform was measured using a 20 GHz digital sampling oscilloscope. The complementary output of the input waveform clock signal was measured at a second separate channel of the oscilloscope. The output of the transistor laser was coupled into a multimode fiber probe with a core diameter of 25 μm. The laser signal was fed into a high-speed (10 Gb/s) wideband (400 to 1700 nm) InGaAs detector. The detector output voltage, base input voltage, and collector output voltage were all displayed simultaneously on a four channel sampling oscilloscope. The input signal modulated at 3 GHz (top trace) and the corresponding electrical and optical outputs are shown in FIGS. 10 (a), (b) and (c), respectively. When the 3 GHz base current is held (decreased) below the threshold current, the optical output waveform was not observed, making evident, in contrast, that stimulated emission defines a much stronger laser output signal.
- In accordance with an embodiment of the invention, a device and technique are set forth for high speed optical signal generation with an enhanced signal to noise ratio and control of “on” and “off” time durations utilizing the stimulated emission process for the “on” state and spontaneous emission process for the “off” state. The operating point and excitation of the transistor laser are selected to obtain cycles that each have an “on” portion of stimulated emission (laser optical output, and electrical signal output) and an “off” portion of spontaneous emission (without optical output, and electrical noise).
- The transistor I-V curves of an HBLET laser with ˜450 μm spacing between the Fabry-Perot facets are shown in
FIG. 11 . At a base current Ib=0.744 mA, the HBLET reaches laser threshold and changes transistor gain, β=DIc/dIb, from β=5.5 to 4.5 or (α=1/(β+1)=0.85→0.81). As above noted, an HBLET transistor laser has an important feature in the I-V curves in the transition from spontaneous emission to stimulated emission.FIG. 12 shows a Gummel plot of base current and collector current with Vce=Vbe and Vbc=0V. The current gain beta increases (spontaneous emission), and the beta decreases when laser operation of the HBLET starts, since the recombination process for stimulated emission become “faster”. - Experiments were conducted on the transistor laser in the common emitter configuration with 3 GHz modulation of the electrical input (controllable in frequency and amplitude) at the base terminal of the device.
- A mode of operation termed a stimulated emission mode had, for example, the following initial operating parameters: Vbe=1.67 V, Vce=2 V, Ib=16 mA and Ic=69.2 mA. As expected, in the stimulated emission mode (i.e., with the input consistently at a level above the threshold for stimulated emission), the electrical input and output, and the optical output as shown in graphs 13(a), 13(b), and 13(c), respectively, of
FIG. 11 , are similar to the corresponding graphs 10(a), 10(b) and 10(c) ofFIG. 10 for a similar device, and the graph 13(d) of the laser power spectrum is similar to the corresponding graph ofFIG. 8 for the similar device. - A mode of operation termed a spontaneous emission mode had, for example, the following initial operating parameters: Vbe=1.47 V, Vce=2 V, Ib=5 mA, and Ic=19.84 mA. The graphs of
FIG. 14 show results for the spontaneous emission mode (i.e., with the input consistently at a level below the threshold for stimulated emission), the graph 14(a) showing the sinusoidal electrical input, the graph 14(b) showing the optical signal output, which is seen to be background noise characteristic of spontaneous emission, and the graph 14(c) showing the optical output power spectrum of the spontaneous emission mode. - A mode of operation termed a near-threshold mode had, for example, the following initial operating parameters: Vbe=1.57 V, Vce=2 V, Ib=10 mA, and Ic=46.2 mA. The graphs of
FIG. 15 show results for the near-threshold mode (i.e., with each cycle of the sinusoidal input signal having an “on” portion during which the base current exceeds the threshold for stimulated emission, and an “off” portion during which the base current is below the threshold for stimulated emission). The graphs 15(a) and 15(b) again show, respectively, the electrical input and output signals. The graph 15(c) shows the optical output, which is seen to have a stimulated emission laser pulse (during the part of the cycle when the base threshold current is exceeded) and spontaneous emission (during the part of the cycle when the base threshold current is not exceeded). In this case, for the 3 GHz input signal (which, it is evident, can be readily exceeded, within the capability of the present device, with better test equipment), the laser pulses, for the conditions set forth, have a half-power pulse width of less than about 100 picoseconds. By adjusting the relative signal amplitude (e.g. by controlling bias and/or the AC signal amplitude and/or load), the pulse width can be advantageously controlled. The graph 15(d) shows the optical output power spectrum for this case. -
FIG. 16 is a diagram of an example of a circuit that can be used to operate the light emitting transistor (LET) 1610, under various conditions, including conditions employed in examples of embodiments hereof. In this example, acontrollable oscillator 1615 is coupled to the base terminal of the LET via abias tee 1620, and the middle branch of thebias tee 1620 is coupled to a controllable bias voltage VBE. The emitter terminal is coupled to ground reference potential and the collector terminal is coupled, via abias tee 1640, to avariable load resistor 1660. The middle branch of thebias tee 1640 is coupled to controllable bias potential VCE. - The graph of
FIG. 17 , which also illustrates exemplary electrical input (above the graph), electrical output (below the graph), and optical output (on the right side of the graph), shows how three different output DC bias conditions can be used to generate optical outputs with controllable pulse widths.FIGS. 19 and 20 respectively show the three electrical and optical outputs, for the three respective operating points, plotted together.
Claims (25)
1. A method for producing controllable light pulses, comprising the steps of:
providing a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials;
providing an optical resonant cavity enclosing at least a portion of said transistor structure; and
coupling electrical signals with respect to said collector, base, and emitter regions, to switch back and forth between a stimulated emission mode that produces output laser pulses and a spontaneous emission mode.
2. The method as defined by claim 1 , wherein said electrical signals include an AC excitation signal, and wherein part of each excitation signal cycle is operative to produce stimulated emission, and another part of each excitation signal cycle is operative to produce spontaneous emission.
3. The method as defined by claim 2 , wherein, during said part of said cycle, the current in the base region exceeds the stimulated emission threshold of said device, and during said other part of said cycle, the current in the base region does not exceed said threshold.
4. The method as defined by claim 3 , further comprising controlling the frequency of said excitation signal to control the frequency of said output laser pulses and controlling the relative amplitude of said excitation signal to control the pulse width of said output laser pulses.
5. The method as defined by claim 3 , further comprising controlling the relative amplitude of said excitation signal to control the pulse width of said output laser pulses.
6. The method as defined by claim 2 , further comprising providing said AC excitation signal at a frequency of at least about 1 GHz.
7. The method as defined by claim 2 , further comprising providing said AC excitation signal at a frequency of at least about 3 GHz.
8. The method as defined by claim 4 , further comprising providing said AC excitation signal at a frequency of at least about 3 GHz.
9. The method as defined by claim 4 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
10. The method as defined by claim 5 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
11. The method as defined by claim 8 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
12. Apparatus for producing controllable light pulses, comprising:
a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials;
an optical resonant cavity enclosing at least a portion of said transistor structure; and
means for coupling electrical signals with respect to said collector, base, and emitter regions, to switch back and forth between a stimulated emission mode that produces output laser pulses and a spontaneous emission mode.
13. Apparatus as defined by claim 9 , wherein said electrical signals include an AC excitation signal, and wherein part of each excitation signal cycle is operative to produce stimulated emission, and another part of each excitation signal cycle is operative to produce spontaneous emission.
14. Apparatus as defined by claim 10 , wherein, during said part of said cycle, the current in the base region exceeds the stimulated emission threshold of said device, and during said other part of said cycle, the current in the base region does not exceed said threshold.
15. Apparatus as defined by claim 11 , further comprising means for controlling the frequency of said excitation signal to control the frequency of said output laser pulses and controlling the relative amplitude of said excitation signal to control the pulse width of said output laser pulses.
16. Apparatus as defined by claim 11 , further comprising means for controlling the relative amplitude of said excitation signal to control the pulse width of said output laser pulses.
17. Apparatus as defined by claim 13 , further comprising means for providing said AC excitation signal at a frequency of at least about 1 GHz.
18. Apparatus as defined by claim 10 , further comprising means for providing said AC excitation signal at a frequency of at least about 3 GHz.
19. Apparatus as defined by claim 15 , further comprising means for providing said AC excitation signal at a frequency of at least about 3 GHz.
20. Apparatus as defined by claim 15 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
21. Apparatus as defined by claim 16 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
22. Apparatus as defined by claim 19 , wherein said pulse width is controlled to have a pulse width of less than about 100 picoseconds.
23. A method for producing high frequency laser pulses, comprising the steps of:
providing a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials;
providing an optical resonant cavity enclosing at least a portion of said transistor structure; and
coupling electrical signals, at least some of which have a frequency of at least about 1 GHz, with respect to said collector, base, and emitter regions, to produce output laser pulses at a frequency of at least about 1 GHz.
24. The method as defined by claim 23 , wherein at least some of said electrical signals have a frequency of at least about 3 GHz, and said output laser pulses have a frequency of at least about 3 GHz.
25. A method for determining the stimulated emission threshold of a light-emitting transistor device, comprising the steps of:
providing a heterojunction bipolar transistor structure comprising collector, base, and emitter regions of semiconductor materials;
providing an optical resonant cavity enclosing at least a portion of said transistor structure;
coupling electrical signals with respect to said collector, base, and emitter regions;
determining the differential current gain transistor structure as a function of the transistor base current; and
determining the stimulated emission threshold base current of said transistor structure as the base current at which said differential current gain begins to decrease with increasing base current.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/974,323 US20080089368A1 (en) | 2003-08-22 | 2007-10-12 | Semiconductor laser devices and methods |
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/646,457 US20050040432A1 (en) | 2003-08-22 | 2003-08-22 | Light emitting device and method |
US10/861,103 US7091082B2 (en) | 2003-08-22 | 2004-06-04 | Semiconductor method and device |
US10/861,320 US7998807B2 (en) | 2003-08-22 | 2004-06-04 | Method for increasing the speed of a light emitting biopolar transistor device |
US11/068,561 US7286583B2 (en) | 2003-08-22 | 2005-02-28 | Semiconductor laser devices and methods |
US11/974,323 US20080089368A1 (en) | 2003-08-22 | 2007-10-12 | Semiconductor laser devices and methods |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/068,561 Division US7286583B2 (en) | 2003-08-22 | 2005-02-28 | Semiconductor laser devices and methods |
Publications (1)
Publication Number | Publication Date |
---|---|
US20080089368A1 true US20080089368A1 (en) | 2008-04-17 |
Family
ID=46325001
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/068,561 Expired - Lifetime US7286583B2 (en) | 2003-08-22 | 2005-02-28 | Semiconductor laser devices and methods |
US11/974,323 Abandoned US20080089368A1 (en) | 2003-08-22 | 2007-10-12 | Semiconductor laser devices and methods |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/068,561 Expired - Lifetime US7286583B2 (en) | 2003-08-22 | 2005-02-28 | Semiconductor laser devices and methods |
Country Status (1)
Country | Link |
---|---|
US (2) | US7286583B2 (en) |
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2010080694A2 (en) * | 2009-01-08 | 2010-07-15 | The Board Of Trustees Of The University Of Illinois | Light emitting and lasing semiconductor devices and methods |
WO2010087948A2 (en) * | 2009-01-29 | 2010-08-05 | The Board Of Trustees Of The University Of Lllinois | Light emitting and lasing transistor devices and methods |
US20100272140A1 (en) * | 2009-01-08 | 2010-10-28 | Quantum Electro Opto Systems Sdn. Bhd. | High speed light emitting semiconductor methods and devices |
US20100289427A1 (en) * | 2009-01-08 | 2010-11-18 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US20100320491A1 (en) * | 2007-06-21 | 2010-12-23 | Jae Cheon Han | Semiconductor light emitting device and method of fabricating the same |
US20110150487A1 (en) * | 2009-11-09 | 2011-06-23 | Gabriel Walter | High speed communication |
US8618575B2 (en) | 2010-09-21 | 2013-12-31 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US8842706B2 (en) | 2011-10-07 | 2014-09-23 | The Board Of Trustees Of The University Of Illinois | Opto-electronic oscillator and method |
US8970126B2 (en) | 2011-10-07 | 2015-03-03 | The Board Of Trustees Of The University Of Illinois | Opto-electronic devices and methods |
US9159873B2 (en) | 2011-11-14 | 2015-10-13 | Quantum Electro Opto Systems Sdn. Bhd. | High speed optical tilted charge devices and methods |
US9304267B2 (en) | 2012-09-11 | 2016-04-05 | Quantum Electro Opto Systems Sdn. Bhd. | Method and apparatus for optical coupling and opto-electronic conversion |
US9431572B2 (en) | 2012-08-02 | 2016-08-30 | Quantum Electro Opto Systems Sdn. Bhd. | Dual mode tilted-charge devices and methods |
US9452928B2 (en) | 2011-09-02 | 2016-09-27 | Quantum Electro Opto Systems Sden. Bhd. | Opto-electronic circuits and techniques |
Families Citing this family (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7535034B2 (en) * | 2006-02-27 | 2009-05-19 | The Board Of Trustees Of The University Of Illinois | PNP light emitting transistor and method |
US20080185038A1 (en) * | 2007-02-02 | 2008-08-07 | Emcore Corporation | Inverted metamorphic solar cell with via for backside contacts |
US7711015B2 (en) * | 2007-04-02 | 2010-05-04 | The Board Of Trustees Of The University Of Illinois | Method for controlling operation of light emitting transistors and laser transistors |
US7953133B2 (en) | 2007-10-12 | 2011-05-31 | The Board Of Trustees Of The University Of Illinois | Light emitting and lasing semiconductor devices and methods |
US7957453B2 (en) * | 2008-03-20 | 2011-06-07 | Raytheon Company | Method for operating a rake receiver |
US7888625B2 (en) * | 2008-09-25 | 2011-02-15 | The Board Of Trustees Of The University Of Illinois | Method and apparatus for producing linearized optical signals with a light-emitting transistor |
US8005124B2 (en) * | 2008-10-15 | 2011-08-23 | The Board Of Trustees Of The University Of Illinois | Optical bandwidth enhancement of light emitting and lasing transistor devices and circuits |
JP5197318B2 (en) * | 2008-11-19 | 2013-05-15 | 株式会社沖データ | Driving circuit, recording head, image forming apparatus, and display device |
US8269431B2 (en) | 2009-06-15 | 2012-09-18 | The Board Of Trustees Of The University Of Illinois | Method and apparatus for producing linearized optical signals |
US8603885B2 (en) | 2011-01-04 | 2013-12-10 | International Business Machines Corporation | Flat response device structures for bipolar junction transistors |
WO2014004375A1 (en) | 2012-06-25 | 2014-01-03 | Quantum Electro Opto Systems Sdn. Bhd. | Method and apparatus for aligning of opto-electronic components |
US8948226B2 (en) | 2012-08-20 | 2015-02-03 | The Board Of Trustees Of The University Of Illinois | Semiconductor device and method for producing light and laser emission |
US9478942B2 (en) | 2012-12-06 | 2016-10-25 | The Board Of Trustees Of The University Of Illinois | Transistor laser optical switching and memory techniques and devices |
US10553633B2 (en) * | 2014-05-30 | 2020-02-04 | Klaus Y.J. Hsu | Phototransistor with body-strapped base |
US10283933B1 (en) | 2017-10-23 | 2019-05-07 | The Board Of Trustees Of The University Of Illinois | Transistor laser electrical and optical bistable switching |
US11804693B2 (en) * | 2020-03-18 | 2023-10-31 | Northrop Grumman Systems Corporation | Method and device for ultraviolet to long wave infrared multiband semiconducting single emitter |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4710936A (en) * | 1984-04-12 | 1987-12-01 | Matsushita Electric Industrial Co., Ltd. | Optoelectronic semiconductor device |
US4849799A (en) * | 1986-07-31 | 1989-07-18 | American Telephone And Telegraph Company At&T Bell Laboratories | Resonant tunneling transistor |
US4958208A (en) * | 1987-08-12 | 1990-09-18 | Nec Corporation | Bipolar transistor with abrupt potential discontinuity in collector region |
US5003366A (en) * | 1986-12-03 | 1991-03-26 | Hitachi, Ltd. | Hetero-junction bipolar transistor |
US6479844B2 (en) * | 2001-03-02 | 2002-11-12 | University Of Connecticut | Modulation doped thyristor and complementary transistor combination for a monolithic optoelectronic integrated circuit |
Family Cites Families (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2569347A (en) * | 1948-06-26 | 1951-09-25 | Bell Telephone Labor Inc | Circuit element utilizing semiconductive material |
FR2493047A1 (en) * | 1980-10-28 | 1982-04-30 | Thomson Csf | LIGHT EMITTING-RECEIVING TRANSISTOR FOR ALTERNATE TELECOMMUNICATIONS ON OPTICAL FIBER |
JPH0611056B2 (en) | 1985-12-03 | 1994-02-09 | 富士通株式会社 | High-speed semiconductor device |
JPS63181486A (en) * | 1987-01-23 | 1988-07-26 | Hiroshima Univ | Semiconductor light emitting device |
US5334854A (en) * | 1990-07-11 | 1994-08-02 | Canon Kabushiki Kaisha | Optical semiconductor device with wavelength selectivity and method for amplifying or emitting the light using the same |
US5239550A (en) * | 1991-12-03 | 1993-08-24 | University Of Connecticut | Transistor lasers |
JPH06260493A (en) | 1993-03-05 | 1994-09-16 | Mitsubishi Electric Corp | Semiconductor device |
US5293050A (en) * | 1993-03-25 | 1994-03-08 | International Business Machines Corporation | Semiconductor quantum dot light emitting/detecting devices |
US5399880A (en) | 1993-08-10 | 1995-03-21 | At&T Corp. | Phototransistor with quantum well base structure |
US5796714A (en) * | 1994-09-28 | 1998-08-18 | Matsushita Electric Industrial Co., Ltd. | Optical module having a vertical-cavity surface-emitting laser |
US5780880A (en) | 1996-05-22 | 1998-07-14 | Research Triangle Institute | High injection bipolar transistor |
KR100275540B1 (en) * | 1997-09-23 | 2000-12-15 | 정선종 | Super self-aligned bipolar transistor and its fabrication method |
US6737684B1 (en) * | 1998-02-20 | 2004-05-18 | Matsushita Electric Industrial Co., Ltd. | Bipolar transistor and semiconductor device |
US6707074B2 (en) * | 2000-07-04 | 2004-03-16 | Matsushita Electric Industrial Co., Ltd. | Semiconductor light-emitting device and apparatus for driving the same |
-
2005
- 2005-02-28 US US11/068,561 patent/US7286583B2/en not_active Expired - Lifetime
-
2007
- 2007-10-12 US US11/974,323 patent/US20080089368A1/en not_active Abandoned
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4710936A (en) * | 1984-04-12 | 1987-12-01 | Matsushita Electric Industrial Co., Ltd. | Optoelectronic semiconductor device |
US4849799A (en) * | 1986-07-31 | 1989-07-18 | American Telephone And Telegraph Company At&T Bell Laboratories | Resonant tunneling transistor |
US5003366A (en) * | 1986-12-03 | 1991-03-26 | Hitachi, Ltd. | Hetero-junction bipolar transistor |
US4958208A (en) * | 1987-08-12 | 1990-09-18 | Nec Corporation | Bipolar transistor with abrupt potential discontinuity in collector region |
US6479844B2 (en) * | 2001-03-02 | 2002-11-12 | University Of Connecticut | Modulation doped thyristor and complementary transistor combination for a monolithic optoelectronic integrated circuit |
Cited By (25)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9450017B2 (en) * | 2007-06-21 | 2016-09-20 | Lg Innotek Co., Ltd. | Semiconductor light emitting device and method of fabricating the same |
US20100320491A1 (en) * | 2007-06-21 | 2010-12-23 | Jae Cheon Han | Semiconductor light emitting device and method of fabricating the same |
US8509274B2 (en) | 2009-01-08 | 2013-08-13 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US20100202483A1 (en) * | 2009-01-08 | 2010-08-12 | Quantum Electro Opto Systems Sdn. Bhd. | Two terminal light emitting and lasing devices and methods |
US20100202484A1 (en) * | 2009-01-08 | 2010-08-12 | Holonyak Jr Nick | Light emitting and lasing semiconductor devices and methods |
WO2010080694A3 (en) * | 2009-01-08 | 2010-10-07 | The Board Of Trustees Of The University Of Illinois | Light emitting and lasing semiconductor devices and methods |
US20100272140A1 (en) * | 2009-01-08 | 2010-10-28 | Quantum Electro Opto Systems Sdn. Bhd. | High speed light emitting semiconductor methods and devices |
WO2010080694A2 (en) * | 2009-01-08 | 2010-07-15 | The Board Of Trustees Of The University Of Illinois | Light emitting and lasing semiconductor devices and methods |
US20100289427A1 (en) * | 2009-01-08 | 2010-11-18 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US8675703B2 (en) | 2009-01-08 | 2014-03-18 | Quantum Electro Opto Systems Sdn. Rhd. | Two terminal light emitting and lasing devices and methods |
US8179937B2 (en) | 2009-01-08 | 2012-05-15 | Quantum Electro Opto Systems Sdn. Bhd. | High speed light emitting semiconductor methods and devices |
US8638830B2 (en) | 2009-01-08 | 2014-01-28 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor devices and methods |
WO2010087948A3 (en) * | 2009-01-29 | 2010-11-18 | The Board Of Trustees Of The University Of Illinois | Light emitting and lasing transistor devices and methods |
WO2010087948A2 (en) * | 2009-01-29 | 2010-08-05 | The Board Of Trustees Of The University Of Lllinois | Light emitting and lasing transistor devices and methods |
US8494375B2 (en) | 2009-11-09 | 2013-07-23 | Quantum Electro Opto Systems Sdn. Bhd. | High speed communication |
US20110150487A1 (en) * | 2009-11-09 | 2011-06-23 | Gabriel Walter | High speed communication |
US9231700B2 (en) | 2009-11-09 | 2016-01-05 | Quamtum Electro Opto Systems Sdn. Bhd. | High speed communication |
US8618575B2 (en) | 2010-09-21 | 2013-12-31 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US9299876B2 (en) | 2010-09-21 | 2016-03-29 | Quantum Electro Opto Systems Sdn. Bhd. | Light emitting and lasing semiconductor methods and devices |
US9452928B2 (en) | 2011-09-02 | 2016-09-27 | Quantum Electro Opto Systems Sden. Bhd. | Opto-electronic circuits and techniques |
US8842706B2 (en) | 2011-10-07 | 2014-09-23 | The Board Of Trustees Of The University Of Illinois | Opto-electronic oscillator and method |
US8970126B2 (en) | 2011-10-07 | 2015-03-03 | The Board Of Trustees Of The University Of Illinois | Opto-electronic devices and methods |
US9159873B2 (en) | 2011-11-14 | 2015-10-13 | Quantum Electro Opto Systems Sdn. Bhd. | High speed optical tilted charge devices and methods |
US9431572B2 (en) | 2012-08-02 | 2016-08-30 | Quantum Electro Opto Systems Sdn. Bhd. | Dual mode tilted-charge devices and methods |
US9304267B2 (en) | 2012-09-11 | 2016-04-05 | Quantum Electro Opto Systems Sdn. Bhd. | Method and apparatus for optical coupling and opto-electronic conversion |
Also Published As
Publication number | Publication date |
---|---|
US20070223547A1 (en) | 2007-09-27 |
US7286583B2 (en) | 2007-10-23 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US7286583B2 (en) | Semiconductor laser devices and methods | |
JP2008532318A (en) | Semiconductor bipolar light emitting and laser device and method thereof | |
US7091082B2 (en) | Semiconductor method and device | |
US7998807B2 (en) | Method for increasing the speed of a light emitting biopolar transistor device | |
US7696536B1 (en) | Semiconductor method and device | |
Feng et al. | Light-emitting transistor: Light emission from InGaP/GaAs heterojunction bipolar transistors | |
US7711015B2 (en) | Method for controlling operation of light emitting transistors and laser transistors | |
US9299876B2 (en) | Light emitting and lasing semiconductor methods and devices | |
Garcia et al. | Epitaxially stacked lasers with Esaki junctions: A bipolar cascade laser | |
TWI517510B (en) | Light emitting and lasing semiconductor devices and methods | |
US20050040432A1 (en) | Light emitting device and method | |
US20100103971A1 (en) | Optical bandwidth enhancement of light emitting and lasing transistor devices and circuits | |
Zandian et al. | HgCdTe double heterostructure injection laser grown by molecular beam epitaxy | |
CN101238619A (en) | Semiconductor bipolar light emitting and laser devices and methods | |
JP2007503710A (en) | Semiconductor device and method | |
US4599632A (en) | Photodetector with graded bandgap region | |
James et al. | Franz–Keldysh photon-assisted voltage-operated switching of a transistor laser | |
Cecchini et al. | High-performance planar light-emitting diodes | |
Harth et al. | Frequency response of GaAlAs light-emitting diodes | |
Feng et al. | Temperature dependence of a high-performance narrow-stripe (1 μm) single quantum-well transistor laser | |
Kim et al. | Sub-Poissonian Light Generation in Light-Emitting Diodes | |
Chen et al. | 1/f Noise Model of 980 nm InGaAs/GaAs Laser Diodes based on Parasitic Parameters under Low Injection Current | |
Liu | Fabrication and characterization of resonant cavity light-emitting transistors | |
Ghosh et al. | Tunnel injection quantum dot lasers | |
Hoskens et al. | Hot Electron Injection Laser Controlled Carrier-Heating Induced Gain Switching |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |