EP2419975A2 - Light emitting semiconductor methods and devices - Google Patents
Light emitting semiconductor methods and devicesInfo
- Publication number
- EP2419975A2 EP2419975A2 EP10764775A EP10764775A EP2419975A2 EP 2419975 A2 EP2419975 A2 EP 2419975A2 EP 10764775 A EP10764775 A EP 10764775A EP 10764775 A EP10764775 A EP 10764775A EP 2419975 A2 EP2419975 A2 EP 2419975A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- region
- emitter
- base
- providing
- drain
- 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.)
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Classifications
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- 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
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- 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
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- 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
- H01S5/0014—Measuring characteristics or properties thereof
- H01S5/0035—Simulations of laser characteristics
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- 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
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
- H01S5/04257—Electrodes, e.g. characterised by the structure characterised by the configuration having positive and negative electrodes on the same side of the substrate
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- 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
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- 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
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
-
- 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
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18311—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement using selective oxidation
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- 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
- H01S5/3095—Tunnel junction
Definitions
- This invention relates to methods and devices for producing light emission and laser emission in response to electrical signals.
- the invention also relates to methods for producing high frequency light emission and laser emission from semiconductor devices with improved efficiency, and to increasing light output from semiconductor light-emitting devices.
- Light-Emitting Transistor Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Heterojunction Bipolar Light- Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-ll GaAsSb/lnP Heterojunction Bipolar Light- Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G.
- Figures 1 and 2 illustrate an example of an existing tilted charge light emitter; that is, a light-emitting transistor ("LET") as described in the above referenced patent documents and publications.
- An n+ GaAs subcollector region 105 has an n-type GaAs collector region 110 deposited thereon, followed by a p+ AIGaAs/GaAs base region 120, having an n-type InGaAs quantum well (QW) 126.
- An emitter mesa is deposited over the base, and includes n-type InGaP emitter layer 130, and n-type AIGaAs aperture layer 140, and an n+ GaAs cladding layer 150.
- FIG. 1 shows a plan view of the Figure 1 metallizations; that is, opposing collector contacts (common connection not shown), the base contact 122 including an outer annular ring, and the emitter contact 152 including an inner annular ring.
- Figure 1 also has arrows that illustrate the flow of electron current and hole current in typical light-emitting transistor operation.
- light-emitting transistors, transistor lasers, and certain two terminal light emitters are sometimes referred to as “tilted charge” devices, owing to the "tilted” base charge distribution (as could be illustrated on the device band diagram) which locks the base electron-hole recombination in "competition” with the charge “collection” at the reverse-biased collector junction, thus selecting ("filtering") and allowing only “fast” recombination in the base (assisted by the quantum well(s)) at an effective lifetime of the order of picoseconds.
- the above-listed documents including reference to a two-terminal tilted charge light emitter disclosed in U.S. Patent Application Publication No. US2010/0034228.
- the optical cavity or window defined in part by an aperture formed with an oxide
- the optical cavity or window is placed after the base and emitter contact. Due to the high base sheet resistant and large current gain (emitter current) of the tilted charge device, the voltage difference across the base emitter junction is the greatest along the edge defined by the oxide aperture. This forces the recombination events (which result in the desired optical output) to localize along the perimeter of the oxide aperture, as current injection is largest in the region where voltage difference is largest. The junction voltage decreases towards the center of the optical cavity.
- This phenomenon is represented in Figures 1 and 2, and can be further understood from the modeling of device operation as shown in the simplified circuit model of Figure 3. In Figure 3, the regions and contacts correspond with those of like reference numerals in Figure 1.
- 307, 320, and 330 respectively represent the collector, base, and emitter resistances
- 308 represents collector current components
- 340 represents the spatial components of base/emitter voltage.
- the path of least resistance for electron conduction is along the edge defined by the oxide aperture.
- V4 being substantially greater than V3
- V1 being substantially greater than V2. This causes most of the recombination events to localize nearer the edge of the base layer, and less recombination at and near the center of the base layer (see sketch of light output representation of Figure 2).
- Figure 4 is a graph showing detected optical output of the device (as detector photo current in ⁇ A) as a function of device base current (in mA).
- the optical output for larger emitter diameter devices saturates at larger base current input. Saturation of light is attributed to quantum well saturation.
- the optical output density and emitter current density for different emitter sizes is conveniently normalized to the aperture perimeter "area" (shaded area of inset in Fig. 5.) The area is determined by assuming a constant shallow penetration into the optical cavity. The result indicates that recombination is localized along the edge of the device. Maximum light output is therefore determined by the active perimeter defined by the oxide aperture rather than the area of the total optical cavity.
- Figure 6 illustrates pulsed current measurement for various emitter sizes showing light output for both 10% and 50% pulsed current measurements to be substantially the same. Results indicate that light saturation for the device was not caused by heating but by localized quantum well saturation.
- Figure 7 is a top view photograph of the type of existing device of Figure 1 , wherein the collector (C), base (B), and emitter (E) metallizations are denoted, and the optical cavity or window is indicated by an arrow.
- the light-emitting transistor of the Figure has a 10 urn emitter mesa and aperture defined optical cavity of 6 um.
- the optical cavity is located after the base and emitter contacts (i.e., above them, as in Figure 1).
- the active perimeter of this device is therefore about 18 ⁇ m.
- Figure 8 shows an existing tilted charge light-emitting diode wherein the emitter (E) and base/drain (BD) metallizations are denoted and, again, the device has a 10 um emitter mesa and aperture defined optical cavity of 6 um. The optical cavity is again located after the base and emitter contacts. Again, the active perimeter of this device is about 18 ⁇ m.
- the optical window or cavity is placed after the base and emitter contact. Due to the high base sheet resistant and large current gain (emitter current) of the tilted charge device, the voltage difference across the base emitter junction is greatest along the edge defined by the oxide aperture. As explained above, this forces the recombination events (which result in the desired optical output) to localize along the perimeter of the oxide aperture, as current injection is largest in the region where voltage difference is largest. The junction voltage decreases towards the center of the optical cavity, with attendant disadvantages.
- LEDs Semiconductor light emitting diodes
- lasers using direct gap IM-V materials, and electron-hole injection and recombination
- CMOS complementary metal-oxide-semiconductor
- ⁇ ext external quantum efficiencies
- HBLET heteroj unction bipolar light emitting transistor
- HBT high-speed heterojunction bipolar transistor
- the room temperature, continuous wave operation of a transistor laser further demonstrates that a practical radiative recombination center (i.e., undoped quantum well) can be incorporated in the heavily doped base region of a HBLET (see M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131 103 (2005)). Due to the short base effect of tilted charge population in transistors, the effective minority carrier lifetime in the base region of the HBLETs can be progressively reduced to sub-100 ps by tailoring the doping and incorporating QW(s) (see H. W. Then, M. Feng, N. Holonyak, Jr, and C. H.
- the light-emitting semiconductor devices are configured to obtain uniformity of carrier injection into the base region, and the optical cavity between base and emitter electrodes does not cause a deleterious non-uniformity of voltage distribution between the emitter and base (or base/drain) electrodes of the device, as in the prior art.
- a heterojunction bipolar light-emitting transistor (LET) or a tilted charge light-emitting diode can improve both electrical and optical characteristics.
- the fast recombination dynamics of the intrinsic transistor can be harnessed by scaling down an emitter aperture to reduce lateral extrinsic "parasitic-like" RC charging.
- a method for producing light emission from a two terminal semiconductor device with improved efficiency, including the following steps: providing a layered semiconductor structure including a semiconductor drain region comprising at least one drain layer, a semiconductor base region disposed on said drain region and including at least one base layer, and a semiconductor emitter region disposed on a portion of said base region and comprising an emitter mesa that includes at least one emitter layer; providing, in said base region, at least one region exhibiting quantum size effects; providing a base/drain electrode having a first portion on an exposed surface of said base region and a further portion coupled with said drain region, and providing an emitter electrode on the surface of said emitter region; applying signals with respect to said base/drain and emitter electrodes to obtain light emission from said base region; and configuring said base/drain and emitter electrodes for substantial uniformity of voltage distribution in the region therebetween.
- the geometry of said emitter mesa between said electrodes is configured to promote substantial uniformity of voltage distribution in the region between the electrodes.
- the emitter mesa has a substantially rectilinear surface portion, and the step of providing said electrodes comprises providing said emitter electrode along one side of said surface portion of the emitter mesa and providing the first portion of said base/drain electrode on a portion of the base region surface adjacent the opposite side of said emitter mesa surface portion.
- the emitter electrode and said first portion of the base/drain electrode can be opposing linear conductive strips.
- a method for producing light emission from a three terminal semiconductor device with improved efficiency including the following steps: providing a layered semiconductor structure including a semiconductor collector region comprising at least one collector layer, a semiconductor base region disposed on said collector region and including at least one base layer, and a semiconductor emitter region disposed on a portion of said base region and comprising an emitter mesa that includes at least one emitter layer; providing, in said base region, at least one region exhibiting quantum size effects; providing a collector electrode on said collector region, providing a base electrode on an exposed surface of said base region, and providing an emitter electrode on the surface of said emitter region; applying signals with respect to said collector, base, and emitter electrodes to obtain light emission from said base region; and configuring said base and emitter electrodes for substantial uniformity of voltage distribution in the region therebetween.
- a method for producing a high frequency optical signal component representative of a high frequency electrical input signal component, including the following steps: providing a semiconductor transistor structure that includes a base region of a first semiconductor type between semiconductor emitter and collector regions of a second semiconductor type; providing, in said base region, at least one region exhibiting quantum size effects; providing emitter, base, and collector electrodes respectively coupled with said emitter, base, and collector regions; applying electrical signals, including said high frequency electrical signal component, with respect to said emitter, base, and collector electrodes to produce output spontaneous light emission from said base region, aided by said quantum size region, said output spontaneous light emission including said high frequency optical signal component representative of said high frequency electrical signal component; providing an optical window or cavity for said light emission in the region between said base and emitter electrodes; and scaling the lateral dimensions of said optical window or cavity to control the speed of light emission response to said high frequency electrical signal component.
- the method further comprises providing an aperture disposed over said emitter region, and said scaling of the lateral dimensions includes scaling the dimensions of said aperture.
- the aperture is generally circular and is scaled to preferably about 10 ⁇ m or less in diameter, and more preferably about 5 ⁇ m or less in diameter.
- the window or cavity is substantially rectangular, and said scaling of lateral dimensions comprises providing the window or cavity with linear dimensions of preferably about 10 ⁇ m or less, and more preferably about 5 ⁇ m or less in diameter.
- the high frequency electrical signal component has a frequency of at least about 2 GHz.
- a method for producing a high frequency optical signal component representative of a high frequency electrical signal component, including the following steps: providing a layered semiconductor structure including a semiconductor drain region comprising at least one drain layer, a semiconductor base region disposed on said drain region and including at least one base layer, and a semiconductor emitter region disposed on a portion of said base region and comprising an emitter mesa that includes at least one emitter layer; providing, in said base region, at least one region exhibiting quantum size effects; providing a base/drain electrode having a first portion on an exposed surface of said base region and a further portion coupled with said drain region, and providing an emitter electrode on the surface of said emitter region; applying signals with respect to said base/drain and emitter electrodes to produce light emission from said base region; providing an optical window or cavity for said light emission in the region between said first portion of the base/drain electrode and said emitter electrode; and scaling the lateral dimensions of said optical window or cavity to
- said emitter mesa has a substantially rectilinear surface portion
- said step of providing said electrodes comprises providing said emitter electrode along one side of said surface portion of the emitter mesa and providing the first portion of said base/drain electrode on a portion of the base region surface adjacent the opposite side of said emitter mesa surface portion.
- the step of providing said electrodes further comprises providing said emitter electrode and the first portion of said base/drain electrode as opposing linear conductive strips, and said scaling of lateral dimensions comprises providing said window or cavity with linear dimensions of preferably about 10 ⁇ m or less, and more preferably about 5 ⁇ m or less.
- Figure 1 is a cross-sectional representation of an example of an existing tilted charge light-emitting transistor device.
- Figure 2 is a plan view of the contacts or electrodes of the Figure 1 device.
- Figure 3 is a circuit model representing the relevant operation of the Figure 1 device.
- Figure 4 is a graph showing optical output (as detector photocurrent) as a function of base current, for devices of different emitter diameters DE.
- Figure 5 shows a graph of normalized optical output density as a function of emitter current over edge density, for devices different emitter diameters, DE.
- the inset shows a representation of the light emitting area, as a normalized aperture perimeter area. The area is determined by assuming a constant shallow penetration into the optical cavity.
- Figure 6 shows photocurrent measurements as a function of emitter current for devices of various emitter sizes (in ⁇ m), showing 10% and 50% pulsed current points on each curve.
- Figure 7 is a top view photograph of the type of existing device of Figure 1 , wherein the collector (C), base (B), and emitter (E) metallizations are denoted, and the optical cavity is indicated by an arrow.
- Figure 8 is a top view photograph of a tilted charge light-emitting diode of the type described in copending U.S. Patent Application Serial No. 12/655,806, filed January 7, 2010, and assigned to the same assignees as the present application.
- Figure 9 is a cross-sectional diagram of an example of an improved tilted charge light-emitting transistor in accordance with an embodiment of the invention and which can be used in practicing an embodiment of the method of the invention.
- Figure 10 shows a circuit model of device operation of the Figure 9 embodiment.
- Figures 11(a) and 11 (b) show opposing base and emitter contact or electrode strips as employed in embodiments of the invention
- Figure 12 is a top view photograph of a titled charge light emitting transistor with a 10 ⁇ m X 10 ⁇ m Type 2 optical cavity design
- Figure 13 shows the light-emitting transistor optical output (detector photo current) vs emitter current for the devices shown in Figure 7 (solid line) and Figure 12 (dashed line).
- Figure 14 is a simplified cross-sectional diagram of a two-junction tilted-charge light emitting diode in accordance with an embodiment of the invention.
- Figure 15 is top view photograph of the device of Figure 14, wherein the emitter (E) and base/dram (BD) metallizations are denoted, and the optical cavity is indicated by an arrow
- Figure 16 is a table showing the semiconductor layers of an example of the Figure 15 device.
- Figure 17 shows the I-V characteristic of the device of Figures 15 and 16.
- Figure 18 shows the optical light output L-I characteristic of the Figure 15, 16 device, measured from the device substrate bottom, and, in the inset, the output optical spectrum in arbitrary units.
- Figure 20 is a simplified cross-sectional diagram of an embodiment of the invention that utilizes a tunnel junction as the device's drain region
- Figure 21 is a simplified cross-section of a device in which embodiments of the improvements of the invention can be employed.
- Figure 22 shows, in graph (a), the collector I-V characteristics and, in graphs (b), the optical output characteristics, of the Figure 21 device.
- the light emission is measured from the bottom of the device with a large-area photodetector.
- Figure 24 is a plot showing F 3dB (in GHz) as a function of I B for EC input port modulation of the HBLET with D A ⁇ 6 ⁇ m and V B c at 0 volts.
- the inset shows the optical output (detector output in microwatts) as a function of I B .
- the inset shows the optical spectrum as arbitrary units as a function of wavelength.
- Figure 29 is a simplified cross-sectional diagram of a tilted-charge light- emitting diode, in which an embodiment of the invention can be employed.
- Figure 9 is a diagram of an improved tilted charge light-emitting transistor device in accordance with an embodiment of the first aspect of the invention.
- the devices hereof can be fabricated using, for example, conventional semiconductor deposition techniques for depositing Hl-V semiconductor layers and device fabricating and finishing techniques as described, for example, in the patents and publications listed in the Background portion hereof.
- the device includes n+ subcollector region 905, n-type collector region 910, and p+ base region 920 containing quantum well 926.
- the emitter mesa includes n-type emitter layer 930 and n+ emitter cladding 950.
- the device is an npn tilted charge light emitting transistor, it being understood that the principles hereof also apply to a pnp device.
- the collector electrode or contact metallization is represented at 907.
- the base contact is represented at 922, and the emitter contact is represented at 952.
- the optical cavity is advantageously placed in between the emitter and base electrodes.
- the emitter resistance (RE) is tuned relative to the emitter current to base current ratio ( ⁇ +1) so that the voltage drop due to electron conduction equals the voltage drop due to base current as holes conduct laterally from the opposite direction. This results in a more uniform voltage drop across the base-emitter junction.
- Emitter resistance can be tuned by changing sheet resistances and by changing the geometry of the emitter mesa (Figure 11, below).
- Figure 10 shows a circuit model of device operation of the Figure 9 embodiment.
- the regions and contacts correspond with those of like reference numerals in Figure 9.
- 1007, 1020, and 1030 respectively represent the collector, base, and emitter resistances
- 1008 represents collector current components
- 1040 represents the spatial components of base/emitter voltage.
- the voltage drops across the base-emitter junction are made substantially uniform so that V1 , V2, V3 and V4 will be approximately the same. This means that the recombination events will be approximately uniform in the optical cavity.
- a substantially symmetrical voltage drop across the base and emitter junction can be achieved by tuning the sheet resistance and geometry of the emitter mesa; e.g. by employing a geometry of the optical window or cavity (defined by in this case the exposed emitter mesa) to obtain the desired resistances.
- the diagrams of Figures 11(a) and 11(b) show opposing base and emitter contact or electrode strips and, as the shaded area, the exposed emitter mesa from which generated light can be emitted.
- the "Type 1" device of Figure 11(b) will exhibit larger emitter resistance and smaller base resistance.
- Figure 13 shows the light-emitting transistor optical output (detector photo current) vs emitter current for the devices shown in Figure 7 (solid line - existing device) and Figure 12 (dashed line - example of an embodiment hereof).
- the distributed design structure hereof despite having an active perimeter of 10 ⁇ m (Figure 12), which is almost half of the 18 ⁇ m perimeter of the existing design ( Figure 7), is seen to be capable of about two times larger emitter current injection before reaching optical saturation. This indicates that a larger effective area of the optical window or cavity is involved in recombination as a result of the distributed design hereof.
- Figures 14 and 15 show a two-terminal tilted charge light-emitting diode having the distributed design feature of an embodiment hereof, with the optical cavity placed between the emitter and base/drain and the tuned emitter resistance.
- a p-type base region 1440 is disposed between unintentionally doped n-type drain region 1433 and n-type emitter region 1450, so that there is a first semiconductor junction between said emitter and base region and second semiconductor junction between the base region and the drain region.
- the base region 1440 includes quantum size region 1441 , such as, for example, one or more quantum wells or one or more regions of the quantum dots.
- Below the drain 1433 is n-type sub-drain 1434.
- the emitter is an emitter cladding and contact region 1460.
- the emitter region has emitter electrode coupled thereto, in the form of emitter contact 1453.
- a base/drain electrode is coupled with the base and drain regions.
- the base/drain electrode is a metallic contact 1470 that is deposited, in this embodiment, on the base region and sub-drain region.
- a positive bias voltage 1491 is applied to the base/drain contact 1470 with respect to the emitter contact 1453, and an AC voltage 1492 is also applied with respect to these contacts.
- the flow of electrons and holes in the Figure 14 device is shown by the arrows in the Figure. Recombination in the base region, aided by the quantum well, results in light emission.
- Waveguide and cavity configurations can be added to this structure in order to allow this device to function as a two junction laser diode, two junction resonance cavity light emitting diode, or two junction vertical cavity transistor laser.
- typical upper and lower distributed Bragg reflectors (DBRs) can be provided in the Figure 14 device to obtain an optical resonant cavity.
- Radiative recombination is optimized in the active optical region, as represented in Figure 14 at 1485. From the top view photograph of Figure15, the emitter and base/drain metallizations, and the optical cavity or window region of the Figure 14 device can be seen.
- the epitaxial layers of the crystal used for making a two-junction tilted- charge light emitting diode includes, upward from the substrate, a 3000 A n- type doped GaAs buffer layer, a 500 A graded Alo.30Gao.7 0 As confining layer, a 213 A graded AI 0 . 30 Ga0.70As to AI 09O Ga 0 ioAs oxide buffer layer, a 595 A n- type AI 0 . 98 Ga0.0 2 As oxidizable aperture layer and another 213 A graded Alo.
- the heterostructure emitter includes of a 511 A n-type In 0 49Ga 0 51 P layer, a 213 A graded Alo.3oGao 7oAs to Al 0 goGao ioAs oxide buffer layer, a 595 A n-type Alo98Ga O o2As oxidizable aperture layer, another 213 A graded AI 0 9O Ga 0 1 OAs to Al 0 3oGao.7oAs oxide buffer layer, and a 500 A graded AI 0 . 3 0Ga0.70As confining layer.
- the structure is completed with a 2000 A GaAs top contact layer.
- the aperture is optional. Reference can be made to the table of Figure 16, the last column of which indicates the layer description relative to the diagram of Figure 15.
- the two-junction tilted-charge LED is fabricated by first performing wet etching steps to form emitter and base-"drain" mesas, followed by an isolation etch from the sub-"drain” layer to the substrate. Metallization steps are then performed to provide the required electrical contacts.
- the completed LED has only two terminals: (a) a contact to the emitter layer, and (b) another across the base and "drain” layers (see Figure 15).
- the base-"drain” forms a p-n junction with a reverse built-in field that is maintained by a common potential (zero potential difference) obtained via the common contact metallization extending to the base.
- the zero base-"drain” potential difference ensures that there is no base charge population density at the base-"drain” boundary, hence establishing the dynamic "tilted” emitter-to-"drain” population in the base, which was first described above.
- the “drain” layer performs therefore a role similar to the collector in a three-terminal HBLET. It allows excess minority carriers to be removed from the base (I 0 ), “swept” from base to "drain” by the built-in field at the base-"drain” p-n junction. Base carriers in transit from the emitter to the "drain” that do not recombine within the base transit time are removed, “drained”. This enables fast modulation of the tilted- charge LED by preventing the build-up of "slow” charge in the base.
- the tilted-charge LED possesses the high speed optical modulation characteristics of an HBLET.
- the tilted-charge LED can be biased as a usual two-terminal device, simply operating faster. Externally the tilted-charge LED displays an electrical I-V characteristic resembling that of a p-n junction diode (see Figure 17).
- the "turn-on" voltage is determined by the emitter-base potential difference since the base and "drain" are metalized and unified in potential.
- the L-I E optical output characteristic shown in Figure 18, is obtained from the bottom emission (through the substrate) of the device.
- the broad radiative emission spectrum (FWHM ⁇ 96 nm) of the inset shows that the LED is operating in spontaneous recombination.
- the optical output for this example is in the low microwatt range because the light extraction efficiency, assuming a single escape cone from the semiconductor GaAs-air interface, is only about 1.4%.
- the optical output is collected from the device top emission through a fiber, and measured with a 12 GHz p- i-n photodetector connected to an Agilent N5230A network analyzer.
- Figure 20 shows another embodiment hereof which utilizes a tunnel junction as the drain region.
- Reference can be made, for example, to Tunnel Junction Transistor Laser, M. Feng, N. Holonyak, Jr., H.W. Then, CH. Wu, and G Walter, Appl. Phys Lett. 94, 04118 (2009).
- elements with like reference numerals to those of Figure 14 correspond to those elements of Figure 14.
- the p+ layer 1930 of the tunnel junction is adjacent the base 1440 and the n+ layer 1931 of the tunnel junction is adjacent an n-type sub drain layer 1434.
- the epitaxial layers of the crystals used for a heterojunction bipolar light emitting transistor (HBLET), fabricated using MOCVD included a 3000 A n-type heavily doped GaAs buffer layer, followed by a 500 A n-type AIo 3 oGao ⁇ oAs layer, a graded AIo 3 oGao 7 oAs to Al 0 goGa o ioAs oxide buffer layer, a 600 A n-type Alo 9 ⁇ Gao o 2 As oxidizable layer, and then a graded AlogoGao ioAs to AI 03 oGao 7 oAs oxide buffer layer that completes the bottom cladding layers.
- HBLET heterojunction bipolar light emitting transistor
- the epitaxial HBTL structure is completed with the growth of the upper cladding layers, which include a 511 A ⁇ -type Ino-igGaosiP wide-gap emitter layer, a graded AIo 3oGao 7oAs to Al 0 goGao ioAs oxide buffer layer, a 600 A n-type Alog ⁇ Gaoo 2 As oxidizable layer, and a graded Al 0 goGao ioAs to Al 0 3 oGao 7oAs oxide buffer layer and a 500 A n-type Alo 3 oGa 0 7 oAs layer.
- the upper cladding layers include a 511 A ⁇ -type Ino-igGaosiP wide-gap emitter layer, a graded AIo 3oGao 7oAs to Al 0 goGao ioAs oxide buffer layer, a 600 A n-type Alog ⁇ Gaoo 2 As
- the HBLET structure is capped with a 2000 A heavily doped n-type GaAs contact layer
- the completed devices of the first example hereof have an oxide aperture diameter, DA, of - 6 ⁇ m on 10 ⁇ m emitter mesas.
- An n+ GaAs subcollector region 2105 has an n-type GaAs collector region 2110 deposited thereon, followed by p+ AIGaAs/GaAs base region 2120, having one or more undoped InGaAs quantum wells (QWs).
- An emitter mesa is formed over the base, and includes, n-type InGaP emitter layer 2130, and n-type AIGaAs aperture layer 2140, and an n+ GaAs cladding layer 2150. Lateral oxidation can be used to form the central aperture.
- the collector contact metallization is shown at 2107, the base contact metallization is shown at 2122, and the emitter metallization is shown at 2152.
- the collector I-V and optical output characteristics are shown in Figure 22(a) and 22(b), respectively.
- the light emission in Figure 3(b) is measured from the bottom of the device with a large-area photodetector.
- a light extraction efficiency of a single escape cone from the GaAs-air surface, assuming Fresnel reflection losses for normal incidence, is approximately 1.4%. (see M. G. Craford, High Brightness Light Emitting Diodes, Semiconductors and Semimetals, Vol. 48, Academic Press, San Diego, CA, p.
- the broad spectral characteristics of the optical output is indicative of the width of the spontaneous recombination of the HBLET operation.
- the HBLET of this example does not incorporate a resonant cavity, it being understood that the use of a resonant cavity will substantially increase optical output extraction.
- the common-collector HBLET with the BC port as the rf-input allows for simultaneous electrical-to-optical output conversion, and electrical output gain at the EC output port. Due to its three-port nature, its optical output can also respond to input modulation signals at the EC-port, although in this configuration, the device does not provide a simultaneous electrical output gain at the BC-port. Deploying the EC-port as the rf-input has the advantage of better matched input impedance (50 ⁇ standard) for maximal power transfer.
- the BC-port input impedance is generally higher than the EC- input impedance due to the reverse-biased BC junction, and can be advantageous where high input impedances are desirable for maximizing circuit performances.
- the optical response is measured with a highspeed p-i-n photodetector with bandwidth > 12 GHz and a 50-GHz electrical spectrum analyzer.
- a frequency generator (0.05 - 20 GHz) is used for the input signal to the device.
- the optical response, H(f) may be expressed as ) where A 0 is the electrical-to-optical conversion efficiency, and f 3 dB is the bandwidth at -3 dB.
- f 3 dB is related to an effective base carrier recombination lifetime r B (absent stimulated recombination but including the effects of undesirable parasitic RC-charging time) by the relation,
- a value for f 3 dB of 4.3 GHz therefore corresponds to a r B of 37 ps.
- a HBLET 1 the holes are built-in by p-doping in the base, and re-supplied by an ohmic base current, while the (minority carrier) electrons are injected from the heterojunction emitter.
- the dynamic 'tilted' charge flow condition is maintained in the base of the transistor with the electrical collector (reverse-biased BC junction) in competition with base recombination. Because of the 'tilted' base population, current flow is a function of the slope in the charge distribution, and high current densities are possible without requiring extreme carrier densities.
- the heteroj unction bipolar transistor (HBT) n-p-n structure therefore, possesses intrinsic advantages (in how charge is handled) over the double heterojunction p-i-n structure.
- the 37 ps carrier lifetime observed in the HBLET hereof indicates that spontaneous recombination can be "fast", and higher modulation speeds are possible by further reducing the undesirable parasitics.
- an HBLET can potentially be deployed at data rates much higher than 4.3 Gb/s, with attendant advantage for short range optical data communications.
- devices are fabricated as previously described, but with emitter aperture widths of 5 ⁇ m, 8 ⁇ m, and 13 ⁇ m, achieved by selective lateral oxidation of the n-AI 0 . 98 Ga 0 . 02 As layer (aperture layer 140 of Figure 1).
- Figure 26 shows the corresponding optical light output characteristic L-IB as measured from the bottom-side of each of the three devices.
- the device with a 5 ⁇ m aperture achieves 2.4 times higher current gain than the 13 ⁇ m device.
- the 13 ⁇ m HBLET produces an optical output 2.4 times higher.
- the current gain, ⁇ , and optical output saturate at high bias conditions (VCE ⁇ 2 V) due to excessive heating as the devices are on semi- insulating substrate and operated without any temperature control. While total recombination radiation increases for the larger device, only a fraction of the radiative recombination occurs within the intrinsic transistor base region.
- the proper intrinsic transistor base spans a concentric region with a radius proportional to DA/2, and an intrinsic device width (active edge) denoted by, say, t.
- an intrinsic device width active edge
- the EC-input impedance, Z E c is well matched to the source impedance (50 ⁇ standard) for maximal power transfer.
- the optical response is again measured with a 12 GHz p-i-n photodetector and a 50-GHz electrical spectrum analyzer. Also, a frequency sweep generator up to 20 GHz is again used for the input signal to the device.
- the plot of the optical bandwidth vs. the bias base current I 8 for HBLETs of various aperture sizes shows the increase in the optical bandwidth as the bias current (I B and hence, I E ) is increased. The maximum bandwidth is achieved where the optical and electrical characteristics begin to saturate due to heating, as is evident from Figures 25 and 26.
- Lateral extrinsic recombination therefore forms an equivalent parasitic-like RC-charging time that limits the optical bandwidth of the device. Therefore, by lateral scaling, the device's performance can be improved by 'channeling' (via high current densities) and 'limiting' (via smaller apertures) the carriers to feed only radiative recombination originating or emanating from the intrinsic transistor base. Due to the presence of a finite (parasitic) lateral edge in the device construction, the ⁇ B obtained of 37 ps is still dominated or limited extrinsically. This shows that the intrinsic transistor base recombination lifetime can be much faster than 37 ps, and implies that an even higher spontaneous optical bandwidth is possible.
- FIGs 14-16 there is disclosed an embodiment of a two terminal tilted-charge light emitting diode having a non-circular (e.g. rectangular) region as its optical window or cavity, between linear emitter and base electrodes or contacts which can be opposing conductive strips.
- this configuration has the advantage of enhanced uniformity of carrier injection in the active region and efficient light output.
- the above- described scaling advantages are also applicable to this configuration.
- QWs InGaAs quantum wells
- An emitter mesa is formed over the base and includes an n-type InGaP emitter layer 2930, and an optional n-type AIGaAs aperture layer 2940, and an n+ GaAs cladding layer 2950.
- the emitter electrode metal is shown at 2952, and base/drain electrode metal at 2960.
- a similar configuration, between linear base and emitter electrodes, can also be employed in a three terminal light-emitting transistor or laser transistor. Again, the above-described scaling advantages are applicable to these device configurations.
Abstract
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US26811909P | 2009-06-09 | 2009-06-09 | |
PCT/US2010/001133 WO2010120372A2 (en) | 2009-04-17 | 2010-04-16 | Light emitting semiconductor methods and devices |
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JP2015529973A (en) * | 2012-08-02 | 2015-10-08 | クワンタム エレクトロ オプト システムズ エスディーエヌ. ビーエイチディー.Quantum Electro Opto Systems Sdn. Bhd. | Dual-mode gradient charge device and method |
CN105633227B (en) * | 2015-12-29 | 2018-04-17 | 华南师范大学 | High Speed Modulation light emitting diode and its manufacture method |
CN105655454B (en) * | 2015-12-29 | 2018-05-08 | 华南师范大学 | High modulation light emitting diode and preparation method thereof |
JP7216270B2 (en) * | 2018-09-28 | 2023-02-01 | 日亜化学工業株式会社 | semiconductor light emitting device |
CN113206448B (en) * | 2021-04-30 | 2023-04-07 | 中国科学院半导体研究所 | Laser with current barrier layer |
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US4513423A (en) * | 1982-06-04 | 1985-04-23 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Arrangement for damping the resonance in a laser diode |
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US5796714A (en) * | 1994-09-28 | 1998-08-18 | Matsushita Electric Industrial Co., Ltd. | Optical module having a vertical-cavity surface-emitting laser |
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US7354780B2 (en) * | 2003-08-22 | 2008-04-08 | The Board Of Trustees Of The University Of Illinois | Semiconductor light emitting devices and methods |
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