Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical
int... more Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials with high absorption coefficients are particularly promising for photodetection in energy-efficient optical links because of the potential to scale down the absorber size, and the resulting capacitance and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar junction phototransistor with a high current gain (53.6), bandwidth (7GHz) and responsivity (9.5A/W) using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The quantum efficiency-bandwidth product of 105GHz is the highest for photodetectors on silicon. The bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
ABSTRACT We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowire... more ABSTRACT We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowires as building blocks to produce antiphase-domain-free GaAs thin films on exact (001) silicon. High quality GaAs nanowires were grown on V-grooved Si (001) substrates using the selective aspect ratio trapping concept. The 4.1% lattice mismatch has been accommodated by the initial GaAs, a few nanometer-thick with high density stacking faults. The bulk of the GaAs wires exhibited smooth facets and a low defect density. An unusual defect trapping mechanism by a “tiara”-like structure formed by Si undercuts was discovered. As a result, we were able to grow large-area antiphase-domain-free GaAs thin films out of the nanowires without using SiO2 sidewalls for defect termination. Analysis from XRD ω-rocking curves yielded full-width-at-half-maximum values of 238 and 154 arc sec from 900 to 2000 nm GaAs thin films, respectively, indicating high crystalline quality. The growth scheme in this work offers a promising path towards integrated III-V electronic, photonic, or photovoltaic devices on large scale silicon platform.
The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etc... more The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etched stripe-patterned substrates were investigated. Footprint-like patterns, located directly above the inclined groove sidewalls, were found on the as-grown LED surface. Cross-sectional transmission electron microscopy (TEM) showed that ‘tumor’-like structures with poor crystal quality were initiated on the inclined sidewalls, seeding dislocation bundles in the subsequently grown crystal. The high dislocation density slowed down the growth above the inclined sidewall, resulting in the uneven morphology. The fabricated devices showed over 30% enhancement in light output power as a result of improvements in both internal and extraction efficiencies.
Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using ta... more Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a novel regrown core-shell p-i-n junction to improve device performance by eliminating shunt current paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced broadband light absorption is also demonstrated over a wide spectral range of 400-800 nm.
We use low-temperature microphotoluminescence and photoluminescence excitation spectroscopy to me... more We use low-temperature microphotoluminescence and photoluminescence excitation spectroscopy to measure the valence band parameters of single wurtzite InGaAs nanoneedles. The effective indium composition is measured by means of polarization-dependent Raman spectroscopy. We find that the heavy-hole and light-hole splitting is ∼95 meV at 10 K and the Stokes shift is in the range of 35-55 meV. These findings provide important insight in the band structure of wurtzite InGaAs that could be used for future bandgap engineering.
We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-base... more We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical wet-etching-patterned sapphire substrate (CWE-PSS) with V-Shaped pit features on the top surface. According to temperature-dependent photoluminescence (PL) measurement and the measured external quantum efficiency, the structure can simultaneously enhance both internal quantum efficiency and light extraction efficiency. Comparing to devices grown on planar sapphire substrate, the threading dislocation defects of LED grown on CWE-PSS are reduced from 1.28 10 9 cm 2 to 3.62 10 8 cm 2 , leading to a 12.5% enhancement in internal quantum efficiency. In terms of the theoretical computing of radiation patterns, the V-Shaped pits roughening surface can be thought of as a strong diffuser with paraboloidal autocorrelation function, increasing the escape probability of trapped photons and achieving a 20% enhancement in light extraction efficiency. Moreover, according to the measurement of optical diffraction power, CWE-PSS demonstrated superior guided light extraction efficiency than that of planar sapphire substrate, thus an extra 7.8% enhancement in light extraction efficiency was obtained. Therefore, comparing to the conventional LED, an overall 45% enhancement in integrated output power was achieved.
The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etc... more The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etched stripe-patterned substrates were investigated. Footprint-like patterns, located directly above the inclined groove sidewalls, were found on the as-grown LED surface. Cross-sectional transmission electron microscopy (TEM) showed that ÔtumorÕ-like structures with poor crystal quality were initiated on the inclined sidewalls, seeding dislocation bundles in the subsequently grown crystal. The high dislocation density slowed down the growth above the inclined sidewall, resulting in the uneven morphology. The fabricated devices showed over 30% enhancement in light output power as a result of improvements in both internal and extraction efficiencies.
Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical int... more Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials with high absorption coefficients are particularly promising for photodetection in energy-efficient optical links because of the potential to scale down the absorber size, and the resulting capacitance and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar junction phototransistor with a high current gain (53.6), bandwidth (7 GHz) and responsivity (9.5 A/W) using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The quantum efficiency-bandwidth product of 105 GHz is the highest for photodetectors on silicon. The bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice... more Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2-3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from ˜100 nm (1.5 min growth) to ˜9 μm length (3 h growth).
The direct growth of III-V nanostructures on silicon has shown great promise in the integration o... more The direct growth of III-V nanostructures on silicon has shown great promise in the integration of optoelectronics with silicon-based technologies. Our previous work showed that scaling up nanostructures to microsize while maintaining high quality heterogeneous integration opens a pathway toward a complete photonic integrated circuit and high-efficiency cost-effective solar cells. In this paper, we present a thorough material study of novel metastable InP micropillars monolithically grown on silicon, focusing on two enabling aspects of this technology-the stress relaxation mechanism at the heterogeneous interface and the microstructure surface quality. Aberration-corrected transmission electron microscopy studies show that InP grows directly on silicon without any amorphous layer in between. A set of periodic dislocations was found at the heterointerface, relaxing the 8% lattice mismatch between InP and Si. Single crystalline InP therefore can grow on top of the fully relaxed templa...
Cavity optomechanics explores the interaction between optical field and mechanical motion. So far... more Cavity optomechanics explores the interaction between optical field and mechanical motion. So far, this interaction has relied on the detuning between a passive optical resonator and an external pump laser. Here, we report a new scheme with mutual coupling between a mechanical oscillator supporting the mirror of a laser and the optical field generated by the laser itself. The optically active cavity greatly enhances the light-matter energy transfer. In this work, we use an electrically-pumped vertical-cavity surface-emitting laser (VCSEL) with an ultra-light-weight (130 pg) high-contrast-grating (HCG) mirror, whose reflectivity spectrum is designed to facilitate strong optomechanical coupling, to demonstrate optomechanically-induced regenerative oscillation of the laser optomechanical cavity. We observe >550 nm self-oscillation amplitude of the micromechanical oscillator, two to three orders of magnitude larger than typical, and correspondingly a 23 nm laser wavelength sweep. In addition to its immediate applications as a high-speed wavelength-swept source, this scheme also offers a new approach for integrated on-chip sensors.
Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy.
Using ta... more Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a novel regrown core−shell p-i-n junction to improve device performance by eliminating shunt current paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced broadband light absorption is also demonstrated over a wide spectral range of 400−800 nm.
ABSTRACT Defect reduction in epitaxial InP on nanopatterned exact Si (001) substrates was investi... more ABSTRACT Defect reduction in epitaxial InP on nanopatterned exact Si (001) substrates was investigated. Top-down lithography and dry etching were used to define 30 nm-wide SiO2 trench openings, with concaves recessed into the Si substrates. Uniformly distributed and position-controlled InP seed arrays were formed by selective area growth. Afterwards, the SiO2 mask was removed and InP overgrowth on the seed arrays proceeded. By localizing defects in the buried Si concaves and promoting defect interactions during the coalescence process, a significant reduction in the x-ray linewidth has been achieved for InP layers grown on the nanopatterned Si as compared to blanket epitaxy. Anisotropic defect distribution in the coalesced InP films was observed and its dependency on seed layer thickness was also studied.
ABSTRACT We report the growth and characterization of InAlGaAs/InAlAs multiquantum wells (MQWs) e... more ABSTRACT We report the growth and characterization of InAlGaAs/InAlAs multiquantum wells (MQWs) emitting at $sim 1310$ -nm grown on silicon by organometallic vapor phase epitaxy. Compared with the same structure grown on a reference planar InP substrate, photoluminescence of the MQWs on Si shows both comparable line widths and internal quantum efficiencies at room temperature. A specially engineered InP buffer with interlayers on a nanopatterned silicon substrate was used. Cross-sectional transmission electron microscopy reveals effective dislocation filtering by the three strained InGaAs interlayers. The high-quality quantum-well structure grown on the InP-on-Si template suggests great potential of integrating III–V photonic devices on the Si platform.
Alloy composition homogeneity plays an important role in the device performance of III-V heterost... more Alloy composition homogeneity plays an important role in the device performance of III-V heterostructures. In this work, we study the spatial composition uniformity of n-In0.12Ga0.88As/i-In0.2Ga0.8As/p-GaAs core-shell nanopillars monolithically grown on silicon. Cross sections extracted along the axial and radial directions are examined with transmission electron microscopy and energy-dispersive X-ray spectroscopy. Interestingly, indium-deficient segments with width ∼5 nm are observed to develop along the radial ⟨112̅0⟩ directions in the InGaAs layers. We attribute this spontaneous ordering to capillarity effect and difference in group-III adatom diffusion lengths. The slight fluctuation in indium content (∼4%), however, does not induce any noticeable misfit defects in the pure wurtzite-phased crystal. In contrast, the heterostructure exhibits excellent alloy composition uniformity along the axial [0001] direction. Furthermore, abrupt transitions of gallium and indium are seen at the heterointerfaces. These remarkable properties give rise to extraordinary optical performances. Lasing is achieved in the core-shell nanopillars upon optical pump despite the observed alloy composition fluctuation in the radial directions. The results here reveal the potential of the InGaAs-based core-shell heterostructures as efficient optoelectronic devices and high-speed heterojunction transistors directly integrated on silicon.
Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical
int... more Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials with high absorption coefficients are particularly promising for photodetection in energy-efficient optical links because of the potential to scale down the absorber size, and the resulting capacitance and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar junction phototransistor with a high current gain (53.6), bandwidth (7GHz) and responsivity (9.5A/W) using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The quantum efficiency-bandwidth product of 105GHz is the highest for photodetectors on silicon. The bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
ABSTRACT We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowire... more ABSTRACT We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowires as building blocks to produce antiphase-domain-free GaAs thin films on exact (001) silicon. High quality GaAs nanowires were grown on V-grooved Si (001) substrates using the selective aspect ratio trapping concept. The 4.1% lattice mismatch has been accommodated by the initial GaAs, a few nanometer-thick with high density stacking faults. The bulk of the GaAs wires exhibited smooth facets and a low defect density. An unusual defect trapping mechanism by a “tiara”-like structure formed by Si undercuts was discovered. As a result, we were able to grow large-area antiphase-domain-free GaAs thin films out of the nanowires without using SiO2 sidewalls for defect termination. Analysis from XRD ω-rocking curves yielded full-width-at-half-maximum values of 238 and 154 arc sec from 900 to 2000 nm GaAs thin films, respectively, indicating high crystalline quality. The growth scheme in this work offers a promising path towards integrated III-V electronic, photonic, or photovoltaic devices on large scale silicon platform.
The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etc... more The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etched stripe-patterned substrates were investigated. Footprint-like patterns, located directly above the inclined groove sidewalls, were found on the as-grown LED surface. Cross-sectional transmission electron microscopy (TEM) showed that ‘tumor’-like structures with poor crystal quality were initiated on the inclined sidewalls, seeding dislocation bundles in the subsequently grown crystal. The high dislocation density slowed down the growth above the inclined sidewall, resulting in the uneven morphology. The fabricated devices showed over 30% enhancement in light output power as a result of improvements in both internal and extraction efficiencies.
Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using ta... more Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a novel regrown core-shell p-i-n junction to improve device performance by eliminating shunt current paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced broadband light absorption is also demonstrated over a wide spectral range of 400-800 nm.
We use low-temperature microphotoluminescence and photoluminescence excitation spectroscopy to me... more We use low-temperature microphotoluminescence and photoluminescence excitation spectroscopy to measure the valence band parameters of single wurtzite InGaAs nanoneedles. The effective indium composition is measured by means of polarization-dependent Raman spectroscopy. We find that the heavy-hole and light-hole splitting is ∼95 meV at 10 K and the Stokes shift is in the range of 35-55 meV. These findings provide important insight in the band structure of wurtzite InGaAs that could be used for future bandgap engineering.
We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-base... more We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical wet-etching-patterned sapphire substrate (CWE-PSS) with V-Shaped pit features on the top surface. According to temperature-dependent photoluminescence (PL) measurement and the measured external quantum efficiency, the structure can simultaneously enhance both internal quantum efficiency and light extraction efficiency. Comparing to devices grown on planar sapphire substrate, the threading dislocation defects of LED grown on CWE-PSS are reduced from 1.28 10 9 cm 2 to 3.62 10 8 cm 2 , leading to a 12.5% enhancement in internal quantum efficiency. In terms of the theoretical computing of radiation patterns, the V-Shaped pits roughening surface can be thought of as a strong diffuser with paraboloidal autocorrelation function, increasing the escape probability of trapped photons and achieving a 20% enhancement in light extraction efficiency. Moreover, according to the measurement of optical diffraction power, CWE-PSS demonstrated superior guided light extraction efficiency than that of planar sapphire substrate, thus an extra 7.8% enhancement in light extraction efficiency was obtained. Therefore, comparing to the conventional LED, an overall 45% enhancement in integrated output power was achieved.
The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etc... more The material and electrical properties of GaN-based light-emitting diodes (LEDs) grown on wet-etched stripe-patterned substrates were investigated. Footprint-like patterns, located directly above the inclined groove sidewalls, were found on the as-grown LED surface. Cross-sectional transmission electron microscopy (TEM) showed that ÔtumorÕ-like structures with poor crystal quality were initiated on the inclined sidewalls, seeding dislocation bundles in the subsequently grown crystal. The high dislocation density slowed down the growth above the inclined sidewall, resulting in the uneven morphology. The fabricated devices showed over 30% enhancement in light output power as a result of improvements in both internal and extraction efficiencies.
Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical int... more Highly sensitive and fast photodetectors can enable low power, high bandwidth on-chip optical interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials with high absorption coefficients are particularly promising for photodetection in energy-efficient optical links because of the potential to scale down the absorber size, and the resulting capacitance and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar junction phototransistor with a high current gain (53.6), bandwidth (7 GHz) and responsivity (9.5 A/W) using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The quantum efficiency-bandwidth product of 105 GHz is the highest for photodetectors on silicon. The bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice... more Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2-3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from ˜100 nm (1.5 min growth) to ˜9 μm length (3 h growth).
The direct growth of III-V nanostructures on silicon has shown great promise in the integration o... more The direct growth of III-V nanostructures on silicon has shown great promise in the integration of optoelectronics with silicon-based technologies. Our previous work showed that scaling up nanostructures to microsize while maintaining high quality heterogeneous integration opens a pathway toward a complete photonic integrated circuit and high-efficiency cost-effective solar cells. In this paper, we present a thorough material study of novel metastable InP micropillars monolithically grown on silicon, focusing on two enabling aspects of this technology-the stress relaxation mechanism at the heterogeneous interface and the microstructure surface quality. Aberration-corrected transmission electron microscopy studies show that InP grows directly on silicon without any amorphous layer in between. A set of periodic dislocations was found at the heterointerface, relaxing the 8% lattice mismatch between InP and Si. Single crystalline InP therefore can grow on top of the fully relaxed templa...
Cavity optomechanics explores the interaction between optical field and mechanical motion. So far... more Cavity optomechanics explores the interaction between optical field and mechanical motion. So far, this interaction has relied on the detuning between a passive optical resonator and an external pump laser. Here, we report a new scheme with mutual coupling between a mechanical oscillator supporting the mirror of a laser and the optical field generated by the laser itself. The optically active cavity greatly enhances the light-matter energy transfer. In this work, we use an electrically-pumped vertical-cavity surface-emitting laser (VCSEL) with an ultra-light-weight (130 pg) high-contrast-grating (HCG) mirror, whose reflectivity spectrum is designed to facilitate strong optomechanical coupling, to demonstrate optomechanically-induced regenerative oscillation of the laser optomechanical cavity. We observe >550 nm self-oscillation amplitude of the micromechanical oscillator, two to three orders of magnitude larger than typical, and correspondingly a 23 nm laser wavelength sweep. In addition to its immediate applications as a high-speed wavelength-swept source, this scheme also offers a new approach for integrated on-chip sensors.
Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy.
Using ta... more Low cost, high efficiency photovoltaic can help accelerate the adoption of solar energy. Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a novel regrown core−shell p-i-n junction to improve device performance by eliminating shunt current paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced broadband light absorption is also demonstrated over a wide spectral range of 400−800 nm.
ABSTRACT Defect reduction in epitaxial InP on nanopatterned exact Si (001) substrates was investi... more ABSTRACT Defect reduction in epitaxial InP on nanopatterned exact Si (001) substrates was investigated. Top-down lithography and dry etching were used to define 30 nm-wide SiO2 trench openings, with concaves recessed into the Si substrates. Uniformly distributed and position-controlled InP seed arrays were formed by selective area growth. Afterwards, the SiO2 mask was removed and InP overgrowth on the seed arrays proceeded. By localizing defects in the buried Si concaves and promoting defect interactions during the coalescence process, a significant reduction in the x-ray linewidth has been achieved for InP layers grown on the nanopatterned Si as compared to blanket epitaxy. Anisotropic defect distribution in the coalesced InP films was observed and its dependency on seed layer thickness was also studied.
ABSTRACT We report the growth and characterization of InAlGaAs/InAlAs multiquantum wells (MQWs) e... more ABSTRACT We report the growth and characterization of InAlGaAs/InAlAs multiquantum wells (MQWs) emitting at $sim 1310$ -nm grown on silicon by organometallic vapor phase epitaxy. Compared with the same structure grown on a reference planar InP substrate, photoluminescence of the MQWs on Si shows both comparable line widths and internal quantum efficiencies at room temperature. A specially engineered InP buffer with interlayers on a nanopatterned silicon substrate was used. Cross-sectional transmission electron microscopy reveals effective dislocation filtering by the three strained InGaAs interlayers. The high-quality quantum-well structure grown on the InP-on-Si template suggests great potential of integrating III–V photonic devices on the Si platform.
Alloy composition homogeneity plays an important role in the device performance of III-V heterost... more Alloy composition homogeneity plays an important role in the device performance of III-V heterostructures. In this work, we study the spatial composition uniformity of n-In0.12Ga0.88As/i-In0.2Ga0.8As/p-GaAs core-shell nanopillars monolithically grown on silicon. Cross sections extracted along the axial and radial directions are examined with transmission electron microscopy and energy-dispersive X-ray spectroscopy. Interestingly, indium-deficient segments with width ∼5 nm are observed to develop along the radial ⟨112̅0⟩ directions in the InGaAs layers. We attribute this spontaneous ordering to capillarity effect and difference in group-III adatom diffusion lengths. The slight fluctuation in indium content (∼4%), however, does not induce any noticeable misfit defects in the pure wurtzite-phased crystal. In contrast, the heterostructure exhibits excellent alloy composition uniformity along the axial [0001] direction. Furthermore, abrupt transitions of gallium and indium are seen at the heterointerfaces. These remarkable properties give rise to extraordinary optical performances. Lasing is achieved in the core-shell nanopillars upon optical pump despite the observed alloy composition fluctuation in the radial directions. The results here reveal the potential of the InGaAs-based core-shell heterostructures as efficient optoelectronic devices and high-speed heterojunction transistors directly integrated on silicon.
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Papers by Kar Wei Ng
interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials
with high absorption coefficients are particularly promising for photodetection in energy-efficient
optical links because of the potential to scale down the absorber size, and the resulting capacitance
and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar
junction phototransistor with a high current gain (53.6), bandwidth (7GHz) and responsivity (9.5A/W)
using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor
gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The
quantum efficiency-bandwidth product of 105GHz is the highest for photodetectors on silicon. The
bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic
integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single
nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a
novel regrown core−shell p-i-n junction to improve device performance by eliminating shunt current
paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced
broadband light absorption is also demonstrated over a wide spectral range of 400−800 nm.
interconnects for silicon integrated electronics. III-V compound semiconductor direct-bandgap materials
with high absorption coefficients are particularly promising for photodetection in energy-efficient
optical links because of the potential to scale down the absorber size, and the resulting capacitance
and dark current, while maintaining high quantum efficiency. We demonstrate a compact bipolar
junction phototransistor with a high current gain (53.6), bandwidth (7GHz) and responsivity (9.5A/W)
using a single crystalline indium phosphide nanopillar directly grown on a silicon substrate. Transistor
gain is obtained at sub-picowatt optical power and collector bias close to the CMOS line voltage. The
quantum efficiency-bandwidth product of 105GHz is the highest for photodetectors on silicon. The
bipolar junction phototransistor combines the receiver front end circuit and absorber into a monolithic
integrated device, eliminating the wire capacitance between the detector and first amplifier stage.
Using tapered indium phosphide nanopillars grown on a silicon substrate, we demonstrate a single
nanopillar photovoltaic exhibiting illumination angle insensitive response. The photovoltaic employs a
novel regrown core−shell p-i-n junction to improve device performance by eliminating shunt current
paths, resulting in a high VOC of 0.534 V and a power conversion efficiency of 19.6%. Enhanced
broadband light absorption is also demonstrated over a wide spectral range of 400−800 nm.