X.Y. Chen

Dark current characteristics of GaAs-based 2.6 µm InGaAs photodetectors on different types of InAlAs buffer layers

GaAs-based In0.83Ga0.17As photodetectors (PDs) with cut-off wavelengths up to 2.6 µm are demonstrated. The effects of continuously-graded or fixed-composition InAlAs buffers on the device performances are investigated. The dark current characteristics of the PDs at various temperatures are analysed in detail. The photocurrents are also measured at 300 K; the detectivity of the PDs is extracted. The two GaAs-based PDs with different buffer schemes show different temperature-dependent dark current behaviours. The around room temperature performances of the GaAs-based device on the fixed-composition buffer are not as good, but comparable to those of InP-based devices, revealing a promising candidate for the GaAs-based PDs and focal plane arrays for many low-end applications.

2.7 μm InAs quantum well lasers on InP-based InAlAs metamorphic buffer layers

This work reports 2.7 μm InAs/In0.6Ga0.4As quantum well lasers on InP-based metamorphic InxAl1−xAs graded buffers. X-ray diffraction measurement shows favorable strain compensation effect in the quantum wells. Type-I photoluminescence emission is observed around 2.7 μm at 77 K and red-shifts to 3 μm at 300 K. The continuous-wave lasing wavelength of the laser reaches 2.7 μm at 77 K, which is the longest wavelength from the interband lasing of InP-based antimony-free structures. The threshold current density is as low as 145 A/cm2 and the continuous-wave output power at injection current of 400 mA is over 5 mW.

Nearly lattice-matched short-wave infrared InGaAsBi detectors on InP

This work reports on the demonstration of a short-wave infrared detector nearly lattice matched to InP substrate using quaternary InGaAsBi as the absorption layer. The bismuth content of about 3.2% has red-shifted the 50% cut-off wavelength from about 1.6 μm to 2.1 μm at room temperature, indicating a bandgap reduction of about 180 meV due to bismuth incorporation. The detector shows an encouraging dark current density of 2.4 × 10−4 A/cm2 at bias voltage of −10 mV at 300 K. This work shows the promising potential of InP-based lattice-matched InGaAsBi detectors for short-wave infrared detection.

InP-based type-I quantum well lasers up to 2.9 μm at 230 K in pulsed mode on a metamorphic buffer

This work reports on up to 2.9 μm lasing at 230 K of InP-based type-I quantum well lasers. This record long wavelength lasing is achieved by applying InP-based Sb-free structures with eight periods of strain-compensated InAs quantum wells grown on metamorphic In0.8Al0.2As template layers. The continuous-wave threshold current density is 797 A/cm2 and the idealized extrapolated threshold current density for infinite cavity length is as low as 58 A/cm2 per quantum well at 120 K. This scheme is a promising pathway for extending the wavelength range of type-I quantum well lasers on InP substrates.

InAs/In0.83Al0.17As quantum wells on GaAs substrate with type-I emission at 2.9 μm

This work reports on InAs quantum wells (QWs) grown on GaAs-based metamorphic In0.83Al0.17As buffers for type-I mid-infrared (MIR) emission. X-ray diffraction and Raman measurements show that the GaAs-based quantum wells have similar lattice and strain conditions with the InP-based structure. Atomic force microscope shows the smoother surface of the structure on GaAs substrate. For the GaAs-based quantum wells, favorable photoluminescence emission at 2.9 μm at 300 K has been achieved, and the optical quality is comparable to the structure on InP substrate. It is promising to employ this metamorphic quantum well structure for the demonstration of GaAs-based antimony-free mid-infrared lasers.

Type-I mid-infrared InAs/InGaAs quantum well lasers on InP-based metamorphic InAlAs buffers

InAs/InGaAs quantum well laser structures have been grown on InP-based metamorphic In0.8Al0.2As buffers by gas source molecular beam epitaxy. The effects of barrier and waveguide layers on the material qualities and device performances were characterized. X-ray diffraction and photoluminescence measurements prove the benefits of the strain compensation in the active quantum well region on the material quality. The device characteristics of the lasers with different waveguide layers reveal that the separate confinement heterostructure plays a crucial role on the device performances of these metamorphic lasers. Type-I emissions in the 2–3 µm range have been achieved in these InP-based metamorphic antimony-free structures. By combining the strain-compensated quantum wells and separate confinement heterostructures, the laser performances have been improved and laser emission up to 2.7 µm has been achieved.

Metamorphic InAs1-xBix/In0.83Al0.17As quantum well structures on InP for mid-infrared emission

This work reports on InP-based metamorphic quantum well structures with bismuth incorporation for mid-infrared applications. InAs1-xBix quantum well structures have been grown on InP-based metamorphic In0.83Al0.17As buffers and photoluminescence beyond 3.1 μm has been achieved at 300 K, which is longer than the referenced InAs quantum well. X-ray diffraction, cross-sectional transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements reveal clear interfaces of InAsBi quantum well with low bismuth, while more defects and bismuth inhomogeneity were observed as more bismuth was incorporated.

Synthesis of nitrogen-doped graphene via pentachloropyridine as the sole solid source

The substitution of nitrogen atoms in the lattice plane of the graphene can adjust the electronic properties of the graphene to translate it from the half-metal to the n-type semiconductor. Here, we report a practicable growth of nitrogen-doped graphene films with the nitrogen atoms doped content of 4.4–7.5% by the sole solid precursor based chemical vapor deposition method. After the post-annealing process at high temperature, the morphology and crystallization quality of the nitrogen-doped graphene film were considerably improved. The as-synthesized nitrogen-doped graphene films exhibit typical n-type behavior with the electron carrier density of approximately 6.55 × 1012 cm−2 and the Hall mobility of around 522 cm2V−1 s−1.The substitution of nitrogen atoms in the lattice plane of the graphene can adjust the electronic properties of the graphene to translate it from the half-metal to the n-type semiconductor. Here, we report a practicable growth of nitrogen-doped graphene films with the nitrogen atoms doped content of 4.4–7.5% by the sole solid precursor based chemical vapor deposition method. After the post-annealing process at high temperature, the morphology and crystallization quality of the nitrogen-doped graphene film were considerably improved. The as-synthesized nitrogen-doped graphene films exhibit typical n-type behavior with the electron carrier density of approximately 6.55 × 1012 cm−2 and the Hall mobility of around 522 cm2V−1 s−1.

Bismuth for tailoring and modification of InP-based detector and laser structures in 2–3 µm band

The effects of bismuth on the performances of InP-based detectors and multiple triangular quantum wells in 2-3 μm band have been investigated. The cut-off wavelength of the InGaAsBi detector is tailored to 2.1 μm by the bismuth incorporation in the absorption layer, but the detector still shows an encouraging dark current due to decreased lattice mismatch to InP substrate. The material quality of the InAs/InGaAs triangular quantum wells has been significantly improved by introducing bismuth as a surfactant during growth. The moderate bismuth reduces the surface roughness, improves the heterostructure interfaces and enhances the photoluminescence intensity obviously, whereas deterioration occurs in the case of excessive bismuth flux. Bismuth shows a promising potential to improve InP-based detector and laser structures both by incorporating into the alloys and acting as a surfactant.

High-performance InP-based InAs triangular quantum well lasers operating beyond 2 μm

InP-based antimony-free In0.53Ga0.47As/InAs/In0.53Ga0.47As strained triangular quantum well lasers have been demonstrated for the light sources with wavelength beyond 2 μm. Theoretical estimation shows that the triangular quantum well owns the longer emission wavelength than the rectangular quantum well with the same strain extent. The triangular quantum well was formed experimentally by using gas source molecular beam epitaxy grown digital alloy, and the growth temperature of the triangular quantum wells was optimized. The triangular quantum well lasers with emission beyond 2.2 μm under continuous-wave operation at temperatures higher than 330 K have been demonstrated. The performances of the triangular quantum well lasers are improved comparing to those of InAs rectangular quantum lasers with the nearly same lasing wavelength.