Xiu Ying Gong

Improved purity of long-wavelength InAsSb epilayers grown by melt epitaxy in fused silica boats

In this study, we first present the process of the melt epitaxial (ME) growth method, and the improvement of low-temperature electron mobility of the long-wavelength InAsSb epilayers grown by ME in a fused silica boat. The electrical properties were investigated by van der Pauw measurement at 300 and 77 K. It is seen that the electron mobility of the InAsSb samples grown by graphite boat decreased from 55,700 to 26,600 cm(2)/V s when the temperature was reduced from 300 to 77 K, while for the samples grown by fused silica boat, the electron mobility increased from 52,600 at 300 K to 54,400 cm(2)/V s at 77 K. The electron mobility of 54,400cm(2)/Vs is the best result, so far, for the InAsSb materials with cutoff wavelength of 8-12 mum at 77 K. This may be attributed to the reduction of the carbon contamination by using a fused silica boat instead of a graphite boat

Room Temperature InAsxP1-x-ySby/InAs Photodetectors with High Quantum Efficiency

Room temperature surface-illuminated InAsxP1-x-ySby/InAs photodiodes with an external quantum efficiency as high as 50–86% in a 1.83–3.53 µm wavelength range have been fabricated for the first time. Lattice matched heterostructures with a wide energy gap InAsPSb cap layer were grown on the InAs substrate using the liquid phase epitaxy technique. According to temperature dependence measurements for a 1 mm diameter photodiode, peak responsivities of 1.83–2.5 A/W have been realized in a temperature range of 296 to 200 K. The Johnson noise limited room temperature detectivities D* are deduced to be 1\endash6 ×109 cm·Hz1/2/W at zero bias. It is demonstrated that the only loss of external quantum efficiency is from the reflection of the entrance face.

Sulphur passivation of InAs(Sb)

Abstract The sulphur passivation for the InAs surface was studied by photoluminescence (PL) and spectroscopic ellipsometry (SE). Effects of the treatment are compared with I - V characteristics and photoresponse (PR) of MESA structure devices fabricated with LPE multilayer of InAs 1− y (Sb y ). It is expected that the dangling bonds at the surface are terminated in the forms of SIn, SSb bonds by the passivation, which results in a remarkable decrease of surface recombination center density. This phenomenon was confirmed by observing increases of PL intensity and of the PR of photodiodes. Four order reductions of dark current and remarkable increase of PR have been observed on sulphur passivated photodetectors. Stability of the effect of the sulphur passivation was also examined by SE as well as PR measurements. SE measurements showed that dielectric function of the surface layer for the InAs wafer has no absorption in the measured spectral range between 1.5 and 5.5 eV. After sulphur passivation, optical absorption appeared due to submonolayer sulphur atoms in good agreement with the results obtained from the InAs(Sb) photodetectors.

Electrical Properties of Melt-Epitaxy-Grown InAs0.04Sb0.96 Layers with Cutoff Wavelength of 12 μm

A study of the electrical properties of melt-epitaxy(ME)-grown InAs_(0.04)Sb_(0.96) epilayers with a cutoff wavelength of 12 μm was performed using Van der Pauw measurements.The temperature dependence of the electrical properties was measured.An electron mobility of 6×10~4 cm~2/Vs with a carrier density of 2.3×10~(16) cm~(-3) at 300 K,and an electron mobility of 1×10~5 cm~2/Vs with a carrier density of 1×10~(15) cm~(-3) at 200 K have been obtained in the experiments.Different behaviors of the electrical properties of samples grown using graphite and fused-silicon boats,were observed and were analyzed in terms of their scattering mechanism.The results showed that ionized impurity scattering is the dominant process at low temperatures for all the samples.Polar optical phonon scattering governs electron mobility at high temperature.C contamination has significant influence on the electron mobility below 200 K of the sample grown using a graphite boat.

Influence of Sulphidation Treatment on the Performance of Mid-Infrared InAsPSb/InAs Detectors

The influence of sulphidation treatment on the performance of room temperature InAsPSb/InAs photodetectors was investigated. Measurements of photoresponsivity, external quantum efficiency and detectivity of the detectors with and without the sulphidation treatment showed that after the sulphidation treatment the sensitivity of the detectors improved 1.5 times. A study of the chemical state of sulphur on an (NH4)2Sx-treated InAs(001) surface was performed by high-resolution X-ray photoelectron spectroscopy (XPS). The chemical state of sulphur bonded to indium (In) and arsenic (As) atoms for the as-treated surface was observed showing the termination of the dangling bonds at the surface by the sulphidation treatment. This gives rise to a remarkable decrease of surface recombination center density and results in the increase of photodetector sensitivity.

Optical Properties of InAsSb Single Crystals with Cutoff Wavelengths of 8–12 µm Grown by Melt-Epitaxy

The transmittance spectra of melt epitaxiy (ME)-grown InAsSb single crystals with cutoff wavelengths of 8–12 µm were measured and calculated under the assumption of a microscopic composition distribution function. A good agreement between the experimental and theoretical transmittance spectra was obtained. The results indicate that a microscopic composition distribution inhomogeneity exists in long-wavelength InAsSb epilayers with different compositions, which may be related to the energy band gap narrowing of this InAsSb.

Room-Temperature Mid-Infrared Light-Emitting Diodes from Liquid-Phase Epitaxial InAs/InAs0.89Sb0.11/InAs0.80P0.12Sb0.08 Heterostructures

Light-emitting diodes (LEDs) in the 3 to 5 µm wavelength range have been fabricated from InAs/InAsSb/InAsPSb heterostructures grown by liquid-phase epitaxy (LPE) between 520 and 500°C. Temperature dependence of the performance for the LEDs was studied using a Fourier transform infrared (FTIR) measurement system with double modulation. Room-temperature operation of LEDs was realized. Under a peak current of 5 A (2% duty cycle), the output powers of the diodes were between 150 and 500 µW indicating their potential applications for CO2 and CO gas sensors.

Mid-infrared photoluminescence from liquid phase epitaxial InAs1-ySby/InAs multilayers

Photoluminescence for InAs1-ySby multilayers grown on InAs substrates by liquid phase epitaxy has been investigated. A 5 K luminescence peak wavelength longer than 5 µm with a full-width at halfmaximum of 10 meV has been obtained. The compositional and temperature dependence of the PL spectra were studied. A band gap energy shift of 50 meV between 5 and 300 K was observed. The results indicate the high quality of the materials. Light emitting diodes with wavelength of 4.2 µm at 77 K have been obtained. The potential applications for a light source operating in 3–5 µm were demonstrated.

Uncooled InAsSb Photoconductors with Long Wavelength

High-sensitivity uncooled InAsSb photoconductors with long wavelength were successfully fabricated. The detectors are based on InAsSb epilayers with the thickness of 100 µm grown on InAs substrates by melt epitaxy (ME). Si optical lenses were set on the photoconductors without any antireflective coatings. At room temperature, the peak detectivity Dλp* (6.5 µm, 1200) reaches 5.3 ×109 cm Hz1/2 W-1 for InAsSb immersion photoconductors. The detectivity D* at the wavelength of 8 µm is 1.5 ×108 cm Hz1/2 W-1, and that at 9 µm is 1.0 ×107 cm Hz1/2 W-1. The excellent performance of the detectors indicates the potential applications for infrared (IR) detection and imaging at room temperature.

InNAsSb Single Crystals with Cutoff Wavelength of 11–13.5 µm Grown by Melt Epitaxy

We grew, for the first time, InNAsSb single crystals with a room temperature cutoff wavelength of 11–13.5 µm on (100) InAs substrates by melt epitaxy (ME). The crystals were characterized using X-ray diffraction, electron-probe microanalysis (EPMA), temperature-dependent transmittance and Van der Pauw measurements. An obvious redshift of cutoff wavelength was observed with increasing N concentration from 13 to 19% in the epilayers. The cutoff wavelength varies from 12.5 to 8.9 µm in the temperature range from 300 to 77 K. The thick epilayers show a good macroscopic homogeneity of the composition. An electron mobility of 55,800 cm2/Vs with a carrier density of 1.08×1016 cm-3 was obtained at 77 K, indicating possible applications for infrared photodevices.