Zhengwei Ren

Growth of GaSb layers on GaAs (0 0 1) substrate by molecular beam epitaxy

GaSb 1 mu m-thick layers were grown by molecular beam epitaxy on GaAs (001). The effects of the growth conditions on the crystalline quality, surface morphology, electrical properties and optical properties were studied by double crystalline x-ray diffraction, atomic force microscopy, Hall measurement and photoluminescence spectroscopy, respectively. It was found that the surface roughness and hole mobility are highly dependent on the antimony-to-gallium flux ratios and growth temperatures. The crystalline quality, electrical properties and optical properties of GaSb layers were also studied as functions of growth rate, and it was found that a suitably low growth rate is beneficial for the crystalline quality and electrical and optical properties. Better crystal quality GaSb layers with a minimum root mean square surface roughness of 0.1 nm and good optical properties were obtained at a growth rate of 0.25 mu m h(-1).

MBE growth of very short period InAs/GaSb type-II superlattices on (0 0 1)GaAs substrates

First, GaSb epilayers were grown on (0 0 1)GaAs substrates by molecular beam epitaxy. We determined that the GaSb layers had very smooth surfaces using atomic force microscopy. Then, very short period InAs/GaSb superlattices (SLs) were grown on the GaSb buffer layer. The optical and crystalline properties of the superlattices were studied by low-temperature photoluminescence spectra and high resolution transition electron microscopy. In order to determine the interface of SLs, the samples were tested by Raman-scattering spectra at room temperature. Results indicated that the peak wavelength of SLs with clear interfaces and integrated periods is between 2.0 and 2.6 µm. The SL interface between InAs and GaSb is InSb-like.

Molecular beam epitaxy growth of high electron mobility InAs/AlSb deep quantum well structure

InAs/AlSb deep quantum well (QW) structures with high electron mobility were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. AlSb and Al0.75Ga0.25Sb buffer layers were grown to accommodate the lattice mismatch (7%) between the InAs/AlSb QW active region and GaAs substrate. Transmission electron microscopy shows abrupt interface and atomic force microscopy measurements display smooth surface morphology. Growth conditions of AlSb and Al0.75Ga0.25Sb buffer were optimized. Al0.75Ga0.25Sb is better than AlSb as a buffer layer as indicated. The sample with optimal Al0.75Ga0.25Sb buffer layer shows a smooth surface morphology with root-mean-square roughness of 6.67 A. The electron mobility has reached as high as 27 000 cm2/Vs with a sheet density of 4.54 × 1011/cm2 at room temperature.

Room-Temperature Operation of 2.4 μm InGaAsSb/AlGaAsSb Quantum-Well Laser Diodes with Low-Threshold Current Density

GaSb-based 2.4 μm InGaAsSb/AlGaAsSb type-I quantum-well laser diode is fabricated. The laser is designed consisting of three In0.35Ga0.65As0.1Sb0.9/Al0.35Ga0.65As0.02Sb0.98 quantum wells with 1% compressive strain located in the central part of an undoped Al0.35Ga0.65As0.02Sb0.98 waveguide layer. The output power of the laser with a 50-μm-wide 1-mm-long cavity is 28mW, and the threshold current density is 400 A/cm2 under continuous wave operation mode at room temperature.

Sulfurizing Method for Passivation Used in InAs/GaSb Type-II Superlattice Photodetectors

Since InAs/GaSb type-II superlattices (T2SL) were first proposed as infrared (IR) sensing materials, T2SL mid-wave IR (MWIR) and long-wave IR (LWIR) are of great importance for a variety of civil and military applications. A very important parameter of IR photodetectors is dark current, which affects the detectivity directly. Chemical and physical passivation has revealed to be an efficient technique to reduce surface component of dark current, which will become a dominant current in focal plane arrays (FPA). In this paper we talk about the electrochemistry and dielectric method for passivation. We choose anodic sulfide and SiO2 passivation. The leakage current as a function of bias voltage (I–V) results show dark current of anodic sulfide device was two orders of magnitude lower than unpassivation one, but reactive magnetron sputtering SiO2 didn’t perform well. The highest R0A we get from the sulfurizing experiment is 657Ω·cm2 in 77K. After fabrication the measured cutoff wavelength is 5.0μm. Finally blackbody test result shows that the peak quantum efficiency (QE) at 3.33μm is 68% and the peak detectivity is 7.16x1011cm·Hz1/2/W.

Long-wavelength light emission from self-assembled heterojunction quantum dots

The authors report the optical characteristics of GaSb/InAs/GaAs self-assembled heterojunction quantum dots (QDs). With increasing GaSb deposition, the room temperature emission wavelength can be extended to 1.56 mu m. The photoluminescence mechanism is considered to be a type-II transition with electrons confined in InAs and holes in GaSb.(C) 2008 American Institute of Physics.

Structural study of undoped and doped Bi2Sr2CuO6 phases by transmission electron microscopy

Bi‐based superconducting phases have been studied by transmission electron microscopy. The strong one‐dimensional modulations in undoped and Ce‐doped monoclinic Bi2 Sr2 CuO6 (2201) samples are different from one another. We have found a new 2201 phase containing Pb and Ca with orthorhombic symmetry in nominal (Bi0.90 Pb0.10 )2 Sr2 CaCu2 O8 crystals. Its structure with space group Bbmb and two‐dimensional modulation are analogous to those of the Pb‐doped higher members of the structural series Bi2 Sr2 Can−1 Cun O2n+4 . Hence, this new orthorhombic rather than the monoclinic 2201 phase should be the first member of the structural series.

Investigation of high hole mobility In0.41Ga0.59Sb/Al0.91Ga0.09Sb quantum well structures grown by molecular beam epitaxy

Modulation-doped In0.41Ga0.59Sb/Al0.91Ga0.09Sb quantum-well (QW) structures were grown by molecular beam epitaxy. Cross-sectional transmission electron microscopy and atomic force microscopy studies show high crystalline quality and smooth surface morphology. X-ray diffraction investigations confirm 1.94% compressive strain within In0.41Ga0.59Sb channel. High room temperature hole mobility with high sheet density of 1000 cm2/Vs, 0.877 × 1012/cm2, and 965 cm2/Vs, 1.112 × 1012/cm2 were obtained with different doping concentrations. Temperature dependent Hall measurements show different scattering mechanisms on hole mobility at different temperature range. The sheet hole density keeps almost constantly from 300 K to 77 K. This study shows great potential of In0.41Ga0.59Sb/Al0.91Ga0.09Sb QW for high-hole-mobility device applications.

Growth and Fabrication of MWIR Dual-color Focal Plane Array Based on Type-II InAs/GaSb Superlattice

We presented a fabrication of MWIR dual-color FPA based on type-II InAs/GaSb strain layer superlattice (SLs). The red and blue channel FPA devices with 128×128 pixels showed a 50% cutoff wavelength of 3.1μm and 4.73μm, the average blackbody detectivity of the detectors are 2.8 × 1010cmHz1/2/W and 1.3× 1010 cmHz1/2/W at 77K separately.

Evolution of surface morphology and photoluminescence characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

Evolution of surface morphology and optical characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are investigated by atomic force microscopy (AFM) and photoluminescence (PL). After deposition of 16 monolayers (ML) of In0.5Ga0.5As, QDs are formed and elongated along the [110] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.