Xingui Zhang

Characteristics of InGaAs quantum dot infrared photodetectors

A quantum dot infrared photodetector (QDIP) consisting of self-assembled InGaAs quantum dots has been demonstrated. Responsivity of 3.25 mA/W at 9.2 μm was obtained for nonpolarized incident light on the detector with a 45° angle facet at 60 K. The QDIPs exhibit some unique electro-optic characteristics such as a strong negative differential photoconductance effect and blueshift of the response peak wavelength.

Polarization dependence of intraband absorption in self-organized quantum dots

Photoluminescence and intraband absorption were investigated in n-doped self-organized InAs and In0.35Ga0.65As quantum dots grown on a GaAs substrate. Intraband absorption of the dots is strongly polarized along the growth axis in the mid infrared spectral range. The absorption is maximum at around 120 meV for InAs dots and at 130 meV for In0.35Ga0.65As dots. The experimental results on InAs dots are in agreement with published theoretical calculations.

Crystal structure and epitaxial relationship of Ni4InGaAs2 films formed on InGaAs by annealing

The structural, compositional, and electrical properties of epitaxial Ni4InGaAs2 (denoted as Ni-InGaAs) film formed by annealing sputtered Ni film on InGaAs were investigated. It was found that Ni-InGaAs adopts a NiAs (B8) structure with lattice parameters of a = 0.396 ± 0.002 nm and c = 0.516 ± 0.002 nm, and exhibits an epitaxial relationship with InGaAs, with orientations given by Ni-InGaAs[1¯10]//InGaAs[001] and Ni-InGaAs[110]//InGaAs[110]. The epitaxial Ni4InGaAs2 film has bulk electrical resistivity of ∼102 μΩ·cm, which increases as the film thickness scales below 10 nm. The results of this work would be useful for the development of contact metallization for high mobility InGaAs metal-oxide-semiconductor field-effect transistors.

The structure and energies of peroxy bipolarons in

We present calculations of the binding energies of peroxy bipolarons in . Our results strongly suggest that these species are weakly bound with respect to isolated hole species. Estimates of the effective mass of the bipolaronic species based on our calculated relaxed geometries are consistent with experimental observation for the superconducting state of the material.

STRONG INFLUENCE OF SIO2 THIN FILM ON PROPERTIES OF GAN EPILAYERS

In this letter, we report strong degradation of photoluminescence (PL) performance of GaN epilayers due to SiO2 layers that were deposited on GaN surfaces by electron-beam evaporation. Secondary ion mass spectrometry measurements show that the oxygen concentration of GaN with SiO2 layers is one order of magnitude more than that of as-grown GaN. This fact indicates that oxygen can very easily replace nitrogen in GaN. It was also found that rapid thermal processing can recover and improve the optical quality of GaN with SiO2 layer. As a reference, SixNy was found to have little effect on PL performance of GaN.

Stability of a self-trapping hole in alpha -quartz

Previous calculations of self-trapping in quartz adopt quantum chemical methods. However, for certain purposes, for example, when more than a few atoms are involved in a defect process, it would be helpful to use instead the shell model methods which work well for halides. We present the first calculation of the self-trapped hole (STH) in alpha -quartz and other forms of silicon dioxide using the classic defect simulation technique. The calculation suggests that the hole can be self-trapped on oxygen atom with a binding energy of 0.41 eV. The self-trapping is accompanied by a large network distortion, in which the O- ion on which the hole is self-trapped shifts 0.14 AA and the nearest-neighbour silicon atoms move 0.4-0.6 AA away from the O- ion. These results are similar to those obtained from the ab initio HF calculation of STH in amorphous SiO2. We have also estimated the effective activation energy of a STH to be 0.12 eV at 180 K though there will also be a significant component of conduction from excitation of the small polaron to the delocalized large-polaron state.

Photoelectron spectroscopy study of band alignment at interface between Ni-InGaAs and In0.53Ga0.47As

The work function of Ni-InGaAs and the band alignment between Ni-InGaAs and In0.53Ga0.47As were investigated using photoelectron spectroscopy. The vacuum work function of Ni-InGaAs is obtained to be ∼5.1 eV using ultraviolet photoelectron spectroscopy (UPS). In addition, it was observed that the Fermi level of Ni-InGaAs is aligned to near conduction band of In0.53Ga0.47As at interface. For Ni-InGaAs formed on p-type In0.53Ga0.47As, this gives a Schottky contact with a hole barrier height of 0.8 ± 0.1 eV. Ni-InGaAs would form an ohmic contact on n-type In0.53Ga0.47As.

Two-dimensional AlGaInP∕GaInP photonic crystal membrane lasers operating in the visible regime at room temperature

The authors report on the fabrication and characterization of visible two-dimensional photonic crystal (PhC) band-edge lasers with AlGaInP∕GaInP multiple-quantum-well active layers. High-quality PhC air-bridge membranes are produced by optimizing the inductively coupled plasma etching process for AlGaInP materials. Room-temperature lasing operation at the wavelengths ranging from 630to690nm is obtained by tuning the PhC lattice parameters. The lasing action originates from high-symmetry band-edge modes, which is verified by three-dimensional finite difference time domain computation.

Band offsets at GaInP/AlGaInP(001) heterostructures lattice matched to GaAs

In this work, the band offsets at the Ga0.5In0.5P/AlxGa0.5−xIn0.5P heterojunction lattice matched to (001) GaAs was calculated over the whole range of aluminum composition from x=0.0 to 0.5 using the first-principles pseudopotential method with virtual crystal approximation. The valence band offset, VBO, varies with x as VBO=0.433x eV, while the inferred conduction band offset CBO at Γ minimum (band-gap difference minus the valence band offset) varies in x as CBOΓ=0.787x eV. Our results are in good agreement with the experimental data.

Self-aligned contact metallization technology for III-V metal-oxide-semiconductor field effect transistors

The demonstration of a salicidelike self-aligned contact technology for III-V metal-oxide-semiconductor field-effect transistors (MOSFETs) is reported. A thin and continuous crystalline germanium-silicon (GeSi) layer was selectively formed on n+ doped gallium arsenide (GaAs) regions by epitaxy. A new self-aligned nickel germanosilicide (NiGeSi) Ohmic contact with good morphology was achieved using a two-step annealing process with precise conversion of the GeSi layer into NiGeSi. NiGeSi contact with the contact resistivity (ρc) of 1.57 Ω mm and sheet resistance (Rsh) of 2.8 Ω/◻ was achieved. The NiGeSi-based self-aligned contact technology is promising for future integration in high performance III-V MOSFETs.