The high Al content AlGaN epilayers have been obtained by metalorganic chemical vapor deposition (MOCVD), and the optical property has been investigated by photoluminescence (PL) spectroscopy. Longitudinal-optic (LO) phonon mode has been studied by Raman scattering. Further analysis shows that the edge dislocation is an important factor influencing optical quality of AlGaN epilayers, and it also shows that the correlation between the A1 (LO) polar modes and the edge dislocation is intensive, which may be expected to become a characterization method of the related crystal defects.

The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation.

The temperature dependence of the I-V characteristics on Au/Ni-HEMT Schottky contacts was measured and analyzed. Large deviations from the thermionic emission and thermionic-field emission model were observed in the I-V-T characteristics. The thin surface barrier model only fits the measured curves in the high bias region, but deviates drastically in the low bias region. Using a revised thin surface barrier model, the calculated curves match well with the measured curves. It is also found that tunneling emission model is the dominant current transport mechanism at low temperature, yet thermionic-field emission model is the dominant current transport mechanism at high temperature.

This is a theoretical study of the InGaN back-barrier on the properties of the Al03Ga0.7N/AlN/GaN/InGaN/GaN HEMT structure by self-consistently solving coupled Schrödinger and Poisson equations. Our calculation shows that by increasing the indium composition, the conduction band of the GaN buffer layer is raised and the confinement of 2DEG is improved. However, the additional quantum well formed by InGaN becomes deeper, inducing and confining more electrons in it. Another conductive channel is formed which may impair the device performance. With the increasing InGaN thickness, the well depth remains the same and the conduction band of GaN buffer layer rises, enhancing the confinement of the 2DEG without inducing more electrons in the well. The 2DEG sheet density decreases slightly with the indium composition and the physical mechanism is discussed. Low indium composition and thick InGaN back-barrier layer are beneficial to mitigate the short-channel effects, especially for high-frequency devices.

VLBI images of the H2O megamaser in NGC 4258 and a time series of spectra taken over several years combine to make a compelling case that there is a compact molecular disk associated with a supermassive object in the nucleus of this galaxy. The images of the maser in the velocity rangenear the systemic velocity show a highly elongated structure with a major axis of about 0.009 pc, along which the gradient in line-of-sight velocity is essentially a constant of 7970 ± 40 km s-1 pc-1. The observed acceleration of these spectral features by about 6-11 km s-1 yr-1, the presence of high-velocity maser satellite emission, and the VLBI results suggest emission from a disk of diameter0.2 pc, rotating with a velocity of ~800 Km s-1, bound by a mass of 1.5×107 M⊙ and denisty of ≳3.6×109 M⊙ pc-3

The photomodulated reflectivity (PR) spectroscopy of modulation-doped diluted magnetic semiconductor Cd0.72 Mn0.28 Te:In/CdTe multiple quantum wells has been measured at 20 K – 300 K. Several spectral features associated with intersubband transitions have been found. The feature associated with Fermi level is first reported in PR spectra of II–VI heterostructures. In addition, a abnormal transition intensity ratio of 22H to 11H caused by electron filled effect has been reported. The Photoluminescence(PL) spectra of the sample have also been measured at 10 K – 300 K. A strong enhancement of the photoluminescence intensity towards the electron Fermi energy, which is caused by multiple electron-hole scattering processes, is reported. The temperature dependence of the Fermiedge singularity has been measured and discussed. The mechanism of the Fermi-edge singularity can be explained by hole localization.

An apparatus design is described. It is for detecting VHE gamma ray point sources by means of the atmospheric Cerenkov technique. Obviously, the improvement of flux sensitivity and discrimination between gamma ray and isotropic proton showers is still a key problem. Of course, it is necessary to set up more observatories and to track an object continuously with several facilities. With this in mind, we decided to develop an experiment for observing VHE gamma ray sources in China. As a first step, we will set up an apparatus which consists of three 1.5 m diameter searchlight morrors at Xinglong station of Beijing Observatory, Xinglong county, Hebei province (40°. 4N, 117°.5E, altitude 940 m). The observation will start in 1988. Then, the second apparatus will be set up at Delingha station of Purple Mountain Observatory, Delingha county, Qinghai porvince (37°.22N, altitude 3204 m). Both the sites are far from air and light pollution, and have suitable meteological condition for Cerenkov light detection as well as quite convenient facilities for transportation. Some probable technical improvements are also discussed in this paper.