Gong Hai-mei

High-Reflectivity AlGaN/AlN Distributed Bragg Reflector in Ultraviolet Region

Thirty-pair Al0.3Ga0.7N/AlN distributed Bragg reflectors centred at 320 nm are designed and grown on sapphire substrates by metalorganic chemical vapour deposition. No cracks are observed in the main area of the 2-inch wafer except for about 4 mm margin under an optical microscope. Regular stack of alternating layers is shown by scanning electron microscopy. Clear two-dimensional growth steps and very low surface roughness are shown by atomic force microscopy (AFM). Well-defined periodicity is shown by high resolution x-ray diffraction. High reflectivity of 93% at 313 nm with a bandwidth of 13 nm is obtained.

Silicon Doping Dependence of n-Type Al0.5Ga0.5 N Layers Grown by Metalorganic Chemical Vapor Deposition.

Abstract The electrical, structure and optical properties of Si-doped Al 0.5 Ga 0.5 N epilayers with a thickness of about 0.5 μ grown on sapphire substrates using an AIN buffer by metalorganic chemical vapor deposition were reported. Hall-effect measurements showed that n-type Al 0.5 Ga 0.5 N was achieved achieved with an electron concentration of 1.2 × 10 19 cm −3 and mobility of 12 cm 2 ·Vs −1 at room temperature. The electron concentration increases with an increase of Si doping level. Lattice constant of c and Raman shift of Si-doped Al 0.5 Ga 0.5 N epilayers with various SiH 4 flow rates was studied by X-ray diffraction (XRD) and Raman scattering spectrum. With increasing SiH 4 flow rate, the decrease of the lattice constant of c and the frequency of E 2 phonon implies gradual relaxation of the stress in the epilayers.

Influence of hydrogenation on the dark current mechanism of HgCdTe photovoltaic detectors

The influence of hydrogenation on the dark current mechanism of HgCdTe photovoltaic detectors is studied. The hydrogenation is achieved by exposing samples to a H2/Ar plasma atmosphere that was produced during a reactive ion etching process. A set of variable-area photomask was specially designed to evaluate the hydrogenation effect. It was found that the current–voltage characteristics were gradually improved when detectors were hydrogenated by different areas. The fitting results of experimental results at reverse bias conditions sustained that the improvement of current–voltage curves was due to the suppression of trap assisted tunneling current and the enhancement of minority lifetime in the depletion region. It was also found that the dominative forward current was gradually converted from a generation–recombination current to a diffusion current with the enlargement of the hydrogenation area, which was infered from the ideality factors by abstraction of forward resistance–voltage curves of different detectors.

MOCVD Growth and Characterization of Epitaxial AlxGa1−xN Films

We study the growth of AlxGa1−x N epilayers on (0001) sapphire by low-pressure MOCVD, using a low-temperature AlN buffer. By varying the input flow rates of trimethylgallium (TMGa), we obtain crack-free AlGaN films in the whole range of composition. A linear relationship between gas and solid Al content is observed. The structural properties of the layers (x = 0−1) are investigated by x-ray diffraction, atomic force microscopy (AFM) and scanning electron microscopy (SEM). It is found that a two-direction growth appears along the c-axis and the (101) directions for x≥0.45. From the results of Raman spectroscopy, we suggest that the compressive stain and the lack of mobility of Al adatoms can induce the formation of (101) grains.

Suppression of extension of the photo-sensitive area for a planar-type front-illuminated InGaAs detector by the LBIC technique

To suppress the extension of the photo-sensitive area of a planar-type InGaAs detector, the structure of the detector was modified, and the small-diffusion-area diffusion method, circle-type covering contact and guard-ring were introduced. The laser-beam-induced-current (LBIC) technique was used to study the photo responsive characteristics of the photo-sensitive area of different detector structures. It was indicated that, by modifying the size of the diffusion area, the width of the circle-type covering contact, the distance between the guard-ring and the photo-sensitive area and the working status of the guard-ring, extension of the photo-sensitive area could be effectively suppressed, and the detector photo-sensitive area could be exactly defined.

Study on oxidation order of the different elements in anodic native oxide of HgCdTe

Owing to the difference between the electrode potentials of the different elements in basic electrolyte, the authors found that the oxidation order is CdrarrTerarrHg and made an oxidation model of anodically grown native oxide of HgCdTe.