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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.

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.

Polarization-induced charges in modulation-doped Al0.22Ga0.78N/GaN heterostructures were investigated by the capacitance-voltage (C-V) method. The C-V profile of the Pt/Al0.22Ga0.78N/GaN Schottky diodes with various Al0.22Ga0.78N thicknesses shows significant differences due to change of the polarization field in the heterostructures. A numerical simulation based on the experimental results indicates that the sheet density of the polarization-induced charges at the heterointerface is 6.78×1012 cm-2 in the samples with the Al0.22Ga0.78N thicknesses of 30 nm or 45 nm. The charge density reduces to 1.30×1012 cm-2 in the sample with the Al0.22Ga0.78N thickness of 75 nm. It is thought that the reduction of the polarization-induced charges at the heterointerface is due to the partial relaxation of the Al0.22Ga0.78N layer on GaN. This work provides a technique for quantitative characterization of the polarization-induced charges in AlxGa1-xN/GaN heterostructures.

GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapour phase epitaxy (HVPE). The deposition temperature of the LT-GaN layers is changed from 400 to 900 degrees C. When the LT-GaN layer is deposited at 600 degrees C, GaN films show only c-oriented GaN (0002) and have the band edge emission at 365 nm with no yellow luminescence bands. The results indicate that the LT-GaN layer can effectively block the unexpected Si etching by reactive gas during the GaN growth. However, the surface roughness of these GaN films grown on Si(111) is larger than that of GaN films on c-plane sapphire.

High quality AlGaN materials used in the DBR structure of ultraviolet detector are grown under different growth conditions. The structure, composition and photographic characteristics are determined by XRD, SEM and AFM. The influence of the growth conditions on the characteristics of the AlGaN materials are discussed.The good performance of the DBR structure of ultraviolet detector is obtained.