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In this study, we have reported on growth of thick AlGaN layer on the c-plane sapphire substrate with low-temperature AlN (LT-AlN) nucleation layer by low-pressure metal–organic chemical vapor deposition (LPMOCVD). High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements have been employed to study the crystal quality, threading dislocation density, surface morphology, and optical properties of thick AlGaN layer. Results indicate that the insertion of LT-AlN nucleation layer between sapphire substrate and high-temperature AlN nucleation layer effectively improves the thick AlGaN crystal quality, reduces the surface roughness and eliminates the threading dislocation density.

In this paper we report that the GaN thin film is grown by metal?organic chemical vapour deposition on a sapphire (0001) substrate with double AlN buffer layers. The buffer layer consists of a low-temperature (LT) AlN layer and a high-temperature (HT) AlN layer that are grown at 600 ?C and 1000 ?C, respectively. It is observed that the thickness of the LT-AlN layer drastically influences the quality of GaN thin film, and that the optimized 4.25-min-LT-AlN layer minimizes the dislocation density of GaN thin film. The reason for the improved properties is discussed in this paper.

First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes (A1 (LO) and E2 (high)) are obtained. We focus our attention on the temperature dependence of E2 (high) mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.

Nonpolar (112?0) a-plane GaN films are grown by metal?organic chemical vapour deposition (MOCVD) on r-plane (11?02) sapphire. The samples are irradiated with neutrons under a dose of 1 ? 1015 cm?2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD) and photoluminescence (PL). The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.

Morphology of nonpolar a-plane GaN epilayers on r-plane sapphire substrate grown by low-pressure metal-organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.

A susceptor structure with a ring channel for a vertical metalorganic chemical vapor deposition reactor by induction heating is proposed. Thus the directions of heat conduction are changed by the channel, and the channel makes the heat in the susceptor redistribute. The pattern of heat transfer in this susceptor is also analyzed. In addition, the location and size of the channel in the susceptor are optimized using the finite element method. A comparison between the optimized and the conventional susceptor shows that the optimized susceptor not only enhances the heating efficiency but also the uniformity of temperature distribution in the wafer, which contributes to improving the quality of the film growth.

The temperature field in the vertical metalorganic chemical vapor deposition (MOCVD) reactor chamber used for the growth of GaN materials is studied using the finite element analysis method (FEM). The effects of the relative position between the coils and the middle section of the susceptor, the radius of the coil, and the height of the susceptor on heating condition are analyzed. All simulation results indicate that the highest heating efficiency can be obtained under the conditions that the coil distributes symmetrically in the middle section of the susceptor and the ratio of the height of the susceptor to that of the coil is three-quarters. Furthermore, the heating efficiency is inversely proportional to the radius of the coil.

The growth of high-performance Mg-doped p-type AlxGa1−xN (x = 0.2) using metal-organic chemical vapor deposition is reported. The influence of growth conditions (growth temperature, magnesium flow, and thermal annealing temperature) on the electrical properties of Mg-doped p-type AlxGa1−xN (x = 0.2) has been investigated. Using the optimized conditions, we obtained a minimum p-type resistivity of 0.71 Ω·cm for p-type AlGaN with 20% Al fraction.