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Free-standing GaN is generally regarded as an ideal substrate for GaN-based devices due to its advantage of low threading dislocation density (TDD) and good thermal conductivity. However, new surface features such as hillocks and ridges appear on the GaN homoepitaxy films. In this paper, the influences of the intermediate GaN (IM-GaN) layer on the surface defects and crystal quality of GaN homoepitaxy films grown on c-plane GaN substrates by metalorganic chemical vapor deposition are investigated. It is found that hexagonal hillocks and ridges on the surface can be avoided by inserting an IM-GaN layer grown at an intermediate temperature (650850℃), prior to the growth of GaN at 1050℃. The results based on X-ray diffraction (XRD) measurements and differential interference contrast microscopy images demonstrate that the growth temperature of the IM-GaN layer has a significant influence on GaN homoepitaxy layer, which is one of the most critical parameters determining the surface morphology and crystal quality. As the IM-GaN growth temperature decreases from 1050℃ to 650℃, thed densities of hillocks and ridges on the surface reduce gradually. While, the XRD full width at half maximum (FWHM) values of (002) and (102) peaks for the homoepitaxy films are increased rapidly, indicating the adding of the TDD in the films. The atomic force microscopy (AFM) images show that the quasi-step growth mode change into layer-layer growth mode with the growth temperature decreasing from 1050℃ to 650℃ during the IM-GaN layer growing. It is speculated that the growth mode is determined by the diffusion length of adatom on the growing surface, which is proportional to the growth temperature. In the case of IM-GaN grown at low temperature, the formation of hillocks can be suppressed by reducing the adatom diffusion length. Finally, High crystal quality GaN homoepitaxy films (2 m) without hillocks is achieved by optimizing the growth parameters of IM-GaN layer, which is about 150 nm in thickness and grown at 850℃. The crystal quality of GaN homoepitaxy film is assessed by XRD rocking curve measured with double-crystal optics. The FWHMs of the (002) and (102) peaks are 125arcsec and 85arcsec respectively, indicating that rather low TDD is formed in the film. And well defined steps are observed on the image of AFM test, the root-mean square roughness value of the which is only about 0.23 nm for 5 m5 m scan area.

An InGaN multiple-quantum-well (MQW) violet-light-emitting diode (LED) is grown by low-pressure metalorganic chemical vapour deposition. It is found that photoluminescence wavelength of the InGaN MQW violet LED is lengthened with increasing growth temperature and with the increasing trimethylindium flow of the InGaN wells. The electroluminescence peak wavelength of the violet LED are about 401 nm with full width at half maximum of 14 nm, and the output power in injection current of 20 mA at room temperature is 4.1 mW.

The effects of dopants on the defects of GaN films were investigated by using different methods, such as wet, etching of pits, x-ray diffraction and photoluminescence (PL). Three kinds of the samples were prepared with different dopants, that is, nominally undoped, Si-doped and Mg-doped GaN films. It was found that the lowest density of the, etched pit was existed in the nominally undoped GaN, while the highest in the Mg-doped sample. The effects of the dopants on the, etching pits were discussed.

InAlN/GaN heterojunction structures are grown on two-inch c-face(0001) sapphire substrates by metalorganic chemical vapour deposition. AlN and AlGaN interlayers are intentionally inserted into the structure to improve the electrical properties. The lowest sheet resistance of 359Ω/sq and the highest room-temperature two-dimensional electron gas (2DEG) mobility of 1051 cm2 V−1s−1 is obtained in the structure with AlN thickness of 1.3 nm. The structure with AlN thickness of 2 nm exhibits the highest 2DEG concentration of 1.84 × 1013 cm−2. The sample with an AlGaN interlayer gives a smoother surface morphology compared to the one using an AlN interlayer, indicating potential applications of this technique in device fabrication.