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InGaN/GaN multi-quantum well structure with Mg-doped p-type GaN was grown by low-pressure metalorganic vapour phase epitaxy. After rapid-thermal-annealing at 700 and 900 degrees C, both the red-shift and the blue-shift of the photoluminescence (PL) peak, the decreased and the enhancement of the PL intensity were observed. The transmission electron microscopic images showed that InGaN multi-quantum-dots-like (MQD-like) structures with dimensions less than 5×10nm were formed in InGaN wells. The changes of PL spectra could be tentatively attributed to the competition between the red-shift mechanism of the quantum-confined Stark effect and the blue-shift mechanism of the quantum size effect due to MQD-like structures.

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 near-ultraviolet lighting-emitting-diodes (UV-LEDs) with the InGaN/GaN multi-quantum-well (MQW) structure were grown by low-pressure metalorganic vapour phase epitaxy. The double crystal x-ray diffraction revealed a distinct second-order satellite peak. The near-ultraviolet InGaN/GaN MQW LEDs have been successfully fabricated to emit at 401.2 nm with narrow FWHM of 14.3 nm and the forward voltage of 3.6 V at 20 mA injection current at room temperature. With increasing forward current from 10 mA to 50 mA, the redshift of the peak wavelength was observed due to the band-gap narrowing caused by heat generation.

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.