Growth Of High Quality GaN Single Crystal By HVPE

Gallium nitride(Ga N) as the third generation of wide band gap semiconductor material, has become more and more popular in recent years. Ga N has direct bandgap with band gap of 3.4 e V, which can be adjusted to achieve coverage spectral range from red light to violet light. This makes it is ideal for UV devices, Blu-ray devices applications. As for physical and chemical properties, Ga N material possesses many advantages such as good chemical stability, anti-corrosion, high melting temperature, good thermal conductivity, anti-radiation and so on. Besides, Ga N can exhibits good electrical properties, including high breakdown voltage, high electron mobility and low dielectric constant. Based on the above advantages, gallium nitride has potential to be used widely in optoelectronic devices and microelectronic devices.This thesis first introduces the development of Ga N, substrate materials used for Ga N growth, characterization techniques. Then, the growth process of Ga N on a sapphire substrate by hydride vapor phase epitaxy(HVPE) technology, including growth technologies of thick layer of high-quality Ga N single crystal, reduction of the curvature of the Ga N single crystal layer and substrate separation technology, is studied. The main findings are as follows:(1)Through testing the effect of different mask patterns, it is found that a strip pattern for a mask is more conducive to the growth and consolidation in the early stages, and can effectively inhibit the dislocation extend then to reduce the dislocation density significantly.(2)Thick layer of Ga N is grown successfully on the substrate by adjusting the process parameters, including V / III ratio, growth temperature, growth pressure, carrier gas, etc., The as-grown thick layer of Ga N has smooth surface without pits, The thickness is greater than 60?m, dislocation density is less than 106, and the surface roughness Ra(2?mx2?m) is less than 0.1nm.(3)Ultrathick layer of Ga N with thickness more than 300?m is grown successfully on the substrate, and the self-supported Ga N single crystal is obtained after removing the substrate by laser lift-off technique. The factors affecting the laser lift-off are analyzed in detail.(4)Ultrathick layer of Ga N is auto-detached from the substrate by using insertion layer technology combined with edge protection technology.The obtained self-supported Ga N single crystal has diameter in 45 mm and thickness greater than 450?m.