The Contrast Of GaN Quality Grown On Al₂O₃and SiC Substrate And Influence Of The Misorientation Of SiC Substrate On The Quality Of GaN Epilayer

GaN is a direct band gap semiconductor material with wide bandgap, its band width is approximately3.45eV at room temperature. In recent years, GaN semiconductors have been considered as the most promising materials for optoelectronic and high power electronic devices in general lighting and microwave applications, such as LED and LD and so on. Because of the lack of a large native substrate, the GaN materials have been mainly epitaxially grown on foreign substrates, such as sapphire (Al2O3), SiC or Si. Among these substrates, Al2O3and SiC are the two major ones. The price of the Al2O3substrate is relatively lower, and the technology of the growth of GaN epilayer on the Al2O3substrate is more mature. But, the lattice constant mismatch of GaN with Al2O3is too large, it will affect the quality of the GaN epilayer. And its poor heat conductivity lead to the problem of the high power components under large current is very significant. The lattice constant mismatch of GaN with SiC is smaller than Al2O3, and Conductivity and thermal conductivity is better, but its price is very expensive, moreover, the GaN epilayer grown on the SiC substrate within a large tensile stress, lead to epilayer to crack. Recently, SiC substrates with misorientation have attracted many attentions, but the conclusion is still unclear. Around the quality of the GaN epilayer grown on sapphire and SiC substrate, this paper contains mainly two research works:(1) Deposited GaN epilayer with the same thickness on sapphire and SiC substrate by AIXTRON MOCVD, Using atomic force microscope (AFM), X-ray diffraction (XRD), Raman spectroscopy (Raman) and optical luminescence (PL) spectrum, etc. Test methods for characterizing the epilayer. The test results show that the epilayer grown on SiC substrate within the larger tensile stress intensity, and screw dislocation density is greater, which indicates that tensile stresses have a much more negative influence on the quality of the GaN epilayer.(2) GaN epilayer has been grown on6H-SiC substrate with different misorientation angle (0°>2°6’、68°) by AIXTRON MOCVD. Use the same test methods as the above for characterizing the epilayer. The surface morphologies of GaN epilayer was examined by atom force microscope (AFM). The structural quality of the samples was assessed by X-ray diffraction and Raman spectra. It was found that the surface roughness of the GaN epilayer increases with the angle of the substrate. The internal tensile stress increases with the substrate angle. Optical quality reduced with the increase of the substrate angle.The result show that misorientation angle can influence dislocation density and the optical properties of epitaxial films.