国产SiC衬底上利用AlN缓冲层生长高质量GaN外延薄膜

Abstract

GaN is considered as a promising material for high power,high temperature and high frequency microwave applications,due to the wide band gap,high thermal stability and high breakdown voltage.Due to lack of suited homosubstrates,GaN is currently grown on heterosubstrates where SiC is the most popular choice for commercial applications.However,it is difficult to obtain high quality GaN because of the 33.1% mismatch of thermal expansion coefficients and the large lattice mismatch(3.5%) between GaN and SiC.In this paper,GaN epitaxial layers were grown on 6H-SiC substrates by metalorganic chemical vapor deposition.Samples employing high temperature AlN as buffer layers produce high quality GaN epitaxial layers. Five samples with different AlN buffer layers were prepared.The effects of the growth parameters of AlN buffer layers on characterizations of GaN were studied.The highest quality GaN layer grown on SiC substrate with AlN buffer was obtained by optimizing the growth parameters of the AlN buffer.The full width at half maximum of High-resolution X-ray diffraction on-axis(0002) and off-axis(1012) diffraction are 130 arcsec and 252 arcsec,respectively.The values are the best result of GaN grown on homemade 6H-SiC.The quality of GaN layers will be deteriorated by increasing the thickness or the growth Ⅴ/Ⅲ ratio of AlN buffer layers,while the low growth temperature of AlN buffers also deteriorate the quality of GaN layers.The strain in GaN also has been studied.It is found that the GaN layer with narrow XRC FWHM has less stress intensity.