在6H-SiC衬底上用低压MOVPE法生长AlN和GaN的过程中用(AlN/GaN)多层缓冲层来控制残余应力

摘要

BAlGaN quaternaries were proposed for use as light-emitting devices operating in the ultraviolet spectral region. GaN and AlN binaries seem to be the basic material for the device applications of the quaternary.rnA 6H-SiC substrate has an advantage in its small lattice mismatch to the nitrides and a thermal expansion coefficient of the SiC substrate is close to that of AlN. However, residual strain control of the AlN epitaxial layer is needed, because compressive strain, which was originated in the lattice mismatch to the substrate, was included in the AlN epitaxial layer directly grown on the SiC substrate. On the other hand, GaN epitaxial layer includes tensile strain, when the GaN is grown directly on the SiC substrate.The origin of the tensile strain is believed to be the larger thermal expansion coefficient of the GaN than that of the substrate. In this paper, effective control of the types and amount of the residual strain in the epitaxial layers are discussed for the 6H-SiC substrate. For this purpose, the (GaN/AlN) multi buffer structure is proposed as an effective tool for not only an AlN but also a GaN layer grown on the 6H-SiC substrate. Also we discuss the relationship between the residual strain and the crystalline quality for an AlN and a GaN epitaxial layer.%人们已提出用BAlGaN四元系材料制备紫外光谱区的光发射器件.GaN和AlN二元系是这种四元材料在器件应用中的基础材料.6H-SiC衬底在氮化物生长中因其晶格失配小是一大优势,而且SiC衬底的热膨胀系数也和AlN的很接近.然而,对于AlN外延层来说,需要控制其中的残余应力,因为在SiC衬底上直接生长的AlN外延层中存在着因晶格失配所产生的压缩应力.另一方面,在SiC衬底上直接生长的GaN外延层中存在着拉伸应力.这种拉伸应力起源于GaN比衬底有着更大的热膨胀系数.本文讨论了在6H-SiC衬底上生长的氮化物外延层中残余应力的类型、数量及控制.为此目的,提出了在6H-SiC衬底上,无论是生长AlN,还是生长GaN,都可以采用(GaN/AlN)多层缓冲层的办法,作为控制残余应力的有效方法.我们还讨论了AlN和GaN外延层的结晶质量和残余应力间的关系.