Origin of surface defects and influence of an in situ deposited SiN nanomask on the properties of strained AlGaN/GaN heterostructures grown on Si(111) using metal–organic vapour phase epitaxy
Herein, the investigation of the defects present on the surface of strained AlGaN/GaN heterostructures grown on Si(111), with and without an in situ deposited SixNx nanomask, was carried out. The SiN nanomask was used to enable the growth of dislocation and biaxial stress reduced AlGaN/GaN/Si(111) HEMT-type structures by the metal–organic vapor phase epitaxy (MOVPE) method. Specifically, the growth process model was proposed for the MOVPE deposition of a GaN layer on SiN/AlN/Si(111) templates, which includes the defects observed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Moreover, X-ray diffraction, photoluminescence and microRaman methods were used to characterize and compare the structural and optical properties of the strained AlGaN/GaN HEMT-type structures grown with and without application of the in situ SixNx nanomask. It was observed that the SiN deposition on top of the HT-AlN, prior to the GaN growth, has substantial effects on the properties of the final AlGaN/GaN heterostructure, such as the biaxial state of stress, threading dislocation density and crystal quality. The influence of the observable defects is discussed, along with their predicted influences on the essential properties of the device structure.