Reduction of threading dislocations in GaN epilayersusing AlGaN epilayers grown on Si(111) by UHVCVD

摘要

Transmission Electron Microscopy (TEM) has been conductedon AlAlxGa Ga1-x 1-xN epilayers grown on exact Si (111) substrates by UltrhighVacuum Chemical Vapour Deposition (UHVCVD). AlN/AlN Al0.5 0.5Ga Ga0.5 0.5Ndouble layers were used as buffer layers between the Si(111) substratesand GaN epilayers. A reference sample consisted of Si(111) substrate,double buffer layers (20 nm-thick AlN and 120 nm-thick AlNAl0.5 0.5Ga Ga0.5 0.5Nepilayers), and 2.5 μm-thick GaN epilayer. Other samples consisted ofSi(111) substrate, double buffer layers (exactly the same as the firststructure), a 0.5 μm-thick GaN epilayer, a 120 nm-thick AlNAlyGa Ga1-y 1-yNepilayer, with the values of y of 0.06 and 0.2, and a top 2 μm-thick GaNepilayer. It was observed that without an intermediate AlNAlyGa Ga1-y 1-yNepilayer, threading dislocations that originate from the interface betweenSi(111) substrate and the AlN buffer layer run parallel to the growthdirection until they reach the epilayer surface. Dislocations parallel tointerface between AlN buffer layer and Si(111) substrate were alsoobserved. With an intermediate AlNAlyGa Ga1-y 1-yN epilayer, however, most of thethreading dislocations that originate at the interface between Si(111)substrate and the AlN buffer layer run parallel to the growth directionand terminate when they reach approximately 300 nm above the AlN AlyGa Ga1-1-yN epilayer. From TEM micrographs obtained, it was found that thedislocation densities in the GaN epilayers can be decreased from ~ 101010 10cmcm-2 -to ~ 10 108 cm cm-2 -using the Al Al0.2 0.2Ga Ga0.8 0.8N epilayer.