The effects of strained sapphire(0001) substrate on the structural quality of GaN epilayer

Abstract

We investigated the structural properties of GaN epilayers grown on strained sapphire (0001) substrate by metal-organic chemical vapor deposition (MOCVD). To minimize the mismatch in lattice constants and thermal expansion coefficients between the sapphire substrate and the GaN epilayer, we imposed the strain onto the sapphire (0001) substrate using high-energy O+, Cl+, and As+ ion implantation. The strained sapphire surfaces result in the different behaviors of defect generation in the GaN epilayer. Not only the ionic species but also the thickness of the low-temperature GaN buffer layer on sapphire affected the structural quality of the GaN epilayer. The present results show that O+ ion-implanted substrate can provide an improved GaN epilayer using only a thin (similar to5 nm) buffer layer rather than using a thicker one. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.