Influence of intentionally strained sapphire substrate on GaN epilayers

The structural and optical properties of GaN epilayers grown on intentionally strained sapphire (0001) substrates were investigated. In general, sapphire substrate experiences the tensile stress whereas GaN epilayer experience the compressive stress in the case of GaN/sapphire system. To examine the effects of intentionally strained sapphire substrate on the GaN epilayers, it was obliquely implanted with 2.4 MeV energy Cl/sup +/ and As/sup +/ ions to 10/sup 15/ cm/sup -1/ dose where TRIM-simulated projection ranges (R/sub p/) are 1.16 and 0.95 /spl mu/m, respectively. Cl/sup +/ ion implantation is expected to generate the lower strain field within the sapphire substrate, since it has smaller ionic radius (r/sub Cl+/ < r/sub As+/) and deeper R/sub p/ (R/sub p/ /sub Cl+/ > R/sub p/ /sub As+/) than the As/sup +/. To recover the disordered sapphire surface caused by implants, rapid thermal annealing was performed. After that, GaN epilayers were deposited on the low temperature GaN buffer layers grown by metal organic chemical vapor deposition (MOCVD) technique.