Epitaxial growth of nitride semiconductor films by laser ablation

GaN epitaxial films on (0001)sapphire substrates were fabricated by laser a blation. An ArF excimer laser(193 nm, 25 ns) with an energy of 140 mJ/pulse was used for ablating cold-pressed GaN targets made from high-purity GaN p owders. Just before the deposition, thermal cleaning of the substrate surfa ce at 1073 K was essential. The substrate temperature was varied between 87 3 and 1073 K. Above 973 K, the epitaxial layers were obtained. When a buffe r layer of GaN was deposited at lower temperatures before the epitaxial gro wth, the crystalline quality and surface morphology were greatly improved. (C) 1999 Elsevier Science S.A. All rights reserved.