Strain variation with sample thickness in GaN grown by hydride vapor phaseepitaxy

High quality GaN crystals can be grown on sapphire by hydride vapor phase e pitaxy. The thermal expansion mismatch between sapphire and GaN produces st rain in the GaN crystal as it is cooled from the growth temperature to room temperature. The strain is evidenced by shifts in the photoluminescence an d reflectance line positions. By analyzing the surface strain as the crysta l thickness is increased, the thickness required to obtain zero surface str ain can be estimated. This structure might provide a lattice matched and th ermally matched substrate for further epitaxial growth of GaN. (C) 2000 Ame rican Institute of Physics. [S0021-8979(00)06315-5].