Residual stresses in cubic and hexagonal GaN grown on sapphire using ion beam-assisted deposition

Heteroepitaxial GaN thin films are deposited on (0001) sapphire substrates using ion-beam-assisted deposition with different content of hexagonal (h-G aN) and cubic (c-GaN) polytypes. X-ray diffraction is used to characterize crystallographic orientation, stresses and unstressed lattice parameters se parately for each polytype. The typical compressive stress values for h- an d c-GaN are about 195 and 155 MPa, respectively. The stress state in h-GaN is not influenced by the presence of c-GaN and, within one layer, stresses formed in c-GaN are always smaller then the stresses in h-GaN. A typical un stressed lattice parameter a for c-GaN is 0.45035(1) nm and, for h-GaN, uns tressed lattice parameters a and c are 0.31881(2) and 0.51831(1) nm, respec tively. In the thin film deposited with high ion energy of 50 eV, two regio ns with different structural properties are detected. The region close to t he interface exhibits significantly higher stresses and also larger unstres sed lattice parameters in comparison to the surface part of the thin film w hich is partly stress-relaxed. (C) 2000 Elsevier Science B.V. All rights re served.