Molecular-beam epitaxy was used to grow Si-doped GaN layers onto GaN/sapphire templates which had been prepared by hydride vapor-phase epitaxy. Positron annihilation experiments indicated that the samples contained open-volume defects which were probably clusters of vacancies and perhaps Ga vacancy-donor complexes. The number of vacancy clusters decreased as the Si concentration was increased. Photoluminescence spectra showed that, while the absolute intensity of both the yellow and ultra-violet band-edge transitions increased with Si doping, the intensity ratio of yellow-to-UV emissions was decreased. Secondary ion mass spectrometry indicated that the impurity concentrations were in qualitative agreement with the carrier concentrations determined in electrical experiments. The data further suggested that Si did not affect the diffusion of

O. Transmission electron microscopy revealed that molecular beam epitaxially grown GaN retained the threading dislocation structure of the GaN/sapphire substrate. The molecular beam epitaxial layer was also shown to grow in the Ga face orientation, but some inversion boundaries were present in the epilayer.

Structural, Electrical, and Optical Properties of Defects in Si-Doped GaN Grown by Molecular-Beam Epitaxy on Hydride Vapor Phase Epitaxy GaN on Sapphire. P.Laukkanen, S.Lehkonen, P.Uusimaa, M.Pessa, J.Oila, S.Hautakangas, K.Saarinen, J.Likonen, J.Keränen: Journal of Applied Physics, 2002, 92[2], 786-92