THE INFLUENCE OF STRAIN AND MOSAIC STRUCTURE ON ELECTRICAL AND OPTICAL-PROPERTIES OF GAN FILMS ON SAPPHIRE SUBSTRATES

Photoluminescence, electron transport measurements, and seven-crystal X-ray diffractometry have been used to analyze high mobility (intentio nally silicon-doped) and highly resistive (unintentionally doped) GaN films grown on a-plane (<11(2)over bar 0>) sapphire substrates. Values of omega/2 theta X-ray rocking curve FWHMs were seen which were lower than typically reported for GaN films on sapphire, and this has been attributed to the increased thickness of the analyzed films. Broadenin g was observed in the tail of the omega/2 theta X-ray rocking curve of a Si-doped GaN film relative to that of unintentionally doped films, indicating diffuse scatter of the X-ray beam. Mosaic structure and cur vature induced in the sapphire substrate by the subsequently grown GaN film was also observed.