Improved crystallinity and polarity manipulation of MOVPE-grown GaN epilayers with deep sapphire-nitridation followed by Al-preflow at high temperatures

摘要

The polarity manipulation and crystallinity of GaN epilayers grown by metalorganic vapor phase epitaxy (MOVPE) on deeply nitrided c-sapphire was studied by using TMAl preflow at high temperatures (HT-TMAl preflow) of 1100 °C. It was found that the HT-TMAl preflow was very effective to change the surface polarity; the successful change to Ga-polarity from N-polarity and the atomic-steps were observed when the Al layer thickness was above two-monolayers, though it was remained N-polarity without the Al layer. The crystallinity of GaN epilayer is increased using HT-TMAl preflow. High quality Ga-polarity GaN epilayers was grown by this technique and typical full width at half maximums (FWHMs) for X-ray rocking curves were 300-320 arcsec and 450-480 arcsec for (002) and (102) diffractions, respectively.