Growth of Al_xGa_(1-x)N and GaN on photo-electrochemically patterned SiC substrates

摘要

The large defect densities in heteroepitaxially grown group-Ⅲ-nitride layers on sapphire or SiC cannot be tolerated in applications such as lasers. As an alternative to the well known ELOG process for defect reduction we report here on overgrowth of patterned 6H-SiC(0001) surfaces. First, we formed mesa structures in the windows of metal masks and then after removal of the masks layers of Al_xGa_(1-x)N and GaN were grown by low-pressure MOVPE under conditions of high lateral growth rates. We demonstrate that layers and layered structures can be grown with smooth surfaces and reduced defect densities (a factor 5-10 lower compared to growth on planar substrates). For a further reduction of defect densities a detailed understanding of the growth process on patterned substrates is necessary. Growth starts at the sidewalls of the mesa. For a defect reduction low pressures and high Ⅴ/Ⅲ-ratios are required. Very high lateral-to-vertical growth rates of more than 8 can be achieved on such structures.