Surface evolution and effect of V/III ratio modulation on etch-pit-density improvement of thin AlN templates on nano-patterned sapphire substrates by metalorganic chemical vapor deposition

Abstract

A low defect-density AlN template film using V/III ratio modulation and nano-patterned sapphire substrate (NPSS) was achieved by metalorganic chemical vapor deposition. In contrast to conventional high-quality AlN/NPSS obtained with high coalescence thickness ( > 6 mu m) using high growth temperatures ( >= 1250 degrees C), this study reveals the high crystallinity of AlN with the lower thickness of 2.55 mu m grown under a lower temperature of 1130 degrees C. It could effectively increase the heater lifetime and reduce the epi-wafer warpage. The growth of AlN/NPSS dominated by epitaxial lateral overgrowth achieves a dramatic reduction of full width at half maximum values along (10 (1) over bar2) plane from 1640 to 714 arcsec, and lowest dislocation density of approximately 1 x 10(8) cm(-2), as well as a ultra-low etching pit density of 2.3 x 10(5) cm(-2). The crack-free AlN/NPSS with a compressive stress owing to the tensile stress was relaxed by the existence of some key-shaped holes upon the patterned region. Details of the surface evolution, mechanism and dislocation behavior of AlN/NPSS will be discussed and these results demonstrate this low-defect template technique of high potential for AlGaN-based device applications.