Effect of initial condition on the quality of GaN film and AlGaN/GaN heterojunction grown on flat sapphire substrate with ex-situ sputtered AlN by MOCVD

The growth condition of initial medium (870 degrees C-920 degrees C) temperature (MT) layer is crucial to the quality of high temperature (HT) GaN layer and AlGaN/GaN heterojunction grown on flat sapphire substrate (FSS) with ex-situ sputtered AlN. The superior wetting of GaN and AlN makes the MT layer tend to directly two-dimensional (2D) growth mode at the initial stage. In this study, it was found that high pressure was effective in lowering Ga adatom diffusion and promoting early three-dimensional (3D) growth, which resulted in reducing (102) X-ray full-width-at-half-maximum as well as edge dislocation density significantly. The lowest X-ray rocking curve fullwidth-at-half-maximum of (002) and (102) were 35 arcsec and 220 arcsec respectively, which were comparable with GaN layer grown on patterned sapphire substrate (PSS). High quality AlGaN/GaN heterojunction was achieved with sheet electron density of 1.18 x 10(13) cm(-2), Hall mobility of 1909 cm(2)/V.s and sheet resistance of 336 Omega/square. Controlled growth interruption was carried out to study the evolution mechanism of MT layer growth.