Suppression of inversion domains and decrease of threading dislocations inmigration enhanced epitaxial GaN by RF-molecular beam epitaxy

GaN epitaxial layers were grown with the migration-enhanced epitaxy (MEE) b y molecular beam epitaxy using rf-plasma nitrogen. GaN films were directly grown on (0001) sapphire substrates without any buffer layers, varying the substrate nitridation time from 0 to 90 min. The inversion domain density w as reduced by increasing, the substrate nitridation time. Meanwhile, the ro om temperature (RT) mobility peaked at 45 min nitridation, with the value o f 362 cm(2)/Vs at the carrier density of 1.7 x 10(17) cm(-3). The photolumi nescence intensity also peaked at 20 min nitridation. The threading disloca tion density of MEE-GaN was estimated to be 1.0 x 10(10) cm(-2) by the cros s-sectional images of transmission electron microscope observation. The dis location density of MEE-GaN was reduced remarkably by the insertion of the high-temperature grown AIN multiple intermediate layer (HT-AlN-MIL) and it was clearly observed that most dislocations were bent during passing throug h the HT-AlN-MIL. The dislocation density of MEE-GaN grown on HT-AIN-MIL wa s evaluated to be about 2.1 x 10(9) cm(-2) by a selective photoelectrochemi cal (PEC) wet etching, as a result, the highest RT mobility of 668 cm(2)/Vs was achieved.