Effect of surface Ga accumulation on the growth of GaN by molecular beam epitaxy

Abstract

AbstractWe investigate the effect of surface Ga accumulation on the growth of GaN by molecular beam epitaxy (MBE) with ammonia as a nitrogen source. Control of the surface Ga condition is very important because the crystallization process strongly depends on the surface Ga coverage. The growth rate rapidly decreases when the supply of Ga exceeds certain amount when growing with ammonia, in contrast to the saturation grown with radio‐frequency plasma source. The critical Ga supply becomes higher by introducing the migration‐enhanced epitaxy (MEE). The growth rate is slightly higher for MEE compared with MBE in the region where it linearly increases with increasing the Ga supply.These phenomena can be explained by the model taking into account the surface coverage of the excess Ga, accumulation of Ga into droplet and diffusion of them during ammonia supply period. At elevated temperatures, surface Ga accumulation is less effective since Ga atoms can evaporate from the surface. The surface morphology becomes smoother by using MEE due to the quick Ga diffusion on the surface during the ammonia supply period. These results shows that MEE is very useful technique for the GaN growth with ammonia since the control of the surface Ga accumulation is very important (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)