Influence of Ga flux on the growth and electron transport properties of AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

The growth and electrical properties of the Al0.15Ga0.85N/GaN two-dimension al electron gas (2DEG) were studied for a range of III/V ratios during grow th. All films were grown by RF-plasma assisted molecular beam epitaxy. Al0. 15Ga0.85N growth in the Ga-rich regime has a surface structure that is cont rolled by the Ga flux, ranging from morphologies indicative of statistical roughening effects to step-flow growth. The 2DEG sheet carrier concentratio n was insensitive to Ga flux-this is because the saturated 2DEG charge is a pproximately equal to the fixed polarization charge at the AlGaN/GaN interf ace. By increasing the Ga flux during growth, the measured low temperature 2DEG mobility was found to increase, reaching a maximum just before Ga drop lets began to form on the surface. In the Ga droplet growth regime, the mob ility decreased and was insensitive to further increase in Ga flux. The hig hest quality surface structure and maximum mobility were realized for struc tures grown with Ga fluxes just below those necessary to form droplets. (C) 2001 Elsevier Science B.V. All rights reserved.