Scanning Tunneling Microscopy Study of Cr-doped GaN Surface Grown by RF Plasma Molecular Beam Epitaxy

Cr doped GaN was grown by rf N-plasma molecular beam epitaxy on sapphire(0001) at a sample temperature of 700 °C. Cr/Ga flux ratio was set to a value from 5% to 20%. Subsequently, scanning tunneling microscopy was performed on these surfaces. Cr incorporates on the GaN surface at 700 °C at a Cr concentration of 5% and less. By increasing the Cr/Ga flux ratio to 20% in CrGaN, linear nano structures were formed on the surface, which were not observed on the bare GaN surface. The RHEED and STM studies reveal that Cr atoms form 3×3 reconstruction when 0.1 ML of Cr was deposited at room temperature on 1×1 adlayer of Ga on GaN(000-1). Cr substitutes Ga on the surface when deposited at 700 °C on the MBE grown GaN(000-1) surface for all the experiments which we have performed provided the Cr concentration is low (∼5%).