Material and Device Characteristics of MBE-Grown GaN Using a New rf Plasma Source

Abstract

ABSTRACTA new rf plasma nitrogen source has been characterized for growth of GaN on basal-plane sapphire by molecular beam epitaxy. For rf power of 500 W and N2 flow rate of 2 sccm, a maximum GaN growth rate of 0.80 μm/hr is obtained, implying a source efficiency greater than 5%. It is found that the GaN surface roughness is extremely sensitive to V:Il ratio near unity and independent of growth rate in the range 0.3-0.8 μm/hr. Roughness as small as 1.0 nm (rms) is measured by atomic-force microscopy. Microstructure of the high-growth-rate films is similar to other GaN films, as observed in cross-section transmission electron microscope images. The electroluminescence spectra from homojunction light-emitting diodes exhibit a band of nearultraviolet emissions corresponding to the energy separation of the intentional donor and acceptor levels on the two sides of the junction. The intensity of these emissions relative to the visible spectrum increases with drive current density, implying saturation of deep trap levels responsible for the visible light output.