New Approach to Clean GaN Surfaces

摘要

We report X-Ray and Ultraviolet Photoelectron Spectroscopic analysis of an air exposed and cleaned undoped epitaxial GaN film and correlate the observed changes in electronic structure and surface properties after employing a simple and effective cleaning procedure. The investigated GaN films were grown by RF Plasma-Assisted Molecular Beam Epitaxy. A new two-step cleaning procedure consisted of ex-situ wet chemical (HCl) etching followed by an in-situ ultrahigh vacuum anneal (up to 750 ℃) was employed and yielded a clean and stoichiometric GaN surface. The major contaminants (Carbon and Oxygen) in the film were removed, where the cleaned GaN film surface was found to be Carbon free with the amount of residual Oxygen was reduced very significantly. The n_OIn_N ratio of the cleaned sample reduced drastically from 1.79 to 0.04 after cleaning. The cleaned GaN sample obtained was well stoichiometric with a N:Ga of 1.0 ±0.04. A shift of 0.6 eV and 0.5 eV in Ga (3d) and N (1s) core level peaks was observed after cleaning. The position of valence band maximum (VBM) was observed to be shifted from 4.0±0.1 eV to 2.8±0.1 eV after cleaning of the surface. The electron affinity and ionization energy of the cleaned sample were observed to be 3.9 eV and 7.3 eV respectively.