Abstract
The surface band bending in Ga-polar n-type GaN surfaces, as well as the effect of Si doping levels and in situ Ar+ ion processing on band bending, was systematically investigated. To precisely determine the valence band maximum (VBM) of GaN beyond instrumental and material surface environments by XPS, a valence band feature fitting procedure based on photoemission spectra and theoretical densities of states has been developed. Poisson calculation with quadratic depletion approximation on surface potential has been used to model the band bending and further correct the VBM energy. Then, the actual surface band bending was correctly evaluated. Upward band bending of 1.55 ± 0.03 eV with highly Si doped n-GaN, which is about 0.88 eV higher than that of the moderately doped sample, was found. After in situ Ar+ plasma treatment, the varying degree of band bending was observed distinctly depending on the Si doping density. The surface components associated with the Ga/N ratio and Ga–O bonding concentration on the n-GaN surface have been used to evaluate the contribution to surface band bending.
Highlights
Surface band bending (BB) is one of the most important properties of wurtzite GaN as it plays an important role in determining the electrical and optical properties of GaN materials and heterostructures.1,2 Polarization effects and various surface states in the wurtzite GaN surface are widely recognized as being directly related to the surface band bending (BB).3 For the Ga-polar n-GaN surface, upward band bending and the electron depletion layer are usually present at the surface.4 This is mainly because of the negative bound polarization charge existing on the Ga-polar GaN surface
We have achieved accurate determination of the valence band maximum (VBM) from X-ray photoelectron spectroscopy (XPS) VB spectra combined with hybrid density function theory (DFT) valence band calculations
Distinct upward surface band bending in the Ga-polar n-GaN surface with different Si-doped levels and Ar+ ion treatment was derived after VBM band bending correction
Summary
Surface band bending (BB) is one of the most important properties of wurtzite GaN as it plays an important role in determining the electrical and optical properties of GaN materials and heterostructures. Polarization effects and various surface states in the wurtzite GaN surface are widely recognized as being directly related to the surface band bending (BB). For the Ga-polar n-GaN surface, upward band bending and the electron depletion layer are usually present at the surface. This is mainly because of the negative bound polarization charge existing on the Ga-polar GaN surface. The Si-doped density is supposed to play a decisive role in related device performance, there are rare studies on the electronic surface band and surface structure of n-GaN systems focusing on the influence of Si doping levels.. The determination of core energies and valence band binding energies at the top surface layer is always influenced by the band bending effect as the photoemission signals constitute integrated intensity contribution from different detection depths and corresponding bending-induced peak shifts.. The determination of core energies and valence band binding energies at the top surface layer is always influenced by the band bending effect as the photoemission signals constitute integrated intensity contribution from different detection depths and corresponding bending-induced peak shifts.21–23 As a result, both effects imply a slightly imprecise surface band bending using this method. We further figured out the origins of the surface band bending associated with Si-doping levels by taking the Ga/N ratio and Ga–O components into the analysis
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