Systematic investigation of surface and bulk electronic structure of undoped In-polar InN epilayers by hard X-ray photoelectron spectroscopy

Abstract

The surface and bulk electronic structure of undoped In-polar InN (u-InN) epilayers with surface electron accumulation (SEA) layer was investigated by soft and hard X-ray photoelectron spectroscopies (SX-PES and HX-PES, respectively). The potential-energy profile was obtained by fitting the N 1s core-level spectra accounting for the probing depth of both SX-PES and HX-PES and the surface downward band bending. In this study, we found that a significant potential-energy bending as large as 1.2 ± 0.05 eV occurred from surface to the depth of ∼20 nm. Taking into account such a large downward bending, the valence band maximum (VBM) with respect to Fermi energy (EF) level in the bulk was determined to be 0.75 ± 0.05 eV. A weak signal with a peak position at 0.3 ± 0.05 eV was reproducibly observed from the VBM to EF level in the HX-PES spectrum. The peak position was in agreement with the calculated energy of the E1 sub-band in the surface quantum well. HX-PES is powerful tool for revealing the intrinsic bulk electronic structure of materials with large potential-energy bending. This work provides important information for the future investigation of electronic structures of undoped and Mg-doped InGaN, as well as Mg-doped InN epilayers with a SEA layer similar to u-InN.