Identification of Surface, Interface, and Bulk States on the Pristine and Passivated InP (001) and (111) Surfaces Using Surface Photovoltage Spectroscopy

Abstract

This study presents a comprehensive investigation of surface, interface, and bulk states of InP crystal, grown by the vertical gradient freze method along (001) and (111) directions. Surface photovoltage spectroscopy (SPS) is implemented to identify the transition originating from the surface states at ≈972 nm, more prominent in the InP (001). Temporal and thermal SPS behavior shows that these surface states have a slow response and significantly influence spectra above ≈160 K. Photoluminescence further confirms their nonradiative nature. X-ray photoelectron spectroscopy attributes these surface states to native oxides of indium and phosphorus, with InP (001) showing higher oxide density due to distinct surface reconstructions. X-ray reflectivity indicates a thicker oxide (≈3.9 nm) on InP (001) than on InP (111) (≈1.8 nm). Despite the differences found in the surface states density under different crystal orientations, the bulk properties such as electron mobility and carrier concentration are found to be similar for both orientations as validated by Hall measurements. Finally, the density of surface states is effectively reduced by SiO2 passivation which is confirmed through SPS analysis. These findings underscore the critical influence of crystallographic orientation on surface chemistry, providing essential insights for the reliable integration of advanced device architectures on InP platforms.