Surface photovoltage studies of n-type and p-type InP

Abstract

Surface photovoltage spectroscopy (SPV) was used to study the initial stages of oxidation of single crystal InP(110) in an attempt to understand the nature and origin of the surface states that develop. Distinct surface states were seen to develop on n-type as the surface was exposed to oxygen. A surface state, associated with cleavage damage, was also observed on p-type. A detailed fit to the experimental data was made by using a model of the dependence of surface charge on photon energy. This was used to unfold the position and intensity of the states. States trailing into the band gap from the bulk bands were seen on both n- and p-types. The analysis also indicated that pairs of isolated states, a donor and an acceptor state, were produced. On p-type, these were present on the clean, cleaved surface while they developed with oxygen exposure on n-type. These states are consistent with the point defect states proposed by the unified defect model. The time response of the SPV signal was also recorded for these surfaces. They were analysed by careful fitting to a model describing the charging and discharging characteristics. This revealed that the midgap state on n-type had a fast and a slow component.