# Photoelectron Spectroscopic Determination of the Interfacial Energetics of Metal Oxide Protection Layers on p‑InP Photocathodes

## TL;DR

This study uses photoelectron spectroscopy to determine how different metal oxides affect the energy levels at the interface with p-InP photocathodes.

## Contribution

The paper provides new insights into the interfacial energetics of metal oxide protection layers on p-InP photocathodes.

## Key findings

- TiO2 and Nb2O5 facilitate electron transfer at the interface with p-InP.
- Ta2O5 and HfO2 block electron transfer at the interface with p-InP.
- All oxides block hole transport, suppressing oxidative degradation of p-InP.

## Abstract

The interfacial energetics
between p-type InP and a series of metal
oxides, including TiO2, Nb2O5, Ta2O5, and HfO2, were evaluated using X-ray
photoelectron spectroscopy, ultraviolet photoelectron spectroscopy,
and optical absorption spectroscopy. The energy of the conduction
band minimum (E
cb) of TiO2 and
Nb2O5 was more negative (i.e., further from
the vacuum level) than the conduction band minimum at the surface
of InP (E
cb,s,InP), whereas E
cb for Ta2O5 and HfO2 was more positive than E
cb,s,InP. The data
are consistent with the electrochemical behavior of p-InP coated with
various metal oxide candidate protection layers, with TiO2 and Nb2O5 facilitating interfacial transfer
of photogenerated minority-carrier electrons in p-InP photocathodes,
and Ta2O5 and HfO2 blocking photogenerated
electrons in p-InP from readily transferring across the oxide-coated
photocathodes. The energy of the valence band maximum (E
vb) for all of the oxides was much more negative than E
vb,s,InP, consistent with observations that these
protection layers effectively block hole transport and consequently
suppress oxidative degradation of the underlying p-InP photocathodes.