Water adsorption on the P-rich GaP(100) surface: Optical spectroscopy from first principles

TL;DR

This study uses first-principles optical spectroscopy to analyze water interaction with the P-rich GaP(100) surface, revealing a water-induced hydrogen-rich phase and demonstrating the feasibility of computational RAS for semiconductor-electrolyte interfaces.

Contribution

It introduces a first-principles approach to interpret RAS spectra of water-adsorbed GaP surfaces, highlighting the surface reordering without oxidation and potential for future interface studies.

Findings

Water induces a hydrogen-rich phase on GaP(100) surface

Computational RAS accurately reproduces experimental spectra

RAS is sensitive to surface electric fields and Helmholtz-layer effects

Abstract

The contact of water with semiconductors typically changes its surface electronic structure by oxidation or corrosion processes. A detailed knowledge - or even control of - the surface structure is highly desirable, as it impacts the performance of opto-electronic devices from gas-sensing to energy conversion applications. It is also a prerequisite for density functional theory-based modelling of the electronic structure in contact with an electrolyte. The P-rich GaP(100) surface is extraordinary with respect to its contact with gas-phase water, as it undergoes a surface reordering, but does not oxidise. We investigate the underlying changes of the surface in contact with water by means of theoretically derived reflection anisotropy spectroscopy (RAS). A comparison of our results with experiment reveals that a water-induced hydrogen-rich phase on the surface is compatible with the boundary conditions from experiment, reproducing the optical spectra. We discuss potential reaction paths that comprise a water-enhanced hydrogen mobility on the surface. Our results also show that computational RAS - required for the interpretation of experimental signatures - is feasible for GaP in contact with water double layers. Here, RAS is sensitive to surface electric fields, which are an important ingredient of the Helmholtz-layer. This paves the way for future investigations of RAS at the semiconductor-electrolyte interface.