Unified mechanism of the surface Fermi level pinning in III-As nanowires

TL;DR

This study reveals a unified Fermi level pinning mechanism at oxidized surfaces of III-As nanowires, linked to arsenic accumulation, using advanced microscopy and spectroscopy techniques.

Contribution

It demonstrates a common Fermi level pinning position across various III-As alloys and identifies surface arsenic as the key factor influencing pinning.

Findings

Fermi level pinned at 4.8 eV for multiple alloys

Photooxidation causes arsenic accumulation on surfaces

Arsenic presence correlates with Fermi level pinning

Abstract

Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs, InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe microscopy, we show that the Fermi level at oxidized cleavage surfaces of ternary Al$_{x}$Ga$_{1-x}$As (0$\le$x$\le$0.45) and Ga$_{x}$In$_{1-x}$As (0$\le$x$\le$1) alloys is pinned at the same position of 4.8$\pm$0.1 eV with regard to the vacuum level. The finding implies a unified mechanism of the Fermi level pinning for such surfaces. Further investigation, performed by Raman scattering and photoluminescence spectroscopy, shows that photooxidation of the Al$_{x}$Ga$_{1-x}$As and Ga$_{x}$In$_{1-x}$As nanowires leads to the accumulation of an excess arsenic on their crystal surfaces which is accompanied by a strong decrease of the band-edge photoluminescence intensity. We conclude that the surface excess arsenic in crystalline or amorphous forms is responsible for the Fermi level pinning at oxidized (110) surfaces of III-As nanowires.