Sacrificial Self-Assembled Monolayers for the Passivation of GaAs (100) Surfaces and Interfaces

The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga-S and As S bonds at the GaAs thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 degrees C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of 0 (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al S bonds without introducing any additional band bending. This indicates that the surface preparation of n type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending.