GaAs deposition on the (100) and (110) planes of gold by electrochemical atomic layer epitaxy: A low-energy electron diffraction, Auger electron spectroscopy, and scanning tunneling microscopy study

Abstract

Preliminary studies on the deposition of GaAs by electrochemical atomic layer epitaxy (ECALE) were performed. ECALE is based on the alternated underpotential deposition (UPD) of atomic layers of different elements to form a compound. Oxidative UPD of As and reductive UPD of Ga on the low-index planes of gold were studied using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and coulometry. AES and LEED were performed in an ultrahigh vacuum (UHV) surface analysis instrument interfaced to an electrochemical cell in an antechamber. This instrument configuration allowed the electrochemical treatment of the samples and their subsequent analysis in UHV without the need to transfer the samples through air. STM was performed under nitrogen at atmospheric pressure. AES and coulometry were used for surface composition analysis while LEED and STM provided structural information. The substrate was a gold single-crystal electrode with three oriented faces, each to a different low-index plane. Oxidative UPD of arsenic was observed only on the (100) and (110) faces. The resulting structures were a Au(100)(2×2)-As at 1/4 coverage and an Au(110)c(2×2)-As at 1/2 coverage. Reductive UPD of Ga was observed on all three faces, although it resulted in disordered layers of Ga oxide upon removal of the substrate from solution, due to partial oxidation of the Ga in contact with water in the absence of potential control. Stoichiometric coverages of Ga and As were obtained on the (100) and (110) surfaces when Ga was underpotentially deposited on the As covered surfaces [Au(100)(2×2)-As at 1/4 coverage and Au(110)c(2×2)-As at 1/2 coverage]. Structures displaying (2×2) and c(2×2) LEED patterns were observed on the (100) and (110) faces, respectively.