Growth, characterization, and stability testing of epitaxial MgO (100) on GaAs (100)

Abstract

Epitaxial MgO (100) films have been grown on GaAs (100) by evaporation of Mg in the presence of 5 × 10 -6 Torr of oxygen. Prior to the growth of MgO, the GaAs (100) substrate was cleaned by Ar ion sputtering and annealing. MgO (100) on GaAs (100) was in situ characterized with Auger electron spectroscopy (AES), and ex situ by scanning electron microscopy (SEM), X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX). X-ray diffraction patterns indicated that the MgO film has grown predominantly in the cubic phase with the (100) plane parallel to the GaAs ( 100) substrate. HRTEM results have confirmed the epitaxial growth of MgO with MgO (100)[001]║ GaAs (100)[001]. Despite the high lattice misfit, the epitaxial MgO ( 100) is grown on GaAs (100) due to the 4 : 3 relationship (4 aMgO : 3 aGaAs) between MgO (100) and GaAs (100). The formation of a 4:3 superstructure reduces the lateral misfit between MgO (100) and GaAs (100) to 0.65%. To test the potential of MgO as a protection layer for III-V semiconductor based photo-electro catalytic devices for water splitting in alkaline media the reaction of MgO films with H2O and NaOH was investigated. Flake-like Mg(OH)2 structures appear to have formed on top of the MgO films treated with NaOH.

Toward Large‐Scale Hydrogen Production from Water: What Have We Learned and What Are the Main Research Hurdles to Cross for Commercialization?

“…There are emerging efforts to protect this front side (made of GaAs, GaInP, and similar III–V semiconductors) by epitaxy layers of a wider‐bandgap metal oxide with the CB edge (or defect states within its bandgap energy) suitable to extract excited electrons. [ 64,65 ] This strategy, if successful, will bring with it further complications. The deposition of metal nanoparticles on top of the protective oxide needs to be in the order of 0.01–0.05 monolayer to prevent light scattering and the formation of bubbles upon H 2 production at high light flux affects light penetration.…”