Thermal Vapor Sulfurization of Ultrathin GaAs Layers on Sapphire Substrates Prepared by Direct Growth and Lift-Off and Transfer

Abstract

We have studied the structural, morphological, and lattice vibrational properties of GaAs thin films upon thermal vapor sulfurization (TVS) at elevated temperatures. The GaAs layers, 10∼30 nm in thickness, directly grown on c-plane sapphire substrates by molecular beam epitaxy (MBE) consisted of (111)-oriented crystallites with noncrystal arsenic inclusions. Upon TVS, nucleation of crystalline arsenic occurred and the nucleation developed at consuming GaAs with increasing the temperatures up to 650°C. X-ray photoelectron spectroscopy (XPS) and transmission-electron microscopy (TEM) revealed that the crystalline arsenic was covered by a thin layer of Ga2S3. In comparison, the GaAs layer grown on a GaAs (111) substrate after an AlAs scarification layer consisted of (111)-oriented micron-sized GaAs islands and crystalline arsenic inclusions. This layer, after lift-off and transferred onto sapphire, was converted to Ga2S3 by TVS without crystalline arsenic incorporations. These results shed light on fabricating Ga2S3 and its layered semiconductor/semimetal composites for consequent metamaterial applications in optical and optoelectronic devices.