Modulated reflectance study of strain in epitaxial GaAs on silicon

Abstract

The electrolyte electroreflectance technique was used to study the nature of the strain in epitaxial layers of GaAs grown by laser-assisted metalorganic chemical vapor deposition on (100) Si substrate. The GaAs epilayer, about 140 nm thick, was chemically etched in steps of about 20 nm and spectra of the differential reflectivity (ΔR/R) versus energy were recorded in the 2.4–4.0 eV region immediately following each etch procedure. The E1 and E1+Δ1 transitions of GaAs and their broadening parameters were calculated using the low-field analysis of the electrolyte electroreflectance line shapes. The uniformity of carriers and the effects of the etching procedure were studied with three-dimensional amplitude maps. The variations of the spectral characteristics are interpreted in terms of strains and electronic changes as one approaches the GaAs-Si interface.