Morphology of the implantation-induced disorder in GaAs studied by Raman spectroscopyand ion channeling

Abstract

Disorder was introduced into GaAs by implantation of $^{30}\mathrm{Si}^{+}$ions, using a very wide range of ion doses, dose rates, and implant temperatures, and studied by Raman scattering (RS) and Rutherford backscattering ion channeling (RBS). RS spectra were deconvoluted consistently and systematically into up to four components, one of them being an apparent background signal interpreted here as a boson peak. Arguments are given that this signal represents the second amorphous phase different from a continuous random network. An intercascade distance model (ICD) was postulated, which estimates the average distance, ${\mathrm{L}}_{\mathrm{ICD}}$, between implantation-induced cascades as a function of ion dose. An analogous parameter, ${\mathrm{L}}_{\mathrm{RBS}}$, was calculated from the RBS damage fraction ${\mathrm{f}}_{\mathrm{RBS}}$. From RS data the correlation length ${\mathrm{L}}_{\mathrm{RS}}$, representing the size of crystalline regions with preserved translational symmetry, was determined by fitting the LO signal within the spatial correlation model. All three L's agree nicely, proving the equivalency of the correlation length and intercascade distance. This enabled a straightforward comparison of relevant signals and a direct correlation between RS and RBS. While measure of damage in RBS (${\mathrm{f}}_{\mathrm{RBS}}$) reflects the disordered volume fraction of the implanted layer, RS measures simultaneously the lowering of the translational symmetry (an effect that prevails at lower doses) and the fraction of disordered volume (prevailing at higher doses). A considerable difference in sensitivity between RS and RBS to particular defects enabled the differentiation of six different types of implantation-introduced disorder.