Influence of ion beam on optical properties of GaAs: Calculation using the fractional-derivative-spectrum method

Semiconductor GaAs (100) was implanted with In+ at a room temperature. Fluences of implanted ions were from 1x 1012 cm-2 to 3x1013 cm-2 and the energy was equal to 85 keV. The detectability of the indium content in near surface layer of GaAs has been studied with the use of the secondary ion mass spectrometry (SIMS). The depths distribution of a indium concentration measured by SIMS method ware compared with depth profiles calculated with the help of SATVAL code. It was noticed that calculated profiles are in a good agreement with the measured values. Additionally, the concentration of indium in the near surface layer increased with growing of the implantation fluence and a maximum of these profiles shift in the side of ions exposed surfaces of GaAs. This effect can be explained by self-diffusion process of target atoms and indium during the implantation. The fractional derivative spectrum (FDS) model in connection with spectroscopic ellipsometry ES was used for particular optical analyses of implanted GaAs substrates. The FDS is especially promising technique when the limitations of the standard treatment by Lorentz shape line analysis occur and it is very helpful to extract basic information on relevant physical quantities from the detected εE2(E) spectra determined by spectroscopic ellipsometry. In particular, using spectroscopic ellipsometry and FDS, the critical points E1 and E1+Δ observed in the εE2(E) spectra in the implanted substrates have been investigated. The differences in complex refractive index and dielectric function (ε=ε1+iε2) between GaAs substrate before and implantation were observed. Moreover, the several nanometres thick oxide layer on GaAs surface was detected. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)