Effect of Heat Treatment on the Optical Properties of Heavily Doped Silicon and Germanium

Abstract

An experimental study has been made of the effect of high‐temperature vacuum heat treatment on the infrared reflectivity of heavily doped germanium and silicon. The heat treatment produces a layer on the surface with optical properties differing from those of the bulk material. From a Kramers‐Kronig analysis of the reflectivity data for an n‐type silicon sample, where the time of heating is sufficiently short to make impurity out‐diffusion unimportant, it is concluded that the changes in free‐carrier electric susceptibility indicate a decrease in the low‐frequency‐scattering relaxation time. The change in relaxation time is attributed to the introduction of extensive surface fracture from the heating. The extinction coefficient was not obtained over a sufficient spectral range to ascertain whether it follows the classical expression; however, the results for the extinction coefficient indicate an increase in the high‐frequency relaxation time.