In situ determination of free-carrier concentrations by reflectance difference spectroscopy

Abstract
We determine types and concentrations of free carriers in GaAs layers under organometallic chemical vapor deposition growth conditions from the linear electro-optic structure observed near 3 eV in reflectance-difference spectroscopy. The sensitivity is about 1017 cm−3 at 400 °C and 1018 cm−3 at 600 °C, sufficient to measure common doping levels at or near growth temperatures. We observed the transition between n- and p-type doping during atomic layer epitaxy of a carbon-doped p-type layer on an n-type substrate at 470 °C.