Determination of the free carrier concentration in ultra-pure GaAs epilayers by a photoreflectance technique

Abstract

A new method for the diagnostics of high-quality n-GaAs epilayers grown by vapor phase epitaxy in an open chloride system has been developed and implemented. As the free carrier concentration in the material decreases from 1015 to 1011 cm−3 and the quality of epilayers increases, the photoreflectance spectra of GaAs exhibit a change from the traditional Franz-Keldysh (FK) oscillations (enhanced by the exciton effects) to a weak oscillatory structure observed in the region of exciton transition energies. It is shown that the periods of this structure are close to that of the FK oscillations.