Noncontact doping level determination in GaAs using photoreflectance spectroscopy

Abstract

Shifts of the band edge in GaAs layers as measured by photoreflectance (PR) spectroscopy have been accurately calibrated to the N‐type doping level (N_d). Samples produced by controlled Si‐doping experiments using ion implantation of GaAs substrates and GaAs doped with Si to known levels during growth by molecular‐beam expitaxy have been investigated with this technique. A measurable change in the location of the band gap (E) determined from PR directly correlates with the maximum N‐type doping level as determined via C‐V for both types of samples with a change of band gap δE/δN_d=5.8±0.5×10⁻²⁰ eV cm³ for 1×10¹⁶ cm⁻³ ≤N_d≤8×10¹⁷ cm⁻³. Correlations were also made to sheet carrier concentration (Hall measurements). This method is shown to be fast, accurate, and easily applicable to uniformity studies and a viable alternative to either C‐V or Hall measurements for nondestructive determination of N_d.