Noncontact doping level determination in GaAs using photoreflectance spectroscopy

Shifts of the band edge in GaAs layers as measured by photoreflectance (PR) spectroscopy have been accurately calibrated to the N-type doping level (Nd). 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/δNd=5.8±0.5×10−20 eV cm3 for 1×1016 cm−3 ≤Nd≤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 Nd.