Optical determination of Fermi-level pinning using electroreflectance

Abstract

We have investigated the low-field electrolyte electroreflectance (EER) spectra of matte, polycrystalline, electrodeposited $n$-CdSe in the vicinity of the ${E}_{0}(A,B)$ transitions (direct gap at $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}=0$. As the applied bias voltage ${V}_{\mathrm{dc}}$ is varied from near flatband to depletion, the EER amplitude for electrodeposited CdSe decreases by a factor of \ensuremath{\sim}40. We interpret this decrease in EER signal as evidence of Fermi-level pinning, which we attribute to the presence of surface states.