Flatband Electroreflectance of Gallium Arsenide. I. Experimental Results

Abstract

The electroreflectance (ER) spectrum of $n$-type gallium arsenide in the 1. 2-5. 3-eV photon energy range has been measured. It was found from examination of the direct-edge $\ensuremath{\Delta}{\ensuremath{\epsilon}}_{1}$ line shapes and collaborative differential capacitance measurements that quite uniform fields were obtained. The interference between the light- and heavy-hole contributions to the ER signal at ${E}_{0}$ was observed. The data were obtained using the electrolyte technique with potentiostatic control. The condition of no space-charge region, flatband, was determined by utilizing the even field dependence of the Franz-Keldysh effect. Square-wave modulation of the space charge from the flatband condition to several depletion-field values was used for the data presented. The ER line shapes at the direct edge provided a means for determining the importance of field inhomogeneity and broadening effects as well as a determination of electric field values. $\ensuremath{\Delta}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\epsilon}}$ was computed from a Kramers-Kronig transformation of $\frac{\ensuremath{\Delta}R}{R}$.