Electro-optical effects at the discrete and continuum exciton states in GaAs

We report electroreflectance spectra from a GaAs-Au Schottky barrier interface, in the region of the fundamental energy gap, at a temperature of ～ 1.8 K. Both the ground exciton level and the continuum of states are investigated separately, by operating in the small modulation and in the on-off field limit, respectively. The field profile is monitored by I–V, C-V, and photovoltage measurements. It is found that, even at ～ 1.8K, a high surface field is generally present. This moves the actual reflecting boundary of the exciton-polariton away from the surface and affects the ER lineshape through field-induced inhomogeneity effects and interference across the high field layer below the surface. The spectra corresponding to the states of the continuum are discussed in terms of the recent calculations of photon-assisted tunneling with coulomb interaction.