Electroreflectance and photoreflectance study of the space-charge region in semiconductors: (In-Sn-O)/InP as a model system

We have investigated the electroreflectance (ER) and photoreflectance (PR) spectra from the space-charge region (SCR) of the model Schottky- barrier system (${\mathrm{In}}_2$ ${\mathrm{O}}_3$ ${)}_{0.91}$(${\mathrm{SnO}}_2$ ${)}_{0.09}$ on p-type InP [(In-Sn-O)/InP]. Both ER and PR were studied as a function of reverse dc bias, $V_{\mathrm{bias}}$. The observed Franz-Keldysh oscillations provide a direct measure of the surface dc electric field, ${\mathrm{scrE}}_{\mathrm{dc}{}^s}$. The ac modulating voltage (for small modulation) affects only the envelope of the FKO but not the period. A generalized Franz-Keldysh theory, taking into consideration the presence of dc fields, accounts for the above experimental results. From a plot of (${\mathrm{scrE}}_{\mathrm{dc}{}^s{)}^2}$ as a function of $V_{\mathrm{bias}}$ we have obtained the built-in potential and net carrier concentration of the structure. Our work demonstrates that electromodulation in Schottky barriers can be used as an optical Mott-Schottky method.