Microwave volt-impedance spectroscopy of semiconductor structure

Microwave voltage-impedance spectroscopy is used to study a semiconductor structure in the form of a doped $n$-$\mathrm{GaAs}$ film grown on a conducting $n^+$-$\mathrm{GaAs}$ substrate with a buffer sublayer. A system of concentric barrier contacts is formed on the structure surface. A technique has been developed for measuring complex impedance spectrum $Z(f,U)$ of the sample as a function of DC bias voltage $U$. Spectra $Z(f,U)$ were measured using a Cascade Microtech probe station in the frequency range $0.01$–$40$ GHz with a lateral resolution of $15$–$30$ $\mu$m at $U = 0-10$ V. The main electrophysical characteristics of a semiconductor film were determined from the spectra: type, concentration and mobility of free charge carriers, electrical conductivity. An excess resistance was found in the range $f = 0.1-20$ GHz. This effect is interpreted as the deep states (traps) recharging for two types of traps – low-frequency l and high-frequency h with characteristic time $\tau_l = 10^{-9}$ s, $\tau_h = 4.2\cdot10^{-11}$ s. A model description is proposed that explains the characteristic shape of the trap resistance spectrum, its dependence on the contact area and voltage $U$.