Small signal electrical circuit of a Schottky diode based on microwave spectrometry data

Microwave volt-impedance spectroscopy was used to study homogeneous $n$-Si and structured $n$-GaAs samples with a system of concentric barrier contacts on the surface. For the Si sample we have reconstructed the spectra of the complex impedance $Z( f , U)$ ($U$ is the bias voltage on the contact). Measurements have been done in the frequency range $f$ = 0.01–67 GHz with a lateral resolution of 20–50 $\mu$m. Based on the spectra, the electrophysical characteristics of the semiconductor were determined: type, concentration and mobility of free charge carriers, specific conductivity, contact potential difference. Excess resistance and capacitance difference $C(f\to0)>C(f\to\infty)$ of the Schottky contact were detected at $f$ = 0.1–20 GHz. The microwave small-signal electric circuit of the Schottky contact is proposed. It is characterized by two time scales: low-frequency $\tau_l=(0.5-1)\cdot 10^{-9}$ s and high-frequency $\tau_h=(3-4)\cdot 10^{-11}$ s. In addition to the previously performed studies of the GaAs sample the microwave spectra $Z(f)$ were measured upon the sample heating to temperature $T$ = 100$^\circ$C and at low frequencies $f$ = 10$^2$–10$^6$ Hz with a temperature pass at $T$ = 77–345 K. Based on all studies, the previously given hypothesis which relate the observed microwave effects with the deep states (traps) recharging was not confirmed. We proposed another interpretation, explaining the effects by the features of charge carrier transport in the depletion layer of the Schottky contact. The possibilities of a physical justification for this mechanism are discussed.