On the characterization of surface states and deep traps in GaAs MESFETs

Abstract

A simple model of frequency-dependent transconductance ( g′ m( f)) is developed for characterizing surface states and bulk traps in GaAs metal semiconductor field effect transistors (MESFETs) by considering the occupancy modulation of the surface states and bulk traps. It is shown that the transconductance dispersion provides information for the determination of surface state and bulk trap energy levels. In particular, it is shown that the peak frequency in the transconductance spectrum, d g′ m( f)/d f vs f, is equal to the characteristic frequency of a surface state or a bulk trap that is responsible for the peak. Thus, the temperature dependence of the peak frequency facilitates the measurement of the surface state or bulk trap energy level. It is found that peaks due to surface states can be distinguished from those due to bulk traps in the gated channel region by their different dependence of peak heights on the gate-source reverse bias. A comparison of the theoretical results and the available experimental observations shows that the model can successfully explain both the surface leakage current dependence of transconductance dispersion magnitude reported by Ozeki et al. [ Inst. Phys. Conf. Ser., No. 63, pp. 323–328 (1982)] and the temperature dependence of transconductance dispersion observed by Blight et al. [ IEEE Trans. Electron Devices ED-35, 257–267 (1988)].