Analysis of trap states effects on the frequency-dependent capacitance and conductance of an AlGaN/GaN heterostructure

The work presented in this paper consists of trap characterization of an Al_0.25Ga_0.75N/GaN heterostructure field effect transistors. Measurements of the gate-source capacitance and conductance of the High Electron Mobility Transistors HEMT Al_0.25Ga _0.75N/GaN were performed in order to study the frequency dependent characteristics induced by the effect of the interface states. By varying the frequency measurement and the bias applied to the gate, the density and the time-constant of the trap states have been determined. The analysis of the measured data was performed assuming models in which the traps are present at the interface of the heterojunction. A time-constant on the order of 4 mus and a density of about 10¹² cm^-2 eV^-1 were calculated.