Trap characterization by gate-drain conductance and capacitance dispersion studies of an AlGaN/GaN heterostructure field-effect transistor

Gate-drain capacitance and conductance measurements were performed on an Al_0.15Ga_0.85N/GaN heterostructure field-effect transistor to study the effects of trap states on frequency-dependent device characteristics. By varying the measurement frequency in addition to the bias applied to the gate, the density and time constants of the trap states have been determined as functions of gate bias. Detailed analysis of the frequency-dependent capacitance and conductance data was performed assuming models in which traps are present at the heterojunction (interface traps), in the AlGaN barrier layer (bulk traps), and at the gate contact (metal-semiconductor traps). Bias-dependent measurements were performed at voltages in the vicinity of the transistor threshold voltage, yielding time constants on the order of 1 μs and trap densities of approximately 10¹²cm^-2eV^-1.