Investigation of trapping effects in AlGaN/GaN/Si field-effect transistors by frequency dependent capacitance and conductance analysis

摘要

We report on frequency dependent capacitance and conductance analysis of the AlGaN/GaN/Si heterostructure field-effect transistors (HFETs) and Al_2O_3/AlGaN/GaN/Si metal-oxide-semiconductor HFETs (MOSHFETs) in order to investigate the trap effects in these devices. The capacitance of the HFETs exhibits significantly higher frequency dispersion than that of the MOSHFETs. Two different types of traps were found from the conductance analysis on both types of devices, fast with the time constant τ ≈ (0.1-1) μs and slow with τ = 8 ms. The density of trap states evaluated on the HFETs was D_T ≈ 2.5 × 10~(12) and up to 10~(13) cm~(-2) eV~(-1) for the fast and slow traps, respectively. Analysis of the MOSHFETs yielded only slightly lower D_T of the fast traps (≈ 1.5 × 10~(12) cm~(-2) eV~(-1)), but nearly two orders of magnitude lower density of slow traps (≤ 4 × 10~(11) cm~(-2) eV~(-1)) than those of the HFETs. This indicates an effective passivation of slow surface related traps but less influence on fast (probably bulk related) trapping states by applying an insulator on the AlGaN/GaN HFET.