Characterization of AlGaN/GaN MISHFETs on a Si substrate by static and high-frequency measurements

AlGaN/GaN/Si metal–insulator–semiconductor heterostructure field-effect transistors (MISHFETs) with SiN and Al2O3 gate insulators are characterized by static and high-frequency measurements, and their performance is compared with nonpassivated and SiN-passivated heterostructure field-effect transistors (HFETs). The saturation drain current increased from ∼500 mA mm−1 for the HFETs to ∼770 mA mm−1 for the MISHFETs. The peak extrinsic transconductance of the MISHFETs (147 mS mm−1 for 8 nm SiN and 220 mS mm−1 for 4 nm Al2O3) is higher than expected due to the increased gate-to-channel separation. Similarly, small signal microwave characterization yielded an increase in the current gain cut-off frequency (from 3.2 to 7.2 GHz) and the maximum frequency of oscillation (from 12.3 to 20.4 GHz) for the MISHFETs with 2 µm gate length compared to the HFET counterparts. Finally, the density of trap states, evaluated from the frequency-dependent conductance measurements, was ≅3 × 1012 cm−2 eV−1 for the HFETs but only ≅1.8 × 1012 cm−2 eV−1 for the MISHFETs. All of these demonstrate the capability of AlGaN/GaN MISHFETs of preparing high-performance and cost-effective devices for high-power microwave applications on a Si substrate