High-Frequency Characteristics of Charge-Injection Transistor-Mode Operation in AlGaAs/InGaAs/GaAs Metal-Insulator-Semiconductor Field-Effect Transistors

An AlGaAs/InGaAs/GaAs pseudomorphic metal-insulator-semiconductor field-effect transistor (MISFET) was investigated both in FET- and charge-injection transistor (CHINT)-mode operation. It is demonstrated that a CHINT-mode operation and a large negative differential resistance as well as good FET characteristics can be obtained in MISFETs with a very thin gate barrier layer. Furthermore, the cutoff frequency in CHINT mode-operation was 32 GHz for a MISFET with a gate length of 1 µm. This is about twice as large as that obtained in FET-mode operation. The equivalent circuit analysis revealed that the output conductance and the source resistance play an important role in determining the cutoff frequency, in contrast to ordinary FETs. The intrinsic cutoff frequency ( R s =0) was as large as 57 GHz.