Enhancement-mode GaAs metal-oxide-semiconductor high-electron-mobility transistors with atomic layer deposited Al2 O3 as gate dielectric

Enhancement-mode GaAs metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with ex situ atomic-layer-deposited Al2 O3 as gate dielectrics are studied. Maximum drain currents of 211 and 263 mAmm are obtained for 1 μm gate-length Al2 O3 MOS-HEMTs with 3 and 6 nm thick gate oxide, respectively. C-V characteristic shows negligible hysteresis and frequency dispersion. The gate leakage current density of the MOS-HEMTs is 3-5 orders of magnitude lower than the conventional HEMTs under similar bias conditions. The drain current on-off ratio of MOS-HEMTs is ∼3× 103 with a subthreshold swing of 90 mV /decade. A maximum cutoff frequency (fT) of 27.3 GHz and maximum oscillation frequency (fmax) of 39.9 GHz and an effective channel mobility of 4250 cm2 V s are measured for the 1 μm gate-length Al2 O3 MOS-HEMT with 6 nm gate oxide. Hooge's constant measured by low frequency noise spectral density characterization is 3.7× 10-5 for the same device.