Enhancement-Mode Pseudomorphic $\hbox {In}_{0.22} \hbox {Ga}_{0.78}\hbox {As}$ -Channel MOSFETs With Ultrathin InAlP Native Oxide Gate Dielectric and a Cutoff Frequency of 6

Enhancement-mode pseudomorphic In_0.22Ga_0.78As-channel MOSFETs with an ultrathin native InAlP oxide gate dielectric are demonstrated. The gate dielectric, a 3.5-nm-thick oxide grown by wet thermal oxidation from epitaxial InAlP, reduces the gate leakage below that of HFETs based on the same epitaxial structure by more than 10⁵ times. The devices operate in enhancement mode, with 0.25-μm gate length devices exhibiting a measured threshold voltage of 0.25 V, a peak intrinsic transconductance of 245 mS/mm, and a saturation drain current density of 165 mA/mm. A record-high current gain cutoff frequency f_T of 60 GHz has also been achieved. These results indicate the applicability of InAlP oxide-based InGaAs-channel MOSFETs for use in single power supply RF applications.