Normally-off metamorphic AlInAs/AlInAs HEMTs on Si substrates grown by MOCVD

A combination of self-aligned fluoride-based plasma treatment and post-gate rapid thermal annealing was developed to fabricate a novel 120-nm T-shaped gate normally-off metamorphic Al_0.49In_0.51As/Ga_0.47In_0.53As HEMT device on a Si substrate grown by metal-organic chemical vapor deposition (MOCVD). A shift of the threshold voltage, from -0.42 V to 0.11 V was obtained and the shift can be effectively adjusted by the process parameter of CF₄ plasma treatment. Furthermore, a side benefit of reducing the leakage current of the device up to two orders of magnitude was also observed. E-mode transistors with 120 nm gate length own f_T up to 160 GHz and f_max of 140 GHz. These characteristics imply the potential of the fluoride-based plasma treatment technology for the fabrication of monolithic enhancement/depletion-mode mHEMTs, which also encourage the massive production with this low-cost technology.