Numerical Investigation of Laterally Downscaled Hydrogen-Terminated Diamond FETs

Hydrogen-terminated diamond (H-diamond) field-effect transistors (FETs) have been the mainstream structure of diamond microwave devices. In this article, the direct current performance and cutoff frequency ( ${f}_{T}$ ) of H-diamond FETs with the gate length ( ${L}_{G}$ ) downscaling from $2 ~\mu \text{m}$ to 50 nm are investigated by 2-D device simulation. For our central-gated device with a 6-nm-thick Al2O3 gate dielectric, the transition point of ${L}_{G}$ from the long-channel behavior to the short-channel one is found to be about 200 nm. Though notable short-channel effects appear for ${L}_{G} \le {200}$ nm such as the negative shift of the threshold voltage and the increase of the drain-induced barrier lowering, the knee voltage at a given gate voltage stays almost constant for all the considered gate length range, which is unfavorable for a small-size device with lower operating voltage. It is found the effective velocity in the channel of short-channel H-diamond FETs at the drain voltage of 7 V is less than half of the saturation velocity. The ${f}_{T}$ versus ${V}_{\text {GS}}$ relation is quite different in the short channel case and long channel case, and it is analyzed in comparison with the ${g}_{m}$ versus ${V}_{\text {GS}}$ relation.