SCALING BEHAVIOR OF DELTA-DOPED ALGAAS/INGAAS HIGH-ELECTRON-MOBILITY TRANSISTORS WITH GATELENGTHS DOWN TO 60 NM AND SOURCE-DRAIN GAPS DOWN TO 230 NM

Pseudomorphic delta-doped AlGaAs/InGaAs/GaAs high electron mobility transistors with gatelengths ranging from 60 to 250 nm have been fabricated in submicron source-drain gaps using high-resolution electron beam lithography. As a consequence of short channel effects, the maximum transconductance g(m) is not improved by decreasing the gatelength from 250 nm (950 mS/mm) to 60 nm (800 mS/mm). When comparing high-frequency (HF) and direct-current values of the peak transconductances for devices with gatelengths shorter than 100 nm, the HF performance is remarkably higher. The difference can be explained by the fact that short channel effects are less important at high frequencies. Due to the decrease of the gate capacitance, the transition frequency f(T) increases as the gatelength is reduced.