Scaling properties and short-channel effects in submicrometer AlGaAs/GaAs MODFET's: A Monte Carlo study

Scaling properties of n/sup +/-Al/sub x/Ga/sub 1-x/As/GaAs MODFETs with submicrometer gate lengths (L/sub G/=0.50 to 0.05 mu m) are examined, using Monte Carlo methods. High-frequency performance of MODFETs can be improved by scaling the gate lengths, but various studies suggest that there exists a lower limit for the gate after which no improvement should be expected. The lower limit is determined here to be approximately=0.10 mu m. Devices with smaller gate lengths than 0.1 mu m exhibit degraded transconductance (g/sub m/), large shift in threshold voltage due to poor charge control in the channel, and a sharp reduction in output resistance (R/sub o/). It is shown that the drain current saturation in MODFETs is not caused by the velocity saturation effect, but by channel pitch-off. Electron velocities calculated from Monte Carlo simulations and extracted from g/sub m/ and f/sub t/ measurements are reconciled.<
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