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

Scaling properties of n⁺-Al_xGa_1-xAs/GaAs MODFETs with submicrometer gate lengths (L_G=0.50 to 0.05 μm) 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 ≈0.10 μm. Devices with smaller gate lengths than 0.1 μm exhibit degraded transconductance (g_m), large shift in threshold voltage due to poor charge control in the channel, and a sharp reduction in output resistance (R_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_m and f_t measurements are reconciled