Monte Carlo study of GaAs/Al/sub x/ Ga/sub 1-x/As MODFETs: effects of Al/sub x/Ga/sub 1-x/As composition

Monte Carlo methods are used to compare electronic transport and device behavior in n/sup +/-Al/sub x/Ga/sub 1-x/As/GaAs modulation-doped field-effect transistors (MODFETs) at 300 K for x=0.10, 0.15, 0.22, 0.30, 0.35, and 0.40. The differences between the x=0.22 and x=0.30 MODFETs with respect to parasitic conduction in Al/sub x/Ga/sub 1-x/As, gate currents, and switching times, are of particular interest. The donor-related deep levels in Al/sub x/Ga/sub 1-x/As, are disregarded by assuming all donors to be fully ionized, and the focus is only on the confinement and transport of the carriers. The following quantities are studied in detail: transfer characteristics (I/sub D/ versus V/sub G/), transconductance (g/sub m/), switching speeds ( tau /sub ON/), parasitic conduction in Al/sub x/Ga/sub 1-x/As, gate current (I/sub G/), average electron velocities and energies in GaAs and Al/sub x/Ga/sub 1-x/As, electron concentration in the device domain, k-space transfer (to low mobility L and X valleys), and details of the real-space transfer process.>