Monte Carlo study of GaAs/Alx Ga1-xAsMODFETs: effects of AlxGa1-xAs composition

Monte Carlo methods are used to compare electronic transport and device behavior in n⁺-Al_xGa_1-xAs/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_xGa_1-xAs, gate currents, and switching times, are of particular interest. The donor-related deep levels in Al_xGa_1-xAs, 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_D versus V _G), transconductance (g_m), switching speeds (τ_ON), parasitic conduction in Al_xGa _1-xAs, gate current (I_G), average electron velocities and energies in GaAs and Al_xGa_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