Single-gated mobility modulation transistor

We have investigated an n-type field effect transistor based on a GaAs/AlGaAs structure with a channel which consists of two tunnel-coupled quantum wells. Modulation of channel conductivity is achieved through a change in electron mobility under the effect of anticrossing of quantization levels in wells while the concentration of carriers remains practically constant. With proper choice of the structural layout and doping profile, the transistor can be effectively controlled by the front gate only. The possibility of obtaining the highest amplitude of conductivity modulation by electron mobility suppression in one of the quantum wells and by varying tunnel coupling between the wells is investigated by numerical simulations. It is shown that. with a gradual decrease of electron mobility in one of the quantum wells, the conductivity modulation amplitude first increases, comes to a maximum, and then decreases due to suppression of tunnel coupling between wells by scattering of longitudinal momentum. The drain current dependence on the gate voltage of the device under investigation shows two maxima; this feature allows the same device to be used as both an n- and p-type transistor.