The importance of contact injection in undoped AlGaAs/GaAs heterostructures

A two-dimensional finite-difference analysis is used to simulate the current flow and charge distribution in undoped AlGaAs/GaAs MODFET structures called heterostructure insulated-gate field-effect transistors (HIGFETs). How an electron channel can be induced at the AlGaAs/GaAs interface when there is no doped supply layer is studied. The origins of the charge in this channel are studied by comparing its behavior in equilibrium with that when a current flows. By considering the different geometries of a Schottky gate and implanted source and drain contacts, the interrelationship between gate control and electron injection from the doped contact regions is shown and a graphic view of the origins of the interfacial charge in a HIGFET is given.>