Back bias effects on two-dimensional electron gas

A new technique is described to study heterostructure field-effect transistors. This technique is based on the application of an electric field perpendicular to the channel via a p-doped substrate. The measurements demonstrate that the centroid of the two-dimensional electron gas resides approximately 10 nm below the heterointerface and that application of a negative substrate potential increases the confinement of these charges towards the interface. A negative substrate voltage decreases the K' factor of the transistor and also reduces the well capacity. Capacitance voltage measurements confirm that a parasitic channel in the donor layer can be formed and that it is shielded from the substrate by the two-dimensional electron gas.