InGaAs/InAlAs heterostructure diodes for application to high-speed semiconductor-gated FET´s

We have investigated n⁺InGaAs/InAlAs/n^-InGaAs heterostructures suitable for application as SISFET gates through capacitance-voltage and current-voltage characteristics of mesa diodes at room temperature. Flat-band voltages are nearly ideal, indicating a low level of fixed charge in the barrier. Current-voltage characteristics are rectifying, due to the formation of a depletion layer in the lightly doped channel. Excess reverse current is attributed to back-diffusion of dopant from the gate into the barrier, and we have shown that it is controlled by the interposition of an undoped spacer layer between the barrier and the gate. Forward current scales with the electric field, rather than the potential, demonstrating the need for an improved theory of conduction at low bias. We have assessed prospects for application of these structures to high-speed FET´s, and find that enhancement-mode operation to voltages above 1 V should be practical.