CHARACTERIZATION OF DEPLETION-TYPE SURFACE TUNNEL TRANSISTORS

A depletion-type Surface Tunnel Transistor (D-STT) is proposed to increase the tunneling current compared to that of the enhancement-type STT (E-STT) previously reported. The most important feature of the D-STT is the use of a modulation doped structure in order to accumulate a high concentration of electrons under the gate. GaAs/AlGaAs D-STTs, which are fabricated by using an MBE regrowth technique, exhibit depletion-mode transistor action with a larger operation current than that displayed by the E-STT. This increase in current is due to a higher two-dimensional electron gas concentration at the i-GaAs surface. Moreover, the high gate leakage current which limits GaAs E-STT operation is reduced in the case of the D-STT by a factor of 10(6).