Quantum interference phenomena and novel switching in split gate high electron mobility transistors

Nanometer scale electronic channels with and without a discontinuity were made in modulation-doped AlGaAs/GaAs heterojunctions using a split gate technique. Quantum interference phenomena in an electron cavity and fast switching behavior due to hot electron effects in a lateral double potential barrier structure were explored. First, one dimensional channels with a double bend discontinuity were examined in the mK temperature range. Low-field ac-conductance measurements have evidenced quantum waveguide effects: resonant features were observed in the one dimensional conductance plateaus in which the number of peaks was directly related to the geometry of the double bend. Temperature and magnetic field studies, along with a standing wave model, have provided a better understanding of quantum interference phenomena in electron wave guide and cavity structures. Secondly, a structure containing two cascaded double bend discontinuities was studied. The structure behaves as a constricted cavity coupling two point-contacts, in which the depletion by the split gate was used to form and control the lateral double potential barriers. The low temperature source-drain characteristics exhibited a pronounced S-shaped negative differential conductance that can be attributed to a nonlinear electron temperature effect along the conducting path. The data presented show two types of conducting state: electron tunneling in the off state and hot electron conduction (thermionic emission) in the on state. The estimated switching speed of the device could be as fast as 5 ps due to short transit time.