DOUBLE-QUANTUM-WELL SEGMENTS IN BALLISTIC DIODE BASES

We consider space charge limited ballistic electron transport in short current-conducting channels formed by single and double quantum well segments. Independent contacts to the bottom-well and the top-well for ming the double quantum well segment is stipulated. Three different st ructures are simulated: a resonant overlap structure, a resonant cover structure, and a coupler structure. It is shown that anode currents i n these structures oscillate with increasing voltage across the struct ure, resulting in repeatedly N-shaped current-voltage (I-V) characteri stics. A modulation level of the current oscillations is close to 100% . The shape of these oscillations is substantially asymmetric both for the overlap and the cover structures. The asymmetry is due to a very strong nonlinear space charge modulation, and N-shaped parts of I-V ch aracteristics can become Z-shaped when a strong tunnel connection in t he double quantum well segment takes place. In the coupler structure t he modulation of partial anode currents flowing out through each of tw o anodes, which are independently contacted to the bottom-well and the top-well, occurs only. The space charge increases monotonously with t he voltage. Justification criteria of the classic approach used in our calculations are discussed in detail. (C) 1998 American Institute of Physics. [S0021-8979(98)00603-3].