Transport Studies in Parallel Two-Dimensional Electron Gases

This thesis presents electron transport studies in GaAs-AlAs double quantum wells (DQW's) where a system of nearby parallel two-dimensional electron gases is formed. It starts from a systematic modeling of the system from a circuit level down to a microscopic quantum mechanical level based on a single electron model. A new concept of "virtual separation of node", in which different circuit nodes represent energies at the Fermi level and at the subband edge of the quantum well, enables the hierarchical modeling of the system, significantly reducing the computation time of the transient analysis. Then, two experiments, done in low temperature, demonstrate physics beyond the above framework. The first experiment shows a sudden charge transfer, when the wells are biased, associated with strong inter-layer Coulomb scattering. The other finds a strong temperature dependence of the resonant tunneling between the two wells in contrast to ordinary electron tunneling process in metal-insulator-metal junctions or semiconductors. It is argued that the electron-electron correlation originating from the small inter-layer electron spacing comparable to the intra-layer electron spacing is responsible for the former and the interaction with the external phonon bath usually neglected at low temperature for the latter. Finally, a couple of possibilities to make device building blocks out of DQW systems are discussed. In particular, a new type of junction, dubbed SD-junction, which consists of an abrupt interface between double- to single-QW interface, is proposed.