Ground-state properties of double-wire semiconducting systems

Abstract

With the recent advances in nanometer-scale semiconductor device fabrication technology, it became experimentally possible to produce strongly confined electron systems. Quantum wires are among these systems, and are attracting increasing interest due to their potential applications in solid-state device technology such as high-speed transistors, efficient photodetectors and lasers. Quantum wires are quasi-one-dimensional systems where electrons are free to move in one dimension, but their motion is restricted in the remaining two dimensions. Various models for qucisi-one-dimensional structures have been proposed in the literature, such as cylindrical, square-well and parabolic confinements. in this thesis, we examine ground-state correlations in double-quantum-wire systems within the self-consistent scheme of Singwi et ai, namely the STLS approximation. The model we adopt consists of two parallel cylindrically-confined quantum wires. The cases when both wires have electrons as charge carriers and when one wire has electrons while the other has holes are considered. Under the assumption that only one subband is occupied in each quantum wire and there is no tunneling between them, we calculate the local-field factors and static correlation functions. Ground-state energy and collective modes are discussed within the RPA, Hubbard and STLS approximations in order to compare the results. Charge-density-wave instabilities in these structures are examined at small and finite q values. Our numerical results are given for systems where the carrier densities and the radii of both wires are equal. As the charge carrier density is lowered, we observe that the importance of local field corrections increases so that the RPA or Hubbard approximations do not give reliable results in this region. We find that the interwire correlations become quite important for electron-hole systems. Taking into account the exchange-correlation hole around electrons, STLS provides a much better description to this many-body problem compared to the previous models.