Physics and applications of semiconductor nanostructures, Spin effects in semiconductors
A semiconductor nanostructure is usually some combination of semiconductors in layered form created by fancy (and expensive)growth methods (See Professor H. Luo), which may be further patterned in one or both of the lateral dimensions either lithographically or by growth techniques. The characteristic dimensions of such structures lie in the range of 1 to 100 nanometers(thus the name). Since these dimensions are comparable to or less than the characteristic wavelength (the deBroglie wavelength) of charge carriers in semiconductors, the resulting structures confine electrons or holes quantum mechanically in one or more directions. This confinement (sounds vaguely criminal, doesn't it?) leads to electronic behavior that is characterized as quasi-two-dimensional, quasi-one-dimensional or quasi-zero-dimensional, and the confining structures are often called quantum wells, quantum wires and quantum dots, respectively. The lowered dimensionality leads to some very interesting behavior, some of which is well-understood and has led to applications such as quantum-well lasers and detectors, quantum cascade lasers, and high electron mobility transistors. Other areas, including electron-electron interactions and spin effects (see below) are not as well understood.
We're interested in contributing to understanding the latter and in devising new applications of these structures.Understanding spin effects in semiconductors is important in the context of the rapidly developing field of Spintronics. In very simple terms conventional electronics is concerned with manipulating the charge of the electron via (usually) electric fields toper form various useful functions (e.g., logic, memory, amplification, etc.). Generally speaking, Spintronics can be described as activities directed at manipulating another intrinsic property of the electron, its spin, to perform improved, or entirely new functions. Producing, characterizing and understanding the basic physics of ferromagnetic semiconductors (particularly materials like GaMnAs, GaMnSb and GaMnAs), as well as fabricating and studying device building blocks, are all areas of interest in Professor McCombe's laboratory (in collaboration with Professor H. Luo and others in the Department). This work is presently part of the research activities of a large consortium funded by a DARPA/ONR SpinS grant; UB is the lead institution.Within these rather broad and rapidly expanding areas his specific interests are: electron-electron and electron-hole interactions, particularly for magneto-excitons and charged magneto-excitons in quantum wells and quantum dots; how reduced dimensionality affects the electron-optical phonon interaction; vibrational modes in nanoparticles; optical, infrared and far infrared properties of Mn in III-V semiconductors; and magnetic and magneto-transport properties of Ferromagnetic semiconductors.Professor McCombe employs visible, near infrared and far infrared spectroscopic techniques and electrical transport technique sat low temperatures and high magnetic fields to obtain information relevant to the above interests.