This research involves a study of the materials science and physics of the growth of very high-quality GaAs/AlxGa1-x heterojunction thin- film structures using the molecular beam epitaxy technique, and the new electron interaction physics expected to manifest in such ideal electron systems. Very low-disorder, dilute two-dimensional (2D) electron and hole systems at the GaAs/AlGaAs interface in the regime of very small Landau level fillings where transitions between quantum liquid and solid states of the system are expected will be studied. Several novel quasi-2d systems with an additional degree of freedom will also be studied. These include systems which contain two or more layers of electrons in close proximity so that interlayer Coulomb interactions are strong, and thick-layer electron systems in wide parabolic wells. The additional degree of freedom in these structures is expected to lead to new collective sates such as the recently observed fractional quantum Hall state at the even 1/2 denominator filling in a double-layer electron system. These systems will be probed via low-temperature magnetotransport measurements. %%% The impact of this advanced materials research program is two-fold. First, optimization of molecular beam epitaxy growth techniques to produce very high-quality, selectively-doped interfaces and heterostructure thin-films with the least amount of imperfections can be useful for the fabrication of other advanced semiconductor structures and devices. Second, these low-disorder structures will make accessible a new regime in semiconductor physics where new physical phenomena are expected to arise from the electron-electron interactions.
