Fabrication and Physics of Low-Disorder Electron and Hole Systems

本研究涉及利用分子束外延技术生长高质量GaAs/AlxGa1-x异质结薄膜结构的材料科学和物理学研究，以及期望在这种理想电子系统中体现的新的电子相互作用物理学。在非常小的朗道能级填充下，GaAs/AlGaAs界面上的非常低无序，稀二维（2D）电子和空穴系统将被研究，其中系统的量子液体和固体状态之间的跃迁是预期的。还将研究几种具有附加自由度的新型准二维系统。这些系统包括包含两层或更多层电子的系统，它们距离很近，因此层间库仑相互作用很强，以及宽抛物线井中的厚层电子系统。这些结构中额外的自由度有望导致新的集体状态，例如最近在双层电子系统中观察到的偶数1/2分母填充的分数量子霍尔态。这些系统将通过低温磁输运测量来探测。这项先进材料研究计划的影响是双重的。首先，优化分子束外延生长技术，以生产高质量、选择性掺杂的界面和具有最少缺陷的异质结构薄膜，这对于制造其他先进的半导体结构和器件是有用的。其次，这些低无序结构将使半导体物理学中的一个新体系易于实现，在这个体系中，新的物理现象有望从电子-电子相互作用中产生。

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.