A study of GaAs/AlGaAs Semiconductor-Insulator- Semiconductor Field Effect Transistors

Semiconductor-insulator-semiconductor field effect transistor (SISFET) devices have a simpler disorder environment at low temperature (< 300mK) than other MBE-grown GaAs/AlGaAs heterostructures, and SISFET devices can be measured over a range of electron densities. Despite the these benefits, SISFET devices are not commonly studied as a number of hurdles need to be overcome. First, though the disorder envir- onment seems simpler in SISFETs, disorder can be difficult to quantify. This makes it challenging to compare SISFETs to other types of GaAs devices. Second SISFETs are difficult to fabricate and have a low yield. Finally SIS- FET devices are not expected to work in high frequency measurements due to their architecture. Disorder can cause electrons to scatter in the 2DEG, affecting the elec- trical transport properties of a device. Disorder can be classified using the ratio of the transport to the quantum scattering times. Quantifying disorder can be difficult due to a divergence in the calculation of the quantum scat- tering time. I show this divergence in the quantum lifetime is due to the nonphysical assumption of an infinitely thick heterostructure. I derive a non- divergent scattering lifetime for finite thickness structures and calculate the quantum and transport lifetimes for electrons in a generic GaAs-AlGaAs het- erostructures. I then compare theoretical results with experimental data from a GaAs 2DEG and obtain excellent agreement between the calculations and experimental data. Due to their complex fabrication process SISFETs typically have a low yield. Furthermore the transport properties of SISFETs are very sensitive to any changes in the fabrication process. I develop a reliable fabrication method for SISFETs to improve their yield and electrical performance. I then demonstrate the electrical reproducibility of transport measurements which are possible with SISFET devices. Finally we demonstrate rf reflectometry is compatible with SISFET quantum dots. SISFET nanostructures have large overall top-gates and thus the rf sig- nal is expected to shorted to the top-gate. Reflectometry is used almost ex- clusively on modulation doped nanostructures in GaAs devices for a range of applications, including fast charge read-out. Being able to integrate SISFET nanostructures into reflectometry measurements may enable similar measure- ments to be performed in SISFET nanostructures

What lurks below the last plateau: Experimental studies of the 0.7 x 2e^2/h conductance anomaly in one-dimensional systems

The integer quantized conductance of one-dimensional electron systems is a well understood effect of quantum confinement. A number of fractionally quantized plateaus are also commonly observed. They are attributed to many-body effects, but their precise origin is still a matter of debate, having attracted considerable interest over the past 15 years. This review reports on experimental studies of fractionally quantized plateaus in semiconductor quantum point contacts and quantum wires, focusing on the 0.7 x 2e^2/h conductance anomaly, its analogs at higher conductances, and the zero bias peak observed in the d.c. source-drain bias for conductances less than 2e^2/h.Comment: Topical Review for J. Phys.: Condens. Matter, published version available at http://iopscience.iop.org/0953-8984/23/44/443201/ Document is 131 pages, 43 figure