Two-dimensional Electron Transport in Gallium Nitride and Gallium Arsenide- based Heterostructures.

[摘要] The emergence of III-V semiconductor heterostructures has enabled the studyof a broad range of two-dimensional phenomena. These heterostructures are thebuilding blocks of high frequency field-effect transistors (FETs).GaN-based heterostructures will have great impact in FET applications as theyhave the highest carrier densities achievable. In this thesis we studied electrontransport in AlGaN/GaN samples covering a broad range of carrier density, from0.5×1012 cm^-2 to 1.0×1013 cm^-2. We found at carrier densities below 5.0×1012 cm^-2,electron scattering from threading dislocations were the dominant scatteringmechanism. The electron mobilities can be greatly enhanced by reducing the densityof threading dislocations based on novel patterned growth techniques. We extendedour studies to even higher carrier densities using lattice matched In0.16Al0.84N/GaNheterostructures. In particular, we investigated the magnetotransport regime in thepresence of two subbands by using gated Hall bar samples.In addition to scattering processes, we also studied the spin-orbit interactionand phase coherence in GaN 2DEG samples by performing weak antilocalization(WAL) measurements. The spin-splitting energies extracted from WAL were found tobe much smaller than the previous reports based on Shubnikov-de Haas measurements.By studying the spin splitting energies as a function of Fermi wave-vector we obtainedthe linear and cubic spin-orbit parameters for GaN 2DEG system. Furthermore, weused the WAL feature as a thermometer for the electron system, which allowed us tostudy energy relaxation processes in GaN.In contrast to GaN heterostructures, we used GaAs/AlGaAs heterostructures tostudy two-dimensional electron transport at very low carrier densities. We focused onthe deep insulation regime of integer quantum Hall liquids (IQHLs), a transport regimenot accessible by ordinary transport measurements. We explored the charge dynamicsin this regime by using single electron transistors (SET) in both unpatterned andantidot structures. SETs allowed us to monitor slow motion of charges in and out ofthe IQHLs. We found that, near zero temperature, IQHLs can be viewed as magneticflux-to-charge transformers and confirmed our ideas by making a SET basedmagnetometer with an SET placed on an AlGaAs/GaAs heterostructure with 25identical quantum wells.

[发布机构] University of Michigan

[效力级别] Semiconductor Physics

[关键词] Quantum Hall Effect;Semiconductor Physics;2-dimensional Electron Gas;Single Electron Transistor;GaAs Heterostructures;GaN Heterostructures;Physics;Science;Physics