Electronic Properties of Strained Narrow-Gap Quantum Wells

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This project addresses materials science and physics of 2DES(two dimensional electronic systems) based on InSb/AlInSb heterostructures. InSb is characterized by extreme values compared to other III-V materials, having the smallest energy gap, the smallest electron effective mass, the largest electron g-factor, and the most non-parabolic conduction band of all III-V semiconductors. These dramatically different parameters make two-dimensional electronic systems (2DESs) in InSb intriguing alternatives to GaAs-based 2DESs. Although the host material can influence the physics of the imbedded 2DES, there has been little motivation to study 2DESs in alternative materials since most are of considerably worse crystalline quality. Now that InSb/AlxIn1-xSb structures have been produced with mobilities comparable to those of GaAs/AlxGa1-xAs structures in which the fractional quantum Hall effect was first observed. These high mobilities, coupled with the vastly different parameter space of InSb 2DESs, provide the impetus for this project. The objectives are to advance the materials science of InSb/AlxIn1-xSb heteroepitaxy and to explore the properties of InSb 2DESs via low-temperature magneto-transport and magneto-optics.Several approaches will be used to improve materials quality. A scanning probe microscope, connected to the same vacuum as the MBE chamber, will be used to assess doping efficiency and buffer layer effectiveness on lattice-mismatched substrates. An atomic hydrogen source will be used to passivate the growth surface and facilitate oxide desorption from InSb substrates. Improvement of the materials quality will increase the relative importance of electron-electron interactions in 2DESs studied at low temperature. Magneto-transport experiments will explore the quantum Hall state to insulator transition and behavior in the fractional quantum Hall regime. Magneto-optical studies will be used characterize the energy band structure of InSb to determine the confinement potential through measurement of interband excitonic transitions in undoped wells; establish the two-dimensional band structure through analysis of excitonic transitions, intersubband resonance, and cyclotron resonance; and probe electron dynamics at low Landau-level fillings. The wide scope of the project requires collaboration between three co-investigators with collective expertise in molecular beam epitaxy, magneto-transport experiments, and optical measurements. %%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic devices. A variety of fundamental issues are to be addressed in these investigations, and the proposed experiments may also develop technologically important material combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***