Optimization of MBE growth of a high-quality 2-Dimensional Electron Gas in InAs/AlGaSb material system for pursuing a top-down approach towards realization of topological qubits.

Abstract

Two-dimensional electron gas (2DEG) in InAs quantum wells grown on nearly lattice-matched GaSb substrates is an ideal platform towards the realization of topological quantum computing with Majorana fermions, due to its low effective mass, high mobility, strong spin-orbit coupling, and high Lande g factor. Sufficient electrical isolation from the substrate, high mobility (to ensure ballistic transport), and full depletion of the 2DEG using lithographic gates are the three key parameters for successful mesoscopic quantum transport experiments. However, these properties of 2DEG in InAs quantum wells on GaSb substrates are still elusive. A material with high charge carrier mobility is needed to favor the formation of Majorana Zero Modes (MZMs). Improving growth techniques and structure designs of InAs quantum wells can enhance their electron mobility. In this thesis, we study the Molecular Beam Epitaxy (MBE) growth of InAs/AlGaSb semiconductor heterostructures on undoped GaSb substrates with lattice-matched quaternary buffer (AlGaAsSb), which ensured sufficient isolation from the substrate. This structure design is practically free of any threading dislocations, and exhibits very high electron mobilities. The quaternary buffer layer is investigated in terms of crystal structure using X-Ray Diffraction (XRD), and its influence on the electron mobility of overgrown quantum wells. We found that quaternary buffer with As mole fraction not equal or very close to 7% grown on GaSb substrates has a significant influence on carrier mobility inside the quantum well. A growth method for the quaternary buffer was developed to achieve the reproducibility of As composition in that buffer. Fabrication of the resulting heterostructures was carried out. The electrical properties of 2DEGs were investigated using magneto-transport measurements including quantum Hall effect and Shubnikov de-Haas oscillations.