Saeed's PhD Thesis.pdf (10.54 MB)
Growth and characterization of two-dimensional III-V semiconductor platforms for mesoscopic physics and quantum devices
Achievements in the growth of ultra-pure III-V semiconductor materials using state of the art molecular beam epitaxy (MBE) machine has led to the discovery of new physics and technological innovations. High mobility two-dimensional electron gas (2DEG) embedded in GaAs/AlxGa1−xAs heterostructures provides an unparalleled platform for many-body physics including fractional quantum Hall effect. On the other hand, single electron devices fabricated on modulation doped GaAs/AlxGa1−xAs heterostructures have been extensively used for fabrication of quantum devices such as spin qubit with application in quantum computing. Furthermore, epitaxial hybrid superconductor-semiconductor heterostructures with ultra clean superconductor-semiconductor interface have been grown using MBE technique to explore rare physical quantum state of the matter namely Majorana zero modes with non-abelian exchange statistics.
Chapter 1 in the manuscript starts with description of GaAs MBE system at Purdue University and continues with the modifications have been made to MBE hardware and growth conditions for growing heterostrcutures with 2DEG mobility exceeding 35 × 106 cm−2/V s. Utilizing an ultra-high pure Ga source material and its further purification by thermal evaporation in the vacuum are determined to have major impact on growth of high mobility GaAs/AlxGa1−xAs heterostructures.
Chapter 2 reports a systematic study on the effect of silicon doping density on low
frequency charge noise and conductance drift in laterally gated nanostructures fabricated on modulation doped GaAs/AlxGa1−xAs heterostructures grown by Molecular Beam Epitaxy (MBE). The primary result of this study is that both charge noise
and conductance drift are strongly impacted by the silicon doping used to create the
two-dimensional electron gas. These findings shed light on the physical origin of the
defect states responsible for charge noise and conductance drift. This is especially
significant for spin qubit devices, which require minimization of conductance drift
and charge noise for stable operation and good coherence.
Chapter 3 demonstrates measurements of the induced superconducting gap in
2D hybrid Al/Al0.15In0.85As/InAs heterostructures which is a promising platform for
scaling topological qubits based on Majorana zero modes. The 2DEG lies in an InAs
quantum well and is separated from the epitaxial Al layer by a barrier of Al0.15In0.85As
with thickness d. Due to hybridization between the wave functions of 2DEG and superconductor, the strength of induced gap in the 2DEG largely depends on the barrier
thickness. This chapter presents a systematic study of the strength of the induced
gap in hybrid Al/Al0.15In0.85As/InAs superconductor/semiconductor heterostructures
as a function of barrier thickness.
History
Degree Type
- Doctor of Philosophy
Department
- Physics and Astronomy
Campus location
- West Lafayette
