May 29 (Wed) @ 10:00am: ”Magnetotransport of III-V Heterostructures with High Spin-Orbit Coupling,” Connor Dempsey, ECE PhD Defense
Zoom Meeting – ID: 854 9852 4740 | Passcode: 089887
https://ucsb.zoom.us/j/85498524740?pwd=TEtVTnJtZ0dNOTVDUTFJbDUyME9iZz09
Abstract
Spin-orbit coupling is a relativistic effect, which causes the spin of a charge carrier to interact with its local electrostatic environment. This leads to the spin of the charge carrier coupling to its momentum, breaking spin degeneracy. The Rashba spin-orbit interaction enables the manipulation of spin through the application of an electric field, a critical property for spintronic devices. Because the Rashba coupling acts as a momentum-dependent effective magnetic field, it can be used in devices intended for spin generation or detection. Additionally, it is crucial in III-V hybrid heterostructures designed to exhibit Majorana zero modes, as spin degeneracy must be broken. This talk focuses on the growth, in situ, and ex situ characterization of compounds, devices, and heterostructures with large bulk spin-orbit coupling.
With its high mobility, narrow bandgap, and large bulk g-factor, InSb has been studied for potential applications in photovoltaics, FETs, and proposed devices for studying Majorana physics. Because of the high cost of substrates directly lattice matched to InSb, GaAs has served as a frequently used cheaper alternative. The large lattice mismatch between GaAs and InSb leads to a high density of dislocations at the interface, the formation of an interfacial sheet charge, and large band bending in the undoped InSb thin film. In this talk, we explore whether the intrinsic band bending breaks structural inversion symmetry, enabling the observation of the Rashba effect without gating or doping the InSb/GaAs heterostructure. If the Rashba effect can be observed, these devices may serve as a cheap testbed for the study of interfacial Rashba physics in InSb semiconductors.
InAs has the second largest large bulk spin-orbit coupling of the binary III-V semiconductor family. Additionally, high mobility quantum wells (QWs) of InAs have been grown on InP (001) exhibiting mobilities μ>1,000,000 cm2/Vs, making them excellent platforms for Rashba devices or platforms for studying Majorana physics. Despite these high mobilities, the observation of more exotic physics, such as the fractional quantum hall effect, has been limited. In this talk, we discuss utilizing strain compensating techniques to improve the mobility of InAs QWs grown on InP (001) substrates. Strain in the active region can be controlled by tuning the In concentration of the QW cladding layers. This enables us to double the critical thickness of the InAs layer compared to all currently grown InAs/InP QWs, leading to a maximum mobility of μ=1,160,000 cm2/Vs. At the time of this talk, this is the highest mobility observed for InAs/InP QWs. Further strain and structural optimization may lead to further improvement of these structures, opening a path for increasing the highest observed mobilities in InAs QWs.
Bio
Connor Dempsey is a member of the Palmstrøm Group at UCSB. Since beginning his time at UCSB, his projects have all related to improving the currently available materials systems for studying Majorana zero mode physics. This includes working to improve the maximum mobility of InAs QWs grown on InP (001) substrates and exploring new opportunities for III-V heterostructures to determine cheap systems, which exhibit Rashba spin-orbit coupling. Additionally, he has been involved in exploring new potential superconductors to interface with III-V semiconductors for studying potential Majorana devices.
Hosted by: Professor Chris Palmstrøm
Submitted by: Connor Dempsey <c_dempsey@ucsb.edu>
