Spintronics and Quantum Information Processing in Wide-Bandgap Semiconductors.

摘要

Spin is a quantum-mechanical angular momentum intrinsic to many particles, including electrons, neutrons, and protons. Just as the charge of an electron has been exploited widely for modern technological gain, the spin of an electron may find future use in a number of advanced information technologies pursued by researchers within the fields of spintronics and quantum information. However, the future success of spin-based technologies relies heavily on identifying materials systems where spins can be easily manipulated with a high degree of quantum control, while remaining relatively robust to outside sources of quantum decoherence that tend to irreversibly alter the quantum state of the spins in an uncontrollable way. Towards these ends, we explore the physics of electronic spins in wide-bandgap semiconductors, which are semiconductors with bandgap energies roughly 2.0 eV or larger. First, we study the spins of spatially-delocalized conduction band electrons in gallium nitride, to determine whether they can be polarized electronically without the use of magnetic fields or magnetic materials. We use optical techniques to show that, despite the rather weak spin-orbit coupling expected to exist in gallium nitride, a current-induced spin polarization can still be observed in electronic Hall bar devices fabricated from bulk n-type epilayers of this material. We then turn our attention to highly-localized electronic spins that are bound to point defects within wide-bandgap semiconductors. Past studies in diamond have shown that a point defect known as the nitrogen-vacancy center possesses an electronic spin state that can be used as an individually-addressable quantum bit even at room temperature. However, no other defect systems with analogous properties were known to exist. We develop a set of screening criteria that can be used in conjunction with computational simulations to systematically identify defects similar to the diamond nitrogen-vacancy center, but in other semiconductors that can be grown and microfabricated more easily than diamond. We identify several promising defects in a variety of semiconductors, focusing in particular on vacancy-related defects in silicon carbide. As a result of these predictions, we engage in several optical and magnetic resonance studies of the 4H polytype of silicon carbide. We succeed in identifying six new species of point defect that can be used as spin qubits in analogy to the diamond nitrogen-vacancy center, with two of these defects exhibiting room temperature operation.