(Invited) Quest for Fully Spin and Optically Polarized Semiconductor Nanostructures for Room-Temperature Opto-Spintronics

Abstract

Spintronics represents a new paradigm for future electronics, photonics and information technology, which explores the spin degree of freedom of the electron for information storage, processing and transfer. Since 1990s, we have witnessed great success of metal-based spintronics that has revolutionized the mass data storage industry. There has also been an enormous push for semiconductor spintronics during the past three decades, with the aim to capitalize the past and current success of charge-based semiconductor technology and to make its spin counterpart the backbone of future spintronics just like semiconductors have done in today’s electronics/photonics. An exclusive advantage of semiconductor spintronics is its potential for opto-spintronics that will allow integration of spin-based information processing and storage with photon-based information transfer and communications. Unfortunately, progresses of semiconductor spintronics have so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at and above room temperature (RT) at which today’s devices operate.In this work, we succeed to achieve conduction electron spin polarization exceeding 90% at RT in a semiconductor nanostructure, which remains steadily high even up to 110°C [1]. This represents the highest RT electron spin polarization ever reported in any semiconductor by any approach! This breakthrough is accomplished by a conceptually new approach of defect-engineered remote spin filtering and amplification of InAs quantum-dot (QD) electrons via an adjacent tunneling-coupled GaNAs quantum well acting as a spin filter. The extraordinary spin filtering effect in GaNAs is enabled by spin-dependent recombination via spin-polarized defects, i.e. grown-in Ga self-interstitials, which selectively deplete conduction electrons with an opposite spin orientation to that of the defect electron. In sharp contrast to the general trend of deteriorating spin polarization with increasing temperature seen in all other approaches of spin generation, our approach is gifted with an opposite temperature dependence up to RT thanks to a thermally accelerated remote spin-filtering effect as a result of thermally activated recombination via the defects [2]. We further show that the QD electron spin can be remotely manipulated by spin control in the adjacent spin filter, paving the way for remote spin encoding and writing of quantum memory as well as for remote spin control of spin-photon interfaces. This work demonstrates the feasibility to implement opto-spintronic functionality under practical device operation conditions in a semiconductor nanostructure system based on the mature III-V semiconductor technology commonly used for today’s optoelectronics and photonics. It could also pave the way for a range of potential spintronic and opto-spintronic applications exploiting the state-of-the-art GaAs technology platform, such as spin-LEDs, spin lasers, spin-polarized single-photon sources, quantum spin-photon interfaces, spin qubits, etc.