Proposal of a Novel Spin Filter Realized in a Triple Barrier Resonant Tunnel Diode using Rashba Spin-Orbit Interaction
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Proposal of a Novel Spin Filter Realized in a Triple Barrier Resonant Tunnel Diode using Rashba Spin-Orbit Interaction Takaaki Koga, Junsaku Nitta, Supriyo Datta* and Hideaki Takayanagi NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, JAPAN * School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN47907, USA ABSTRACT A spin rectifying diode, which utilizes Rashba spin-orbit coupling, is proposed using semiconducting triple barrier structures. This spin diode makes use of spin-dependent resonant tunneling levels that are formed in the triple barrier structures. We found that, for a certain emitter-collector bias voltage, it is possible to engineer the structure in such a way that a resonant level formed within the first quantum well matches that of the second quantum well only for a selected spin state, thus realizing an electronic spin rectifier. The calculated spin polarization of the transmitted current through the device, which is defined as |I↑–I↓|/(I↑+I↓), is found to be higher than 99.9%. INTRODUCTION There has been growing interest in the field of “spintronics”, where extra degrees of freedom provided by electron spins, in addition to those provided by electron charges, are expected to play fundamentally different roles in future electronic devices than those played by the electron charges in the conventional electronic devices [1]. In order to explore these new features of “spintronics”, it is essential to have a spin-polarized current source with which to inject spin-polarized electrons into non-magnetic semiconductors. Various properties of electron spins, including their dynamical motions in semiconducting solids, can then be studied using the injected spin-polarized electrons. Various magnetic properties of the materials, including ferromagnetism in ferromagnetic metals [2-4] and diluted magnetic semiconductors [5,6], and Zeeman splitting of the electron energy levels in a strong magnetic field [7,8], have been utilized to provide spin-polarized injection sources or spin-filters for injecting spin-polarized electrons. In addition, combinations between the resonant tunneling phenomena and the above-mentioned conventional spin-filter devices are among the most recent efforts in this research area in order to enhance the spin-filtering performance of the proposed devices [9-12]. In the present report, we propose a new device that is capable of rectifying electrons according to their spin states without using magnetic properties of the material. This device, which can be used as a spin filter, utilizes Rashba spin-orbit coupling [13] in semiconducting heterostructures, and can be fabricated using non-magnetic semiconductors only. PROPOSED DEVICE STRUCTURE We propose to realize the above-mentioned spin-rectifier device using an In1–xGaxAs (collector lead)-In0.52Al0.48As (barrier 1)-In0.53Ga0.47As (well 1)-In0.52Al0.48As (barrier 2)-In0.53Ga0.47As (well 2)-In0.52Al0.48As (barrier 3)-In0.53Ga0.47As (emitter lead) triple barrier F7
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