Theory of Electrically Controlled Resonant Tunneling Spin Devices
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Theory of Electrically Controlled Resonant Tunneling Spin Devices David Z.-Y. Ting and Xavier Cartoixà 1,* Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, U.S.A. 1 Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A. ABSTRACT We report device concepts that exploit spin-orbit coupling for creating spin polarized current sources using nonmagnetic semiconductor resonant tunneling heterostructures, without external magnetic fields. The resonant interband tunneling spin filter exploits large valence band spinorbit interaction to provide strong spin selectivity. The bi-directional spin pump induces the simultaneous flow of oppositely spin-polarized current components in opposite directions through spin-dependent resonant tunneling. The efficiency of resonant tunneling spin devices can be improved when the effects of structural inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) are combined properly, and incorporated into device design. The current spin polarizations of the proposed devices are electrically controllable, and potentially amenable to high-speed modulation. In principle, the electrically modulated spin-polarized current source could be integrated in optoelectronic devices for added functionality.
INTRODUCTION An important component of semiconductor spintronics (spin-based electronics) research is the development of spin-polarized current sources [1]. One interesting approach uses nonmagnetic semiconductor heterostructures, without external magnetic fields or optical excitation. The idea originated with the resonant tunneling spin filter proposed by Voskoboynikov et al. [2]. Subsequently, a number of new device concepts emerged, including the triple-barrier resonant tunneling diode (TB-RTD) [3], the asymmetric resonant interband tunneling diode (aRITD) [4,5], the bi-directional resonant tunneling spin pump [6], and the [110]-RITD [7]. In this paper we present an overview of some of these concepts, and discuss their prospects.
DEVICE CONCEPTS We illustrate the concept of nonmagnetic heterostructure spin filters using the asymmetric resonant tunneling structure (aRTS) as an example. Quantized states in aRTS are spin-split by the Rashba effect [8]. Spin filtering is done by exploiting the phenomenon that the spin of a resonantly transmitted electron aligns with that of the quasibound state traversed [2, 9]. Figure 1(a) illustrates the properties of quasibound quantum well states in an aRTS. Rashba effect induced spin splitting in the lowest conduction band (cb1) states are shown in the left panel. The shaded disks in the right panel are k||-space representations of available quasibound states with energy below the Fermi level in the incident electron reservoir. These are the states that participate in resonant tunneling, and their spin directions determine the spin polarization of the transmitted electrons in the collector. When the spin directions of two spin-split subbands are
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