Optoelectric spin injection in semiconductor heterostructures without a ferromagnet

Abstract

We have shown that electron spin density can be generated by a dc current flowing across a pn junction with an embedded asymmetric quantum well. Spin polarization is created in the quantum well by radiative electron-hole recombination when the conduction electron momentum distribution is shifted with respect to the momentum distribution of holes in the spin split valence subbands. Spin current appears when the spin polarization is injected from the quantum well into the n-doped region of the pn junction. The accompanied emission of circularly polarized light from the quantum well can serve as a spin polarization detector. 73.40.Kp, 78.60.Fi One of the most important problems in spintronics is the efficient injection of spin currents into semiconductor structures. A possible way is to inject spin polarization from a ferromagnet by passing a dc current across the interface [1]. If the ferromagnet is metallic, the efficiency of such injection is controversial [2], and the observed weak spin current has been attributed to the large mismatch of spin diffusion constants between the adjacent semiconductor and metal [3]. Spin injection can be enhanced by using an appropriate interface tunneling barrier [4]. On the other hand, rather high degree of spin current polarization has been detected if the spin is injected from magnetic semiconductors [5], although its high efficiency is restricted to low temperatures.In this Letter we propose a new method to use a dc current to inject spin polarization, not from any ferromagnetic material, but from a quantum well (QW) embedded into a pn junction. The spin polarized current is generated during the radiative electron-hole recombination in the QW, accompanied by the emission of circularly polarized light. Our new injection mechanism can be easily explained. It is well known that in a QW which is asymmetric along the growth direction, at each finite wave vector k the spin degeneracy of hole subbands is removed. The corresponding splitting of hole energies increases with k and can reach a quite high value. For example, in a p inversion layer of a GaAs-AlGaAs heterojunction, the splitting of the topmost heavy-hole subband was calculated [6] to be about 5 meV at k=2·10 6 cm −1 . Each of the split states is a linear combination of four angular momentum eigenstates which are specified by the z-component J z =±3/2 and ±1/2. The resulting mean spins of hole states are parallel to the QW interfaces. For a given k the spins in each pair of spin-split subbands have opposite directions, and in a given spin-split subband the mean spin at k is equal and opposite to that at -k. The spin orientations in the topmost heavy-hole subband are shown in Fig. 1, where the Fermi energy µ e (or µ h ) of the quasiequilibrium degenerate electron gas (or hole gas) is indicated. When a σ-spin electron in the k state of the conduction band makes a radiative transition to the topmost heavy-hole subband, as marked by the downward vertical arrow line in Fig. 1, the probability of this process depends on σ beca...

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

“…The latter, in turn, is a reciprocal phenomenon to the SOT. Following theoretical predictions (Aronov and Lyanda-Geller, 1989;Edelstein, 1990;Inoue et al, 2003;Ivchenko et al, 1989;Ivchenko and Pikus, 1978;Mal'shukov and Chao, 2002), the SGE was initially observed in an asymmetrically confined GaAs quantum well (Ganichev et al, 2002). The key signature of the SGE is the electrical current induced by a non-equilibrium, but uniform, polarization of electron spins.…”

“…In analogy to the galvanic (voltaic) cell, the term spin galvanic effect (SGE) was coined for a phenomenon in which an externally induced non-equilibrium spin polarization generates an electrical current (voltage) (Ganichev et al, 2002). Inversely the iSGE, sometimes also called the Rashba-Edelstein effect, then refers to an externally applied electrical current that generates a spin polarization (Aronov and Lyanda-Geller, 1989;Edelstein, 1990;Inoue et al, 2003;Ivchenko et al, 1989;Ivchenko and Pikus, 1978;Mal'shukov and Chao, 2002). The theory of iSGE was discussed in details in Subsection III.D.…”

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

“…In analogy to the galvanic (voltaic) cell, the term spin galvanic effect (SGE) was coined for a phenomenon in which an externally induced non-equilibrium spin density generates an electrical current (voltage) (Ganichev et al, 2002). Inversely the iSGE, sometimes also called the Rashba-Edelstein effect, then refers to an externally applied electrical current that generates a spin density (Aronov and Lyanda-Geller, 1989;Edelstein, 1990;Inoue et al, 2003;Ivchenko et al, 1989;Ivchenko and Pikus, 1978;Mal'shukov and Chao, 2002). The theory of iSGE was discussed in details in Subsection III.D.…”

Complementary spin-Hall and inverse spin-galvanic effect torques in a ferromagnet/semiconductor bilayer

“…The original theoretical proposals [12][13][14] and experimental observations 10,11,15,16 of the ISGE were made in paramagnets with no ferromagnetic component in the structure. The corresponding non-equilibrium spin density, generated in the ISGE by inversion-asymmetry terms in the relativistic Hamiltonian, has naturally no dependence on magnetization.…”