Full band structure LDA andk∙pcalculations of optical spin-injection

Abstract

We present a study of optical electron spin-injection ͑optical orientation͒ in the bulk semiconductors GaAs, Si, and CdSe from direct optical excitation with circularly polarized light. For GaAs and Si, we compare pseudopotential calculations with calculations of a recent full-zone k • p model. For GaAs, we find that there can be up to 30% spin-injection at energies well above the band gap. For Si, which has very weak spin-orbit coupling, we find that there can be up to 30% spin polarization from direct transitions. The relatively low symmetry of wurtzite CdSe leads to an orientation dependent spin-injection, which can be up to 100% polarized at the band edge. For each of these systems, full-zone calculations are made, which allow us to consider excitation well above the band gap. An adaptive Brillouin zone sampling scheme is used, which allows us to obtain rapid convergence of our spectra. A derivation of the spin-injection rate, which accounts for the coherences excited in a semiconductor with spin-split bands, is also included.

Optical injection and control in germanium: Thirty-bandk⋅ptheory

“…39 We prefer the present k · p approach over an ab initio treatment for two main reasons. First, computational times, both overhead and per k point, are significantly less in a k · p calculation than in even a local-densityapproximation calculation.…”

Progress towards Spin-Based Light Emission in Group IV Semiconductors

“…They demonstrated that the degree of spin polarization (DSP) is 50% (−83.3%) for electrons (holes) at the direct gap energy threshold (i.e., 0.89 eV), as expected by considering the atomic-like character of the zone center energy levels. It was also shown that the spectral dependence of the electronic DSP, as summarized in the left panel of Figure 4 mimics the one of GaAs [130] and decreases at the onset of the absorption from the SO band. This behavior was shown to be mainly caused by the LH rather than the commonly argued transitions related to the SO band [129].…”

Optical Orientation and Inverse Spin Hall Effect as Effective Tools to Investigate Spin-Dependent Diffusion

“…with Φ 0 being the photon flux into the semiconductor, P(hν) the initial polarization of the photo-generated electrons [47,48] and α(hν) the absorption coefficient [46]. Figure 4 also shows the comparison between the experimental data and the ISHE signal obtained by using this simplified model (dashed lines).…”

“…The electron mobility at the doping density of our samples was assumed equal to µ Ge = 3560 cm 2 ·V −1 ·s −1 and µ GaAs = 2051 cm 2 ·V −1 ·s −1 [45], corresponding to a diffusion coefficient D e = µk B T/e approximately equal to 89 cm 2 ·s −1 for Ge and 50 cm 2 ·s −1 for GaAs, respectively. The generation term was explicitly accounted for by considering the semiconductor absorption coefficient [46] and the spin polarization theoretically expected for illumination with 100% circularly polarized light [47,48], while carrier recombination was described by the Shockley-Read term [49] and spin relaxation by a decay time τ s . The model portrays the spatial distribution of spins residing at the Γ valley for GaAs and at the L valleys for Ge under the approximation that all the electrons are thermalized.…”