Pure circular polarization electroluminescence at room temperature with spin-polarized light-emitting diodes.

Nishizawa, Nozomi; Nishibayashi, Kazuhiro; Munekata, Hiro · Proc Natl Acad Sci U S A · 2017

basic_science · Level V

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Abstract

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: first, the stripe-laser-like structure that helps intensify the EL light at the cleaved side walls below the spin injector Fe slab, and second, the crystalline AlO <sub><i>x</i></sub> spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (<i>J</i>) region, whereas it increases steeply and reaches close to the pure CP when <i>J</i> > 100 A/cm<sup>2</sup> There, either right- or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-dependent reabsorption, spin-induced birefringence, and optical spin-axis conversion are suggested to account for the observed experimental results.