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

Abstract

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spinpolarized 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 x spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region, whereas it increases steeply and reaches close to the pure CP when J > 100 A/cm 2 . 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.A s well represented by the giant magnetoresistance, tunneling magnetoresistance, and spin-transfer-torque magnetic random access memory, spintronics research based on spin transport in magnetic metals has been contributing significantly in the progress of electronics through the advancement in recording bit density and low-power memory retention (1, 2). Proposal of the spin-current modulation with an electric field (3) and invention of diluted magnetic III-V semiconductors (4) have opened the opportunity of introducing spin degree of freedom in semiconductor technology (5). After those works, light-induced magnetism (6), electric-field-controlled magnetism (7), spin qubits in semiconductors (8, 9), spin-polarized light-emitting diodes (spinLEDs) (10, 11), and spin-metal-oxide-semiconductor field-effect transistor (12) were either demonstrated or proposed, which have caused an impact on the metal-based spintronics and applied physics that is not small. However, works that assure the roomtemperature (RT) operation of those semiconductor-based devices have not been accomplished to date.Concerning spin-LEDs, studies on a spin injector consisting of a ferromagnetic metal (FmM) and a tunnel barrier (TB) (13-15) succeeded those using semiconductor-based spin injectors (10, 11). The idea of the FmM-TB injector is to take advantage of spin-polarized carriers at RT with FmM and to simultaneously suppress with the TB the backward flow of unpolarized carriers that is unavoidable in the diffusive transport (16, 17). Many works have been carried out with the FmM-TB injector since then. Among those, the highest circular polarization (CP) value,) and I(σ − ) the intensity of right-and left-handed EL component, respectively, was P CP ∼ 0.3 ∼ 0.35 at RT in the external magnetic flux of B = 0.8 T, which was achieved in the context of studying the spinfiltering effect of the MgO TB (18,19). Most of the past works regarding spin-LED were carried out under the vertical arrangement with low J ranging from 0.1 to 1 A/cm 2 and forcing spins aligned vertically by applying out-of-pla...

Ultrafast spin-lasers

“…While recent advances in spintronics show a versatile control of light polarization [16] and THz generation [17], the ultrafast operation of spin-lasers and its fundamental limitations are largely unexplored. A tantalizing prediction of spinlasers is that modulating the polarization of light can be realized much faster than intensity modulation (IM) and thus overcome the limitations imposed by f R of coupled carrier-photon systems [18].…”

Circularly Polarized Thermal Radiation From Nonequilibrium Coupled Antennas

“…Antennas at equal temperatures: For small separation distances k 0 d 1, the phase factor e ik0d(ê d ·ê R ) ∼ 1 simplifies Eq. (8). It then follows that for two antennas of polarizabilities α 1 , α 2 having equal temperatures (T 1 = T 2 ), radial spin S R ∝ Imκ[Imα 1 Reα 2 − Imα 2 Reα 1 ].…”

“…For small distances (k 0 d 1), the phase factor e ik0d(ê d ·ê R ) ∼ 1 in Eq. (8). Under this condition, one can realize maximum purity CP thermal emission with small polarizabilities (αk 3 0 < 1) using nonequilibrium antennas discussed above.…”

Bias Dependence of the Electrical Spin Injection into GaAs from Co−Fe−B/MgO Injectors with Different MgO Growth Processes

“…This link allows us to quantify the efficiency of the spin injection. For future applications, these spin LEDs present the ability to transfer the electron spin information into the photon helicity and could be used in potential optical telecommunication devices [12][13][14].…”