Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field

Abstract

The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region. We measure an Overhauser shift of several microelectronvolts at zero magnetic field for the positively charged exciton (trion X) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. This study paves the way for electrical control of nuclear spin polarization in a single quantum dot without any external magnetic field.

Spin Injection and Relaxation in p -Doped (In,Ga)As/GaAs Quantum-Dot Spin Light-Emitting Diodes at Zero Magnetic Field

“…The long spin-relaxation time in our system is linked to the intrinsically long spin relaxation of time of the electron within the positively charged exciton and the dynamical polarization of nuclear spins [11,12]. In our previous work [25], we have measured a nuclear field of about 200 mT generated by the nuclear spin polarization at 034017-7 zero magnetic field after electron spin injection. This large nuclear field can protect the electron spin polarization and effectively enhance the spin-relaxation time.…”

“…The high electron spin injection also results in an efficient nuclear spin polarization. This has been identified from the nuclear spin-field-induced splitting in EL between the two circularly polarized states at zero magnetic field [25].…”

Evidence of a strong perpendicular magnetic anisotropy in Au/Co/MgO/GaN heterostructures

“…For this reason, the development of spin injectors exhibiting perpendicular magnetic anisotropy (PMA) is indispensable. 11,12,14,15 In this work, we have demonstrated a strong perpendicular magnetic anisotropy in Au/Co/MgO/GaN heterostructures from both experiments and rst-principles calculations. The Au/Co/ MgO heterostructures have been epitaxially grown by molecular beam epitaxy (MBE) on GaN/sapphire substrates.…”

“…The injected spin-polarized electrons from the spininjector recombine with the unpolarized holes in the semiconductor active region to emit circularly polarized light. [9][10][11][12][13][14][15] Potential devices have been proposed based on this advanced semiconductor technology, ranging from memory elements with optical readout and optical transport of spin information, 16 advanced optical switches, 17 circularly polarized single photon emitters for quantum cryptography 18 to medical chiral analysis, 19 and three-dimensional (3D) display screens. 20 Recently, results of GaN-based visible spin-LED and spin lasers have been reported.…”

Structural and Optical Properties of Zn1‐xMgxO Prepared by Calcination of ZnO + Mg(OH)2 after Hydro Micro Mechanical Activation

“…However, a general trend between III‐V and II‐VI compounds is that at similar value of the bandgap (same emission wavelength) II‐VIs are more performing: their light–matter interaction process is more efficient. The dramatic efficiency of electrical initialization of electron and nuclear spins in a single quantum‐based LED has been recently demonstrated by sandwiching an MgO interlayer in between the Ta/CoFeB carrier injector and the GaAs‐based light emitter . The MgO part of the device was grown by MBE‐sputtering (Molecular Beam Epitaxy‐sputtering), a process fully integrated in the whole technological protocol.…”