Oblique Hanle measurements of InAs∕GaAs quantum dot spin-light emitting diodes

Abstract

We report on studies of electrical spin injection from ferromagnetic Fe contacts into semiconductor light emitting diodes containing single layers of InAs/ GaAs self-assembled quantum dots ͑QDs͒. An oblique magnetic field is used to manipulate the spin of the injected electrons in the semiconductor. This approach allows us to measure the injected steady-state spin polarization in the QDs, P spin as well as estimate the spin losses in the QD spin detector. After subtraction of magneto-optical effects not related to spin injection, we measured a P spin of 7.5% at 15 K and estimated an injected spin polarization before QD recombination of around 20%. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2163074͔ Electrical injection of spin polarized carriers from a magnetic contact into a semiconductor is essential for the implementation of spintronic devices.1,2 An accurate way to quantify the spin injection process is to utilize a spin-light emitting diode ͑spin-LED͒. Such a device uses a magnetic contact to electrically inject spin polarized carriers into a LED structure and employs the radiative selection rules to relate the degree of the circular polarization of the emitted light to the injected carrier spin polarization. Ferromagnetic metals are attractive as magnetic contacts in spin-LEDs due to their high Curie temperatures and their well-studied structural and magnetic properties. Recently, high spin injection efficiencies have been achieved in devices where a conventional ferromagnetic metal such as Fe, Co, Ni and their alloys were used to electrically inject spin-polarized electrons via a Schottky 3-5 or an oxide tunnel barrier 6-9 into a semiconductor LED structure.In the great majority of these devices, bulk semiconductors or quantum wells have been used as the recombination region. Spin relaxation in these is mainly caused by momentum-dependent spin interactions that are in general fast because of the availability of a continuum of energy states. These mechanisms should be inefficient in spin-LEDs based on quantum dots ͑QDs͒ due to their three-dimensional carrier confinement, which results in a discrete density of states. Yet, there have been few reports on electrical spin injection in QD-based spin-LEDs, 10-12 only one of which 12 used a ferromagnetic contact as injector. In the latter, a large magnetic field ͑B Ͼ 2 T͒ was used to bring the Fe film magnetization out of plane ͑hard axis͒ and inject electrons with spins along the surface normal ͑Faraday geometry͒. An injected spin polarization in the QDs, P spin of 5% was measured; importantly the polarization was insensitive to the temperature and persisted to 300 K, confirming the potential of quantum dots as spin detectors in spin-LEDs. We demonstrate here electrical spin injection from ferromagnetic Fe contacts into semiconductor LED structures containing single layers of InAs/ GaAs self-assembled quantum dots ͑QDs͒. The spins are injected along the sample layers ͑Fe easy axis͒ under application of a small oblique magnetic field ͑B Ͻ 100 mT͒. The ...

Double detected spin-dependent quantum dot

“…Experimentally, the analyzed model can be implemented by semiconductor spin-light emitting diode structures containing single layers of InAs/GaAs self-assembled quantum dots [3].…”

“…Spin manipulation and magnetization detection in quantum dot was studied in experiment by Ref. [3]. An external field, used for spin manipulation, can be viewed as an environment of the subsystem, the quantum dot.…”

Spin injection in lateral InAs quantum dot structures by optical orientation spectroscopy

“…This results in extremely long spin lifetimes of carriers 6 7 -89 , which can exceed 20 ms at 1K for electron spins in the InGaAs QD structures 7 . In(Ga)As QDs fabricated, e.g., by strain driven self-assembly are particularly attractive for these applications as they can be controllably positioned 10 and embedded into active device structures 1,11 1213 -14 . Moreover, due to major advances in fabrication, implementation of complex QD structures containing either vertically stacked or laterally aligned self-assembled QDs has recently become possible with a high degree of precision.…”

Electroluminescence And Spin-Polarized Hole Injection In InAs∕GaAs Quantum Dot Heterostructures

“…Secondly, this is a promising way of spin injection into the dots, which is of great importance for spintronics [2]. During the last years, reversebiased SDs have been used as a tool for studies of the spin injection from ferromagnetic metals (FMs) to semiconductor layers [3,4]. In such structures, the injection occurs via tunneling through the barrier depending on the doping level of the semiconductor.…”