Spin Light-emitting Diodes Research Articles

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

Dimensional and Doping Engineering of Chiral Perovskites with Enhanced Spin Selectivity for Green Emissive Spin Light-Emitting Diodes.

Chiral perovskites play a pivotal role in spintronics and optoelectronic systems attributed to their chiral-induced spin selectivity (CISS) effect. Specifically, they allow for spin-polarized charge transport in spin light-emitting diodes (LEDs), yielding circularly polarized electroluminescence at room temperature without external magnetic fields. However, chiral lead bromide-based perovskites have yet to achieve high-performance green emissive spin-LEDs, owing to limited CISS effects and charge transport. Herein, we employ dimensional regulation and Sn2+-doping to optimize chiral bromide-based perovskite architecture for green emissive spin-LEDs. The optimized (PEA)x(S/R-PRDA)2-xSn0.1Pb0.9Br4 chiral perovskite film exhibits an enhanced CISS effect, higher hole mobility, and better energy level alignment with the emissive layer. These improvements allow us to fabricate green emissive spin-LEDs with an external quantum efficiency (EQE) of 5.7% and an asymmetry factor |gCP-EL| of 1.1 × 10-3. This work highlights the importance of tailored perovskite architectures and doping strategies in advancing spintronics for optoelectronic applications.

Topology-induced chiral photon emission from a large-scale meron lattice

AbstractMerons are a class of topologically protected particle-like structures created in in-plane magnetized magnetic films. The structures can act as information carriers and could be used for magnetic storage. However, the development of such applications is hampered by limitations in the size, thermal stability and magnetic-field requirements of the systems. Here we report the construction of millimetre-scale meron lattices that are stable at room temperature and under zero magnetic field. Our system is based on a trilayer structure composed of a thin iron film sandwiched between films of palladium and magnesium oxide (Pd/Fe/MgO) on a gallium nitride wafer. It is fabricated using a molecular-beam epitaxy approach that is assisted by a high magnetic field, which leads to a strong Dzyaloshinskii–Moriya interaction. The lattices can be used for chirality transfer from merons to electrons and then to photons, and we show that the meron lattices can be used as spin injectors in nitride-based light-emitting diodes. The topology-induced spin light-emitting diode can provide 22.5% circularly polarized electroluminescence at room temperature and under zero magnetic field.

Lattice-Distortion-Induced Change in the Magnetic Properties in Br-Defect Host CsPbBr3Perovskite Quantum Dots

Herein, we report temperature- and field-induced magnetic states in CsPbBr3 perovskite quantum dots (PQDs) attributed to Br defects. We find that temperature-dependent structural distortion is the main source of various temperature-induced magnetic states in Br-defect host CsPbBr3 PQDs. Comprehensively examined magnetization data through Arrott plots, Langevin and Brillouin function fitting, and structural analysis reveal the presence of various oxidation states (i.e., Pb0, Pb+, Pb2+, and Pb3+) yielding different magnetic states, such as diamagnetic states above 90 K, paramagnetic states below ≈90 K, and perhaps locally ordered states between 58 and 90 K. It is realized from theoretical fits that paramagnetic ions exist (i.e., superparamagnetic behavior) due to Br defects causing Pb+ (and/or Pb3+ ions) in the diamagnetic region. We anticipate that our findings will spur future research of the development of spin-optoelectronics, such as spin light-emitting diodes, and spintronics devices based on CsPbBr3 PQDs.

Opportunities and challenges of chiral perovskites for spin-LEDs

Chiral perovskites have drawn intensive attention in recent years due to their promising optospintronic applications. In this forum article, the unique properties of chiral perovskites and their applications in circularly polarized light emission (CP-LE) and spin light-emitting diodes (LEDs) are briefly introduced, along with the challenges and plausible prospects in this field.

Core-Shell Three-Dimensional Perovskite Nanocrystals with Chiral-Induced Spin Selectivity for Room-Temperature Spin Light-Emitting Diodes.

We developed type-II core-shell nanocrystals (NCs) with a chiral low-dimensional perovskite shell and an achiral 3D MAPbBr3 core. The core-shell NCs exhibit spin-polarized luminescence at the first excitation band of the achiral core, which is due to the chiral-induced spin selectivity (CISS) effect-governed spin-dependent shell-to-core electron transportation and the subsequent electron-hole recombination in the core. The preferred spin state of the transferred electrons is determined by the handness of the chiral shell. For the core-shell NCs film, a photoluminescence quantum yield (PLQY) of 54% and a circularly polarized luminescence (CPL) with a maximum |glum| of 4.0 × 10-3 are obtained at room temperature. Finally, we achieved a spin-polarized light-emitting diode (spin-LED), affording a circularly polarized electroluminescence (CP-EL) with a |gCP-EL|of 6.0 × 10-3 under ambient conditions.

Circularly Polarized Electroluminescence of InGaAs/GaAs/CoPt Spin Light Emitting Diodes Placed in a Strong and Weak Magnetic Field

A comparative study of the circular polarization degree dependences on external magnetic field was carried out in spin light-emitting diodes including semiconductor InGaAs/GaAs heterostructure and a magnetic CoPt contact and in control non-magnetic structures with an Au contact. In a weak magnetic field, the magnetic field dependence of electroluminescence circular polarization degree is similar to the magnetic field dependence of magnetization: it represents a hysteresis loop with saturation in a field of ~0.3 T. In a strong magnetic field, an additional linear contribution to the circular polarization degree is detected. This contribution is associated with the Zeeman splitting of energy levels. The magnitude of the linear contribution depends on the position of the quantum well relative to the ferromagnet/semiconductor interface. The obtained dependence is associated with the influence of the magnetic field of the inhomogeneously magnetized CoPt electrode on the spin relaxation time of carriers. Keywords: spin injection, quantum well, Zeeman splitting.

Circularly polarized electroluminescence at room temperature in heterostructures based on GaAs:Fe diluted magnetic semiconductor

In this work, we demonstrate the possibility of using a diluted magnetic semiconductor GaAs:Fe as a ferromagnetic injector in a spin light-emitting diode based on a GaAs/InGaAs quantum well heterostructure. It is shown that in such a device it is possible to observe partially circularly polarized electroluminescence at room temperature. Keywords: spin light-emitting diodes, diluted magnetic semiconductors, A3B5 semiconductors, spin injection.

Циркулярно-поляризованная электролюминесценция спиновых светоизлучающих диодов InGaAs/GaAs/CoPt, помещенных в сильное и слабое магнитное поле

A comparative study of the circular polarization degree dependences on external magnetic field was carried out in spin light-emitting diodes including semiconductor InGaAs/GaAs heterostructure and a magnetic CoPt contact and in control non-magnetic structures with an Au contact. In a weak magnetic field, the magnetic field dependence of electroluminescence circular polarization degree is similar to the magnetic field dependence of magnetization: it represents a hysteresis loop with saturation in a field of ~ 0.3 T. In a strong magnetic field, an additional linear contribution to the circular polarization degree is detected. This contribution is associated with the Zeeman splitting of energy levels. The magnitude of the linear contribution depends on the position of the quantum well relative to the ferromagnet/semiconductor interface. The obtained dependence is associated with the influence of the magnetic field of the inhomogeneously magnetized CoPt electrode on the spin relaxation time of carriers.

Chiral Perovskites for Next‐Generation Photonics: From Chirality Transfer to Chiroptical Activity (Adv. Mater. 47/2021)

Chiral Perovskite Materials In article number 2005760, Jooho Moon and co-workers discuss recent advances in the chiroptical activities of chiral organic–inorganic hybrid halide perovskites (OIHPs) and polarization-based devices adopting chiral OIHPs. They also present insight into the underlying chirality-transfer mechanism based on theoretical considerations. Chiral OIHPs have a wide variety of applications, such as spin light-emitting diodes, spintronics, biosensing, and optoelectronic devices.

Циркулярно поляризованная электролюминесценция при комнатной температуре в гетероструктурах на основе разбавленного магнитного полупроводника GaAs:Fe

In this work, we demonstrate the possibility of using a diluted magnetic semiconductor GaAs:Fe as a ferromagnetic injector in a spin light-emitting diode based on a GaAs/InGaAs quantum well heterostructure. It is shown that in such a device it is possible to observe partially circularly polarized electroluminescence at room temperature.

Electrical detection of light helicity using a quantum-dot-based hybrid device at zero magnetic field

Photon helicity-dependent photocurrent is measured at zero magnetic field on a device based on an ensemble of (In,Ga)As/GaAs quantum dots that are embedded into a GaAs-based $p$-$i$-$n$ diode. This device can be also operated as a spin light-emitting diode to emit the light with a circular polarization up to 20% at zero magnetic field. The demonstration of the multifunctional capabilities of the device gives valuable insights into the spin relaxation of the electrons in the quantum dots and paves the way for future spin-optoelectronic applications.

Room-temperature spin injection and optical polarization in nitride-based blue and ultra-violet spin light-emitting diodes

RT spin injection and optical polarization in nitride-based spin-LEDs are investigated. By employing CoFeB/MgO as the spin injector, the spin relaxation time and diffusion length in n-type GaN film are revealed to be 54.9 ps and 214.4 nm, respectively, through the three-terminal Hanle measurement. As the spin injector structure is applied to blue spin-LED, a maximal circular polarization of 3.3% is detected in electroluminescence, with the surface-emitting geometry and under a vertical magnetic field. UV spin-LED with n-Al0.05Ga0.95N transport layer is also fabricated, whose optical polarization is relatively smaller due to the larger spin–orbit coupling in Al atoms.

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

We report on efficient spin injection in p-doped $(\mathrm{In},\mathrm{Ga})\mathrm{As}/\mathrm{Ga}\mathrm{As}$ quantum-dot (QD) spin light-emitting diodes (spin LEDs) under zero applied magnetic field. A high degree of electroluminescence circular polarization (${P}_{c}$) \ensuremath{\sim}19% is measured in remanence up to 100 K. This result is obtained thanks to the combination of a perpendicularly magnetized $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}/\mathrm{Mg}\mathrm{O}$ spin injector allowing efficient spin injection and an appropriate p-doped $(\mathrm{In},\mathrm{Ga})\mathrm{As}/\mathrm{Ga}\mathrm{As}$ QD layer in the active region. By analyzing the bias and temperature dependence of the electroluminescence circular polarization, we evidence a two-step spin-relaxation process. The first step occurs when electrons tunnel through the $\mathrm{Mg}\mathrm{O}$ barrier and travel across the $\mathrm{Ga}\mathrm{As}$ depletion layer. The spin relaxation is dominated by the Dyakonov-Perel mechanism related to the kinetic energy of electrons, which is characterized by a bias-dependent ${P}_{c}$. The second step occurs when electrons are captured into QDs prior to their radiative recombination with holes. The temperature dependence of ${P}_{c}$ reflects the temperature-induced modification of the QD doping, together with the variation of the ratio between the charge-carrier lifetime and the spin-relaxation time inside the QDs. The understanding of these spin-relaxation mechanisms is essential to improve the performance of spin LEDs for future spin optoelectronic applications at room temperature under zero applied magnetic field.

Формирование углеродных слоев методом термического разложения четыреххлористого углерода в реакторе МОС-гидридной эпитаксии

Abstract A new method for depositing carbon films by the thermal decomposition of carbon tetrachloride (CCl_4) in a hydrogen flux in a reactor for metal-organic chemical vapor deposition (MOCVD) at atmospheric pressure is developed. From the results obtained by Raman spectroscopy, it can be conceived that the carbon layers produced by this method are the disordered nanocrystalline graphite. It is shown that such carbon layers can be used in the technological cycle of the production of gallium-arsenide optoelectronic device structures (among them spin light-emitting diodes with a CoPt injector).

Fabrication and luminescent properties of(In,Fe)Sb/GaAs/InGaAs diodes

The electrical and luminescent characteristics of InGaAs/GaAs spin light-emitting diodes with an injector based on (In,Fe)Sb were investigated and the circular polarization of the electroluminescence was obtained for such structure. It has been established that the deposition of (In,Fe)Sb layer does not introduce any additional defects into the region of near-surface quantum wells, but directly affects the (In,Fe)Sb/GaAs interface. It was found that the application of a thin protective layer of MgO between the ferromagnetic (In,Fe)Sb injector and the light-emitting structure minimizes this effect.

Enhancing the Circular Polarization of Spin Light-Emitting Diodes by Processing in Selenium Vapor

Spin light-emitting diodes based on InGaAs/GaAs heterostructures with a CoPt ferromagnetic injector were fabricated. It was demonstrated that the processing of these structures in selenium vapor prior to the deposition of a CoPt contact provides an opportunity to enhance the circular polarization degree of diode emission. The observed increase in the polarization degree is attributed to the suppression of spin relaxation at the metal/semiconductor interface due to surface passivation and a reduction in the density of surface electron states as a result of processing in selenium vapor.

On the mechanism of spin-polarized injection in (Ga,Mn)As/n+GaAs/InGaAs Zener tunnel diode

In the present work we have investigated the spin light-emitting diode structures based on InGaAs/GaAs quantum well and a (Ga,Mn)As dilute magnetic semiconductor as an injecting layer. The luminescent properties and the magnetic-field dependence of the circular polarization degree of the initial and annealed samples were measured. It was experimentally shown that the temperature dependence of circular polarization degree below the Curie point (∼ 110 K) is determined by the thermally activated tunnelling of bound electrons from energetically split spin-up and spin-down subbands of magnetized (Ga,Mn)As. The approximation parameters allowed us to derive the values of the spin energy splitting in (Ga,Mn)As subband and the spin depolarization during the transfer from (Ga,Mn)As to the device active region.

Methods for spin injection managing in inGaAs/GaAs/Al2O3/CoPt spin light-emitting diodes

Spin injection in CoPt/Al2O3/(Al)GaAs spin light-emitting diodes (SLEDs) was studied. The oscillations of the degree of circular polarization upon variation of a distance between the active region of the SLED and a CoPt ferromagnetic injector were observed. The oscillations depend neither on a SLED material (GaAs or AlGaAs), nor on the type of injected spin-polarized carriers (electrons and holes) and are related to the action of a perpendicular magnetic field on the injected spin-polarized carriers that causes their precession. During the transfer to the active region through a distance of 50–100 nm from the injector, a z–component of a spin changes a phase that is detected experimentally as the change in sign of the degree of circular polarization of luminescence. Conceivably, a source of the internal magnetic field leading to spin precession is the magnetic field of the nonuniformly magnetized CoPt contact.

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.