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1.
The spin polarization of optically created conduction electrons in p-type AlGaAs/GaAs heterostructures was observed via the degree of circular polarization of the photoluminescence. Application of a magnetic field perpendicular to the propagation of the light allows one to determine the spin relaxation time T1 and the electron lifetime τ in the conduction band. By tilting the magnetic field with respect to an estimate of the effective nuclear field acting on the electrons can be obtained.  相似文献   

2.
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.  相似文献   

3.
We report on a field-dependent photoluminescence (PL) emission rate for the transitions between band states in modulation-doped CdTe/Cd1−xMgxTe single quantum wells in the integer quantum Hall region. The recombination time observed for the magneto-PL spectra varies in concomitance with the integer quantum Hall plateaus. Furthermore, different PL decay times were observed for the two circular polarizations, i.e. for the transitions between the Zeeman split subbands of the Landau levels. We analyzed the data in comparison with the experimentally determined spin polarization of the conduction electrons and the Zeeman splitting of the valence band. Furthermore, we discuss the relevance of the spin polarization of the conduction electrons, the electron–hole exchange interaction and the spin-flip processes of the hole states for the PL decay time.  相似文献   

4.
We present a comparison of the band alignment of the Ga1−xInxNyAs1−y active layers on GaAs and InP substrates in the case of conventionally strained and strain-compensated quantum wells. Our calculated results present that the band alignment of the tensile-strained Ga1−xInxNyAs1−y quantum wells on InP substrates is better than than that of the compressively strained Ga1−xInxNyAs1−y quantum wells on GaAs substrates and both substrates provide deeper conduction wells. Therefore, tensile-strained Ga1−xInxNyAs1−y quantum wells with In concentrations of x0.53 on InP substrates can be used safely from the band alignment point of view when TM polarisation is required. Our calculated results also confirm that strain compensation can be used to balance the strain in the well material and it improves especially the band alignment of dilute nitride Ga1−xInxNyAs1−y active layers on GaAs substrates. Our calculations enlighten the intrinsic superiority of N-based lasers and offer the conventionally strained and strain-compensated Ga1−xInxNyAs1−y laser system on GaAs and InP substrates as ideal candidates for high temperature operation.  相似文献   

5.
We report on optical orientation of electrons in n-doped InAs/GaAs quantum dots. Under non-resonant cw optical pumping, we measure a negative circular polarization of the luminescence of charged excitons (or trions) at low temperature (T=10 K). The dynamics of the recombination and of the circular polarization is studied by time-resolved spectroscopy. We discuss a simple theoretical model for the trion relaxation, that accounts for this remarkable polarization reversal. The interpretation relies on the bypass of Pauli blocking allowed by the anisotropic electron–hole exchange. Eventually, the spin relaxation time of doping electrons trapped in quantum dots is measured by a non-resonant pump–probe experiment.  相似文献   

6.
The influence of the Dresselhaus spin-orbit coupling on spin polarization by tunneling through a disordered semiconductor superlattice was investigated. The Dresselhaus spin-orbit coupling causes the spin polarization of the electron due to transmission possibilities difference between spin up and spin down electrons. The electron tunneling through a zinc-blende semiconductor superlattice with InAs and GaAs layers and two variable distance InxGa(1−x)As impurity layers was studied. One hundred percent spin polarization was obtained by optimizing the distance between two impurity layers and impurity percent in disordered layers in the presence of Dresselhaus spin-orbit coupling. In addition, the electron transmission probability through the mentioned superlattice is too much near to one and an efficient spin filtering was recommended.  相似文献   

7.
Negative electron affinity GaAs1–x P x -photocathodes emit spin-polarized electrons if irradiated with circularly polarized light. The spectra of spin polarization of photoelectrons emitted from crystals with different phosphorus contentx resemble each other in shape but shift to shorter wavelengths with increasingx. Polarization values up to 40% are observed for electrons from crystals withx=0 andx=0.38. Cathodes with higher phosphorus contents increasing fromx=0.65 tox=0.87 and tox = 1.0 deliver photoelectrons with decreasing degrees of spin polarization of 17%, 15%, and 9%, respectively, at maximum.  相似文献   

8.
In this paper, a simulation and analysis on the short-circuit current density (Jsc) of the P-GaSb window/P-GaxIn1−xAs1−ySby emitter/N-GaxIn1−xAs1−ySby base/N-GaSb substrate structure is performed. The simulations are carried out with a fixed spectral control filter at a radiator temperature (Trad) of 950 °C, diode temperature (Tdio) of 27 °C and diode bandgap (Eg) of 0.5 eV. The radiation photons are injected from the front P-side. Expressions for minority carrier mobility and absorption coefficient of GaxIn1−xAs1−ySby semiconductors are derived from Caughey–Thomas and Adachi’s model, respectively. The P-GaxIn1−xAs1−ySby emitter with a much longer diffusion length is adopted as the main optical absorption region and the N-GaxIn1−xAs1−ySby base region contribute little to Jsc. The effect of P-GaSb window and P-GaxIn1−xAs1−ySby emitter region parameters on Jsc is mainly analyzed. Dependence of Jsc on thickness and carrier concentration of the window are analyzed; these two parameters need to be properly selected to improve Jsc. Contributions from the main carrier recombination mechanisms in the emitter region are considered; Jsc can be improved by suppressing the carrier recombination rate. Dependence of Jsc on the carrier concentration and layer thickness of the emitter P-region are also analyzed; these two parameters have strong effect on Jsc. Moreover, adding a back surface reflector (BSR) to the diode can improve Jsc. The simulated results are compared with the available experimental data and are found to be in good agreement. These theoretical simulations help us to better understand the electro-optical behavior of GaxIn1−xAs1−ySby TPV diode and can be utilized for performance enhancement through optimization of the device structure.  相似文献   

9.
Conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs1−x N x alloys with a small nitrogen content (x = 2.1, 2.7, and 3.4%) is studied both experimentally and theoretically. It is found that the photoluminescence circular polarization determined by the mean spin of free electrons reaches 40–45% and this giant value persists within 2 ns. Simultaneously, the total free-electron spin decays rapidly with the characteristic time ≈ 150 ps. The results are explained by spin-dependent capture of free conduction electrons on deep paramagnetic centers resulting in the dynamical polarization of bound electrons. A nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers has been developed which describes the experimental dependencies, in particular, the electron spin quantum beats observed in a transverse magnetic field. The text was submitted by the authors in English.  相似文献   

10.
A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the GaxIn1−xAsyP1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all y compositions whatever the lattice matching to the substrates of interest. The (ΓΓ) band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of y and the substrate, GaxIn1−xAsyP1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties.  相似文献   

11.
We investigate characteristics of spin tunneling time in ZnSe/Ze1-xMnxSe multilayers under the influence of both an electric field and a magnetic field. The results indicate that the tunneling time shows complicated oscillations and significant spin separation for electrons with different spin orientations traversing semimagnetic semiconductor heterostructures. It is also shown that the tunneling time exhibits obvious asymmetry in opposite tunneling directions for electrons tunneling through asymmetric heterostructures, which mainly occurs in resonant regions. The degree of the asymmetry of the tunneling time is not only spin-polarization dependent but also external-field induced. Received 10 July 2001  相似文献   

12.
We fabricated GaAs-based spin-LED (light emitting diode) structures using half-metallic Fe3O4 as spin injectors and measured the circular polarization of the electroluminescence (EL). The circular polarization of the EL due to the spin injection was improved by the low temperature growth of the ferromagnetic layer, compared to the room temperature growth. We also studied the excitation wavelength dependence of the photoluminescence (PL) spectra and the variation of the EL spectra with increasing current. The excess carrier dependence of the EL peaks was found to be different from that of the PL peaks, which was explained by the carrier injection into the buffer layer.  相似文献   

13.
In this work, a series of identical InxGa1−xAs/AlyGa1−yAs single quantum well laser diodes, grown on (1 0 0) and (1 1 1)B GaAs substrates, have been thoroughly studied. For all samples, clear evidence of reduced threshold current densities in the (1 1 1)B substrate has been observed in electroluminescence spectra at 17 and 300 K. Modelling of the devices, based on a self-consistent solution of Schrödinger–Poisson's equations, was utilised in order to reproduce the experimental results. The model incorporates strain and piezoelectric effects on the quantum well states, free carrier screening, overlap integral computation, and optical gain calculation. The underlying mechanism, that explains the threshold reduction observed in the (1 1 1)B laser diodes, is discussed based on the results of the modelling.  相似文献   

14.
The possibility of the epitaxial growth of ferromagnetic manganese gallide (Mn3Ga5) layers on a the GaAs(100) surface was demonstrated. The ferromagnetic properties of epitaxial Mn3Ga5 at room temperature were evaluated from measurements of the anomalous Hall effect. A diode structure based on the Mn3Ga5/GaAs contact was formed, and the low-temperature electroluminescence of this diode was measured. The possibility of electroluminescence and the high crystal quality of the structures under study showed promises of their application in light-emitting diodes with spin injection.  相似文献   

15.
The electrical spin injection from Fe into an n-doped GaAs channel through Schottky-tunnel-barrier is observed from 1.8 K to room temperature. The magnitude of local spin valve signal (ΔR/R0) decreases as the temperature increases. In each temperature, we calculated the injected polarization (η) considering the spin drift effect induced by the electric field. The interfacial polarizations of 19.3% and 12.6% are acquired for Fe/GaAs junction at T=1.8 and 300 K, respectively. The temperature dependence of spin injection efficiency is matched with interface resistance variation. As the temperature increases, Schottky-tunnel-barrier property is diminished so that the spin injection efficiency would be reduced.  相似文献   

16.
The transverse and longitudinal magnetoresistance are measured on a quaternary semimagnetic semiconductor, n-type Hg1−xyCdxMnyTe with 0.01 < x < 0.23 and y ≈ 0.14, at different temperatures. The peaks of the Landau-spin states are assigned using the selection rules already developed for HgCdTe. The Landau-spin states are modified by an exchange interaction between the Mn2+ ions localized spin and the band electrons, thus it becomes possible to compare directly the extent of the spin modification between the negative gap side and the open gap side of the new alloys.  相似文献   

17.
Unpolarized light ejects spin polarized electrons from Pt(111) and Au(111) even if the electron emission occurs normal to the surface. For off normal incidence of 11.8 eV, 16.9 eV, and 21.2 eV radiation, and for the main peaks in the photoemission spectra, a degree of spin polarization of up to 30% or more is found for the spin polarization component P y perpendicular to the reaction plane. A crystal rotation about its surface normal does not change P y . P y is largest for transitions from bands with symmetry 6 3 . All these experimental findings agree with a recent theoretical prediction [1] of a new spin effect by Tamura and Feder.  相似文献   

18.
Injection of spin-polarized current into spintronic devices is a challenge to the semiconductor physicists and technologists. II-VI compound semiconductors can act as the spin aligner on the top of GaAs light emitting diode. However, II-VI compound semiconductor like Cd1−xMnxTe is still suffering from contacting problem. Application of electroless deposited magnetic NiP:Mn contact would enhance efficient current injection into Cd1−xMnxTe than the standard gold contact. A technique for electroless deposition of NiP:Mn on Cd1−xMnxTe have been described here. The electronic and magnetic properties of the contact material NiP:Mn and the contact performance of NiP:Mn relative to evaporated gold have been evaluated. The contact fulfills the requirements of resistivity and ferromagnetism for application to Cd1−xMnxTe.  相似文献   

19.
The electron spin resonance (ESR) spectra of undoped and manganese-doped BSCCO (2212) crystals (nominal composition Bi2Sr2CaCu2–x MnxOy, where x=0.1) are compared. Zh. Tekh. Fiz. 67, 137–138 (October 1997)  相似文献   

20.
We studied the influence of the nuclear spin diffusion on the dynamical nuclear polarization of low dimensional nanostructures subject to optical pumping. Our analysis shows that the induced nuclear spin polarization in semiconductor nanostructures will develop both a time and position dependence due to a nonuniform hyperfine interaction as a result of the geometrical confinement provided by the system. In particular, for the case of semiconductor quantum wells, nuclear spin diffusion is responsible for a nonzero nuclear spin polarization in the quantum well barriers. As an example we considered a 57 Å GaAs square quantum well and a 1000 Å Al x Ga1?x As parabolic quantum well both within 500 Å Al0.4Ga0.6As barriers. We found that the average nuclear spin polarization in the quantum well barriers depends on the strength of the geometrical confinement provided by the structure and is characterized by a saturation time of the order of few hundred seconds. Depending on the value of the nuclear spin diffusion constant, the average nuclear spin polarization in the quantum well barriers can get as high as 70% for the square quantum well and 40% for the parabolic quantum well. These results should be relevant for both time resolved Faraday rotation and optical nuclear magnetic resonance experimental techniques.  相似文献   

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