Carrier density dependence of electron spin relaxation in an intrinsic GaAs quantum well is investigated at room temperature using time-resolved circularly polarized pump-probe spectroscopy. It is revealed that the spin relaxation time first increases with density in the relatively low density regime where the linear D'yakonov-Perel' spin-orbit coupling terms are dominant, and then tends to decrease when the density is large and the cubic D'yakonov-Perel' spin-orbit coupling terms become important. These features are in good agreement with theoritical predictions by Lü {\em et al.} [Phys. Rev. B {\bf 73}, 125314 (2006)]. A fully microscopic calculation based on numerically solving the kinetic spin Bloch equations with both the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms included, reproduces the density dependence of spin relaxation very well.
Spin relaxation under identical Dresselhaus and Rashba coupling strengths in GaAs quantum wells is studied in both the traditional collinear statistics, where the energy spectra do not contain the spin-orbit coupling terms, and the helix statistics, where the spin-orbit couplings are included in the energy spectra. We show that there is only marginal difference between the spin relaxation times obtained from these two different statistics. We further show that with the cubic term of the Dresselhaus spin-orbit coupling included, the spin relaxation time along the (1,1,0) direction becomes finit…
We investigate the spin relaxation and spin dephasing of $n$-type GaAs quantum wells. We obtain the spin relaxation time $T_1$, the spin dephasing time $T_2$ and the ensemble spin dephasing time $T_2^{\ast}$ by solving the full microscopic kinetic spin Bloch equations, and we show that, analogous to the common sense in an isotropic system for conduction electrons, $T_1$, $T_2$ and $T_2^{\ast}$ are identical due to the short correlation time. The inhomogeneous broadening induced by the D'yakonov-Perel term is suppressed by the scattering, especially the Coulomb scattering, in this system.
We study the electron spin dynamics in p-type GaAs doped with magnetic Mn acceptors by means of time-resolved pump-probe and photoluminescence techniques. Measurements in transverse magnetic fields show a long spin relaxation time of 20 ns that can be uniquely related to electrons. Application of weak longitudinal magnetic fields above 100 mT extends the spin relaxation times up to microseconds which is explained by suppression of the Bir-Aronov-Pikus spin relaxation for the electron on the Mn acceptor.
We comment on the conclusion by Teng et al. [J. Phys. D: Appl. Phys. {\bf 42}, 135111 (2009)] that the Bir-Aronov-Pikus mechanism is more important than the D'yakonov-Perel' mechanism at high carrier density in intrinsic bulk GaAs. We point out that the spin relaxation is solely from the D'yakonov-Perel' mechanism.
We calculate the P-shell--to-S-shell decay lifetime τ(P->S) of electrons in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole scattering within an atomistic pseudopotential-based approach. We find that this relaxation mechanism leads to fast decay of τ(P->S)~1-7 ps for dots of different sizes. Our calculated Auger-type P-shell--to-S-shell decay lifetimes τ(P->S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as holes are present there is no need for an alternative polaron mechanism.
Magnetic semiconductors have aroused interest due to their various functionalities related to spintronic devices. Manganese (Mn) as a substitutional impurity in A3B5 semiconductors supplies not only holes, but also localized spins. The ejection of Mn atoms with an uncompensated magnetic moment leads to the appearance of ferromagnetic properties. The most suitable material characterized by long-term spin dynamics is n-type GaAs. In p-type GaAs, the spin relaxation time of electrons is generally much shorter. For purposes of this research, electron-spin relaxation times in 3D and 2D p-type GaAs …
We demonstrate that the peak in the density dependence of electron spin relaxation time in $n$-type bulk GaAs in the metallic regime predicted by Jiang and Wu [Phys. Rev. B {\bf 79}, 125206 (2009)] has been realized experimentally in the latest work by Krauß{\em et al}. [arXiv:0902.0270].
The electron spin relaxation in $n$-type and intrinsic GaAs$_{1-x}$Bi$_x$ with Bi composition $0\le x \le 0.1$ is investigated from the microscopic kinetic spin Bloch equation approach. The incorporation of Bi is shown to markedly decrease the spin relaxation time as a consequence of the modification of the spin-orbit interaction. We demonstrate that the density and temperature dependences of spin relaxation time in GaAs$_{1-x}$Bi$_x$ resemble the ones in GaAs. Meanwhile, the Bir-Aronov-Pikus mechanism is found to be negligible compared to the D'yakonov-Perel' mechanism in intrinsic sample. Du…
We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.
The mechanisms for spin relaxation in semiconductors are reviewed, and the mechanism prevalent in p-doped semiconductors, namely spin relaxation due to the electron-hole exchange interaction, is presented in some depth. It is shown that the solution of Boltzmann-type kinetic equations allows one to obtain quantitative results for spin relaxation in semiconductors that go beyond the original Bir-Aronov-Pikus relaxation-rate approximation. Experimental results using surface sensitive two-photon photoemission techniques show that the spin relaxation-time of electrons in p-doped GaAs at a semicond…
We investigate the spin relaxation of $p$-type GaAs quantum wires by numerically solving the fully microscopic kinetic spin Bloch equations. We find that the quantum-wire size influences the spin relaxation time effectively by modulating the energy spectrum and the heavy-hole--light-hole mixing of wire states. The effects of quantum-wire size, temperature, hole density, and initial polarization are investigated in detail. We show that, depending on the situation, the spin relaxation time can either increase or decrease with hole density. Due to the different subband structure and effects arisi…
Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is temporally resolved with picosecond time resolution. The emission spectra consisting of the multiexciton structures are observed to depend on the delay time and the excitation intensity. Quantitative agreement is found between the experimental data and the calculation based on a model which characterizes the successive relaxation of multiexcitons. Through the analysis we can determine the carrier relaxation time as a function of population of photoinjected carriers. Enhancement of the intra-dot carrier relaxation is dem…
We study the electron spin relaxation in intrinsic and $p$-type (001) GaAs quantum wells by constructing and numerically solving the kinetic spin Bloch equations. All the relevant scatterings are explicitly included, especially the spin-flip electron-heavy hole exchange scattering which leads to the Bir-Aronov-Pikus spin relaxation. We show that, due to the neglection of the nonlinear terms in the electron-heavy hole exchange scattering in the Fermi-golden-rule approach, the spin relaxation due to the Bir-Aronov-Pikus mechanism is greatly exaggerated at moderately high electron density and low…
Convergence of density-functional supercell calculations for defect formation energies, charge transition levels, localized defect state properties, and defect atomic structure and relaxation is investigated using the arsenic split interstitial in GaAs as an example. Supercells containing up to 217 atoms and a variety of {\bf k}-space sampling schemes are considered. It is shown that a good description of the localized defect state dispersion and charge state transition levels requires at least a 217-atom supercell, although the defect structure and atomic relaxations can be well converged in …
We study spin relaxation in n-type bulk GaAs, due to the Dyakonov--Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into accou…
We calculate the acoustic phonon-assisted exciton spin relaxation in single self-assembled In$_{1-x}$Ga$_x$As/GaAs quantum dots using an atomic empirical pseudopotential method. We show that the transition from bright to dark exciton states is induced by Coulomb correlation effects. The exciton spin relaxation time obtained from sophisticated configuration interaction calculations is approximately 15--55 $μ$s in pure InAs/GaAs QDs and even longer in alloy dots. These results contradict previous theoretical and experimental results, which suggest very short exciton spin times (a few ns), but ag…
Hole spin relaxation in $p$-type (111) GaAs quantum wells is investigated in the case with only the lowest hole subband, which is heavy-hole like in (111) GaAs/AlAs and light-hole like in (111) GaAs/InP quantum wells, being relevant. The subband Löwdin perturbation method is applied to obtain the effective Hamiltonian including the Dresselhaus and Rashba spin-orbit couplings. Under a proper gate voltage, the total in-plane effective magnetic field in (111) GaAs/AlAs quantum wells can be strongly suppressed in the whole momentum space, while the one in (111) GaAs/InP quantum wells can be suppre…
The electron spin dynamics in (111)-oriented GaAs/AlGaAs quantum wells is studied by timeresolved photoluminescence spectroscopy. By applying an external field of 50 kV/cm a two-order of magnitude increase of the spin relaxation time can be observed reaching values larger than 30 ns; this is a consequence of the electric field tuning of the spin-orbit conduction band splitting which can almost vanish when the Rashba term compensates exactly the Dresselhaus one. The measurements under transverse magnetic field demonstrate that the electron spin relaxation time for the three space directions can…
We measure the lifetime of the zone-center 340 GHz longitudinal phonon mode in a GaAs-AlAs superlattice excited and probed with femtosecond laser pulses. By comparing measurements conducted at room temperature and liquid nitrogen temperature we separate the intrinsic (phonon-phonon scattering) and extrinsic contributions to phonon relaxation. The estimated room temperature intrinsic lifetime of 0.95 ns is compared to available calculations and experimental data for bulk GaAs. We conclude that ~0.3 THz phonons are in the transition zone between Akhiezer and Landau-Rumer regimes of phonon-phonon…
We report on the measurements of spin relaxation in GaAs quasi-one-dimensional mesowires, relying on spin noise spectroscopy, thus adding to the existing body of spin relaxation studies in bulk, two-dimensional and zero dimensional systems. In addition to temperature and magnetic field dependence, we modify the spin relaxation time via applied electric field and aspect ratio of the mesowires, suggesting that scalable spintronics devices with controllable spin relaxation are achievable. Overall, we observed higher spin-relaxation time in mesowires compared to bulk with a spin noise exhibiting D…
We have studied the effect of nonequilibrium longitudinal optical phonons on hot-electron spin relaxation in $n$-type GaAs quantum wells. The longitudinal optical phonons, due to the finite relaxation rate, are driven to nonequilibrium states by electrons under an in-plane electric field. The nonequilibrium phonons then in turn influence the electron spin relaxation properties via modifying the electron heating and drifting. The spin relaxation time is elongated due to the enhanced electron heating and thus the electron-phonon scattering in the presence of nonequilibrium phonons. The frequency…
We report on both experimental and theoretical study of conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1, 2.7, 3.4%). 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 c…
The giant transverse magnetoresistance is observed in the case of photoinduced nonequilibrium carriers in an asymmetric undoped system of three GaAs/AlGaAs quantum wells at room temperature. In a magnetic field of 75 kOe, the resistance of nanostructure being studied increases by a factor of 1.85. The magnetoresistance depends quadratically on the magnetic field in low fields and tends to saturation in high fields. This phenomenon is attributed to the rearrangement of the electron wave function in magnetic field. Using the fact that the incoherent part of the scattering probability for electro…
We investigate the electric field tuning of the phonon-assisted hole spin relaxation in single self-assembled In$_{1-x}$Ga$_{x}$As/GaAs quantum dots, using an atomistic empirical pseudopotential method. We find that the electric field along the growth direction can tune the hole spin relaxation time for more than one order of magnitude. The electric field can prolong or shorten the hole spin lifetime and the tuning shows an asymmetry in terms of the field direction. The asymmetry is more pronounced for the taller the dot. The results show that the electric field is an effective way to tune the…
The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here we present room temperature photoluminescence and ellipsometry measurements of Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the red shift of the room temperature near band gap emission from the Ga_{100%-x}Mn_{x}As alloy with increasing Mn content. It is shown that even a doping b…
We present full atomistic calculations of the spin-flip time (T$_{1}$) of electrons and holes mediated by acoustic phonons in self-assembled In$_{1-x}$Ga$_x$As/GaAs quantum dots at zero magnetic field. At low magnetic field, the first-order process is suppressed, and the second-order process becomes dominant. We find that the spin-phonon-interaction induced spin relaxation time is 40 - 80 s for electrons, and 1 - 20 ms for holes at 4.2 K. The calculated hole-spin relaxation times are in good agreement with recent experiments, which suggests that the two-phonon process is the main relaxation me…
We investigate the spin relaxation limited by the D'yakonov-Perel' mechanism in $n$-type (111) GaAs quantum wells, by means of the kinetic spin Bloch equation approach. In (111) GaAs quantum wells, the in-plane effective magnetic field from the D'yakonov-Perel' term can be suppressed to zero on a special momentum circle under the proper gate voltage, by the cancellation between the Dresselhaus and Rashba spin-orbit coupling terms. When the spin-polarized electrons mainly distribute around this special circle, the in-plane inhomogeneous broadening is small and the spin relaxation can be suppres…
We investigate electron spin relaxation in $p$-type GaAs quantum wells from a fully microscopic kinetic spin Bloch equation approach, with all the relevant scatterings, such as the electron-impurity, electron-phonon, electron-electron Coulomb, electron-hole Coulomb and electron-hole exchange (the Bir-Aronov-Pikus mechanism) scatterings explicitly included. From this approach, we examine the relative importance of the D'yakonov-Perel' and Bir-Aronov-Pikus mechanisms in wide ranges of temperature, hole density, excitation density and impurity density, and present a phase-diagram--like picture sh…
We study the effect of the Singwi-Tosi-Land-Sjölander local field correction on spin relaxation/dephasing in $n$-type GaAs quantum wells at low temperature by constructing and numerically solving the kinetic spin Bloch equations. We calculate the local field factor $G(q)$ in quantum wells by numerically solving three equations which link the local field factor, the structure factor, and the dielectric function, self-consistently. Such a correction reduces both the electron-electron Coulomb scattering and the Coulomb Hartree-Fock term. We compare the spin relaxation times with and without this …
Electron-spin relaxation at different surfaces of p-doped GaAs is investigated by means of spin, time and energy resolved 2-photon photoemission. These results are contrasted with bulk results obtained by time-resolved Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus spin-flip mechanism. Due to the reduced hole density in the band bending region at the (100) surface the spin-relaxation time increases over two orders of magnitude towards lower energies. At the flat-band (011) surface a constant spin relaxation time in agreement with our measurements and calculations…
The sub-bandgap absorption and ultrafast relaxation in a GaAs/ErAs/GaAs heterostructure are reported. The infrared absorption and 1550 nm-excited ultrafast photo-response are studied by Fourier transform infrared (FTIR) spectrometry and time-domain pump-probe technique. The two absorption peaks located at 2.0 um (0.62 eV) and 2.7 um (0.45 eV) are originated from the ErAs/GaAs interfacial Schottky states and sub-bandgap transition within GaAs, respectively. The photo-induced carrier lifetime, excited using 1550 nm light, is measured to be as low as 190 fs for the GaAs/ErAs/GaAs heterostructure,…
We present an investigation of electron-spin dynamics in p-doped bulk GaAs due to the electron-hole exchange interaction, aka the Bir-Aronov-Pikus mechanism. We discuss under which conditions a spin relaxation times for this mechanism is, in principle, accessible to experimental techniques, in particular to 2-photon photoemission, but also Faraday/Kerr effect measurements. We give numerical results for the spin relaxation time for a range of p-doping densities and temperatures. We then go beyond the relaxation time approximation and calculate numerically the spin-dependent electron dynamics by…
We investigate hole spin relaxation in intrinsic and $p$-type bulk GaAs from a fully microscopic kinetic spin Bloch equation approach. In contrast to the previous study on hole spin dynamics, we explicitly include the intraband coherence and the nonpolar hole-optical-phonon interaction, both of which are demonstrated to be of great importance to the hole spin relaxation. The relative contributions of the D'yakonov-Perel' and Elliott-Yafet mechanisms on hole spin relaxation are also analyzed. In our calculation, the screening constant, playing an important role in the hole spin relaxation, is t…
Multivalley spin relaxation in $n$-type bulk GaAs in the presence of high electric field is investigated from the microscopic kinetic spin Bloch equation approach with the $Γ$ and $L$ valleys included. We show that the spin relaxation time decreases monotonically with the electric field, which differs from the two-dimensional case and is recognized due to to the cubic form of the Dresselhauss spin-orbit coupling of the $Γ$ valley in bulk. In addition to the direct modulation of the spin relaxation time, the electric field also strongly influences the density and temperature dependences of the …
We report theoretical and experimental studies of ambipolar spin diffusion in a semiconductor. A circularly polarized laser pulse is used to excite spin-polarized carriers in a GaAs multiple quantum well sample at 80 K. Diffusion of electron and spin densities is simultaneously measured using a spatially and temporally resolved pump-probe technique. Two regimes of diffusion for spin-polarized electrons are observed. Initially, the rate of spin diffusion is similar to that of density diffusion and is controlled by the ambipolar diffusion coefficient. At later times, the spin diffusion slows dow…
We report on efficient spin injection in p-doped InGaAs/GaAs quantum-dot (QD) spin light emitting diode (spin-LED) under zero applied magnetic field. A high degree of electroluminescence circular polarization (Pc) ~19% is measured in remanence up to 100K. This result is obtained thanks to the combination of a perpendicularly magnetized CoFeB/MgO spin injector allowing efficient spin injection and an appropriate p-doped InGaAs/GaAs QD layer in the active region. By analyzing the bias and temperature dependence of the electroluminescence circular polarization, we have evidenced a two-step spin r…
We applied the recently developed technique of force-detected nuclear magnetic resonance (NMR) to observe 71Ga, 69Ga, and 75As in GaAs. The nuclear spin-lattice relaxation time is 21$\pm$5 min for 69Ga at $\sim 5$ K and 4.6 Tesla. We have exploited this long relaxation time to first create and then observe spatially varying nuclear spin polarization within the sample, demonstrating a new form of contrast for magnetic resonance force microscopy (MRFM). Such nuclear spin contrast could be used to indirectly image electron spin polarization in GaAs-based spintronic devices.
Spin dephasing via the spin-orbit interaction (SOI) is a major mechanism limiting the electron spin lifetime in III-V zincblende quantum wells. The dephasing can be suppressed in GaAs(111) quantum wells by applying an electric field. The suppression has been attributed to the compensation of the intrinsic SOI associated by the bulk inversion asymmetry (BIA) of the GaAs lattice by a structural induced asymmetry (SIA) SOI term induced by an electric field. We provide direct experimental evidence for this mechanism by demonstrating the transition between the BIA-dominated to a SIA-dominated regim…
We investigate the nonlinear response of GaAs-based photonic crystal cavities at time scales which are much faster than the typical thermal relaxation rate in photonic devices. We demonstrate a strong interplay between thermal and carrier induced nonlinear effects. We have introduced a dynamical model entailing two thermal relaxation constants which is in very good agreement with experiments. These results will be very important for Photonic Crystal-based nonlinear devices intended to deal with practical high repetition rate optical signals.
We perform a full microscopic investigation on the spin relaxation in $n$-type (001) GaAs quantum wells with Al$_{0.4}$Ga$_{0.6}$As barrier due to the D'yakonov-perel' mechanism from nearly 20 K to the room temperature by constructing and numerically solving the kinetic spin Bloch equations. We consider all the relevant scattering such as the electron--acoustic-phonon, the electron--longitudinal-optical-phonon, the electron--nonmagnetic-impurity and the electron-electron Coulomb scattering to the spin relaxation. The spin relaxation times calculated from our theory with a fitting spin splittin…
Multi-valley spin relaxation in $n$-type GaAs quantum wells with in-plane electric field is investigated at high temperature by means of kinetic spin Bloch equation approach. The spin relaxation time first increases and then decreases with electric field, especially when the temperature is relatively low. We show that $L$ valleys play the role of a ``drain'' of the total spin polarization due to the large spin-orbit coupling in $L$ valleys and the strong $Γ$-$L$ inter-valley scattering, and thus can enhance spin relaxation of the total system effectively when the in-plane electric field is hig…
The spin relaxation time of electrons in GaAs and GaN are determined with a model that includes momentum scattering by phonons and ionized impurities, and spin scattering by the Elliot-Yafet, D'yakonov-Perel, and Bir-Aronov-Pikus mechanisms. Accurate bands generated using a long-range tight-binding Hamiltonian obtained from empirical pseudopotentials are used. The inferred temperature-dependence of the spin relaxation lifetime agrees well with measured values in GaAs. We further show that the spin lifetimes decrease rapidly with injected electrons energy and reach a local maximum at the longit…
In this paper, thermal conductivity of crystalline GaAs is calculated using first-principles lattice dynamics. The harmonic and cubic force constants are obtained by fitting them to the force-displacement data from density functional theory calculations. Phonon dispersion is calculated from dynamical matrix constructed using the harmonic force constants and phonon relaxation times are calculated using Fermi Golden rule. The calculated GaAs thermal conductivity agrees well with experimental data. Thermal conductivity accumulations as a function of phonon mean free path and as a function of wave…
Photoluminescence (PL) and reflectivity spectra of a high-quality InGaAs/GaAs quantum well structure reveal a series of ultra-narrow peaks attributed to the quantum confined exciton states. The intensity of these peaks decreases as a function of temperature, while the linewidths demonstrate a complex and peculiar behavior. At low pumping the widths of all peaks remain quite narrow ($< 0.1$ meV) in the whole temperature range studied, $4 - 30K$. At the stronger pumping, the linewidth first increases and than drops down with the temperature rise. Pump-probe experiments show two characteristic ti…
The carrier spin dynamics in a n-doped (In,Ga)As/GaAs quantum well has been studied by time-resolved Faraday rotation and ellipticity techniques in the temperature range down to 430 milliKelvin. These techniques give data with very different spectral dependencies, from which nonetheless consistent information on the spin dynamics can be obtained, in agreement with theoretical predictions. The mechanisms of long-lived spin coherence generation are discussed for the cases of trion and exciton resonant excitation. We demonstrate that carrier localization leads to a saturation of spin relaxation t…
We report on the influence of hyperfine interaction on the optical orientation of singly charged excitons X+ and X- in self-assembled InAs/GaAs quantum dots. All measurements were carried out on individual quantum dots studied by micro-photoluminescence at low temperature. We show that the hyperfine interaction leads to an effective partial spin relaxation, under 50kHz modulated excitation polarization, which becomes however strongly inhibited under steady optical pumping conditions because of dynamical nuclear polarization. This optically created magnetic-like nuclear field can become very st…
By solving the kinetic spin Bloch equations, we study the time evolution of the transient spin grating, whose spin polarization varies periodically in real space, confined in (001) GaAs quantum wells. With this study we can investigate the properties of both the spin transport and the spin relaxation at the same time. The Fourier component of the spin signal decays double exponentially with two decay rates $1/τ_+$ and $1/τ_-$. In high temperature regime, the average of these two rates varies with the grating wave-vector $q$ quadratically, i.e., $(1/τ_++1/τ_-)/2=D_sq^2+1/\tildeτ_s$, with $D_s$ …
We have studied spin dephasing in a high-mobility two-dimensional electron system (2DES), confined in a GaAs/AlGaAs quantum well grown in the [110] direction, using the resonant spin amplification (RSA) technique. From the characteristic shape of the RSA spectra, we are able to extract the spin dephasing times (SDT) for electron spins aligned along the growth direction or within the sample plane, as well as the $g$ factor. We observe a strong anisotropy in the spin dephasing times. While the in-plane SDT remains almost constant as the temperature is varied between 4 K and 50 K, the out-of-plan…
We report on photoluminescence in the 3-7 $μ$m mid-wave infrared (MWIR) range from sub-100 nm strained thin films of rocksalt PbSe(001) grown on GaAs(001) substrates by molecular beam epitaxy. These bare films, grown epitaxially at temperatures below 400 °C, luminesce brightly at room temperature and have minority carrier lifetimes as long as 172 ns. The relatively long lifetimes in PbSe thin films are achievable despite threading dislocation densities exceeding $10^9$ $cm^{-2}$ arising from island growth on the nearly 8% lattice- and crystal-structure-mismatched GaAs substrate. Using quasi-co…
We study the spin decoherence in n-type bulk GaAs for moderate electronic densities at room temperature using Ensemble Monte Carlo method. We demonstrate that the third-body rejection method devised by Ridley can be successfully adapted to Ensemble Monte Carlo algorithm, and used to tackle the problem of the electron-electron contribution to spin decoherence.
Optical orientation experiments have been performed in GaAs epilayers with photoexcitation energies in the 3 eV region yielding the photogeneration of spin-polarized electrons in the satellite L valley. We demonstrate that a significant fraction of the electron spin memory can be conserved when the electron is scattered from the L to the $Γ$ valley following an energy relaxation of several hundreds of meV. Combining these high energy photo-excitation experiments with time-resolved photoluminescence spectroscopy of $Γ$ valley spin-polarized photogenerated electrons allows us to deduce a typical…
We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on Si substrates using molecular-beam epitaxy. Transmission electron microscopy (TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows domination of the zinc-blende phase. This is further confirmed in optics of single NWs, studied using cw and time-resolved photoluminescence (PL). A detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP capping in suppressing the non-radiative surface states: significant PL enhancement in the core-shell structures exceeding 2000 times at 10K i…
We study the effect of charged impurity screening on spin decoherence in bulk {\it n}-type GaAs, and analyse in details the effect of the use of different Born approximations applied to a linearized Thomas-Fermi screening theory. The spin relaxation times are calculated by ensemble Monte Carlo techniques, including electron-electron, electron-impurities, and electron-phonons scattering. We carefully choose a parameter region so that all the physical approximations hold, and, in particular, a Yukawa-type potential can be used to describe the screened Coulomb interaction and the Born series conv…
We investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions. The tunneling magnetoresistance effect (TMR) was probed for different types of Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is increased and observable at room temperature. If an epitaxial Fe/GaAs(001) interface is involved, the tunnel junction exhibits a bias dependent inversion of the TMR effect. This is a first experimental signature for band structure effects at a Fe/GaAs interface and relevant for spin injection experiments.
The equilibrium shape of strained InAs quantum dots grown epitaxially on a GaAs(001) substrate is derived as a function of volume. InAs surface energies are calculated within density-functional theory, and a continuum approach is applied for the elastic relaxation energies.
Sub-picosecond ac spin current pulses are generated optically in GaAs bulk and quantum wells at room temperature and 90K through quantum interference between one-photon and two-photon absorptions driven by two phase-locked ultrafast laser pulses that are both circularly polarized. The dynamics of the current pulses are detected optically by monitoring in real time and real space nanoscale motion of electrons with high-resolution pump-probe techniques.
Precise control of doping in single nanowires (NWs) is essential for the development of NW-based devices. Here, we investigate a series of MBE-grown GaAs NWs with Be (p-type) and Si (n-type) doping using high-resolution cathodoluminescence (CL) mapping at low- and room-temperature. CL spectra are analyzed selectively in different regions of the NWs. Room-temperature luminescence is fitted with the generalized Planck law and an absorption model, and the bandgap and band tail width are extracted. For Be-doped GaAs NWs, the bandgap narrowing provides a quantitative determination of the hole conce…
It is known in the literature that InGaP alloy synthesized within a certain range of growth temperature (520 - 720 degree Centrigrade) shows Cu-Pt crystal ordering. This ordering reduces the band gap energy . It was predicted that the ordering induced modification of energy levels of InGaP lowers its conduction band edge, which could change a type I band alignment at a GaAs/InGaP heterojunction to type II . Here we report the first observation of this ordering related type I/II transition for a GaAs/InGaP heterojunction by C-V profiling experiments done at room temperature .
We use the ab initio local-density approximation (LDA) to study of exchange interactions and Tc of Ga1−xMnxAs grown in digitally doped structures. We analyze the crystallographic dependence of exchange interactions predicted by the LDA in terms of the Mn t2 and e levels, and explain the origin of the antiferromagnetic contribution to the total exchange interactions. We exploit this dependence and consider delta-doping in specific orientations where the antiferromagnetic interactions are minimized, to optimize Tc of the system. By including hole doping with the addition of Be in the GaAs …
