Interaction In GaAs Research Articles

Effect of hydrostatic pressure on the electron-phonon scattering in GaAs

Electron-phonon (e-ph) interaction in semiconductors is responsible for many phenomena such as electron mobility and hot electron thermalization, which are important to compute charge transport in semiconductors. In semiconductors, the application of hydrostatic pressure modifies the character of conduction band valleys, changing the effective mass of carriers, and, consequently, changing the carrier mobility. This, in turn, may limit electron transport in the semiconductor. Here, we present the effect of hydrostatic pressure on the e-ph interaction in GaAs, which goes from a direct to an indirect bandgap semiconductor at high pressures. A detailed study of e-ph self-energy and the resulting scattering rates is presented for hydrostatic pressure ranging between 0 and 9.2 GPa. Individual contributions from phonon modes to the total scattering rates indicate that short wavelength LO phonon scattering is found to be the dominant mechanism at low pressures; and at higher pressures, acoustic as well as optic phonons contribute toward the overall e-ph scattering. Finally, relaxation times are evaluated and we find that at pressures above 2.9 GPa, electron relaxation times are an order of magnitude lower than at equilibrium. These results will influence transport properties at higher pressures.

Exciton-phonon and exciton-exciton interactions in GaAs by time-resolved optical reflectivity

Abstract We present the study of the ultrafast carrier dynamics in bulk GaAs at 6 K, by time-resolved optical reflectivity in a wide range of excitation densities. We observe an exciton-phonon interaction at low excitation densities, in terms of a mono-exponential relaxation. Further increase of excitation density above a critical value n c , stimulates a bi-exponential relaxation in which the fast one is added owing to an exciton-exciton scattering channel. Our results reveal n c ∼ 2 × 10 24 photons / m 3 , about an order of magnitude higher than the Mott density previously determined by photoluminescence and terahertz spectroscopy measurements and theoretical calculations.

X-ray and optical pulse interactions in GaAs.

Absorption of hard x-rays in GaAs creates excitations that can dramatically alter the propagation of optical laser pulses with photon energies near the bandgap. Measurements of optical transmission through a thin crystalline wafer of GaAs after absorption of an intense x-ray synchrotron pulse demonstrate how x-ray induced optical transparency depends on the recombination of excited conduction band electrons and valence band holes via Auger, spontaneous emission, and especially stimulated emission processes. The x-ray induced band fluorescence spectrum also reveals amplified spontaneous emission at the high x-ray fluences used, confirming the importance of stimulated emission. For laser pulses with sufficiently high fluence, the interaction of optically excited electrons with x-ray excited electrons can quench the enhanced laser transmission.

Temperature dependence of the Rashba and Dresselhaus spin–orbit interactions in GaAs wells

We have recently shown [Fu and Egues, Phys. Rev. B 91 (2015) 075408] unusual properties of the spin–orbit (SO) interaction in relatively wide quantum wells, e.g., the second subband Rashba term can vanish even in asymmetric configurations. Here we report our theoretical investigation on the temperature dependence of Rashba and Dresselhaus SO interactions in GaAs both relatively narrow and wide wells, having the electron occupancy of one and two subbands, respectively. We consider all relevant intra- and intersubband SO terms. We find that the variation of intrasubband couplings as temperatures range from 0.3 to 300K could attain, ∼meVÅ, the order of usual magnitudes for SO terms in GaAs wells. Moreover, we observe distinct behaviors of the SO interaction of the two subbands, as functions of temperature. On the other band, we find that the intersubband SO terms have a relatively weak temperature dependence.

Heterodyne spectroscopy of polariton spinor interactions

We report on spinor polariton interactions in GaAs based microcavities. This investigation is carried out by means of heterodyne polarized pump-probe spectroscopy. We show the dependence of the energy renormalization of the lower and upper polariton resonances with cavity detuning for different polariton densities. We use the exciton-photon based Gross-Pitaevskii equation to model the experiment for both lower and upper polariton modes. The theoretical results reproduce qualitatively the experimental observations revealing the magnitude and the sign of the parallel and anti-parallel spin interaction strength. We evidence the strong influence of the biexciton resonance on the anti-parallel spin polariton energy shift and provide the exciton-biexciton coupling constant. We derive our results in the lower polariton basis using Gross-Pitaevskii equation from which, we express analytically the spinor polariton interactions and identify the clear role of the biexciton resonance.

Etching behavior of GaAs, GaSb, InAs, and InSb in aqueous H2O2-HBr-ethylene glycol solutions

The chemical interaction of GaAs, GaSb, InAs, and InSb single crystals with H2O2-HBr-ethylene glycol bromine-releasing etchants has been studied under reproducible hydrodynamic conditions. We have located boundaries between regions of polishing and nonpolishing solutions, assessed the surface condition of the crystals using microstructural analysis and surface profiling, and optimized the compositions of the polishing solutions and dynamic chemical polishing conditions for the materials studied.

Analytic many-body potential for GaAs(001) homoepitaxy: Bulk and surface properties

We employ atomic-scale simulation methods to investigate bulk and surface properties of an analytic Tersoff-Abell type potential for describing interatomic interactions in GaAs. The potential is a modified form of that proposed by Albe and colleagues [Phys. Rev. B 66, 035205 (2002)] in which the cut-off parameters for the As-As interaction have been shortened. With this modification, many bulk properties predicted by the potential for solid GaAs are the same as those in the original potential, but properties of the GaAs(001) surface better match results from first-principles calculations with density-functional theory (DFT). We tested the ability of the potential to reproduce the phonon dispersion and heat capacity of bulk solid GaAs by comparing it to experiment and the overall agreement is good. In the modified potential, the GaAs(001) $\ensuremath{\beta}2(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction is favored under As-rich growth conditions in agreement with DFT calculations. Additionally, the binding energies and diffusion barriers for a Ga adatom on the $\ensuremath{\beta}2(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction generally match results from DFT calculations. These studies indicate that the potential is suitable for investigating aspects of GaAs(001) homoepitaxy.

Polaron effects on the second-order susceptibilities in asymmetrical semi-parabolic quantum wells

The effect of the electron–phonon interaction on the second-order susceptibilities are investigated theoretically for electrons confined in half parabolic quantum wells. We found that the electron–phonon interaction in GaAs based wells increases the second-order susceptibilities with up to a factor of 10–40.

Effects of Weak Localization and Electron–Electron Interaction in GaAs–AlGaAs Heterostructures

The influence of the processes of weak localization and electron–electron interaction in an inhomogeneous two-dimensional electron gas of a single GaAs–AlGaAs heterojunction on the low-temperature transport characteristics in the case of occupation of two quantum subbands has been investigated. The transport characteristics have been interpreted from the viewpoint of a two-layer model taking into account the existence of two bypass conduction channels corresponding to the two-dimensional and three-dimensional electron gas. Both the electrical and optical measurements point to the existence of large-scale fluctuations of the potential, which determine the dependence of the conduction and the Hall resistance of the heterostructures on the magnetic field. It has been established that the weak localization determines the charge transport in a weak magnetic field, and the electron–electron interaction determines this transport in a strong magnetic field.

High-precision determination of the temperature-dependent band-gap shrinkage due to the electron-phonon interaction in GaAs

We use temperature-dependent, spatially resolved photoluminescence on a $\ensuremath{\mu}\mathrm{m}$ scale (\ensuremath{\mu}-PL) to perform high-precision measurements of the band-gap shift in three type-II GaAs/AlAs heterostructures that exhibit narrow luminescence lines from local type-I states. The accuracy of the energy measurements is better than $5\ensuremath{\mu}\mathrm{eV},$ which allows us to distinguish between the two contributions to the temperature shift, namely lattice expansion and electron-phonon interaction. We explicitly determine the contribution due to electron-phonon interaction at low temperatures. We find that the approach to the electron-phonon spectral function from Collins et al. [Phys. Rev. Lett. 65, 891 (1990)] leads to an excellent fitting function for the high-precision data. From the fit to our data, we determine that the electron-phonon interaction contributes to the asymptotic band-gap shift at high temperatures with ${limop}_{\stackrel{\ensuremath{\rightarrow}}{T}\ensuremath{\infty}}{(dE}_{g}/dT)=(\ensuremath{-}{198}_{\ensuremath{-}8}^{+5})\ensuremath{\mu}{\mathrm{eV}\mathrm{}\mathrm{K}}^{\ensuremath{-}1}.$

Ultrafast hole–phonon interactions in GaAs

Ultrafast heating of cold holes is investigated in bulk GaAs using a high-sensitivity two-color absorption saturation technique. Measurements performed as a function of the lattice temperature and of the carrier excess energy show that absorption of optical phonons is the main hole heating mechanism for the investigated temperatures in the range 100–300 K. Using a numerical model for carrier dynamics, the optical deformation potential is estimated to be d0∼40 eV.

Quantum Kinetic Electron-Phonon Interaction in GaAs: Energy Nonconserving Scattering Events and Memory Effects

Highly energetic electrons in GaAs emitting LO phonons are studied via femtosecond transmission spectroscopy. It is demonstrated for the first time that energy is not conserved on a time scale as short as a LO oscillation period: A replica of the initial distribution starts spectrally broadened before it sharpens into the excitation shape. This scenario is repeated for every step in the phonon cascade. Simulations combining an exact solution of quantum kinetics within a simplified model and a calculation of the polarization including Coulomb effects quantitatively agree with the data.

The s, p- d exchange interaction in GaAs heavily doped with Mn

The exciton splitting induced by the s, p- d exchange interaction in Ga 1− x Mn x As ( x < 0.001) was studied by polarized magnetoreflectance. Data were taken at 2 K in magnetic fields up to 5T. Combining these results with magnetization data, a value ( N 0 α − N 0 β) = − (2.3 ± 0.6) eV was obtained for the difference between the s- d and p- d exchange constants. Assuming that N 0 α ≈ +0.2 eV, the p- d exchange is ferromagnetic, with a magnitude N 0 β ≈ +2.5 eV. Copyright

Near-resonance acousto-optical interactions in GaAs and InP

Acousto-optical properties of GaAs and InP are thoroughly investigated for photon energies tending to the band gap from below, and the whole set of photoelastic constants is determined as a function of the wavelength λ for λ≤1.06 μm. Figures of merit as high as 1200 times those of silica have been measured. It is shown how one can take advantage of the near-resonance acousto-optical properties of GaAs and InP in device design, in spite of the optical absorption. Such devices could be broadband, fast, compact, and insensitive to light polarization and may involve other direct-gap III-V crystals, adapted to the laser radiation.

Charged point defects in GaAs crystals evaluated by nuclear-magnetic-resonance spin echo

Separation of the quadrupolar interaction in GaAs is of practical importance since the interaction magnitude is proportional to the density of charged point defects in the crystal. For this purpose, nuclear-magnetic-resonance spin-echo experiments were carried out and the results were analyzed with a theory extended from a conventional spin-echo theory. Spin echoes were obtained for 75As under a static magnetic field H0=11.7 T at room temperature. The analysis included effects of incoherent spins which are not in phase at the formation of echoes. With a combination of a Gaussian-type relaxation function for the dipolar interaction and an exp(−Kt3/2) type for the quadrupolar interaction, the theoretical fitting in the analysis showed an excellent agreement with the experiment. A pair of fitting parameters thus obtained corresponded to the strengths of the above two interactions. Each of the two parameters showed consistent orientation dependence with theoretical predictions: A+Bf(θ) for the dipolar parameter and A+Bf(θ)3/4 for the quadrupolar parameter, where f(θ)=4 cos2 θ−3 cos4 θ with θ the angle between H0 and the [110] direction of the crystal. Considering that the anisotropic amplitude B in the quadrupolar parameter represents the virtual strength of the quadrupolar interaction, the charged point-defect density in the crystal was obtained and compared with the values of optical measurements.

Exciton effects in stress-induced doubly resonant Raman scattering: GaAs.

We have calculated the Raman tensor components, including exciton effects, in the case of stress-induced doubly resonant Raman scattering via deformation-potential interaction in GaAs. Our results are in agreement with experiments as a function of stress and incident photon energy. From the fit we obtain the lifetime broadening of the heavy- and light-hole excitons, ${\ensuremath{\Gamma}}^{(3/2)}$=3.7 meV and ${\ensuremath{\Gamma}}^{(1/2)}$=1.5 meV, respectively. The evolution of the resonance upon application of uniaxial stress towards the double resonance is shown. It is also demonstrated that near resonance the discrete exciton states give a dominant contribution and that the replacement of the continuous excitonic contribution with uncorrelated electron-hole pairs changes only slightly the value of the total Raman tensor component near resonance.

Effects Induced by Dislocation-Impurity Interaction in GaAs

Effects Induced by Dislocation-Impurity Interaction in GaAs

Population relaxation time of nonequilibrium LO phonons and electron-phonon interactions in GaAs-AlxGa1-xAs multiple-quantum-well structures.

Population relaxation time of nonequilibrium LO phonons and electron-phonon interactions in GaAs-AlxGa1-xAs multiple-quantum-well structures.

Vacancy interactions in GaAs

Isochronal annealing of zinc- or silicon-doped GaAs as well as undoped semi-insulating or low-resistivity materials has been investigated by positron lifetime measurements. For impurity concentrations larger than 4.5×1017 cm−3, only monovacancy complexes such as ZnGaVAs, SiAsVGa, or AsGaVGa are observed and they yield a positron lifetime of 265±5 ps. For impurity concentrations less than 1×1017 cm−3, divacancies dominate and yield a lifetime of 295±5 ps. The concentrations of grown-in vacancies, either VAs or VGa, are both estimated to be in the range of (1–4)×1017 cm−3.

Impurity defect interactions in GaAs

Bulk Czochralski (CZ) and vapor phase epitaxy (VPE) layers of n GaAs have been irradiated with 1-MeV electrons, with doses ranging from 2×1015 to 1017 cm−2 and temperatures ranging from 240 to 330 °C. In CZ material, up to seven defects are detected. In VPE layers, five defects are observed. The variation of their introduction rates have been determined versus the temperature of irradiation. This study allows us to show that these traps are complex defects, due to the interaction of arsenic interstitial (IAs) with the impurities contained in the material. The fact that we detected the introduction of traps having the same electrical characteristics as the well-known EL5 and EL2 traps found usually in unirradiated materials provides information on their nature. Finally, a complete compensation of the material can be obtained, which demonstrates the feasibility of producing semi-insulating layers by irradiation.