Electrons In GaAs Research Articles

Electrically Driven Spin Dynamics of Paramagnetic Impurities

The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.

Ab initioMethod for Calculating Electron-Phonon Scattering Times in Semiconductors: Application to GaAs and GaP

We propose a fully ab initio approach to calculate electron-phonon scattering times for excited electrons interacting with short-wavelength (intervalley) phonons in semiconductors. Our approach is based on density functional perturbation theory and on the direct integration of electronic scattering probabilities over all possible final states with no ad hoc assumptions. We apply it to the deexcitation of hot electrons in GaAs, and calculate the lifetime of the direct exciton in GaP, both in excellent agreement with experiments. Matrix elements of the electron-phonon coupling, and their dependence on the wave vector of the final state and on the phonon modes, are shown to be crucial ingredients of the evaluation of electron-phonon scattering times.

Reply to “Comment on ‘Spin and cyclotron energies of electrons inGaAs∕Ga1−xAlxAsquantum wells’ ”

Responding to the previous Comment we quote the exact spin $g$ values of conduction electrons in bulk GaAs resulting from the three-level $\mathbf{P}∙\mathbf{p}$ model (3LM). We show that the approximate description of Ivchenko and Kiselev based on 3LM considerably overestimates the $g$ values for the interesting region of large ${k}_{z}$. We conclude that the three-level $\mathbf{P}∙\mathbf{p}$ model does not give an adequate description of orbital and spin electron energies in bulk GaAs and in $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ quantum wells.

Research directions in beyond CMOS computing

The International Technology Roadmap for Semiconductors has identified five promising research directions in beyond CMOS computing technology that are discussed here. Alternate state variables beyond electronic charge are introduced. Momentum and spin relaxation times for electrons in GaAs are calculated and show that magnetic systems are less strongly coupled to the thermal environment than systems based on electronic charge.

Effect of the Rashba and Dresselhaus spin-splitting terms on the electron g factor in semiconductor quantum wells under applied magnetic fields

We use the Ogg–McCombe Hamiltonian together with the Dresselhaus and Rashba spin-splitting terms to find the g factor of conduction electrons in GaAs-(Ga,Al)As semiconductor quantum wells (QWS) (either symmetric or asymmetric) under a magnetic field applied along the growth direction. The combined effects of non-parabolicity, anisotropy and spin-splitting terms are taken into account. Theoretical results are given as functions of the QW width and compared with available experimental data and previous theoretical works.

Effect of the Dresselhaus spin splitting on the effective Landé g-factor in GaAs–(Ga,Al)As quantum wells under in-plane or growth-direction magnetic fields

Using the non-parabolic and anisotropic Ogg–McCombe effective Hamiltonian, we study the effect of the Dresselhaus spin splitting on the cyclotron effective mass and Landé g-factor associated to conduction electrons in GaAs–(Ga,Al)As quantum wells under applied magnetic fields, both along the growth- and in-plane directions of the heterostructure. Theoretical results are found in good agreement with available experimental measurements.

Experimental and numerical study on AlGaInAs/AlGaAs distributed feedback lasers with GaInP gratings

Ridge-waveguide AlGaInAs/AlGaAs distributed feedback lasers with lattice-matched GaInP gratings were fabricated and their light-current characteristics, spectrum and far-field characteristics were measured. On the basis of our experimental results we analyze the effect of the electron stopper layer on light-current performance using the commercial laser simulation software PICS3D. The simulator is based on the self-consistent solution of drift diffusion equations, the Schrodinger equation, and the photon rate equation. The simulation results suggest that, with the use of a 80 nm-width p-doped Al0.6GaAs electron stopper layer, the slope efficiency can be increased and the threshold current can be reduced by more than 10 mA.

QUANTUM HALL EFFECT IN A MULTI-VALLEY TWO-DIMENSIONAL ELECTRON SYSTEM

Two-dimensional electrons in an AlAs quantum well occupy multiple conduction-band minima at the X-points of the Brillouin zone. These valleys have large effective mass and g-factor compared to the standard GaAs electrons, and are highly anisotropic. With proper choice of well width and by applying symmetry-breaking strain in the plane, one can control the occupation of different valleys thus rendering a system with tuneable effective mass, g-factor, Fermi contour anisotropy, and valley degeneracy. Here we review some of the rich physics that this system has allowed us to explore.

Optically detected cyclotron resonance studies of InxGa1−xNyAs1−y∕GaAs quantum wells sandwiched between type-II AlAs∕GaAs superlattices

We report on our results from a systematic study of layered structures containing an InGaNAs∕GaAs single quantum well (SQW) enclosed between staggered type II AlAs∕GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, the predominant ODCR peak is shown to be related to carriers with a two-dimensional character and a cyclotron resonance effective mass of m*≈(0.51–0.56)m0. The responsible carriers are ascribed to electrons on the ellipsoidal equienergy surface at the AlAs X point of the Brillouin zone within the SL, based on results from angular and spectral dependences of the ODCR signal. No ODCR signal related to the InGaNAs SQW was detected, presumably due to low carrier mobility despite the high optical quality. Multiple absorption of photons with energy below the band gap energy of the SL and the GaAs barriers was observed, which bears implication on the efficiency of light-emitting devices based on these structures.

Electron density dependence of in-plane spin relaxation anisotropy in GaAs∕AlGaAs two-dimensional electron gas

The authors investigated the spin dynamics of two-dimensional electrons in (001) GaAs∕AlGaAs heterostructure using the time-resolved Kerr rotation technique under a transverse magnetic field. The in-plane spin lifetime is found to be anisotropic below 150K due to the interference of Rashba [J. Phys. C 17, 6039 (1984)] and Dresselhaus [Phys. Rev. 100, 580 (1955)] spin-orbit coupling and D’yakonov-Perel [Sov. Phys. Solid State 13, 3023 (1972)] spin relaxation. The ratio of in-plane spin lifetimes is measured directly as a function of temperature and pump power, showing that the electron density in two-dimensional electron gas channel strongly affects the Rashba spin-orbit coupling.

Effective Landé factor [formula omitted] of conduction electrons in GaAs and AlSb

Using third and fourth order perturbation theory inside a 14-band and 30-band k ⋅ p model, we have calculated the effective Landé factor g ∗ of Γ 6 C conduction electrons in GaAs and AlSb. A strong variation between both models is observed. We show that the 14-band formalism even in fourth order perturbation theory is not sufficient to predict an experimental data of g ∗ . However, results deduced by the 30-band k ⋅ p model are consistent with experimental data. In particular, the k ⋅ p Hamiltonian parameters are adjusted such that the g ∗ of GaAs and AlSb are respectively −0.391 and 0.81, in excellent agreement with the experimental values of −0.44 and 0.84.

Two‐dimensional electrons occupying multiple valleys in AlAs

AbstractTwo‐dimensional electrons in AlAs quantum wells occupy multiple conduction‐band minima at the X‐points of the Brillouin zone. These valleys have large effective mass and g ‐factor compared to the standard GaAs electrons, and are also highly anisotropic. With proper choice of well width and by applying symmetry‐breaking strain in the plane, one can control the occupation of different valleys thus rendering a system with tuneable effective mass, g ‐factor, Fermi contour anisotropy, and valley degeneracy. Here we review some of the rich physics that this system has allowed us to explore. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detection of magnetic resonance of donor-bound electrons in GaAs by Kerr rotation

Detection of magnetic resonance of donor-bound electrons in GaAs by Kerr rotation

Effects of in-plane magnetic fields on the electronic cyclotron effective mass and Landé factor in GaAs-(Ga,Al)As quantum wells

The dependence of the electron Lande g-factor on carrier confinement in quantum wells recently gained both experimental and theoretical interest. The g factor of electrons in GaAs-(Ga,Al)As quantum wells is of special interest, as it changes its sign at a certain value of the well width. In the present work, the effects of an in-plane magnetic field on the cyclotron effective mass and on the Lande g^-factor in single GaAs-(Ga,Al)As quantum wells are studied. Theoretical calculations are performed in the framework of the effective-mass and non-parabolic-band approximations. The Ogg-McCombe Hamiltonian is used for the conduction-band electrons in the semiconductor heterostructure, and the Lande g^-factor theoretically evaluated is found in good agrement with available experimental measurements.

Evidence of electron and hole inversion in GaAs metal-oxide-semiconductor capacitors with HfO2 gate dielectrics and α-Si∕SiO2 interlayers

Evidence of inversion in GaAs metal-oxide-semiconductor capacitors with HfO2 gate dielectrics and α-Si∕SiO2 interlayers is reported. Capacitors formed on n-GaAs with atomic layer-deposited HfO2 displayed C-V characteristics with minimum Dit of 7×1011cm−2∕eV, while capacitors with molecular beam epitaxy-deposited HfO2 on p-GaAs had Dit=3×1012cm−2∕eV. Lateral charge transport was confirmed using illuminated C-V measurements on capacitors fabricated with thick Al electrodes. Under these conditions, capacitors on n-GaAs (p-GaAs) showed “low-frequency” C-V behavior, indicated by a sharp capacitance increase and saturation at negative (positive) gate bias, confirming the presence of mobile charge at the semiconductor/dielectric interface.

Effects of non-parabolicity and in-plane magnetic fields on the cyclotron effective mass andg⊥-factor in GaAs-(Ga,Al)As quantum wells

The envelope-function approach is used to theoretically study the effects of in-plane magnetic fields on the cyclotron effective mass and Land\'e ${g}_{\ensuremath{\perp}}$-factor associated to conduction electrons in single GaAs-(Ga,Al)As quantum wells. Non-parabolic and anisotropy effects are included in the calculations within the Ogg-McCombe effective Hamiltonian to describe the electron states in the semiconductor heterostructure. The electronic structure and both the cyclotron effective mass and Land\'e ${g}_{\ensuremath{\perp}}$-factor were obtained, by expanding the corresponding envelope wave functions in terms of harmonic-oscillator wave functions, as functions of the in-plane magnetic field, cyclotron orbit-center position, and quantum-well widths. This procedure allows us to consider the different terms in the Hamiltonian on equal footing, avoiding therefore the use of approximate methods to obtain the envelope wave functions and the corresponding energy spectrum. Results obtained for the Land\'e ${g}_{\ensuremath{\perp}}$-factor were found in quite good agreement with available experimental measurements.

Conductance quantization and the 0.7×2e2∕h conductance anomaly in one-dimensional hole systems

We have studied ballistic transport in a one-dimensional (1D) channel formed using surface gate techniques on a back-gated, high-mobility, bilayer two-dimensional hole system. At millikelvin temperatures, robust conductance quantization is observed in the quantum wire formed in the top layer of the bilayer system, without the gate instabilities that have hampered previous studies of 1D hole systems. Using source drain bias spectroscopy, we have measured the 1D subband spacings, which are 5–10 times smaller than in comparable GaAs electron systems, but 2–3 times larger than in previous studies of 1D holes. We also report the first observation of the anomalous conductance plateau at G=0.7×2e2∕h in a 1D hole system.

Studies on the temperature and energy dependence of g factor in GaAs by femtosecond laser absorption quantum beats

Time-resolved elliptically polarized pump-probe spectroscopy developed by us is used to study spin relaxation dynamics of electrons in an intrinsic GaAs under an external magnetic field. Absorption quantum beats are observed and attributed to Larmor precession of electron spin around the magnetic field. The frequency of this quantum beat is used as a new method to measure electronic g factor with high accuracy. In this paper, this new method is utilized to investigate the temperature and energy dependence of electronic g factor in the intrinsic GaAs. It is found that electronic g factor increases with the temperature and energy of electrons, which is guitc different from the dependence predicted by k·p theory. An empirical formula is given to describe the temperature and energy dependence of g factor by fitting experimental data.

Interaction correction to the longitudinal conductivity and Hall resistivity in high-quality two-dimensional GaAs electron and hole systems

We present a systematic study of the corrections to both the longitudinal conductivity and Hall resistivity due to electron-electron interactions in high quality GaAs systems using the recent theory of Zala et al. [Phys. Rev. B 64, 214204 (2001)]. We demonstrate that the interaction corrections to the longitudinal conductivity and Hall resistivity predicted by the theory are consistent with each other. This suggests that the anomalous metallic drop in resistivity at B=0 is due to interaction effects and supports the theory of Zala et al.

Effect of dc and ac excitations on the longitudinal resistance of a two-dimensional electron gas in highly doped GaAs quantum wells

Linear ac $(888\phantom{\rule{0.3em}{0ex}}\mathrm{Hz})$ resistance of highly mobile two-dimensional electrons in GaAs heavily doped quantum wells is studied at different magnitudes of dc and ac $(10\phantom{\rule{0.3em}{0ex}}\mathrm{KHz}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}20\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$ excitations. In the dc excitation regime the differential resistance oscillates with the dc current and external magnetic field similar to that observed earlier in $\mathrm{Al}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ heterostructures [C. L. Yang et al., Phys. Rev. Lett. 89, 076801 (2002)]. At external ac excitations the resistance is also found to be oscillating with the magnetic field. However the form of the oscillations is considerably different from the dc case. We show that at frequency below $100\phantom{\rule{0.3em}{0ex}}\mathrm{KHz}$ the difference is the result of a specific average of the dc differential resistance during the period of the external ac excitations.