Conduction Electrons In GaAs Research Articles

Electron Landé g factor in GaAs–(Ga,Al)As quantum wells under applied magnetic fields: Effects of Dresselhaus spin splitting

The effects of the Dresselhaus spin splitting on the Landé g factor associated with conduction electrons in GaAs–(Ga,Al)As quantum wells are studied by using the nonparabolic Ogg–McCombe effective Hamiltonian. The g factor and cyclotron effective mass are calculated as functions of applied magnetic fields (along both the growth and in-plane directions) and GaAs well widths of the heterostructure. Present calculations indicate that in GaAs–(Ga,Al)As heterostructures, the inclusion of the Dresselhaus term leads to very small corrections in the effective Landé factor. Taking into account the effects of nonparabolic and anisotropic terms in the Hamiltonian is fundamental in obtaining quantitative agreement with experimental measurements. Moreover, the present results suggest that previous theoretical work on the Dresselhaus spin-splitting effects on the effective Landé factor should be viewed with caution if nonparabolic and anisotropic effects are not taken into account.

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.

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.

Drift Transport of Spin-Polarized Electrons in GaAs

We studied the transport properties of spin-polarized conduction electrons in GaAs by time-resolved photoinjection and photoluminescence polarization measurements. Under an electric field of a few kV/cm, the degree of the spin polarization considerably decreases during drift transport over the distance shorter than 4 μm. Spin relaxation by D'yakonov–Perel' mechanism is suggested to be the cause of such a rapid spin depolarization for hot electrons under a moderate electric field at low temperatures.

Electronic Structure and Optical Properties of GaAs1-xNxand Ga1-xBxAs Alloys

The electronic band structure of GaAs 1 - x N x (x = 0.016 and 0.031) and Ga 1 - x B x As (x = 0.031) is studied by ab initio calculations using a supercell approach. Based on ab initio calculations and group theory we present a comprehensive analysis of the electronic structure of GaAs:N and GaAs:B alloys. In particular, we study the effective mass of conduction electrons in GaAs:N as a function of pressure and the Fermi energy. We find that the lowest conduction band is strongly non-parabolic, which leads to an increase in the effective mass with the electron energy. The rate of the increase is enhanced by the hydrostatic pressure. Theoretical results are compared to experimental data, and a qualitative agreement is found.

Cyclotron resonance of conduction electrons in GaAs at very high magnetic fields

Cyclotron resonance of conduction electrons in GaAs at very high magnetic fields

Evolution of a nonthermal electron energy distribution in GaAs.

We have observed the thermalization of conduction electrons in GaAs from a nonthermal to a Maxwell-Boltzmann kinetic-energy distribution. A streak camera is used to observe the time-resolved spectrum of the band-to-acceptor luminescence following a short (5-ps) near-resonant laser pulse of very low excitation power. At electron density less than ${10}^{14}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ the thermalization of the electron energy distribution occurs with a rate independent of density on a time scale of 50 ps. Inelastic electron-phonon scattering is too slow to produce this thermalization. We examine electron-donor scattering in detail, and find that this scattering mechanism also does not cause the thermalization at low density. We conclude that the primary scattering mechanism at low density is electron-hole scattering in which electrons are spatially correlated with holes. At higher density, thermalization occurs via electron-electron scattering. We have performed extensive modeling of the thermalization with a Boltzmann-equation approach. In the case of the low-density thermalization, we find that a model of short-range electron-hole scattering provides a good fit to the nonthermal distribution we observe. At higher density, we calculate the time scale of weakly screened Coulomb scattering and find that it agrees with our observations. We compare our results to those of other experiments on electron thermalization in GaAs and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As.

Nonthermalized distribution of electrons on picosecond time scale in GaAs.

We have observed the thermalization of conduction electrons in GaAs from a Gaussian to a Maxwell-Boltzmann distribution, by time-resolved observation of the band-to-acceptor luminescence folllowing a short (5 ps) near-resonant laser pulse of very low excitation power. At electron density less than ${10}^{14}$/${\mathrm{cm}}^{3}$ the thermalization of the electron density distribution occurs on a time scale of 50 ps with a rate independent of density. At higher density, thermalization occurs via electron-electron scattering with a total cross section of approximately 6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ ${\mathrm{cm}}^{2}$.

Magnetic g factor of electrons in GaAs/AlxGa1-xAs quantum wells.

The magnitude and sign of the effective magnetic splitting factor ${\mathit{g}}^{\mathrm{*}}$ for conduction electrons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells have been determined as a function of well width down to 5 nm. The experimental method is based on combined measurements of the decay time of photoluminescence and of the suppression of its circular polarization under polarized optical pumping in a magnetic field perpendicular to the growth axis (Hanle effect). Measurements as a function of hole sheet density in the wells reveal a transition from excitonic behavior with very small apparent g value for low density, to larger absolute values characteristic of free electrons at higher densities. For 20-nm wells ${\mathit{g}}^{\mathrm{*}}$ for electrons is close to the bulk value (-0.44), and increases for narrower wells passing through zero for well width close to 5.5 nm. A theoretical analysis based on three-band k\ensuremath{\cdot}p theory, including allowance for conduction-band nonparabolicity and for wave-function penetration into the barriers, gives a reasonable representation of the data, leading to the conclusion that ${\mathit{g}}^{\mathrm{*}}$ in quantum wells has a value close to that of electrons in the bulk at the confinement energy above the band minimum.

GaAs as a narrow-gap semiconductor

Conduction electrons in GaAs are described theoretically using a five-level k.p model and including effects of the electron-optic phonon interaction. The dispersion relation E(k) in the band and in the forbidden gap, the energy dependence of the effective mass and the spin g-value, as well as the resulting peculiarities of the cyclotron resonance are calculated and compared with experimental data of various authors. It is shown that the electrons in GaAs exhibit typical narrow-gap properties.

Conduction electrons in GaAs: Five-level k

Properties of conduction electrons in GaAs are described theoretically using a five-level k\ensuremath{\cdot}p model, which consistently accounts for inversion asymmetry of the material. The dispersion relation E(k) is computed and it is shown that the conduction band is both nonparabolic and nonspherical. The energy dependence of the electron effective mass, the energy-momentum relation in the forbidden gap, and the spin splitting of the band are calculated. Analytical expressions for the band-edge effective mass, the spin splitting, and the Land\'e factor ${g}^{\mathrm{*}}$ are presented, taking explicitly into account an interband matrix element of the spin-orbit interaction. A five-level P\ensuremath{\cdot}p theory for the conduction band in the presence of an external magnetic field is developed. Resonant and nonresonant effects due to polar electron--optic-phonon interaction are included in the theory. The spin g value of conduction electrons is calculated as a function of energy and magnetic field. Spin-doublet splitting of the cyclotron resonance and the cyclotron-resonance-mass anisotropy are described. A comparison of the theory with experimental data of various authors is used to determine important band parameters for GaAs. It is shown that away from the band edge the polaron effects in GaAs are comparable to the band-structure effects.

Five-level k · p model for conduction electrons in GaAs. Description of cyclotron resonance experiments

Five-level k·p model for the conduction electrons in GaAs in the presence of a quantising magnetic field is developed and used to describe spin splittings of the cyclotron resonance and the donor-shifted cyclotron resonance peaks, observed in this material up to fields of 22.5 T. It is shown that the spin splittings are insensitive to polaron effects and that their values can be very well described by the model. Required band parameters correctly account for the rate of electron spin relaxation in GaAs due to inversion asymmetry, as determined by other authors.

Spin relaxation of conduction electrons in GaAs

We have used optical spin orientation techniques to measure T 1 of conduction electrons in GaAs ( NinA ≈ 10 17 cm -3) for 4.7 K ⩽ T ⩽ 200 K. From Hall effect measurements we estimated the electron momentum relaxation time τ p . For 50 K ⩽ T ⩽ 200 K, the product T 1τ p agrees with our earlier order of magnitude estimate of the D'yakonov-Perel' mechanism, in which band structure induced precession is strongly narrowed by momentum relaxation. The Elliott mechanism is one to two orders of magnitude weaker.

Effect of Johnson noise on l.s.a. oscillators

The r.m.s. electron-density fluctuations (Johnson noise) within the GaAs of l.s.a. oscillators are shown to be about 10% of the mean density. The effect of these fluctuations is determined by an analytic calculation of l.s.a.-oscillator efficiency (similar to that of Bott and Hilsum, 1967). The specification of the velocity/field characteristic of conduction electrons in GaAs in an analytical form, which separates the importance of peak/valley ratio and negative differential mobility, permits an indication of the optimum form of the characteristic for the l.s.a. mode. The calculated efficiencies are somewhat smaller than those of previous calculations.