Magnetic field dependence of cyclotron resonance linewidth for acoustic polarons in the extreme quantum limit

The magnetic field dependence of cyclotron resonance linewidth (CRLW) due to electron-acoustic phonon interactions in the extreme quantum limit is obtained on the basis of Kubo's formula and Fujita's diagram method. The 2-dimensional electron-piezoelectric phonon interaction generates a finite maximum CRLW as a function of magnetic field while CRLW for all other acoustic polarons increase with the magnetic field.     

Temperature dependence of the schottky barrier height in gallium arsenide

The Schottky barrier height is measured in Ni-low doped n-type gallium arsenide and found to decrease with increasing temperature. The temperature dependence of the barrier height is nearly equal to that of the energy gap in GaAs.     

Wavelength dependence of picosecond absorption saturation in gallium arsenide

Absorption saturation in the picosecond regime has been observed in GaAs MBE-grown epitaxial layers at low temperature, and its wavelength dependence in the range 700–820 nm has been observed using 7 psec pulses from a tunable infrared LiIO₃ parametric generator. For peak intensities up to 1 GW cm^?2 almost complete saturation of band-to-band absorption could be achieved without damaging the sample. Although the direct saturation of optically coupled states is expected to become the dominant contribution in the ultrashort limit, our experimental results are quantitatively described with the band-filling model, which includes the dynamic Burstein shift and bandgap renormalization.     

Magnetic field dependence of hole levels in InAs quantum dots

We have studied the charging of InAs quantum dots with holes in perpendicular fields up to 16 T by capacitance—voltage spectroscopy. The first two charging peaks show almost no shift with magnetic field which is consistent with the filling of a twofold degenerate s-like state with no orbital angular momentum. The next four charging peaks shift towards lower and higher energy in an alternating fashion. Peaks 5 and 6 shift approximately twice as strong as peaks 3 and 4. This behavior cannot be explained by the charging of a fourfold degenerate p-shell according to Hund′s first rule. We speculate that the p-shell is not completely filled before the filling of the d-shell starts.     

Cyclotron spin-flip mode in the extreme quantum limit

In a two-dimensional electron system, the combined excitation (the cyclotron spin-flip mode) associated with changes in both orbital and spin quantum numbers is investigated. The energy of the cyclotron spin-flip mode is studied as a function of the electron filling factor. Comparative dependences of the decay times of the cyclotron spin-flip mode and the magnetoplasmon are measured. It is shown that, as the filling factor increases from v = 0 or decreases from v = 1, the damping of the cyclotron spin-flip mode increases significantly, while the magnetoplasma mode remains undamped.     

Magnetic field dependence of the domain wall resistance in a quantum wire

For an ideal one-dimensional ferromagnetic wire with a magnetic domain wall (DW), contribution of the DW to the resistivity of the system has been investigated. We have studied the resistance due to the magnetic impurities in the domain wall which was suspended in a weak magnetic field for two types of chiralities. The analysis has been based on Boltzmann transport equation, within the relaxation time approximation. Through this formalism, both increasing and decreasing of the resistance due to the DW have been predicted in presence of Zeeman interaction as an extrinsic mechanism.     

Photoquenching effect and its consequence in p type gallium arsenide

In order to examine the origin of the occasionally observed shift in the photoconductivity peak with respect to the band gap value; optical and electro-optical investigation of a p type GaAs crystal was carried out. The absorption and photochonductivity spectra were recorded and by comparing both spectra, a model based on the transition of electrons from the oxygen “adsorbate surface states” is proposed to explain the strong photoquenching observed on the high energy side of the band gap value. This also explains the observed shift.     

Magnetic susceptibility of a two-dimensional electron gas in the quantum strong magnetic field limit

It is shown that the peak values of the magnetic susceptibility of a two-dimensional electron gas in the quantum strong magnetic field limit are integral multiples of $\text{μ}{}^2{}_{\mathrm{B}}\text{2π}$.     

Formation of a system of InGaAs quantum wires in a gallium arsenide matrix

The formation of a system of one-dimensional quantum conductors in porous multilayer In_xGa_1?xAs/GaAs structures with a two-dimensional charge-carrier gas in the In_xGa_1?xAs layers is discussed. The transition from the single-crystalline to porous matrix is studied with scanning atomic force microcopy. A decrease in the dimensionality of the electron-hole gas in the objects, i.e., a transition from the two-dimensional to a one-dimensional system, is established by analyzing the dependences of the position and width of a spectral line in the photoluminescence spectra on the etching time. Both multilayer periodic superlattices and a structure with a single In_xGa_1?xAs layer located near the surface of gallium arsenide are studied. The electrophysical characteristics of electrons in the porous superlattices are measured as functions of temperature. They confirm the formation of a new structure and indicate a change in the mechanism of electron scattering in the quasi-one-dimensional transport channels formed in the system.     

Zero-point plasmon motion in the extreme quantum limit in InSb

Further experiments at helium temperatures are described on the anomalous NMR relaxation peak, first reported by Bridges and Clark, in the extreme quantum limit in doped InSb, extending the previously reported density range of the phenomenon up to 5 × 10²² m^?3 of donor electrons. New features of the anomaly, in particular an isotope effect, are reported.The large density range over which the effect has now been observed, taken with the new features, render many of the previous theories of the peak untenable. Based on the zero-point plasmon motion of the electron gas, we put forward an interpretation which appears to explain the various aspects of the phenomenon.     

Magnetic field rotation in the screw gallium flow

The magnetic field induced by the nonstationary screw flow of gallium in a toroidal channel has been investigated experimentally using a gallium prototype of the sodium apparatus developed in the frame of the experimental dynamo program at the Institute of Continuous Media Mechanics, Perm, Russia. The experimental set-up is a rapidly rotating toroidal channel subjected to abrupt braking. The screw flow is initiated by inertial forces pushing liquid gallium through diverters. The regular structure of the induced magnetic field is generated about 0.1 s after the stop of the channel and persists up to 1 s. The induced field is measured by sensors placed outside the channel. The inductive effects observed are attributed to the mean screw flow. The decay laws of the induced regular magnetic field and turbulent magnetic fluctuations are studied.Received: 27 August 2004, Published online: 5 November 2004PACS: 47.65. + a Magnetohydrodynamics and electrohydrodynamics - 07.55.Dd Generation of magnetic fields     

Thermoelectric power of semiconductors in the extreme quantum limit—I: The ‘electron-diffusion’ contribution

A study is made of the effect of the quantization of the electron energy levels in a strong magnetic field on the ‘electron-diffusion’ contribution, S_e, of the transverse thermoelectric power of a high-purity isotropic semiconductor (n-type gallium arsenide GaAs) in the extreme quantum limit, when all the carriers in the conduction band are in the lowest Landau level. A theoretical expression for S_e is derived, taking into account of spin splitting. The sign of S_e is either positive or negative, depending on the sign of the conducting carriers. The transition to nondegeneracy, which takes place when the lowest Landau level is driven through the Fermi level, has a large effect on the variation of S_e with magnetic field. This effect is characterized by a large and rapid increase in |S_e|. Spin splitting effects, even with a small effective mass ($\text{m1 = 0·07 m}{}_0$, where m₀ is the free-electron mass) and a very small g-factor (g ≈ 0·32), greatly modify and reduce |S_e| a a function of field. For large fields, |S_e| increases monotonically with H. Calculations are carried out for n-type GaAs at T = 0·5°K with N = 1·2 × 10¹⁶cm^?3 carriers.     

Quantum efficiency dependence on built-in electric fields in exponential-doped and graded-doped gallium arsenide photocathodes

We calculated the intensities and widths of the built-in electric fields of exponential-doped and graded-doped gallium arsenide (GaAs) photocathode for the first time. We analyzed the quantum efficiency (QE)for both samples with these two factors, along with the absorption coefficient and found out that although the exponential-doped sample was more complicated in structure than the graded-doped sample, the QE was not enhanced in the full experimental waveband as we expected, especially for those electrons with lower energy. It shows that the escape probability and diffusion length mainly depend on the intensity of the electric fields, which is believed the most decisive factor for the QE enhancement.