The results of magnetoconductivity measurements in GaInAs quantum wells are presented. The observed magnetoconductivity appears due to the quantum interference, which lead to the weak localization effect. It is established that the details of the weak localization are controlled by the spin splitting of electron spectra. A theory is developed which takes into account both linear and cubic in electron wave vector terms in spin splitting, which arise due to the lack of inversion center in the crystal, as well as the linear terms which appear when the well itself is asymmetric. It is established that, unlike spin relaxation rate, contributions of different terms into magnetoconductivity are not additive. It is demonstrated that in the interval of electron densities under investigation ((0.98 − 1.85)·1012 cm −2 ) all three contribution are comparable and have to be taken into account to achieve a good agreement between the theory and experiment. The results obtained from comparison of the experiment and the theory have allowed us to determine what mechanisms dominate the spin relaxation in quantum wells and to improve the accuracy of determination of spin splitting parameters in A3B5 crystals and 2D structures. 73.20.Fz,73.70.Jt,71.20.Ej,72.20.My

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We report magnetoconductivity experiments carried out on pseudomorphic AlGaAs/InGaAs/GaAs quantum wells in a wide range of magnetic fields (0.1 to 80 kG). Pressure-illumination cycles were used for tuning the free electron density. Measurements of the Shubnikov-de Haas and Hall effects allowed us to determine the transport and quantum relaxation times. Corrections to the magnetoconductivity due to weak localization and weak antilocalization were determined and used to calculate the phase and spin relaxation times. We analyzed phase, spin, quantum, and transport relaxation rates as a function of electron density which allowed for a characterization of the dominant scattering processes.

A nonlinear dynamics of self-generated current oscillations in semi-insulating GaAs was studied by the reconstruction of an attractor from a short (14500 points) time series. Two methods of choosing of a time constant (τ) for this reconstruction are compared. One of them assumes τ to be an argument of the first zero of the autocorrelation function and the other takes τ as an argument of the first minimum of the mutual information. It is shown that for periodic oscillations both methods are equivalent, but for chaotic ones only the mutual information gives a time constant which does not depend on a time series used for calculations.

Quantum (single particle) and classical (transport) scattering times have been measured and analyzed as a function of density of the two-dimensional electron gas (2DEG) in pseudomorphic AlGaAs/InGaAs/GaAs heterostructures. Hydrostatic pressure was used to decrease and infrared LED light pulses to increase the 2DEG density. Our experimental results allow us to distinguish two different persistent photoionization mechanisms induced by the light pulses, which have quite different effects on the two kinds of scattering times. We have also found evidence that a modification of the spatial correlation of charges on remote donors in the barrier (by means of pressure and/or illumination by light pulses) affects the quantum lifetime much more than the transport scattering time.

Heating of electrons by electric fields smaller than that required for generation of domain oscillations was investigated in samples of ΕL2-rich semi-insulating GaAs. Current-voltage characteristics were measured as a function of temperature between 268 K and 330 K. They exhibit a sublinear shape which is interpreted as a result of an enhanced electron capture on the ΕL2. The capture rate and the electron temperature as a function of the electric field was determined. A fitting procedure gave the value of electron capture cross-section on the ΕL2 to be 2.7 x 10 -13 cm' which agrees with literature data.PACS numbers: 72.20.Ht Long known spontaneous current oscillations in semi-insulating (SI) GaAs caused by high electric field domains propagation [1] have also been investigated during last years [2,3]. The mechanism responsible for this phenomenon is electric field enhanced capture of electrons from the conduction band on a deep centre. In particular, it is proposed that in undoped SI GaAs the level involved is the EL2 [4]. This idea was first put forward by Kamińska et al. [5] who explained the phenomenon as the following.When the electric field E applied to the sample is sufficiently high, the electrons in the conduction band gain enough energy to come over the configurational barrier which separates a free electron from its bound state on the EL2. This leads to a decrease in the free electron concentration and thus to a negative differential conductivity (NDC). The observed current oscillations are a result of drowning the system into the NDC regime.This reasoning was recently put into a quantitative model by Johnson et al. [2] and Surma and Łusakowski [6]. The principal idea is to describe the electron gas by an electron temperature Te which is different from the crystal lattice temperature Τ. The present paper deals with the range of electric fields below that (777) 778 A. Zduniak, J. Łusakowski' G. Nowak required for the oscillations. An analysis of the experimental data allows to calculate Te as a function of Ε and shows that the capture rate of electrons from the conduction band on the EL2 increases with Ε.All the experiments described below were performed on samples cut from one LEC wafer of undoped SI GaAs. A sample with six contacts was used for low field Hall measurements which gave the temperature dependence of the zero electric field mobility (which is constant for electric fields below 3 kV/cm [7]). Current-voltage (I-V) characteristics were measured as a function of the temperature on another sample with two bar-shaped contacts (Fig. 1). The known value of the electron mobility allowed to calculate the concentration of free electrons n as a function of the temperature and the electric field. Under the assumption that the occupancy of the EL2 changes only as a result of transitions to and from the conduction band, the condition of a stationary state takes the form ncn (Nt -nt ) = en nt , where cn is the capture rate, en is the emission rate of the inverse process, Nt and nt is the concentration...

Spin relaxation in degenerated two-dimensional (2D) electron gas is studied by measurements of the magnetic field dependence of the weak antilocalization corrections to the conductivity in GaInAs quantum wells. Consistent quantitative (up to order of magnitude) description of weak antilocalization data on GaAs like heterojunctions and quantum wells was obtained. Our results show that spin precession around the effective magnetic field direction as described by the Dyakonov-Perel model is the main spin relaxation mechanism in degenerated 2D electron gas in semiconductors with no inversion symmetry.

Relaxation and domain current oscillations in undoped semi-insulating GaAs were observed at room temperature for a broad range of voltage applied to a sample. The oscillations were characterized by a reconstruction of an attractor of the system. An analysis of the attractor helped to discriminate between the two likes of oscillations. A transition from one like of oscillations to the other was connected with a chaotization of the current. A chaotic state of the system was analyzed by calculations of fractal dimensions D q for -0.6 < g < 40 and the f (α) function.