N. S. Averkiev

Spin relaxation in asymmetrical heterostructures

Electron spin relaxation by the D’yakonov-Perel’ mechanism is investigated theoretically in asymmetrical III–V heterostructures. Spin relaxation anisotropy for all three dimensions is demonstrated for a wide range of structural parameters and temperatures. Dependences of spin relaxation rates are obtained both for a GaAs-based heterojunctions and triangular quantum wells. The calculations show a several-orders-of-magnitude difference between spin relaxation times for heterostructure parameters realized in experiments.

Quantum size effect in the photoluminescence of porous silicon layers

Abstract A fine structure of the visible photoluminescence band of porous silicon is reported. It is shown that the set of fine structure lines may be described by confinement of electrons and holes inside quantum Si wires of various widths, which are quantized in size. Data obtained is a direct evidence that high porosity silicon layers represent a network of quantum Si wires.

Carrier transport in porous silicon

Carrier transport in porous silicon layers has been studied by the time-of-flight method in the strong injection mode at temperatures T=290–350 K and electric field strengths F=(1.5–7)×104 V cm−1. The electron and hole drift mobilities μe≈2×10−3 cm2 V−1 s−1 and μh≈6×10−4 cm2 V−1 s−1 were obtained at T=292 K and F=4×104 V cm−1. An exponential temperature dependence of drift mobility with activation energy of ∼0.38 and ∼0.41 eV for, respectively, electrons and holes was established. It is shown that the type of time dependences of the photocurrent associated with carrier drift and the superlinear dependence of the transit time on the reciprocal of the voltage applied to a sample allow use of the concept of space-charge-limited currents under the conditions of anomalous dispersive transport. The experimental data are accounted for in terms of the model of transport controlled by carrier trapping into localized states with energy distribution near the conduction and valence band edges described by an exponential function with a characteristic energy of ∼0.03 eV.

Acoustoelectron interaction in quantum laser heterostructures

The effect of ultrasonic deformation on the polarization properties of semiconductor quantum-well laser radiation is experimentally and theoretically studied at room temperature. It is shown that the observed rotation of the polarization plane is caused by mixing of the light- and heavy-hole levels in the quantum well. Data on the splitting energy of these levels are obtained. The unique capability of the ultrasonic technique for obtaining data on the value and distribution of technological strains in the heterostructure is shown.

Diamagnetic Exciton Polariton in the Interband Magnetooptics of Semiconductors

The experimentally observed magnetic-field dependence of the integrated absorption coefficient in Al0.15Ga0.85As samples at 1.7 K is interpreted. It is established that the dependence results from the competition of two mechanisms: an increase in integrated absorption due to an increase in the oscillator strength as a result of magnetic-field-induced compression of the exciton wave function and a decrease associated with the magnetic freezing-out of charged scattering centers. An analysis of the integrated absorption shows that diamagnetic exciton polaritons are formed in the samples in a magnetic field.

Polarization-resolved photoluminescence piezospectroscopy of GaAs/Al0.35Ga0.65As:Be quantum wells

The photoluminescence (PL) of GaAs/Al0.35Ga0.65As:Be quantum wells is studied at temperatures of 77 and 300 K under conditions of uniaxial compression along the [110] direction. There are two main lines in the PL spectra; at zero pressure and T = 77 K, the peaks appear at 1.517 and 1.532 eV. Comparison of the pressure dependences of the peak positions and the polarization of the PL measured experimentally with those calculated theoretically gives evidence that, at T ≥ 77 K, these bands originate from the recombination of free electrons with heavy and light holes in the GaAs valence band.

Resonance and relaxation ultrasonic attenuation in p-GaAs: Mn at low temperature

Abstract Resonance and relaxation ultrasonic attenuation due to the MnGa neutral acceptor in GaAs is calculated in the model considering the exchange interaction of the bound hole and 3d-electrons of Mn (the exchange interaction constant is A) and taking into account comparatively small splitting δ1 (|δ1| ⪡ kT ⪡ |A|) of the ground state in random local fields. The calculations of occupation relaxation of the split levels have been made in the elastic continuum approximation. Comparison with the known measurements of low temperature (T = 1 ÷ 15 K) ultrasonic attenuation in p-GaAs: Mn demonstrates reasonable agreement between experimental data and calculations with the values of the MnGa center parameters (A, σ1 and deformation potential constants) found from other experiments. Raman relaxation processes are shown to be the main mechanism of occupation relaxation.

Circular polarization of luminescence caused by the current in quantum wells

The degree of circular polarization of photoluminescence from an n-type III–V-based [001] quantum well (QW) is calculated under an electric current flow in the well plane. It is shown that mixing of the states of light and heavy holes leads to circular polarization of photoluminescence during the propagation of light in the plane of the structure. The role of various terms that are linear in the wave vector in the electron energy spectrum is analyzed for the effects of spin orientation and emergence of circular polarization of radiation in the electric field.

Transient photocurrent and photoluminescence in porous silicon

Transient photocurrent in porous silicon samples subjected to prolonged storage in air has been studied using the time-of-flight technique at temperatures in the range 300–350 K and electric field strengths of 104–105 V/cm. Photoluminescence has been studied in the same samples at T=300 K using time-resolved spectroscopy. A conclusion is made on the basis of comparison of the data obtained that localized states play important part in both the processes at characteristic times of these processes falling within the microsecond range.

Resonant and relaxation absorption of ultrasound by anisotropic Jahn-Teller centers in GaAs

The contribution of the Jahn-Teller effect to absorption of an ultrasonic wave by a GaAs crystal doped with copper has been investigated theoretically. The distinguishing feature of the problem under consideration is the existence of two holes in the state of the complex valence band. The magnitude of the tunneling splitting in Jahn-Teller centers has been determined. The theoretical values of the absorption coefficients for the resonant and relaxation types of absorption have been obtained. The magnitudes of these coefficients have been estimated.