L. V. Gavrilenko

Kinetics of terahertz photoconductivity in p-Ge under impurity breakdown conditions

Relaxation times of impurity photoconductivity in p-Ge samples excited by a nanosecond narrow-band source of terahertz radiation are studied at various bias voltages. It is shown that the relaxation time in prebreakdown fields increases with the applied electric field and decreases as the impurity breakdown field is exceeded. Nonmonotonic photoconductivity kinetics is observed in the studied samples differing by acceptor concentrations and degrees of compensation when approaching the impurity breakdown field.

Impurity resonance states in semiconductors

The present-day situation in studies of localized and resonance impurity states in quantum-dimensional structures and stressed semiconductors is discussed. Resonance optical transitions caused by interaction with optical phonons are also considered. Various methods for calculating the characteristics of both donor and acceptor resonance and localized states are analyzed; a large body of experimental data is reported and discussed.

Terahertz emission and photoconductivity in n-type GaAs/AlGaAs quantum wells: the role of resonant impurity states

Terahertz emission spectra in a longitudinal electric field and lateral photoconductivity spectra under terahertz illumination have been studied in structures with GaAs/AlGaAs quantum wells (QWs). It is shown that the spectra contain features associated with electron transitions involving resonant impurity states related to the second quantum-well subband. Calculations of the energy spectrum of impurity states and matrix elements of optical transitions made by taking into account various positions of the impurity relative to the QW center confirm the assumptions made.

Picosecond photoluminescence dynamics in an InGaAs/GaAs quantum-well heterostructure

The results of experimental studies of the subpicosecond relaxation dynamics of photoexcited charge carriers in an In0.22Ga0.78As/GaAs quantum-well heterostructure are reported. From photoluminescence studies of the structure by the upconversion technique, the cooling rate of charge carriers in the quantum well and the time of charge-carrier trapping into the well are estimated to be ∼1 ps at 300 K and at ∼6.5 ps at 10 K.

Relaxation of the impurity photoconductivity in p-Ge/Ge1−xSix quantum well heterostructures

In this paper we report a study on relaxation of the impurity photoresponse in strained p-Ge/GeSi heterostructures excited by pulsed THz radiation. The relaxation time is found to increase with the applied dc electric field, which is interpreted within the model of cascade carrier capture by the impurity centers. A second time scale of the impurity photoconductivity relaxation is observed near the impurity breakdown field, and in post-breakdown electric fields the relaxation time (decreasing with the field) is shown to be governed by the impact ionization rather than by the recombination.

Dynamics of the cascade capture of electrons by charged donors in GaAs and InP

The times for the cascade capture of an electron by a charged impurity have been calculated for pulsed and stationary excitations of impurity photoconductivity in GaAs and InP. The characteristic capture times under pulsed and continuous excitations are shown to differ noticeably both from each other and from the value given by the Abakumov–Perel–Yassievich formula for a charged impurity concentration greater than 1010 cm–3. The cause of this difference has been established. The Abakumov–Perel–Yassievich formula for the cascade capture cross section in the case of stationary excitation has been generalized. The dependences of the cascade capture rate on the charged impurity concentration in GaAs and InP have been found for three temperatures in the case of pulsed excitation.

Calculation of the parameters for the Fano resonance in the impurity photocurrent spectrum of semiconductors doped with hydrogen-like donors

The paper presents the theoretical investigation of the Fano resonance in the spectra of impurity photocurrent for bulk semiconductors doped with donors. Calculation is made for the parameters describing the Fano resonance. These parameters can be evaluated with the use of two general dimensionless functions that are calculated numerically. Two kinds of donor impurity are considered: a hydrogen-like charged center and an impurity influenced by the central cell potential.

Nonresonant radiative exciton transfer by near field between quantum wells

We experimentally observed an increase in the intensity of photoluminescence from a wider quantum well (QW) when an exciton transition was induced in the neighboring narrower QW separated from the former one by a tunneling-nontransparent AlGaAs barrier. The dependence of the efficiency of the near-field radiative transfer of excitons on the distance between QWs was studied in heterostructures without coincidence of exciton resonances in the adjacent QWs. Theoretical results were qualitatively consistent with the available experimental data.

Near-field mechanism of photoluminescence excitation in quantum well heterostructures

We report a study into the process of energy transfer between quantum wells divided by 30-nm-thick opaque barriers. It was experimentally observed that the intensity of a photoluminescence signal from a quantum well increased by 15% under resonant excitation of exciton transition in the adjacent quantum well. The quantum wells were 30 nm apart. A radiative mechanism of energy transfer in the near-field region of emitting exciton is proposed. Within this theoretical model, the efficiency of the energy transfer decreases by a power law with greater distance between the quantum wells. The theory is found to be in qualitative agreement with the experimental results.

Calculation of the states of shallow donors in quantum wells in a magnetic field using plane wave expansion

A nonvariational method for calculating the states of shallow donors in quantum wells in a magnetic field is suggested. The method can be used in a wide range of magnetic fields, starting with zero. The method is based on the expansion of the electron-wave function in a basis of eigenfunctions of the Hamiltonian operator that describes a rectangular quantum well. The results obtained by this method are compared to the experimental data and to the results of calculations using different theoretical methods. The comparison shows that our method describes the observed spectrum of the shallow-donor states in quantum wells in a magnetic field with a higher accuracy than the methods used in the study by Chen et al.