Yu. G. Sadofyev

Exchange enhancement of the g factor in InAs/AlSb heterostructures

The evolution of the Shubnikov-de Haas oscillations in InAs/AlSb heterostructures with twodimensional electron gas in InAs quantum wells 12–18 nm wide with considerable variation in the electron concentration (3–8) × 1011 cm−2 due to the effect of negative persistent photoconductivity is studied. The values of the effective Landé factor for electrons g* = −(15–35) are determined. It is shown that the value of the g* factor increases as the quantum well width increases.

Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands

We report on the cyclotron resonance (CR) study in InAs/AlSb (001) quantum well (QW) heterostructures with two occupied electronic subbands. Experimental results are compared with the CR energy calculations in the self-consistent Hartree approximation. Our theoretical approach is based on the 8-band k · p Hamiltonian and takes into account the band nonparabolicity, lattice-mismatch deformation, and spin-orbit coupling. We find out a large splitting of CR line associated with a difference in cyclotron energies in the first and second electronic subbands. The results of CR study in InAs/AlSb QW heterostructures reveal pronounced effect of the “built-in” electric field on CR spectra in the samples with two occupied electronic subbands.

Rashba spin splitting and exchange enhancement of the g factor in InAs/AlSb heterostructures with a two-dimensional electron gas

The exchange enhancement of the g factor of quasiparticles in InAs/AlSb heterostructures with a two-dimensional electron gas exhibiting Rashba spin splitting is investigated using the 8-band k · p Hamiltonian. It is shown that, in low magnetic fields, Rashba spin splitting yields a profound increase in the amplitude of oscillations of the quasiparticle g factor renormalized by exchange interaction. From analysis of Shubnikov-de Haas oscillations at the temperature 250 mK, the energy of Rashba splitting and the g factor of quasiparticles are determined. The values determined experimentally are in good agreement with the results of theoretical calculations carried out with consideration for the asymmetric built-in electric field in InAs/AlSb heterostructures.

Effect of electron-electron interaction on cyclotron resonance in high-mobility InAs/AlSb quantum wells

We report observation of electron-electron (e-e) interaction effect on cyclotron resonance (CR) in InAs/AlSb quantum well heterostructures. High mobility values allow us to observe strongly pronounced triple splitting of CR line at noninteger filling factors of Landau levels ν. At magnetic fields, corresponding to ν > 4, experimental values of CR energies are in good agreement with single-electron calculations on the basis of eight-band k ⋅ p Hamiltonian. In the range of filling factors 3 < ν < 4 pronounced, splitting of CR line, exceeding significantly the difference in single-electron CR energies, is discovered. The strength of the splitting increases when occupation of the partially filled Landau level tends to a half, being in qualitative agreement with previous prediction by MacDonald and Kallin [Phys. Rev. B 40, 5795 (1989)]. We demonstrate that such behaviour of CR modes can be quantitatively described if one takes into account both electron correlations and the mixing between conduction and valence bands in the calculations of matrix elements of e-e interaction.

Persistent photoconductivity in InAs/AlSb heterostructures with double quantum wells

Effects of persistent photoconductivity in InAs/AlSb heterostructures with the cap GaSb layer and two-dimensional electron gas in the InAs double quantum wells at T = 4.2 K are studied. From Fourier analysis of the Shubnikov-de Haas oscillations, electron concentrations in each quantum well are determined at various wavelengths of illumination and pronounced asymmetry of the structure caused by the built-in electric field is demonstrated explicitly. The self-consistent calculations of the energy profile of the double quantum well are performed and the concentrations of ionized donors on both sides of the well are determined, which provided concretization of the previously suggested mechanism of bipolar persistent photoconductivity in such structures.

Features of the persistent photoconductivity in InAs/AlSb heterostructures with double quantum wells and a tunneling-transparent barrier

The spectra of persistent photoconductivity for InAs/AlSb heterostructures with double quantum wells and a separation AlSb barrier with varying thickness between 0.6–1.8 nm are measured at T = 4.2 K. The electron concentrations in the wells at various illumination wavelengths are determined from the Fourier analysis of Shubnikov-de Haas oscillations. The features associated with the tunneling transparency of a separation barrier 0.6 nm thick (two monolayers) are revealed. The performed self-consistent calculations of the energy profile of a double quantum well showed that a symmetric profile is established in the structures in the region of negative residual photoconductivity, while the region of positive persistent photoconductivity has an asymmetric potential profile, which leads to Rashba spin splitting (>2 meV at the Fermi level). It is shown that the introduction of the tunneling-transparent separation barrier increases the Rashba splitting.

Photoluminescence of Yb Doped ZnTe

The photoluminescence from ZnTe : Yb films grown on (100) GaAs by MBE was studied at different temperatures (4.2-350) K. The efficient Yb 3+ -related emission in ZnTe was observed up to room temperature. The analysis of the fine structure of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f 13 levels for the dominant complex center based on Yb ion.

E-Beam Longitudinally Pumped Laser Based on ZnCdSe/ZnSe MQW Structure Grown by MBE on ZnSe(001) Substrate

Electron beam longitudinally pumped laser based on 15 ZnCdSe/ZnSe QW periodic-gain structure grown by molecular beam epitaxy on ZnSe(001) substrate was studied. An output power of 0.3 W was achieved. The laser wavelength was in 518-536 nm range, being at the short wavelength side of the QW emission line at low excitation level. Such unusual feature was explained by the participation of excited QW levels in the creation of the optical gain.

Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

Type II–type I conversion of GaAs/GaAsSb heterostructure energy spectrum under optical pumping

We present the experimental results of time-resolved photoluminescence spectroscopy in type II GaAs/GaAs0.64Sb0.36 quantum well heterostructures. At moderate optical excitation densities (below 103 W/cm2), we observe blue shift of the photoluminescence peak with increasing pump power which results from band bending at the type II heterointerface due to photo-excited charge carriers. With further increase in the excitation density, the observed peak undergoes red shift accompanied by significant drop in the luminescence decay time (from 10 ns to 1 ns) which is caused by extreme band bending and increasing contribution of type I radiative transitions to the photoluminescence signal.