Vol 51, No 11 (2017)

The possibility of creating thyristor structures with external optical control by laser radiation with a wavelength of ~800 nm, based on single-crystal wafers of semi-insulating GaAs and layers of InGaP with the lattice parameter compatible with GaAs, is shown.

The results of numerical modeling and investigation of a hybrid microcavity based on a semiconductor Bragg reflector and a microlens selectively positioned above a single (111) In(Ga)As quantum dot are presented. Emitters based on the hybrid microcavity demonstrate the effective pumping of a single quantum dot and high emission output efficiency. The microcavity design can be used to implement emitters of polarization- entangled photon pairs based on single semiconductor quantum dots.

The size-quantized energy subbands and envelope wave functions for [001] quantum wells based on zinc-blende III–V semiconductors are numerically calculated using the eight-band Kane model and finite-difference discretization scheme in coordinate space. The effect of the quantum-well band parameters and external electric field oriented along the structure growth direction on the ratio between the Rashba and Dresselhaus spin–orbit coupling parameters is studied. It is demonstrated that at certain electric-field values the spin–orbit coupling parameters in GaAs/InGaAs structures can be equal, which ensures the condition for forming stable spin helices. In addition, it is established that the spin–orbit coupling linear in wave vector in symmetric GaAs/InGaAs wells can disappear under certain well widths and barrier chemical compositions.

Single manganese and carbon δ-layers in undoped GaAs are analyzed by photoreflectance spectroscopy. The strength of built-in electric fields, determined by this method, is shown to increase with increasing layer concentration of introduced impurities and well correlate with technological and Hall data. The use of phase-sensitive photoreflectance makes it possible to measure the surface field and the field induced by δ-doping separately. This fact allows one to determine without contact the fraction of electrically active Mn impurity and reveal the contribution of carbon δ-layers to the characteristics of GaAs-based heterostructures.

The molecular-beam epitaxy of InGaAs/InAlAs/AlAs structures for heterobarrier varactors is studied and optimized. The choice of the substrate-holder temperature, growth rate and III/V ratio in the synthesis of individual heterostructure regions, the thickness of AlAs inserts and barrier-layer quality are critical parameters to achieve the optimal characteristics of heterobarrier varactors. The proposed triple-barrier structures of heterobarrier varactors with thin InGaAs strained layers immediately adjacent to an InAlAs/AlAs/InAlAs heterobarrier, mismatched with respect to the InP lattice constant at an AlAs insert thickness of 2.5 nm, provides a leakage current density at the level of the best values for heterobarrier varactor structures with 12 barriers and an insert thickness of 3 nm.

Previously, GaAs/AlAs superlattices with a small active area (~1 μm²) were used by us to design mixer diodes. It was established that these superlattices can efficiently be used in the terahertz (THz) range. It was theoretically and experimentally shown that short-period (i.e., containing few periods) superlattices in the composition of harmonic mixers have significant advantages in comparison with multi-period (with 50–100 or more periods) superlattices at frequencies of up to 5.3 THz. In this study, the superlattice design is optimized and the operation efficiency of short-period superlattices is shown to be determined to a large extent by the transition regions located at the superlattice edges.

SiN_x films on silicon are grown in SiH₄/Ar + N₂ inductively coupled plasma under high silane dilution with argon. The dependences of the deposition rate and properties of silicon nitride on the plasmagas composition, pressure, radio-frequency power and inductive power are studied. In some cases, the found dependences differ from published data for undiluted reagents. It is found that the lowest impurity content in films and their best properties are implemented at a nitrogen-to-silane ratio close to 1.4. An increase in the radio-frequency power results in smoother samples due to the polishing effect of argon ions.

The capabilities of a technique based on combined photoluminescence and Raman-spectroscopy measurements upon lateral scanning across the cleaved edge of heterostructures for monitoring the strain profile and the thickness of epitaxial layers are demonstrated. The characteristics of a laser heterostructure with InGaAs/GaAsP quantum wells are investigated by this technique. It is shown that photoluminescence from different layers of the structure can be recorded separately. It is established that both the frequency of the InP-like phonon mode and the photoluminescence energy can be used to determine the composition of the In_xGa_1–xP alloy. The two methods yield close results.

Calculation is performed for a flux of charge carriers in the structure of a GaAs bipolar transistor with a thin base in the case where a single cluster of radiation-induced defects is formed in the operating region of a transistor. It is shown that the site of the appearance of a cluster of radiation-induced defects greatly affects the degree of degradation of the gain of a bipolar transistor. The probabilistic assessment of radiation-induced puncture of the base in relation to its thickness and to the neutron fluence is obtained.

InGaAs/GaAs/AlGaAs laser diodes with quantum wells are grown by the metal-organic chemical vapor deposition (MOCVD) method on an exact Si (001) substrate with a Ge buffer layer. The diodes generate stimulated emission in the pulsed mode at room temperature in the spectral range from 1.09 to 1.11 μm.

Three deep acceptor levels with activation energies of ~0.7, ~0.41, and ~0.16 eV are found in GaAs structures, which have the hole type of conductivity and are grown by liquid-phase epitaxy, by the methods of capacitance spectroscopy (admittance spectroscopy and deep-level transient spectroscopy). The first two levels are known as HL2 and HL5 and are related to the features of GaAs-layer growth by liquid-phase epitaxy. They are effective recombination centers determining reverse currents in p–i–n diodes, which is confirmed by studying the temperature dependences of reverse currents. The level with the energy E_v + 0.16 eV can be related to the two-charge acceptor level of the inherent antisite defect in GaAs, which also determines the doping concentration of structures in the singly charged state.

The specific features of the cyclotron resonance in topological insulators of the Bi₂Te₃ family are analyzed. The energy spectrum of electron excitation on the surface of these compounds in a magnetic field has the C_3V symmetry. With the use of quasiclassical equations of motion, which take into account the Berry curvature and magnetic moment, it is found that the cyclotron frequency spectrum contains additional harmonics due to spectrum anisotropy. An analysis of these harmonics makes it possible to reveal the contribution from the topological characteristics to the observables.

The calculation of energy relaxation rates due to transitions involving phonons is performed for quantum dots of varying size which are formed by magnetic barriers at the edge of a two-dimensional topological insulator based on a HgTe/CdTe quantum well. Relaxation both into the discrete and continuous spectrum of edge states is considered, as well as into the continuous spectrum of the bulk material. The obtained results demonstrate the existence of a region of system parameters which provide relatively slow energy relaxation, indicating that the considered objects are promising, e.g., for the design of novel types of solid state qubits.

The effect of the surface on the I–V characteristics of PbSnTe:In film-based structures is investigated in zero magnetic field and in a magnetic field of B ≤ 4 T with different orientations, including in the mode of current limited by space charge. Analysis of the features in the experimental data obtained at different magnetic-field directions and upon layer-by-layer etching of the films shows that the contributions of the free film surface and interface with the substrate to transport phenomena are significantly different and can be caused by a difference in the parameters of localization centers near these surfaces.

The growth of InGaAs/GaAs/AlGaAs laser structures by MOCVD at low pressures on Si(001) substrates with a Ge epitaxial metamorphic buffer layer of various thicknesses is studied. The results of the influence of the growth temperature and incorporation of additional AlAs layers at the boundary with the Ge/Si(001) substrate on the crystalline and optical quality of the formed III–V structures are presented. It is shown that the incorporation of the AlAs/GaAs/AlAs lattice at the initial growth stages of III–V heterostructures on Ge buffer layers grown on exact Si(001) substrates makes it possible to considerably decrease the density of threading defects and, consequently, form effectively emitting laser structures. The possibility of growing strained InGaAs quantum wells on Si(001) substrates allowing stimulated radiation in a wavelength region longer than 1100 nm is shown.