Том 53, № 10 (2019)

The first results on the development of an original power GaAs-based field-effect transistor with a vertical channel controlled by a p–n junction are presented. The main manufacturing feature is the use of two separate epitaxial growth processes when forming the transistor structure. The transistor part containing the drain, drift, and gate regions is grown by liquid-phase epitaxy. Metalorganic gas-phase epitaxy is used to form the channel and source regions.

On the basis of numerical solution to the Maxwell–Bloch equations within the one-dimensional two-level model of a superradiant laser with a symmetric cavity in which the photon lifetime is less than the incoherent relaxation time of the optical-dipole oscillations of active centers, the phenomenon of the spontaneous asymmetric generation of counter-propagating waves under continuous uniform pumping of the active medium is revealed. It is shown that the observed symmetry breaking of the spatial profiles of counter-propagating waves of the electromagnetic field and, the polarization and inversion of the population of active-medium levels in the case of a small inhomogeneous broadening of the spectral line of its working transition occurs due to the asymmetric half-wave nonlinear grating of inversion of the energy-level population produced by these waves.

The results of investigations of the optical characteristics of nonclassical light sources based on selectively positioned microlens structures and single (111) In(Ga)As quantum dots grown on a (111) BGaAs substrate are presented. The single-photon nature of the radiation is confirmed by measuring and analyzing second-order correlation functions g⁽²⁾(τ); g⁽²⁾(0) = 0.07. The fine structure of the exciton states of (111) In(Ga)As quantum dots is investigated. It is shown that, in the energy range of 1.320–1.345 eV, the splitting of exciton states is comparable to the natural width of the exciton lines, which is of interest for developing photon-pair emitters based on them.

The interaction of a Tamm plasmon with an exciton in an organic material in the strong coupling mode is investigated theoretically. The structure consists of five pairs of layers of silicon oxide and tantalum oxide, an organic light-emitting layer of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl, and a silver layer. It is shown that the splitting of polariton modes (Rabi splitting) with a magnitude of >400 meV can occur in such a structure, which can be accompanied by an increase in the luminescence bandwidth up to 700 meV.

The results on the formation of locally strained Ge microstructures on silicon-on-insulator (SOI) substrates and investigation of their optical properties are presented. Suspended Ge structures are formed by optical lithography and plasmachemical and selective chemical etching using the “stress concentration” approach. To provide a heat sink from Ge microstructures, their formation scheme is modified so as to provide the mechanical contact of a part of the suspended microstructure with lower-lying layers. To implement this scheme, SOI substrates with a thin upper Si layer 100 nm in thickness are used. It is shown using the measurements of Raman spectra depending on the pumping power that local heating in such structures decreases. Measurements of the microphotoluminescence spectra show a considerable increase in the signal intensity from strained regions of Ge microstructures as well as the possibility of increasing the maximal optical pumping power (not leading to irreversible changes) for microstructures, in which the mechanical contact of the strained part with lower-lying layers is provided, when compared with suspended structures.

Long-wavelength acoustic phonon-assisted relaxation rates for the excited 1s(T), 2p₀, 2s, 3p₀, 2p_±, 4p₀, and 3p_± states of antimony donors in a germanium crystal are calculated. The effect of the uniaxial compressive strain of a crystal along the [111] crystallographic direction on the relaxation rates is discussed. The results of calculations are compared with the measured times of relaxation of nonequilibrium states of donor centers by the pump-probe method. A comparison with the times obtained experimentally by the submillimeter photoconductivity method is made.

Various methods for the formation of ohmic contacts to boron-doped δ layers in CVD-diamond epitaxial structures are investigated. In the first variant, an additional thin heavily doped layer was formed on the diamond surface to which an ohmic contact is formed. Then, the surface p⁺ layer between the contact pads is etched out; therefore, the current in the structure flows only through a buried δ layer. In the second approach, the doped diamond selectively grows in the contact windows under a metallic mask after preliminary etching of the undoped diamond layer (cap) up to the δ layer. In this case, the heavily doped p⁺ layer forms an end contact to the δ layer. These two variants differ in terms of the conditions of applicability, the complexity of the manufacturing technology, the value of the contact resistance, and can be used to solve problems in which it is necessary to have a different quality of the contacts, such as the formation of transistor structures or test cells for measuring physical characteristics.

The results of studies of the spontaneous photoluminescence and stimulated emission spectra of epitaxial n-InN layers with a concentration of free electrons of ~10¹⁹ cm^–3 are reported. The layers are grown by molecular-beam epitaxy with the plasma activation of nitrogen on sapphire substrates with AlN and GaN buffer layers. It is found that, as the InN layers are grown under conditions with enrichment with nitrogen at a growth temperature elevated to 470°C close to the beginning of the decomposition of InN, the crystal quality of the layers is improved and the stimulated-emission threshold is lowered. As the conditions of growth change to conditions with enrichment with the metal, two emission bands separated by an energy of 100 meV are observed in the spontaneous-photoluminescence spectra of InN. For such layers, a substantial increase in the stimulated-emission threshold and, in some cases, the lack of a transition to stimulated emission are observed. In the study, an interpretation of the observed emission bands is given and some inferences as to their nature are made.

The properties of highly viscous fluids at high frequencies become similar to those of amorphous solids. In particular, the propagation of not only longitudinal acoustic waves (plasmons in the case of an electron fluid), but also transverse acoustic waves associated with shear deformations becomes possible. In this work, the formation of transverse acoustic waves at high frequencies in a two-dimensional electron fluid in a magnetic field is studied. Consideration is performed within Landau’s Fermi-liquid model. It is shown that the dynamics of Fermi-liquid excitations is described by hydrodynamic equations at a rather strong quasiparticle interaction. The Navier–Stokes equation and expressions for high-frequency shear viscosity coefficients are derived. Based on the equations obtained, dispersion laws are calculated for transverse and longitudinal magnetosonic waves. It is shown that the cyclotron frequency entering the viscosity coefficients and the dispersion relation of transverse magnetosonic waves is renormalized and typically becomes lower than the ordinary cyclotron frequency determining cyclotron resonance. The latter fact was apparently observed in the photoresistance of high-mobility GaAs quantum wells in which two-dimensional electrons form a viscous fluid.

The electronic structure of nanosystems based on cadmium sulfide in the zinc-blende form (zb-CdS) is investigated using the method of density functional theory with the application of pseudopotentials. It is shown that this approach makes it possible to adequately describe the electronic states of this material. It is found that the (100)-zb-CdS surface is characterized by a metal-like electronic-state density, while the (110)-zb-CdS surface corresponds to the band gap at the Fermi level and nanofilms with this orientation can be used as a material for semiconductor devices. Epitaxial layered (110)-zb-CdS–Si nanosystems also manifest semiconductor properties.

The influence of hydrogen on the electrical properties of Pd/n-InP and Pd/oxide/n-InP structures is studied. It is found that a variation in the cutoff voltage \(\Delta {{U}_{{{\text{cut-off}}}}}\) in the current–voltage characteristics of the structures under study upon exposure to hydrogen with concentrations of 0–1 vol % in a nitrogen–hydrogen mixture is described by the exponential dependence: \(\Delta {{U}_{{{\text{cut-off}}}}}\) = a[1 – exp(–b ⋅ N_H)], where N_H is the hydrogen concentration (vol %), and a and b are constants dependent on the type of structures. It is shown that a decisive influence on how the potential-barrier height changes in the Pd/InP and Pd/oxide/InP structures in the presence of H₂ in a gas medium is exerted by a change in the Pd work function in an atmosphere of hydrogen. It is found that, in the structures under study, tunneling and thermal-tunneling charge-transport mechanisms operate at 90–300 K in the presence of hydrogen and without it. With increasing hydrogen concentration in the gas mixture, the predominance of the tunneling charge-transport mechanism becomes more pronounced.

The temperature dependences of the capacitance–voltage characteristics and deep-level spectra of a Au–n-Si:Au–Si–p-Si heterostructure based on a composite layer of Au and Si nanoparticles are investigated. The structure manifests the properties of a transistor connected to a circuit with a common emitter with a disconnected base and an emitter Schottky barrier between the Au point contact and the n–(Si:Au) layer. Nanoparticles in this layer form finite clusters with hopping conductivity; herewith, charge accumulation is observed in the region of the Au point contact. The system at a measurement temperature below 180 K transitions from the finite-cluster phase to the infinite-cluster phase due to the percolation effect. This phase manifests metallic properties in the lateral plane of the heterostructure, which transforms into a p–n diode.

It is shown, both analytically and numerically, that the hole mobility in boron δ-doped (i.e., with a thickness on the order of several lattice constants) diamond layers drops with a decrease in their two-dimensional concentration during depletion of the δ-doped layer by an external voltage. This drop is most pronounced for the maximum initial two-dimensional hole concentrations ~ 3 × 10¹³ cm^–2 (limited from above by the condition for the possibility of their significant reduction without the electrical breakdown of diamond). This is explained by a decrease in the degree of screening of scattering Coulomb potentials of ionized boron atoms and an increase in the scattering efficiency of degenerate holes from these atoms due to a drop in the kinetic energy of holes. The corresponding calculations of the transport scattering cross section of holes are performed beyond the Born approximation (i.e., perturbation theory), which is inapplicable for boron δ-doped diamond layers. The predicted effect can be used to increase the efficiency of source-to-drain current modulation by a gate voltage in diamond field-effect transistors (FETs) with δ-doped conduction channels.

The construction of a semiconductor laser with a stripe waveguide is proposed, the geometry of which can make it possible to obtain radiation similar to that of a phase-locked laser array. The requirements for the parameters of the laser quasi-array and the technological feasibility of the proposed approach are discussed.