Valeriy Nikolaevich Sokolov

National Academy of Sciences of Ukraine | ISP · Department of Theoretical Physics

We analyze steady-state and transient electron transport in the group III-nitride materials at high and ultra-high electric fields for different electron concentration regimes. At high electron concentrations where the electron distribution function assumes a shifted Maxwellian, we investigate different time-dependent transient transport regimes th...

A theoretical model is developed for the intrinsic generation-recombination (G-R) noise in bipolar graphene that stems from stochastic processes of interband carrier transitions in the zero-gap single layer. The correlation functions are obtained for microscopic Langevin sources of fluctuations relevant to the considered G-R processes. The spectral...

We consider transverse redistributions of the electrons and holes in intrinsic graphene ribbons under the influence of crossed electric and magnetic fields, i.e., the magnetoconcentration effect. The electron and hole transport is described from the Boltzmann kinetic equation assuming the local quasiequilibrium distributions of the carriers over en...

We investigate thermal emission characteristics mediated by surface plasmon polaritons (SPPs) resonantly excited at a semiconductor-vacuum interface. The characteristic plasma and SPP resonant frequencies in the interval from 0.3 to 10 THz can be controlled with conventional doping densities. All of the cases under consideration (n-doped GaAs, GaN,...

The conditions for microwave power generation in a submicrometer GaN diode, with a relatively lightly doped active channel, coupled to an external resonant circuit are investigated. Applying a high-field electron transport model based on the local quasi-static approximation, we show that oscillations in group III-nitride diodes can be supported in...

The conditions for pulsed regime operation of terahertz power generation in vertical nanoscale GaN-based diodes are investigated via self-consistent simulation of the high-field electron transport in the active channel and thermal transport in the entire device structure. The combined electrothermal model allows for a detailed analysis of the dynam...

The conditions for terahertz power generation are investigated theoretically in a nanoscale GaN-based diode coupled to an external resonant circuit for operation in the limited space-charge accumulation (LSA) mode under the high-field transport regime. The generation criteria are revisited in terms of a phase plane analysis of the diode high-field...

Doped semiconductors with one-dimensional surface gratings are studied theoretically for application to terahertz emission. The presence of free carriers supports thermally excited surface plasmon polaritons at the semiconductor-vacuum interface whose resonance frequency can be controlled by doping. The calculation based on the fluctuational electr...

A physical mechanism of electrical instability in the terahertz frequency range is explored in a nanoscale two-terminal configuration of nitride-based structures under a high-field transport regime. The investigated instability utilizes the negative differential resistance effect that is known to occur in bulk group-III nitride semiconductors. A di...

The near-field spectra of the electromagnetic field emitted from a planar surface are theoretically investigated for a number of polar semiconductor and dielectric materials that support surface phonon polaritons. All of the studied materials, InP, GaAs, GaN, SiC, and alpha-Al2O3 (sapphire), exhibit quasimonochromatic thermal emission symbolized by...

This paper describes measurements of the velocity of electrons at electric fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule heating effect, a pulse technique with a time sweep of 10-30 ns was used. The experimental results indicate that overheating of the 2DEG does not exceed 1000 K in this electric field range and...

The conditions for microwave power generation with hot-electron transport are investigated in a submicron GaN diode when it operates in the limited space-charge accumulation (LSA) mode. Applying a transport model based on the local quasistatic approximation, the analysis shows that the nitride diodes can support the LSA mode of oscillation in the t...

We study effects of electron-hole (e-h) plasma density N and a uniform electric field F on the ground and first excited eigenstates, energy levels and electron and hole wave functions, resulting from many-particle (Hartree and exchange) Coulomb interactions in a 2D e-h plasma. The coupled Schro¨dinger equations for electrons and holes are solved se...

We present a theoretical study of two-terminal nitride-based oscillators utilizing two different hot-electron transport regimes determined by the interaction of the electrons with polar optical phonons, which are capable to generate current/voltage oscillations in the THz-frequency range. The first is the limited space-charge accumulation (LSA) reg...

We discuss the basic properties of the transient hot-electron transport and dynamic mobility in group-III nitrides under dominant electron–polar-optical-phonon scattering determining their capability for applications in THz frequency range. For bulk samples with high electron concentration, we provide the phase-plane analysis of the time-dependent...

We present a detailed theoretical analysis of steady-state, transient time-dependent, and spatially dependent electron transport in the group-III nitrides at high and ultrahigh electric fields. To develop an analytical model, we derive time-dependent differential equations describing the hot-electron rates of momentum and energy relaxation in elect...

We investigate the small-signal conductivity of the electrons in group-III nitrides under a high steady-state electric field. The resulting calculation indicates a frequency dependence of the conductivity that is drastically different from that given by the Drude formula. A large and very fast response of the hot electrons in the nitrides is reveal...

In this paper, we presented results of steady state and pulse measurement of AlGaN/GaN heterostructures up to ultra high electric fields accompanied by low frequency noise measurements. Hot electron relaxation process were analysed. The contact resistance was measured in low field (ohmic) region and taken into account when calculating the average e...

We report on experimental and theoretical studies of low and high field transport in AlGaN/GaN two-dimensional electron gas (2DEG). Magnetotransport of 2DEG created as a result of polarization effects at the heterointerface has been studied. The velocity-electric field characteristics extracted from pulsed current-voltage measurements in AlGaN/GaN...

We address experimental and theoretical study of a two-dimensional electron gas transport at low and moderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN) gateless heterostructures grown on sapphire. The transmission line model patterns of different channel lengths, L, and of the same channel width are used. A st...

This report addresses the study of two-dimensional electron gas (2DEG) transport at low and moderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN) gateless heterostructures grown on sapphire for HEMT applications. The transmission line model (TLM) patterns of different channel lengths L and the same channel width...

In this report, we discuss the basic properties of transient hot-electron transport and high-frequency conductivity in group-III nitrides that determine their capability for applications in THz frequency range. Bulk samples, ultra-short diodes as well as quantum heterostructures are considered.

We present a theory of the surface noise in a nonhomogeneous conductive channel adjacent to an insulating layer. The theory is based on the Langevin approach which accounts for the microscopic sources of fluctuations originated from trapping–detrapping processes at the interface and intrachannel electron scattering. The general formulas for the flu...

TEMPERATURE SENSORS FOR EXTREME ELECTRONICS (theory, technology, experiment, application) Yu. M. Shwarts, V. N. Sokolov, M. M. Shwarts, E. F. Venger Institute of Semiconductor Physics, National Academy of Sciences of Ukraine pr. Nauki 45, 03028 Kiev, Ukraine; Phone /Fax # (044) 265-7463 shwarts@isp.kiev.ua The development of advanced semiconduc...

We present a new type of silicon diode temperature sensors (DTSs) with high radiation resistance up to the dose of gamma irradiation ∼107rad. Investigations of electrophysical and metrological characteristics of DTSs have been carried out in the range of temperatures 220–350K and currents 10−11 to 10−2A under gamma irradiation that allowed to revea...

The low-frequency 1/f noise characteristics of AlGaN/GaN high-electron-mobility transistors with gate length scaled down to 150 nm grown on sapphire by metalorganic chemical vapor deposition have been studied. Certain features of the 1/f noise have been revealed in these short-gate transistors. The low-frequency noise spectra show drastically diffe...

We have generalized the model of the surface noise taking into account the self-consistent electrostatic interaction and transverse electron transport in a conductive channel. Analyzing this model, we have found that the Coulomb correlations between trapped and conducting electrons considerably suppress the surface noise. The suppression effect is...

The known types of semiconductor temperature sensors show fast degradation of their main characteristics under influence of gamma irradiation. We present a new type of diode temperature sensors (DTSs) developed on the base of heavily doped silicon structures with high irradiation resistance for use in radiation environments. These DTSs are advanced...

The criteria are formulated, which allow determination of the sets of electrophysical and design parameters of the diode temperature sensors (DTSs) providing either maximal extent of the temperature response curve (TRC) or the maximal sensitivity of DTSs. New method for a self-consistent device optimization is developed in the framework of model of...

Heterostructures with electrically biased quantum wells show bistable absorption in both, hybrid electro-optical devices (SEED’s) [1] and all-optical devices (wireless SEED’s [2], and multiple quantum well structures [3],[4]). We report a new phenomenon of formation of transversal electron patterns under bistable electro-optical absorption in wirel...

A physical model is proposed for limitation and suppression of spectral intensity of hot-electron fluctuations in submicrometre semiconductor layers, where the thickness 2d of the sample is comparable to the electron energy relaxation length Lepsilon . We suppose two identical layer surfaces, no space charge and surface charges at zero bias, the el...

We present the results of theoretical investigation of inhomogeneous fluctuations in submicrometer active layers of many-valley semiconductors with equivalent valleys (Ge, Si type), where the layer dimension, 2d, is comparable to or less than the intervalley diffusion relaxation length, Liv. The study is based on the Boltzmann-Langevin kinetic equa...

We have formulated and analyzed a model of in-plane self-sustained pattern formation in a quantum well heterostructure under bistable electro-optical absorption. We have found a number of patterns which contain regions (quasi-neutral or charged) with different spreading of the electron and hole wave functions and different densities of the two-dime...

It is proposed a physical model for limitation and suppression of spectral intensity of electron fluctuations in submicrometer semiconductor layers, where the thickness 2d of the sample is comparable to one of the relaxation lengths. Three types of size effects in the fluctuations are considered: hot electron size effect, the Fuchs effect and size...

We present theoretical investigations of fluctuations of hot electrons in sub‐micron active regions, where the dimension 2d of the region is comparable to the electron energy relaxation length L ε. In the low‐frequency limit, we find an exact solution of the Langevin equation for space‐dependent electron fluctuations. The numerical calculations of...

The results of numerical calculations of the band edge absorption dependence on photoexcitation density for hexagonal CdS, CdSe, and cubic ZnSe are presented. The calculations are based on the recent plasma screening theory of Banyai and Koch modified to take into account the band structure and anisotropy of these materials. At low temperatures the...

The influence of sample thickness and carrier surface recombination on the characteristics of resonatorless dissipative optical bistability (RDOB) is investigated. The RDOB under consideration is caused by the excitation density nonlinearities of band-edge absorption of laser radiation in semiconductors. The diversity of multivalued spatial carrier...

Temporal evolution of the transmission coefficient and of the output light intensity during the laser pulse is investigated for CdSe single crystals. The nonlinear bleaching observed in the Urbach region of the absorption spectrum at room temperature has a threshold character. With the increase of the laser pulse energy exceeding the threshold valu...

A theoretical analysis is presented of spatial distributions of the concentration of nonequilibrium carriers in a semiconductor with absorption saturation (AS) in the edge region of the fundamental photoabsorption band. It is shown that, when the AS effect is most extreme, there arises in the semiconductor a spatial domain of finite size which is c...

The motion of light-induced concentration domains of nonlinear carriers in semiconductors with dissipative nonresonator optical bistability and the light transmission characteristics associated with this motion are investigated theoretically. It is shown that stationary illumination of a thin plate (the thickness of the plate, d, is of the order of...

The paper develops a theory for laser-radiation propagation in semiconductors with a strong concentration nonlinearity of the edge absorption of light, due to the dependence of the absorption threshold on the concentration of the nonequilibrium carriers generated. Stationary profiles of inhomogeneous distributions of nonequilibrium-carrier concentr...

An instability theory of the homogeneous distribution of current carriers and lattice deformations in semiconductors with electron-phonon interaction via deformation potential in a quantizing magnetic field is developed. It is shown that the instability takes place in a number of regions on the concentration-temperature plane, their mutual position...

(For abstract see issue 01, p. 105, Accession no. A74-10211)