Pulsed laser deposition in vacuum at 220°C of GaAs layers heavily doped with Mn and/or Bi has been used to form nanostructures on i-GaAs (100) substrates. It is shown that, for the electrical activation of manganese, it is expedient to use subsequent annealing with an excimer laser pulse with a wavelength of 248 nm and a duration of 30 ns. The structures show an anomalous Hall effect with a hysteresis loop on the magnetic field dependence up to a Curie temperature of about 70 K. Negative magnetoresistance is observed up to temperatures of ≈150 K. Bismuth does not prevent the activation of Mn atoms during annealing and contributes to an increase in the coercive field of the GaMnAs ferromagnetic semiconductor.

Исследованы слои GaMnAs, изготовленные методом импульсного лазерного нанесения в вакууме на подложках полуизолирующего GaAs. В процессе создания структур варьировалась температура подложки в интервале от 200 до 350oC, а толщина слоев составила ~ 50 nm. Образцы изготовленных структур подвергались отжигу импульсами эксимерного KrF-лазера. Анализ спектров комбинационного рассеяния отожженных образцов с использованием аппроксимации их функциями Лоренца показал, помимо пиков в области LO- и ТО-мод GaAs, наличие связанной фонон-плазмонной моды. В результате отжига наблюдается значительное возрастание дырочной проводимости слоев (сопротивление уменьшается от значений Rs~107-109 Ω до Rs~ 900-3000 Ω). Существенным образом изменяется вид магнитополевой зависимости намагниченности при комнатной температуре: происходит переход от нелинейной характеристики с петлей гистерезиса для исходного образца (появляющейся вследствие присутствия в нем включений соединения MnAs c температурой Кюри выше комнатной) к линейному характеру поведения для отожженного образца. Изучение гальваномагнитных свойств при температурах от 10 до 150 K показывает существование ферромагнетизма в слоях GaMnAs с температурой Кюри, достигающей 90 K. Наблюдаемые эффекты позволяют заключить, что применяемое импульсное лазерное воздействие приводит к модификации (растворению) включений MnAs, электрической активации Mn и, как следствие, к образованию однофазного ферромагнитного полупроводника GaMnAs. Ключевые слова: импульсное лазерное нанесение, импульсный лазерный отжиг, ферромагнитный полупроводник.

Earlier [V. P. Lesnikov, Ukr. J. Phys. 64, 126 (2019)] it was pointed out that for thermal hydrodynamic fluctuations in open hydrodynamic steady states (OHSS) the determining factor for derivation of reciprocal relations is not the principle of microscopic reversibility, but the presence or absence of a flux. In the present work this idea is applied to open chemical steady states (OCSS), where chemical oscillations are possible. The behavior of concentration fluctuations when there are no macroscopic oscillations yet is considered. The reciprocal relations for such OCSS are found.

Low-temperature device-quality GaAs layers with high resistivity were obtained by pulsed laser deposition. The properties of GaAs layers are sensitive to the process temperature. At a growth temperature of less than 300 o C, the layers have low electron mobility and a shift of the GaAs stoichiometry towards the region of arsenic enrichment at a level of 1-2 at.%. At a growth temperature of more than 300 o C, the layers show an improved crystalline quality. The dependence of the relative intensity of the As 3d photoelectron line on the growth temperature confirms this trend with a change in the growth temperature. Keywords: pulsed laser deposition, Hall effect, X-ray photoelectron spectroscopy.

Low-temperature device-quality GaAs layers with high resistivity were obtained by pulsed laser deposition. The properties of GaAs layers are sensitive to the process temperature. At a growth temperature of less than 300°C, the layers have low electron mobility and a shift of the GaAs stoichiometry towards the region of arsenic enrichment at a level of 1–2 at.%. At a growth temperature of more than 300° C., the layers show an improved crystalline quality. The dependence of the relative intensity of the As 3d photoelectron line on the growth temperature confirms this trend with a change in the growth temperature.

GaMnAs layers made by pulsed laser deposition in vacuum on semi-insulating GaAs substrates have been studied. During the creation of the structures, the substrate temperature varied in the range from 200 to 350 o C, and the thickness of the layers was ~ 50 nm. Samples of the manufactured structures were annealed by pulses of an excimer KrF-laser. The analysis of the Raman scattering spectra of annealed samples using their approximation by Lorentz functions showed, in addition to peaks in the LO- and TO-GaAs modes, the presence of a coupled phonon-plasmon mode. As a result of annealing, a significant increase in the hole conductivity of the layers is observed (the resistance decreases from R s ~10 7 -10 9 Ω to R s ~ 900-3000 Ω). The type of magnetic field dependence of magnetization at room temperature changes significantly: there is a transition from a nonlinear characteristic with a hysteresis loop for the initial sample (appearing due to the presence of MnAs compound inclusions with a Curie temperature above room temperature) to a linear behavior for the annealed sample. The study of galvanomagnetic properties at temperatures from 10 to 150 K shows the existence of ferromagnetism in GaMnAs layers with a Curie temperature reaching 90 K. The observed effects allow us to conclude that the applied pulsed laser action leads to modification (dissolution) of MnAs inclusions, electrical activation of Mn and, as a consequence, to the formation of a single-phase ferromagnetic semiconductor GaMnAs. Keywords:: pulsed laser deposition, pulsed laser annealing, ferromagnetic semiconductor.

A new method of forming the β-FeSi 2 phase on silicon and sapphire substrates by pulsed laser deposition in vacuum is considered. A series of structures is prepared with variations in the iron content in the target to be sputtered. The phase composition of films is analyzed by identifying peaks in the Raman spectra. The magnetic properties of samples are studied by recording the magnetic-field dependence of their Hall resistance. It is shown that the additional Fe 3 Si and FeSi phases are formed under conditions of growth that provide the more efficient inclusion of Fe atoms in the growing layer. Phase analysis of the films formed on silicon and sapphire substrates at identical technological parameters of growth is carried out.

A new method for the formation of a diluted magnetic semiconductor based on gallium arsenide doped with iron and manganese atoms is considered. The method consists in diffusion doping during pulsed laser deposition in vacuum. Using the method of X-ray photoelectron spectroscopy, the profile of the chemical elements distribution was obtained. The magnetic phases influence on the behavior of the magnetic field dependence of the Hall resistance is analyzed. The technological parameters for the growth of the structure exhibiting ferromagnetic properties at room temperature were selected.

The GaAs semiconductor structures for the application as betavoltaic power sources were investigated. Three types of structures underwent a comparative study: a Schottky diode, a p-n junction and Schottky structure modified by deposition of a carbon layer. The power characteristics were estimated by Monte-Carlo simulation and collected current calculation using parameters obtained from the electron beam induced current technique. It was shown that carbon deposition on the top of n-GaAs allows passivating the surface states and thus improving betavoltaic performance.

The possibilities of doping carbon layers grown by pulsed laser deposition with transition-metal impurities are analyzed. The composition and optical and electrical parameters of structures on GaAs and Si/SiO2 substrates are studied. It is shown that the introduction of such atoms as Fe ones modifies the magnetic properties of layers, which are responsible for nonlinear magnetic-field dependences of the Hall effect at temperatures of up to 300 K.

In this work, we demonstrate the possibility of using a diluted magnetic semiconductor GaAs:Fe as a ferromagnetic injector in a spin light-emitting diode based on a GaAs/InGaAs quantum well heterostructure. It is shown that in such a device it is possible to observe partially circularly polarized electroluminescence at room temperature. Keywords: spin light-emitting diodes, diluted magnetic semiconductors, A3B5 semiconductors, spin injection.

The theory of thermal fluctuations in open hydrodynamic steady states (OHSS) is presented exclusively within the framework of hydrodynamics. The history of studies of fluctuations in a continuous medium with a stationary flux is described. It is shown that the application the fluctuation-dissipation theorem (FDT) to the OHSS with the requirement of fulfilling the Onsager's reciprocal relations (fluctuating hydrodynamics), is erroneous. The reason is that the flux, changing the dynamics and initial values of the fluctuations, violates the detailed balance existing in equilibrium. This is demonstrated by the example of the Mandelstam problem on fluctuations in a medium with a heat flux. For this problem, the structure dynamic factor is calculated for an isotropic solid and a liquid. The loss of time symmetry by the correlation functions of fluctuations and the asymmetry of their spectral representations in this problem is due to the spatial temperature variation, which determines the flux. In order to show the generality of this result for all OHSS with spatial heterogeneity, the Kelvin problem on thermal fluctuations of the interface displacements between two liquids is also considered. The upper moving liquid has velocity potential changes as the temperature in the Mandelstam problem. Reciprocal relations for both the Mandelstam and the Kelvin problems are pointed out.

In this work, we demonstrate the possibility of using a diluted magnetic semiconductor GaAs:Fe as a ferromagnetic injector in a spin light-emitting diode based on a GaAs/InGaAs quantum well heterostructure. It is shown that in such a device it is possible to observe partially circularly polarized electroluminescence at room temperature.

This paper presents a method for the formation of the β-FeSi 2 phase on silicon and sapphire substrates by pulsed laser deposition in vacuum. The analysis of the phase composition of the films, based on the identification of Raman peaks is presented. The magnetic properties of the samples were studied by measuring the magnetic field dependence of the Hall resistance. The presence of a magnetic Fe 3 Si phase on a silicon substrate was shown.

Использование углеродных (С) слоев (однослойного и многослойного графена) для разработки комбинированных с полупроводниками A3B 5 приборов наноэлектроники затруднено из-за отсутствия подходящих методов формирования С-слоев непосредственно на поверхности полупроводниковых структур с сохранением их свойств. В данной работе показана возможность получения углеродных нанослоев непосредственно на поверхности GaAs структур методом импульсного лазерного распыления пирографита в вакууме. Для нанесения С-слоев использован лазер YAG:Nd (длина волны 532 нм). Подложка при выращивании поддерживалась при 500°С, а толщина С-слоя определялась временем испарения и составляла от 4 до 20 нм. По результатам исследований комбинационного рассеяния света и рентгеновской фотоэлектронной спектроскопии полученные углеродные слои представляют собой сплошную пленку нанокристаллического графита, состоящую из зерен многослойного графена.

Diode structures with ferromagnetic narrow-gap semiconductors A3FeB5 as only p-region (p-GaFeSb/n-InGaAs), only n-region (n-InFeSb/p-InGaAs), p- and n-regions (p-GaFeSb/n-InFeSb, p-GaFeSb/n-InFeAs) for p-n junction were fabricated by pulsed laser deposition in vacuum. The composition of ferromagnetic semiconductor layers and their thicknesses, determined by X-ray photoelectron spectroscopy, generally correspond to the technological data for diode structures. In particular, the thickness of the GaFeSb layer is 25–30 nm, and the thickness of the InFeAs and InFeSb layers is 35–40 nm. The iron content in InFeSb ranges from 25 to 35 at.%. The GaFeSb layer contains from 15 to 41 iron at. %, and the InFeAs layer - 35 iron at. %. The chemical analysis of the structures revealed the presence of chemical bonds Fe-As (Sb), In-Fe and Fe-Ga. Therefore, it can be assumed that Fe atoms in the fabricated structures can substitute for elements of groups III and V simultaneously. All structures exhibit the effect of negative magnetoresistance at sufficiently low observation voltages of the effect (up to 50 mV), in low magnetic fields (up to 3600 Oe), and at high measurement temperatures. For GaFeSb/InFeSb, GaFeSb/InFeAs diodes, negative magnetoresistance was first observed at room temperature. The hysteresis form of the dependences of the resistance on the magnetic field suggests the effect of the ferromagnetic properties of the layers of narrow-gap semiconductors on the transport of carriers in the structures.

The diode structures with narrow-gap ferromagnetic A3FeB5 semiconductors in the function of only p-region (p-GaFeSb/n-InGaAs), only n-region (n-InFeSb/p-InGaAs), p- and n-regions (p‑GaFeSb/ n-InFeSb, p-GaFeSb/n-InFeAs) of the p–n junction were manufactured by the method of pulsed laser deposition in vacuum. Composition of the ferromagnetic semiconductor layers and their thicknesses determined by the results of X-ray photoelectron spectroscopy in total correspond to the technological information for diode structures. More specifically, thickness of the GaFeSb layer is 25–30 nm, thicknesses of the InFeAs and InFeSb layers is 35–40 nm. The iron content in InFeSb ranges from 25 to 35 at %. The GaFeSb layer contains from 15 to 41 at % of iron, while 35 at % of iron is registered in InFeAs layer. Presence of Fe‒As(Sb), In–Fe, and Fe–Ga chemical bonds was found at chemical analysis of the structures. Because of this, it may be assumed that, in the manufactured structures, the Fe atoms can displace the elements of III and V groups simultaneously. All the structures demonstrates the effect of negative magnetoresistance at sufficiently low potentials of observation of the effect (to 50 mV), in small magnetic fields (to 3600 Oe) and at high temperature of measurements. For the GaFeSb/InFeSb, GaFeSb/InFeAs diodes, the negative magnetoresistance was observed for the first time up to room temperature. The hysteresis form of the dependences of resistance on magnetic field suggests an effect of ferromagnetic properties of the narrow-gap semiconductor layers on the carrier transport in the structures.

The paper considers a new method for the formation of the β-FeSi2 phase on silicon and sapphire substrates by pulsed laser deposition in vacuum. A series of structures with varying iron concentration in the sputtered target was prepared. The phase composition of the films is analyzed from the identification of peaks in the Raman spectra. The study of the magnetic properties of the samples was carried out by recording the magnetic field dependence of the Hall resistance. The formation of additional magnetic phases Fe3Si and FeSi is shown under growth conditions that provide an increased incorporation of Fe atoms into the formed layer. The analysis of the phase composition of films formed on silicon and sapphire substrates with the same technological growth parameters is carried out.

Исследованы возможности легирования углеродных слоев, выращиваемых методом импульсного лазерного нанесения, примесями переходных металлов. Изучены состав, оптические и электрические параметры структур на подложках GaAs и Si/SiO2. Показано, что введение таких атомов, как Fe, модифицирует магнитные свойства слоев, вызывая нелинейные магнитополевые зависимости эффекта Холла при температурах вплоть до 300 K. Ключевые слова: импульсное лазерное нанесение, углеродные слои, легирование, примеси переходных металлов.

The possibility of using a diluted magnetic semiconductor (In,Fe)Sb as a functional layer for use in spintronics, namely, as a ferromagnetic injector in a spin light emitting diode, has been investigated. We studied the luminescent characteristics, as well as the temperature dependence of the circular polarization degree of a spin LED electroluminescence with an (In,Fe)Sb injector.