The magnetoresistance and the Hall effect in transistor structures fabricated on films of the three-dimensional topological insulator (Bi,Sb)2(Te,Se)3 are studied. It is shown that the negative magnetoresistance at low magnetic field is described in terms of quantum corrections to the conductivity. The magnitude of these corrections depends on the gate voltage and increases when approaching the charge neutrality point. The Hall coefficient RH is nonlinear at low magnetic fields for any gate voltage, and the RH nonlinearity is the most pronounced at high negative gate voltages. At high fields, the slope of the magnetic field dependence of the Hall coefficient changes its sign at some gate voltage.

The current-voltage (I-V) characteristics and spectral dependences of the photocurrent of p-i-n structures, including GeSiSn/Si multiple quantum wells (MQWs) with the Sn content up to 15%, are studied. It is shown that the increase in the Sn content from 4.5 to 13% leads to a gradual increase in the dark current density from 6x10-6 A/cm2 to 5x10-5 A/cm2 at the reverse bias of 1 V. The further rise in the Sn content to 15% results in the increase of the dark current density to 5x10-4 A/cm2, which is an order of magnitude lower than the known values for GeSn-based photodiodes. The shift of the cutoff wavelength of the photoresponse with the Sn content increase in heterostructures is demonstrated. The photoresponse spectrum of the detector extends up to wavelengths of larger than 2 & mu;m at the Sn content of more than 10%.

Уважаемые коллеги!Благодарим Вас за проявленный интерес к Четвертой российской конференции «Графен: молекула и 2D кристалл» и желание принять участие в её работе.Конференция проходит в научно-образовательном центре города Новосибирска -Академгородке.Мероприятие посвящено актуальным направлениям исследований и разработок в области углеродных и низкоразмерных материалов.Проведение конференции поможет координации усилий ученых в решении современных проблем материаловедения и привлечению молодых исследователей для решения актуальных научных задач.Оргкомитет выражает особую благодарность НГУ, Центру компетенций НТИ «Моделирование и разработка новых функциональных материалов с заданными свойствами», компаниям «Диаэм», «НТ-МДТ Спектрум Инструментс» и корпорации "Графеновая Долина" за финансовую поддержку и журналам Аналитика, Наноиндустрия и РЭНСИТ за информационную поддержку.Искренне надеемся, что пребывание в Новосибирском Академгородке и в стенах Новосибирского государственного университета оставит множество положительных эмоций и

Electron states with the spin-momentum-locked Dirac dispersion at the surface of a three-dimensional (3D) topological insulator are known to lead to weak antilocalization (WAL), i.e. low temperature and low-magnetic field quantum interference-induced positive magnetoresistance (MR). In this work we report on the MR measurements in (Bi,Sb)$_2$(Te,Se)$_3$ 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL can not be explained by parabolic or linear MR and indicates the existence of an additional, MR mechanism. Another supporting observation is not linear in the classically weak magnetic field Hall effect in the same films. The increase of the low-field Hall coefficient, with respect to the higher-field value, reaches 10$\%$. We consistently explain both transport features within a two-liquid model, where the mobility of one of the components drops strongly in a weak magnetic field. We argue that this dependence may arise from the Zeeman field induced gap opening mechanism.

The spectral characteristics of the photocurrent in the near-infrared range in vertical Ge/Si p – i – n photodiodes with Ge quantum dots embedded in a two-dimensional photonic crystal are investigated. The interaction of the quantum dots with photonic Bloch modes leads to the resonant enhancement of the sensitivity of photodiodes. The dependences of the photocurrent on the angle of incidence of light are used to determine the dispersion relations of the Bloch modes. Regions in the dispersion characteristics where the group velocity of photons is close to zero are revealed. It is established that the maximum enhancement of the photocurrent relative to a photodiode without photonic crystal, which can be up to a factor of ~60, results from the interaction of quantum dots with “slow” Bloch modes.

Electron states with the spin-momentum-locked Dirac dispersion at the surface of a three-dimensional (3D) topological insulator are known to lead to weak antilocalization (WAL), i.e., low temperature and low -magnetic-field quantum interference-induced positive magnetoresistance (MR). In this work, we report on the MR measurements in (Bi, Sb)2(Te, Se)3 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL cannot be explained by parabolic or linear MR and indicates the existence of an additional MR mechanism. Another supporting observation is not linear in the classically weak magnetic field Hall effect in the same films. The increase of the low-field Hall coefficient, with respect to the higher-field value, reaches 10%. We consistently explain both transport features within a two-liquid model, where the mobility of one of the components strongly drops in a weak magnetic field. We argue that this dependence may arise from the Zeeman-field-induced gap opening mechanism.

Plasmon-enhanced planar Ge/Si photodetectors with Ge quantum dots on silicon-on-insulator substrates coupled with regular arrays of metal nanodisks on their surface are developed. It is found that the introduction of adhesive layers necessary for the formation of stable nanostructures from noble metals leads to the suppression of surface plasmon resonance. The selection of aluminum nanodiscs, which require no adhesive layers, increases the efficiency of photodetectors by 40 times at a wavelength of 1.2 μm and by 15 times at λ = 1.65 μm.

Magneto-transport properties were studied on thin films of a 3D topological insulator (TI) Bi2Se3 grown on graphene (Gr) by physical vapor deposition. It was shown that the main contribution to the conductance is from the bulk states, whereas magnetoresistance is determined by both surface and bulk channels. The input of the charge transport over the surface states in the Si/SiO2/Gr/Bi2Se3 structure reveals itself in the weak antilocalization effect. The transition from a weak antilocalization to a weak localization is observed with decreasing the film thickness. The band bending on both interfaces makes it possible to explain the contribution to a weak antilocalization from different surfaces at different TI film thicknesses.

Исследованы различные методы усиления фотоотклика в ближем инфракрасном диапазоне гетросструктур Ge/Si с квантовыми точками Ge, сопряженных с различными поверхностными наноструктарами. С помощью математического моделирования установлены пространственные конфигурации электромагнитных полей, в таких гетероструктрах, а так же спектральная зависимость фактора усиления интенсивности электрического поля. Рассматривались три основных типа структур

Heterostructures of Bi2Se3 topological insulators were epitaxially grown on graphene by means of the physical vapor deposition at 500 °C. Micrometer-sized flakes with thickness 1 QL (quintuple layer ~ 1 nm) and films of millimeter-scale with thicknesses 2–6 QL had been grown on CVD graphene. The minimum thickness of large-scaled continuous Bi2Se3 films was found to be ~ 8 QL for the regime used. The heterostructures with a Bi2Se3 film thickness of > 10 QL had resistivity as low as 200–500 Ω/sq and a high room temperature carrier mobility ~ 1000–3400 cm2/Vs in the Bi2Se3/graphene interface channel. Moreover, the coexistence of a p-type graphene-related conductive channel, simultaneously with the n-type conductive surface channel of Bi2Se3, was observed. The improvement of the bottom Bi2Se3/graphene interface with the increase in the growth time clearly manifested itself in the increase of conductivity and carrier mobility in the grown layer. The grown Bi2Se3/G structures have lower resistivities and more than one order of magnitude higher carrier mobilities in comparison with the van der Waals Bi2Se3/graphene heterostructures created employing exfoliation of thin Bi2Se3 layers. The grown heterostructures demonstrated the properties that are perspective for new functional devices, for a variety of signal processing and logic applications.

Обнаружено, что встраивание слоев квантовых точек Ge/Si в двумерный фотонный кристалл (ФК) приводит к многократному (до 30 раз) усилению фототока в ближнем ИК-диапазоне, что связывается с возбуждением падающей световой волной планарных мод ФК, взаимодействущих с межзонными переходами в квантовых точках.

Разработаны планарные плазмонные фотодетекторы Ge/Si с квантовыми точками Ge на подложках кремний-на-изоляторе, сопряженные с регулярными массивами металлических нанодисков на их поверхности. Обнаружено, что введение адгезионных слоев, необходимых для формирования стабильных наноструктур из благородных металлов, ведет к подавлению поверхностного плазмонного резонанса. Выбор алюминиевых нанодисков, не требующих адгезионных слоев, позволяет повысить эффективность фотоприемников в 40 раз на длине волны 1.2 мкм и в 15 раз при λ=1.65 мкм. Ключевые слова: локализованные поверхностные плазмоны, квантовые точки Ge/Si, фотоприемники.

It has been found that the introduction of layers of Ge/Si quantum dots in a two-dimensional photonic crystal leads to a strong (up to a factor of 5) increase in the photocurrent in the near infrared range. The photonic crystal is a regular triangular array of holes in a Si/Ge/Si heterostructure grown on a silicon-on-insulator substrate. The results have been explained by the excitation of planar modes of the photonic crystal, which propagate along the Ge/Si layers and effectively interact with interband transitions in quantum dots, by the incident light wave.

The paper is devoted to optical testing of mid-infrared Ge/Si photodetectors obtained by stacking of self-assembled Ge quantum dots in multilayer structures, which are near-field coupled to the adjacent nanoplasmonic arrays of subwavelength holes in metallic films. It is shown that photocurrent and near-field spectra consist of several sets of peaks, which are attributted to surface plasmon waves, localized surface plasmon modes or diffractive Rayleigh anomaly depending on the hole diameter and the angle of incidence θ. We find that for small holes the greatest contribution to the photocurrent enhancement is due to the excitation of the surface plasmon-polariton waves for all θ. As the hole diameter is increased and becomes comparable with the array periodicity, the normal-incident photoresponse improvement is provided by the Rayleigh anomaly. With the increase of incident angle, the photocurrent enhancement is supposed to arise from coupling of the localized shape resonance and propagating plasmon modes.

An array of plasmonic nanoparticles can sustain surface plasmon modes from visible to infrared spectral range and thus offers effective surface light trapping, enhancement of local fields, and interaction with the thin active regions of optical devices. We report the fabrication and optical characterization of a planar Ge/Si quantum dot (QD) detector grown on silicon-on-insulator (SOI) substrate for photodetection in the near-infrared telecommunication wavelength range. The multilayer Ge/Si QD heterostructures are near-field coupled to the adjacent layers of aluminum nanodisks on the detector top. The periodic Al disk arrays have the square lattice symmetry with a lattice constant of 400 nm and the disk diameter varying from 150 to 225 nm. A significant enhancement in the room-temperature detector sensitivity is achieved due to the excitation of localized surface plasmons supported by the metallic disks and radiative coupling to the SOI waveguide modes. Through extinction spectroscopy and numerical modeling, we confirm the emergence of nanoparticle-induced plasmon resonances near the Si–Al interface. We demonstrate that an appropriate choice of the array periodicity and the size of the metal disks is able to increase the photodetector's efficiency by ∼ 40× at λ=1.2μm and by 15× at λ≈1.55μm relative to a bare detector with no plasmonic structure. These outcomes pave the way toward the use of Al as a low-cost plasmonic material with potential applications in infrared photodetection similar to those of the noble metals.

Thin Bi2Se3 films were deposited on mica substrates by physical vapor deposition without the use of the carrier gas. It was found that the films with high structural quality and high conductivity are grown at a source temperature of approximately 500 degrees C. The resistance of 20-300 nm thick films is in the range of 10(2)-10(4) Omega/sq as compared with similar to 10 Omega/sq for thicker films. Bi2O2Se crystals with a similar resistivity are revealed to grow at higher temperatures (600-700 degrees C). It was suggested that the decrease of the thin film resistance is due to the contribution of the surface channels. Low resistivity of the Bi2Se3 films expands the scope of their possible applications as infra-red transparent electrodes.

We report the modification of magnetic properties due to variation of the structure of Fe-contain granules in SiCxNy:Fe films grown by chemical vapor deposition at different temperatures from various gaseous mixtures. It was shown that formation of large composite Fe-granules in the case of structures created using hexamethyldisilazane as source of Si, C, and N atoms results in the hysteresis loop in the magnetization curve appeared only at low temperature (5 K). The ESR spectra are characterized by many ESR lines with sharp asymmetrical shapes and different line widths. The samples with a dense arrays of small homogeneously distributed alpha-Fe granules, obtained with hexamethylcyclotrisilazane, demonstrate the large saturation magnetization, the hysteresis loop (similar to 135 Oe at 300 K and similar to 680 Oe at 5 K) and the collective ferromagnetic resonance signal. The pronounced magnetic properties are explained by the formation of the single magnetic domain due to quantum-mechanical tunneling between small coupled alpha-Fe clusters. Conductivity measurements confirm the existence of the tunneling coupling between Fe-granules even in case of lowest Fe concentration in the samples under study.

The initial stages of G(1-x-y)Si(x)Sn(y) film growth on Ge substrate were investigated and the kinetic diagram of the morphological state for GeSiSn films was built. The kinetic diagram for the GeSiSn films on the Ge substrate was compared to the kinetic diagram for GeSiSn films on Si substrate. New phase diagrams of the superstructural changes on the Sn surface were obtained at different initial conditions of the Sn cover deposition. The Sn film growth was performed at room temperature and 200 degrees C. Superstructures such as (7 x 1), (8 x 1) and (10 x 1) were first obtained on the Sn surface. The phase diagrams allow for determining and controlling the surface Sn cover during the multilayer periodical structures growth, as well as demonstrating the separate interest in obtaining the epitaxial thin Sn films The multilayer structure growth with the pseudomorphic GeSiSn films on Ge and Si substrates was investigated using the phase diagrams for the superstructural changes of the Sn film and reflection high energy electron diffraction (RHEED) pattern. The rocking curves obtained by x-ray diffraction from the multilayer structures containing the GeSiSn layers with the Sn content up to 14% on the Ge and Si substrates demonstrate the pseudomorphic GeSiSn film state, sharp interfaces, as well as the conservation of the periodicity and content in all periods. The comparison of band diagrams based on Ge1-x-ySixSny/Si and Ge1-x-ySixSny/Ge heterostructures was performed, and the conditions, which correspond to the transition to the direct bandgap Ge1x-ySixSny material, were determined. Based on the multilayer structures with the Ge1-x-ySixSny/Si heterojunction, p-i-n diodes were created and a vertical photocurrent was measured in the photovoltaic regime at zero bias. The p-i-n diode photocurrent extends at least to 4 mu m.