Search

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.

Group-IV photonic devices that contain Si and Ge are very attractive due to their compatibility with integrated silicon photonics platforms. Despite the recent progress in fabrication of Ge/Si quantum dot (QD) photodetectors, their low quantum efficiency still remains a major challenge and different approaches to improve the QD photoresponse are under investigation. In this paper, we report on the fabrication and optical characterization of Ge/Si QD pin photodiodes integrated with photon-trapping microstructures for near-infrared photodetection. The photon traps represent vertical holes having 2D periodicity with a feature size of about 1 μm on the diode surface, which significantly increase the normal incidence light absorption of Ge/Si QDs due to generation of lateral optical modes in the wide telecommunication wavelength range. For a hole array periodicity of 1700 nm and hole diameter of 1130 nm, the responsivity of the photon-trapping device is found to be enhanced by about 25 times at λ=1.2 μm and by 34 times at λ≈1.6 μm relative to a bare detector without holes. These results make the micro/nanohole Ge/Si QD photodiodes promising to cover the operation wavelength range from the telecom O-band (1260–1360 nm) up to the L-band (1565–1625 nm).

Amorphous ferromagnetic materials with variable composition are promising candidates for application in rapidly-growing technological fields, such as spintronics. However, the significant downside of current state-of-the-art materials is a conductivity mismatch between the injector and the semiconductor, which often is associated with the inability to control and precisely tailor the magnetic properties and conductivity. We report on the synthesis of soft-magnetic SiCxNy:Fe films with a saturation magnetization of 20 emu cm−3 and a conductivity similar to the one of Si, which is crucial for possible applications. XRD with synchrotron radiation and EXAFS revealed the complex composite structure of the films: crystals of Fe3Si, Fe5Si3, SiC and graphite are embedded into the amorphous matrix of SiCxNy. Variation of the deposition conditions allowed us to separately control the magnetic properties through the iron concentration and the conductivity of the material through the amorphous SiCxNy matrix composition. The reported results revealed significant potential of SiCxNy:Fe films as a prospective object for analysis of spin-polarized transport in amorphous semiconductors and for application in the field of spintronics.

In this work investigated crystal structure of films formed by molecular beam epitaxy (MBE) of CaSi2 on Si (111), under electron irradiation by the method of Raman light scattering (RS), it was found that a CaSi2 film is formed at the interface between the silicon substrate and the epitaxially growing CaF2 film under the influence of an electron beam.

Many studies are dedicated to the problem of optical anomalies, focusing mainly on the case of metallic gratings. In the mean time, there is an increasing interest in resonant all-dielectric elements, as they offer a low-loss alternative to plasmonic structures.

The crystal structure of films formed by molecular beam epitaxy (MBE) CaSi2 on Si (111) under electron irradiation was investigated [1]. It was found by the method of Raman scattering (RS) that with an increase in the thickness of the CaF2 film, a structural transition occurs in the CaSi2 film of the space group R3̅m from the 3-layer to 6-layer translational period of the crystal lattice (from 3R to 6R).

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.

The spectral characteristics of the hole photocurrent in plasmon photodetectors based on Ge/Si heterostructures with Ge quantum dots combined with regular arrays of subwavelength apertures of various shapes in a gold film on the semiconductor surface are investigated. Dispersion relations characterizing the propagation of surface plasmon waves along the metal–semiconductor interface are determined from the dependences of the photocurrent on the angle of incidence of light. It is established that the plasmonic enhancement of the photocurrent in rectangular aperture array is suppressed as compared to that in circular and square aperture arrays. It is found that, in hybrid structures with rectangular apertures, there exists a range of wave vectors where the energy of surface plasmons is independent of the wave vector of incident radiation. The results are explained by the excitation of dipole modes localized at rectangular apertures with a large aspect ratio by light waves.

New approaches to enhance properties of silicon based quantum dot heterostructures for optical device application were developed. That is strain driven heteroepitaxy, small-sized quantum dots, elemental compositions of the heterointerface, virtual substrate, plasmonic effects, and the quantum dot charging occupation with holes in epitaxially grown Ge quantum dots (QDs) on Si (100). Experiments have shown extraordinary optical properties of Ge/Si QDs heterostructures and mid-infrared quantum dot photodetectors performance.

It is found that the integration of Ge/Si heterostructures containing layers of Ge quantum dots with twodimensional regular lattices of subwave holes in a gold film on the surface of a semiconductor leads to the multiple (to 20 times) enhancement of the hole photocurrent in narrow wavelength regions of the mid-infrared range. The results are explained by the light wave excitation of the surface plasmon–polaritons at the metal–semiconductor interface effectively interacting with intraband transitions of holes in quantum dots.

The photoconductive gain, hole photocurrent spectra in the mid-infrared range, and band-to-band photoluminescence spectra in arrays of Ge/Si quantum dots with different elemental compositions of the heterointerface are measured. The diffusive mixing of the materials of the matrix and the dots is controlled by varying the temperature at which the Ge layers are overgrown with Si. It is found that the formation of abrupt heterointerfaces leads to the enhancement of the hole photocurrent and quenching of photoluminescence. The results are explained by an increase in the lifetime of nonequilibrium holes owing to the suppression of their capture into the bound states of quantum dots.

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 = 1.2 μ m and by 15× at λ ≈ 1.55 μ m 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.

Surface plasmon waves and Rayleigh anomaly are characteristic optical phenomena exhibited

We report the modification of magnetic properties due to variation of the structure of Fe-contain granules in SiC x N y :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 α -Fe granules, obtained with hexamethylcyclotrisilazane, demonstrate the large saturation magnetization, the hysteresis loop ( ~ 135 Oe at 300 K and ~ 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 α -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.

We study the effect of quantum dot size on the mid-infrared photocurrent, photoconductive gain, and hole capture probability in ten-period p-type Ge/Si quantum dot heterostructures. The dot dimensions are varied by changing the Ge coverage during molecular beam epitaxy of Ge/Si(001) system in the Stranski–Krastanov growth mode while keeping the deposition temperature to be the same. A device with smaller dots is found to exhibit a lower capture probability and a higher photoconductive gain and photoresponse. The integrated responsivity in the mid-wave atmospheric window (λ = (3–5) μm) is improved by a factor of about 8 when the average in-plane dot dimension changes from 18 to 11 nm. The decrease in the dot size is expected to reduce the carrier relaxation rate due to phonon bottleneck by providing strong zero-dimensional quantum mechanical confinement.

Electronic states in multilayer Ge/Si heterostructures with different periods of the arrangement of layers of Ge quantum dots have been studied by the photocurrent spectroscopy method. It has been found that the binding energy of electrons increases with a decrease in the thickness of a silicon spacer and with the extension of Si layers near the vortices of Ge nanoclusters. The results constitute experimental evidence of the deformation mechanism of the formation of localized electronic states in Ge/Si heterostructures with second-type quantum dots.

This paper is devoted to the development and characterization of a microfluidic electric generator based on a silicon microchannel membrane. The voltage and current produced by the generator and the power dissipated on the load resistance during fluid passage through the membrane for different values of the load resistance were determined in experiments using deionized water. The performance of the device is estimated. The possibility of using silicon membranes as the working element of the microfluidic generator is demonstrated. It is suggested that, based on this device, generators suitable for low-power supply can be manufactured. The device can be used as a sensor element for determining fluid flow rate.

We report the fabrication and characterization of a multilayer Ge quantum dot detector grown on Si1−xGex virtual substrate (x = 0.18) for photovoltaic mid-wave infrared photodetection. Detector displays an over 100% photovoltaic response enhancement as compared to a conventional Ge/Si device due to smaller hole effective mass in the SiGe barriers. A further enhancement in sensitivity is achieved by excitation of surface plasmon polariton waves in a Ge/SiGe photodetector coupled with a two-dimensional plasmonic structure. The plasmonic resonance induced photocurrent enhancement is found to be larger when the incident infrared light illuminates the detector from its substrate side. At zero bias and 90 K, the responsivity of 40 mA/W and peak detectivity of 1.4 × 1011 cm·Hz1/2/W are determined at a wavelength of 4 µm.

Spectra of the photocurrent of holes in δ-doped Si layers with Ge quantum dots in weak external electric fields have been studied. It has been established that the photocurrent of the holes in the photovoltaic mode changes its sign with the increase in the impurity concentration in the δ layers. It has been found that there is a voltage range in the vicinity of the zero bias in which the direction of the photocurrent is determined by the wavelength of the exciting radiation.

This paper is devoted to the design and characterization of an electroosmotic pump based on asymmetric microchannel silicon membranes. A pronounced dependence of the pump flow rate on the structural asymmetry of microchannels was first found in experiments using deionized water. Pump flow rate was determined as a function of the applied voltage and the orientation of the matrix with respect to the volume of water pumped. An analytical description of the spatial structure of the microchannel matrices is proposed, which makes it possible to more accurately relate the structural and transport characteristics of the device. The data were used to calculate the zeta potential of the deionized water-silica-silicon system. It is assumed that the observed effect can be used as the basis for designing electroosmotic micropumps for modern bioanalytical micro- and nanofluidic systems.

Optical absorption spectra of polarized infrared radiation in p-type SiGe quantum-well structures have been investigated. Three types of structures with different magnitudes and signs of biaxial elastic strains have been studied. The light absorption factor has been found to double in the region of interband transitions under the in-plane tensile strain of the quantum-well heterojunction. The results are attributed to a change in the order of light- and heavy-hole bands caused by the tensile strain and to the formation of the ground state of charge carriers in the light-hole band.

The work presented here is on manufacturing a sensing structure based on ordered microchannel silicon, for electrophysical detection of liquids. The behavior in time of various organic and inorganic matter (deionized water, ethanol, aqueous ethanol solutions, acetic acid, and ammonium hydroxide) applied to a porous body was studied by the method of measuring the conductivity of a microchannel membrane (a sensing element of a sensor). It was found that a microchannel resistor had a specific response for any liquid applied drop-wise to the sensing element. The proposed electrophysical method allowed us to identify the liquids with which the sensor interacted.

We analyze and compare two complementary 2D plasmonic structures, a gold film perforated with a subwavelength hole array and a periodic lattice of gold disks, for infrared detector applications and argue that the former gives the best results when integrated on top of a Ge/Si quantum dot mid-infrared photodetector (QDIP). The periodicity of both metasurfaces is the same and equal to 1.2 µm. The QDIP coupled with the metal disk array exhibits about 3.7 times plasmonic responsivity enhacement as compared to a conventional Ge/Si device and displays an over 11 times enhacement when integrated with the holey Au film. At 78 K, the quantum efficency of about 2% and photovoltaic peak detectivity of 4.5 × 1012 cm·Hz1/2/W are determined at a wavelength of 4.2 µm in a hybrid QDIP with the perforated gold film.

Results of investigations into the time characteristics of photosensitive layers based on Ge/Si nanoheterostructures excited by femtosecond laser pulses with a wavelength of 1.55 μm are given. It is demonstrated that the leading front duration of the photoresponse pulse for the examined specimens excited by laser pulses of 120 fs duration does not exceed 30–40 пs.

The photodetection improvement previously observed in mid-infrared (IR) quantum dot photodetectors (QDIPs) coupled with periodic metal metasurfaces is usually attributed to the surface light trapping and confinement due to generation of surface plasmon waves (SPWs). In the present work, a Ge/Si QDIP integrated with a metal plasmonic structure is fabricated to experimentally measure the photoresponse enhancement and verify that this enhancement is caused by the excitation of the mid-IR surface plasmons. A 50 nm-thick gold film perforated with a 1.2 μm-period two-dimensional square array of subwavelength holes is employed as a plasmonic coupler to convert the incident electromagnetic IR radiation into SPWs. Measurements of the polarization and angular dependencies of the photoresponse allow us to determine the dispersion of plasmon modes. We find that experimental dispersion relations agree well with that derived from a computer simulation for fundamental plasmon resonance, which indicates that the photodetection improvement in the mid-IR spectral region is actually caused by the excitations of surface plasmon Bloch waves.The photodetection improvement previously observed in mid-infrared (IR) quantum dot photodetectors (QDIPs) coupled with periodic metal metasurfaces is usually attributed to the surface light trapping and confinement due to generation of surface plasmon waves (SPWs). In the present work, a Ge/Si QDIP integrated with a metal plasmonic structure is fabricated to experimentally measure the photoresponse enhancement and verify that this enhancement is caused by the excitation of the mid-IR surface plasmons. A 50 nm-thick gold film perforated with a 1.2 μm-period two-dimensional square array of subwavelength holes is employed as a plasmonic coupler to convert the incident electromagnetic IR radiation into SPWs. Measurements of the polarization and angular dependencies of the photoresponse allow us to determine the dispersion of plasmon modes. We find that experimental dispersion relations agree well with that derived from a computer simulation for fundamental plasmon resonance, which indicates that the photodet...

A floating gate memory structure, utilizing Ge nanocrystals (NCs) deposited on tunnel SiO2, have been fabricated using pulsed low energy ion-beam induced molecular-beam deposition (MBD) in ultra-high vacuum. The ion-beam action is shown to stimulate the nucleation of Ge NCs when being applied after thin Ge layer deposition. Growth conditions for independent change of NCs size and array density were established allowing to optimize the structure parameters required for memory device. Activation energy E = 0.25 eV was determined from the temperature dependence of NCs array density. Monte Carlo simulation has shown that the process, determining NCs array density, is the surface diffusion. Embedding of the crystalline Ge dots into silicon oxide was carried out by selective oxidation of Si(100)/SiO2 /Ge(NCs)/poly-Si structure. MOS-capacitor obtained after oxidation showed a hysteresis in its C–V curves attributed to charge retention in the Ge dots.

It is established that admixture of Ag, Al, Cu, Ni, Zn, and Fe 3 O 4 nanoparticles to a rhodamine 6G solution in ethanol with a concentration of 10−2 mol/L that fills a cell with a thickness of 600 µm results in a decrease in the superluminescence thresholds by no less than 50 folds.

Thin silicon carbonitride films were synthesized by PECVD using siliconorganic compound as single-source precursor within a temperature range of 373–623 K. IR and Raman spectroscopy, AES, XPS, ellipsometry, XRD using the synchrotron radiation, EDS, SEM, AFM, measurements of electrophysical, mechanical characteristics and optical properties were applied to study their physicochemical and functional properties. It was shown that low temperature films are low-k dielectrics with the following characteristics: a dielectric constant of 3.0–7.0, specific resistance, ρ = 1013–1016 Om × cm, Edielectric breakdown ∼ 1 MV/cm, surface state density Nss ∼ 2.4·1011 cm− 2·eV− 1 and fixed charge density of about 1.6 × 1011 cm− 2. The bandgap of the films changes from 5.35 up to ∼ 3.30 eV. Obtained films are very flat and smooth, root mean square roughness Rms equals to ∼ 0.5–1.0 nm. Microhardness of these films changes from 1.9 up to 2.4 GPa, and Young's modulus changes from 12.2 up to 15.9 GPa.

We report on intraband photocurrent spectroscopy of dome-shaped GeSi islands embedded in a Si matrix with n+-type bottom and top Si layers. An in-plane polarized photoresponse in the 85–160 meV energy region has been observed and ascribed to the optical excitation of electrons from states confined in the strained Si near the dome apexes to the continuum states of unstrained Si. The electron confinement is caused by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried GeSi quantum dots. Sensitivity of the device to the normal incidence radiation proves a zero-dimensional nature of confined electronic wave functions.

The photoconduction in a tunnel-coupled Ge/Si quantum dot (QD) array has been studied. The photoconductance (PC) sign can be either positive or negative, depending on the initial filling of QDs with holes. The PC kinetics has a long-term character (102−104 s at T = 4.2 K) and is accompanied by persistent photoconduction (PPC), whereby the PC value is not restored on the initial level even after relaxation for several hours. These phenomena are observed upon illumination by light with photon energies both greater and smaller than the silicon bandgap. A threshold light wavelength corresponding to a long-term PC kinetics depends on the QD filling with holes. A model describing the observed PC kinetics is proposed, according to which the main contribution to the PC is related to the degree of QD filling with holes. By applying the proposed model to the analysis of PC kinetics at various excitation levels, it is possible to determine the dependence of the hopping conductance on the number of holes per QD. The rate of the charge carrier density relaxation exponentially depends on the carrier density.

Nanocrystalline films of a ternary compound, namely, silicon carbonitride SiCxNy, are prepared by plasma-enhanced chemical vapor deposition at temperatures of 473–1173 K with the use of a complex gaseous mixture of hexamethyldisilazane Si2NH(CH3)6, ammonia, and helium. The chemical and phase compositions and the physicochemical properties of the films are investigated using IR, Auger electron, and X-ray photoelectron spectroscopy; ellipsometry; synchrotron X-ray powder diffraction; electron and atomic-force microscopy; microhardness measurements with a nanoindenter; and electrical measurements. Correlations of the composition of the initial gas phase and the synthesis temperature with a number of functional properties of the SiCxNy silicon carbonitride films are revealed.

Thin nanocrystalline silicon oxynitride films were synthesized for the first time at low temperatures (373–750 K) by inductively coupled plasma chemical vapor deposition (ICP-CVD) using gas mixture of oxygen and hexamethyldisilazane Si 2 NH(CH 3 ) 6 (HMDS) as precursors. Single crystal Si (1 0 0) wafers 100 mm in diameter were used as substrates. Physicochemical properties of the thin films were examined using ellipsometry, IR spectroscopy, Auger electron and X-ray photoelectron spectroscopy and XRD using synchrotron radiation (SR). The studies of the phase composition of nanocrystalline films of silicon oxynitride showed that in the case of oxygen excess in the initial gas mixture, they contain a mixture of hexagonal phases: h-SiO 2 and α-Si 3 N 4 . These phases consist of oriented nanocrystals of 2–3 nm size. In case of decrease of oxygen concentration in the initial gas mixture, the fraction of the α-Si 3 N 4 phase increases.

The results of research aimed at the development of high-efficiency Ge/Si-based photodetectors for fiber-optic communication applications are reported. The photodetectors are designed as vertical p-i-n diodes on silicon-on-insulator substrates in combination with waveguide lateral geometry and contain Ge quantum-dot layers. The layer density of quantum dots is 1×1012 cm−2; the dot size in the plane of growth is ∼8 nm. Unprecedentedly high quantum efficiency suitable for the range of telecommunication wavelengths is attained; specifically, in the waveguides illuminated from the end side, the efficiency was as high as 21 and 16% at 1.3 and 1.55 µm, respectively.

Quantum dot based infrared (IR) photodetectors (QDIPs) have the potential to provide meaningful advances to the next generation of imaging systems due to their sensitivity to normal incidence radiation, large optical gain, low dark currents, and high operating temperature. SiGe-based QDIPs are of particular interest as they are compatible with silicon integration technology but suffer from the low absorption coefficient and hence small photoresponse in the mid-wavelength IR region. Here, we report on the plasmonic enhanced Ge/Si QDIPs with tailorable wavelength optical response and polarization selectivity. Ge/Si heterostructures with self-assembled Ge quantum dots are monolithically integrated with periodic two-dimensional arrays of subwavelength holes (2DHAs) perforated in gold films to convert the incident electromagnetic IR radiation into the surface plasmon polariton (SPP) waves. The resonant responsivity of the plasmonic detector at a wavelength of 5.4 μm shows an enhancement of up to thirty times over a narrow spectral bandwidth (FWHM = 0.3 μm), demonstrating the potentiality of this approach for the realization of high-performance Ge/Si QDIPs that require high spectral resolution. The possibility of the polarization-sensitive detection in Ge/Si QDIPs enhanced with a stretched-lattice 2DHA is reported. The excitation of SPP modes and the near-field components are investigated with the three-dimensional finite-element frequency-domain method. The role that plasmonic electric field plays in QDIP enhancement is discussed.

An array of $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ Ge self-assembled quantum dots is embedded into the active channel of a Si metal-oxide-field-effect transistor. Conductance oscillations with a gate voltage resulting from a successive loading of holes into the dots are observed. Based on measurements of the temperature dependence of the conductance maxima, the charge-transfer mechanism in the channel is identified as being due to variable-range hopping between the dots, with the typical hopping energy determined by interdot Coulomb interaction. The characteristic spatial dimension of the hole wave functions as well as the charging energies of the dots are determined from the conductance data. The effect of the proximity of a bulk conductor on hopping transport is studied. We find that putting a metal plane close to the dot layer causes a crossover from Efros-Shklovskii variable-range hopping conductance to two-dimensional Mott behavior as the temperature is reduced. At the crossover temperature the hopping activation energy is observed to fall off. The metal plane is shown not to affect the conductance of samples which show Mott hopping. In the Efros-Shklovskii hopping regime, the conductance prefactor was found to be $\ensuremath{\simeq}{e}^{2}/h,$ and the conductance to scale with the temperature. In the fully screened limit, the universal behavior of the prefactor is destroyed, and it begins to depend on the localization length. The experimental results are explained by a screening of long-range Coulomb potentials, and provide evidence for strong electron-electron interaction between dots in the absence of screening.

An array of 3 × 107 Ge self-assembled quantum dots is embedded into the active channel of a Si metal-oxide field-effect transistor. Conductance oscillations with the gate voltage resulting from successive loading of holes into the dots are observed. On the basis of measurements of the temperature dependence of the conductance maxima, the charge-transfer mechanism in the channel is identified as being due to variable-range hopping between the dots, with the typical hopping energy determined by inter-dot Coulomb interaction. The characteristic spatial dimension of the hole wavefunctions as well as the charging energies of the dots are determined from the conductance data.

We report the fabrication and characterization of a ten-period Ge quantum dot photodetector grown on SiGe pseudosubstrate. The detector exhibits tunable photoresponse in both 3- to 5- μ m and 8- to 12- μ m spectral regions with responsivity values up to about 1 mA/W at a bias of −3 V and operates under normal incidence radiation with background limited performance at 100 K. The relative response in the mid- and long-wave atmospheric windows could be controlled through the applied voltage.

Porous silicon layers formed on p+ substrates were investigated by secondary ion mass spectrometry technique. It has been found for the first time that the dopant impurity (boron) does not escape from the porous silicon (PS) layer during the anodization. Analysis of the boron excess in PS in relation to the crystalline substrate provides a means by which to study the porosity depth distribution. The resistivity of the PS layer has been observed to depend strongly on depth: in particular, in the high-porosity layers (50-65%) a relatively thin insulating sublayer (about 300 nm) is found to form at the surface. After annealing of the PS layers in an oxidizing atmosphere, the high-resistivity regions disappear.

We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

We report on the operation of Si metal–oxide–semiconductor field-effect transistor with an array of ∼103 10 nm diameter Ge self-assembled quantum dots embedded into the active channel. The drain current versus gate voltage characteristics show oscillations caused by Coulomb interaction of holes in the fourfold-degenerate excited state of the dots at T⩽200 K. A dot charging energy of ∼43 meV (i.e., >kT=26 meV at T=300 K) and disorder energy of ∼20 meV are determined from the oscillation period and the temperature dependence study of current maxima, respectively.

The electronic and optical phenomena, as well as possible device-oriented application in Ge/Si and Ge/SiO2 nanodots that have been synthesized by molecular-beam growth are the scope of this article. We focus on the fundamental aspects and device applications of the small size dots whose electronic states resemble those of an atom even at room temperature. A new branch of semiconductor physics that studies the behavior of electrons confined in precisely tailored potential emerged during the last 20 years. This field has developed from the progress in technology that now allows for the routine fabrication of nanometer-scale solid state structures that contain small numbers of conduction electrons (

Pulsed low-energy (200 eV) ion-beam-induced nucleation during Ge deposition on thin SiO2 film was used to form dense homogeneous arrays of Ge nanocrystals. The ion-beam action is shown to stimulate the nucleation of Ge nanocrystals when being applied after thin Ge layer deposition. Temperature and flux variation was used to optimize the nanocrystal size and array density required for memory device. Kinetic Monte Carlo simulation shows that ion impacts open an additional channel of atom displacement from a nanocrystal onto SiO2 surface. This results both in decrease of the average nanocrystal size and in increase of nanocrystal density.

Comprehensive stomatologic examination of 45 patients with chronic generalized parodontitis (CGP) was combined with parallel determination of immunoreactive insulin (IRI) in blood. In 30 patients CGP developed on the background of metabolic syndrome (MS). Clinical and X-ray examination of periodontal tissues disclosed that CGP in patients with MS was characterized by active and aggressive course. A correlation between CGP severity degree and level of IRI in blood was established.

We report on the transport properties of Si field-effect transistors with an array of iO 10-nm-diameter Ge self-assembled quantum dots embedded into the active channel. The drain current versus gate voltage characteristicsshow oscillations caused by Coulomb interaction of holes in the fourfold-degenerate excited state of the dots even at room temperature. A dot charging energy of 43 meV (i.e., > kT = 26 meV at T = 300 K) and disorder energy of '-20 meV are determined from the oscillation period and the temperature dependence studyof current maxima, respectively.Keywords: quantum dots, Coulomb blockade, MOSFET INTRODUCTION Epitaxial growth of highly strained semiconductors in the Stranski—Krastanov growth mode enables in situfabrication of arrays of 10-nm-scale quantum dots (so called self-assembled quantum dots (SAQDs)). Electronicand opto-electronic nanodevices implemented on Ge self-assembled quantum dots in Si matrix have attractedmuch attention due to their compatibility with modern Si-based complementary metal-oxide-semiconductor(CMOS) circuitry. This would offer a substantial reduction in complexity and cost of future high performance

The epitaxial system Si—porous Si—Si substrate possesses unusual properties for microelectronic structures and is promising for use in instruments, especially after converting the three-layer system into a Si-on-insulator structure via oxidation of the porous sublayer [1-8]. Anodic etching regimes enabling the surface layer of p+-type Si to be converted into a porous material with a significant pore volume are known. The physical properties of porous Si, mainly mechanical and optical, differ significantly from those of single-crystalline Si. In particular, the Young’s modulus of Si with 54% porosity is 1.7.1010N/m2[9], which is an order of magnitude less than that of a single crystal. The Poisson coefficient is 0.09, which is also much less than for compact crystalline Si, which has a Poisson coefficient of 0.26. Thus, porous Si is much weaker than the starting compact substrate material. Its strength decreases with increasing porosity. However, the crystal structure of Si within the porous layer is nearly identical to that of Si without pores. It has been noted [9] that the x-ray rocking curves of porous and nonporous Si are very similar. Immediately after anodic etching the lattice constant of porous Si perpendicular to the interface is hundredths of a percent greater than that of the substrate and depends on the porosity and the average pore size, increasing as they increase.

We studied the effect of hydrogen plasma treatment on room-temperature photoluminescence ofself-assembled Ge/Si quantum dots by varying temperature and duration of treatment. Hydrogenplasma exposure at 300 C° for 30min was found to result in the improvement in the radiativeefficiency of the Ge quantum dots by one order of magnitude. The enhancement of thephotoluminescence intensity is thought to be due to the passivation of nonradiative centerslocated nearby or inside the dots via formation of Si–H bonds. Infrared absorption spectroscopywas used to correlate photoluminescence results.Keywords: quantum dots, photoluminescence, hydrogen passivation(Some figures may appear in colour only in the online journal)A major drawback in the development of silicon optoelec-tronic integrated circuits is the difficulty in fabricating effi-cient light-emitting devices. Various semiconductor structureshave been studied to design Si-based light emitters operatingon telecom wavelengths, including Si layers on oxidized Sisurface [1], Ge-on-Si structures [2], Er doped Si-basedmaterials [3], and GeSn alloys [4]. The light emission in thetelecom wavelength range of 1.3–1.6μm can be realized inself-assembled Ge/Si quantum dots (QDs) fabricated viaStranski–Krastanov mechanism [5–7]. Small sizes of Geislands in Si matrix, their high areal density, and abruptinterfaces are the crucial issues when ensembles of QDs areconsidered for both device applications and fundamentalphysical studies. The above mentioned requirements can befulfilled with the use of a low-temperature deposition tech-nique [8–10]. However, the low-temperature growth isaccompanied by formation of point defects in either interfaceof QDs or in surrounding Si layers resulting in a degradationof the Ge QD photoluminescence (PL) [9].The most serious problem for the application of Ge/SiQDs up to now is the low luminescence efficiency, especiallyat room temperature. A few approaches have been exploitedto achieve a room-temperature PL, such as manipulating theovergrowth temperatures [11, 12] and the Si spacer thickness[13], doping the Ge nanoislands with antimony [14],formation of Ge/Si QD superlattices [15]. For InAs/GaAsQDs, it has been previously found that improvement in the PLefficiency can be achieved by exposure of samples tohydrogen plasma [16, 17]. The enhancement of the emissionwas supposed to originate from the passivation of non-radiative centers located nearby or inside the dots [18]. Si-based heterostructures can also exhibit point defects mainly inthe form of Si dangling bonds. These dangling bonds act aselectrically active recombination centers for charge carriersand thus cause the optical emission to deteriorate. It has beenclearly demonstrated that introducing atomic hydrogen intoamorphous, crystalline, and polycrystalline Si films results ina reduction of the Si dangling-bond concentration on thesurface and grain boundaries through the formation of Si–Hbonds [19–22].Sobolev et al [23] reported on the enhance-ment of the low-temperature PL from the hydrogen passivatedGe/Si quantum dots. However neither the enhancement factornor the optimal parameters for passivation have been estab-lished. In this paper we study the effect of hydrogen passi-vation on the more practically important room temperatureemission from Ge/Si self-assembled QDs. The optimalhydrogenation temperature and the exposure time, whichensure the enhancement of the dot radiative efficiency by oneorder of magnitude, were determined.

We present intersubband absorption measurements performed on p-type Si1 − xGex/Si(0 0 1) quantum wells (x = 0.35) in the presence of an external strain. We find that the in-plane polarized absorption band is rather insensitive to the strain. For the incident light polarized along the growth direction, the absorption strength increases under the tensile strain. The latter observation is well accounted for by a six-band k · p model and is explained by redistribution of hole population between the heavy- and the light-hole subbands caused by the strain-induced energy shifts of the bands.