The present work demonstrates the possibility to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures, including nanoscaled ones. The structures are grown from Ga - and GaIn - melts containing polycrystalline GaN as a nitrogen source. The red shift of the absorption spectra corresponds to nitrogen content in the epitaxial layers near or less than 0.2 at %. Photoluminescence spectra of dilute nitride GaAsN and GaInAsN show emission from localized nitrogen states - N-nanoclusters of more than two N atoms. These studies show that the melt grown dilute GaAsN and GaInAsN nanostructures can be used for solar cells with extended long wavelength edge.

This paper presents investigation of electronic transport properties of GaAsN and InGaAsN epitaxial layers with low nitrogen content, the so called dilute nitrides, grown by liquid-phase epitaxy (LPE). The layers up to 2 microns thick have been grown from Ga- and In-rich melt at different initial epitaxy temperatures in the range 660-620 degrees C. Polycrystalline GaN has been used as a source for nitrogen. As grown, unintentionally doped GaAsN and InGaNAs are n-type with free carrier concentrations one order of magnitude higher than those for the reference nitrogen free undoped GaAs and InGaAs layers. Lattice matched to GaAs substrate InGaAsN layers exhibit Hall mobility values higher than 2000 V/cm(2).s

Low-cost single-junction GaAs solar cells on the base of p-AlGaAs/p-GaAs/ n-GaAs heterostructures grown by low-temperature liquid-phase epitaxy have been fabricated. For analyzing the factors contributing to solar cell efficiency the program products PC1D have been used. The optimal doping concentrations and thicknesses of the layers which correspond to the maximum values of the solar cell output parameters have been determined. The multilayer solar cell structure has been optimized on the base of this simulation. Low cost technological processes and masks, necessary for fabrication of the cells on the base of the grown heterostructures, have been developed, too. The front and back metallization of the cell is Ni/Al system deposited by magnetron sputtering. A double layer Al2O3 /ZrO2 antireflection coating is deposited on the front side of a solar cell structure by the spin coating technique. The conversion efficiencies of 19 % at one sun AM1.5 conditions have been measured.

Group III-V-nitrides, the so called dilute nitrides, are promising materials for multi-junction solar cells, telecommunications, heterojunction bipolar transistors and high frequency (THz) applications. The introduction of a tiny fraction (similar to 1 %) of nitrogen in GaAs or GaP induces a decrease of the band gap energy and a deformation of the conduction band structure, which extends the range of its applicability. In the present work, we demonstrate the possibility of incorporating nitrogen in melt-grown GaAs layers. The dilute gallium arsenide-nitride layers were grown on GaAs substrates by liquid-phase epitaxy, using polycrystalline GaN as a source of nitrogen in the melt. Characterisation of the structural and electrical properties was done by XRD, XPS analysis, FTIR spectra and Hall effect measurements in the range 80-300K.

We report the fabrication of buried contact solar cells using porous silicon as sacrificial layer to create well-defined channels (for buried contacts) in silicon. In this paper, the salient features of the technology have been presented. No detrimental effect was found in the performance of buried contact solar cell with partially filled contact area compared to the solar cells having conventional planar contacts. However, a marked difference in the short circuit current density was seen when channel was fully filled with metal by screen printing, without degradation in the open-circuit voltage. It is expected that improved processing in combination with optimized buried metallic contact parameters may yield higher efficiencies that may result in substantial decrease in solar cell cost.

Samples prepared by ion-beam synthesis are studied. A two-step 56Fe+ ion implantation process was performed on n-type Si wafers with (100) orientation. Subsequently, the samples, implanted with the same dose and energies, were subjected to rapid thermal annealing at two different temperatures – 800°C and 900°C for the same time – 90s. A remarkable difference in the infrared spectra and in the refractive index dispersions near the band edge of samples annealed at different temperatures was found. The behaviour of the optical properties was related to different morphology of the samples.

In this paper, we present the preparation of multilayer AlGaAs/GaAs heterostructures for photovoltaic application. The structures developed consist of several layers grown on a highly conducting GaAs substrate: n-GaAs base, p-GaAs emitter embedded between two AlGaAs layers, and heavily doped p+GaAs capping contact layer. The second 0.03 μm thick 'window' AlGaAs layer has band gap energy of 2.1 eV and ensures penetration of the higher-energy photons in the active region of the p-n junction. The electrical and optical parameters of the multilayer heterostructure as well as the layers thickness are designed by numerical simulation using computer modeling. The optimized heterostructure has a back-surface-field AlGaAs layer of several microns and an ultra thin (20-40 nm) window layer providing the best conversion efficiency and a maximum spectral response in the range 300-900 nm.

The behaviour of Fe implanted into Si(100) during subsequent pulsed ion - beam treatment (PIBT) has been studied. A two-step Fe-56(+) ion implantation at energies of 60 and 20 keV and total doses of 10(16) - 2x10(17) cm(-2) was used. As crystallization due to PIBT took place, Fe segregated towards the surface of the samples for the lower dose used (10(16) cm(-2)) and diffusion into the bulk of the Si samples or-cured for higher doses (1x10(17) cm(-2) and 2x10(17) cm(-2)). The Fe concentration profile was shifted rigidly, without Fe losses. Both the movement of the Fe layer and the maximum concentration of Fe in the Si crystallized region were characterized by Rutherford backscattering spectroscopy (RBS) in combination with channelling (RBS/C).

The current-voltage dependences of heterojunctions between the silicon and the semiconducting metal silicides β-FeSi2 and MgSi2, prepared by ion-beam synthesis, followed by rapid thermal annealing, are reported. It was found that the anisotype junctions showed a rectifying behavior, reflecting the heterojunctions energy band diagrams, constructed on the base of the previous optical and structural investigations.

Future of analytical and manufacturing methods based on micro-mechanical cantilevers, depends critically on the ability to implement parallel operation and fast signal processing [1]. There are two mean reasons: high throughput requirement and complexity (multidimensionality) of analyzed value. In order to get parallel function, any single device should be simultaneously: recognizable, autonomously actuated and independently accessible for readout. Devices, fulfilling these requirements, are suffering from a substantial increase in complexity of both layout and manufacturing technology. In present paper, we demonstrate a novel design of a MEMS (Micro-Electro-Mechanical Systems) cell designed for e-NOSE applications, using results of previous works [2,3], which solves above mentioned problems. The cell consists of four integrated cantilevers, each having a separate piezoresistor. Additionally, the cantilevers are designed to be different in length and thus having different resonance frequencies. Thus, individual cantilevers are frequency recognizable/addressable. Samples of self-actuated piezoresistive cantilever sensor have been fabricated on n-type, <100> silicon, applying combined surface and bulk micromachining techniques. The cantilever dimensions were chosen to provide approx. 1.8 kHz resonance frequency gap between neighbor individual sensors. The new micro-machined cell is suitable for chemical and biological recognition as a micro-balance.

The polarized Raman spectra of ion-beam synthesized Mg2Si, embedded in (001) and (111) Si substrates were studied. The relative intensities of the F-2g mode measured in several exact scattering configurations are compared with those calculated under the condition for minimum mismatch between the Si and Mg2Si lattices. A conclusion for the orientational growth of the Mg2Si phase in Si is drawn.

The samples under investigation were prepared by implantation of Mg+ ions into high resistivity (780 - 850) Omega cm, n-type Si wafers with (111) orientation. Two different doses of Mg+ ions were implanted: D1 = 2x 10(17)cm(-2) and D2 = 4x 10(17) cm(-2), at an energy of 40 keV. Subsequently, the implanted samples were annealed at a temperature T-a = 500 degrees C for different times t(a) = 30, 60 and 300 s. The Mg+ ion concentration distribution was simulated by TRIDYN (dynamic computer simulation code), and the initial profiles of the implanted Mg+ were estimated. The composition and the thickness of the implanted layer, both as-implanted and annealed, were evaluated from the computer simulations of the measured Rutherford backscattering profiles, and were compared with the TRIDYN simulation.

Resonant Raman scattering by ion beam synthesized in silicon matrix Mg2Si phase is studied. The samples are prepared with the implantation of Mg-24(+) ions with dose 4x10(17) cm(-2) and with two different energies 40 and 60 keV into (100)Si substrates. The far infrared spectra are used as criteria for the formation of the Mg2Si phase. The Raman spectra are excited with different lines of Ar+ laser, with energies of the lines lying in the interval from 2.40 to 2.75 eV. The resonant scattering can be investigated using these laser lines, as far as according to the Mg2Si band structure, there are direct gaps with energies in the same region. The energy dependences of the scattered intensities in the case of the scattering by the allowed F-2g and the forbidden LO-type modes are experimentally obtained and theoretically interpreted. On the base of the investigation energies of the interband transitions in the Mg2Si are determined. It is found also that the resonant Raman scattering appears to be a powerful tool for characterization of a material with inclusions in it. In the particular case it is concluded that the Mg2Si phase is present in the form of a surface layer in the sample, prepared with implantation energy 40 keV and as low-dimensional precipitates, embedded in the silicon matrix, in the sample, prepared with the higher implantation energy.

The crystal structure of beta-FeSi2 phase, prepared by ion beam synthesis (IBS) method, followed by rapid thermal annealing (RTA) is investigated by grazing incident asymmetric X-ray diffraction (GIAXRD). The X-ray spectra, obtained at different grazing angles, indicated that the beta-FeSi2 phase is formed in the whole implantation range. From the comparison of the reflections intensities ratios, it is found that in the metal-deficient regions, where the beta-FeSi2 phase is present in the form of precipitates, the crystallites orientation is influenced by the one of the silicon substrates, while the orientation in the metal-rich region is different and depends on the annealing temperature. (C) 2004 Elsevier Ltd. All rights reserved.

Quasi-continuous layers of β-FeSi2 phase, formed by ion beam synthesis (IBS), followed by rapid thermal annealing (RTA), are studied. The infrared spectra (IR) of the samples under investigation indicate different prevailing orientation of the β-FeSi2 crystallites in samples, produced at different fabrication regimes. The optical constants are calculated from the experimental reflectance (R) and transmittance (T) spectra, using a general matrix method. The value of the optical dielectric function of samples with different orientations of the crystallites is determined from the quantitative interpretation of the refractive index dispersions in the range of transparency.

Continuous layers and precipitates of the β-FeSi2 phase were formed by ion-beam synthesis followed by rapid thermal annealing. Two steps of Fe+ ion implantation in Si, at energies of 20 and 60 keV, were performed, using three different doses – 5×1015, 5×1016, and 1017 cm−2. The infrared spectra were used as a criterion for the formation of the β-FeSi2 phase. The refractive-index-energy dependences were calculated from the transmittance and reflectance spectra, using the general matrix method. From these dependences, the energy band gap and the energies of the higher-energy transitions in the vicinity of the gap were determined.

The β-FeSi2 phase was fabricated using ion beam synthesis with high doses of implantation followed by rapid thermal annealing. The as-implanted samples and samples annealed under different conditions are studied by grazing incidence asymmetric X-ray diffraction and atomic force microscopy. The effect of the annealing temperature and time on the β-FeSi2 crystal structure and surface morphology is investigated.

Monophase β-FeSi2 layers, fabricated using ion beam synthesis with high implantation doses followed by rapid thermal annealing are studied. The structure of the films was analyzed by Rutherford backscattering, X-ray diffraction and atomic force microscopy. The average grain sizes of the layers, formed under different annealing regimes were determined. The room temperature reflectance and transmittance spectra were measured in the range from 0.2 to 1.3eV. The spectra were analyzed in terms of a multilayered structure. The dispersion of the optical constants was calculated using a generalized matrix method, accounting for the surface and interface roughness. From the optical constants dispersions the effective optical conductivity and that in the grains were estimated. The grain sizes were found to influence the optical conductivity.

The influence of the emitter thickness on the photovoltaic properties of monocrystalline silicon solar cells with porous silicon was investigated. The measurements were carried out on n+p silicon junction whose emitter depth was varied between 0.5 and 2.2μm. A thin porous silicon layer (PSL), less than 100nm, was formed on the n+ emitter. The electrical properties of the samples with PS were improved with decrease of the n+p junction depth. Our results demonstrate short-circuit current values of about 35–37mA/cm2 using n+ region with 0.5μm depth. The observed increase of the short-circuit current for samples with PS and thin emitter could be explained not only by the reduction of the reflection loss and surface recombination but also by the additional photogenerated carriers within the PSL. This assumption was confirmed by numerical modeling. The spectral response measurements were performed at a wavelength range of 0.4–1.1μm. The relative spectral response showed a significant increase in the quantum efficiency of shorter wavelengths of 400–500nm as a result of the PS coating. The obtained results point out that it would be possible to prepare a solar cell with 19–20% efficiency by the proposed simple technology.