V. M. Aroutiounian

Wide gap semiconductor microwave devices

A review of properties of wide gap semiconductor materials such as diamond, diamond-like carbon films, SiC, GaP, GaN and AlGaN/GaN that are relevant to electronic, optoelectronic and microwave applications is presented.We discuss the latest situation and perspectives based on experimental and theoretical results obtained for wide gap semiconductor devices. Parameters are taken from the literature and from some of our theoretical works. The correspondence between theoretical results and parameters of devices is critically analysed.

Investigation of ceramic Fe2O3〈Ta〉 photoelectrodes for solar energy photoelectrochemical converters

Abstract Photocurrent and electrochemical impedance spectroscopy of a polycrystalline semiconductor photoelectrode, Fe 2 O 3 〈Ta〉, was carried out. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance allowed us to obtain an equivalent circuit for the electrochemical cell. The capacitance of the space-charge layer in the semiconductor electrode was isolated, and the limiting step of the electrode process was determined. Measurements of the temperature dependencies of the electroconductivity were used to determine the activation energy for the mobility of the charge carriers. A pair of simultaneously illuminated n-Fe 2 O 3 〈Ta〉 and p-Cu 2 O photoelectrodes were shown to split water spontaneously.

Low reflectance of diamond-like carbon/porous silicon double layer antireflection coating for silicon solar cells

Reflectance calculations for diamond-like carbon (DLC) antireflection thin-film coatings on porous silicon (PS) have been carried out using the optical matrix approach method. Comparison with the reflectance spectrum obtained for other antireflection coatings shows a much lower reflectance with a larger energy range including the ultraviolet, visible and infrared regions of the solar spectrum for the DLC/PS double layer. This finding is relevant in solar cell applications.

Almost zero reflectance of a silicon oxynitride/porous silicon double layer antireflection coating for silicon photovoltaic cells

Reflectance spectrum calculations for a silicon oxynitride (SiOxNy)–porous silicon (PS) double layer antireflection coating is performed using the matrix method. The results are compared with the corresponding spectrum of diamond-like carbon (DLC)/PS and SiO2/TiO2 double layer coatings. A lower reflectance in the visible and infrared regions of the solar spectrum for the SiOxNy/PS double layer is obtained, especially in the 450–600 nm spectral range (with a flat reflectance response remaining as low as ≈0.01%), which corresponds to the maximum intensity of solar irradiation. These findings are of importance in solar cell applications.

The efficiency of solar cells immersed in liquid dielectrics

The effect of an increase in the efficiency of solar cells (SCs) (in particular, common silicon SCs) by their immersion in an isotropic liquid dielectric is described. The presence of a dielectric thin film results in an increase in the SCs efficiency by 40–60% from the reference value. The current–voltage characteristic, fill factor and other characteristics of SCs are analyzed. The mechanisms of the increase in the efficiency of SCs are discussed.

Investigations of solar cells with porous silicon as antireflection layer

Abstract The possibility of using porous silicon layers as antireflection coating instead of the antireflection coatings in common silicon solar cells was investigated. A technology for the manufacture of porous silicon antireflection layers was developed. The comparison of the photovoltaic and optical characteristics of investigated samples of solar cells with ZnS antireflection coating and with porous silicon antireflection coating is presented. It is shown that the formation of the porous layer under optimal technological regimes leads to significant improvement of the main photovoltaic parameters–short-circuit current and open-circuit voltage.

Smoke sensor on the base of Bi2O3 sesquioxide

Abstract The proposed smoke sensing element is a thin film of bismuth sesquioxide made by different deposition methods by use of a corresponding heat treatment. The resistance of thin films placed in smoke medium is changed by about five orders of the magnitude at room temperature. The films influence on neutral and changed solid smoke particles on the thin film resistance was investigated. It is shown that the contribution of the particles on the resistance is negligible up to 30% of the smoke concentration in air and the sensitivity of the samples investigated is caused by gases, formed by the combustion.

Noise Spectroscopy of Gas Sensors

We study current-voltages and low-frequency noise characteristics of the metal-porous silicon-silicon single crystal-metal structure with 50% and 73% porosity of porous silicon. The study is performed in dry air and in a mix of dry air with carbon monoxide of different concentrations. The Hooge noise parameter and the parameter in the frequency dependence of the noise voltage spectral density were determined from experimental data. High sensitivity of spectral dependence of noise to gas concentration allows offering powerful method for determination of gas concentration in the air or environment.

Investigations of the Fe1.99Ti0.01O3-electrolyte interface

The Fe1.99Ti0.01O3–electrolyte interface is investigated using electrochemical impedance spectroscopy. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance at various electrode potentials allows us to define the equivalent circuit for the electrochemical cell and calculate its associated parameters. The capacitance of the space-charge layer in the semiconductor electrode is isolated, and the limiting step of the electrode process is determined.

Fractal model of a porous semiconductor

Abstract In the present paper, it is shown that a porous silicon can be presented as a set of clusters of silicon atoms surrounded by SiO x , whereas the single crystalline silicon substrate can be considered as an infinite cluster. The formulae for the estimation of variable porosity of the material (including the value of critical porosity — the percolation threshold, after which the characteristic phenomena are expected in porous silicon) and the forbidden bandgap value of clusters are suggested as functions of sizes of nanocrystallites. A new fractal model of the pore creation on the surface of a material is also proposed. The cases of semi-spherical, conical (V-groove dielectric isolation technology) and cylindrical (U-groove dielectric isolation technology) are considered. Formulae for the formed surface area S , porosity p of the material as a function of the depth and fractal dimension are obtained.