Papers by Author: M.D. Efremov

Abstract: Thin (90 nm) a-Si:H films on Corning 7059 glass substrates have been crystallized by 120 fs pulses of Ti:sapphire and nanosecond pulse XeCl and KrF excimer lasers. Initial films were deposited using low-temperature plasma enhanced deposition technique. The structural properties of the films were characterized using the spectroscopy of Raman scattering, excited by the argon laser (line 514.5 nm) and using electron microscopy. For the femtosecond pulse treatments the ablation threshold was found to be some more than 65 mJ/cm2. When pulse energy density was lower than ~30 mJ/cm2 no structural changes were observed. In optimal regimes the films were found to be fully crystallized with needle grain structure, according to the Raman scattering and electron microscopy data. Estimates show the pulse energy density was lower than the Si melting threshold, so non-thermal “explosive” impacts may play some role. The main result in nanosecond XeCl and KrF laser pulse crystallization is the narrower window between beginning of crystallization and ablation for KrF laser (wavelength 248 nm) than for the XeCl laser (wavelength 308 nm). So, the possibility of the femtosecond and nanosecond laser pulses to crystallize a-Si films on non refractory glass substrates was shown. The results obtained are of great importance for manufacturing of polycrystalline silicon layers on non-refractory large-scale substrates for giant microelectronics.

Abstract: Characterisation of three-layer dielectric embedded into MDS-structure (Metal- Dielectric-Silicon) was provided in the dark and under light illumination. In the dark, increasing of differential capacitance, simultaneously, with variation of differential conductivity of MDSstructures was detected. In the light strong changing of capacitance part of impedance was firstly observed, demonstrating decreasing almost to zero values and restoring up to maximal values in narrow bang of voltage applied. Variation of capacitance exceeds significantly so called dielectric layer capacitance, what interpreted as carriers exchanging between substrate and electronic states in SiNx probably due to three-layered kind of its nature.

Abstract: In present work temperature stable conductivity is considered for neutron-doped FZ silicon with point radiation defects. It was shown that divacancy formed after electron irradiation allow to increase resistivity of silicon at room temperature, what lead to less variation of conductivity in a range of temperatures 20-160C. Discrepancy between experimental and theoretical data was evaluated and corrected with introduction in the model deep level center Ec-0.6eV. As result of investigation power resistors were elaborated with 10% deviation from nominal value within the range of temperatures.

Abstract: Ge nanocrystals (NCs) in GeO2 films obtained with the use of two methods were studied. The first method is a film deposition from supersaturated GeO vapor with subsequent dissociation of metastable GeO on heterophase system Ge:GeO2. The second method is growth of anomalous thick native germanium oxide layers with chemical composition GeOx(H2O) during catalytically enhanced Ge oxidation. The obtained films were studied with the use of photoluminescence (PL), Raman scattering spectroscopy, high-resolution electron microscopy (HREM). Strong PL signals were detected in GeO2 films with Ge-NCs at room temperature. “Blue-shift” of PL maximum was observed with reducing of Ge excess in anomalous thick native germanium oxide films. Also a correlation between reducing of the NC sizes (estimated from position of Raman peaks) and PL “blue-shift” was observed. The Ge NCs presence was confirmed by HREM data. The optical gap in Ge-NCs was calculated with taking into account quantum size effects and compared with the position of the experimental PL peaks. It can be concluded that a Ge-NC in GeO2 matrix is a quantum dot of type I.

Abstract: Silicon nanopowders were produced using electron-beam-induced evaporation of bulk silicon ingots in various gas atmosphere. Optical properties of the nanopowders were studied with the use of photoluminescence and Raman spectroscopy techniques. Photoluminescence peaks in the visible region of the spectrum have been detected at room temperature in silicon nanopowders, produced in argon gas atmosphere. Strong short-wavelength shift of the photoluminescence peaks can be result of quantum confinement effect for electrons and holes in small silicon nanocrystals (down to 2 nm in diameter). The size of silicon nanocrystals was estimated from Raman spectroscopy data. The calculated in frame of effective mass model optical gaps for silicon nanocrystals of spherical shape are in good correlation with experimental photoluminescence data. The attempts of deposition of silicon nanocrystal films from the nanopowders on silicon substrates were carried out.

Abstract: The laser assisted formation of silicon nanocrystals in SiNx films deposited on quartz and silicon substrates is studied. The Raman spectroscopy revealed creation of the Si cluster and crystallite after excimer laser treatments. Photoluminescence signal from the samples was detected at room temperatures. I-V and C-V measurements were carried out to examine carries transfer through dielectrics film as well as recharging of electronics states.