acta physica slovaca

Abstract: Silicon nitride films are widely used in VLSI fabrication due to their high breakdown strength and resistivity. A major topic of interest in this material is the origin of Poole-Frenkel emission which is frequently observed, and typically attributed to centres associated with Si-N bonds. However, in films with aluminium electrodes, prepared by RF magnetron sputtering and using nitrogen as the sputtering gas to ensure stoichiometry, Poole-Frenkel conductivity was absent. In the present work similar films were prepared, but with gold electrodes. Capacitance measurements suggested that the Au electrodes provide ohmic contacts to the silicon nitride films, and that the relative permittivity $\varepsilon _{r} \sim $ 6.8, slightly higher than is the case with Al electrodes. At low DC voltages Ohm's law was obeyed, followed by Poole-Frenkel conductivity with coefficient $\beta \sim $ 1.95 $\times $ 10$^{ - 5}$ eV m$^{1 / 2}$ V$^{ - 1 / 2}$, in contrast to films with Al electrodes. For voltages exceeding 2 V electroforming and differential negative resistance behaviour were observed, as in many thin film insulators having certain noble metal electrodes. The AC conductivity was frequency dependent with index $s$ in the range 0.83 - 1.31. Frequency and temperature variations were typical of a carrier hopping process with an estimated density of localised states $N \sim $ 10$^{24}$ m$^{ - 3}$. Carrier activation energies were in the range 0.006 - 0.1 eV, further indicating the presence of hopping conductivity. The dependences of capacitance and loss tangent were consistent with an existing model of dielectric behaviour in sandwich samples having ohmic contacts. It was concluded that the Poole-Frenkel conductivity was associated with centres originating from the Au electrodes, and not from the Si-N bonds.

Abstract: In situ electrochemical attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy has been used to study the etching process on a Si (100), (110) and (111) surface in dilute HF solution. On the other hand I-V characteristic of the p-Si-HF system was used for the interface reactions and kinetics study. Infrared results show that monohydride (SiH) and hydroxyl (Si-OH) species surface concentration depend on the applied potential to the electrode. I-V characteristics show a relative variation in magnitude of the first peak as the substrate orientation is changed. A mechanism of silicon dissolution is proposed.

Abstract: In this paper a new dispersion model of the optical constants of amorphous solids enabled us to perform an efficient parameterization of the optical constants of diamond like carbon (DLC) thin films. The model was based on the mathematical modeling of the density of electronic states (DOS) corresponding to both the valence and conduction bands. Moreover, the existence of the $\sigma$ and $\pi$ electronic states was taken into account, \ie two valence and two conduction bands were supposed. The imaginary and real parts of the dielectric function were then calculated by the numerical convolution of the DOS and using a corresponding Kramers--Kronig relation, respectively. According to the model the DOS as well as the optical constants were calculated from ellipsometric measurements in the range 240-830~nm and estimated even outside this range. From the parameters of the model we evaluated also the ratio of $\pi$-to-$\sigma$ electrons and consequently the sp$^3$-to-sp$^2$ ratio using a known hydrogen atomic fraction. The optical constants of DLC films with addition of SiO$_\mathrm{x}$ were determined and compared with DLC too.

Abstract: We studied the growth of microcrystalline diamond films on pre-treated Si and WC-Co substrates by microwave plasma chemical vapour deposition (MPCVD). The pre-treatment was varied and its effect on diamond film was studied.

Abstract: Experimental investigation of VA characteristics of unipolar corona discharge and current pulsation in unipolar corona discharge is presented in this contribution. Experiments for negative corona discharge for the applied voltage from onset votlage to 10~kV and for single-needle and multi-needle configuration were performed. In the air at atmospheric pressure current pulses have a very fast rise time of order 1.4--1.5~ns and short duration. Amplitude and interval of these pulses are not generally constant and depend on many variables. Repetition rate and amplitude of pulses fluctuate in time. Dependence of behavior of corona pulses on gap lengths, applied voltage and number of electrodes (in multiple point mode) was investigated.

Abstract: When a small amount of impurity (O$_2$, H$_2$, Ar, Ne, \dots) is added to a molecular gas, one observes increased dissociation in the discharge afterglow. In this work we compare two cases: when admixtures are added upstream or downstream of the discharge. Concentration of atoms was measured by means of electron paramgnetic resonance (EPR).

Abstract: The main part of this work is focused on the identification of the spectra measured during the plasma deposition using the vinyltriethoxysilane. The deposition process was carried out in a continual regime as well as in a pulsed regime with the varied relative pulse duration. The vinyltriethoxysilane was mixed in various ratios with oxygen. The oxygen to vinyltriethoxysilane flow rate ratios varied in the range from 0 to 73. We observed a decrease of the relative intensity of $\rm C_2$ spectral bands with increasing pulse duration and a decrease of this spectral band with increasing flow rate of oxygen.

Abstract: Till this time known methods of the excitation of the discharge between electrodes are using either secondary or thermo emission of electrons by the cathode. Usually we speak about the self-maintained discharge. Lifetime of the cathode, that is shortened by the emission, limits in principle, the lifetime of the whole discharge tube. The discharge can, according to the present state of the art, be induced also by the inductive way. Arrangement for excitation of such discharge is rather expensive. The construction of the inductive excited discharge tube is considerably influenced by the necessity of the limitation of the losses in excitation magnetic circuits. Especially length of the discharge and pressure of the working gas are limited by the economic standpoints. Function of the discharge is always connected with unwanted electromegnetic radiation, whose restraint is expensive and represents limiting factor for arrangement of the discharge tube.

Abstract: A narrow-linewidth wavelength tunable semiconductor fiber ring laser is demonstrated. Tunability is achieved through computer-based electro-optical polarization control. Fine rapid tunability of 30 nm in the 1550 nm region is shown. The tuning properties and working principles are also discussed.