Papers by Author: Pavel Škarvada

Abstract: Experiments were carried out for n-channel devices, processed in a 300 nm CMOS technology. The investigated devices have a gate oxide thickness of 6 nm and the effective interface area is AG = 1.5 m2. The RTS measurements were performed for constant gate voltage, where the drain current was changed by varying the drain voltage. The capture time constant increases with increasing drain current. The model explaining the experimentally observed capture time constant dependence on the lateral electric field and the trap position is given. From the dependence of the capture time constant c on the drain current we can calculate x-coordinate of the trap position. Electron concentration in the channel decreases linearly from the source to the drain contact. Diffusion current component is independent on the x-coordinate and it is equal to the drift current component for the low electric field. Lateral component of the electric field intensity is inhomogeneous in the channel and it has a minimum value near the source contact and increases with the distance from the source to the drain. It reaches maximum value near the drain electrode.

Abstract: This article discusses the issue of noise measurements application for the quality assessment of the solar cells themselves and production technology alike. The main focus of our research is the random n-level (in most case just two-level) impulse noise, usually referred to as microplasma noise. This noise was found to be in a direct consequence of local breakdowns in micro-sized regions and brings about a reduction of lifetime or a destruction of the pn junction. Non-destructive measurement methodology as presented here is suitable for testing of a large number of various semiconductor devices not only for solar cells. In this paper experimental measurement of noise signals in the frequency and time domain is presented. Furthermore the microplasma noise behaviour and defect geometry is discussed.

Abstract: Solar cells, or photovoltaic cells, are used to convert sunlight into electrical power. The defects or imperfections in silicon solar cells lower the light-current conversion and consequently also an efficiency of the device. These defects in the semiconductor structure are normally detected by electric measurements. The thermal dependency of breakdown voltage is positive and the defects can be revealed by surface inhomogenity. To ensure a higher quality of the solar cells, advanced local quality assessment is provided and experimental results of solar cell defect measurement in microscale region are presented. Using Near-field optical beam induced current and voltage method, both current and voltage in defect area were detected and individual defects were localized with higher spatial resolution. This measurement also verifies that in reverse biased electroluminescence spots the quantum efficiency is lower and so these spots affect overall quality of the cell.

Abstract: The local spatial distribution of photoluminescence due to the creation of hot luminescence centers was measured in the optical near-field by Scanning near-field optical microscope at emission peaks of materials (λ =595nm), which is due to the luminescence of Mn2+ in ZnS. The excitation bandgap of ZnS forms exitons, and these excitons get the center of Mn2+ through nonradiation dominates, by means of transition of 4T1 – 6A1 luminescence. This spectrum is evidence that Mn2+ has been incorporated into the ZnS nanoparticles. In comparison with the bulk ZnS:Mn phosphors these nanoparticles have clearly higher luminescent efficiency with its luminescent decay time at least 4 orders of magnitude slower. It means that the oscillator intensity of luminescent centers in ZnS:Mn nanocrystal enhances at least 4 orders of magnitude than that in corresponding bulk ZnS:Mn.