Lucie Prušáková

Preparation of transparent conductive AZO thin films for solar cells

A study of the effect of technology parameters (sputtering power, substrate temperature and post-deposition annealing) on structural, electrical and optical properties of aluminium-doped zinc oxide (AZO) thin films was carried out. The optimal technology parameters of preparation were found to get necessary properties of AZO thin films for application in solar cells - the high figure of merit (F ges 4 %/Omega), low electrical sheet resistance (Rs les 10 Omega/square) and high optical transmittance (T ges 82%, including the glass substrate).

Structural Analysis of Silicon Nanostructures Obtained from Thermal Annealing of a-Si:H/SiO2 Superlattices

This paper reports the synthesis and characterization of silicon quantum dots (QDs) obtained by thermal annealing of hydrogenated amorphous silicon (a-Si:H)/silicon oxide (SiO2) supperlattices deposited by plasma-enhanced chemical vapour deposition (PE-CVD). The as-deposited supperlattices have been annealed in high-temperature vacuum chamber, at temperatures up to 1100 °C, where in-situ phase transformation was monitored by x-ray diffractometry, XRD. It is shown that onset of crystallization and phase separation occur at different annealing temperature depending on the a-Si:H sub-layer thickness. Complete crystallization of the films and precipitation of the QDs occur at 1000 °C.

Dispersive and BEMA investigation on optical properties of photovoltaic thin films

The paper reports results obtained from optical spectrophotometry complemented with data from FTIR, Raman scattering and XRD measurements to characterize hydrogenated silicon (Si:H) thin films deposited by PECVD deposition from silane – argon plasma diluted with hydrogen. The dispersive optical properties and microstructure have been determined as a function of the hydrogen dilution which has been found to result in an inhomogeneous growth during which the material evolves from amorphous Si:H to microcrystalline Si:H. Porosity originating from microvoids has been discovered and calculated using effective medium approximations. Bruggeman effective medium approximation (BEMA) has been used to calculate volume fractions of microvoids and amorphous and crystalline phase.

Influence of deposition conditions of ZnO thin films on their photonic properties

The effects of deposition conditions (especially lateral position against target during deposition and deposition temperature) on optical properties and structure are presented. The X-ray diffraction (XRD) analysis showed that all the films were polycrystalline with hexagonal structure and preferred orientation in [001] direction perpendicular to the substrate surface. Micro-structure properties as crystallite size and micro-strains were not too influenced by deposition conditions and values of crystallites were evaluated in tens of nanometers and micro-strains were about 10-2. Film thicknesses obtained from transmittance spectra decreased more than two times with increased lateral position of the samples against the target. Dispersion of the spectral refractive index was observed depending on the sample position in deposition chamber. Smaller dispersion was observed in series containing more redundant oxygen in their structure.

Influence of different dopants on physical properties of ZnO for photovoltaic applications

The paper deals with influence of aluminum, gallium and scandium as dopants on structure, electrical and optical properties of zinc oxide (ZnO) thin films as a material suitable for photovoltaic applications. Mainly optical (integral transmittance, optical band-gap energy and refractive index), structural (biaxial lattice stress, micro-strains and crystallite size) and electrical (resistivity) properties were studied. Comparison between the physical properties of the materials with different dopant elements was performed.

Study of re-crystallization processes in amorphous silicon films

Technology of amorphous hydrogenated silicon (a-Si:H) thin films is a subject of interest of many researchers. This paper deals with the re-crystallization processes in a-Si:H thin films prepared by plasma enhanced chemical vapour deposition (PECVD) using a SAMCO PD-220N unit. Evaluation of crystallization process was monitored in a high temperature chamber AP1200 by using “in-situ” X-ray diffraction (XRD). The experiments have given information about phase transformation from the amorphous to polycrystalline phase and were carried out at temperatures in the range of 580 °C to 620 °C. The average crystalline size of crystallized films was found from 40 to 50 nm. Structural properties of the initial amorphous and re-crystallized films were also investigated by Raman spectroscopy. Optical properties (refractive indices, extinction coefficients) of a-Si:H and poly-Si films were analyzed by UV Vis spectrophotometry. The absorption properties of the films were carried out from the UV Vis experimental data.

Study of ZnO films grown with different dopants - physical properties and their comparison

Transparent and electrically conductive (TCO) thin films of ZnO:Al, ZnO:Ga and ZnO:Sc, used in solar cells as well as optoelectronic devices, have been successfully deposited by rf magnetron sputter deposition using ZnO(98%) / X2O3(2%) ceramic target, X ∈{Al, Ga, Sc}, in the inert atmosphere of argon. In this contribution we focused on the changes in physical properties and their comparison in dependence on doping element. The XRD analyses, four probe measurements and UV-VIS spectroscopy were applied to investigate the structure (texture, lattice stress, grain size), electrical (resistivity) and optical (transmittance, optical band gap) properties of TCOs on the glass substrates.

Quantum Size Effects in a Si:H Films Prepared by PECVD with Different Hydrogen-Diluted Silane

Quantum size effect (QSE) comprises a novel phenomenon where structural, mechanical, thermal, electronic and optical properties of solids are affected by the reduction in particle size. Size-dependent properties in semiconductors and dielectrics come into play especially by making one (thin films) or more (quantum wires and dots) dimensions of a sample very small, particularly going from micro to nano-dimensions. One or more dimensional QSE is accompanied with an increase of the light absorption and the blue-shift of the optical band-gap due to a creation or reduction of the crystallite sizes having different dielectric constants (relative permitivity). Understanding the nature of the size-induced properties is of fundamental importance for advanced technological applications. The size-dependent band-gap makes a material attractive for optical absorption-based applications. In this work, a-Si:H films different in thickness were prepared by PECVD technology using different hydrogen-diluted silane. One-dimensional QSE (when film thickness decreased) and three-dimensional QSE (when due to a high hydrogen-silane dilution the nano-crystalline structure of the films appeared) were observed.