Pavel Šutta

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).

Influence of deposition temperature on amorphous structure of PECVD deposited a-Si:H thin films

The effect of deposition temperature on the structural and optical properties of amorphous hydrogenated silicon (a-Si:H) thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane diluted with hydrogen was under study. The series of thin films deposited at the deposition temperatures of 50–200°C were inspected by XRD, Raman spectroscopy and UV Vis spectrophotometry. All samples were found to be amorphous with no presence of the crystalline phase. Ordered silicon hydride regions were proved by XRD. Raman measurement analysis substantiated the results received from XRD showing that with increasing deposition temperature silicon-silicon bond-angle fluctuation decreases. The optical characterization based on transmittance spectra in the visible region presented that the refractive index exhibits upward trend with increasing deposition temperature, which can be caused by the densification of the amorphous network. We found out that the scale factor of the Tauc plot increases with the deposition temperature. This behaviour can be attributed to the increasing ordering of silicon hydride regions. The Tauc band gap energy, the iso-absorption value their difference were not particularly influenced by the deposition temperature. Improvements of the microstructure of the Si amorphous network have been deduced from the analysis.

Experimental Studies on Doped and Co-Doped ZnO Thin Films Prepared by RF Diode Sputtering

For decades zinc oxide (ZnO) has been in the spotlight due to its unique combination of semiconductor, piezoelectric, optical, and magnetic properties, which open perspectives for wide range of applications from optoelectronic and transparent electronic devices (Ohta & Hosono, 2004), surface and bulk acoustic wave devices and piezoelectric transducers (Wang et al., 2008), spintronics (Ji et al., 2008), to chemical and gas sensors (Carotta et al., 2009), and solar cells (Ganguly et al., 2004). Great industrial advantages of ZnO are its eco-friendly nature, wide abundant sources and low costs of metal Zn. ZnO is a group II-VI semiconductor with a direct band gap of 3.37 eV at room temperature, which can be modified (∼3 eV– 4 eV) via extrinsic doping with either cadmium (Cd) or magnesium (Mg). By its semiconductor properties ZnO is similar to gallium nitride (GaN) (Table 1).

Microstructure related optical characterization of technologically relevant hydrogenated silicon thin films

We report results obtained from measurements of UV Vis, FTIR and Raman spectra carried out on a series of silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from silane diluted with hydrogen. Spectral refractive indices, extinction coefficients, optical band gap energies, hydrogen content, the microstructure factor, and grain size were determined as a function of the hydrogen dilution. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (µc-Si:H). With increasing dilution Si:H films become mixed-phase materials with changing volume fractions of crystalline and amorphous phases and voids. The optical band gap energies were determined from transmittance spectra. The grain size was determined from Raman spectra and the contribution of small and large grains was detected.

Study of the effect of boron doping on the solid phase crystallisation of hydrogenated amorphous silicon films

Thin-film polycrystalline silicon on glass obtained by crystallization of hydrogenated amorphous silicon (a-Si:H) films is an interesting alternative for thin-film silicon solar cells. Although the solar-cell efficiencies are still limited, this technique offers excellent opportunity to study the influence of B-doping on the crystallisation process of a-Si:H. Our approach is to slowly crystallize B-doped a-Si:H films by solid phase crystallization in the temperature range 580–600°C. We use plasma-enhanced chemical vapour deposition (PECVD) and expanding thermal plasma chemical vapour deposition (ETPCVD) for the B-doped a-Si:H deposition. In this work we show the first in-situ study of the crystallization process of B-doped a-Si:H films produced by ETPCVD and make a comparison to the crystallization of intrinsic ETPCVD deposited a-Si:H as well as intrinsic and B-doped a-Si:H films deposited by PECVD. The crystallization process is investigated by in-situ x-ray diffraction, using a high temperature chamber for the annealing procedure. The study shows a strong decrease in the time required for full crystallisation for B-doped a-Si:H films compared to the intrinsic films. The time before the onset of crystallisation is reduced by the incorporation of B as is the grain growth velocity. The time to full crystallisation can be manipulated by the B2H6-to-SiH4 ratio used during the deposition and by the microstructure of the as-deposited a-Si:H films.

Transition from A-Si:H to Si 3 N 4 in thin films deposited by PECVD technology from silane diluted with nitrogen

Series of a-SiN:H thin films similar in thickness (380 ± 10 nm) and a-Si:H/a-Si3N4 multi-layered films (515 ± 20 nm) were prepared by PECVD technology from silane mixed with argon (90 % Ar/10 % SiH4) on Corning Eagle 2000 glass, SiO2 and silicon substrates. Deposition of thin films was carried out on a Samco PD 220 NA PECVD system. Multi-layered films were consequently annealed at high temperatures (700-1100°C) in order to obtain silicon nanocrystals embedded in a dielectric matrix suitable for photovoltaic and photonic applications. X-ray diffraction, Raman and FTIR spectroscopies, TEM, SEM, UV Vis spectrophotometry and spectroscopic ellipsometry were used for the evaluation of material properties of the films.

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.