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The effects of postdeposition air exposure of microcrystalline silicon films, prepared at varied deposition rates, are investigated. The changes in the oxygen content, evaluated from Fourier transform infrared spectroscopy measurements, were studied over a period of time after deposition (up to 180 days) depending on deposition rate and Raman intensity ratio. Two types of behavior were identified: in the case of highly crystalline samples, an oxygen uptake increases with increasing Raman intensity ratio; while less crystalline samples were found to be more stable against oxygen incorporation. These observations are related to the film microstructure and porosity and are linked to the variations in Raman intensity ratio and growth rate of microcrystalline silicon films. PACS Nos.: 68.55.-a, 68.55.J-, 78.30.Ly, 81.15.Gh. Nous etudions les effets d'une exposition a l'air apres deposition de films de silicium microcristallin, prepares a divers taux de deposition. Nous utilisons des mesures FTIR pour etudier le changement dans le contenu en oxygene pendant une periode de temps apres la deposition (jusqu'a 180 jours) en fonction du taux de deposition et du rapport d'intensite Raman. Nous identifions deux types de comportement : pour des echantillons hautement cristallins, le gain en oxygene croit avec le rapport d'intensite Raman, alors que les echantillons moins cristallins sont beaucoup plus stables face a l'incorporation d'oxygene. Ces observations sont reliees a la microstructure et a la porosite du film et liees aux variations dans le rapport d'intensite Raman et au taux de croissance des films de silicium microcristallin. [Traduit par la Redaction], Introduction Microciystalline silicon (µc-Si:H) is used as an absorber material in thin film silicon solar cells [1, 2]. It is a phase mixture consisting of crystalline grains and disordered regions [...]

The influence of implanted hydrogen (up to a concentration level of 3 at. %) on the microstructure of silicon (Si) materials is investigated by Fourier transform infrared spectroscopy as well as by effusion of hydrogen and of (low dose) implanted helium. Three materials of low original hydrogen concentration, crystalline Si, electron beam evaporated amorphous Si, and plasma-deposited hydrogenated amorphous Si (using high deposition temperature) were investigated. Significant differences between crystalline and amorphous materials were observed. In crystalline Si, implanted hydrogen is found to generate multivacancies that trap diffusing helium while this is not the case in amorphous Si. Accordingly, cavities where hydrogen is located in amorphous Si must be smaller than divacancies. Those cavities in amorphous Si, present from the growth process, that trap helium tend to disappear when the implanted hydrogen concentration increases. Annealing of the materials up to temperatures of 575°C was also studied. No significant change in the density of voids (trapping helium) occur but in case of crystalline Si the bonding sites of hydrogen as well as the diffusion paths of helium change. PACS Nos.: 61.43.Dq, 61.72.uf, 81.40.-z. Nous utilisons la spectroscopie infrarouge a transformee de Fourier, l'effusion d'hydrogene (H) et l'implantation d'helium (He; a basse dose), pour etudier l'influence de l'implantation d'H (jusqu'a des concentration de 3 at. %) sur les microstructures de materiaux de silicium. Nous etudions trois de ces materiaux de faible concentration initiale en H, le silicium cristallin, le silicium amorphe evapore par faisceau electronique et le silicium amorphe hydrogene par depot (a haute temperature). Des differences importantes apparaissent entre materiaux cristallins et amorphes. Dans le silicium cristallin, l'H implante cree des multi-lacunes qui piegent l'He en diffusion, ce qui n'est pas le cas pour le silicium amorphe. Consequemment, les cavites ou se trouve l'H dans le Si amorphe doivent etre plus petites que des bi- lacunes. Ces cavites qui piegent l'He dans le silicium amorphe, presentes lors de l'elaboration du materiau, tendent a disparaitre lorsque la concentration de l'H implante augmente. Nous etudions aussi l'effet d'un recuit des materiaux jusqu'il 575°C. Aucun changement significatif de la densite de pieges n'apparait, mais dans le cas cristallin, les sites de capture de H et les trajectoires de diffusion de He changent. [Traduit par la Redaction], 1. Introduction Void-related microstructure is an important issue in hydrogenated amorphous silicon (a-Si:H) technology as it may limit the performance and the lifetime of a-Si:H based devices. The relation between [...]

The influence of oxygen and nitrogen impurities on the performance of thin-film solar cells based on microcrystalline silicon (μc-Si:H) has been systematically investigated. Single μc-Si:H layers and complete μc-Si:H solar cells have been prepared with intentional contamination by admitting oxygen and/or nitrogen during the deposition process. The conversion efficiency of ∼1.2 μm thick μc-Si:H solar cells is deteriorated if the oxygen content in absorber layers exceeds the range from 1.2×1019 to 2×1019 cm-3; in the case of nitrogen contamination the critical impurity level is lower ([N]critical=6×1018–8×1018 cm-3). It was revealed that both oxygen and nitrogen impurities thereby modify structural and electrical properties of μc-Si:H films. It was observed that the both contaminant types act as donors. Efficiency losses due to oxygen or nitrogen impurities are attributed to fill factor decreases and to a reduced external quantum efficiency at wavelengths of >500 nm. In the case of an air leak during the μc-Si:H deposition process, the cell performance drops at an air leak fraction from 140 to 200 ppm compared to the total gas flow during i-layer deposition. It is demonstrated that oxygen and nitrogen impurities close to the p/i-interface have a stronger effect on the cell performance compared to impurities close to the n/i-interface. Moreover, thick μc-Si:H solar cells are found to be more impurity-sensitive than thinner cells. [ABSTRACT FROM AUTHOR]

The influence of atmospheric contaminants oxygen and nitrogen on the performance of thin-film hydrogenated amorphous silicon (a-Si:H) solar cells grown by plasma-enhanced chemical vapor deposition at 13.56 MHz was systematically investigated. The question is addressed as to what degree of high base pressures (up to 10-4 Torr) are compatible with the preparation of good quality amorphous silicon based solar cells. The data show that for the intrinsic a-Si:H absorber layer exists critical oxygen and nitrogen contamination levels (about 2×1019 atoms/cm3 and 4×1018 atoms/cm3, respectively). These levels define the minimum impurity concentration that causes a deterioration in solar cell performance. This critical concentration is found to depend little on the applied deposition regime. By enhancing, for example, the flow of process gases, a higher base pressure (and leak rate) can be tolerated before reaching the critical contamination level. The electrical properties of the corresponding films show that increasing oxygen and nitrogen contamination results in an increase in dark conductivity and photoconductivity, while activation energy and photosensitivity are decreased. These effects are attributed to nitrogen and oxygen induced donor states, which cause a shift of the Fermi level toward the conduction band and presumably deteriorate the built-in electric field in the solar cells. Higher doping efficiencies are observed for nitrogen compared to oxygen. Alloying effects (formation of SiOx) are observed for oxygen contaminations above 1020 atoms/cm3, leading to an increase in the band gap. [ABSTRACT FROM AUTHOR]

This study addresses the electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide (ZnO:Al) films. The main focus was on the improvement in carrier mobility μ to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity. The influence of Al concentration in the target, film thickness, sputter power, deposition pressure, and substrate temperature on material properties was investigated. The structural, compositional, electrical and optical properties were studied using x-ray diffraction, secondary ion mass spectrometry (SIMS), room temperature Hall effect measurements and spectral photometry, respectively. All ZnO:Al films were polycrystalline and preferentially oriented along [002]. The grain size along the direction of growth increased with higher Al doping and with increasing film thickness. The SIMS measurements revealed that the Al concentration in the film was nearly the same as in the target. Carrier concentration N and mobility μ are determined by the target Al concentration. In addition μ is influenced by the film thickness and the sputter pressure. For each Al concentration, the highest μ was generally observed at low deposition pressures. By using a target with low Al[sub 2]O[sub 3] concentration of 0.5 wt %, μ could be improved up to 44.2 cm[sup 2]/V s while maintaining the electrical resistivity ρ as low as 3.8×10[sup -4] Ω cm. For these films the transparency in the near-infrared wavelength range strongly improved which makes them particularly interesting for the application in optoelectronic devices like thin-film solar cells. The μ-N dependence for films deposited under diverse conditions was studied to identify a practical limit for μ. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide (ZnO:Al) films are addressed. The improvement in carrier mobility mu to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity is focused.

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Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)