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Amorphous-nanocrystalline silicon thin films: structural and optical properties

Juraić, Krunoslav (2012) Amorphous-nanocrystalline silicon thin films: structural and optical properties. Doctoral thesis, University of Zagreb, Faculty of Science.

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Abstract

Structural and optical properties of amorphous-nanocrystalline silicon thin films, 100-400 nm thick, prepared by plasma-enhanced chemical-vapor deposition using silane and hydrogen mixture were investigated. By using increased discharge power (100-180 W/m2) and highly diluted mixture of silane and hydrogen (94-95% hydrogen), nanocrystalline silicon thin films with crystallinity from completely amorphous up to 38% percent and wide log-normal size distribution of nanocrystals with average size 2-9 nm were obtained. Thin film growth appears to be governed both by deposition and plasma etching forming completely amorphous layer in the beginning stages of deposition. During the etching process ordered centers for nanocrystals formation are formed. In that way the samples are completely amorphous close to substrate, and the crystallinity and size of nanocrystals are larger close to the surface. Defects density (mainly dangling bonds that are mostly concentrated at grain boundaries) increased with the volume contribution of nanocrystals. Optical properties (absorption coefficient and optical band gap) are highly correlated to the size and crystallinity of nanocrystals. That is result of quantum size effect. By varying size and volume fraction of silicon nanocrystals incorporated in amorphous matrix it were obtained samples with increased optical bandgap from 1.7 eV (value characteristic for a-Si:H) up to 2.1 eV for the most crystalline sample. Those samples are incorporated in p-i-n structure of thin film solar cells. It results in the blue shift of up to 20 nm in the quantum efficiency maximum, compared to the value characteristic for completely amorphous silicon.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: amorphous-nanocrystalline silicon; nanocrystals; thin films; HRTEM; Raman; GIXRD; GISAXS; PDS; optical properties; structural properties; solar cell quantum efficiency
Subjects: NATURAL SCIENCES > Physics > Condensed Matter Physics
Divisions: Division of Materials Physics
Projects:
Project titleProject leaderProject codeProject type
Tanki filmovi legura silicija na prijelazu iz amorfne u uređenu strukturu[82826] Davor Gracin098-0982886-2894MZOS
Depositing User: Krunoslav Juraić
Date Deposited: 10 Jun 2013 18:27
Last Modified: 10 Jan 2014 16:09
URI: http://fulir.irb.hr/id/eprint/555

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