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Research on silicon-carbon alloys and interfaces. Final subcontract report, 15 February 1991--31 July 1994

Description: This report describes work performed to develop improved p-type wide-band-gap hydrogenated amorphous silicon-carbon alloy (a-Si{sub 1-x}C{sub x:}H) thin films and interfaces for the ``top junction`` in hydrogenated amorphous silicon (a-Si:H)-based p-i-n solar cells. We used direct current reactive magnetron sputtering to deposit undoped a-Si{sub 1-x}C{sub x}H films with a Tauc band gap E{sub g} of 1.90 eV, a sub-band-gap absorption of 0.4 (at 1.2 eV), an Urbach energy of 55 MeV, an ambipolar diffusion length of 100 nm, an air-mass-one photoconductivity of 10{sup {minus}6}/{Omega}-cm, and a dark conductivity of 8{times} 1O{sup {minus}11}/{Omega}-cm. p{sup +}a-Si{sub 1-x}C{sub x}:H films with a Tauc band gap of 1.85 eV have a dark conductivity of 8 {times} 10{sup {minus}6}/{Omega}-cm and thermal activation energy of 0.28 eV. We used in-situ spectroscopic ellipsometry and post-growth X-ray photoelectron spectroscopy to determine the relative roles of H and Si in the chemical reduction of SnO{sub 2} in the early stages of film growth. We used in-situ spectroscopic ellipsometry to show that a-Si:H can be transformed into {mu}c-Si:H in a subsurface region under appropriate growth conditions. We also determined substrate cleaning and ion bombardment conditions which improve the adhesion of a-Si{sub 1-x}C{sub x}:H films.
Date: July 1, 1995
Creator: Abelson, J. R.
Partner: UNT Libraries Government Documents Department

Experimental methods and data analysis for fluctuation microscopy

Description: The authors have developed a new electron microscopy technique called fluctuation microscopy which is sensitive to medium-range order in disordered materials. The technique relies on quantitative statistical analysis of low-resolution dark-field electron micrographs. Extracting useful information from such micrographs involves correcting for the effects of the imaging system, incoherent image contrast caused by large scale structure in the sample, and the effects of the foil thickness.
Date: February 16, 2000
Creator: Voyles, P. M.; Treacy, M. M. J.; Gibson, J. M.; Jin, H.-C. & Abelson, J. R.
Partner: UNT Libraries Government Documents Department

Medium-range order in hydrogenated amorphous silicon measured by fluctuation microscopy

Description: The authors have characterized with fluctuation electron microscopy the medium-range order of hydrogenated amorphous silicon thin films deposited by a variety of methods. Films were deposited by reactive magnetron sputtering, hot-wire chemical vapor deposition, and plasma enhanced chemical vapor deposition with and without H{sub 2} dilution of the SiH{sub 4} precursor gas. All of the films show the signature of the paracrystalline structure typical of amorphous Si. There are small variations in the degree of medium-range order with deposition methods and H{sub 2} content. The PECVD film grown with high H{sub 2} dilution contains Si crystals {approximately} 5 nm in diameter at a density of {approximately} 10{sup 9} cm{sup 2}. The amorphous matrix surrounding these crystals shows no difference in medium-range order from the standard PECVD film.
Date: April 17, 2000
Creator: Voyles, P. M.; Treacy, M. M. J.; Jin, H.-C.; Abelson, J. R.; Gibson, J. M.; Guha, S. et al.
Partner: UNT Libraries Government Documents Department