Hostname: page-component-848d4c4894-r5zm4 Total loading time: 0 Render date: 2024-07-07T04:57:14.143Z Has data issue: false hasContentIssue false

Influence of Filament and Substrate Temperatures on Structural and Optoelectronic Properties of Narrow Gap a-SiGe:H Alloys Deposited by Hot-Wire CVD

Published online by Cambridge University Press:  01 February 2011

Yueqin Xu
Affiliation:
National Renewable Energy Laboratory1617 Cole Blvd., Golden CO 80401, USA
Brent P. Nelson
Affiliation:
National Renewable Energy Laboratory1617 Cole Blvd., Golden CO 80401, USA
D.L. Williamson
Affiliation:
Colorado School of Mines, Department of Physics Golden, CO 80401, U.S.A.
Lynn M. Gedvilas
Affiliation:
National Renewable Energy Laboratory1617 Cole Blvd., Golden CO 80401, USA
Robert C. Reedy
Affiliation:
National Renewable Energy Laboratory1617 Cole Blvd., Golden CO 80401, USA
Get access

Abstract

We have found that narrow-bandgap—1.25 < Tauc Gap < 1.50 eV—amorphous silicon germanium (a-SiGe:H) alloys grown by hot-wire chemical vapor deposition (hot-wire CVD) can be improved by lowering both substrate and filament temperatures. We systematically study films deposited using a one-tungsten filament, decreasing filament temperature (Tf) from our standard temperature of 2150° down to 1750°C, and fixing all other deposition parameters. By decreasing Tf at the fixed substrate temperature (Ts) of 180°C, the Ge-H bonding increases, whereas the Si-H2 bonding is eliminated. Films with higher Ge-H bonding and less Si-H2 have improved photoconductivity. For the series of films deposited using the same germane gas fraction at 35%, the energy where the optical absorption is 1x104 (E04) drops from 1.54 to 1.41 eV with decreasing Tf. This is mainly due to the combination of an increasing Ge solid fraction (x) in the film, and an improved homogeneity and compactness due to significant reduction of microvoids, which was confirmed by small angle X-ray scattering (SAXS). We also studied a series of films grown by decreasing the Ts from our previous standard temperature of 350°C down to 125°C, fixing all other deposition parameters including Tf at 1800°C. By decreasing Ts, both the total hydrogen content (CH) and the Ge-H bonding increased, but the Si-H2 bonding is not measurable in the Ts range of 180°-300°C. The E04 increases from 1.40 to 1.51 eV as Ts decreased from 350° to 125°C, mainly due to the increased total hydrogen content (CH). At the same time, the photo-to-dark conductivity ratio increases almost three orders of magnitude over this range of Ts.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1. Nelson, B.P., Xu, Y., Williamson, D.L., Roedern, B. von, Mason, A., Heck, S., Mahan, A.H., Schmitt, S.E., Gallagher, A.C., Webb, J., and Reedy, R., Mat. Res. Soc. Symp. Proc. 507 (1998) 447.Google Scholar
2. Wang, Q., Iwaniczco, E., Yang, J., Lord, K., and Guha, S., Mat. Res. Soc. Symp. Proc. 664 (2001) A7.5.Google Scholar
3. Xu, Y., Nelson, B.P., Gedvilas, L.M., and Reedy, R.C., Sept. 2002, 2nd Intern. Conf. on CatCVD (Hot-Wire CVD) Process, Denver, Colorado, Thin Solid Films (in press).Google Scholar
4. Nelson, B. P., Xu, Y., Williamson, D. L., Han, D., Braunstein, R., Boshta, M., and Alavi, B., Sept. 2002, 2nd Intern. Conf. on Cat-CVD Process, Denver, Colorado, Thin Solid Films (in press).Google Scholar
5. Hishkawa, Yoshihilo, Nakamura, NoBoru, Tsuda, Shinya, Nakano, Shoichi, Kishi, Yasuo, and Kuwano, Yukinori, Jpn. J. Appl. Phys. 30 (1991) 1008.Google Scholar
6. Fang, C.J., Gruntz, K.J., Ley, L., Cardona, M., Demond, F.J., Muller, G., Kalbitzer, S., J. NonCryst. Solids 35 & 36 (1980) 255.Google Scholar
7. Cardona, M., Phys. Stat. Sol. (b) 118 (1983) 463.Google Scholar
8. Langford, A.A., Fleet, M.L., Nelson, B.P., Lanford, W.A., Maley, N., Phys. Rev. B45 (1992) 13367.Google Scholar
9. Bhan, Mohan Krishan, Malhotra, L.K., and Kashyap, Subhash C., J. Appl. Phys. 66 (1989) 2528.Google Scholar
10. Lucovsky, G., J. Non-Cryst. Solids 76 (1985) 173.Google Scholar
11. Williamson, D.L., Mat. Res. Soc. Symp. Proc. 377 (1995) 251.Google Scholar
12. Reedy, R.C., Mason, A.R., Nelson, B.P., Xu, Y., American Institute of Physics, NICH Report No. 27431 (1999) pp. 537541.Google Scholar