Transport in microcrystalline silicon thin films deposited at low temperature by hot-wire chemical vapor deposition

• Published in: Thin solid films Vol. 501; no. 1; pp. 133 - 136
• Main Authors: Bourée, Jean-Eric, Jadkar, Sandesh R., Kasouit, Samir, Vanderhaghen, Régis
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 20.04.2006; Elsevier Science
• Subjects: Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity of specific materials; Cross-disciplinary physics: materials science; rheology; Electronic transport; Electronic transport in condensed matter; Elemental semiconductors; Exact sciences and technology; Hot-wire chemical vapor deposition; Hydrogen; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Microcrystalline silicon; Physics; Hot-wire chemical vapor deposition; Microcrystalline silicon; Hydrogen; Electronic transport; Solar cells; Temperature dependence; Inorganic compounds; Electrical conductivity; Semiconductor materials; Phase transformations; Microwave radiation; Crystallization; Amorphous state; Experimental study; Hot wire; Thin films; CVD; Time dependence; Ultraviolet visible spectrum; Silicon; Carrier mobility; Microcrystal; Low temperature
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2005.07.140

This work is focused on the determination of the variation of local mobility of charge carriers with thickness (< 1 μm) for undoped microcrystalline silicon layers deposited by the hot-wire chemical vapor deposition technique. We observed that the temperature of the layers T s evolves with the deposition time, once the tungsten filament has been heated from room temperature to a fixed definite value. Thus, experiments have been realized by fixing the gas pressure (41 mTorr), the dilution of silane in hydrogen (50%), by setting the filament temperature (1600 °C) and letting the time run. An average substrate temperature T s,av has been defined, whose value depends on deposition time. As a result, the local mobility deduced from time-resolved microwave conductivity increases almost linearly with T s,av up to 193 °C, i.e. with thickness up to 400 nm corresponding approximately to the amorphous–microcrystalline transition and then increases sublinearly up to T s,av = 221 °C, i.e. a 900-nm-thick layer. These results, compatible with the highest AM1.5 efficiency (> 9%) reported so far for p–i–n μc-Si:H solar cells realized at T s = 185 °C [S. Klein, F. Finger, R. Carius, T. Dylla, B. Rech, M. Grimm, L. Houben, M. Stutzmann, Thin Solid Films 430 (2003) 202], suggest that in the range of T s,av from 190 °C to 220 °C, hydrogen plays a dominant role in the HWCVD growth of μc-Si:H films.