Eur. Phys. J. AP
Volume 10, Number 3, June 2000
|Page(s)||185 - 191|
|Published online||15 June 2000|
Effect of the hydrogen dilution on the local microstructure in hydrogenated amorphous silicon films deposited by radiofrequency magnetron sputtering
Faculté des Sciences de Bizerte, Zarzouna, Bizerte, Tunisia
2 Laboratoire de Physique de la Matière Condensée, Faculté des Sciences d'Amiens, 33 rue Saint-Leu, 80039 Amiens Cedex, France
3 Faculté des Sciences de Tunis, Campus Universitaire Elmenzeh, 1060 Tunis, Tunisia
4 Laboratoire de Physique des Solides de Bellevue, CNRS, 1 place Aristide Briand, 92195 Meudon Cedex, France
Corresponding author: Kacem.Zellama@sc.u-picardie.fr
Revised: 15 October 1999
Accepted: 30 March 2000
Published online: 15 June 2000
The nature of the hydrogen bonding and content and their influence on the film microstructure have been investigated in detail, as a function of the H2 dilution and the residual pressure, in hydrogenated amorphous silicon (a-Si:H) films prepared by radiofrequency (rf) magnetron sputtering at a common substrate temperature (~ 250 °C) and pressure (5 × 10−4 torr) and high rates (11−15 Å/s). H2 percentages in the gas phase mixture (Ar + % H2) of 5, 10, 15 and 20% have been introduced during growth. For the 20% of H2, two different pressures of 5 × 10−4 and 50 × 10−4 torr were used. A combination of infrared absorption, optical transmission and elastic recoil detection analysis experiments have been carried out to fully characterize the samples in their as-deposited state. The results clearly indicate that for H2 percentage equal to or lower than 15% , the total bonded H content in the films increases as the H2 percentage increases, and then reaches a saturation value or even decreases for higher H2 percentage. Moreover, the microstructure is also found to be deeply affected by the H2 dilution and pressure. In particular, for high H2 percentage (20%) and high pressure (50 × 10−4 torr), unbounded H as well as polyhydride (Si-H2)n chains, possibly located in structural inhomogeneities such as voids, are also present in the films in addition to the isolated monohydride Si-H and polyhydride Si-H2 complexes. As a result, a reduction of the compactness of the film structure associated with a decrease of the refractive index n is observed. The optical gap is found to be rather controlled by the total bonded hydrogen content. The lowest proportion of isolated polyhydride Si-H2 complexes and the highest density are observed for films deposited with 10% of H2 in the gas phase and a pressure of 5 × 10−4 torr.
PACS: 61.43.Dq – Amorphous semiconductors, metals and alloys / 78.30.Ly – Disordered solids / 78.30.-j – Infrared and Raman spectra
© EDP Sciences, 2000
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