Properties of high growth rate amorphous silicon deposited by MC-RF-PECVD

Abstract

Hydrogenated amorphous silicon (a-Si : H) thin films have been deposited on glass and crystalline silicon substrates by magnetically confined RF-PECVD (MC-RF-PECVD) at different RF power densities in order to verify the influence of this deposition parameter on the density of states (DOS) and growth rate ( R G). It was found that the highest growth rate, 7.8 Å/s, is obtained for a-Si : H films deposited with an RF power density of 14.3 mW/cm 3. For the DOS calculation, constant photocurrent method (CPM) data have been used. The lowest value of DOS is approximately 8×10 15/eV/cm 3 and was obtained for a-Si : H films produced with an RF power density in the range of 10–20 mW/cm 3. Infrared spectroscopy shows that when the RF power density increases, the concentration of SiH 3 groups decreases and the concentration of SiH groups increases. At 8 mW/cm 3, a maximum of the SiH 2 concentration is obtained. At this point, a maximum of the optical gap (1.9 eV) is observed and a minimum of the dark conductivity is verified. We conclude that the best films are achieved in an RF power density range (7.1–21.4 mW/cm 3) for which an increase of SiH and a decrease of both SiH 2 and SiH 3 are simultaneously obtained. Thereafter, for higher power densities, an inversion of DOS and growth rate behaviour are observed due to ion bombardment.