New nanostructured silicon films grown by PECVD technique under controlledpowder formation conditions

In this paper the influence of the DC grid bias on the plasma impedance and the I-V behaviour of silane plasmas used to grow undoped amorphous silicon films by plasma enhanced chemical vapour deposition technique using a trio de configuration at or close to the powder regime is studied. The aim is to determine the correlation between the r.f. power and the DC grid voltage w ith the plasma parameters, under isothermal gas conditions. The results sho uld lead to the production of nanostructured films, with the required optoe lectronic characteristics for photovoltaic applications. The results achiev ed show the existence of a boundary region close to the gamma -regime (powd er formed) where nanoparticles can be formed by moderated ion bombardment o f the growing surface. This is characterised by the plasma resistance of th e same order of magnitude of the plasma reactance. Under this condition, it is possible to grow amorphous silicon films that can incorporate nanoparti cles, exhibiting photosensitivities of about 10(7) (two orders of magnitude larger than the one exhibited by films grown under conventional conditions ) with densities of states determined by the constant photocurrent method b elow 3 x 10(15) cm(-3). Apart from that, the growth of the films is less af fected by light soaking than the conventional Films grown by standard techn iques. (C) 2001 Elsevier Science Ltd, All rights reserved.