New approaches for the production of nano‐, micro‐, and polycrystalline silicon thin films

Abstract

We review current models and propose new approaches for the production of silicon thin films by low temperature plasma processes. Growth models have often been borrowed from those developed for hydrogenated amorphous silicon and are based on surface diffusion of SiH 3 . However, in situ growth studies have also pointed out the fast diffusion of hydrogen and its role in the crystallization of the film through subsurface reactions. Moreover, ions and silicon nanocrystals can also play a crucial role in microcrystalline silicon deposition. We show that ion bombardment is responsible for the formation of a disorderd subsurface layer while deposition on a cooled substrate allows us to trap the silicon nanocrystals and to prevent their growth, thus leading to nanocrystalline thin films. The deposition at 200 °C on substrates with a low density of surface defects allows for the surface mobility of the nanocrystals and their agglomeration to form large grains, thus resulting in polycrystalline silicon thin films.

Large grain μc-Si:H films deposited at low temperature: Growth process and electronic properties

“…For example, we have deposition rates V d = 0.9 Å /s and V d = 0.5 Å /s for SiH 4 + H 2 + Ar and SiH 4 + H 2 gas mixtures, respectively, at the same power density 63 mW/ cm 2 , pressure 2500 mTorr and deposition temperature of 200°C (Table 1). This increase of deposition rate in the case of H 2 + Ar dilution can be explained by the increase of silane dissociation degree that can lead to both: to increase of radicals flow towards substrate, and to increase nanoparticle formation in the bulk of plasma and their subsequent contribution in the lc-Si:H film growth [1,9]. Fig.…”

High Pressure Growth of Nanocrystalline Silicon Films

“…18 Using this region of high pressure where powder formation take place has been used as precursors to deposit silicon nano crystals using square wave modulated discharge. 19 In addition, the use of very high frequency or high pressure could be used to achieve high deposition rates. In the present investigation nc-Si:H films were deposited in a PECVD system at a relatively high rf power 60 W (∼500 mW/cm 2 ) in the pressure range of 2 Torr to 8 Torr.…”

Alternative designs for nanocrystalline silicon solar cells

“…Two families of growth models have been postulated for PECVD of thin film microcrystalline silicon [10].…”