Hydrogen plasma treatment of very thin p-type nanocrystalline Si films grown by RF-PECVD in the presence of B(CH₃)₃

Abstract

We have characterized the structure and electrical properties of p-type nanocrystalline silicon films prepared by radio-frequency plasma-enhanced chemical vapor deposition and explored optimization methods of such layers for potential applications in thin-film solar cells. Particular attention was paid to the characterization of very thin (∼20 nm) films. The cross-sectional morphology of the layers was studied by fitting the ellipsometry spectra using a multilayer model. The results suggest that the crystallization process in a high-pressure growth regime is mostly realized through a subsurface mechanism in the absence of the incubation layer at the substrate-film interface. Hydrogen plasma treatment of a 22-nm-thick film improved its electrical properties (conductivity increased more than ten times) owing to hydrogen insertion and Si structure rearrangements throughout the entire thickness of the film.

Investigation of p-type nanocrystalline silicon emitters for silicon heterojunction solar cells

“…It can be seen that d and X c increase sharply in the narrow thickness range from 10 nm to 20 nm, and then rises slowly when further increasing film thickness to 130 nm. Similar thickness dependence of the conductivity was also reported by other groups [3,36]. This can be interpreted in terms of percolation theory by formation of a percolation cluster composed of Si nanocrystallites as the film thickness becomes comparable to the grain size [37].…”

Nanocrystalline thin film silicon solar cells: A deeper look into p/i interface formation

“…According to previous studies [30], the p-layer can be damaged during the initial stages of the intrinsic layer deposition due to light and heavy ion bombardment. Consequently, the higher the growth rate of the intrinsic nc-Si:H material the more severely can the previously deposited p-layer be affected.…”

“…[30]. Then, in order to simulate the initial stages of growth of the intrinsic nc-Si:H on top of the ptype layer, HPT was performed at different conditions (f = 75 MHz; 1.0 < p w < 2.13…”

“…This model consisted in dividing the film into three layers: bulk, subsurface and surface layers [30]. In these layers, a variable percentage mixture (i.e.…”

“…Consequently, the higher the growth rate of the intrinsic nc-Si:H material the more severely can the previously deposited p-layer be affected. In order to verify this, the deposited p-layers, without any amorphous incubation layer [30], were exposed for 30 seconds to HPT (light ion bombardment) and…”