Hybrid-phase growth in microcrystalline silicon thin films deposited by plasma enhanced chemical vapor deposition at low temperatures

Abstract

Crystallographic studies on microcrystalline silicon (μc-Si) films, which were prepared by very-high-frequency plasma-enhanced chemical vapor deposition at a low temperature of 180°C, have been performed employing thickness evolutions of x-ray and electron diffraction measurements. The experimental results revealed that amorphous phase in μc-Si is transited to crystalline phase in solid phase in whole region from the top to the bottom, and the transition to the (220) orientation is dominantly found. These growth phenomena are interpreted in terms of a proposed model, i.e., the hybrid-phase growth model consisting of conventional vapor-phase growth at the surface plus the solid-phase crystallization occurring in the film. Moreover, the hybrid-phase growth, particularly solid-phase crystallization at low temperatures, is discussed in conjunction with the further results on the thickness evolutions associated with μc-Si films deposited on various underlayers or at substrate temperatures of 160–350°C, or at SiH4 concentrations of 3%–5%.

Scaling properties of growing surfaces of microcrystalline silicon

“…Raman scattering measurements revealed that the prepared lc-Si films were in the amorphous-crystalline transition region with the crystalline fractions of 42-66% [12]. The degree of (2 2 0) preferential orientation, I (220) /I (111) , where I (hkl) denotes the integrated intensity of X-ray diffraction at Si(h k l) plane, revealed that the crystallographic preferential orientations of lc-Si films were varied from (1 1 1) plane to (2 2 0) plane.…”

“…Undoped lc-Si films were prepared by very-high-frequency (VHF) (100 MHz) plasma enhanced chemical vapor deposition (PECVD) at a substrate temperature of 180°C [12]. The cumulative thicknesses, d, which were estimated from the deposition time, t, were 0.5-4 lm.…”

“…Topological features of the lc-Si films are related to crystallographic properties, which have been revealed by electron diffraction and X-ray diffraction (XRD) measurements as described in our reports [10,[12][13][14]. From the aspect of crystallographic orientations, the lc-Si films containing the columnar grains usually exhibit (2 2 0) preferential orientations, whereas the lc-Si films containing the isolated grains often exhibit (1 1 1) preferential orientations.…”

“…From the aspect of crystallographic orientations, the lc-Si films containing the columnar grains usually exhibit (2 2 0) preferential orientations, whereas the lc-Si films containing the isolated grains often exhibit (1 1 1) preferential orientations. In the case of some lc-Si films that contain columnar grains, the preferential orientation of the lc-Si films changed to the (2 2 0) plane during deposition, particularly at the bottom of the film, indicating the solid-phase growth in the film [10,[12][13][14].…”

Microstructures of high-growth-rate (up to 8.3nm/s) microcrystalline silicon photovoltaic layers and their influence on the photovoltaic performance of thin-film solar cells

“…In order to break the tendency, fundamental material properties of high-growth-rate lc-Si should be investigated. In our previous reports [9][10][11][12][13], we have reported structural properties of low-growth-rate (<0.5 nm/s) lc-Si centered upon the lc-Si deposited at 0.38 nm/s used as the i-layer of 9% efficiency solar cell, and summarized the structural features required for the device-grade lc-Si.…”