Dilution effect of Ar/H2 on the microstructures and photovoltaic properties of nc-Si:H deposited in low frequency inductively coupled plasma

Abstract

This work reports upon the dilution effect of Ar + H2 on the microstructures, optical, and photovoltaic properties of the hydrogenated nanocrystalline silicon (nc-Si:H) thin films. High crystallinity (up to 82.6%) nc-Si:H thin films were fabricated from silane diluted by Ar + H2 in a low-frequency inductively coupled plasma (LFICP) facility at a low temperature of 300 °C. The substitution of H2 by Ar in the diluent gas leads to an increase of the deposition rate, grain size, and crystallinity, and a decrease of the optical bandgap. Varying the Ar content caused a fluctuation of the H concentration and a change of the preferential orientation from (111) to (220) in the synthesized thin films. These effects physically originated from changes of the Ar + H2 + SiH4 plasma environment in the LFICP system. The enhancement of the dissociation of SiH4/H2 molecules by ion Ar+ and the metastable state Ar* were discussed in terms of related chemical reactions between the diluent gases and silane. Furthermore, it was found that a heterojunction solar cell prototype based on the as-deposited nc-Si:H thin films exhibits an excellent photovoltaic response.

Crystalline silicon surface passivation by intrinsic silicon thin films deposited by low-frequency inductively coupled plasma

“…Although it was recognized that the Tauc method will lead to a larger value for E g , it will give a correct variation trend of the value with an independent parameter like RF power, substrate temperature, and so on. Herein the values of E g are above 2 eV, larger than the values (<1.9 eV) 12 obtained in earlier works performed on the direct-plasma ICP system with other similar deposition parameters. This should be correlated to the increased hydrogen content (following FTIR results) in the thin films.…”

“…(5), a low E A value will point to a high reaction rate 1/s reac or a short reaction time s reac . In earlier works, 12,23 we have analyzed the effect of high-density hydrogen plasma from the LFICP source on the crystallinity of deposited lc-Si:H thin films. Abundant atomic hydrogen resulted from the dissociation of SiH 4 and H 2 will result in high surface coverage by hydrogen, which reduces the activation energy E A and the reaction time s reac .…”

“…These values are about half of those before the modification of the ICP system. 12 We can deduce that there should be a compromise between the deposition rate and the high quality thin film with low level interface defects.…”

“…In our previous works, we reported the development of low frequency inductively coupled plasma (LFICP) source 9 and its applications in nanotechnology fabrication 10,11 and also, the deposition of intrinsic and doped silicon thin films. 12,13 It was acknowledged that this LFICP source features various inherent advantages such as a high density, axial/radial uniformity plasma, and also independent control of electron number density and the energy of ions impinging on the growing surface. In order to decrease the ion bombardment on semiconductor surface generating more "soft" plasma for high quality interface in solar cell application, this ICP source has been modified into a new version.…”

Phase evolution and room-temperature photoluminescence in amorphous SiC alloy

“…15 In the present experiments, the hydrogen content in the deposited films is in a comparatively lower level evidenced by following FTIR spectra and previous quantitative calculation results. 21 Thus, the models focusing on the radicals of hydrides can be excluded. In terms of QSE model, the emission energy is expected to blueshift to high energy orientation because of the quantum confinement effect with the size shrink of the nano-particle.…”