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Abstract
Hydrogenated Nanocrystalline Silicon (nc-Si:H) thin films using SiH4/H2 mixture by glow discharged decomposition were investigated on c-Si and glass substrates. The effects of substrate temperature on the Structural, Optical and Electrical properties of the films were investigated by X-ray diffraction, Raman scattering, FT/IR, Optical transmission and Atomic Force Microscopy (AFM). Substrate temperatures ([TSB]) of the films were changed from 100oC to 250oC. It has been revealed the strong dependence on the film’s properties with the substrate temperatures. XRD and Raman measurements were shown that the higher substrate temperature (250oC) exhibits the highest crystalline volume fraction ([ρ] = 95%) and the lowest crystalline size ([Ω] = 3.5 nm) as well, having the highest H-content and the lowest O-content. At 250oC, the lowest mobility and the highest resistivity were also found to be ~37.5 cm2/v.s and 7.35 Ω-cm. Refractive index and the optical energy gap (Eg) were estimated by 3.8 and 1.9 eV having the growth rate of 4.2 nm/min. At 250oC, it was resulted in a blue shift of the absorption edge having uniform grain distributions. Results indicate that in situ hydrogen cleaning effects is prominent and localized orderly high density Si-Si bonds are exhibiting quantum size effects at highest substrate temperature.
Highlights
Hydrogenated nanocrystalline silicon thin films has attracted as a promising material in the application of optoelectronic devices such as solar cells, thin film transistors due to the quantum size effects of silicon nanocrystallites implanted in amorphous silicon medium (Gudovskikh et al, 2004)
The nanocrystalline silicon (nc-Si):H thin films of ~200 nm were prepared by a home-built 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) system (Figure 1) using SiH4/H2 mixture in a fused quartz reactor employing capacitively coupled by two parallel electrodes with a distance of 5 cm and area of 28 cm2 and inserted into an electric furnace (Ritikos et al, 2009)
(2) The cleaned substrates were treated by exposing them for 20 min to H2 plasma excited using RF power value of 80 W. (3) nc-Si:H films were prepared at 5 different substrate temperatures of 100 °C, 150 °C, 200 °C and 250°C
Summary
Hydrogenated nanocrystalline silicon (nc-Si:H) thin films has attracted as a promising material in the application of optoelectronic devices such as solar cells, thin film transistors due to the quantum size effects of silicon nanocrystallites implanted in amorphous silicon medium (Gudovskikh et al, 2004). The photoluminescent intensities and band gap of these nano-materials are found to be increased with the existence of Si nano-crystallites Luminescent properties of these films are found to be strongly reliant on crystallite size and crystalline volume fraction of nano-crystallites Si in the films (Liu et al, 1995). Various techniques have been used to prepare nc-Si:H films, including plasma enhanced chemical vapor deposition (PECVD)], electron beam evaporation, electron cyclotron resonance plasma CVD, magnetron sputtering, hot-wire CVD and Si ion implantation. Among these deposition techniques, only PECVD had been established for industrial applications. In order to enhance the device performance, improving the crystal quality using lower temperature is one of the pressing outlines in the use of PECVD
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