Abstract
Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below the softening point of glass substrate. The initial a-Si films were grown by plasma enhanced chemical vapor deposition (PECVD). Reflectance measurement indicated characteristic peak in the UV region ~280 nm for the furnace annealed (>550 °C) and flash lamp annealed films, which provided evidence of crystallization. The film surface roughness increased with increasing the annealing temperature as well as after the flash lamp annealing. X-ray diffraction (XRD) measurement indicated that the as-deposited samples were purely amorphous and after furnace crystallization, the crystallites tended to align in one single direction (202) with uniform size that increased with the annealing temperature. On the other hand, the flash lamp crystalized films had randomly oriented crystallites with different sizes. Raman spectroscopy showed the crystalline volume fraction of 23.5%, 47.3%, and 61.3% for the samples annealed at 550 °C, 650 °C, and with flash lamp, respectively. The flash lamp annealed film was better crystallized with rougher surface compared to furnace annealed ones.
Highlights
Microcrystalline silicon thin films have many promising applications in optoelectronic devices including thin film transistors, light emitting diode, and solar cells due to their high charge carrier mobility and high electrical conductivity compared to its counterpart amorphous silicon [1,2]
Mc-Si thin films are often formed by post crystallization of amorphous Si (a-Si) or nanocrystalline silicon; both are usually prepared by plasma enhanced chemical vapor deposition (PECVD) at temperatures below 300 ◦ C [4]
The peak points of the interference fringe in the reflectance spectrum for the sample annealed at 650 ◦ C shifted obviously towards shorter wavelength
Summary
Microcrystalline silicon (mc-Si) thin films have many promising applications in optoelectronic devices including thin film transistors, light emitting diode, and solar cells due to their high charge carrier mobility and high electrical conductivity compared to its counterpart amorphous silicon [1,2]. The conventional way to grow mc-Si requires high temperature (>600 ◦ C) and is slow [3]. Mc-Si thin films are often formed by post crystallization of amorphous Si (a-Si) or nanocrystalline silicon; both are usually prepared by plasma enhanced chemical vapor deposition (PECVD) at temperatures below 300 ◦ C [4]. High quality mc-Si has been achieved by furnace annealing of PECVD grown a-Si thin films. Furnace annealing is not suitable for low melting substrates such as common glass or plastics and it requires long processing time (~16 h) [5].
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