Femtosecond-laser-induced-crystallization and simultaneous formation of light trapping microstructures in thin a-Si:H films |
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Authors: | BK Nayak MC Gupta |
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Institution: | (1) Charles L. Brown Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904, USA |
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Abstract: | We report the observation of crystallization and simultaneous formation of surface microstructures in hydrogenated amorphous
silicon (a-Si:H) thin films as one step laser processing. Light trapping microstructures of around 300 nm in height were formed
on a-Si:H films of thickness in the range of 1.5 μm to 2 μm deposited on soda lime glass after exposure to femtosecond laser
pulses. Scanning electron microscope (SEM) images show the formation of spikes that are around 1 μm part and their heights
could be controlled by the laser fluences. Atomic force microscope (AFM) images were taken to study the roughness created
on the surface. The mean roughness of the textured surface increases with laser fluence at smaller power densities, and for
power densities beyond 0.5 J/cm2 the film removal deteriorates the texturing. X-ray diffraction results indicate the formation of a nano-crystalline structure
with (111) and (311) crystal orientation after the laser treatment. The observed black color and enhanced optical absorption
in the near infrared region in laser treated films may be due to a combined effect of light trapping in the micro-structured
silicon surface because of multiple total internal reflections, phase change in the film, possible defect sites induced after
laser treatment and formation of SiOx. Demonstration of light trapping microstructures in thin a-Si:H films and simultaneous crystallization could provide new
opportunities for optoelectronic devices.
PACS 42.55.Px; 42.62.Cf; 81.05.Ge |
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Keywords: | |
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