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Evolution of microstructures on silicon induced by femtosecond laser with multiple pulses

Yuan D. Q., Zhou M., Lu D. Q., Xu J. T.

Optica Applicata

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2011

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Vol. 41, nr 3

727--734

EN

The effect of multiple pulses of Ti:sapphire femtosecond laser system on silicon wafer was investigated. Using the pulse energy exceed the threshold of silicon to investigate the evolvement of structures and found that exceed certain fluence no any periodic structure will appearance. For 1.91 J/cm2, the pattern of columnar structure was formed in the central region of irradiation area. In further experiment, using the subthreshold multiple pulse femtosecond laser irradiation of 0.91 J/cm2, the periodic ripple structures and nanohole array were presented in the whole irradiation area due to the incubation effection. Also, we obtained the threshold of nanohole array to be higher than that of the periodic ripple structures.

2

Processing microstructure on film by femtosecond laser

Yuan D. Q., Zhou M., Cai L., Xu J. T.

Optica Applicata

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2009

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Vol. 39, nr 3

629-635

EN

Selective laser patterning of thin films in a multilayer film is an emerging technology for fabrication of MEMS devices. A 775 nm Ti:sapphire laser (130 fs, 1 kHZ) was used to irradiate the thin film stacks with variations in process parameters such as feed rate and numerical aperture of objective lens. Femtosecond laser patterning of Au/Cr films which have the same thickness of about 1000 nm and are coated on glass substrate has been investiged to determine optimal parameters of the patterning process. Through a SEM and an AFM, we investigate the morphology of pattern, including the linewidth, groove depth and the laser-induced periodic surface structures (LIPSSs). The depth of the ablated groove was observed to depend on the scanning speed. And from the energy spectrum we find out which layer has been removed completely. The experimental results show that precise micromachining with desired stability and reproducibility can be achieved by controlling the ablation energy and the feed rate using appropriate numerical aperture (NA).

3

Study on high signal-to-noise ratio (SNR) silicon p-n junction photodetector

Fu X.S., Yao S.Y., Xu J.T., Lu Y., Zheng Y.G.

Optica Applicata

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2006

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Vol. 36, nr 2-3

421-428

EN

On the basis of n-type single-crystal (100) silicon substrate, a silicon p-n junction photodetector has been successfully developed. Three methods to improve photoresponse signal-to-noise ratio (SNR) were profoundly studied: the p-n junction depth was optimized to enhance the spectral responsivity within the wavelength range of 500-600 nm, an antireflection layer with the appropriate thickness was added to reduce the reflected light and enhance the sensitivity, the adjustment technique of spectral band response was adopted to remove the noise signal with normal silicon absorptive wavelengths. Eventually, the spectral responsivity SNR can be over 104 at 500-600 nm while the peak of spectral responsivity is 0.48 A/W at about 520 nm. After being optimized, silicon p-n junction photodetectors, which possess the properties of lower dark current, higher sensitivity, shorter response time and larger SNR, can be achieved.