Formation of regular arrays of silicon microspikes by femtosecond laser irradiation through a mask

Shen, Mengyan; Crouch, Catherine H.; Carey, James E.; Younkin, R.; Mazur, Eric; Sheehy, Michael; Friend, Cynthia M.

doi:10.1063/1.1561162

Cited by 139 publications

(89 citation statements)

References 9 publications

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“…The way in which this molten surface evolves and interacts with its environment determines the final micrometer-scale morphology, chemical composition, and nanoscale structure of the surface layer. From the evidence we have collected, we feel that it is a combination of fluid dynamics, material removal/redeposition, and implantation of chemical species that yield sharp, conical microstructures [56]. All of these processes require the presence of a molten surface layer.…”

Section: Discussionmentioning

confidence: 99%

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

Carey¹,

Mazur²

2005

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Executive SummaryWith support from this award we studied a novel silicon microtexturing process and its application in silicon-based infrared photodetectors. By irradiating the surface of a silicon wafer with intense femtosecond laser pulses in the presence of certain gases or liquids, the originally shiny, flat surface is transformed into a dark array of microstructures. The resulting microtextured surface has near-unity absorption from near-ultraviolet to infrared wavelengths well below the band gap. The high, broad absorption of microtextured silicon could enable the production of silicon-based photodiodes for use as inexpensive, room-temperature multi-spectral photodetectors. Such detectors would find use in numerous applications including environmental sensors, solar energy, and infrared imaging.The goals of this study were to learn about microtextured surfaces and then develop and test prototype silicon detectors for the visible and infrared. We were extremely successful in achieving our goals. During the first two years of this award, we learned a great deal about how microtextured surfaces form and what leads to their remarkable optical properties. We used this knowledge to build prototype detectors with high sensitivity in both the visible and in the near-infrared. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, two orders of magnitude higher than standard silicon photodiodes. For wavelengths below the band gap, we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm, close to the responsivity of InGaAs photodiodes and five orders of magnitude higher than silicon devices in this wavelength region.The following Project Summary includes: Summary of important resultsPrior to receipt of this contract, we developed a process for microtexturing silicon surfaces with laser-assisted etching [1, 2]. The silicon sample is irradiated with a train of high-power ultrashort (100 fs) laser pulses in the presence of SF 6 or Cl 2 . Where the laser strikes the surface, material is etched away in a pattern of conical spikes, with the spike tips at the level of the unetched surface and the spike bases tens of microns below the surface. The surrounding non-irradiated silicon is unaffected, so areas as small as tens of microns on a side can be made. Figure 1 shows a scanning electron micrograph of a microtextured silicon surface.After etching, the silicon surface appears black to the eye (see Figure 2), and the surface absorbs over 90% of incident light from 0.25 µm to 2.5 µm [3]. Flat crystalline silicon absorbs only about 65% of incident light for wavelengths shorter than 1 µm, and absorbs less than 20% at longer wavelengths, with very low absorptance from 1.1 to 1.4 µm. Creation of a prototype microtextured silicon based p-i-n detector.Much of the work done in Year One and Year Two characterized the effects of laser fluence, shot number, gas pressure, and ambient gas on the absorption properties of microtextured silicon [4][5][6][7]. Using this data, we attempted to make...

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Section: Discussionmentioning

confidence: 99%

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

Carey¹,

Mazur²

2005

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“…al, to investigate argon and oxygen implantation on switching speeds in silicon microring resonators [10]. The penetration depth with a wavelength of 800nm in silicon is much larger than the waveguide height in this experiment [11]; hence a distribution of carriers will exist throughout the waveguide which will behave in the same manner as those generated by the co-linear approach [12].…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

“…5 the lower ion implantation doses result in the highest Raman gain, even though the lifetime reduction is not as small as for the highest dose. The intrinsic waveguide produces the highest net gain up to ~450mW since it has the lowest linear loss; however TPA generated FCA dominates as the pump power is increased resulting in the 5x10 11 …”

Section: Raman Simulationmentioning

confidence: 99%

Free carrier lifetime modification for silicon waveguide based devices

Wright

Thomson

Litvinenko

et al. 2008

2008 5th IEEE International Conference on Group IV Photonics

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Abstract:We investigate the effect of silicon ion irradiation on free carrier lifetime in silicon waveguides, and thus its ability to reduce the density of two-photon-absorption (TPA) generated free carriers. Our experimental results show that free carrier lifetime can be reduced significantly by silicon ion implantation. Associated excess optical absorption from the implanted ions can be reduced to an acceptable level if irradiation energy and dose are correctly chosen. Simulations of Raman scattering suggest that net gain can be achieved in certain cases without the need for an integrated diode in reverse bias to remove the photo-generated free carriers.

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“…For example, Shen et al reported the fabrication of regular arrays of silicon microspikes by fs laser irradiation through a mask. 15 Zywietz et al demonstrated a laser printing technique for fabricating periodic arrays of silicon nanoparticles. 16 Wang et al reported a micro/nanopatterning by fs laser irradiation through a pinhole.…”

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confidence: 99%