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Optical hyperdoping: black silicon

We have developed a novel technique that creates highly doped and structured silicon. Focusing a train of femtosecond laser pulses on silicon wafers in the presence of heavy chalcogens (e.g. S, Se, or Te) dopes a thin layer of silicon at the surface to non-equilibrium levels. This optical hyperdoping process creates black silicon, a highly absorbing surface with extended spectral sensitivity. This material offers new opportunities for silicon-based optoelectronic devices. Black silicon is strongly light-absorbing. During hyperdoping, the polished surface of a silicon wafer is transformed from shiny gray to deep black. In addition to near-unity absorption in the visible, black silicon absorbs over 80 percent of below band-gap, infrared light for wavelengths as long as 2500 nm. This can be used to make photodiodes with remarkable responsivity in both the visible and infrared. It is also possible that this extended absorption range can improve the efficiency of silicon solar cells.
Black silicon, at Research Seminar, University of Twente (Enschede, The Netherlands), Friday, June 12, 2009:
talk_1484.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Serendipity, science, and engineering, at Faculty Seminar, REU Program, Harvard University (Cambridge, MA), Thursday, July 15, 2010:
talk_1693.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Femtosecond laser doped and nanostructured TiO2 for photocatalysis, at American Physical Society March Meeting (Boston, MA), Monday, February 27, 2012:
talk_1914.pdf
We present a novel method for femtosecond-laser doping of titanium dioxide (TiO2) for above bandgap absorptance by irradiating titanium metal in the presence of oxygen and dopants. With a bandgap of 3.2 eV for the anatase crystalline phase, TiO2 most strongly absorbs in the UV range (λ< 387 nm). However, doping with metals and nitrogen has been shown to create intermediate states in the bandgap. Using femtosecond laser doping techniques on titanium in a gaseous environment, we produce laser-induced periodic surface structures. Altering the gas composition and pressure does not change the... Read more about Femtosecond laser doped and nanostructured TiO2 for photocatalysis
Black silicon, at Physics Seminar, Wright State University (Dayton, OH), Friday, November 30, 2012:
talk_2038.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Ultrashort Lasers to Increase Efficiency in Solar Energy Harvesting via Intermediate States, at 2014 High Power Laser Ablation and Beamed Energy Propulsion Conference (Santa Fe, NM), Wednesday, April 23, 2014:
talk_2309.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Ultrashort Lasers to Increase Efficiency in Solar Energy Harvesting via Intermediate States
Black silicon: using lasers to make novel materials, at Condensed Matter Physics Seminar, Harvard University (Cambridge, MA), Friday, February 14, 2003:
talk_454.pdf
Irradiating the surface of a crystalline silicon wafer with intense laser pulses in a reactive gas environment changes the structure and properties of the wafer dramatically: the formerly smooth, highly reflective surface becomes covered with a forest of sharp microspikes. In addition to changing the surface morphology, this microstructuring process also dramatically alters the optical properties of the silicon. The microstructured surface is highly absorbing even at wavelengths to which the original wafer is transparent. We find that the laser structuring process incorporates high... Read more about Black silicon: using lasers to make novel materials
Black silicon, at Zhejiang University (Hangzhou, China), Wednesday, March 28, 2007:
talk_1306.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Black silicon, at SPIE Photonics West (San Francisco, CA), Monday, January 25, 2010:
talk_1491.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Femtosecond laser doped silicon for photovoltaic applications, at Photonics West 2011 (San Francisco, CA), Thursday, January 27, 2011:
talk_1666.pdf
Doping silicon to concentrations above the metal-insulator transition threshold yields a novel material that has potential for photovoltaic applications. By focusing femtosecond laser pulses on the surface of a silicon wafe in a sulfur hexafluoride (SF6) environment, silicon is doped with 1% atomic sulfur. This material exhibits near-unity, broadband absorption from the visible to the near infrared (< 0.5 eV, deep below the silicon bandgap), and metallic-like conduction. These unusual optical and electronic properties suggest the formation of an intermediate band. We report on the... Read more about Femtosecond laser doped silicon for photovoltaic applications
Black silicon, at Physics Colloquium, University of Pretoria (Pretoria, South Africa), Thursday, May 31, 2012:
talk_1942.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Towards increased efficiency in solar energy harvesting via intermediate states, at SPIE Laser Material Processing for Solar Energy Devices II (San Diego, CA), Wednesday, August 28, 2013:
talk_2070.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel... Read more about Towards increased efficiency in solar energy harvesting via intermediate states
Black silicon, at Institute for Atomic and Molecular Science, Academia Sinica (Taipei, Taiwan), Friday, January 29, 2016:
talk_2581.pdf
Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
Black Silicon, at XI International Symposium Ultrafast Phenomena in Spectroscopy, Academia Sinica (Taipei, Taiwan), Monday, October 25, 1999:
talk_354.pdf

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