Optical hyperdoping: black silicon

Black silicon, at École Polytechnique de Montréal (Montreal, QC, Canada), Wednesday, May 19, 2010:
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 doping of TiO2 for solar harvesting, at Photonics West (San Fransisco, CA), Tuesday, January 24, 2012:
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 doping of TiO2 for solar harvesting
Black silicon, at Optoelectronics Research Centre Seminar, University of Southampton (Southampton, UK), Wednesday, November 7, 2012:
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 2014 International High Power Laser Ablation Conference (Santa Fe, NM), Monday, April 21, 2014:
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 Gordon Conference on Nonlinear Optics and Lasers, Colby Sawyer College (New London, NH), Monday, July 26, 1999:
Femtosecond laser-structured silicon: properties and structure, at Gordon Conference on Laser Interactions With Materials (Andover, NH), Tuesday, July 23, 2002:
Silicon surfaces that are microstructured with femtosecond laser pulses in a sulfur hexafluoride environment exhibit several remarkable properties, including near-unity below-band gap optical absorption (C. Wu et al., Appl. Phys. Lett. 78, 1850 (2001)). We report new structural and chemical characterization of this material, including cross-sectional TEM images of the microstructures. Our results indicate that the below-band gap absorption most likely comes from a surface layer of polycrystalline silicon roughly 1 micrometer thick, which includes nanopores, nanocrystals, and a high... Read more about Femtosecond laser-structured silicon: properties and structure
Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies, at 41st Annual Technical Meeting of the Society of Engineering Science, University of Nebraska, Lincoln (Lincoln, NE), Monday, October 11, 2004:
Irridiating silicon surfaces with trains of ultrashort laser pulses in the presence of a sulfur containing gas drastically changes the structure and properties of silicon. The normally smooth and highly reflective surface develops a forest of sharp microscopic spikes. The microstructured surface is highly absorbing even at wavelengths beyond the bandgap of silicon and has many interesting novel applications.
Femtosecond laser doping of silicon: Electronic structure, at CLEO 2008 (San Jose, CA), Thursday, May 8, 2008:
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. We have performed... Read more about Femtosecond laser doping of silicon: Electronic structure
Black silicon, at University of Queensland (Brisbane, Australia), Friday, January 15, 2010:
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.
Transforming the optical properties of silicon using femtosecond laser pulses, at Horizons of Nanophotonics and Nanoelectronics, a Keio-Harvard Workshop, Harvard University (Cambridge, MA), Monday, December 20, 2010:
We developed a technique, optical hyperdoping (OHD), for doping semiconductors to unusually high levels and endowing them with remarkable optoelectronic properties. By irradiating Si with a train of femtosecond laser pulses in the presence of chalcogen (column VI) compounds, a 300-nm thin layer of Si is doped to previously unreported, non-equilibrium levels (about 1%). When the dopant is chosen from the heavy chalcogens (sulfur, selenium, tellurium), the doped silicon exhibits remarkable optoelectronic properties: near-unity absorptance from the ultraviolet ( λ < 250 nm) to the near-... Read more about Transforming the optical properties of silicon using femtosecond laser pulses
Femtosecond laser doping of TiO2 for photocatalysis, at Gordon Research Conference on Renewable Energy: Solar Fuels (Barga, Italy), Wednesday, May 16, 2012:
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 doping of TiO2 for photocatalysis
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:
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
Laser doping and texturing of silicon for advanced optoelectronic devices, at 11th Conference on Lasers and Electro- Optics Pacific Rim (CLEO-PR 2015) (Busan, South Korea), Tuesday, August 25, 2015:
Irradiating a semiconductor sample with intense laser pulses in the presence of dopants drastically changes the optical, material and electronic properties of the sample. The properties of these processed semiconductors make them useful for photodetectors and, potentially, intermediate band solar cells. This talk discusses the processes that lead to doping and surface texturing, which both increase the optical absorption of the material. We will discuss the properties of the resulting material including the formation of an intermediate band. We have developed laser-processed silicon... Read more about Laser doping and texturing of silicon for advanced optoelectronic devices
Black silicon: hot properties and many open questions, at Atomic and molecular physics at surfaces, ITAMP (Cambridge, MA), Thursday, June 14, 2001:
A serendipitous discovery in our lab produced a novel form of microstructured silicon ("black silicon") that has many surprising properties: near unity absorption, even below the bandgap; production of photoelectrons in the visible and infrared; visible luminescence; and a strong field emission current. We are beginning to shed light on what might cause some of the material's remarkable properties. Much additional experimental and theoretical work is required to understand the surface physics and chemistry that leads to the formation of black silicon.

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