Optical hyperdoping: black silicon

Femtosecond laser ablation of silicon: nanoparticles, doping and photovoltaics, at Harvard University (Thesis Defense) (Cambridge, MA), Friday, April 27, 2007:

In this thesis, we investigate the irradiation of silicon in a background gas of near atmospheric pressure with intense femtosecond laser pulses at energy densities exceeding the threshold for ablation (the macroscopic removal of material). We study the resulting structure and properties of the material ejected in the ablation plume as well as the laser irradiated surface itself.

The material collected from the ablation plume is a mixture of single crystal silicon nanoparticles and a highly porous network of amorphous silicon. The crystalline nanoparticles form by nucleation...

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Black silicon, at Technical University of Denmark (Copenhagen, Denmark), Tuesday, June 16, 2009:
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.
Infrared absorption limits of femtosecond laser doped silicon – effect of dopant types and thermal treatments, at Black Silicon Symposium (Albany, NY), Friday, August 20, 2010
Silicon doped with non-equilibrium concentrations of chalcogen exhibits strong sub-bandgap photon absorption. In this work, we investigate mid-infrared absorption of femtosecond laser doped silicon. Fourier transform infrared spectroscopy could shed light on energy levels of dopant states or bands. We study samples doped with sulfur, selenium and tellurium. In addition, we also investigate the effect of annealing temperature. Preliminary results suggest that near-unity absorption of sulfur doped silicon extends to mid-infrared. However, absorption decreases for photons with energy less than... Read more about Infrared absorption limits of femtosecond laser doped silicon – effect of dopant types and thermal treatments
Femtosecond-laser hyperdoping: controlling sulfur concentrations in silicon for band gap engineering, at APS March meeting (Boston, MA), Tuesday, February 28, 2012:
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 wafer 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 hyperdoping: controlling sulfur concentrations in silicon for band gap engineering
Black silicon and the quest for intermediate band semiconductors, at Zhejiang University (Hangzhou, China), Thursday, December 13, 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.
Femtosecond-Laser Hyperdoping and Texturing of Silicon for Advanced Non-equilibrium Materials, at 2014 AFOSR Ultrashort Pulse Laser-Matter Interactions Program Review (Arlington, VA), Friday, May 30, 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 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 Femtosecond-Laser Hyperdoping and Texturing of Silicon for Advanced Non-equilibrium Materials
Below-band gap absorption in microstructured silicon, at Optical Society of America Annual Meeting (Providence, RI), Tuesday, October 24, 2000:
We report two remarkable properties of silicon surfaces that are microstructured with laser-assisted etching: the absorptance for wavelengths between 0.25 and 2.5 micrometers is 97% or more, and photoelectrons are produced at 1.3 micrometers. We also report chemical and structural analysis of the microstructured material.
Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies, at Department of Physics Seminar, Fudan University (Shanghai, China), Wednesday, October 16, 2002:
Arrays of sharp, conical microstructures are obtained by texturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless texturing process drastically changes the optical and electronic properties of the original silicon wafer. These properties make the textured silicon viable for use in a wide range of commercial devices. Near-unity absorption of light, from visible to infrared wavelengths, offer opportunities for use in optically active devices such as solar cells and detectors. Significant enhancement of below-band-gap photocurrent... Read more about Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies
Optically hyperdoped silicon, at The 39th Winter Colloquium on the Physics of Quantum Electronics (Snowbird, UT), Thursday, January 8, 2009:
By irradiating silicon with a train of femtosecond laser pulses in the presence of chalcogen (column VI) compounds, a thin layer of Si is doped to previously unreported, non-equilibrium levels (about 2%). This optical hyperdoping (OHD) process creates a highly absorbing surface and extends silicon’s spectral sensitivity, even for infrared photons with energy less than the band gap. The optoelectronic properties of this 'black silicon' make it useful for a wide range of commercial devices in communications, remote sensing, and solar energy harvesting. Prototype OHD silicon photodiodes exhibit... Read more about Optically hyperdoped silicon
Black silicon, at Konopinski Colloquium Series, Indiana University Bloomington (Bloomington, IN), Wednesday, March 3, 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.
Serendipity, science, and engineering, at Sophomore forum, Harvard University (Cambridge, MA), Monday, February 7, 2011:
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 Nanostructuring of Semiconductors and Metals, at 13th International Symposium on Laser Precision Microfabrication (LPM), The Catholic University of America (Washington, DC), Thursday, June 14, 2012:
We have developed a unique technique to change the optoelectronic properties of many materials through hyperdoping and texturing [1]. By irradiating materials, such as silicon and titanium dioxide, with a train of amplified femtosecond (fs) laser pulses in the presence of a wide variety of dopant precursors, we can introduce dopants above the solubility limit while producing surface structures that have excellent anti-reflection and light-trapping properties.

Femtosecond-laser texturing originates from the formation of laser induced period surface structures (LIPSS) and consists of semi...

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Black silicon, at Annual Meeting of the Stanford Photonics Research Center, Stanford University (Palo Alto, CA), Monday, September 16, 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 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 photodetectors and imagers using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in imaging and energy harvesting.
Nonequilibrium materials: using ultrafast laser pulses to change band structures, at SPIE Conference on Ultrafast Bandgap Photonics (Baltimore, MD), Sunday, April 17, 2016:
Soon after it was discovered that intense laser pulses of nanosecond duration from a ruby laser could anneal the lattice of silicon, it was established that this so-called pulsed laser annealing is a thermal process. The past two decades have show that ultrashort laser pulses in the femtosecond regime can induce athermal, nonequilibrium processes that lead to either transient phase changes in semiconductors through ultrafast ionization or permanent phase changes through nonequilibrium doping. In this talk we will review work in both of these regimes and show how ultrafast lasers can be used... Read more about Nonequilibrium materials: using ultrafast laser pulses to change band structures

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