Berkeley Lab Researchers Discover Universal Law for Light Absorption in 2D Semiconductors (http://newscenter.lbl.gov/news-releases/2013/07/31/berkeley-lab-researchers-discover-universal-law-for-light-absorption-in-2d-semiconductors/)
From solar cells to optoelectronic sensors to lasers and imaging devices, many of today's semiconductor technologies hinge upon the absorption of light. Absorption is especially critical for nano-sized structures at the interface between two energy barriers called quantum wells, in which the movement of charge carriers is confined to two-dimensions. Now, for the first time, a simple law of light absorption for 2D semiconductors has been demonstrated.
Working with ultrathin membranes of the semiconductor indium arsenide, a team of researchers with the
"We used free-standing indium arsenide membranes down to three nanometers in thickness as a model material system to accurately probe the absorption properties of 2D semiconductors as a function of membrane thickness and electron band structure," says
Javey is one of two corresponding authors of a paper describing this research in the Proceedings of the
Previous work has shown that graphene, a two-dimensional sheet of carbon, has a universal value of light absorption. Javey, Yablonovitch and their colleagues have now found that a similar generalized law applies to all 2D semiconductors. This discovery was made possible by a unique process that Javey and his research group developed in which thin films of indium arsenide are transferred onto an optically transparent substrate, in this case calcium fluoride.
"This provided us with ultrathin membranes of indium arsenide, only a few unit cells in thickness, that absorb light on a substrate that absorbed no light," Javey says. "We were then able to investigate the optical absorption properties of membranes that ranged in thickness from three to 19 nanometers as a function of band structure and thickness."
Using the Fourier transform infrared spectroscopy (FTIR) capabilities of Beamline 1.4.3 at
"This absorption law appears to be universal for all 2D semiconductor systems," says Yablonovitch. "Our results add to the basic understanding of electron-photon interactions under strong quantum confinement and provide a unique insight toward the use of 2D semiconductors for novel photonic and optoelectronic applications."
This research was supported by
The Advanced Light Source is a third-generation synchrotron light source producing light in the x-ray region of the spectrum that is a billion times brighter than the sun. A DOE national user facility, the ALS attracts scientists from around the world and supports its users in doing outstanding science in a safe environment. For more information visit www-als.lbl.gov/.The Advanced Light Source is a third-generation synchrotron light source producing light in the x-ray region of the spectrum that is a billion times brighter than the sun. A DOE national user facility, the ALS attracts scientists from around the world and supports its users in doing outstanding science in a safe environment. For more information visit http://www.als.lbl.gov/.
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