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 U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) has discovered a quantum unit of photon absorption, which they have dubbed "AQ," that should be general to all 2D semiconductors, including compound semiconductors of the III-V family that are favored for solar films and optoelectronic devices. This discovery not only provides new insight into the optical properties of 2D semiconductors and quantum wells, it should also open doors to exotic new optoelectronic and photonic technologies.
"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 Ali Javey, a faculty scientist in Berkeley Lab's Materials Sciences Division and a professor of electrical engineering and computer science at the University of California (UC) Berkeley. "We discovered that the magnitude of step-wise absorptance in these materials is independent of thickness and band structure details."
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