AsianScientist (Aug. 19, 2015) – A team of Korean scientists have figured out how to tune black phosphorous’ (BP) band gap to form a superior semiconductor. This research, published in Science, potentially allows for greater flexibility in the design and optimization of electronic and optoelectronic devices like solar panels and telecommunication lasers.
The research team operating out of Pohang University of Science and Technology (POSTECH), affiliated with the Institute for Basic Science’s (IBS) Center for Artificial Low Dimensional Electronic Systems (CALDES), effectively modified BP from a semiconductor to a gapless Dirac semimetal with properties similar to graphene.
Graphene has a band gap of zero in its natural state and so acts like a conductor. Because the conductivity of graphene cannot be shut off, even at low temperatures, graphene is difficult to use as a semiconductor.
Like graphene, BP is a semiconductor and also cheap to mass produce. The one big difference between the two is BP’s natural band gap, allowing the material to switch its electrical current on and off.
“Graphene is a Dirac semimetal. It’s more efficient in its natural state than black phosphorus but it’s difficult to open its band gap. Therefore we tuned BP’s band gap to resemble the natural state of graphene, a unique state of matter that is different from conventional semiconductors,” explained Kim Keun Su, a professor at POSTECH.
“We transferred electrons from the dopant—potassium—to the surface of the black phosphorus, which confined the electrons and allowed us to manipulate this state. Potassium produces a strong electrical field which is what we required to tune the size of the band gap,” explained Kim Keun Su, a professor at POSTECH.
The potassium doping induced a giant Stark effect, which tuned the band gap allowing the valence and conductive bands to move closer together. This effectively lowered the band gap and drastically altered it to a value between 0.0 ~ 0.6 electron Volt (eV) from its original intrinsic value of 0.35 eV.
This improved form of black phosphorus could potentially be applied to several sectors including engineering where electrical engineers can adjust the band gap and create devises with the exact behavior desired.
The article can be found at: Kim et al. (2015) Observation of Tunable Band Gap and Anisotropic Dirac Semimetal State in Black Phosphorus.
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Source: Institute for Basic Science.
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