Recently, Professor Chen Xianhui of the University of Science and Technology of China has made progress in the study of two-dimensional graphene field effect transistors. The research team cooperated with professors Zhang Yuanbo, Feng Donglai and Wu Hao of Fudan University to successfully prepare two-dimensional black phosphorus field effect transistors with several nanometer thicknesses. The research results were published online on March 2nd in the journal Nature Nanotechnology.
The discovery of monolayer-thickness graphene marks the emergence of two-dimensional crystals as a class of materials that may affect human future electronic technology. However, the energy structure of the two-dimensional graphene does not have an energy gap, so that the current cannot be turned “on†and “off†in an electronic application, which weakens the use of a semiconductor switch in a computer circuit. Scientists began to explore alternative materials, hoping to overcome the defects of graphene, and proposed several possible replacement materials, such as silicene (single-layer silicon), germanene (single-layer helium), but these materials are not stable in the air. Not conducive to practical application. It is of great value and challenge to further explore and characterize two-dimensional materials with new functions and practical applications.
In response to the aforementioned challenges, Chen Xianhui's research group cooperated with Zhang Yuanbo's research group to successfully prepare a field-effect transistor based on a two-dimensional black phosphorus single crystal (phosphorene) with energy gap. Compared to other two-dimensional crystal materials, two-dimensional black phosphorus single crystal materials are more stable, but their single crystals do not easily grow under normal pressure. Ye Guojun, a doctoral student of the research group, succeeded in growing high-quality black phosphorus single crystal materials under the extreme conditions of high temperature and high pressure, paving the way for the realization of two-dimensional black phosphorus single crystal materials. Subsequently, they stripped the flakes from the bulk single crystals onto a degenerately doped silicon wafer with a layer of thermally grown silicon dioxide using mechanical tape to mechanically exfoliate them, and on this basis, fabricated field effect transistors.
When the thickness of the two-dimensional black phosphorus material is less than 7.5 nm, reliable transistor performance can be obtained at room temperature, and its leakage current modulation amplitude is on the order of 105. The IV characteristic curve exhibits a good current saturation effect. The charge carrier mobility of the transistor also exhibits thickness dependence. When the thickness of the two-dimensional black phosphor material is 10 nm, the highest mobility value of ~1,000 cm2 V-1 s-1 is obtained. These properties show that two-dimensional black phosphorus field effect transistors have a very high potential for application. In addition, transistors based on two-dimensional black phosphor materials also have direct band gaps in the infrared range, which makes black phosphors a candidate for future nanoelectronic and optoelectronic applications.
Relevant work has received extensive attention from the international academic community. Nature has published a review article highlighting the work of two two-dimensional black phosphorus field effect transistors including this work.
The above research work was funded by the National Natural Science Foundation of China, the major research plan of the Ministry of Science and Technology and the pilot project of the Chinese Academy of Sciences.
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