He Jing,Ge Jifeng,Xue Junying,Xia Tingyi,Dai Yongping,Wang Shengqi,Li Wenjie,Lin Zhaoyang
Solution-processed two-dimensional semiconductors could be used to create electronic devices on large scales and at low cost. However, the electronic performance of devices based on such materials is typically below that of devices based on materials grown via high-temperature chemical vapour deposition. Here we report the fabrication of indium selenide (InSe) semiconductor thin films using a colloidal solution of monolayer nanosheets (monolayer purity more than 98%). The InSe thin films are assembled on 4-inch wafers with conformal and intimate van der Waals contacts between the monolayer building blocks. We use the solution-processed films to fabricate InSe transistors that exhibit electron mobilities of 90–120 cm 2 V −1 s −1 , current on/off ratios of up to 10 7 and a small current hysteresis. We also show that InSe transistors with oxide encapsulation can remain stable in air for 3 months.
Valleytronics, focusing on the charge carriers occupying valleys (local energy extrema) of the energy bands in semiconductors, demonstrates an additional degree of freedom besides the spin and charge. Usually, the inequivalent valley “states” in transition metal disulfides (TMDs) could be manipulated by external magnetic fields by controlling the valley-polarized carriers in spin-coupled valleys. Here, we found that the valley polarization of the photocurrent in ε-InSe could be intrinsically manipulated without the external field by the all-optical contactless method. The transient circular photogalvanic effect (CPGE)-induced photocurrent revealed by terahertz emission could be reversed only by selected pumping carriers from vertically split valence bands into different Rashba valleys. The switchable Rashba valley polarization, i.e., the optical orienting valley degree of freedom, could be fulfilled by the synergetic effects between the momentum-dependent Zeeman-like field due to the emergent nonzero Berry curvature and the Rashba splitting. Our results suggest that the spontaneous symmetry breaking could degenerate the given valley in ε-InSe and give a new roadmap for the manipulation of the valley degree of freedom intrinsically.
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