Transition metal dichalcogenides (TMDCs) have recently been the focus of extensive research activity owing to their fascinating physical properties. As a new member of TMDCs, Mo doped ReSe2 (Mo:ReSe2) is an octahedral structure semiconductor being optically biaxial and highly anisotropic, different from most of hexagonal layered TMDCs with optically uniaxial and relatively high crystal symmetry. We investigated the effects of physisorption of gas molecule on the few-layer Mo:ReSe2 nanosheet based photodetectors. We compared the photoresponse of the as-exfoliated device with annealed device both in air or ammonia (NH3) environment. After annealing at sub-decomposition temperatures, the Mo:ReSe2 photodetectors show a better photoresponsivity (~55.5 A/W) and higher EQE (10893%) in NH3 than in air. By theoretical investigation, we conclude that the physisorption of NH3 molecule on Mo:ReSe2 monolayer can cause the charge transfer between NH3 molecule and Mo:ReSe2 monolayer, increasing the n-type carrier density of Mo:ReSe2 monolayer. The prompt photoswitching, high photoresponsivity and different sensitivity to surrounding environment from the few-layer anisotropic Mo:ReSe2 can be used to design multifunctional optoelectronic and sensing devices.
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机译：过渡金属二卤化物（TMDCs）由于其引人入胜的物理性能，近来已成为广泛研究的焦点。作为TMDC的新成员，Mo掺杂的ReSe2（Mo：ReSe2）是一种光学双轴且高度各向异性的八面体结构半导体，与大多数具有光学单轴且晶体对称性较高的六边形层状TMDC不同。我们研究了基于分子层的Mo：ReSe2纳米片光电探测器对气体分子的物理吸附作用。我们在空气或氨水（NH3）环境中比较了脱落后的设备与退火设备的光响应。在亚分解温度下退火后，与空气相比，Mo：ReSe2光电探测器在NH3中显示出更好的光响应性（〜55.5 A / W）和更高的EQE（10893％）。通过理论研究，我们得出结论，NH3分子在Mo：ReSe2单层上的物理吸附可引起NH3分子与Mo：ReSe2单层之间的电荷转移，从而增加Mo：ReSe2单层的n型载流子密度。几层各向异性的Mo：ReSe2具有迅速的光电转换，高的光响应性和对周围环境的不同敏感性，可用于设计多功能光电和传感设备。
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