关键词: 化学气相沉积法/
MoS2(1-x) Se2x合金/
堆叠生长/
电子结构
English Abstract
Effect of layer variation on the electronic structure of stacked MoS2(1-x) Se2x alloy
Wang Wen-Jie,Kang Zhi-Lin,
Song Qian,
Wang Xin,
Deng Jia-Jun,
Ding Xun-Lei,
Che Jian-Tao
Department of Physics, School of Mathematics and Physics, North China Electric Power University, Beijing 102206, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 91545122) and the Fundamental Research Fund for the Central Universities, China (Grant Nos. JB2015RCY03, 2016MS68).Received Date:06 August 2018
Accepted Date:05 September 2018
Published Online:20 December 2019
Abstract:Two-dimensional transition metal dichalcogenides (TMDCs) have the extensive application prospect in multifunctional electronics and photonics due to their unique electro-optical properties. In order to further expand their application scope in micro-nano optoelectronic devices and improve the performance of devices, the band-gap and defective engineering have been studied to tune the band-gap, morphology and structure of two-dimensional semiconductor materials. The tunning of the bandgap of MoS2(1-x) Se2x alloy has been typically achieved by controlling the Se concentration. Theoretical calculations revealed that layered stacked two-dimensional alloy materials with a larger aspect ratio, exposed edges and obvious edge dangling bonds show enhanced HER activity as compared with TMDCs. In this paper, the properties of stacked MoS2(1-x) Se2x alloy grown by the chemical vapor deposition method in a quartz tube furnace are investigated by using optical microscopy (OM), atomic force microscopy (AFM), scanning tunneling microscopy (SEM), Raman, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The OM and SEM images of the as-synthesized stacked MoS2(1-x)Se2x alloy show apparent interface between layers and their thickness is further acquired by AFM. Unlike most of single-layer or few-layer MoS2(1-x)Se2x alloys, stack-grown stepped MoS2(1-x) Se2x alloy materials all present the strong luminescence properties despite the thickness increasing from 2.2 nm (~3 layers) to 5.6 nm (~7 layers). And even till 100 nm, the emission spectrum with two luminescence peaks can still be observed. The two exciton luminescence peaks A and B are derived from the valence band splitting caused by the spin-orbit coupling, respectively. As the thickness increases, the two luminescence peaks are red-shifted and exhibit a band-bending effect that is only present when the alloy doping concentration is changed. As the sample thickness is 5.6 nm, a C-peak at 650 nm at the high energy end of the PL spectrum is observed, which may be attributed to the transition luminescence from the defect energy level introduced by Se (S) substitution, interstice or cluster. When the number of layers is small, the number of defects is small, so that the luminescence is not observed. As the number of layers increases, the defects increase to form a defect energy level. However, when the material thickness continuously increases until the bulk material is formed, the luminescence disappears in the PL spectrum because the band gap is reduced and the band gap is made smaller than the defect energy level. Raman spectroscopy gives two sets of vibration modes:like-MoS2 and like-MoSe2. The Raman peak is almost unchanged as the thickness increases, but the two vibration modes E2g (Mo-Se) and E2 g (Mo-S) in the plane gradually appear and increase. At the same time, the intensity ratio and line width of Mo-Se related vibration mode E2g/A1g increase with thickness increasing, which indicates the enhancement of the Mo-Se in-plane vibration mode and the incorporation of randomness of Se into the lattice. Obviously, the defects and stress are the main factors affecting the electronic structure of stacked MoS2(1-x) Se2x alloy, which provides a meaningful reference for preparing the special functional devices and studying the controllable defect engineering.
Keywords: chemical vapor deposition/
MoS2(1-x) Se2x alloy/
stack growth/
electronic structure
