Zhou Jiangpeng, Wu Yaping, Wang Hao, Wu Zhiming, Li Xu, Yang Weihuang, Ke Congming, Lu Shiqiang, Zhang Chunmiao, Kang Junyong
Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Insititute, Xiamen University, Xiamen, 361005, P. R. China.
Key Laboratory of RF Circuits and System of Ministry of Education, Hangzhou Dianzi University, Hangzhou 310018, P. R. China.
Nanoscale. 2020 Feb 14;12(6):4069-4076. doi: 10.1039/c9nr09057f. Epub 2020 Feb 5.
We report tunable optical performances of gallium selenide (GaSe) layers in phonon vibrations, band edge emission, circular polarization, and anisotropic response via strain manipulation. By applying a uniaxial tensile strain, frequency shift and peak broadening are observed in Raman spectra. A shrink in bandgap is demonstrated in photoluminescence (PL) spectra and confirmed by first-principles calculations. A continuously growing circular polarization from 3.8% to 37.9% is detected at room temperature when the tensile strain is increased from 0% to 0.35%, which is almost a ten-fold enhancement compared with that under the non-resonant excitation. Through the theoretical calculations, the decrease in exciton lifetime is revealed to be responsible for the overwhelming enhanced circular polarization. By deforing the lattices of GaSe layers, the Raman intensity was found to be suppressed in the strain direction. The intrinsic fourfold-symmetry of the E mode in angle-dependent Raman spectra is tuned to a two-fold symmetry. An anisotropic PL response is further regulated by changing the structural symmetry of GaSe lattices. A maximal polarization of 66.0% is achieved when the detection polarizations are perpendicular to the strain direction. All the findings in this study suggest a route for tuning the optical properties, particularly the polarized response in two-dimensional (2D) materials, and provide a strategy for developing flexible and anisotropic 2D optical devices.
我们报告了通过应变操纵，硒化镓（GaSe）层在声子振动、带边发射、圆偏振和各向异性响应方面的可调光学性能。通过施加单轴拉伸应变，在拉曼光谱中观察到频率偏移和峰展宽。光致发光（PL）光谱显示带隙缩小，并通过第一性原理计算得到证实。当拉伸应变从0%增加到0.35%时，在室温下检测到圆偏振从3.8%持续增长到37.9%，与非共振激发下相比，这几乎是十倍的增强。通过理论计算，发现激子寿命的缩短是圆偏振显著增强的原因。通过使GaSe层的晶格变形，发现拉曼强度在应变方向上受到抑制。角度相关拉曼光谱中E模式的固有四重对称性被调谐为二重对称性。通过改变GaSe晶格的结构对称性，进一步调节了各向异性PL响应。当检测偏振方向垂直于应变方向时，实现了66.0%的最大偏振度。本研究中的所有发现为调节光学性质，特别是二维（2D）材料中的偏振响应提供了一条途径，并为开发柔性和各向异性2D光学器件提供了一种策略。
