In recent years, there has been ongoing effort in achieving efficient transport of excitons in monolayer transition metal dichalcogenides subjected to highly non-uniform strain. Here we investigate the transport of excitons and trions in monolayer semiconductor WS₂ subjected to controlled non-uniform mechanical strain. An atomic force microscope (AFM)-based setup is applied to actively control and tune the strain profiles by indenting the monolayer with an AFM tip. Optical spectroscopy is used to reveal the dynamics of the excited carriers. The non-uniform strain configuration locally changes the valence and conduction bands of WS₂, giving rise to effective forces attracting excitons and trions towards the point of maximum strain underneath the AFM tip. We observe large changes in the photoluminescence spectra of WS₂ under strain, which we interpret using a drift–diffusion model. We show that the transport of neutral excitons, a process that was previously thought to be efficient in non-uniformly strained two-dimensional semiconductors and termed as funnelling, is negligible at room temperature, in contrast to previous observations. Conversely, we discover that redistribution of free carriers under non-uniform strain profiles leads to highly efficient conversion of excitons to trions. Conversion efficiency reaches up to about 100% even without electrical gating. Our results explain inconsistencies in previous experiments and pave the way towards new types of optoelectronic devices.

近年来，人们一直在努力进行激子在单层过渡金属二卤化硅化物中的转运，该激子经受了高度不均匀的应变。在这里，我们研究激子和三重子在单层半导体WS _2中受受控非均匀机械应变的传输。基于原子力显微镜（AFM）的设置可用于通过使用AFM尖端压入单层来主动控制和调整应变曲线。光谱学用于揭示激发的载流子的动力学。非均匀应变配置会局部改变WS ₂的价态和导带，从而产生有效力，将激子和三重子吸引到AFM尖端下方的最大应变点。我们观察到WS ₂的光致发光光谱发生了巨大变化在应变下，我们用漂移扩散模型来解释。我们显示，与以前的观察结果相比，在室温下，中性激子的运输在室温下可以忽略不计，该过程以前被认为在非均匀应变的二维半导体中很有效，并且被称为“ Funnelling”。相反，我们发现在非均匀应变曲线下自由载流子的重新分布导致激子向三重子的高效转化。即使没有电气选通，转换效率也可达到约100％。我们的结果解释了先前实验中的不一致之处，并为新型光电器件铺平了道路。