School of Electrical and Computer Engineering, Cornell University , Ithaca, New York 14853, United States.
Nano Lett. 2015 Dec 9;15(12):8204-10. doi: 10.1021/acs.nanolett.5b03708. Epub 2015 Nov 6.
We present results on photoexcited carrier lifetimes in few-layer transition metal dichalcogenide MoS2 using nondegenerate ultrafast optical pump-probe technique. Our results show a sharp increase of the carrier lifetimes with the number of layers in the sample. Carrier lifetimes increase from few tens of picoseconds in monolayer samples to more than a nanosecond in 10-layer samples. The inverse carrier lifetime was found to scale according to the probability of the carriers being present at the surface layers, as given by the carrier wave function in few layer samples, which can be treated as quantum wells. The carrier lifetimes were found to be largely independent of the temperature, and the inverse carrier lifetimes scaled linearly with the photoexcited carrier density. These observations are consistent with defect-assisted carrier recombination, in which the capture of electrons and holes by defects occurs via Auger scatterings. Our results suggest that carrier lifetimes in few-layer samples are surface recombination limited due to the much larger defect densities at surface layers compared with the inner layers.
我们使用非简并超快光泵浦探测技术呈现了少层过渡金属二硫化钼 MoS2 中光激发载流子寿命的结果。我们的结果表明，载流子寿命随样品层数的增加而急剧增加。载流子寿命从单层样品的几十皮秒增加到 10 层样品的超过 1 纳秒。发现反向载流子寿命与载流子存在于表面层的概率成比例，这由少层样品中的载流子波函数给出，这可以被视为量子阱。载流子寿命与温度基本无关，反向载流子寿命与光激发载流子密度呈线性关系。这些观察结果与缺陷辅助载流子复合一致，其中缺陷通过俄歇散射捕获电子和空穴。我们的结果表明，由于与内层相比，表面层的缺陷密度大得多，因此少层样品中的载流子寿命受到表面复合的限制。
