Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder
Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder
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DOI：
10.1103/physrevmaterials.5.044001
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发表时间：
2021-04-05
影响因子：
3.4
通讯作者：
Crooker, S. A.
中科院分区：
文献类型：
--
作者：
Li, Jing;Goryca, M.;Crooker, S. A.
使用时间分辨的光学克尔旋转，我们测量的低温谷动力学的居民电子和空穴在剥离的WSe 2单分子膜作为一个系统的载流子密度的函数。为了调和迄今为止报道的单层半导体中载流子谷动力学的许多不同的时间尺度，我们直接比较了具有不同介电环境的两个静电门控WSe 2单层中的掺杂依赖的谷弛豫。在一个完全封装的结构（hBN/WSe 2/hBN，其中hBN是六方氮化硼），谷弛豫被发现是单指数。谷弛豫时间τ（v）在低载流子密度下相当长（类似于10 μ s），但在大于或类似于2 × 10（12）cm（-2）的高电子或空穴密度下迅速减小到小于100 ns。相比之下，在直接放置在二氧化硅（hBN/WSe 2/SiO2）的部分封装的WSe 2单层，载流子谷弛豫是多指数在低载流子密度。这种差异归因于来自SiO2衬底的环境无序。出乎意料的是，非常小的平面外磁场可以增加电视，特别是在hBN/WSe 2/SiO2结构，这表明由无序引起的局部状态可以发挥重要作用，在去极化自旋和介导的谷弛豫的居民载流子在单层过渡金属二硫族化物半导体。
Using time-resolved optical Kerr rotation, we measure the low-temperature valley dynamics of resident electrons and holes in exfoliated WSe2 monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically gated WSe2 monolayers having different dielectric environments. In a fully encapsulated structure (hBN/WSe2/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time tau(v) is quite long (similar to 10 mu s) at low carrier densities, but decreases rapidly to less than 100 ns at high electron or hole densities greater than or similar to 2 x 10(12) cm(-2). In contrast, in a partially encapsulated WSe2 monolayer placed directly on silicon dioxide (hBN/WSe2/SiO2), carrier valley relaxation is multiexponential at low carrier densities. The difference is attributed to environmental disorder from the SiO2 substrate. Unexpectedly, very small out-of-plane magnetic fields can increase tv, especially in the hBN/WSe2/SiO2 structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition-metal dichalcogenide semiconductors.