Monolayer transition metal dichalcogenides (TMDCs) including WS2, MoS2, WSe2 and WS2, are two-dimensional semiconductors with direct bandgap, providing an excellent field for exploration of many-body effects in 2-dimensions (2D) through optical measurements. To fully explore the physics of TMDCs, the prerequisite is preparation of high-quality samples to observe their intrinsic properties. For this purpose, we have focused on high-quality samples, WS2 grown by chemical vapor deposition method with hexagonal boron nitride as substrates. We observed sharp exciton emissions, whose linewidth is typically 22~23 meV, in photoluminescence spectra at room temperature, which result clearly demonstrates the high-quality of the current samples. We found that biexcitons formed with extremely low-excitation power (240 W/cm2) at 80 K, and this should originate from the minimal amount of localization centers in the present high-quality samples. The results clearly demonstrate that the present samples can provide an excellent field, where one can observe various excitonic states, offering possibility of exploring optical physics in 2D and finding new condensates.

译文

包括WS2,MoS2,WSe2和WS2在内的单层过渡金属二卤化物 (TMDCs) 是具有直接带隙的二维半导体,为通过光学测量探索二维 (2D) 的多体效应提供了极好的领域。要充分探索TMDCs的物理原理,前提是准备高质量的样品以观察其固有特性。为此,我们专注于高质量的样品,WS2通过化学气相沉积法以六方氮化硼为基底生长。我们在室温下的光致发光光谱中观察到明显的激子发射,其线宽通常为22〜23  meV,结果清楚地表明了当前样品的高质量。我们发现双激子在80  K时具有极低的激发功率 (240  W/cm2),这应该源于目前高质量样品中最小的定位中心。结果清楚地表明,本样品可以提供一个极好的领域,可以观察到各种激子态,为探索2D光学物理和寻找新的冷凝物提供了可能性。

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