High efficiency optoelectronic devices require materials with suitable band gap, excellent carrier mobility, strong light-matter interaction, and high thermal- and photo-stability. Herein, we report two layered materials of group-VI, namely SeS${}_2$ and TeS${}_2$, which meet all those desired criteria. Both materials are stable with 1T-MoS${}_2$-like structure, and exhibit in-direct gap semiconducting feature and possess extraordinary electronic transport properties with isotropic carrier mobilities outperforming their MoS${}_2$ analog. Using the GW approach for determining the quasi-particle electronic structure and Bethe-Salpeter equation accounting for the many-body excitonic effects, the optical properties of both materials have been identified. We find that exciton effects are significant in both materials that is characterized by the large binding energy of 0.66 eV and 0.84 eV for monolayer SeS${}_2$ and TeS${}_2$, respectively. The absorption edges lie in the optimal energy window of 1.0 $\sim$ 1.5 eV, which enables strong photo-absorption covering the whole visible-light region. Finally and importantly, we demonstrate that the in-direct nature of those materials can be violated by capping them with 2H-MoS${}_2$ to form a van der Waals heterostructure, while keep the gap in the energy favourable region. Those physical and optical characteristics make few-layer SeS${}_2$ and TeS${}_2$ highly appealing for room-temperature light-emitting devices, and particularly solar harvesting devices.

中文翻译：

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几层SeS2和TeS2的结构，电子和激子性质

高效的光电设备需要具有合适的带隙，出色的载流子迁移率，强的光物质相互作用以及高的热稳定性和光稳定性的材料。在这里，我们报告第六组的两层材料，即硒${}_2$ 和TeS${}_2$，这些条件符合所有所需条件。两种材料均在1T-MoS下稳定${}_2$类结构，并表现出间接的间隙半导体特性，并具有非同寻常的电子传输特性，各向同性载流子的性能优于MoS${}_2$模拟。使用GW方法确定准粒子电子结构和考虑了多体激子效应的Bethe-Salpeter方程，已经确定了这两种材料的光学性质。我们发现，在两种材料中，激子效应都是显着的，其特征是单层SeS具有0.66 eV和0.84 eV的大结合能${}_2$ 和TeS${}_2$， 分别。吸收边缘位于1.0的最佳能量窗口中$〜$1.5 eV，可实现覆盖整个可见光区域的强光吸收。最后且重要的是，我们证明了通过用2H-MoS封盖它们可以破坏这些材料的间接性质。${}_2$形成范德华力异质结构，同时将间隙保持在能量有利区域。那些物理和光学特性使几层SeS${}_2$ 和TeS${}_2$ 对于室温发光装置，特别是太阳能收集装置，非常有吸引力。