Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, CA, 94720, USA.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Nat Commun. 2017 Sep 20;8(1):608. doi: 10.1038/s41467-017-00516-5.
The application of strain to semiconductors allows for controlled modification of their band structure. This principle is employed for the manufacturing of devices ranging from high-performance transistors to solid-state lasers. Traditionally, strain is typically achieved via growth on lattice-mismatched substrates. For two-dimensional (2D) semiconductors, this is not feasible as they typically do not interact epitaxially with the substrate. Here, we demonstrate controlled strain engineering of 2D semiconductors during synthesis by utilizing the thermal coefficient of expansion mismatch between the substrate and semiconductor. Using WSe as a model system, we demonstrate stable built-in strains ranging from 1% tensile to 0.2% compressive on substrates with different thermal coefficient of expansion. Consequently, we observe a dramatic modulation of the band structure, manifested by a strain-driven indirect-to-direct bandgap transition and brightening of the dark exciton in bilayer and monolayer WSe, respectively. The growth method developed here should enable flexibility in design of more sophisticated devices based on 2D materials.Strain engineering is an essential tool for modifying local electronic properties in silicon-based electronics. Here, Ahn et al. demonstrate control of biaxial strain in two-dimensional materials based on the growth substrate, enabling more complex low-dimensional electronics.
应变在半导体中的应用允许对其能带结构进行可控的修改。这一原理被应用于制造各种器件，从高性能晶体管到固态激光器。传统上，应变通常是通过在晶格失配的衬底上生长来实现的。对于二维（2D）半导体，这是不可行的，因为它们通常不会与衬底外延相互作用。在这里，我们通过利用衬底和半导体之间的热膨胀系数失配，在合成过程中展示了对 2D 半导体的可控应变工程。我们使用 WSe 作为模型系统，在具有不同热膨胀系数的衬底上演示了从 1%拉伸到 0.2%压缩的稳定内置应变。因此，我们观察到能带结构的剧烈调制，表现为应变驱动的间接到直接带隙跃迁，以及双层和单层 WSe 中暗激子的变亮。这里开发的生长方法应该能够在基于二维材料的更复杂器件的设计中实现灵活性。应变工程是在基于硅的电子器件中修改局部电子特性的重要工具。在这里，Ahn 等人展示了基于生长衬底的二维材料的双轴应变控制，从而实现更复杂的低维电子学。
