A type-I van der Waals heterostructure formed by monolayer WS₂ and trilayer PdSe₂

Two-dimensional (2D) heterostructures, formed by stacking 2D semiconductors through the van der Waals force, have been extensively studied recently. However, the majority of the heterostructures discovered so far possess type-II interfaces that facilitate interlayer charge separation. Type-I interfaces, on the other hand, confine both electrons and holes in one layer, which is beneficial for optical applications that utilize electron–hole radiative recombination. So far, only a few type-I 2D heterostructures have been achieved, which has limited the construction of multilayer heterostructures with sophisticated band landscapes. Here, we report experimental evidence of a type-I interface between monolayer WS₂ and trilayer PdSe₂. Two-dimensional PdSe₂ has emerged as a promising material for infrared optoelectronic and other applications. We fabricated the heterostructure by stacking an exfoliated monolayer WS₂ flake on top of a trilayer PdSe₂ film, synthesized by chemical vapor deposition. Photoluminescence spectroscopy measurements revealed that the WS₂ exciton peak is significantly quenched in the heterostructure, confirming efficient excitation transfer from WS₂ to PdSe₂. Femtosecond transient absorption measurements with various pump/probe configurations showed that both electrons and holes photoexcited in the WS₂ layer of the heterostructure can efficiently transfer to PdSe₂, while neither type of carriers excited in PdSe₂ can transfer to WS₂. These experimental findings establish a type-I band alignment between monolayer WS₂ and trilayer PdSe₂. Furthermore, our results further highlight PdSe₂ as an important 2D material for constructing van der Waals heterostructures with emergent electronic and optoelectronic properties.. Authors: Li, Guili [Beijing Jiaotong University (China); The University of Kansas] (ORCID:0009000079680851); Zhang, Xiaoxian [Beijing Jiaotong University (China)] (ORCID:0000000242158274); Wang, Yongsheng [Beijing Jiaotong University (China)] (ORCID:0000000264553937); Liu, XiaoJing [Beijing Jiaotong University (China)]; Ren, FangYing [Beijing Jiaotong University (China)]. DOE Contract: SC0020995. Subjects: 77 NANOSCIENCE AND NANOTECHNOLOGY; Two-dimensional materials; band alignment; charge transfer; photocarriers