Abstract
Two-dimensional (2D) layered semiconductors are current research hotspots on account of their wide variety of applications in electronics and optoelectronics due to their particular ultrathin nature. In this review, the band alignment engineering in heterojunctions composed of 2D van der Waals (vdW) layered semiconductors and their device applications in optoelectronics are provided. Various approaches that induced adjustability of vdW heterojunctions are summarized, mainly including composition and thickness modulations, strain, and electric fields. Furthermore, their perspectives on future developments in optoelectronics and electronics devices based on the newly unique physical and chemical properties are outlined.
Highlights
According to “Moore’s law,” the number of transistors that can be placed on an integrated circuit doubles roughly every 18 months, and this rapid development depends on the constant upgrading of electronic components
In 2H-TiS2/zinc oxide (ZnO) van der Waals heterojunctions (vdWHs), the heterojunction appears as a narrow indirect bandgap of 0.34 eV with the formation of type-II band alignment; a large potential drop (3.75 eV) and band offset are formed which improve charge separation efficiency and make the heterojunction desirable for optoelectronic applications (Rahimi, 2021)
The band alignment of WTe2/HfS2 van der Waals (vdW) heterojunctions transforms from type-III to type-II with biaxial strain, which is because the position of high symmetry points of the band edge changes with strain (Lei et al, 2019)
Summary
According to “Moore’s law,” the number of transistors that can be placed on an integrated circuit doubles roughly every 18 months, and this rapid development depends on the constant upgrading of electronic components. Semiconductor van der Waals heterojunctions (vdWHs) can be classified into type I (symmetric), type II (staggered), and type III (broken) according to band arrangement of semiconductors (Özçelik et al, 2016; Kahn et al, 2020). The type-I heterojunctions are suitable for applications in photoluminescence and photoluminescence excitation detections (Yamaoka et al, 2018), since the photo-excited electrons tend to transfer within the CBM and VBM of the narrow bandgap rather than in the broad one, spatially confine the charge carriers, and efficiently reduce the undesirable dissociation of excitons, which in turn greatly. Type II heterojunctions are widely used for photoelectric, photocatalysis, and unipolar electronic devices (Palummo et al, 2015), with the staggered band alignment which spatially separated holes and electrons. We mainly introduce these approaches and the application of vdWHs in photoelectric and electronic devices
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