PtSe<sub>2</sub>/MoSe<sub>2</sub> heterojunction: Unconventional type-V band alignment and its stability under various physical field coupling
Abstract
<p indent="0mm">The van der Waals heterojunction is a research frontier and hotspot in 2D materials, especially for its band alignment method, which determines the essential electronic behaviors. Using a first-principles approach based on density functional theory, the structural stability and electronic properties of PtSe<sub>2</sub>/MoSe<sub>2</sub> heterojunctions are systematically studied. The calculated binding energy and phonon spectrum, molecular dynamics simulations, and study on mechanical properties show that the PtSe<sub>2</sub>/MoSe<sub>2</sub> heterojunction is highly stable, thus, its experimental fabrication might be feasible. Interestingly, we find that such a heterojunction features a special type-V band alignment, which is different from the numerous heterojunctions studied so far. This is because there exists an interlayer coupling between the Se-<italic>p</italic><sub>z</sub> and Mo-<inline-formula id="INLINE41"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub other="0"><mml:mi other="0">d</mml:mi><mml:mrow other="1"><mml:msup other="1"><mml:mtext other="1">z</mml:mtext><mml:mn other="2">2</mml:mn></mml:msup></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> orbits in the MoSe<sub>2</sub> layer and the Se-<italic>p</italic><sub>z</sub> orbit in the PtSe<sub>2</sub> layer, perpendicularly to the 2D interface and with similar energies, which induces delocalized VBM (valance band maximum) hybrid states. In addition, we also test the stability of this type-V band alignment under the coupling of various physical fields (external electric field, strain), we find that the VBM and CBM (conduction band minimum) of heterojunctions have completely different responses to the external physical field. At smaller negative electric fields and over the entire range of positive electric fields, or under smaller vertical stretching and over the entire range of vertical compressive strain, the VBM maintains stronger orbital coupling, which is not eliminated by physical field effects, resulting in synchronous unconventional movement of the VBM states in the PtSe<sub>2</sub> and MoSe<sub>2</sub> layers, so that the heterojunction always maintains a type-V band alignment. This novel unconventional band alignment and high stability have great potential for the development of high-performance PtSe<sub>2</sub>/MoSe<sub>2</sub> heterojunction-based optoelectronic devices.</p>
