Interfacial charge transfer-mediated Fermi level pinning in MBE-grown 2D 2H-MoSe₂/2H-MoTe₂ heterostructures

MoSe₂ and MoTe₂ based heterostructures, owing to their remarkable photoresponsivity and tunable electrical characteristics, have emerged as promising candidates for field-effect transistors (FETs) and near-infrared (NIR) optoelectronic applications. However, the contributions of different interfacial processes impose limitations on the band tunability and carrier dynamics of the heterostructure, posing challenges in their device engineering. In this work, we present the scalable, layer-by-layer growth of a trilayer MoSe₂/MoTe₂ heterostructure over a SiO₂ substrate via molecular beam epitaxy (MBE). By leveraging the tunable probing depth of AR-XPS, we successfully resolve the interfacial bonding modifications, such as Te migration across the interface and localized Mo-Se-Te bonding. Our investigations show that these site-specific processes at the interface induce asymmetric energy level shifts, Fermi level pinning, and modulation of the valence band edge. Consequently, deviations from predicted band alignment are observed, with the Fermi level pinned around 0.58 eV above the valence band edge on the MoTe₂ side and the anomalous upshift of the valence band maximum of MoSe₂ in the heterostructure. These interfacial effects also result in a reduced barrier for hole injection, which can improve bidirectional carrier transport and gate-tunable hole conduction in such heterostructure-based devices. The findings highlight the critical role of interfacial interactions in governing band alignment of the ultrathin transition metal dichalcogenide (TMDC) heterostructures, providing key insights for advancing nanoelectronic and optoelectronic devices through heterostructure band engineering.