Modulated interlayer charge transfer dynamics in a monolayer TMD/metal junction

The performance of optoelectronic devices based on monolayer transition-metal dichalcogenide (mTMD) semiconductors is significantly affected by the contact at the mTMD-metal interface, which is dependent on interlayer interactions and coupling. Here, we report a systematic optical method to investigate the interlayer charge transfer and coupling in a mTMD-metal heterojunction. Giant photoluminescence (PL) quenching was observed in a monolayer MoS ₂ /Pd (1L MoS ₂ /Pd) junction which is mainly due to the efficient interlayer charge transfer between Pd and MoS ₂ . 1L MoS ₂ /Pd also exhibits an increase in the PL quenching factor (η) as the temperature decreases, due to a reduction of the interlayer spacing. Annealing experiments were also performed which supported interlayer charge transfer as the main mechanism for the increase of η. Moreover, a monolayer MoS ₂ /Au (1L MoS ₂ /Au) junction was fabricated for engineering the interlayer charge transfer. Interestingly, a narrowing effect of the full width at half maximum (FWHM) was encountered as the junctions changed from 1L MoS ₂ /SiO ₂ → 1L MoS ₂ /Au → 1L MoS ₂ /Pd, possibly originating from a change of the doping level induced weakening of exciton-carrier scattering. Our results deepen the understanding of metal-semiconductor junctions for further exploring fundamental phenomena and enabling high-performance devices using mTMD-metal junctions.