Efficient ReSe₂ Photodetectors with CVD Single-Crystal Graphene Contacts

Rhenium-based 2D transition metal dichalcogenides such as ReSe₂ are suitable candidates as photoactive materials for optoelectronic devices. Here, photodetectors based on mechanically exfoliated ReSe₂ crystals were fabricated using chemical vapor deposited (CVD) graphene single-crystal (GSC) as lateral contacts. A "pick & place" method was adopted to transfer the desired crystals to the intended position, easing the device fabrication while reducing potential contaminations. A similar device with Au was fabricated to compare contacts' performance. Lastly, a CVD hexagonal boron nitride (hBN) substrate passivation layer was designed and introduced in the device architecture. Raman spectroscopy was carried out to evaluate the device materials' structural and electronic properties. Kelvin probe force measurements were done to calculate the materials' work function, measuring a minimal Schottky barrier height for the GSC/ReSe₂ contact (0.06 eV). Regarding the electrical performance, I-V curves showed sizable currents in the GSC/ReSe₂ devices in the dark and under illumination. The devices presented high photocurrent and responsivity, along with an external quantum efficiency greatly exceeding 100%, confirming the non-blocking nature of the GSC contacts at high bias voltage (above 2 V). When introducing the hBN passivation layer, the device under white light reached a photo-to-dark current ratio up to 10⁶.