Interface Engineering in Hybrid Quantum Dot–2D Phototransistors

The hybridization of two-dimensional transition metal dichalcogenides (TMDCs) with colloidal quantum dots (QDs) has been demonstrated to be an ideal platform for low dark-current and highly sensitive photodetection due to a carrier recirculation mechanism producing very high gain. However, TMDCs react sensitively to surface modifications, and the sensitizing quantum dots introduce uncontrolled doping, which prevent these hybrids from reaching large on/off ratios, present in pristine 2D transistors. In this work, we report on a new hybrid device architecture with a semiconducting TiO₂ buffer layer at the interface of molybdenum disulfide (MoS₂) and lead sulfide (PbS) QDs. The buffer layer encapsulates the MoS₂ transistor and preserves the gate modulation by suppressing the high density of localized sub-band-gap states that pin the Fermi level. The maintained gate control over carrier density in the conduction channel allows for low noise operation similar to pristine MoS₂ devices. We report on effective charge transfer with a quantum efficiency of 28%, a photoconductive gain that can be tuned with gate voltage yielding a responsivity of 10³–10⁵ A/W, and a specific detectivity of 5 × 10¹² Jones, an improvement of more than 1 order of magnitude compared to MoS₂/PbS devices without a buffer layer. The present methodology discloses a new path to control interface and degenerate doping effects of 2D-crystal-based hybrid devices