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.