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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., Peer Reviewed, Postprint (author's final draft)

The large diversity of applications in our daily lives that rely on photodetection technology requires photodetectors with distinct properties. The choice of an adequate photodetecting system depends on its application, where aspects such as spectral selectivity, speed, and sensitivity play a critical role. High-sensitivity photodetection covering a large spectral range from the UV to IR is dominated by photodiodes. To overcome existing limitations in sensitivity and cost of state-of-the-art systems, new device architectures and material systems are needed with low-cost fabrication and high performance. Low-dimensional nanomaterials (0D, 1D, 2D) are promising candidates with many unique electrical and optical properties and additional functionalities such as flexibility and transparency. In this Perspective, the physical mechanism of photo-FETs (field-effect transistors) is described and recent advances in the field of low-dimensional photo-FETs and hybrids thereof are discussed. Several requirements for the channel material are addressed in view of the photon absorption and carrier transport process, and a fundamental trade-off between them is pointed out for single-material-based devices. We further clarify how hybrid devices, consisting of an ultrathin channel sensitized with strongly absorbing semiconductors, can circumvent these limitations and lead to a new generation of highly sensitive photodetectors. Recent advances in the development of sensitized low-dimensional photo-FETs are discussed, and several promising future directions for their application in high-sensitivity photodetection are proposed., Peer Reviewed, Postprint (author's final draft)

Semiconducting, two-dimensional molybdenum disulfide (MoS2) is considered a promising new material for highly sensitive photodetection, because of its atomically thin profile and favorable bandgap. However, reported photodetectors to date show strong variation in performance due to the detrimental and uncontrollable effects of environmental adsorbates on devices due to large surface to volume ratio. Here, we report on highly stable and high-performance monolayer and bilayer MoS2 photodetectors encapsulated with atomic layer deposited hafnium oxide. The protected devices show enhanced electronic properties by isolating them from the ambience as strong n-type doping, vanishing hysteresis, and reduced device resistance. By controlling the gate voltage the responsivity and temporal response can be tuned by several orders of magnitude with R ∼ 10–104 A/W and t ∼ 10 ms to 10 s. At strong negative gate voltage, the detector is operated at higher speed and simultaneously exhibits a low-bound, record sensitivity of D* ≥ 7.7 × 1011 Jones. Our results lead the way for future application of ultrathin, flexible, and high-performance MoS2 detectors and prompt for further investigation in encapsulated transition metal dichalcogenide optoelectronics., Peer Reviewed, Postprint (author's final draft)

High-sensitivity photodetection is at the heart of many optoelectronic applications, including spectroscopy, imaging, surveillance, remote sensing and medical diagnostics. Achieving the highest possible sensitivity for a given photodetector technology requires the development of ultra-small-footprint detectors, as the noise sources scale with the area of the detector. This must be accomplished while sacrificing neither the optically active area of the detector nor its responsivity. Currently, such designs are based on diffraction-limited approaches using optical lenses. Here, we employ a plasmonic flat-lens bull’s eye structure (BES) to concentrate and focus light into a nanoscale colloidal quantum dot (CQD) photodetector. The plasmonic lenses function as nanofocusing resonant structures that simultaneously offer color selectivity and enhanced sensitivity. Herein, we demonstrate the first CQD photodetector with a nanoscale footprint, the optically active area of which is determined by the BES; this detector represents an exciting opportunity for high-sensitivity sensing., Peer Reviewed, Postprint (published version)