Enhanced Photogating Gain in Scalable MoS2 Plasmonic Photodetectors via Resonant Plasmonic Metasurfaces.

Absorption of photons in atomically thin materials has become a challenge in the realization of ultrathin, high-performance optoelectronics. While numerous schemes have been used to enhance absorption in 2D semiconductors, such enhanced device performance in scalable monolayer photodetectors remains unattained. Here, we demonstrate wafer-scale integration of monolayer single-crystal MoS2 photodetectors with a nitride-based resonant plasmonic metasurface to achieve a high detectivity of 2.58 × 1012 Jones with a record-low dark current of 8 pA and long-term stability over 40 days. Upon comparison with control devices, we observe an overall enhancement factor of >100; this can be attributed to the local strong EM field enhanced photogating effect by the resonant plasmonic metasurface. Considering the compatibility of 2D semiconductors and hafnium nitride with the Si CMOS process and their scalability across wafer sizes, our results facilitate the smooth incorporation of 2D semiconductor-based photodetectors into the fields of imaging, sensing, and optical communication applications.

Nanoscale Gap-Plasmon-Enhanced Superconducting Photon Detectors at Single-Photon Level.

With a growing demand for detecting light at the single-photon level in various fields, researchers are focused on optimizing the performance of superconducting single-photon detectors (SSPDs) by using multiple approaches. However, input light coupling for visible light has remained a challenge in the development of efficient SSPDs. To overcome these limitations, we developed a novel system that integrates NbN superconducting microwire photon detectors (SMPDs) with gap-plasmon resonators to improve the photon detection efficiency to 98% while preserving all detector performance features, such as polarization insensitivity. The plasmonic SMPDs exhibit a hot-belt effect that generates a nonlinear photoresponse in the visible range operated at 9 K (∼0.64Tc), resulting in a 233-fold increase in phonon-electron interaction factor (γ) compared to pristine SMPDs at resonance under CW illumination. These findings open up new opportunities for ultrasensitive single-photon detection in areas like quantum information processing, quantum optics, imaging, and sensing at visible wavelengths.

Oriented lateral growth of two-dimensional materials on c-plane sapphire.

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) represent the ultimate thickness for scaling down channel materials. They provide a tantalizing solution to push the limit of semiconductor technology nodes in the sub-1 nm range. One key challenge with 2D semiconducting TMD channel materials is to achieve large-scale batch growth on insulating substrates of single crystals with spatial homogeneity and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on a c-plane sapphire substrate with deliberately engineered off-cut angles. It has been postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. Here we show that a more dominant factor should be considered: in particular, the interaction of 2D TMD grains with the exposed oxygen-aluminium atomic plane establishes an energy-minimized 2D TMD-sapphire configuration. Reconstructing the surfaces of c-plane sapphire substrates to only a single type of atomic plane (plane symmetry) already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results evidence the structural uniformity of the monolayers. Our findings elucidate a long-standing question that curbs the wafer-scale batch epitaxy of 2D TMD single crystals-an important step towards using 2D materials for future electronics. Experiments extended to perovskite materials also support the argument that the interaction with sapphire atomic surfaces is more dominant than step-edge docking.

Manetoresistance of Ultralow-Hole-Density Monolayer Epitaxial Graphene Grown on SiC.

Silicon carbide (SiC) has already found useful applications in high-power electronic devices and light-emitting diodes (LEDs). Interestingly, SiC is a suitable substrate for growing monolayer epitaxial graphene and GaN-based devices. Therefore, it provides the opportunity for integration of high-power devices, LEDs, atomically thin electronics, and high-frequency devices, all of which can be prepared on the same SiC substrate. In this paper, we concentrate on detailed measurements on ultralow-density p-type monolayer epitaxial graphene, which has yet to be extensively studied. The measured resistivity ρxx shows insulating behavior in the sense that ρxx decreases with increasing temperature T over a wide range of T (1.5 K ≤ T ≤ 300 K). The crossover from negative magnetoresistivity (MR) to positive magnetoresistivity at T = 40 K in the low-field regime is ascribed to a transition from low-T quantum transport to high-T classical transport. For T ≥ 120 K, the measured positive MR ratio [ρxx(B) - ρxx(B = 0)]/ρxx(B = 0) at B = 2 T decreases with increasing T, but the positive MR persists up to room temperature. Our experimental results suggest that the large MR ratio (~100% at B = 9 T) is an intrinsic property of ultralow-charge-density graphene, regardless of the carrier type. This effect may find applications in magnetic sensors and magnetoresistance devices.