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Understanding the fundamental charge carrier dynamics is of great significance for photodetectors with both high speed and high responsivity. Devices based on two-dimensional (2D) transition metal dichalcogenides can exhibit picosecond photoresponse speed. However, 2D materials naturally have low absorption, and when increasing thickness to gain higher responsivity, the response time usually slows to nanoseconds, limiting their photodetection performance. Here, by taking time-resolved photocurrent measurements, we demonstrated that graphene/MoTe2 van der Waals heterojunctions realize a fast 10 ps photoresponse time owing to the reduced average photocurrent drift time in the heterojunction, which is fundamentally distinct from traditional Dirac semimetal photodetectors such as graphene or Cd3As2 and implies a photodetection bandwidth as wide as 100 GHz. Furthermore, we found that an additional charge carrier transport channel provided by graphene can effectively decrease the photocurrent recombination loss to the entire device, preserving a high responsivity in the near-infrared region. Our study provides a deeper understanding of the ultrafast electrical response in van der Waals heterojunctions and offers a promising approach for the realization of photodetectors with both high responsivity and ultrafast electrical response.

Mix-dimensional van der Waals heterostructures (vdWHs) have inspired worldwide interests and efforts in the field of advanced electronics and optoelectronics. The fundamental understanding of interfacial charge transfer is of vital importance for guiding the design of functional optoelectronic applications. In this work, type-II 0D-2D CdSe/ZnS quantum dots/MoS2 vdWHs are designed to study the light-triggered interfacial charge behaviors and enhanced optoelectronic performances. From spectral measurements in both steady and transient states, the phenomena of suppressed photoluminescence (PL) emissions, shifted Raman signals and changed PL lifetimes provide strong evidences of efficient charge transfer at the 0D-2D interface. A series of spectral evolutions of heterostructures with various QDs overlapping concentrations at different laser powers are analyzed in details, which clarifies the dynamic competition between exciton and trion during an efficient doping of 3.9×1013 cm−2. The enhanced photoresponses (1.57×104 A·W–1) and detectivities (2.86×1011 Jones) in 0D/2D phototransistors further demonstrate that the light-induced charge transfer is still a feasible way to optimize the performance of optoelectronic devices. These results are expected to inspire the basic understanding of interfacial physics at 0D/2D interfaces, and shed the light on promoting the development of mixed-dimensional optoelectronic devices in the near future.

The development of optoelectronic devices requires breakthroughs in new material systems and novel device mechanisms, and the demand recently changes from the detection of signal intensity and responsivity to the exploration of sensitivity of polarized state information. Two-dimensional (2D) materials are a rich family exhibiting diverse physical and electronic properties for polarization device applications, including anisotropic materials, valleytronic materials, and other hybrid heterostructures. In this review, we first review the polarized-light-dependent physical mechanism in 2D materials, then present detailed descriptions in optical and optoelectronic properties, involving Raman shift, optical absorption, and light emission and functional optoelectronic devices. Finally, a comment is made on future developments and challenges. The plethora of 2D materials and their heterostructures offers the promise of polarization-dependent scientific discovery and optoelectronic device application.