PbS, HgCdTe, etc. [4] These materials are currently dominating the industry due to their mature technology readiness level. The high stiffness of these materials in bulk crystal or epitaxial layer form has prompted interest on low-dimensional materials for flexible photodetectors, an emerging prospective toward wearable electronics. [5,6] In order to meet with the speediness at which the present electronics industry is evolving, photodetectors featuring diverse functionalities with excellent figures of merits (high photo gain, ultrafast photoresponse, broad spectral selectivity) and facile integration with existing universal platforms like complementary metal-oxide semiconductor (CMOS) and silicon photonics, are highly desired. [7][8][9] Given the atomically thin nature, strong light-matter coupling, ultrafast carrier dynamics, flexibility, dangling bond free surface, and effective property manipulation by artificial stacking of different layered materials one over the other (called vdW stacking) without the restraints of lattice matching, 2D materials stand out as promising candidates for high performance photodetectors. During the past one decade, several 2D materials have witnessed a remarkable journey in this arena and have been the topic of several review articles. [10][11][12][13][14][15][16][17][18][19] The nearly constant light absorption in the entire electromagnetic spectrum witnessed in graphene due to gapless energy-momentum dispersion has permitted realization of first 2D material based photodetectors operating over a broad spectral range from UV to terahertz limit. [20][21][22][23] Furthermore, the high carrier mobility and associated ultrafast carrier dynamics in graphene enabled extremely fast photodetection, [24] which has been found beneficial to process images faster than existing photodetectors. [25,26] Meanwhile, layered transition metal dichalcogenides (TMDs), represented generically as MX 2 , where M is a transition metal element of groups 4-10 and X is a chalcogen atom (S, Se, Te), have become more popular due to their exotic electronic and optical properties. [27][28][29][30] In contrast to graphene, most sulfides-and selenides-based Group VI and Group VII TMDs (MoS 2 , WS 2 , ReS 2 , MoSe 2 , WSe 2 , ReSe 2 ) have a band gap covering the visible-near infrared spectral range. [31,32] For instance, the most extensively studied Group VI TMDs such as MoS 2 and WS 2 at monolayer thickness limit are direct bandgap
