Reverse distribution of self-driven photocurrent response hotspots in layer-dependent MoS2 devices

In van der Waals materials, the electronic property, including the bandgap as well as the charge carrier mobility and lifetime, significantly changes as its thickness shrinks to the monolayer limit. While such characteristic brings additional freedom and convenience in regard to device design and fabrication, it also raises uncertainty in terms of the semiconductor device functionality due to the competing roles of those factors in tuning the charge carrier transport. In this work, we perform scanning photocurrent microscopy experiments on different sets of MoS2 homojunctions under zero bias voltage and show the reverse photocurrent distribution among them. Specifically, in the combination of 1L–3L MoS2, the band offset is large and thus dominates the photocarrier separation. In the combination of 3L–7L MoS2, by contrast, the effect of band offset is negligible, and the mismatch in minority carrier diffusion length takes charge of the photoresponse. The authors hope that the findings presented here offer a perspective on the current transport and thus functionality realization in layered materials.