Electrical and optical analysis of $MoTe_2$/Graphene heterostructure

Abstract

Graphene has been focused as an attractive candidate for future optoelectronic applications due to their high electric conductivity, excellent optical transparency, and extremely thin layered structure. Nevertheless, short carrier lifetime and weak absorption limit the photo-responsivity up to the range of a few mA/W. To overcome this advantages, heterostructures of graphene with 2D semiconductors have been reported. $MoTe_2$, one of the 2D semiconductors, is favorable to NIR range photo-detecting due to its small bandgap (0.9~1.1 eV). The major advantage of $MoTe_2$/Graphene photodetectors is carrier injection from $MoTe_2$ to graphene, while opposite carrier remains trapped in the $MoTe_2$ layer. Injected carriers are moved through the graphene which has high carrier mobility. In this study, $MoTe_2$ was transferred on monolayer dry-transferred graphene with pick-up transfer method. Source/Drain was contacted only graphene channel and $MoTe_2$ was fitted with graphene precisely. The fabricated $MoTe_2$/Graphene phototransistor showed high photo-responsivity (~40 A/W @ 10 nW) which compared with a silicon-based photodetector. In addition, it was observed photocurrent polarity change occurs with increasing laser intensity. For figuring out the reason of phenomenon, some variables were removed with measurement and analyzing. Furthermore, the phase transition of $MoTe_2$ was observed by Raman measurement with drain bias. In short, photocurrent polarity change was analyzed and it was verified that this phenomenon is related to the phase transition of $MoTe_2$. Consequently, this phase-transition-originated photocurrent polarity change is expected to be applied to a future memory device, sensor and optoelectronic devices.