Photocarrier generation mechanism of graphene-based field effect device

The carrier generation in a photodetecting device plays a critical role in the enhancement of photocurrent. Here we perform photocurrent measurements on graphene-based photodetecting device and unveil three carrier generation mechanisms, namely, (I) thermally assisted- and (II) optically induced- excitation of in-gap defect state electron, and (III) inter-band optical absorption of bulk Si. We further determine their carrier supply strength defined as P = dn/dt, which are P(I) = 2.09×10¹⁰ /cm⋅2 s, P(II) = 2.15×10¹⁰ /cm⋅2s, and P(III) = 3.55×10¹¹ /cm⋅2s, respectively. In addition, we show that the characteristic IV behavior induced by the gate voltage cycling can be interpreted in terms of the three carrier generation mechanisms. This study provides a useful guide to designing practical graphene-based photodetecting devices.