Fractional photo-current dependence of graphene quantum dots prepared from carbon nanotubes

We report on the photo-conductivity studies of chemically synthesized graphene quantum dots (GQDs) of average size 12 nm obtained by the oxidative acid treatment of MWCNTs. The dependence of photocurrent I_ph (I_ph = I_ill - I_dark) on the laser intensity P under a wide range of laser intensities (5 mW ≤ P ≤ 60 mW) shows a fractional power dependence of I_ph on light intensity. The temperature dependence (300 K < T < 50 K) of I_ph observed in thin films of these GQDs indicates that in the higher temperature region (T > ∼100 K), as the temperature increases, the number of thermally generated carriers increase resulting in increased I_ph. At sufficiently low temperatures (T ≤ 100 K), a constant I_ph is observed, indicating a constant photo-carrier density. Such a behavior is typically observed in many photoactive disordered semiconductors, which are often used in a variety of applications. We believe that the investigations presented here will enhance our understanding of the photocurrent generation phenomenon in chemically obtained GQDs.