Electrical Transport Properties and Ultrafast Optical Nonlinearity of rGO-Metal Chalcogenide Ensembles

In recent times, nanomaterials that harvest solar radiation and transform it into other forms of energy are of considerable interest. Herein, the electrical transport properties of reduced graphene oxide (rGO), rGO- zinc selenide (rGO-ZnSe) and rGO- zinc telluride (rGO-ZnTe) thin films have been investigated in 87 - 473K both under dark and illumination conditions. Comparative study of photosensitivity (P) and charge carrier mobility (μ), calculated using trap-free space charge limited current model, show highest values for 54 wt. % ZnSe and 50 wt. % ZnTe contents (namely sample C1 and C2), respectively. A decreasing trend in P values with increasing temperature is seen in all the samples (rGO, C1, C2) and has been attributed to enhanced electron-phonon scattering. Also, photosensitivity and change in mobility under illumination show a maximum change for C2 in the entire temperature range. The nonlinear absorption coefficient (β) of C2 is ~1.6 times higher than C1 and both the samples depict positive nonlinear refractive index when measured with 630 nm femtosecond pulses. Moreover, C2 shows two fold faster electron transfer rate as revealed by time resolved fluorescence study than C1. This, along with better dispersion of ZnTe nanoparticle in rGO matrix, explains why rGO-ZnTe have better optoelectronic properties as compared to rGO-ZnSe composite. These results in turn make rGO-ZnTe composite a promising candidate for optoelectronic as well as photonic device applications.