Transport properties of graphene devices transferred to STO substrates

The effect of substrate on graphene transport properties can help us understand the scattering mechanisms relevant to its carrier mobility. Single-layer graphene is easily located on the surface of Silicon with 300nm SiO$_{2}$ using optical microscopy. We have developed a technique for wet-etching the SiO$_{2}$, peeling the device with metallic leads from the surface, and transferring it to any substrate. This technique eliminates the need to locate the graphene flake on the target substrate for aligning and patterning. A direct comparison can be made between the transport properties of graphene on SiO$_{2}$ and the target substrate. A device has been transferred to 500um and 200um thick Strontium Titanate (STO) substrates as well as 250nm thick layer of STO that has been grown epitaxially on Nb-doped STO via Pulsed Laser Deposition. The STO layer, with a higher dielectric constant than SiO$_{2}$, has a higher capacitance and produces a more effective graphene FET. A higher mobility is expected for a device on the surface of a material with a higher dielectric constant if charged impurity scattering is a primary limiting factor. The devices transferred to STO display a gate voltage dependent hysteresis in both the longitudinal and Hall resistances. However, the mobility obtained from these measurements remains the same as that of the device on SiO$_{2}$. Possible reasons for the absence of the high dielectric substrate effect on graphene carrier mobility and hysteretic behavior will be discussed.