Silicon- and oxygen-codoped graphene from polycarbosilane and its application in graphene/n-type silicon photodetectors

Properties of graphene can be modified by doping heteroatoms. Here we report the synthesis of a monolayer of silicon- and oxygen-codoped graphene (SiOG) using polycarbosilane as both the C and Si sources in a thermal chemical vapor deposition process and compare the SiOG with primitive graphene (PG). Composition and structure of the PG and SiOG are analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The SiOG produced from polycarbosilane has a ratio of [Si] to [Si]+[C] of 8.9%. Meanwhile, doping Si forms SiC and CSiO bonds in graphene. Doping Si in graphene also introduces a defective structure in the graphene lattice. Graphene/Si Schottky diodes are prepared for performance comparison. Doping Si increases the barrier height of the graphene/Si Schottky diodes from 0.76 eV to 0.78 eV and changes the ideal factor from 3.8 to 2.8. The graphene/Si photodetectors are self-powered under UV irradiation. The ON/OFF ratios in 0.3 mW cm-2 of 365 nm light at a zero bias voltage are respectively 3500 and 7600, and the rise times/fall times are respectively 11.6 ms/53.6 ms and 4.8 ms/14.3 ms for the PG/Si and SiOG/Si photodetectors. The relatively better performance of the SiOG/Si over PG/Si in UV sensing is possibly due to the lowering of the Fermi level of graphene by incorporation of Si and O.