Keywords: ion beam sputtering deposition, charge transfer, Ge QDs/graphene, first-principles calculations
Summary:The quantum dots (QDs)/graphene hybrid structure shows excellent photoresponse abilities in photodefectivity devices due to the unique QDs quantum confinement and the ultrahigh carrier mobility of graphene. Thus, this project invented the ion beam sputtering deposition technique (IBSD) to realize the directly growth of Ge quantum dots (QDs) on single-layer graphene on a SiO2/Si substrate. The morphology results illustrate that the Ge QDs size and morphology on graphene can be modulated via tuning the Ge coverage by IBSD technique. The results also indicate that increasing the sputtering time of Ge, the density of Ge dots increased, but the sizes (both diameter and height) of Ge dots tend to decrease. All morphology evolution route of Ge islands agrees well with the Zinsmeister theory. Secondly, the existence of interaction like doping effects at the interface of Ge QDs with graphene has been demonstrated. The strength of the interaction can be enhanced remarkably by reducing the Ge coverage in a certain scope, which indicates that the interaction can be modulated via controlling the coverage of Ge. The charge transfer behaviour at the interface of Ge/graphene has been demonstrated also. Comparing with traditional methods for Ge dots grown on Si substrate, the IBSD treatment changes the positions of corresponding photoluminescence (PL) peaks of Ge QDs/ graphene hybrid structure undergo a large red-shift, which was attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to the first principle calculation, the Ge growth on the graphene follows the Volmer– Weber mode instead of the traditional Ge QDs/Si system Stranski–Krastanow mode. The theoretical study also suggests that decreasing the Ge coverage enhances the interaction between Ge and graphene layer, which highly agree with the experimental results. The final products were applied in a FET photodetectors, the device demonstrates the responsivity of 4.3 AW-1 at 808nm infrared light irradiation and relatively large values (0.92) of β in absolute. The optoelectronic features indicate that the device using IBSD fabricated Ge QDs/graphene improves the efficiency of carrier transfer and overcome the limit of ligand barrier at the interface of Ge/graphene. This project supplies a new technique for fabricating hybrid nanostructure QDs/graphene for novel optoelectronic devices application.