Amplifying photocurrent of graphene on GeSn film by sandwiching a thin oxide between them

We report an investigation of the photoresponse of a GeSn film with a graphene layer placed on top and a thin GeO2 layer sandwiched between them. Both wavelength- and power-dependent amplification of the photocurrent are demonstrated. These results are associated with the spatial separation of photoexcited electrons and holes enabled by the thin oxide layer, where electrons and holes accumulate in graphene and the GeSn film, respectively. This spatial separation of negative and positive charges generates a mutual gating that increases the number of carriers in both layers, yielding the amplification observed in the measurement. A quantitative method based on an equivalent circuit model is provided, and the numerical results agree well with the experimental data. Our results represent an advance toward the realization of high-performance heterostructured photodetectors, and the modeling provides a framework for analyzing the photodetection capability of other two-dimensional materials on semiconductor films.