Graphene Double-Layer Heterostructure Photodetectors with Broadband, High and Fast Responsivity at Room Temperature*

The hybrid semiconductor/graphene photodetectors have been intensively investigating due to their applications ranging from imaging, sensing to communications in the infrared region. Integration of colloidal semiconductor quantum dots with graphene can increase the responsivity of such photodetectors. However, the response time is in millisecond to second scale, caused by optical traps at interfaces between semiconductor quantum dots and graphene. Another limitation is that the operation bandwidth still has not expanded beyond near-infrared region due to the bandgap of semiconductor quantum dots. Here, we report photodetectors based on two graphene single-layers separated by a 5-nm Ti₂O₃ thin-film engineered by the e-beam evaporation method. The Ti₂O₃ barrier is utilized as a tunneling charge transport channel between two graphene layers to reduce the charge recombination, and also as a mean for light absorber. Our devices show a high responsivity together with a fast response time in the nano-second scale, and a broadband spectral response at room temperature.