Picosecond photoresponse in van der Waals heterostructures

摘要

Two-dimensional (2D) crystals, such as graphene and transition metaldichalcogenides (TMDs), present a collection of unique and complementaryoptoelectronic properties. Assembling different 2D materials in verticalheterostructures enables the combination of these properties in one device,thus creating multi-functional optoelectronic systems with superiorperformance. Here we demonstrate that graphene/WSe2/graphene heterostructuresally the high photodetection efficiency of TMDs with a picosecond photoresponsecomparable to that of graphene, thereby optimizing both speed and efficiency ina single photodetector. We follow in time the extraction of photoexcitedcarriers in these devices using time-resolved photocurrent measurements anddemonstrate a photoresponse time as short as 5.5 ps, which we tune by applyinga bias and by varying the TMD layer thickness. Our study provides directinsight into the physical processes governing the detection speed and quantumefficiency of these van der Waals (vdW) heterostuctures, such as out-of-planecarrier drift and recombination. The observation and understanding of ultrafastand efficient photodetection demonstrate the potential of hybrid TMD-basedheterostructures as a platform for future optoelectronic devices.