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Despite the broadband response, limited optical absorption at a particularwavelength hinders the development of optoelectronics based on Dirac fermions.Heterostructures of graphene and various semiconductors have been explored forthis purpose, while non-ideal interfaces often limit the performance. Thetopological insulator is a natural hybrid system, with the surface stateshosting high-mobility Dirac fermions and the small-bandgap semiconducting bulkstate strongly absorbing light. In this work, we show a large photocurrentresponse from a field effect transistor device based on intrinsic topologicalinsulator Sn-Bi1.1Sb0.9Te2S. The photocurrent response is non-volatile andsensitively depends on the initial Fermi energy of the surface state, and itcan be erased by controlling the gate voltage. Our observations can beexplained with a remote photo-doping mechanism, in which the light excites thedefects in the bulk and frees the localized carriers to the surface state. Thisphotodoping modulates the surface state conductivity without compromising themobility, and it also significantly modify the quantum Hall effect of thesurface state. Our work thus illustrates a route to reversibly manipulate thesurface states through optical excitation, shedding light into utilizingtopological surface states for quantum optoelectronics.

Reversible Engineering of Topological Insulator Surface State Conductivity through Optical Excitation