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