  The protected surface conduction of topological insulators is in high demand
for the next generation of electronic devices. What is needed to move forward
are robust settings where topological surface currents can be controlled by
simple means, ideally by the application of external stimuli. Surprisingly,
this direction is only little explored. In this work we demonstrate that we can
boost the surface conduction of a topological insulator by both light and
electric field. This happens in a fully controlled way, and the additional
Dirac carriers exhibit ultra-long lifetimes. We provide a comprehensive
understanding, namely that carriers are injected from the bulk to the surface
states across an intrinsic Schottky barrier. We expect this mechanism to be at
play in a broad range of materials and experimental settings.
