  We show that the resonant tunnel current through a single energy level of an
individual quantum dot within an ensemble of dots is strongly sensitive to
photoexcited holes that become bound in the close vicinity of the dot. The
presence of these holes lowers the electrostatic energy of the quantum dot
state and switches the current carrying channel from fully open to fully closed
with a high on/off ratio (> 50). The device can be reset by means of a bias
voltage pulse. These properties are of interest for charge sensitive photon
counting devices.
