  Electrical field and light-illumination have been two most widely used
stimuli in tuning the conductivity of semiconductor devices. Via capacitive
effect electrical field modifies the carrier density of the devices, while
light-illumination generates extra carriers by exciting trapped electrons into
conduction band1. Here, we report on an unexpected light illumination enhanced
field effect in a quasi-two-dimensional electron gas (q2DEG) confined at the
LaAlO3/SrTiO3 (LAO/STO) interface which has been the focus of emergent
phenomenon exploration2-14. We found that light illumination greatly
accelerates and amplifies the field effect, driving the field-induced
resistance growth which originally lasts for thousands of seconds into an
abrupt resistance jump more than two orders of magnitude. Also, the
field-induced change in carrier density is much larger than that expected from
the capacitive effect, and can even be opposite to the conventional
photoelectric effect. This work expands the space for novel effect exploration
and multifunctional device design at complex oxide interfaces.
