  Materials with in-plane electrical anisotropy have great potential for
designing artificial synaptic devices. However, natural materials with strong
intrinsic in-plane electrical anisotropy are rare. We introduce a simple
strategy to produce extremely large electrical anisotropy via grating gating of
a semiconductor two-dimensional electron gas (2DEG) of AlGaN/GaN. We show that
periodically modulated electric potential in the 2DEG induces in-plane
electrical anisotropy, which is significantly enhanced in a magnetic field,
leading to an ultra large electrical anisotropy. This is induced by a giant
positive magnetoresistance and a giant negative magnetoresistance under two
orthogonally oriented in-plane current flows, respectively. This giant
electrical anisotropy is in-situ tunable by tailoring both the grating gate
voltage and the magnetic field. Our semiconductor device with controllable
giant electrical anisotropy will stimulate new device applications, such as
multi-terminal memtransistors and bionic synapses.
