  We report on experimental evidence of directed electron transport, induced by
external linear-polarized microwave irradiation, in a two-dimensional
spatially-periodic asymmetrical system called ratchet. The broken spatial
symmetry was introduced in a high mobility two-dimensional electron gas based
on AlGaAs/GaAs heterojunction, by patterning an array of artificial
semi-discs-shaped antidots. We show that the direction of the transport is
efficiently changed by microwave polarization. The dependence of the effect on
magnetic field and temperature is investigated. This represents a significant
step towards the realization of new microwave detectors and current generators.
