  Within a quasiclassical transport theory for 2D electron system we analyze a
recently observed effect of microwave rectification at the boundary between two
2D metals of different carrier densities. Nonlinear response is employed to
explain the effect. It is shown that the effect of rectification arises due to
inhomogeneity of the electron density which breaks space symmetry of the
system. The results agree with the above experiments.
