  We study the lateral tunneling through the gate-voltage-controlled barrier,
which arises as a result of partial elimination of the donor layer of a
heterostructure along a fine strip using an atomic force microscope, between
edge channels at the depletion-induced edges of a gated two-dimensional
electron system. For a sufficiently high barrier a typical current-voltage
characteristic is found to be strongly asymmetric and include, apart from a
positive tunneling branch, the negative branch that corresponds to the current
overflowing the barrier. We establish the barrier height depends linearly on
both gate voltage and magnetic field and we describe the data in terms of
electron tunneling between the outermost edge channels.
