IMAGING OF EDGE CHANNELS IN THE INTEGER QUANTUM HALL REGIME BY THE LATERAL PHOTOELECTRIC EFFECT

We have studied experimentally the widths and positions of edge channe ls in an inhomogeneous two-dimensional electron gas (2DEG) under quant um Hall conditions. The locations and widths of the edge channels are controlled by a low mobility two-dimensional hole gas (2DHG) in betwee n the GaAs substrate and the 2DEG, which acts as an interior gate. Add itionally, this 2DHG-2DEG system actually behaves like a p-i-n photodi ode: a lateral photovoltage develops across two contacts attached to t he 2DEG when the structure is illuminated locally. By modulating the i lluminated area with respect to position, the differential lateral pho tovoltage is obtained. We present measurements of the differential lat eral photovoltage as a function of the spot position in a sample under quantum Hall conditions. Two-dimensional images made across large are as of the Hall bar clearly show the edge channels. The measurements ar e interpreted as macroscopically wide compressible strips alternated w ith incompressible strips.