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. Thi s 2DHG-2DEG system works as a p-i-n photodiode. A later al photovoltag e develops across two contacts attached to the 2DEG, when the structur e is illuminated locally. By modulating the illuminated area with resp ect to position, the differential lateral photovoltage is obtained. We present such measurements as a function of the spot position in a sam ple under quantum Hall conditions. Two-dimensional images made across large areas of the Hall bar clearly show the edge channels. The measur ements are interpreted in terms of macroscopically wide compressible s trips alternated with incompressible strips.