  The Teraherz (THz) photoresponse of a two-dimensional electron gas in the
quantum Hall regime is investigated. We use a sample structure which is
topologically equivalent to a Corbino geometry combined with a cross-gate
technique. This quasi-Corbino geometry allows us to directly investigate the
THz-induced transport between adjacent edge-states, thus avoiding bulk effects.
We find a pronounced photo voltage at zero applied bias, which rapidly
decreases when an external current bias is applied. The photo voltage and its
dependence on the bias current can be described using the model of an
illuminated photodiode, resulting from the reconstruction of the Landau bands
at the sample edge. Using the sample as a detector in a Fourier transform
spectrometer setup, we find a resonant response from which we extract a reduced
effective cyclotron mass. The findings support a non-bolometric mechanism of
the induced photo voltage and the proposed edge-channel diode model.
