We attempt to deal with the physical processes involved in the temperature-dependent photoreflectance of single AlGaAs/GaAs modulation-doped heterojunction structures. Building on the assumption that photomodulation mechanism is due chiefly to modification of the band bending in the buffer layer, we apply the Franz-Keldysh theory to simulate the temperature-dependent photoreflectance spectra of single AlGaAs/GaAs modulation-doped heterojunction structures. In view of the nonuniformity of the electric field within the buffer layer, the field profile of which is calculated through the application of self-consistent variational approach, the WKB method is used to approximate the effective change in the dielectric function. A comparison between the experimental and the simulated results attests the validity of our assumption. The effects of temperature on the electric-field strengths, estimated from the extrema of the Franz-Keldysh oscillations, can be accounted for by considering the temperature dependence of the Fermi level. (C) 1995 American Institute of Physics.