Electroreflectance spectroscopy is applied to reexamine the theoretical model which has been devised to explicate the temperature-dependent photoreflectance spectra of single AlxGa1-xAs/GaAs modulation-doped heterojunctions. Building on the presumption that the modulation mechanism is mainly due to the electromodulation of the band bending in the buffer layer, we apply the Franz-Keldysh theory to simulate the photoreflectance and electroreflectance spectra at room temperature. As the sample temperature is decreased to 10 K in the photoreflectance experiment, there appears a large number of oscillations extending for more than ten periods. This phenomenon manifests existence of a fairly uniform electric field in the buffer layer.
