Magnetospectroscopy of shallow donors in two dimensions in the presence of fluctuations of the electrostatic potential

Spectroscopy of shallow donors is a tool to test theoretical models and to reveal properties of semiconductors. In this work we consider intra-shallow impurity transitions by studying a CdTe/(Cd, Mg)Te structure grown by a molecular beam epitaxy in which both a CdTe quantum well and (Cd, Mg)Te barries are uniformly doped with iodine donors. Measurements of a photocurrent (PC) at the far-infrared were carried out at 4.2 K and magnetic fields B up to 7 T with the energy of photons originated from a molecular laser in the range 2.2 meV-12.8 meV. Spectra (a PC signal vs. B, at a constant energy of photons) show lines which position does not depend on the photon energy but shifts with the in-plane electric field. These dependencies, which do not follow a well-established picture of shallow donor magnetospectroscopy in quantum wells, are explained within a model which unifies the role of fluctuations of the electrostatic potential and a magnetic-field induced electron localization.