Two-Dimensional Electron Gas Recombination in Undoped AlGaN/GaN Heterostructures

The radiative recombination of a two-dimensional electron gas (2DEG) was investigated in Al_0.30Ga_0.70N/GaN single heterostructures (SHs) without intentionally doping the barrier material, i.e., where the 2DEG appears at the interface due only to polarization effects. In addition to the typical excitonic transitions and the LO-phonon replicas originating from the GaN flat-band region, the photoluminescence spectra displayed three well-defined transitions. Their small binding energies and the observed blue shift with the excitation density suggested the association of these new emissions to quasi-2D excitons. On the basis of the thermal and excitation power dependences, the transitions were assigned to interface excitonic lines. Applying a weak electric field parallel to the growth direction, which depletes the triangular well, corroborated the 2DEG nature.