Photoluminescence from two-dimensional electron gas in modulation-doped AlxGa1−xN/GaN heterostructures

Photoluminescence (PL) of the modulation-doped Al0.22Ga0.78N/GaN heterostructures was investigated. The PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes at the heterointerfaces is located at 3.4480 eV at 40 K, which is 45.2 meV lower than that of the free excitons (FE) emission in GaN. The peak can be observed at the temperature as high as 80 K. The PL intensity is enhanced by incorporating a thin Al0.12Ga0.88N layer into the GaN layer to confine photoexcited holes inside the heterointerface region. The energy distance between the PL peak related to 2DEG and the FE emission decreases with increasing temperature. Meanwhile, the peak energy increases roughly linearly with the logarithm of the excitation intensity. They are attributed to the screening effect of electrons on the bending of the conduction band at the heterointerface, which becomes stronger when temperature or the excitation intensity is increased.