Radiative recombination between two dimensional electron gas and photoexcited holes in modulation-doped Al_xGa_(1-x)N/GaN heterostructures

摘要

Photoluminescence (PL) of modulation-doped Al_(0.22)Ga_(0.78)N/GaN heterostructures was investigated. The PL peak related to recombination between the two-dimensional electron gases (2DEG) and photoexcited hoes is located at 3.448 keV at 4K, which is 45 meV below the free excitons (FE) emission in GaN. The peak can be observed at temperatures as high as 80 K. The intensity of the 2DEG PL peak is enhanced sgnificantly by incorporating a thin Al(0.12)Ga_(0.88)N layer into the GaN layer near the heteroninterface to suppress the diffusion of photexcited holes. The energy separation of the 2DEG peak and the GaN FE emission decreases with increasing temperature.Meanwhile, the 2DEG peak energy increases with increasing excitation intentsity. These results arre attributed to the screening effect of electrons on the bending of the conduction band at the heterointerface, which becomes stronger when temperature or excitation intensity is increased.