Micro-photoluminescence (PL) spectra of Si-doped GaN epilayers and three-period In0.1Ga0.9N/In0.02Ga0.98N:Si quantum-well (QW) structures were studied and compared with macro-PL spectra. The shift of the macro-PL peak with increasing Si concentration was found to be similar to that with increasing excitation density in both GaN:Si and InxGa1-xN QWs. Also, it was observed that the macro-PL intensity increased with increasing Si concentration in GaN:Si and InxGa1-xN QWs, but the micro-PL intensity was independent of doping concentration. These results indicate that the changes of PL spectra with Si doping are mainly due to the increase of carriers. © 2000 American Institute of Physics.