Photoluminescence and reflectance spectroscopy of excitonic transitions inhigh-quality homoepitaxial GaN films

We report on highly resolved photoluminescence (PL) and reflectance (RF) sp ectra of a homoepitaxial GaN layer grown by metal-organic vapor phase epita xy. This sample exhibits narrow linewidths of several PL emission peaks, do wn to approximate to 100 mu eV full width at half maximum for some bound ex citon transitions. As a consequence, we have detected new PL features as, e .g., a fivefold fine structure of the donor-bound exciton line at approxima te to 3.471 eV, and other known PL transitions could be determined with hig h precision. In RF measurements, the extraordinary quality of the epitaxial layer allowed observation of weakly damped excitonic groundstate transitio ns and of narrow excited exciton transitions with high signal-to-noise rati o. [S0163-1829(99)14027-X].