Optical properties of bound excitons and biexcitons in GaN

Excitonic optical properties of GaN homoepitaxial layers have been studied by means of magnetoluminescence and time-resolved luminescence spectroscopy . The luminescence lines due to the radiative recombination of excitons bou nd to neutral donors and accepters have been measured under magnetic field up to 8T, which was aligned perpendicular and parallel to the hexagonal c-a xis. Under the magnetic field aligned perpendicular to the hexagonal c-axis , both the donor- and acceptor-bound-exciton lines clearly split into two c omponents. which originated from the Zeeman splitting. The effective g-fact ors for both the donor- and acceptor-bound excitons were estimated to be 2. 02 and 2.47. respectively. Under the magnetic field aligned parallel to the hexagonal c-axis, slight broadening of the bound-exciton lines was observe d and the Zeeman splitting was too small to be detected. On the other hand, the diamagnetic shift for both the donor- and acceptor-bound-exciton lumin escence lines was observed under the magnetic field aligned both perpendicu lar and parallel to the hexagonal c-axis. It was found that the diamagnetic shift of the donor-bound exciton was smaller than that of the acceptor-bou nd exciton. Furthermore, recombination dynamics of excitonic transitions wa s measured under high-density excitation. An excitation-density-dependent t ransition of the dominant radiative recombination process from donor-bound excitons to biexcitons was clearly observed in the temporal behavior. In ad dition, double-exponential decay of biexciton luminescence was observed, wh ich is one of the characteristics of biexciton luminescence at high excitat ion densities.