Stimulated emission mechanism of aluminum nitride

Photoluminescence and stimulated emission spectroscopies were performed on transparent aluminum nitride (AlN) substrates grown by hydride vapor-phase epitaxy. The stimulated emission was observed from cryogenic to room temperatures and its origin was assigned on the basis of the spontaneous emission spectra and existing theories. Two stimulated emission mechanism crossovers were also found. One was a temperature-induced crossover from a purely excitonic mechanism to a carrier-involved mechanism, which is a universal behavior in semiconducting materials. The other was an excitation-power--induced crossover from an exciton--exciton scattering mechanism to a phonon-mediated mechanism, which is a unique behavior attributed to the peculiar excitonic structure (negative crystal-field splitting and positive electron--hole exchange interaction energies) of AlN.