Photoluminescence Excitation Spectroscopy of Stimulated Emission from AlGaN‐Based Multiple Quantum Wells with an Emission Wavelength Around 280 Nm

Stimulated emission properties of AlGaN‐based multiple quantum wells with an emission wavelength of about 280 nm are studied by photoluminescence excitation (PLE) spectroscopy. The excitation power density dependence of the PLE spectra is evaluated at excitation energies from 4.4788 to 4.6293 eV, which allows the spontaneous and stimulated emission PLE spectra to be obtained. A clear peak is observed in the PLE spectrum for spontaneous emission, indicating that the spontaneous emission is due to the excitonic optical transition. A clear peak is also observed in the PLE spectrum for stimulated emission, suggesting that excitons are involved in the stimulated emission process. Furthermore, the threshold excitation power density for stimulated emission is analyzed as a function of the excitation energy and the threshold excitation power density depends on the excitation energy. The excitation energy at which the threshold excitation power density is minimized agrees with the peak of the stimulated emission PLE spectrum. This observation directly indicates that excitons are important in optical gain formation.