Internal quantum efficiency (IQE) and stimulated emission properties of AlGaN-based UV-C multiple quantum wells grown on c-plane sapphire substrates were assessed using photoluminescence spectroscopy. The IQEs were estimated to be 53% at room temperature and 16% at 750 K. Furthermore, optically pumped stimulated emission was clearly observed at room temperature. The threshold excitation power densities were estimated to be 13 kW/cm2 at 10 K and 69 kW/cm2 at room temperature. The temperature dependence of the threshold excitation power density suggested that the mechanism of optical gain formation changed from excitonic transition to degenerated electron–hole plasma between 200 and 250 K.

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