Ultralow threshold powers for optical pumping of homoepitaxial InGaN/GaN/AlGaN lasers

We report ultralow threshold powers for optically pumped laser emission from InGaN/GaN/AlGaN laser structures grown on bulk GaN substrates. The threshold powers at room temperature (for excitation with 355 nm third harmonic of Nd:YAG laser) are between 2.4 and 5.8 kW/cm2, depending on a cavity length. We believe that this is the consequence of a significant reduction of concentration of nonradiative centers in the active layer of homoepitaxial structures. We report also that spacing of the longitudinal laser modes exceeds by a factor of 6–7 the values predicted from the standard calculations.