Group III-Nitride-Based UV Laser Diodes

Recent progress in the development of deep ultraviolet lasers is reviewed as well as challenges for the heterostructure design and epitaxial growth for AlGaN-based laser diodes are discussed. The growth of AlN on sapphire and AlGaN heterostructures is reviewed and its impact on the performance characteristics of lasers in the UVC spectral range is presented. We achieve optically pumped AlGaN multiple quantum well (MQW) lasers near 270 nm with threshold power densities of less than 800 kW/cm2 and optically pumped AlGaN MQW lasers emitting at record shortest wavelength of 237 nm. We discuss critical stepping stones towards the development of current injection deep UV laser diodes including studies on Si- and Mg-doping of AlGaN with high aluminum mole fractions. n-Al0.8Ga0.2N cladding layers with resistances as low as 0.026 Ω cm are realized and UVC-transparent p-AlGaN cladding layers are developed. Finally, electroluminescence from current injection broad area UV laser diodes is demonstrated with maximum current densities of 4.7 kA/cm2. At the end, we provide an outlook of future prospect for deep UV laser diodes and discuss alternative approaches, e.g., electron beam pumping.