Design and growth of GaN-based blue and green laser diodes

GaN-based laser diodes (LDs) extend the wavelength of semiconductor LDs into the visible and ultraviolet spectrum ranges, and are therefore expected to be widely used in quantum technology, bio & medical instruments, laser displays, lighting and materials processing. The development of blue and green LDs is still challenging, even though they are based on the same III-nitride materials as GaN-based light-emitting diodes. The challenges and progress of GaN-based blue and green LDs are reviewed from the aspects of epitaxial growth and layer structure design. Due to large differences in lattice constants and growth conditions for InN, GaN, and AlN, considerable effort is required to improve the quality of InGaN multiple quantum well (MQW) gain medium for blue and especially green LDs. p-type doping profiles, conditions and layer structures are critical to reduce the internal losses and to mitigate the degradation of InGaN MQWs. Hole injection is also a key issue for GaN-based LDs.