Ultraviolet semiconductor laser diodes on bulk AlN

Current-injection ultraviolet lasers are demonstrated on low-dislocation-density bulk AlN substrates. The AlGaInN heterostructures were grown by metalorganic chemical vapor deposition. Requisite smooth surface morphologies were obtained by growing on near-c-plane AlN substrates, with a nominal off-axis orientation of less than 0.5°. Lasing was obtained from gain-guided laser diodes with uncoated facets and cavity lengths ranging from 200 to 1500 μm. Threshold current densities as low as 13 kA/cm2 were achieved for laser emission wavelengths as short as 368 nm, under pulsed operation. The maximum light output power was near 300 mW with a differential quantum efficiency of 6.7%. This (first) demonstration of nitride laser diodes on bulk AlN substrates suggests the feasibility of using such substrates to realize nitride laser diodes emitting from the near to deep ultraviolet spectral regions.