We present a deep-ultraviolet semiconductor laser diode that operates under current injection at room temperature and at a very short wavelength. The laser structure was grown on the (0001) face of a single-crystal aluminum nitride substrate. The measured lasing wavelength was 271.8 nm with a pulsed duration of 50 ns and a repetition frequency of 2 kHz. A polarization-induced doping cladding layer was employed to achieve hole conductivity and injection without intentional impurity doping. Even with this undoped layer, we were still able to achieve a low operation voltage of 13.8 V at a lasing threshold current of 0.4 A.

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Continuous-wave operation at room-temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on low-dislocation-density n-GaN substrates with a backside n-contact. The current, current density and voltage at the lasing threshold were 144 mA, 10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode with high-reflection dielectric coated mirrors. Single-transverse-mode emission was observed in the far-field pattern of the LDs and the beam full width at half power in the parallel and perpendicular directions was 6° and 25°, respectively.

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The origin of the internal loss in ridge‐type laser diodes (LDs) fabricated using selective re‐growth is investigated through a systematic device characterization and additional optical measurements. We found that the internal loss of this LD is mainly caused by the absorptive layers at the re‐growth boundary and Mg‐doped GaN layer. The internal loss can be significantly reduced through a re‐design of the LD structure to avoid these absorptive regions by shifting the perpendicular optical field to the n‐cladding side. The re‐designed LDs had a very low threshold current of 10 mA and superior gain characteristics. These results indicate, that the InGaN‐quantum‐well (QW) active layer has a large differential gain and fewer non‐radiative defects. The fabrication method of this LD, i.e. epitaxial growth on low‐dislocation‐density GaN substrates combined with a process without dry‐etching, is responsible for the high quality of the QWs.