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The dependence of resonator length on the threshold power and emission wavelength of electron-beam-pumped UV-A edge-type emitting lasers is demonstrated. The lowest pump power thresholds are achieved for 100-200 μm long resonators, where there is good overlap of the focused e-beam spot with the resonator cavity. For longer resonator lengths the focused circular e-beam spot excites only a segment of the resonator cavity, yet lasing is observed. Absorption of the e-beam generated photons in the un-pumped sections of the resonator results in increased absorption losses and, consequently, higher laser thresholds. In addition, a significant wavelength shift from 375 nm for the 50 μm resonators to 385 nm for the 600 μm resonators is observed due to absorption of the higher energy photons and re-emission at longer wavelengths in the un-pumped sections.

AlGaN multiple quantum well lasers for optical pumping have been grown by metal-organic vapor phase epitaxy on high and low dislocation density AlN/sapphire templates. Lasers on planar templates exhibited high dislocation densities and high V-pit densities, but a smooth surface morphology leading to inefficient, but laterally very homogeneous optical emission. Lasing was not observed when optically pumped with up to 50 MW/cm2. Epitaxially laterally overgrown templates on patterned sapphire showed much lower dislocation densities, but also step bunching on the surface. This resulted in good photoluminescence efficiencies of up to 20%, but also in a higher lateral inhomogeneity of the emission. Lasers on these templates exhibited lasing at $\sim 240$ nm with low full-width at half-maximum of 1 nm and threshold power densities of 11–15 MW/cm2.

The defect distribution in thick AlN layers obtained by epitaxial lateral overgrowth (ELO-AlN) has been analyzed as a function of the miscut direction of the patterned sapphire substrate. A 0.25° miscut toward the sapphire a -plane leads to formation of smooth ELO-AlN layers containing vertical coalescence grain boundaries and exhibiting an almost homogeneous threading dislocation (TD) distribution with a TD density ranging from 5×10 8 cm −2 to 8×10 8 cm −2 . In contrast, a 0.25° miscut toward the sapphire m -plane results in formation of periodically arranged macrosteps on the surface of the coalesced ELO-AlN layers as well as formation of inclined coalescence grain boundaries leading to an inhomogeneous TD distribution. A subsequent Al x Ga 1− x N deposition onto ELO-AlN template with surface macrosteps leads to Ga enrichment on the step sidewalls and, for lower Al-contents (e.g. x =0.5), even to additional defect formation. For higher Al contents (e.g. x =0.8) no additional threading dislocations are formed in the AlGaN layers and the observed TD density corresponds to that of the ELO-AlN template: less than 10 8 cm −2 in the wing regions and from 6×10 8 cm −2 to 9×10 8 cm −2 above the ridges. Compressive strain during growth of Al 0.8 Ga 0.2 N on ELO-AlN tends to be compensated by threading dislocation inclination. However, due to the low TD densities the inclination angles are more than 3 times larger than those observed in Al 0.8 Ga 0.2 N layers on planar AlN/sapphire templates.

Al x Ga1− x N layers with high aluminum content of x ∼ 0.68–0.73 were grown in an 11 × 2-in. AIX 2400 G3 HT planetary reactor by metal–organic vapor phase epitaxy. Growth trends are analyzed by reaction-transport modeling in a wide range of growth conditions. Gas-phase nucleation resulting in both Al and Ga consumption into nanoparticles is a major mechanism affecting the growth efficiencies of AlN and GaN. Process windows suitable to grow multiple quantum wells (MQWs) for deep UV applications are found for a range of pressures, temperatures, and V/III ratios.

The lateral near field patterns and filamentation effects of gain guided broad area (Al,In)GaN-based laser diodes emitting around 415 nm have been investigated. Diodes from the same laser bar, which are close to each other, show nearly the same number and widths of filaments. Comparison of different bars, which are from the same wafer but further apart from each other, reveals that a higher number of filaments correlates with a higher laser threshold and broader spectral linewidth. Cathodoluminescence mappings at 80 K show strong variations of the quantum well band gap and hence of the emission wavelength for the bars with strong filamentation. These observations confirm previous theoretical predictions stating that large band gap fluctuations increase the threshold current and spectral linewidth. Furthermore, filamentation is enhanced as well because of a reduction of the carrier diffusion length.