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Previously, we attempted to the optically-pumped AlGaN ultraviolet (UV) laser diodes (LDs) on AlN template on c-Sapphire substrate, using low-cost epitaxial growth technique in low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE). As a result, stimulated lasing spectra at 274 nm were observed for the first time at room temperature (RT) in the optically pumped LD. However, the electrically-pumped AlGaN-based (270–298 nm)-band UV LD was quite challenging due to both the issue of low injection current density and light confinement factor (Г). In this paper, the injection current density in the electrically pumped AlGaN UV LD at 283 nm emission was remarkably improved up to 200 kA-cm−2 by using undoped Al-graded cladding and Al-graded Mg-doped p-AlGaN hole source layer (HSL). Also, some weak oscillation at 296 nm near to the main spontaneous emission peak of 298 nm-band LD under the 600 mA (24 V) current using pulse width of 50 ns at RT was observed. To further improve the lasing phenomenon, some theoretical studies was conducted, by making the p-side waveguide (p-WG) layer non-doped (Mg = 0) and also increasing the quantum-well (QW) thickness from 2 nm to 4 nm in the multiquantum-wells (MQWs). Consequently, the optical-loss was significantly reduced from 22.7 to 8.7 cm−1 and the Г was enhanced from 1.77% (Experimental LD) to 4.65% (simulated LD). • Optically-pumped AlGaN ultraviolet (UV) laser diodes (LDs) on low-cost AlN template on c-Sapphire substrate in low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) was realized. • Stimulated lasing spectra at 274 nm were observed at room temperature (RT) in the optically pumped UV LD. • Electrically pumped UV LD was also attempted. The injection current density in the electrically pumped AlGaN UV LD at 283 nm emission was remarkably improved up to 200 kA-cm−2. • Some weak oscillation at 296 nm near the main spontaneous emission peak of 298 nm-band UV LD under injection current of 600 mA (24 V) was observed using pulse width of 50 ns at RT. • The optical-loss was significantly reduced from 22.7 to 8.7 cm−1 and light confinement factor (Г) was remarkably enhanced from 1.77% (Experimental UV LD) to 4.65% (simulated UV LD). [ABSTRACT FROM AUTHOR]

• ELO-AlN was performed by varying off-cut angle of sapphire using MOVPE. • Dislocations were reduced by increasing off-cut angle of sapphire substrate. • Increasing off-cut angle, low dislocation region of ELO became smaller. • ELO-AlN layer exhibited low dislocation density of 2.1 × 106cm−2. Using a metal–organic vapor phase epitaxy, the epitaxial lateral overgrowth (ELO) of AlN was performed by varying a vicinal off-cut angle from 0.15 to 2.0° of sapphire substrates oriented to the m -axis, i.e., the a -axis of AlN. During overgrowth, step bunching resulted in the efficient conversion of dislocations to elongated voids. The dislocations were terminated at the voids formed over the groove regions and the low and high etch pit density (EPD) regions were observed. The dislocation was reduced by increasing the off-cut angle of the sapphire substrates up to 0.8°; however, low-EPD region became small in the ELO. Thus, we have attempted to achieve a longer growth of the ELO-AlN layer on the sapphire substrate with the off-cut angle of 0.15°. As a result, the EPD decreased with the increasing thickness. The ELO-AlN layer with the thickness of 15.9 µm exhibited the EPD of 2.1 × 106 cm−2 in the low dislocation region. [ABSTRACT FROM AUTHOR]