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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]

Nonradiative recombination (NRR) processes through defect states and their temperature dependence in UV-B AlGaN MQW sample on sapphire substrate grown by MOCVD technique have been studied by photoluminescence (PL) spectroscopy. We detected NRR centers by adding a below-gap excitation light with photon energies from 0.93 eV to 1.46 eV on an above-gap excitation light of 4.66 eV. All the BGE energies decreased PL intensity at 25 K, and the most-distinct quenching is observed by 1.27 eV BGE at the same BGE photon number density. The temperature-dependent PL intensity for the BGE energy of 1.27 eV is interpreted by three NRR centers. The one-level model dominates over that of two-level model in the temperature range 58 K < T < 88 K. The two-level model prevails in other region of temperature. The combination of one-level and two-level models is consistent with the spectral peak-energy shift as a function of temperature. • Investigates NRR processes in UV-B AlGaN MQW by adding below-gap excitation light. • Detects NRR centers by observing PL-intensity change due to below-gap excitation. • Identifies correlation of T -dependent NRR processes with T -dependent PL peak-energy. • Interpret T -dependent NRR processes by a model based on SRH statistics. [ABSTRACT FROM AUTHOR]