Realizing high injection current density up to 200 kA-cm-2 in electrically pumped AlGaN ultraviolet laser diodes on c-Sapphire substrate

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 (Gamma). 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 Gamma was enhanced from 1.77% (Experimental LD) to 4.65% (simulated LD).

Automated summary

This paper reports on the improvement of electrically-pumped AlGaN UV LD performance by modifying the structure and adding materials. By using specific cladding and doping materials, the injection current density was increased, and weak oscillation was observed near the main spontaneous emission peak. Further theoretical studies showed that changing the waveguide layer material and quantum well thickness can significantly reduce optical-loss and increase the Gamma value.