Lasing Threshold Reduction of AlGaN-Based Ultraviolet-C Laser Diodes Using Strain Relaxed Lower Cladding Layer

The dependence of the performance of ultraviolet-C (UV-C) laser diodes on the strain relaxation of lower cladding layer (LCL) is numerically investigated. As the strain relaxation increases from 0% to 100%, the threshold current density decreases from 25 to 12.7 kA cm(-2), and the slope efficiency increases from 0.039 to 0.087 W A(-1), thanks to an increase in internal quantum efficiency (IQE). The improvement of IQE is mainly due to the enhanced hole injection resulting from the increased hole concentration in the distributed polarization doping layers and the reduced hole blocking barrier height of the upper waveguide layer with increasing the strain relaxation. Additionally, the effective screening of the polarization field within the quantum well ameliorates the quantum-confined Stark effect, further improving the IQE. Our study reveals that strain relaxed LCL is imperative to achieve low-threshold UV-C laser diodes.