Reduction of Threshold Current in Deep-ultraviolet Laser Diodes With a Lattice-matched Waveguide Layer

The waveguide layer of deep-ultraviolet laser diodes (DUV LDs) can utilize the refractive index difference between itself and the active region material to confine light within the LD's resonant cavity and sustain laser oscillation. However, the injection current can diffuse laterally within the waveguide layer instead of being effectively confined to the active region. This lateral current spreading reduces the carrier density in the active region. Furthermore, defects or impurities in the waveguide layer can introduce non-radiative recombination centers, leading to additional carrier loss and a decrease in LD efficiency. Therefore, this study proposes a p -type waveguide layer ( p -WG) with a tapered AlN composition. This design introduces bulk polarization charges to mitigate the polarization electric field and achieves better lattice matching with the adjacent layers. It reduces carrier accumulation in the waveguide region, improves carrier transport, and promotes more efficient carrier injection into the quantum wells. Additionally, the tapered p -WG increases the refractive index near the active region. This enhances the optical confinement, reduces photon leakage, improves the optical confinement factor, and consequently lowers the threshold current of the LD. This study also compares the inverse tapered p -WG with the traditional p -WG structure. The threshold current of the structure is reduced to 203.4 mA, and the optical confinement factor is increased to 6.03%.