Band structure engineering for efficient hole injection in a laser diode through a polarization-assisted hole injection layer of AlGaN

Achieving efficient hole injection remains a fundamental challenge in AlGaN-based ultraviolet (UV) laser diodes (LDs) due to the poor hole transport characteristics of Al-rich AlGaN materials. In this work, we present a numerical simulation study of a six-layer AlGaN LD structure incorporating a Mg-doped distributed p-type polarization-assisted (p-PA) hole injection layer (HIL) to address this limitation. Using SiLENSe™ drift–diffusion simulations, we systematically investigate the effect of Al composition gradient within the p-PA HIL layer on optical gain, far-field radiation patterns, band structure, hole concentration, and current density characteristics. Our results demonstrate that the p-PA HIL (1–0) (composition grading from the Al-rich side (normalized Al composition = 100%) to the Ga-rich side (normalized Al composition = 0 %) p-PA HIL configuration yields the highest peak net optical gain of 5.3 × 10 3 cm⁻ 1 at 4.8 eV and the most favorable far-field emission pattern, with superior transverse-electric (TE) mode. Under forward bias, a minimum Al composition gradient of 1.0–0.7 (composition grading from the Al-rich side (normalized Al composition = 100 % to the Ga-rich side (normalized Al composition = 70 %) in p-PA HIL is required to achieve a current density of 10 kA/cm 2 , highlighting the critical role of polarization-induced electric fields in driving drift-dominated hole transport. Band structure analysis reveals that Mg-doping in the p-PA HIL reduces local barrier width near the waveguide interface, enhancing hole injection under applied bias. In addition, hole mobility is identified as a key performance-limiting parameter, with device performance improving monotonically from μ h = 1 to 5 cm 2 /V.s. These findings offer design guidelines for band structure engineering through distributed p-PA HIL to achieve high-performance AlGaN UV LD.