Impact of Al content in the n-AlGaN hole current confinement layer on the performance of GaN-based VCSELs

The impact of Al content in the AlGaN hole current confinement layer (HCCL) on the optoelectronic properties of the GaN-based blue vertical-cavity surface-emitting lasers (VCSELs) is systematically studied through numerical simulation. As the Al content in HCCL increases from 0 to 0.25, the barrier height in the valence band for holes shows a significant increase in both vertical and lateral directions, which enhances hole confinement capability and suppresses hole leak outside the aperture. These contribute to the improvement of light output power (LOP) and wall-plug efficiency (WPE), as well as the reduction in threshold current. However, the hole leakage current remains almost unchanged with further increasing Al content to 0.3 in the HCCL. An in-depth analysis of the leakage path in VCSEL confirms that the leakage current is predominantly composed of holes that bypass the HCCL, as the current flowing across the HCCL is suppressed to nearly zero. As a result, further increasing the Al content to 0.3 yields only marginal improvements in LOP and WPE, and a reduction in threshold current. To achieve an optimal trade-off between the optical and electrical performances of the VCSEL, the optimum value of Al content in HCCL is around 0.25. This work has clarified the hole leakage paths and the effectiveness of tuning Al content in AlGaN HCCL for regulating hole transport, which provides theoretical guidance for the design and optimization of high-performance GaN-based VCSELs.