Enhanced Static and Dynamic Performance for GaN-Based VCSELs With ITO/p-GaN Resistive Current Injection Structure

In this study, we develop advanced numerical models to comprehensively investigate the static and dynamic performances for GaN-based vertical cavity surface emitting lasers (VCSELs) with optimized current injection efficiency. We propose using indium tin oxide (ITO) instead of SiO₂ as the current confinement layer. The ITO/p-GaN forms a resistive junction, which improves hole injection efficiency and suppresses the hole leakage out of the aperture for GaN-based VCSELs. The ITO/p-GaN design eliminates the capacitance arising from the SiO₂, and the VCSELs can be stabilized within a reduced time upon being turned on. We have also found that the defects on the recessed p-GaN region have significant impact on the static and dynamic characteristics for the proposed VCSELs, such that the surface defects generate charging/discharging processes. This may cause very significant laser power oscillation before the device is stabilized. As a result, we investigate the impact of defect density and defect energy levels on the device performances. We find that, besides decreasing the defect density, defects with shallow energy level may also have strong impact on delaying the device stabilization process. In order to suppress the defect-induced capturing effect for injected holes, we then design u-AlGaN/p-GaN/u-AlGaN/p-GaN so that the hetero-junctions can spread the current into the aperture center. This favors the hole to be apart from the surface defects, which enables the increased hole injection. Therefore, the designed VCSELs will reduce the oscillation duration before reaching the stabilized on-state.