UC Santa Barbara

The III-Nitride edge-emitting laser diode (LD) shows promise in diverse applications such as directed illumination e.g. automotive and spot lighting, communication e.g. Li-Fi communication, fundamental science, and others. While significant recent progress has been made in improving the efficiency of the III-Nitride edge-emitting LD, continuing progress must be made for it to become and remain competitive in these applications. The tunnel junction (TJ) presents unique design opportunities for many III-Nitride devices, including in edge-emitting LDs where it is most often used as a substitute p-side contact that in principle allows p-type material on one side of the TJ to be replaced with less absorbing and more conductive n-type material on the other side. However, the TJ presents challenges in p-type GaN activation, where typical metal-organic chemical vapor deposition (MOCVD) growth conditions are known to introduce hydrogen and re-passivate p-type material. The TJ presents additional challenges in absorption, where the highly-doped layers of the TJ can contribute significant optical absorption loss to LDs, reducing device efficiencies. Both of these challenges must be addressed for the tunnel junction to be a part of viable III-Nitride edge-emitting LD designs.

In this work, we demonstrate high-power LDs using TJ contacts grown by molecular beam epitaxy (MBE), which preserves p-GaN activation, and we also demonstrate LDs using TJ contacts grown by MOCVD that employ a p-GaN activation scheme utilizing lateral diffusion of hydrogen through the LD ridge sidewalls. Next, we model the lasing mode and internal optical absorption loss profiles of III-Nitride edge-emitting LD designs using the transfer matrix method and identify new designs showing reduced modeled internal optical absorption loss in III-Nitride edge-emitting LDs using TJ contacts. Last, LDs using TJ contacts and distributed feedback (DFB) gratings in tandem are designed and evaluated in a joint film mode matching-analytical model, showing the tunnel junction facilitates DFB LD designs with higher-order gratings, benefiting fabrication tolerances and complexity.