Air-Hybrid Dbr Structure for the Improvement of Light Output Power in Algainp-Based LED
The conceptual light paths reflected from conventional DBR and AH-DBR structures are depicted in Fig. 1. The conventional DBRs mainly reflect the light within the yellow region propagating vertically. However, the reflectivity becomes negligible when the incident angle is larger than the critical angle (θc) and the only small portion of light can be extracted out of chip through side facet. For supplementing this drawback of the conventional DBR structures, air gap is inserted in the side of the DBR structures. In the AH-DBR structures, the incident light larger than the θc can be effectively reflected by the air gap to enhance the light extraction through the side facet of the chip.
To verify the performance of our proposed LED structures, AlGaInP-based LEDs with the conventional DBRs and AH-DBR structures are prepared. Fig. 2 shows the cross-sectional schematics and actual scanning electron microscope (SEM) images of the conventional DBR LED structures and the AH-DBR LED structures. The AlxGa1-xAs DBRs are well etched away to 38 mm in depth and formed relatively well-defined AH-DBR structures as shown in Fig. 2(b). Also, phosphide LED structures are not etched seriously and well maintained.