Air-Hybrid Dbr Structure for the Improvement of Light Output Power in Algainp-Based LED

In this paper, we report the air gap induced hybrid DBR-based LED (AH-DBR LED) structures for the efficient light extraction efficiency. For verifying the influence of the AH-DBR structures in 630 nm emitting LED devices, we compare two LED structures with conventional and air gap induced hybrid DBRs.

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 (θ_c) 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 θ_c 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 Al_xGa_1-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.