Vertical-geometry GaN-based light-emitting diodes: Improving current injection and light extraction efficiencies

The effect of an indium middle layer on the structural, thermal and electrical properties of Ag contacts for high-power GaN-based vertical LEDs was investigated. As the temperature increases, agglomeration is initiated by the formation of hillocks, followed by the generation of holes, leading to agglomeration. The In layer effectively prevents agglomeration. Consequently, the In-inserted Ag reflectors exhibit better reflectivity at 500°C than Ag only contacts. The In-inserted Ag sample was less <111>-textured than the Ag only sample. On the basis of the scanning electron microscopy, and X-ray phi scan and pole figure results, the improved stability is described by means of the <111>-texture and the modification of the surface energy of Ag films. The In-inserted Ag reflectors exhibit better specific contact resistivity at 500°C than Ag only contacts. The output power (at 20 mA) of LEDs with the In-inserted Ag contacts is higher than that of LEDs with Ag only contacts.