Cascaded GaN Light-Emitting Diodes With Hybrid Tunnel Junction Layers

We report the fabrication of cascaded GaN light-emitting diodes (LEDs) with previously reported p⁺⁺-GaN/i-InGaN/n⁺⁺-GaN tunnel junction layers (TJLs) and with hybrid TJL. Compared with the conventional LED, it was found that we could enhance the output power by 35% and 80% from the LED with p⁺⁺-GaN/i-InGaN/n⁺⁺-GaN TJL and the LED with hybrid TJL. It was also found that the TJ resistances were 6.05 × 10^-3 and 1.95 × 10^-3Ω · cm² for the LED with p⁺⁺-GaN/i-InGaN/n⁺⁺-GaN TJL and the LED with hybrid TJL, respectively. It was also found that the use of hybrid TJL could result in smaller efficiency droop. These improvements could all be attributed to the larger polarization charges induced at the AlGaN/InGaN interface which could enhance the tunneling current. Furthermore, it was found that the cascaded GaN LEDs with hybrid TJL were also reliable.