Highly reliable nitride-based LEDs with internal ESD protection diodes

Nitride-based light-emitting diodes (LEDs) with internal electrostatic-discharge (ESD) protection diodes emitting at 460 nm were proposed and realized. By building an internal GaN p-n junction diode, a negative ESD-induced pulse current is expected to flow through the protection diode without damaging the major LED. The ESD characteristic of the fabricated LEDs was obviously improved with this design. Furthermore, the dimension of the internal p-n diode would influence the capacity for tolerating the ESD stress. It was found that a negative ESD threshold could be significantly increased from 300-400 to 2000 V. On the other hand, the authors managed to bring down the 20-mA operation voltage to 3.29 V using the n-metal finger, which entails a good current spreading under operation as the result of a reduced current-crowding effect. Since a good current spreading beneficially alleviates the thermal effect under long-term operation, an effective pattern layout design clearly would also prolong the lifetime of the proposed LEDs.