Performance of high power deep ultraviolet light-emitting diodes and factors limiting the lifetime

Abstract

The carrier recombination ABC model is a powerful tool to understand the performance of Light-Emitting Diodes (LEDs) such as Light Extraction Efficiency (LEE), Internal Quantum Efficiency (IQE), and lifetime. Starting from the ABC model we demonstrate that the optical-output-power junction-temperature dependence can be used to obtain an LED’s LEE and IQE. Using this analysis to a high power Deep Ultraviolet (DUV) LED and a state-of-the-art blue LED we obtain LEE values of 16% and 80% for the DUV and blue LEDs, respectively. This points LEE to be the main factor for efficiency improvement of DUV LEDs. Also, if IQE (not LEE) is responsible for the optical power decay, an LED lifetime model based on the ABC carrier recombination can be established to predict LED’s lifetime, and the model shows that the LED lifetime is mainly determined by the initial defect density and the defect generation interest rate. We present room temperature lifetime measurement data up to 3,000 hours for some 267 nm DUV LEDs, and the lifetime to maintain 70% of the initial optical power (L70) according to the lifetime model can be extrapolated to be of 20,000 to 120,000 hours. In view of the data presented in this paper, high-efficiency, long-lifetime DUV LEDs can be realized if the light extraction efficiency, initial defect density and uniform current spreading can be optimized.