Research on the degradation of AlGaInP Ultra High Brightness LEDs influenced by ohmic metal design

• Four ohmic metal structures were fabricated and burn-in at 1 A for 6000 h.
• Less average ohmic metal structure results in higher voltage and power.
• Temperature arises from power of four ohmic design lead to degradation divergence.
• Exponential regressions based on international regulations were demonstrated.
• A constructive ohmic metal design guideline was conceptualized for commercial use.

AlGaInP Ultra High Brightness LEDs (UHB-LEDs) are widely used as light sources in various applications. With their high efficiency, UHB-LEDs require a higher light output power at a higher current density to fulfill the cost requirements of its market. As a consequence, reliability at high current density is a major issue in promoting the use of optoelectronic devices for general lighting. The degradation of commercial HB-LED chips has been widely studied, and numerous accelerated tests of current, temperature, and humidity have been conducted. However, few researches on the degradation of AlGaInP UHB-LEDs with the chip’s ohmic metal structure design have been conducted. To understand the relationship between the ohmic metal percentage of the chip and its reliability, the chips were designed with an ohmic metal ratio which ranges from 2% to 50% and burn-in at 1 A for 6000 h. In addition, to determine the resulting temperature in relation to the ohmic metal design, the chips were examined via infrared image microscope. After 100 h burn-in, the aging results of the 10 μA current drives showed that varying designs had almost similar voltage degradations due to the same epitaxy quality within a wafer. Moreover, the aging results at 1 A current drives showed that the lower ohmic metal ratio resulted in higher power output and intensity degradations. The stress temperature which arises from the power output is the main mechanism that accelerated the diffusion of the doping into a multi-quantum well and generated non-recombination centers within 100 h aging; this temperature was examined by using an infrared imaging microscope. Slight degradations were observed after 100 to 6000 h aging. With an exponential regression of different designs based on regulations, a constructive design guideline was conceptualized for commercial use.

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