Research on efficiency droop mechanism and improvement in AlGaInP Ultra-High-Brightness LEDs using the transient measurement method

• Transient measurement method was demonstrated to minimize the self-heating effect.
• The AlGaInP LEDs droop behavior contributed by IQE, IE, and EE was investigated.
• EE loss was the main mechanism of WPE droop in AlGaInP LEDs rather than IQE and IE.
• Recommendations for AlGaInP LEDs design were proposed to eliminate droop effect.

This study proposes a transient measurement method (TMM) for minimizing self-heating in AlGaInP Ultra-High-Brightness LEDs (UHB-LEDs) under low-to-high bias current. The TMM was validated by the wavelength shift method. The luminous intensity ratio measured by the TMM was similar to that in the ideal device under low-to-high current. The contribution of internal quantum efficiency loss to self-heating temperature and electrical efficiency loss affecting the efficiency droop of AlGaInP UHB-LEDs were determined by TMM because of the temperature dependence of injection efficiency and internal quantum efficiency. The analytical results showed 2.4% difference in wall-plug efficiency (WPE) droop at 1.6 A was contributed by internal quantum efficiency and injection efficiency loss. The remaining 10.1% difference was contributed by electrical efficiency loss. This study also discussed the main mechanism, the high contact and sheet resistance resulting in current crowding, that affects electrical efficiency loss, and a qualitative analysis and recommendations for AlGaInP UHB-LEDs design were demonstrated to eliminate efficiency droop.

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