Analysis of the wavelength-power performance roll-off in green light emitting diodes

Progress of light emission efficiency in the green and deep green spectral range is crucial for the success of all solid state lighting. Yet, power performance in GaInN/GaN quantum well light emitting diodes (LEDs) in the green still lag far behind the development of red and blue. A key signature is a steep roll-off in emission power when the wavelength is increased from 460 nm in the blue to 525 nm in the green and 550 nm in the deep green. The physical reason needs to be identified to overcome such limitations. A meaningful study requires a large base of sample data to meliorate the effects of sample variations. We analyze the data of hundreds of growth runs for several distinct epi development stages. In particular, when comparing data for two different epi optimization concepts we find a strong variation of their respective roll-off slopes in the green. These findings show that the roll-off slopes are not universal and can be controlled at a high performance level by advanced epi optimization. We find that an optimization of the quantum well smoothness leads to much weaker roll-off behavior and boosts performance of newly optimized green LED dies (2.4 mW at 20 mA, unpackaged, 527 nm dominant). Our results should open pathways on how to further extend power performance of deep green LEDs.