NanoCL reveals the optical properties of III-nitride LEDs webinar

III-nitride quantum well light emitting diodes (LEDs) show high optical efficiencies over the UV, blue and into the green spectrum. They also form the basis of white LEDS, which have superior energy efficiency compared to traditional forms of lighting. The higher energy efficiencies have led to vast reductions in energy consumption and correspondingly air pollutants and greenhouse gases.

Modern LEDs use quantum wells, which serve to confine the carriers leading to high recombination efficiencies. A persistent challenge though to the development of higher efficiency devices is the presence of a strong internal electric field across the quantum wells in traditional devices. The electric field serves to separate the electron and hole wave functions leading to a reduction in the radiative recombination rate. Yet, simulations have shown that the device efficiency may theoretically be improved by inclusion of silicon dopants which serve to screen the internal electric field, and to achieve the highest efficiencies requires careful design and optimisation. Here we show how the combination of simulations and experimental nanocathodoluminescence (nanoCL) can be a powerful technique in the development of optoelectronic devices.

We show how nanoCL can reveal the optical properties of individual InGaN QWs in high efficiency light emitting diodes. The structural properties of the QWs may also be measured simultaneously, including by electron energy loss spectroscopy. We are able to show a direct correlation between the level of silicon doping and variations in the emission wavelength of individual quantum wells. The experimental variations observed by nanoCL also correlate directly with the simulated variations in the emission wavelength and confirm that the observed variations in the emission wavelength are due to the mitigation of the electric field. Hence, we show that nanoCL can serve as experimental approach to study and refine the design of future optoelectronic nanostructures, including the effects from doping and lead to greater improvements in device efficiencies and functionality.

Presenter: James Griffiths, Ph.D., Cambridge Centre for Gallium Nitride

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Tuesday, June 14, 2016
8:00 am - 9:00 am