Characterization of GaN-based light-emitting diodes

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Antuna-Presa, Silvino Jose
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University College Cork
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Maximizing the performance of light-emitting diodes (LEDs) is essential for the widespread uptake of solid-state lighting. To contribute towards this goal, this thesis focuses on the electrical and optical characterization of InGaN/GaN-based multi quantum well LEDs. In this work a wide range of characterization methodologies are introduced. A new development is the study of the emission spectra under resonant optical pumping and varying electrical bias. This has proven to be useful to obtain insights into the carrier dynamics and is used here to investigate LED samples containing different numbers of quantum wells (QWs) with different thicknesses for the barriers. Despite having only small structural differences, these samples have shown strong differences in their performance, which are attributed to a stronger piezoelectric field in the QWs in the sample with thinner barriers. Fluorescence microscopy with selective excitation of the QWs also allows the study of the spatially dependent luminescent properties of LEDs. In this case ohmic contacts create an equipotential surface and influence the collective emission. Strong carrier escape is observed in photovoltaic mode under both open and short circuit conditions. To help identify the underlying recombination mechanisms, different voltage ideality factors are extracted and compared with each other. This thesis shows that the use of photovoltaic measurements together with biasdependent spectrally resolved luminescence is a powerful tool to investigate GaN LEDs. The methodologies presented here provide experimental tools to better understand carrier recombination processes in different LED samples. These methods can extended to samples grown on different crystallographic orientations or to study the effects of additional layers in novel LED structures.
Light emitting diodes , Electroluminescence , Fluorescence , Optical resonant luminescence , Gallium nitride , Piezoelectric fields
Antuna-Presa, S. J. 2016. TitCharacterization of GaN-based light-emitting diodes. PhD Thesis, University College Cork.
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