Fabrication and characterization of UV-LEDs

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Pampili, Pietro
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University College Cork
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This thesis investigates the emerging technology of ultraviolet light-emitting diodes (UV LEDs) based on III-nitride materials. Despite the incredible improvement of these devices over the past decade, if compared with visible LEDs based on the same semiconductor system, UV LEDs still suffer from a much reduced efficiency that severely limits their potential. The technological issues responsible for this problem have been analysed and possible solutions and mitigation strategies have been proposed, both at growth and fabrication level. In particular, the n-type doping of the AlGaN materials used in the cladding layers of these devices has been optimized, for AlN concentrations in the range of 50–85%. The transport mechanism in these materials has also been studied, and the presence of a significant impurity conduction at room temperature has been detected; the consequences of this fact on the doping optimization have been highlighted. A deep-UV LED for space application emitting below 250 nm, and a near-UV LED emitting at 340 nm—in whose active region an InAlN alloy has been used in place of the more common AlGaN—have both been successfully demonstrated. The use of micron-sized emitters has been investigated with the aim of improving switching characteristics and light-extraction efficiency of these devices. An optical bandwidth of over 20 MHz has been demonstrated for the deep-UV LED, as required by the funding agency. Thanks to the optimization work performed on the reflective sidewalls of the micro-emitters, an increase of light-extraction efficiency up to four times was shown.
UV LED , AlGaN , InAlN , Doping , Device fabrication , Micro-LED
Pampili, P. 2019. Fabrication and characterization of UV-LEDs. PhD Thesis, University College Cork.