686593 event 1763796130 1763796198 <![CDATA[Ph.D. Dissertation Defense - AndrĂ© Perepeliuc]]> Title:  Hexagonal boron nitride for deep UV applications

Committee:

Dr. Abdallah Ougazzaden, ECE, Chair, Advisor

Dr. Jean-Paul Salvestrini, ECE, Co-Advisor

Dr. David Citrin, ECE

Dr. Paul Voss, ECE

Dr. Jennifer Hasler, ECE

Dr. Luis Barrales-Mora, ME

]]> Current UVC LEDs based on AlGaN technology face major challenges, primarily due to the drastic reduction in conductivity caused by the difficulty of achieving efficient p-type doping as the aluminum content increases. Additionally, light extraction efficiency decreases with higher aluminum content. Hexagonal boron nitride (hBN) has emerged as a promising material to overcome these limitations. Owing to its unique properties, such as efficient p-type dopability, high UV transparency, strong luminescence, and excellent light extraction, hBN can potentially replace or complement conventional AlGaN layers. In particular, hBN can be integrated into AlGaN-based LEDs to form heterostructures with improved performance, simultaneously serving as both a hole injection layer and an electron blocking layer. The objective of this thesis is to demonstrate the feasibility of such heterostructures by fabricating operational UV LEDs that incorporate hBN as a hole injection layer. Moreover, during this PhD, an extraordinary phenomenon, extremely long-lived persistent photoconductivity in hBN at room temperature, has been discovered. This PPC effect, which can last for years, enables a novel photoinduced doping approach. Notably, the doping type can be tuned by varying the excitation wavelength. The understanding and utilization of this surprising effect constitute a central part of this work. The results presented in this thesis represent a significant step toward efficient UVC emission using hBN/AlGaN heterostructures, providing a potential solution to the p-doping challenges at high aluminum content. Furthermore, the ability to optically induce both n-type and p-type doping in hBN opens the door to the realization of homojunction devices, paving the way toward entirely hBN-based LEDs with unprecedented efficiency, particularly since conventional doping techniques in hBN are still in their early stages.

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