HEXAGONAL BORON NITRIDE FOR DEEP UV APPLICATIONS
by André Perepeliuc on 28/11/2025
Summary: 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 (PPC) 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.
Chapter 1 introduces the context and applications of UV light along with the scope of this thesis. Chapter 2 reviews the current state of the art in AlGaN-based UV LEDs.
Chapter 3 presents the properties of hBN and its potential for deep-UV emission. Chapter 4 details the growth, fabrication, and characterization of functional hBN/MQWs/AlGaN LED structures. Finally, Chapter 5 discusses the mechanisms and implications of photoinduced doping in hBN, as well as the devices developed using this technique.