Thesis presented October 08, 2024
Abstract:
In this work, I present the growth and characterization of UV-C emitters based on GaN and AlN nanowires. Initially, I optimized the growth of →m-oriented AlN using metal organic vapor phase epitaxy (MOVPE) with GaN self-assembled wire sidewalls as templates. We identified that the NH3 flux is a crucial parameter, and high flux resulted in good quality AlN layers. I successfully grew GaN/AlN heterostructures, demonstrating UV-C emission at 278 nm. Next, I investigated the anisotropic roughness of AlN, discovering that growth temperature and layer strain significantly influence surface roughness. These findings enabled the growth of (Al)GaN/Al(Ga)N heterostructures with a thickness of only two monolayers, which were integrated as the active region of a micro-LED. To prevent defect formation and light absorption, we developed a hybrid method combining top-down etching and MOVPE overgrowth to fabricate AlN nanowire arrays. Post-etching, we observed strain relaxation using CL and Raman spectroscopy. I also created a model to describe the growth mechanisms within an organized array. Notably, →a-oriented AlN exhibited superior optical properties compared to ?m oriented AlN, attributed to variations in point defect incorporation based on plane orientation. Finally, I grew (Al)GaN/AlN heterostructures on the sidewalls of AlN nanowires, achieving deep UV emission below 240 nm. I found that the optical and morphological properties of the wires depended on array parameters such as wire spacing, initial wire diameter, and orientation (→a or →m). We conducted a thorough investigation of the efficiency of these emitters and an unusual CL and time-resolved CL decay behaviors have led to the development of a recombination dynamics model. I calculated an internal quantum efficiency (IQE) of 10% and, using integrating sphere measurements, an external quantum efficiency (EQE) of 0.2%.
Keywords:
UV, core-shell, epitaxy, GaN, nanofils, AlN, MOVPE, UV-C emitter