Conference Agenda

This lecture provides a comprehensive overview of bulk GaN crystallization,

tracing its evolution, key milestones, recent advancements, and future

prospects. Various growth techniques will be examined, including halide

vapor phase epitaxy (HVPE) and the ammonothermal method, the latter

being the most promising. A comparative analysis of acidic and basic

ammonothermal growth will highlight their advantages, limitations, and

technological challenges. The integration of ammonothermal and HVPE

technologies presents significant potential for further advancements.

However, scaling GaN crystal growth for commercial applications remains

a critical challenge. This lecture will explore current progress and realistic

development timelines. Additionally, the transition from bulk crystal

growth to usable substrates requires precise processing techniques, such

as wafer cutting and surface treatment. The discussion will conclude with

key applications of GaN substrates in optoelectronic and electronic devices.

InGaN Multiple Quantum Wells (MQWs) were examined in situ during annealing in the KARA synchrotron. The high brightness of the X-ray beam enabled us to measure the reciprocal space maps fast enough to monitor the changes in the InGaN lattice. At moderate temperatures, we observed homogenization of the QWs. At temperatures close to 1000oC, the wells got decomposed. Still, this phenomenon depended not only on In-content in InGaN and temperature but also on the microstructure (defect density) layers below the QWs.

This work aims to find a correlation between the high-value Young’s modulus of silicon carbide and the high frequencies and quality (Q) factors in resonant devices built with 3C-SiC Double-Clamped (DC) beams grown on (111) silicon substrates. The study is important for understanding the sensitivity of the device’s eigenfrequencies with respect to variations in length and thickness. We aim to verify if our data[1], along with results from the literature, confirm the Quality factor model proposed by Romero et al. [2], extending the range of film thickness to about 1 µm.

Thermal annealing plays a crucial role in the optimization of 4H-SiC electronic devices, particularly in passivating interface defects. In this work, we investigate the effects of high-pressure (800 PSI) thermal annealing in Oxygen and Helium atmospheres of 4H-SiC at 400 °C by studying the exciton lifetime. We studied three different wafer types representing different stages of the fabrication process: a bare epitaxial layer A(epi), an oxide-covered sample B(epi+ox), and a sample subjected to post-deposition annealing in NO C(epi+ox+NO). Photoluminescence decay measurements reveal a significant decrease in exciton lifetime for the bare epitaxial sample after annealing, while the oxide-covered sample exhibits an increase in lifetime in oxygen-rich conditions. Comparisons with helium treatments highlight the role of oxygen in defects passivation, suggesting that O₂-based annealing could be a cost-effective alternative to NO treatments.

This study presents an innovative approach for fabricating monoclinic gallium oxide (β-Ga2O3) microtubes and nanomembranes by ion-beam-induced exfoliation. Using Cr ion implantation as a case-study, the evolution of the defects, strain and stress profiles are assessed by a combination of X-ray Diffraction, Rutherford Backscattering Spectrometry in Channelling mode and Molecular Dynamics. The developed strain engineering method is shown to lead to a self-rolling of the surface layers of (100)-oriented single-crystals, yielding microtubes. A subsequent thermal annealing leads to strain relaxation, and these structures unroll, forming nanomembranes with bulk-like crystalline quality. This novel technique has the potential of becoming a scalable and reproducible method compared to conventional exfoliation techniques, while also enabling the simultaneous doping of the membranes, which can be customised in terms of their optical, electrical, and magnetic properties. This work thus contributes to better understand the elastic properties of this material under ion irradiation, as well as enhanced its potential for applications in power electronics, photonics, and sensors.