Point defects control in Ga2O3 thin films grown via molecular beam epitaxy

Our research project explores the role of defects in monoclinic gallium oxide (ß-Ga₂O₃), a wide bandgap semiconductor material with great application potential in power electronics and solar blind photodetectors. Despite extensive research over the past decade, a significant disparity persists between the projected properties and practical performance of devices. Point defects, including oxygen and gallium vacancies, are crucial in bridging this gap by impacting doping, electron mobility, and power dissipation during device operation.

Our pioneering methodology encompasses a comprehensive study of point defects in Ga₂O₃ and their influence on its functional properties. To achieve this, we employ molecular beam epitaxy (MBE) to deposit thin films under controlled conditions, including metal-rich and oxygen-rich regimes. By depositing thin films with different oxygen isotopes, we use Raman spectroscopy to gain unprecedented insights into the impact of oxygen and gallium sublattices on various Raman modes. Ab-initio calculations support this step by correlating Raman mode variations with the formation of Ga and O-related point defects under different MBE conditions.

We complement these findings with secondary ion mass spectrometry-based anion and cation tracer diffusion studies, as well as positron annihilation spectroscopy, to provide independent evidence of vacancy defects. Electrical transport measurements on donor-doped layers help us understand how different point defects affect the functional properties of thin films.

Building upon these results, we focus on a unique MBE deposition mechanism, In-mediated metal-exchange catalysis, to elucidate its role in the formation of various point defects compared to standard deposition processes. Ultimately, our goal is to establish guidelines for ß-Ga₂O₃ synthesis that allow us to prevent or engineer point defects, providing control over the material's functional properties. This research represents a significant step towards understanding ß-Ga₂O₃ device functionality and uncovering the material's fundamental limits.

This project is a collaboration between the Paul-Drude-Institute, the RWTH Aachen, Germany, and the University Parma, Italy. It is supported by collaboration partners at the FAU Erlangen-Nürnberg and the University of Helsinki, Finland. The project is funded by the Deutsche Forschungsgemeinschaft (DFG) with the project number 446185170.