The aim of the GaloRE project is to test the feasibility of obtaining efficient and durable light emitters based on β-Ga2O3 doped with rare earth ions, which could be used in harsh environments with high exposure to radiation or chemical contamination . The project investigates the level and type of structural defects induced by implantation doping of this material, as well as their roles in luminescence processes. Experimental and computational techniques, including RBS/c, HRTEM, HRXRD, Raman spectroscopy, as well as optical, electrical and subtle structure studies will be used in the structural studies.

Project Name: Comprehensive study of gallium oxide implanted with rare earth ions for future applications in optoelectronic devices

Project acronym: GaloRE

Project budget: PLN 2,371,400

Additional information: project to be carried out in 2023-2027 fully funded by NCN within the OPUS-23 competition no. 2022/45/B/ST5/02810.

Project Manager: Renata Ratajczak

Project Description:

Nowadays, materials research is driven by new technologies that aim to improve existing materials or replace them with cheaper and more efficient counterparts. For several decades, semiconductor compound technology has fit perfectly into this trend. This technology is irreplaceable in optoelectronic applications such as lasers, displays or white LEDs, where the ubiquitous silicon cannot be used due to its intermediate and not very wide energy gap. Thermally stable beta-phase gallium oxide (β-Ga2O3) is a transparent semiconductor with a very wide bandgap of about ~ 4.9 eV, much larger than other transparent wide-bandgap oxide materials. Recent work has shown the great potential of this semiconductor in optoelectronic and electronic applications, mainly in high-power devices, light-emitting diodes (LEDs), lasers, transparent 'smart' windows and solar cells. The very wide band gap of this material is the reason for its increased thermal and chemical resistance, which makes the material less susceptible to damage under high irradiation conditions, therefore ideal for space applications and military systems. Moreover, with the development of the technology for growing large β-Ga2O3 monocrystals and the possibility of depositing β-Ga2O3 thin films, this material has also become a prospect for future low-cost production and industrial-scale applications.

The primary light emission from β-Ga2O3 lies in the ultraviolet region, but can be relatively easily tuned to the visible region by doping this material with rare earth (RE from Rare Earth) ions. β-Ga2O3 is an excellent host for RE ions, as it allows the most efficient and intense luminescence from doping due to its widest band gap. The doping of β-Ga2O3 with RE ions at the growth stage is very difficult due to their low solubility in the beta phase, leading to atom segregation and precipitation of other phases. An alternative doping method is the ion implantation technique. Despite its many advantages, a significant limitation of this implantation technique is the introduction of crystal lattice disorder (defects) due to the ballistic nature of the process. Structural defects suppress luminescence as well as adversely affecting the lifetime of devices built on the basis of the defective material. Therefore, thermal annealing is required to rebuild the defective implanted crystal. Annealing, in turn, leads to defect interaction, cluster formation and many other interesting phenomena. Therefore, knowledge of the fundamental properties of β-Ga2O3 implanted with various RE ions, the nature of the resulting defects as well as the mechanism of their transformation is crucial for future possible applications of β-Ga2O3:RE as efficient monochromatic white light emitters that would operate even under harsh conditions.

The GaloRE project takes a novel approach to the analysis of defect accumulation and transformation in β-Ga2O3 crystals exposed to ion bombardment, with a focus on experimental and computational (simulation) approaches. The main technique for structural studies in the project is the RBS/c technique. The research will be conducted at the IBC HZDR in Germany. The collected RBS/c data will be analysed using Monte Carlo simulations with the McChasy programme. In order to provide a complete picture of the analysed defect structures, it is planned to use a number of other research techniques, including HRTEM for defect imaging, HRXRD for the study of lattice stress accumulation and phase precipitation, and Raman spectroscopy, which will also be used to assess potential phase changes in irradiated materials.

In addition, it is also planned to investigate the optical and electrical activation mechanisms of the RE dopant atoms and its interaction with the matrix atoms occurring due to annealing. In this connection, optical, electrical and fine structure studies will also be carried out. The project also plans to develop β-Ga2O3 crystal growth technology using the ALD technique.