Characterizing and Identifying Vacancy Defects in β and γ-Ga₂O₃

Positron annihilation spectroscopy is a powerful method for detecting, quantifying and identifying vacancy defects in crystalline matter, and has made important contributions in elucidating their role, for example, in compound semiconductors. The phases of Ga₂O₃ have posed a challenge to the method due to their structural complexity and low symmetry of both the defect-free structures and the vacancy defects trapping positrons in real experiments. The large anisotropy of positron data seen both in experiments and first-principles modeling of monoclinic β-Ga₂O₃ makes quantitative interpretations cumbersome, but on the other hand, one can try to identify and utilize anisotropy-related "fingerprints" of defects in the analysis [1-4].

This talk focuses on the use of first-principles modeling in understanding the positron signal measured from β or γ-Ga₂O₃. Recently, our past work has been extended to the defective spinel γ-Ga₂O₃. This preliminary work addresses the role of the "built-in" Ga vacancies of the disoredered Ga sublattice of the γ phase and helps to understand to what extent the detected Ga vacancies can be expected to appear different between β and γ phases, in terms of anisotropy or otherwise.

[1 ]A. Karjalainen, V. Prozheeva, K. Simula, I. Makkonen, V. Callewaert, J. B. Varley, and F. Tuomisto, Phys. Rev. B 102, 195207 (2020).
[2] A. Karjalainen, I. Makkonen, J. Etula, K. Goto, H. Murakami, Y. Kumagai, and F. Tuomisto, Appl. Phys. Lett. 118, 072104 (2021).
[3] A. Karjalainen, P. M. Weiser, I. Makkonen, V. Reinertsen, L. Vines, and F. Tuomisto, J. Appl. Phys. 129, 165702 (2021).
[4] I. Zhelezova, I. Makkonen, F. Tuomisto, J. Appl. Phys. 136, 065702 (2024).