Unusual Formation of Point Defects and Their Complexes in Ultra-wide Band Gap Beta-Ga2O3

Beta-Ga2O3 has unique advantages including high breakdown voltage and availability as bulk substrates, which make it a viable candidate for next-generation power device applications. We present the first direct microscopic observation of the unusual formation of interstitial-divacancy complexes within beta-Ga2O3 lattice using atomic resolution scanning transmission electron microscopy. We observed that cation atoms are present in multiple interstitial sites, and each interstitial atom is paired with two adjacent vacancies. The observed structure is consistent with density functional theory calculation , which predicts them to be compensating acceptors. The number of the complexes increase as a function of Sn doping, which matches with the increase of the trap state at Ec - 2.1 eV measured using deep level optical spectroscopy, strongly suggesting that the defects correspond to that trap level. We also show that two neighboring complexes can further relax the structure in between, creating more cation vacancies. Our finding provides new crucial information on the exact structural origin of the properties of beta-Ga2O3 that has been unobtainable using other methods.