Relation between Electron Band Structure and Magnetic Bistability of Conduction Electrons in β-Ga2O3

Abstract

When slightly oxygen-deficient, β-Ga2O3 is an n -type semiconductor with conduction electrons exhibiting a bistable spin resonance. In this paper, we discuss the relation between the electronic structure of gallium oxide and this peculiar magnetic property. The electron band structure of β-Ga2O3 is computed with the extended Hückel method. The calculations show that the conduction hand has a strong 4s gallium character (≈ 60%), with a quasi-exclusive contribution of the octahedral gallium ions to the band edge. The conduction band also exhibits a quasi-one-dimensional character with bandwidths much larger along the b* axis than along the a* or c* axes. Therefore, conduction electrons are essentially delocalized along the octahedral chains of the structure, whereas the surrounding tetrahedral chains are not occupied. The low-dimensional character of the electronic structure of β-Ga2O3 is confirmed by ESR and ENDOR spectroscopies of Ti3+ ions in substitutional octahedral sites, which provide evidence for predominant Ti-Ga superhyperfine interactions extending as far as the second neighboring Ga in the chain direction. It is also shown that the two conditions necessary for the existence of bistable conduction electron spin resonance, i.e., a strong dynamic nuclear polarization and a narrow ESR line, can be quantitatively accounted for by the important 4s gallium character of the conduction band and by its pronounced anisotropy.