RELATION BETWEEN ELECTRON BAND-STRUCTURE AND MAGNETIC BISTABILITY OF CONDUCTION ELECTRONS IN BETA-GA2O3

When slightly oxygen-deficient, beta-Ga2O3 is an n-type semiconductor with conduction electrons exhibiting a bistable spin resonance. In thi s paper, we discuss the relation between the electronic structure of g allium oxide and this peculiar magnetic property. The electron band st ructure of beta-Ga2O3 is computed with the extended Huckel method. The calculations show that the conduction band has a strong 4s gallium ch aracter (almost-equal-to 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 large r along the b axis than along the a* or c* axes. Therefore, conductio n electrons are essentially delocalized along the octahedral chains of the structure, whereas the surrounding tetrahedral chains are not occ upied. The low-dimensional character of the electronic structure of be ta-Ga2O3 is confirmed by ESR and ENDOR spectroscopies of Ti3+ ions in substitutional octahedral sites, which provide evidence for predominan t Ti-Ga superhyperfine interactions extending as far as the second nei ghboring Ga in the chain direction. It is also shown that the two cond itions necessary for the existence of bistable conduction electron spi n resonance, i.e., a strong dynamic nuclear polarization and a narrow ESR line, can be quantitatively accounted for by the important 4s gall ium character of the conduction band and by its pronounced anisotropy. (C) 1994 Academic Press, Inc.