First-principles study of native point defects in crystalline indium gallium zinc oxide

Abstract

Articles you may be interested inA thermalization energy analysis of the threshold voltage shift in amorphous indium gallium zinc oxide thin film transistors under simultaneous negative gate bias and illumination Materials in In-Ga-Zn-O system are promising candidates for channel layers of high-performance thin-film transistors ͑TFTs͒. We investigated the atomic arrangements and the electronic structures of crystalline InGaZnO 4 containing point defects such as oxygen vacancy ͑V O ͒, interstitial hydrogen ͑H i ͒, and interstitial oxygen ͑O i ͒ by density functional theory ͑DFT͒ using a plane-wave pseudopotential method. The calculations for the atomic structure relaxation suggest that H i bonds to a lattice oxygen ͑O O ͒, and O i occupies a split interstitial site ͓O i ͑split͔͒ forming a chemical bond with O O which is similar to O 2 molecule, or O i occupies an octahedral interstitial site ͓O i ͑oct͔͒. The electronic structure calculations reveal that V O forms fully occupied states around the middle of the DFT band gap, while H i does not form a defect level in the band gap but raises the Fermi level above the conduction band minimum. O i ͑split͒ forms fully occupied states above the valence band maximum of the defect-free model ͑VBM 0 ͒, while O i ͑oct͒ forms both occupied and unoccupied states above the VBM 0 . It is thus suggested that V O and O i ͑split͒ are electrically inactive for electrons but work as hole traps, H i acts as a donor, and O i ͑oct͒ is electrically active, trapping both electrons and holes. These observations imply that V O and O i ͑split͒ do not but H i and O i ͑oct͒ influence electrical properties of the n-channel TFTs based on the In-Ga-Zn-O semiconductor materials.

Composition-dependent oxygen vacancy formation in multicomponent wide-band-gap oxides

“…The oxygen vacancy formation in InGaZnO 4 and the defect state location with respect to the conduction band edge of the oxide have been determined earlier [23,52]. In this work, we investigate how the presence of light-metal cations (Ca and/or Al) affects the distribution of the oxygen vacancies within the structurally and chemically distinct layers of multicomponent oxides.…”

Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

“…Electronic band structure investigations of undoped stoichiometric InGaZnO 4 have been performed earlier for the crystalline [29,30] and amorphous oxide [63]. Most importantly, it was found that despite the different band gap values of the constituent single-cation oxides, cf., Table I, all cations give comparable contributions to the conduction band bottom of the complex oxide.…”

“…Also, it was assumed that each vacancy donates two extra electrons, i.e., there is no charge compensation via natural defects or defect complexes. However, it was shown theoretically [30] that uncompensated oxygen vacancy in InGaZnO 4 results in a deep level within the band gap and, thus, free carriers cannot be efficiently generated. Therefore, oxygen vacancy cannot explain the observed conducting behavior in this material.…”

Low turn-on voltage due to conduction band lowering effect in crystalline indium gallium zinc oxide transistors

“…1. The negative shift of the characteristics means the increase of shallow donor defects generating carrier electrons in the channel region, which is thought to be caused by the heat treatment at 400°C for 1 h. Although the origin of the shallow donor defects is still controversial, [28][29][30][31][32] we believe that it strongly correlates with oxygen vacancies in the CAAC-IGZO active layer. Instead of the origin of the shallow donor defects, we discuss, in the subsequent section, the influence of the donor concentration in the channel region on the I d -V g characteristics of an IGZO transistor, including an extreme case of the intrinsic channel.…”

“…[28][29][30][31][32] As a result, it is believed that an IGZO transistor is also an n-type channel device in which electrons serving as majority carriers are controlled by a gate voltage. Actually, the transistor tends to be normally-on and it is hard to shift the threshold voltage in the positive direction.…”