Energetic and Electronic Structure Analysis of Intrinsic Defects in SnO₂

Abstract

Empirically, intrinsic defects in SnO2 are known to give rise to a net oxygen substoichiometry and n-type conductivity; however, the atomistic nature of the defects is unclear. Through first-principles density functional theory calculations, we present detailed analysis of both the formation energies and electronic properties of the most probable isolated defects and their clustered pairs. While stoichiometric Frenkel and Schottky defects are found to have a high energetic cost, oxygen vacancies, compensated through Sn reduction, are predicted to be the most abundant intrinsic defect under oxygen-poor conditions. These are likely to lead to conductivity through the mobility of electrons from Sn(II) to Sn(IV) sites. The formation of Sn interstitials is found to be higher in energy, under all charge states and chemical environments. Although oxygen interstitials have low formation energies under extreme oxygen-rich conditions, they relax to form peroxide ions (O2 2−) with no possible mechanism for p-type conductivity.

Conductivity in transparent oxide semiconductors

“…This is shown for In 2 O 3 in Fig. 12 [170], but can also be seen in calculations of the electronic structure of the other TCOs [68,[171][172][173][174]. Such a band structure means that the Brillouin-zone-averaged band gap, and consequently also the CNL [175], are situated above the low-lying CBM, rather than within the fundamental band gap [63,167].…”

“…In fact, its formation energy decreases with increasing Fermi level, making these especially important for typical Fermi level positions of n-type TCOs. However, such defects are acceptors [51,68], and so cannot contribute to this n-type conductivity. Rather, these defects may play an important role as compensating centres, limiting the attainable carrier densities and conductivities of TCOs.…”

“…Look et al [75] have argued that a complex of the Zn-interstitial with a nitrogen impurity on the oxygen site is also a strong candidate for a shallow donor in ZnO. In SnO 2 , Godinho et al [68] found that oxygen vacancies compensated through tin reduction could be present in significant quantities, and contribute to the n-type conductivity. More generally, they concluded that isolated defects often relax to give completely different defect structures, a feature which is neglected in the majority of calculations of defect formation energies.…”

Ab initio thermodynamic study of the SnO2(110) surface in an O2 and NO environment: a fundamental understanding of the gas sensing mechanism for NO and NO2

“…Using density functional theory (DFT) calculations, it was found that oxygen vacancies (V O ) are the main cause of the (unintentional) n-type conductivity by forming shallow donor levels at the bottom of the conduction band with the mobility of electrons from Sn(II) to Sn(IV) sites in bulk SnO 2 [25], though other point defects such as Sn interstitial (Sn i ) and substitutional hydrogen impurities (H O ) play a certain role in the growth and processing environment [26,27]. This prediction was proved to be consistent with the experiment [28,29], and extended from bulk vacancy to surface oxygen vacancies at the SnO 2 surface [30][31][32][33][34][35][36].…”

The Influence of Al and Zn Co-Doping on Optical and Structural Properties of Transparent and Conducting SnO2 Thin Films Prepared by Spray Pyrolysis Technique

“…It has good adsorptive properties and chemical stability. It can be deposited onto glass ceramics, oxides and substrate materials [1,2]. It has a high melting point and good transmission and does not easily react with oxygen and water vapor in the air, so it has a high specific volume and good cycling performance.…”