Energetic, Electronic, and Optical Properties of Intrinsic Charge Carrier-Trapping Defects in KTaO₃: Insights from a Hybrid DFT Study

Abstract

Potassium tantalate (KTaO3) has emerged as a leading material for various industrial and technological applications owing to its excellent stability and electronic properties. In spite of extensive research conducted in the past decades, key defects in KTaO3 are still being investigated. In this study, a detailed systematic calculation using hybrid density functional theory has been carried out to investigate geometry, defect formation energies, and electronic properties of all possible neutral and charged intrinsic vacancy defects in KTaO3 under various growth conditions. We also extensively examine the role of a vacancy defect cluster in tuning the electronic properties of KTaO3. Furthermore, we elucidate the role of self-trapped electrons and holes and antisite defects in the optical properties of KTaO3, and thus a new perspective on the process of different intrinsic point defects in KTaO3 has been proposed. The formation energy calculation indicates that K-vacancy and its clusters will be readily formed in KTaO3 in all growth conditions, except under a K-rich environment. We find that O-vacancy, Ta-antisite, and K–O divacancy clusters are deep donors in KTaO3, while Ta-vacancy, K-antisite, and Ta–O divacancy clusters are deep acceptors. On the other hand, K-vacancy is a shallow acceptor in KTaO3, and K–O–K trivacancy clusters can act as both acceptors and donors. Based on analysis of formation energies and charge transition level, the present study reveals that O-vacancy, Ta–O, and K–O vacancy clusters mainly contribute to the prominent emission behavior of KTaO3 in the red–blue–green region. The present study provides critical insights into the microscopic picture of the optical behavior of KTaO3 perovskites. Thus, this study provides important guidelines for tuning the synthesis conditions to optimize functionalities based on different intrinsic vacancies.

Visible-Light-Driven Semiconductor–Metal Transition in Electron Gas at the (100) Surface of KTaO3

“…In general, the photogenerated carriers in 2DEG mainly come from the in-gap state-related transition in KTO. Considering that the photon energy in the current experiment (∼3.1 eV) is smaller than the band gap of KTO crystal (∼3.6 eV) [46], light illumination can only excite the in-gap states in KTO. When irradiated with the same laser power, the amount of photogenerated carriers should be the same for the two samples, supposing the recombination rates of carriers in the two samples are the same.…”

“…For the 2DEG at the KTO surface obtained by Ar ion bombardment, the bombardment time determines the amount of oxygen vacancies and hence the electron doping level [47]. It has been well recognized that the introduction of oxygen vacancies in the KTO surface results in a broad in-gap state in KTO located at 1.63 and 0.87 eV below the CBM [46]. In the study, the energy of all photons (1.0~3.06 eV) is smaller than the band gap of KTO, suggesting that the in-gap band associated with oxygen vacancies plays a key role in the photoresponse of the 2DEG at the KTO surface.…”

Enhancement of Photoactivity of TiO2 for Potential Applications in CO2 Conversion and Water Splitting: A Hybrid Density Functional Theory Study

“…Brillouin zone sampling has been performed by a Γ-centered k -point mesh value of 6 × 6 × 6 for the supercell using the Monkhorst and Pack scheme . To overcome the limitation of standard DFT during band gap calculations, we employed the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), which is shown to reproduce the experimental band gap for a wide range of materials. − According to this functional, the ion-core interaction is separated into two parts: short range (SR) and long range (LR). The interaction in the SR is described by both exact Hartree–Fock (HF) exchange and PBE exchange, while the LR is solely described by PBE.…”

Hybrid density functional study on band structure engineering of ZnS(110) surface by anion–cation codoping for overall water splitting

“…However, the states appearing around the CBM are localized and unoccupied, which may trap the photoexcited electrons and holes, and enhance the recombination possibility. 67,68 The photoconversion efficiency of the Ru-monodoped ZnS(110) surface would be potentially suppressed.…”