Charge transport properties of bulkTa3N5from first principles

Abstract

Tantalum nitride is considered a promising material for photoelectrochemical water splitting, however its charge transport properties remain poorly understood. We investigated polaronic and band transport in Ta 3 N 5 using first-principles calculations. We first studied the formation of small polarons using density-functional theory (DFT) including DFT+U and hybrid functionals. We found that electron small polarons may occur but hole polarons are not energetically favorable.The estimated polaronic mobility for electrons is at least three orders of magnitude smaller than that measured in Ta 3 N 5 films, suggesting that the main transport mechanism for both electrons and holes is band-like. Since band transport is strongly affected by the carrier effective masses, and Ta 3 N 5 in known to have large electron and hole effective masses, we also investigated whether substitutional impurities or strain may help lower the effective masses. We found significant reduction in both electron and hole effective masses (up to 17% for electron and 39% for hole) under applied strain, which may lead to substantial improvement (up to 30% for electron and 15% for hole) in the carrier mobilities.

Single- and few-layer BiOI as promising photocatalysts for solar water splitting

“…The photo-generated electrons have a relatively lighter effective mass with values of 0.36m e , which are smaller than those of some common photocatalysts. 64,65 The relatively small m * e indicates that the migration of photogenerated electrons to the reactive sites would be easier in the photocatalytic process. This is consistent with the high carrier mobility reported by Fan et al 41 On the other hand, the m * h at the VBM is calculated to be 2.46m e along X-G, thus, the photo-generated holes diffuse relatively slowly.…”

Nonempirical range-separated hybrid functionals for solids and molecules

“…Among DDHs, is one in which the dielectric constant is determined self-consistently, 8,9,12 which is referred to as a sc-hybrid. 12 This sc-hybrid functional has found recent use in the study of pristine oxides, 12,14,15 defects in oxides, [16][17][18] nitrides, 19,20 aqueous solutions, 21 and spin-defects in wide band gap semiconductors. 22 The adaptation of non self-consistent DDHs to a time-dependent framework was recently pursued by Yang et al, 23 Ferrari et al, 24 and Refaely-Abramson et al, 25 with the goal of obtaining optical spectra of solids.…”

Charge Carrier Transport Mechanism in Ta2O5, TaON, and Ta3N5 Studied by Applying Polaron Hopping and Bandlike Models

“…We noticed that the polaron formation energy E f defined as E f ¼ E P tol À E NP tol to determine the stability of the polarons in materials, [12,13] where E P tol and E NP tol is the DFT total energy of polaronic and non-polaronic structures. Negative values of E f indicate that the polaron is stable in this material.…”

“…This indicates that the DFT error is over-corrected using the hybrid functional with α = 0.6. All these results show that the polarons do not occur in Ta 3 N 5 , and the charge transport mechanism may be bandlike which Morboc [12] In this section, we use the effective mass approximation to investigate the bandlike charge transport in Ta 2 O 5 , TaON and Ta 3 N 5 . The effective mass of these materials are taken from Cui and Jiang's [29] results.…”

“…Lee [11] et al have predicted the formation of spin-polarized polarons in Ta 2 O 5 with oxygen vacancies using hybrid functional. Morbec and Galli [12] reported charge transport properties of the Ta 3 N 5 from first principles. They found small electron polarons may occur but hole polarons are not energetically using DFT + U approach.…”