Role of copper interstitials in CuInSe2: First-principles calculations

Abstract

Formation enthalpies and migration barriers of copper interstitials and Frenkel pairs in CuInSe 2 (CIS) are determined by first-principles calculations within density functional theory using the nonlocal screened exchange Heyd-Scuseria-Ernzerhof (HSE06) functional. Interstitials occur on four symmetrically inequivalent sites with formation enthalpies of 0.17-0.38 eV, which are much lower than previously reported values based on local approximations. A direct interstitial and indirect interstitialcy diffusion mechanism with migration barriers as low as 0.22 and 0.34 eV are identified. The results provide evidence that the fast interstitial diffusion of copper is important for understanding metastabilities, Fermi-level pinning at interfaces, electric-field-induced creation of p-n junctions, and widely varying experimentally measured diffusion coefficients in CIS devices.

Mass transport in CuInSe2 from first principles

“…Besides vacancies, it was then suggested that another mechanism such as interstitials could be operational at least under Cu-rich conditions. 10 Only recently, the feasibility of Cu i migration was demonstrated by theoretical calculations, 17 which we now confirm and extend with an explicit analysis of the effect of chemical conditions and temperature. TABLE I.…”

“…7 The migration barrier values for copper computed in this work agree closely with the previous HSE06 calculations. 16,17 Evidence supporting interstitial-driven copper transport has been accumulating little by little. In an early experimental work, copper vacancies were suspected to mediate copper diffusion based on indirect evidence of presumed vacancy concentrations correlating with diffusion coefficients.…”

“…The exchange-correlation potential has been modelled with the range-separated hybrid functional HSE06, 23 which has shown considerable improvement over (semi)local functionals in the description of the atomic and electronic properties of CIS. 16,17,24 The portion of Hartree-Fock exchange, a, has been set to the value of 0.25 derived from theory. 25 The formation energies E f for each mass-mediating agent have been computed following the procedure outlined in our previous work, 24 including finite-size scaling.…”

“…First-principles simulations offer the possibility to examine viable migration paths and mechanisms atom-wise and quantify their corresponding contributions to mass transport. A few copper-related reports on the topic have recently been published, 16,17 but they treat the diffusion of copper vacancies and interstitials separately and do not state conditions under which each mechanism would dominate. In the present work, we will go more in depth to the topic than previous studies, considering all three components of CIS.…”

Diffusion coefficients of two mobile ions in three AB3In7VI12 single crystals (AB=Cu and Ag VI=Se or Te). Proposition of an equivalent electrical circuit

“…For example, copper vacancies (V Cu ) are regarded as the main acceptor, whereas selenium vacancies (V Se ) and indium copper antisites (In Cu ) are considered as the main donors. The electrical and optical properties seem to be governed mainly by native defects [11][12][13][14]. In rich chalcopyrite structures are Cu n À 3 In n þ 1 Se 2n compounds with n ¼4, 5, 6, 7, 8, 9 and present similar structure than ABIIIVI 2 with a deficiency of either one or two cations over the anions.…”