Native point defects in multicomponent transparent conducting oxides
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Native point defects in multicomponent transparent conducting oxides Altynbek Murat and Julia E. Medvedeva Department of Physics, Missouri University of Science & Technology, Rolla, MO 65409, USA ABSTRACT The formation of native point defects in layered multicomponent InAMO4 oxides with A3+=Al or Ga, and M2+=Ca, Mg, or Zn, is investigated using first-principles density functional calculations. We calculated the formation energy of acceptor (cation vacancies, acceptor antisites) and donor (oxygen vacancy, donor antisites) defects within the structurally and chemically distinct layers of InAMO4 oxides. We find that the antisite donor defect, in particular, the A atom substituted on the M atom site (AM) in InAMO4 oxides, have lower formation energies, hence, higher concentrations, as compared to those of the oxygen vacancy which is know to be the major donor defect in binary constituent oxides. The major acceptor (electron “killer”) defects are cation vacancies except for InAlCaO4 where the antisite CaAl is the most abundant acceptor defect. The results of the defect formation analysis help explain the changes in the observed carrier concentrations as a function of chemical composition in InAMO4, and also why the InAlZnO4 samples are unstable under a wide range of growing conditions. INTRODUCTION Multicomponent transparent conducting oxides [1-5] with the composition of both posttransition metals (In, Ga, and Zn) and main-group light-metals (Al, Mg, and Ca) are highly attractive since the presence of the main-group light-metal cations (i) may stabilize the multication structure; (ii) allows for a broader optical transmission window due to a larger band gap, (iii) changes the work function via tunable band edges; and (iv) also helps control the carrier content while preserving the carrier mobility [3]. In order to determine the carrier generation mechanism(s) and the role of each constituent cation in the carrier generation and transport, all possible native point defects in a multicomponent oxide must be carefully studied. In this work, first-principles density functional approach is employed to systematically calculate the formation energies of possible acceptor and donor point defects in InGaZnO4 as well as in light-metal containing InAlZnO4, InGaMgO4, and InAlCaO4. Next, we determine the equilibrium defect and electron densities as a function of growth temperature and oxygen partial pressure. The results reveal that the oxygen vacancies, long believed to be the carrier source in these oxides, are scarce, and cation antisite defects are the major electron donors in the conductive oxides. The proposed carrier generation mechanism helps explain the observed behavior of the conductivity and carrier concentration as a function of composition. The defect analysis also reveals the reasons for instability of InAlZnO4 samples. THEORY Ab-initio full-potential linearized augmented plane wave method (FLAPW) [6,7] with the local density approximation (LDA) and with the screened-exchanged LDA [8] is employed for the investigation
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