| 1. |
- Carvahlo, A., et al.
(author)
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Cation-site intrinsic defects in Zn-doped CdTe
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:7, s. 75215-
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Journal article (peer-reviewed)abstract
- The properties of the cation vacancy and the Te antisite, two dominant defects in CdTe and Cd1-xZnxTe alloys grown in Te-rich conditions, are examined using first-principles calculations. First, the structure, electronic levels, and migration paths of V-Cd and Te-Cd in CdTe are studied in detail. Additionally, we analyze the evolution of the stability and electronic properties in Cd1-xZnxTe alloys, taking into account both the role of alloying in the position of the ionization levels and its effects on the equilibrium concentration of those two defects. It is shown that the formation of cation vacancies becomes progressively more favorable as x increases, whereas Te antisites become less stable, backing the trend towards p-type conductivity in dilute Cd1-xZnxTe.
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| 2. |
- Carvahlo, A., et al.
(author)
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Electronic properties, doping, and defects in chlorinated silicon nanocrystals
- 2012
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4
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Journal article (peer-reviewed)abstract
- Silicon nanocrystals with diameters between 1 and 3 nm and surfaces passivated by chlorine or a mixture of chlorine and hydrogen were modeled using density functional theory, and their properties compared with those of fully hydrogenated nanocrystals. It is found that fully and partially chlorinated nanocrystals are stable, and have higher electron affinity, higher ionization energy, and lower optical absorption energy threshold. As the hydrogenated silicon nanocrystals, chlorinated silicon nanocrystals doped with phosphorus or boron require a high activation energy to transfer an electron or hole, respectively, to undoped silicon nanocrystals. The electronic levels of surface dangling bonds are similar for both types of surface passivation, although in the chlorinated silicon nanocrystals some fall outside the narrower energy gap.
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| 3. |
- Carvahlo, A., et al.
(author)
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Electronic structure modification of Si nanocrystals with F(4)-TCNQ
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12
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Journal article (peer-reviewed)abstract
- We use first-principles models to demonstrate how an organic oxidizing agent F(4)-TCNQ (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) modifies the electronic structure of silicon nanocrystals, suggesting it may enhance p-type carrier density and mobility. The proximity of the lowest unoccupied level of F(4)-TCNQ to the highest occupied level of the Si nanocrystals leads to the formation of an empty hybrid state overlapping both the nanocrystal and molecule, reducing the excitation energy to similar to 0.8-1 eV in vacuum. Hence, it is suggested that F(4)-TCNQ can serve both as a surface oxidant and as a mediator for hole hopping between adjacent nanocrystals in p-type doped silicon nanocrystal networks
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| 4. |
- Carvahlo, A., et al.
(author)
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Studies of the VO centre in Ge using first principles cluster calculations
- 2006
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In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 9:4-5, s. 489-493
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Journal article (peer-reviewed)abstract
- The small or near-zero band gap of germanium found by supercell local density functional treatments causes difficulties in the study of the properties of charged defects in Ge. Here, we use large H-terminated Ge clusters together with a non-linear core corrected (NLCC) Ge pseudopotential to explore the structure, vibrational and electrical properties of the vacancy-oxygen complex (VO). The cluster possesses a gap sufficiently wide to contain defect related energy levels, thus allowing us to model the three charge states of the defect. The local vibrational modes (LVM) calculated for the neutral (VO0), negatively charged (VO-) and double negative (VO=) defect are 602, 684 and 694 cm- 1, and can be favourably compared with experimental values of 621, 669 and 716 cm- 1, respectively [Markevich VP, et al. Physica B 2003; 340-2, 844-8]. Using substitutional gold (Aus) as a marker defect, electric levels of VO are found at E (-/ 0) = Ev + 0.30 eV and E (= /-) = Ec - 0.29 eV, in excellent agreement with the respective experimental enthalpies for hole and electron emission Δ Hh (-/ 0) ≃ 0.32 eV and Δ He (= /-) = 0.26 eV, respectively. Finally, the migration, dissociation and reorientation energies of the defect are also reported.
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