ZnO has a significant advantage for applications in optical devices. Especially ZnO doped with the rare earths (RE)
shows great electronic and optical properties. Based on the density functional theory, using the first-principles
calculations method, the crystal structure, electronic structure and optical properties of ZnO doped with various
concentrations of Er were investigated. The calculated results show that with the increase of concentrations of Er, the
volume of ZnO system is expanded. Simultaneously, the band gap of ZnO with dopant system becomes broad. However, the conductivity of system is enhanced with the decrease of Er concentration. On the other hand, imaginary part of the dielectric function of ZnO doped with Er also changes certainly. A new peak is observed in the low energy region. The results are helpful to gain a systematic understanding of geometrical structures, electrical structures and optical properties of Er-doped ZnO.
We have investigated the geometrical structures, the electronic properties, and the formation energies of nN-Mg codoped
ZnO in neutral state by adopting the first-principles calculations based on the density function theory (DFT). The
calculated results indicate that N atoms prefer to occupy the substitution O site and Mg substitutes the Zn site of the
nearest site of N, which act as an acceptor. Compared with the formation energies of various configurations in neutral
state, it is found that 4N-Mg complex has the lowest formation energy using NO as dopant resource under Zn-rich
condition, indicating that 4N-Mg codoping can enhance the N dopant solubility under this condition. Meanwhile, the Znrich
condition is better for p-type doping than the O-rich condition. It demonstrates that 4N-Mg complex is in favor of
achieving p-type conduction in ZnO. Simultaneously, analysis of density of states (DOS) of nN-Mg complex find that
the valence band maximum (VBM) has a little raise near the Fermi energy level, indicating that the complexes are the
typical p-type characteristic. However, for 4N-Mg complex, the Fermi level is located near the top of valence band.
Furthermore, from the band structure and PDOS of 4N-Mg complex, it is observed that the complex produces an
additional impurity band at the top of the valence band. Meanwhile, the PDOS value of 4N-Mg complex at the Fermi
level is relatively large. In addition, 4N-Mg complex has much lower ionization energy of 0.167eV than that of other
complexes. Therefore, better quality p-type conductivity is achieved by codoping 4N-Mg in ZnO.
Ag monodoped, N monodoped and (nN, Ag) codoped ZnO have been investigated by the first-principles calculations,
where the formation energies and ionization energies of various complexes and the electronic structure for 3N-Ag
complex are studied. The calculated results are that N prefers to substitute O site, and Ag substitutes Zn site under the
most growth condition, which indicate NO and AgZn all act as acceptors. Meanwhile, it's shown that N-Ag, 2N-Ag
complex contribute little to p-type conduction because of the relatively higher ionization energy. However, 3N-Ag
complex may have the lowest ionization energy among various complexes, while the formation energy of 3N-Ag is
lower than that of N monodoped, Ag monodoped, N-Ag and 2N-Ag complex under the Zn-rich condition, which
indicates that 3N-Ag complex is energetically favorable for the formation of p-type ZnO. Furthermore, by studying the
electronic structure of 3N-Ag complex, it may generate an additional impurity band above the valence band maximum of
ZnO. It is found that NO generated holes around the top of the valence band, and at the same time, N 2p states hybridized
with 4d states of AgZn at the Fermi energy, and the hybridization lowered the repulsive interaction between the two dual
acceptors, which enhance the concentration of impurities and the stability of the system, indicating that the dual
acceptors evidently improve p-type conductivity of ZnO. Thus, it is found that 3N-Ag complex is the better dopant
configuration. That can gain a better quality p-type ZnO under the Zn-rich condition. Our theoretical results are
consistent with the experiment results.
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