In this paper, a POF connector based on a two ball lens system is researched. To analysis the coupling efficiency of the
connector, a numerical model was established using ray tracing method and four defects of transverse offset, longitudinal
offset, angular misalignment and gap between two ball lenses in the coupling system are calculated. The calculation
results show that the POF connector based on a two ball lens system can improve the coupling efficiency between two
fibers and has good tolerance to the connection defects of transverse, longitudinal and angular misalignments.
The first-principles with pseudopotentials method based on the density functional theory was applied to calculate the
electronic structure of ZnO doped with carbon. It optimized the wurtzite structure of ZnO when carbon was on the
substitutional O site (CO), the substitutional Zn site (CZn) or in the interstitial site (Ci) respectively. The calculated conclusions show that the CZn and Ci behave as donor. However, CO results in acceptor. It is illuminated that CO is helpful to achieve p-type 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.
In this paper we have studied AgxZn1-xO alloys by the method of the density functional theory with the generalized
gradient approximation and the projector augmented wave pseudopotentials. In order to calculate the crystal structure of
the AgxZn1-xO alloys with wurtzite structure, we adopt a 32-atom AgnZn16-nO16 supercell which allows the simulation of
the silver composition x=0.0, 0.0625, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875, and 1.0. The calculated results show
that the formation energies and the calculated lattice constants of AgxZn1-xO increases by the x increasing. As a result, the
doping of Ag becomes more difficult with the increment of Ag concentration. Furthermore,the solid solubility of Ag in
wurtzite ZnO is small.
Except for the group-V dopants, Ag, as a group IB element, could also act as an acceptor in ZnO, if incorporated on
substitutional Zn sites. In this paper, first-principles density-functional calculations have been performed to investigate
various distributions of Ag in ZnO. The first-principles calculations were carried out using the density functional theory
with the generalized gradient approximation (GGA) and the projector augmented wave (PAW) pseudopotentials. The
supercell employed contained 32 atoms that corresponded to a 2×2×2 supercell of ZnO. The various distributions of Ag
in ZnO have been calculated corresponding to each possible location. In conclusion, the calculation results show that the
formation energies of Ag on the substitutional Zn site (AgZn) and incorporation in the interstitial site (Agi) are smaller
than that of Ag on the O site (AgO). When AgZn and Agi coexist and are partitioned by an oxygen atom layer, the
formation energy and the total energy is the smallest. As a result, Ag prefers to distribute discretely in Ag doped ZnO. It
is also found that our results are in agreement with other experimental results.
Using first-principles calculations, we investigated the structure and electronic properties of Ag-related defects in
ZnO. The calculation results indicate that AgZn behaves as acceptor. Simultaneously, by comparing the formation energy
and electronic structure of Ag-related defects in ZnO, Oi-AgZn behaves as acceptor in Ag-doped ZnO and it is better to
gain p-type ZnO. However, Hi-AgZn complex has the lowest formation energy. Thus, the formation of the other point
defects is greatly suppressed by the formation of Hi in Ag-doped ZnO. Moreover, the H atoms can be easily dissociated
from hydrogen-passivated complexes by post-annealing at moderate temperatures, thus, codoping Ag with H may be a
good method to achieve p-type in Ag-doped ZnO.
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