Lu Peng-Fei

Electronic Structure and Optical Properties of Antimony-Doped SnO2 from First-Principle Study

A first-principles study has been performed to calculate the electronic and optical properties of the SbxSn1−xO system. The simulations are based upon the method of generalized gradient approximations with the Perdew—Burke—Ernzerhof form in the framework of density functional theory. The supercell structure shows a trend from expanding to shrinking with the increasing Sb concentration. The increasing Sb concentration induces the band gap narrowing. Optical transition has shifted to the low energy range with increasing Sb concentration. Other important optical constants such as the dielectric function, reflectivity, refractive index, and electron energy loss function for Sb-doped SnO2 are discussed. The optical absorption edge of SnO2 doped with Sb also shows a redshift.

Electronic Structure and Optical Properties of Zinc-Blende InxGa1−xNyAs1−y by a First-Principles Study

Electronic structure and optical properties of the zinc-blende InxGa1−xNyAs1−y system are calculated from the first-principles. Some relative simulations are performed using CA-PZ form of local density approximation in the framework of density functional theory. The supercell of intrinsic GaAs is calculated and optimized by using different methods, and the LDA-CA-PZ gives the most stable structure. The band gap of InxGa1−xAs tends to decrease with the increasing In concentration. For the case of In0.0625Ga0.9375NyAs1−y, the band gap will show slight difference when N concentration is larger than 18.75%. The optical transition of In dopant in GaAs exhibits a red shift, while it is a blue shift for the N dopant in InGaAs. Besides, dielectric function, reflectivity, refractive index and loss function in different doping model of InxGa1−xNyAs1−y are also discussed.

The electronic and magnetic properties of (Mn,C)-codoped ZnO diluted magnetic semiconductor

The electronic and magnetic properties of (Mn,C)-codoped ZnO are studied in the Perdew—Burke—Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic (FM) interaction without acceptor co-doping. We observe that the FM interaction for (Mn,C)-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, we demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the (Mn,C)-codoped ZnO is FM semiconductor with super-high Curie temperature (TC = 5475 K). These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.

Ferromagnetism in ZnO with (Mn,Li) codoping

First-principles calculations were performed to investigate the magnetic properties of Zn(Mn,Li)O based on the Perdew-Burke-Ernzerhof form of the generalized gradient approximation. Antiferromagnetic (AFM) ordering is the ground state in Mn-doped ZnO system without the codopant of Li, while seven different geometrical configurations of Zn(Mn,Li)O prefer stable ferromagnetic (FM) ordering. We found that dopant Li can effectively change the magnetic coupling in the ZnMnO system. The Curie temperature (TC) of FM ordering depends on the geometric configuration, and the highest TC is about 1388 K. The FM stabilization is greatly affected by Mn-Mn distance rather than by the position of dopant Li. We propose that dopant Li mediates FM coupling through a double exchange interaction or an RKKY interaction when Li is located, respectively, near or far from Mn ions.

Electronic Structure Magnetic Properties and Optical Properties of Co-doped AlN from First Principles

The electronic structure, magnetic properties, and optical properties of Co-doped AlN are investigated based upon the Perdew—Burke—Ernzerhof form of generalized gradient approximation within the density functional theory. The band gaps narrowing of Al1−xCoxN are found with the increase of Co concentrations. The analyses of the band structures and density of states show that Al1−xCoxN alloys exhibit a half-metallic character. Moreover, we have succeeded in demonstrating that Co doped AlN system in x = 0.125 is always antiferromagnetic, which is in good agreement with the experimental results. Besides, it is shown that the insertion of Co atom leads to redshift of the optical absorption edge. Finally, the optical constants of pure AlN and Al1−xCoxN alloy, such as loss function, refractive index and reflectivity, are discussed.

The effect of near laterally and vertically neighboring quantum dots on the composition of uncapped InxGa1−xAs/GaAs quantum dots

The composition of quantum dots has a direct effect on the optical and electronic properties of quantum-dot-based devices. In this paper, we combine the method of moving asymptotes and finite element tools to compute the composition distribution by minimizing the Gibbs free energy of quantum dots, and use this method to study the effect of near laterally and vertically neighboring quantum dots on the composition distribution. The simulation results indicate that the effect from the laterally neighboring quantum dot is very small, and the vertically neighboring quantum dot can significantly influence the composition by the coupled strain field.

First-principles study of electronic and optical properties in wurtzite Zn1–xCuxO

We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1–xCuxO. The simulations are based upon the Perdew–Burke–Ernzerhof form of generalised gradient approximation within the density functional theory. Calculations are carried out in different concentrations. With increasing Cu concentration, the band gap of Zn1–xCuxO decreases due to the shift of valence band. The imaginary part of the dielectric function indicates that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases. Besides, it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge. Meanwhile, the optical constants of pure ZnO and Zn0.75Cu0.25O, such as loss function, refractive index and reflectivity, are discussed.

The equilibrium composition in GexSi1−x/Si self-assembled alloy quantum dot

The equilibrium composition in strained quantum dot is the result of both elastic relaxation and chemical mixing effects, which have a direct relationship to the optical and electronic properties of the quantum-dot-based device. Using the method of moving asymptotes and finite element tools, an efficient technique has been developed to compute the composition profile by minimising the Gibbs free energy in self-assembled alloy quantum dot. In this paper, the composition of dome-shaped GexSi1−x/Si quantum dot is optimized, and the contribution of the different energy to equilibrium composition is discussed. The effect of composition on the critical size for shape transition of pyramid-shaped GeSi quantum dot is also studied.

Electronic and optical properties of GaN//AlN quantum dots with adjacent threading dislocations

We present a theory to simulate a coherent GaN QD with an adjacent pure edge threading dislocation by using a finite element method. The piezoelectric effects and the strain modified band edges are investigated in the framework of multi-band k p theory to calculate the electron and the heavy hole energy levels. The linear optical absorption coefficients corresponding to the interband ground state transition are obtained via the density matrix approach and perturbation expansion method. The results indicate that the strain distribution of the threading dislocation affects the electronic structure. Moreover, the ground state transition behaviour is also influenced by the position of the adjacent threading dislocation.

A new method for optimization of a photonic crystal waveguide termination

The work in this paper is based on a powerful function--fmincon in matlab and Finite Element Method, optimizing the shape and the position of dielectric rods surrounding the termination of a photonic crystal waveguide, in order to increase the directional emission. The method is simple, but can lead to useful results efficiently. More than fivefold improvement in power incident upon a target area over a simple termination is achieved, and the optimized structure is easier for fabrication.