Wei Shu-Yi

Donor Binding Energy in GaAs/Ga1−x AlxAs Quantum Well: the Laser Field and Temperature Effects

Based on the effective-mass approximation theory and variational method, the laser field and temperature effects on the ground-state donor binding energy in the GaAs/Ga1−xAlxAs quantum well (QW) are investigated. Numerical results show that the donor binding energy depends on the impurity position, laser parameter, temperature, Al composition, and well width. The donor binding energy is decreased when the laser field and temperature are increased in the QW for any impurity position and QW parameter case. Moreover, the laser field has an obvious influence on the donor binding energy of impurity located at the vicinity of the QW center. In addition, our results also show that the donor binding energy decreases (or increases) as the well width (or Al composition x) increases in the QW.

Exciton States in Wurtzite InGaN Coupled Quantum Dots

Based on the effective-mass approximation, exciton states confined in wurtzite InxGa1−xN/GaN strained coupled quantum dots (QDs) are investigated, in which the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization are considered. We find that the barrier thickness between the two QDs has a considerable influence on the exciton states and the interband optical transitions. If the barrier thickness is increased, the exciton binding energy is decreased, the emission wavelength is increased, and the electron–hole recombination rate is obviously reduced. Our theoretical results are in qualitative agreement with the experimental measurements.

Chemisorption of Au on Si(001) surface

The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B1 site(bridge site), resulting in a Au–Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.

First-Principles Studies the Lattice Constants and the Electronic Structures of Diluted Magnetic Semiconductors （In,Mn）As

Lattice constants and electronic structures of diluted magnetic semiconductors (In, Mn) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the3d impurities were studied (x=1/2, 1/4, 1/8). The effect of varying Mn concentrations on the lattice constants and the electronic structures are shown.

First-Principles Studies for the Electronic Structures of Diluted Magnetic Semiconductors (Ga, Fe)As*

First-principles LMTO-ASA band calculations are performed for Ga1-xFexAs (x=1, 1/4, 1/8) by assuming supercell structures. It is found that the antiferromagnetic (AFM) state is stable for x=1/4. For x=1/8, ferromagnetic (FM) state is more stable than AFM state, and no stable magnetic state exists for x=1. In both the cases the magnetic moments of As and Ga atoms are parallel to those of the nearest Fe atoms due to the p-d hybridization. Further, the band structure shows rather localized Fe 3d state in the gap, and the parallel polarization is confined rather in the vicinity of Fe site.

The chemisorption of Mg on the Si (100)−(2 × 1) surface

The adsorption of a half monolayer of Mg atoms on the Si (100)−(2 × 1) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption systems of Mg atoms on the different sites are calculated. It has been found that the adsorbed Mg atoms are more favorable on the cave site above the surface than any other sites on the Si (100)−(2 × 1) surface and a metastable shallow site also exists above the surface. This is in agreement with the experimental results. The charge transfer and the layer projected density of states are also studied.

First-Principles Calculations of Atomic and Electronic Properties of Tl and In on Si(111)

The atomic and electronic structures of Tl and In on Si(111) surfaces are investigated using the first-principles total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML Tl adsorbed at the T4 sites on Si(111) surfaces. The adsorption energy difference of one Tl adatom between (√3 × √3) and (1 × 1) is less than that of each In adatom. The DOS indicates that Tl 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of Tl adatoms on Si(111) surfaces is mainly polar covalent, which is weaker than that of In on Si(111). So Tl atom is more easy to be migrated than In atom in the same external electric field and the structures of Tl on Si(111) is prone to switch between (√3 × √3) and (1 × 1).

Surfactant Effects of Au on Polar ZnO Surfaces

The electronic properties of one monolayer of Au atoms on polar ZnO surfaces are examined by first-principles slab calculations. It is found that an Au ad-layer on top of the surface is energetically more favourable than other gold diffused cases, and Au capping layer on the ZnO polar surfaces may modify the growing properties of ZnO nanostructures by enhancing the binding energy.

Initial Processes of Hydrogen Adsorption on Si(100) Surface

The adsorption of one monolayer H atoms on an ideal Si(100) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of adsorption systems of H atoms on different sites are calculated. It is found that the adsorbed H atoms are more favorable on B1 site (bridge site) with a distance 0.056 nm above the Si surface. There does not exist reaction barrier at the Si surface. The layer projected density states are calculated and compared with those of the clean surface. The charge transfers are also investigated.

Chemisorption of Fe on Au-passivated Si(001) surface

The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au–Fe mixed layer at the Fe/Au–Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au–Si(001) interface effectively, which is in agreement with the experimental results.