Huang Mei-Chun

Electronic structure of ScN and YN: density-functional theory LDA and GW approximation calculations

The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of 0.142 eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544 eV respectively, as revealed by calculations performed using GW approximation.

Electronic Structures of the Filled Tetrahedral Semiconductor LiMgN with a Zincblende-Type Structure

An ab initio method with mixed-basis norm-conserving non-local pseudo-potentials has been employed to investigate the electronic structures of LiMgN. The band structure, electronic density of states and charge density contour plot of LiMgN are also presented. By the calculation, we have found that LiMgN with a zincblende-type structure was an indirect gap semiconductor, and the value of indirect (Γ-X) energy band gap under the local density approximation was 2.97 eV. In addition, the strong covalent character for Li-N and Mg-N has also been found in LiMgN.

Electronic and Magnetic Properties of 3d Transition-Metal-Doped III–V Magnetic Semiconductor

A systematic study based on an ab initio calculation within a local spin density approximation is applied to material design of GaAs- and GaP-base doped by 3d transition metals. It is found that the ferromagnetic (FM) state is ready to achieve by V-, Cr- and Mn-doped GaP and GaAs. (Ga, Cr)P and (Ga, Cr)As are the most promising candidates for high Curie temperature (above room temperature). In order to increase the Curie temperature, the Mg co-doped method is applied to (Ga, Mn)P and (Ga, Mn)As. By the co-doping, the energy difference between the antiferromagnetic state and the FM state is enlarged, and the partial density of states of 3d-Mn at Fermi energy EF is increased, which increases the Curie temperature of the diluted magnetic semiconductors. By this co-doping, the anti-bonding state of 3d-Mn is pushed up to a higher region, hence the 3d electrons are more delocalized and itinerated. This makes double exchange dominant, and (Ga, Mn)P and (Ga, Mn)As more stable.

Structural and Electronic Properties of RuSi, RuGe and OsSi

Structural and electronic properties of RuSi, RuGe and OsSi are investigated by first-principle density-functional calculations based on ultrasoft pseudopotential and generalized gradient approximations for the exchange-correlation functional. The bulk moduli for RuGe and OsSi which have not been available from experiments are predicted to be 2.08 and 2.65 Mbar. Though all these compounds with a B20 structure are semiconductors according to the calculation, their band gaps are overestimated compared to those from experiments by a factor of about two.

Formation energies of lithium intercalations in AlSb, GaSb and InSb

By using the ab initio norm-conserving pseudopotential method, the lithium intercalations in AlSb, GaSb and InSb have been studied. The formation energies, changes of volumes, electronic structures and charge densities of the lithium interactions in zinc blende-type antimonides LixMSb (M = Al, Ga, In) are presented. Our calculations show that during lithium insertion in MSb the lithium intercalation formation energy per lithium atom are all around 2.0 eV. The volume expansions of AlSb, GaSb and InSb due to lithium insertions are relatively large, which might imply that the limit of Li intercalation in antimonides should be small.

Theoretical modeling of the interface recombination effect on the performance of III-V tandem solar cells

A typical GalnP/GalnAs/Ge tandem solar cell structure operating under AM0 illumination is proposed, and the current-voltage curves are calculated for different recombination velocities at both front and back-surfaces of the three subcells by using a theoretical model including optical and electrical modules. It is found that the surface recombination at the top GaInP cell is the main limitation for obtaining high efficiency tandem solar cells.

First-principles electronic structure of Cu+ luminescence centers in Cu-doped ZnS

The electronic structures of various Cu+ luminescence centers in wurtzite ZnS are studied by using first-principles linear muffin-tin-orbital method combining atomic sphere approximation. The results for ZnS:Cu:Cl and ZnS:Cu:Al show that Cu acceptor states are anomalously deep (beyond 2.7 eV above the top of valence band) and located near the bottom of conduction band in these two cases. On the other hand, the results for ZnS:Cu with sulfur vacancies manifest that the Cu+ center is an associated center, whose Cu d-like states are situated above the top of valence band.

STUDY OF MICROSTRUCTURE AND ELECTROLUMINESCENCE OF ZINC SULFIDE THIN FILM

The electroluminscent zinc sulfide thin film doped with erbium, fabricated by thermal evaporation with two boats, are examined. The surface and internal electronic states of ZnS thin film are measured by means of x-ray diffraction and x-ray photoemission spectroscopy. The information on the relations between electroluminescent characteristics and internal electronic states of the film is obtained. And the effects of the microstructure of thin film doped with rare earth erbium on electroluminescence are discussed as well.

Quasiparticle Band Structure of BaS

We calculate the band structure of BaS using the local density approximation and the GW approximation (GWA), i.e. in combination of the Green function G and the screened Coulomb interaction W. The Ba 4d states are treated as valence states. We find that BaS is a direct band-gap semiconductor. The result shows that the GWA band gap (Eg−GW = 3.921 eV) agrees excellently with the experimental result (Eg−EXPT = 3.88 eV or 3.9 eV).

Change of Work Function of Pd, Ag, K on Al(001) as a Function of External Electric Field

We present a local density functional calculation of the effect of an external electric field on the work function change of Pd and Ag adsorption on an Al(001) surface. The adsorption of K has also been considered for comparison. We found that the work functions for all the systems increased linearly when the strength of the external electric field was increased. Since the polarized electrons at the interstitial regions between the adsorbate and substrate for Pd/Al(001) and Ag/Al(001) react to the external electric field differently, the subtle differences between Pd/Al(001) and Ag/Al(001) bondings has been characterized through the comparison of the slopes of the work function change versus electric field.