Hao Tian

Density functional theory study of 3R– and 2H–CuAlO2 under pressure

We present a first-principles density-functional theory based study of the impact of pressure on the structural and elastic properties of bulk 3R– and 2H–CuAlO2. The ground state properties of 3R– and 2H–CuAlO2 are obtained, which are in good agreement with previous experimental and theoretical data. The analysis of enthalpy variation with pressure indicates the phase transition pressure between 3R and 2H is 15.4 GPa. The independent elastic constants of 3R– and 2H–CuAlO2 are calculated. As the applied pressure increases, the calculations show the presences of mechanical instability at 26.2 and 27.8 GPa for 3R– and 2H–CuAlO2, which are possibly related with the phase transitions.

Current conduction mechanisms in HfO2 and SrHfON thin films prepared by magnetron sputtering

Metal–oxide–semiconductor (MOS) capacitors incorporating HfO2 and SrHfON gate dielectrics were fabricated by magnetron sputtering. The interface quality, thermal stability, and electrical properties of the MOS capacitors have been investigated. Compared to HfO2 dielectric film, SrHfON dielectric film has thin interface layer with Si substrate, good thermal stability, and low leakage current densities. The dominant current conduction mechanisms (CCMs) of HfO2 film are Schottky emission or Poole–Frenkel emission at low and high electric fields. The main CCMs of SrHfON film are Schottky emission or Poole–Frenkel emission at low electric field, whereas, the CCMs are replaced by space charge limited current at high electric field.

The doping effect of N substituting for different atoms in orthorhombic SrHfO3

The first-principles density-functional theory has been carried out to study the structural, electronic, and optical properties of N-doped orthorhombic SrHfO3. The calculated results show the doping of N substituting for O is most favorable. When the doping of N substituting for Hf(Sr), the impurity energy level of N 2p states is introduced in the forbidden band. When the doping of N substituting for O1(O2), the width of the valence bands increases due to the presence of N 2p states in the top of valence bands. The doping of N resulting in red-shift has been studied by analysing the imaginary part of dielectric function

Theoretical Calculations on Electronic Structure and Optical Properties of Orthorhombic SrHfO3 in Cmcm Space Group

\varepsilon_{2} (\omega )

First-Principles Study on the Electronic Structure of N-Doped Orthorhombic SrHfO3

of N-doped orthorhombic SrHfO3.

Structure and optical properties of HfO2 thin films on silicon after rapid thermal annealing

Ab initio calculations are used to investigate the electronic structure and dielectric properties of crystalline monoclinic hafnium silicates (Hf1-xSixO2) as a function of silicon content x (x = 0, 0.25, 0.50, and 0.75). Densities of states (DOS), electronic band gaps, dielectric constants of Hf1-xSixO2 are calculated through a screened exchange (sX) method within the local density approximation (LDA). The sX method has been found to give good band gap for HfO2 dielectric. Band gaps of Hf1-xSixO2 are shown to increase with increasing concentration x of silicon. Static dielectric constants of Hf1-xSixO2 are observed to decrease with increasing the Si content. Results suggest that the optimal Si concentration should be below 25%, for which the permittivity higher than 13 can be achieved. Our calculations are in very good agreement with recent experimental findings.

First-principles study of structural, elastic, electronic and optical properties of rutile GeO2 and α-quartz GeO2

Abstract Electronic structure and optical properties of Cmcm orthorhombic SrHfO 3 were computed, using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The equilibrium lattice parameters of orthorhombic SrHfO 3 are in good agreement with experimental values. The band structure, the densities of states (DOS) and charge densities of Cmcm orthorhombic SrHfO 3 have been obtained. The band structure shows that Cmcm orthorhombic SrHfO 3 has direct band gap. The charge densities of Cmcm orthorhombic SrHfO 3 indicate that bonding between Hf and O is mainly covalent whereas the bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index and absorption coefficient of Cmcm orthorhombic SrHfO 3 have been predicted. The imaginary and real parts of the calculated complex dielectric function are close to the results of experimental measurements.

First-principles study of structural, elastic, electronic and optical properties of orthorhombic NaAlF4

We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, electronic structure, chemical bonding and optical properties of orthorhombic Li2BeSiO4. The calculated lattice parameters are in agreement with experimental data. The band structure shows a direct band gap. From the DOS analysis, charge densities and population analysis, electronic and chemical bonding properties have been studied. Furthermore, in order to understand the mechanism of optical transitions of orthorhombic Li2BeSiO4, the complex dielectric functions are calculated and analysed.