Investigation of optoelectronic properties of pure and Co substituted α-Al_2O_3 by Hubbard and modified Becke–Johnson exchange potentials

Advanced GGA ＋ U（Hubbard） and modified Becke–Johnson（mBJ） techniques are used for the calculation of the structural, electronic, and optical parameters of α-Al2-x CoxO3（x = 0.0, 0.167） compounds. The direct band gaps calculated by GGA and m BJ for pure alumina are 6.3 eV and 8.5 eV, respectively. The m BJ approximation provides results very close to the experimental one（8.7 eV）. The substitution of Al with Co reduces the band gap of alumina. The wide and direct band gap of the doped alumina predicts that it can efficiently be used in optoelectronic devices. The optical properties of the compounds like dielectric functions and energy loss function are also calculated. The rhombohedral structure of theα-Al2-x CoxO3（x = 0.0, 0.167） compounds reveal the birefringence properties.

Optoelectronic Properties of Pure and Co Doped Indium Oxide by Hubbard and modified Becke–Johnson Exchange Potentials

Structural and optoelectronic properties of pure and Co doped In2O3 are studied by employing the full-potential linearized augmented plane wave method,which is known to produce highly accurate results.First principles calculations are performed with ordinary generalized gradient approximation(GGA)along with new Hubbard and modified Becke-Johnson exchange(mBJ)potential techniques.Improved band gap results are obtained for In2O3 with GGA+U and mBJ.In the case of mBJ,the band gap values are 3.5 eV and 3.4 eV for rhombohedral and cubic phases,which are in close agreement with the experimental data.Substitution of In by Co 25%alters the energy gap and a spin splitting effect is observed in these phases.For the spin-up state,it remains semiconductor,whereas for the spin-down state it shows semimetallic behavior.The value of static refractive index n(0)is 1.74 for the cubic phase,while in rhombohedral phase the values of n(0)are 1.77 and 1.74 along xx and zz optical axes,respectively.The calculated optical properties conform anisotropy in the rhombohedral phase and these materials can be potential candidates for the optoelectronics applications.

Structural and Optoelectronic Properties of Cubic CsPbF3 for Novel Applications

Chemical bonding as well as structural,electronic and optical properties of CsPbF3 are calculated using the highly accurate full potential linearized augmented plane-wave method within the framework of density functional theory(DFT).The calculated lattice constant is found to be in good agreement with the experimental results.The electron density plots reveal strong ionic bonding in Cs-F and strong covalent bonding in Pb-F.The calculations show that the material is a direct and wide bandgap semiconductor with a fundamental gap at the R-symmetry point.Optical properties such as the real and imaginary parts of the dielectric function,refractive index,extinction coefficient,reflectivity,optical conductivity and absorption coefficient are also calculated.Based on the calculated wide and direct bandgap,as well as other optical properties of the compound,it is predicted that CsPbF_(3) is suitable for optoelectronic devices and anti-reflecting coatings.

Effects of ⅢB transition metals on optoelectronic and magnetic properties of HoMnO_3: A first principles study

The optoelectronic and magnetic properties of pure HoMnO3 and Ho0.67T0.33MnO3 （T = La, Y） alloys in hexagonal phase are theoretically investigated by using the first-principles calculations. The investigations are performed by means of the density functional theory through using the spin polarized generalized gradient approximation plus the Hubbard potential （SPGGA ＋ U, Ueff =3 eV）. The studied material HoMnO3 exhibits two indirect band gaps： 1.58 eV for the spin- up state and 0.72 eV for the spin-down state along the S-G direction within the SPGGA ＋ U approximation. It is found that the band gap of pure HoMnO3 for the spin-up state increases with increasing La and Y dopants. The results show that all of the studied materials have semi-metallic behaviors for the spin-up state and semiconducting character for the spin-down state. The substitutions of La and Y for Ho in HoMnO3 cause the static dielectric constant （ε0） to increase in the x direction but to decrease in the z direction. The calculated optical conductivity spectrum of HoMnO3 in a low energy range is in good agreement with the recent experimental data.

An Insight into the Structural, Electronic and Transport Characteristics of XIn_(2)S_(4) (X = Zn, Hg) Thiospinels using a Highly Accurate All-Electron FP-LAPW+Lo Method

The highly accurate full-potential linearized augmented plane wave plus local orbital method is employed to calculate the structural,electronic and transport properties of HgIn_(2)S_(4) and ZnIn_(2)S_(4).For ZnIn_(2)S_(4),the calculated In–S bond length is in good agreement with the experimental data.Bulk moduli results suggest that ZnIn_(2)S_(4) can afford more compressional effects than HgIn_(2)S_(4).The present study confirms that both HgIn_(2)S_(4) and ZnIn_(2)S_(4) are indirect band gap materials with band gap values of 0.705 eV and 1.533 eV respectively.The localized region existing in the most bottom valance band of both materials splits into states by 1 eV energy difference under the spin orbital coupling effect.Contour plots of charge density predict that chemical bonding in these compounds is a mixture of ionic and covalent characteristics.Effective mass results reveal that mobility of charge carriers in ZnIn_(2)S_(4) is greater than that in HgIn_(2)S_(4).

Electronic Band Structure and Optical Parameters of Spinel SnMg_(2)O_(4) by Modified Becke–Johnson Potential

The electronic band structure and optical parameters of SnMg_(2)O_(4) are investigated by the first-principles technique based on a new potential approximation known as modified Becke–Johnson(mBJ).The direct band gap values by LDA,GGA and EV-GGA are underestimated significantly as compared to mBJ-GGA,which generally provides the results comparable to the experimental values.Similarly,the present band gap value(4.85 eV)using mBJ-GGA is greatly enhanced to the previous value by EV-GGA(2.823 eV).The optical parametric quantities(dielectric constant,index of refraction,reflectivity,optical conductivity and absorption coefficient)relying on the band structure are presented and examined.The first critical point(optical absorption's edge)in SnMg_(2)O_(4) occurs at about 4.85 eV.A strong absorption region is observed,extending between 5.4 eV to 25.0 eV.For SnMg_(2)O_(4),static dielectric constantε1(0),static refractive index n(0),and the magnitude of the coefficient of reflectivity at zero frequency R(0)are 2.296,1.515 and 0.0419,respectively.The optoelectronic properties indicate that this material can be successfully used in optical devices.

Robust Half-Metallicity in a Chromium-Substituted AlN

We investigate half metallicity in a chromium(Cr)-substituted AlN dilute magnetic semiconductor using the full-potential linearized augmented plane-wave method.Our results show that Al_(0.75)Cr_(0.25)N is half metal and holds a net integer magnetic moment of 3μβwith lattice compression.The half−metallic nature is maintained from the relaxed lattice constant 4.36Åto 4.09Å.An abrupt change of the physical properties is observed at a robust transition lattice constant of 4.09Å,and the material transforms from half metal to metal.We find that up to 6%compression,the material maintains its half-metallic nature.Furthermore,we also confirm that the origin of ferromagnetism in Al_(0.75)Cr_(0.25)N is double exchange.