Theoretical study of the insulating oxides and nitrides: SiO2, GeO2, Al2O3, Si3N4, and Ge3N4

Abstract

An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO2, GeO2, Al 2O3, Si3N4, and Ge3N 4. Their important polymorphs are considered which are for SiO 2: α-quartz, α- and β-cristobalite and stishovite, for GeO2: α-quartz, and rutile, for Al2O 3: α-phase, for Si3N4 and Ge 3N4: α- and β-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density functional theory within the local density approximation. Two different norm-conserving ab initio pseudopotentials have been tested which agree in all respects with the only exception arising for the elastic properties of rutile GeO2. The agreement with experimental values, when available, are seen to be highly satisfactory. The uniformity and the well convergence of this approach enables an unbiased assessment of important physical parameters within each material and among different insulating oxide and nitrides. The computed static electric susceptibilities are observed to display a strong correlation with their mass densities. There is a marked discrepancy between the considered oxides and nitrides with the latter having sudden increase of density of states away from the respective band edges. This is expected to give rise to excessive carrier scattering which can practically preclude bulk impact ionization process in Si3N4 and Ge3N4. © Springer Science+Business Media, LLC 2007

Formation of a two-dimensional layered structure in silica under shear stresses: Anab initiostudy

“…The bandgap ␣-cristobalite is calculated to be 5.47 eV, in good agreement with the previous DFT results of 5.58 and 5.52 eV. 26,27 The band-gap energy of the P4m2 phase and the single layer is predicted to be 3.54 eV and 4.38 eV, respectively. These values are noticeably smaller than that of ␣-cristobalite.…”

Systematic study of the influence of different equations of states on the calculation of elastic properties†

“…The fitted equilibrium volume, the bulk modulus and the pressure derivative of the bulk modulus are in good agreement with other experimental [46][47][48][49] and theoretical [50][51][52][53][54] studies. As shown in Table 4 and already discussed for the AlN compounds, the predicted equilibrium volume V 0 and bulk modulus K of α-SiO 2 and st-SiO 2 do not depend on the chosen EOS for small compression up to V /V 0 = 0.9.…”

Anodization of aluminium thin films on p++Si and annihilation of strong luminescence from Al2O3

“…For comparison, each spectrum was normalised to the absorption observed at 1100 nm. Theoretical band gap of Al 2 O 3 is given as 6.2 eV [10]. However, an effective absorption within the band gap is evident and gets stronger after annealing at 550 1C.…”

“…Alumina is optically transparent from deep UV to IR region because of wide band gap (6.2 eV) [10]. High temperature stability of Al 2 O 3 and compatibility of Al anodization with Si process technology lead to a new route for the optical path fabrication within Si based chips in future.…”