Band Structure and Optical Response in Ga _x Al _1—x N

Abstract

The calculation of the optical functions for Ga x Al 1Àx N (x 0X85 and 0.65) solid alloys is conducted using the ab initio norm-conserving pseudopotential (NCPP) and linear combination of atomic orbitals (LCAO) methods. Simultaneously, we have carried out experimental investigations of the reflection spectra and using Kramers-Kronig relations the imaginary part of the dielectric susceptibility is evaluated. Calculations of the solid alloys are performed using the superposition of the particular pure single crystalline compounds with an appropriate weighting factor. Calculations are performed as a function of energy cut-off as well as the degree of orthogonalization of the normconserving pseudo-wavefunction to the LCAO wavefunctions. The optical functions at zero frequency give an overestimated value compared with the experimental data. The best agreement with the experiment can be achieved by using the orthogonalization procedure between the pseudowave and LCAO wavefunctions. The latter ones help to understand the appearance of incommensurate modulations in the mentioned compounds. The possibility of achieving good agreement between experimental and theoretical data is shown.

Influence of Non-Stoichiometric Defects on Electrooptics in KNbO3

“…Based on the band energy structure calculations, we evaluate spectral dependences of the imaginary part of the dielectric susceptibility for various values of the parameter X c and we determine particular contributions of the different cluster groups to the optical spectra. A similar approach has been successfully applied to the disordered materials: glasses [10], guest±host polymers [11], and complex and doped crystals [12,13].…”

“…This procedure for the particular cases of vacancy-induced states and solid alloys is described in Refs. [13,19]. The Fourier transformations of the pseudopotential for the a-th kinds of ions take the form…”

“…A procedure of orthogonalisation of the NCPP with respect to local states has been described in Refs. [12,13] for the case of GaAlN and KLiSO 4 single crystals.…”

Quantum Yield of GaN and (Ga, Al)N Band-Gap Graded Ultraviolet p–n Detectors

“…s 1 is the surface recombination rate on the illuminated side and d is the width of the linearly graded n-type layer. Since Al x Ga 1± ± x N is a direct-band-gap material [13,14], the absorption coefficient a is modeled as [15] a zY l 2X2 Â 10 5…”

Influence of Non-Stoichiometric Defects on Optical Properties in LiNbO3

“…We have successfully applied the similar approach to the disordered materials: glasses ), guest-host polymers (SAHRAOUI et al (1999)) complex and doped crystals (MALACHOWSKI et al (1998)). We have successfully applied the similar approach to the disordered materials: glasses ), guest-host polymers (SAHRAOUI et al (1999)) complex and doped crystals (MALACHOWSKI et al (1998)).…”