Ab initio study of the bandgap engineering of Al1−xGaxN for optoelectronic applications

Abstract

A theoretical study of Al 1−x Ga x N, based on the full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap, optical properties, and nonlinear behavior of the compound with the change in the Ga concentration. It is found that the bandgap decreases with the increase in Ga. A maximum value of 5.50 eV is determined for the bandgap of pure AlN, which reaches a minimum value of 3.0 eV when Al is completely replaced by Ga. The static index of refraction and dielectric constant decreases with the increase in the bandgap of the material, assigning a high index of refraction to pure GaN when compared to pure AlN. The refractive index drops below 1 for higher energy photons, larger than 14 eV. The group velocity of these photons is larger than the vacuum velocity of light. This astonishing result shows that at higher energies the optical properties of the material shifts from linear to nonlinear. Furthermore, frequency dependent reflectivity and absorption coefficients show that peak values of the absorption coefficient and reflectivity shift toward lower energy in the ultraviolet ͑UV͒ spectrum with the increase in Ga concentration. This comprehensive theoretical study of the optoelectronic properties predicts that the material can be effectively used in the optical devices working in the visible and UV spectrum.

Transition energies and direct-indirect band gap crossing in zinc-blende AlxGa1−xN

“…Guerrero et al 23 carried out room temperature reflectivity measurements on MBE grown zb-Al An analysis of reported theoretical data reveals inconsistencies in the numerical description of the composition dependence of the fundamental zb-Al x Ga 1−x N band gaps as well. Recently, Amin et al 27 employed the Wu-Cohen generalized gradient approximation (GGA) within a full-potential linearized augmented plane wave approach (FLAPW) to calculate the zb-Al x Ga 1−x N band gaps over the entire composition range. Consistent with the band gap data of Okumura et al, the alloy band gap was found to be direct for the entire composition range, increasing linearly from a direct band gap of 3.00 eV in zb-GaN to a direct band gap of 5.50 eV in zb-AlN.…”

Ab initio study on the electronic, optical and electrical properties of Ti-, Sn- and Zr-doped ZnO

“…The imaginary part of the dielectric function, ε 2 (ω), represents the light absorption in the crystal, which can be obtained by calculating the momentum matrix elements between the occupied and the unoccupied states [26], obeying the selection rule. Then, the real part of the dielectric function, ε 1 (ω), governs the propagation behaviour of electromagnetic field in a material, is derived from the imaginary part using the Kramers-Kronig transformation [27].…”

EFFECT OF Al DOPING CONCENTRATION ON MICROSTRUCTURE, PHOTOELECTRIC PROPERTIES AND DOPED MECHANISM OF AZO FILMS

“…5, wavelength of tangent of transmittance upheaval place was at about 367-375 nm, indicating that characteristics of wavelength was¯rst blue shift and then red shift. A detailed research about the variations in the optical properties, bandgap, and nonlinear behavior of the compound with the change in the Ga doping concentration was carried out by Amin 14 and Maqbool. 17 The above conclusion was similar to Dai Jielin's, 18 who prepared ZnO thin¯lms with doping In.…”