Temperature dependence of Effective band gap, Refractive index, Dielectric function and Model parameters C (x, T), A (x, T) of AlXGa1-XN. (original) (raw)

Anisotropic optical constants, birefringence, and dichroism of wurtzite GaN between 0.6 eV and 6 eV

Journal of Applied Physics, 2017

We report the room-temperature anisotropic dielectric functions (DFs), refractive indices, and absorption coefficients as well as birefringence and dichroism of wurtzite GaN in the spectral range between 0.6 eV and 6 eV. They have been determined by combined spectroscopic ellipsometry, optical retardation, and transmission measurements on a series of m-and c-plane bulk substrates prepared from crystals grown by hydride vapor phase epitaxy. The accuracy of the derived DFs is estimated by investigation of the role of mosaicity-related crystal imperfections, self-consistency test based on a Kramers-Kronig analysis, and examination of the influence of kind of overlayer. We also briefly discuss optical properties of a highly defective near-surface layer of GaN crystals introduced by their mechanical polishing. Published by AIP Publishing.

Optical properties of wurtzite AlxGa1-xN (x < 0.1) parallel and perpendicular to the c axis

Physical Review B, 2001

Measurements of the dielectric function components parallel and perpendicular to the optical axis of wurtzite GaN are presented. The results are obtained on a multilayer Al x Ga 1Ϫx N / GaN film grown on ␥-LiAlO 2 which exhibits a very small amount of Al (xϽ0.1) in the uppermost layer. We use the spectroscopic ellipsometry to determine () around the interband critical points of GaN up to 9 eV. Since the optical axis of the films are parallel to the surface, a separation of the different components is possible. The line shape of the measured tensor components ʈ and Ќ is in very good agreement with results of recently published band-structure calculations. By comparison with the calculations we assign structures in the dielectric function to critical points in the Brillouin zone. In addition, a comparison with similar spectra for CdS and CdSe is presented, together with a discussion of possible spin-orbit splitting effects.

Systematic measurement of AlxGa1−xN refractive indices

Applied Physics Letters, 2001

Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic Al x Ga 1Ϫx N epitaxial layers with 0.0рxр1.0 throughout the visible wavelength region. The dispersion, measured by a prism coupling waveguide technique, is found to be well described by a Sellmeier relation. Discrepancies among previous measurements of refractive index dispersion, as a consequence of different growth conditions and corresponding band gap bowing parameter, are reconciled when the Sellmeier relation is parameterized not by x but by band gap energy.

Birefringence of GaN/AlGaN optical waveguides

Applied Physics Letters, 2003

We have experimentally studied the birefringence of wurtzite GaN grown on a sapphire substrate. The measurements were done with single-mode GaN/AlGaN planar optical waveguides on c-plane grown heterostructure films. The refractive indices were found to be different for signal optical field perpendicular or parallel to the crystal c axis (n⊥≠n∥). More importantly, we found an approximately 10% change in index difference Δn=n∥−n⊥ with variation of the waveguide orientation in the a–b plane, and a 60° periodicity was clearly observed. This is attributed to the hexagonal structure of nitride materials.

Temperature Dependence of Hexagonal-GaN Optical Properties below the Bandgap

physica status solidi (b), 1999

First, spectroscopic ellipsometry (SE) is carried out at 300 K together with reflectivity measurements versus temperature from 4 to 300 K, in order to determine the temperature dependence of the refractive index of h-GaN films in the transparent region (350 to 600 nm). The SE measurements are carried out at two angles of incidence (72 and 75 ) and the refractive index is well described with a Sellmeier's dispersion law. Secondly, the reflectivity related to the A, B and C excitons is detected and analysed within a multi-polariton model including the spatial dispersion. The temperature dependence of excitonic transition energies, broadening parameters and oscillator strengths are deduced between 4.5 and 250 K. The energy variation is analysed in terms of a Bose-Einstein expression. Concerning the behaviour of the broadening parameters at low temperature, the participation of either the acoustic phonons or the E 2 phonon mode to the exciton±phonon interaction is considered. The latter contribution is in better agreement with experimental data.

Temperature-dependent optical band gap of the metastable zinc-blende structure beta-GaN

Physical Review B, 1994

The temperature-dependent (10-300 K) optical band gap Eo(T} of the epitaxial metastable zincblende-structure P-GaN{001)4 X 1 has been determined by modulated photoreflectance and used to interpret low-temperature photoluminescence spectra. Eo in P-GaN was found to vary from 3.302%0.004 eV at 10 K to 3.231+0.008 eV at 300 K with a temperature dependence given by Eo( T) =3.302-6.697X10 T /(T+600} eV. The spin-orbit splitting ho in the valence band was determined to be 17+1 meV. The oscillations in the photore6ectance spectra were very sharp with a broadening parameter I of only 10 meV at 10 K. The dominant transition observed in temperature-dependent photoluminescence was attributed to radiative recombination between a shallow donor, at -= 11 meV below the conduction-band edge and the valence band.