The complex dielectric functions, ε(E)=ε
1(E)+ iε
2(E), of ZnO have been measured by spectroscopic ellipsometry (SE) in the photon-energy range between 1.5 and 5.0 eV at room temperature. The SE measurements are carried out on the surface parallel to the optic axis c, which allows the determination of the optical constants for light polarized perpendicular (E⊥c) and parallel to the c -axis (E//c). The measured SE spectra show the exciton peaks at ∼3.4 eV (E
0 edge). These ε(E) spectra are analyzed on the basis of a simplified model of the interband transitions. Excellent agreement is achieved between the calculated and experimental results over the entire range of photon energies. Dielectric-function-related optical constants, such as the complex refractive index n
*(E)=n(E)+ ik(E), absorption coefficient α(E) and normal-incidence reflectivity R(E), of ZnO have also been reported.
Single-crystalline hexagonal GaN (α-GaN) films have been grown on (0001) sapphire substrates by metalorganic chemical vapor deposition at 1040 °C. The complex dielectric functions, ε(E)=ε1(E)+iε2(E), of the epitaxial films have been measured by spectroscopic ellipsometry (SE) for E⊥c in the region between 1.5 and 5.0 eV at room temperature. Previously published ultraviolet SE spectra of α-GaN are examined by considering the effects of surface roughness using an analysis based on an effective medium model. Ex situ atomic force microscopy is used to assess independently surface flatness. By mathematically removing the effects of surface roughness, the most reliable ε(E) values for α-GaN are presented in the 1.25–10 eV photon–energy range. Theoretical dispersion analysis suggests that the E0 structure could be characterized by a three-dimensional M0 critical point and the E1α (α=A,B,C) structures by two-dimensional M1 critical points. To facilitate design of various optoelectronic devices, dielectric-function-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity of α-GaN are also presented.
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