Abstract
The complex dielectric function ɛ and the E0 excitonic and band-edge critical-point structures of hexagonal GaN are reported for temperatures from 30 to 690 K and energies from 0.74 to 6.42 eV, obtained by rotating-compensator spectroscopic ellipsometry on a 1.9 μm thick GaN film deposited on a c-plane (0001) sapphire substrate by molecular beam epitaxy. Direct inversion and B-splines in a multilayer-structure calculation were used to extract the optical properties of the film from the measured pseudodielectric function ⟨ɛ⟩. At low temperature sharp E0 excitonic and critical-point interband transitions are separately observed. Their temperature dependences were determined by fitting the data to the empirical Varshni relation and the phenomenological expression that contains the Bose-Einstein statistical factor.
Highlights
GaN has been used successfully to fabricate optoelectronic devices covering the visible and nearultraviolet spectrum
The complex dielectric function ε and the E0 excitonic and band-edge critical-point structures of hexagonal GaN are reported for temperatures from 30 to 690 K and energies from 0.74 to 6.42 eV, obtained by rotating-compensator spectroscopic ellipsometry on a 1.9 μm thick GaN film deposited on a c-plane (0001) sapphire substrate by molecular beam epitaxy
The thickness of the surface overlayer is physically reasonable, while that of GaN film is equal to the planned value
Summary
GaN has been used successfully to fabricate optoelectronic devices covering the visible and nearultraviolet spectrum. We report the ordinary (E ⊥ c) component ε of the dielectric tensor of hexagonal GaN film for temperatures from 30 to 690 K and for energies from 0.74 to 6.42 eV. Ε almost exactly corresponds to the ordinary response because the contribution that dominates SE data is the projection of the dielectric tensor along the line formed by the surface and the plane of incidence.[15] In any case the difference between the GaN refractive indices for E ⊥ c and E c is just under 3%.18. A blue shift and an enhancement of structures are observed with decreasing temperature as a result of the reducing lattice constant and electron-phonon interactions.[21]
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