The electrical and luminescent properties of the GaN epitaxial films grown on AlN-coated sapphire by reactive molecular beam epitaxy have been studied. The GaN films on AlN epitaxial films have larger Hall mobilities and show more intense cathodoluminescence peaks at a wavelength of 360 nm than those of the GaN films grown directly on sapphire, which suggests that the crystal qualities of GaN films are improved by use of AlN-coated sapphire as substrates. The lattice matching and small difference of the thermal expansion coefficients between GaN and AlN are considered to result in the improvements.
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Irradiation of fast particles like 1 MeV electrons and 2 MeV protons was made for single crystalline cubic silicon carbide (3C‐SiC) grown epitaxially on Si by chemical vapor deposition in order to introduce point defects in the material. Intrinsic point defects in 3C‐SiC have been characterized by electron spin resonance (ESR), positron annihilation spectroscopy (PAS), Hall and photoluminescence (PL) techniques. The structure and annealing behavior of intrinsic defects, e.g. monovacancies at silicon and carbon sublattice sites, are described based on the results obtained by ESR and PAS. The contributions of such point defects to electrical and optical properties of 3C‐SiC are discussed using the Hall and PL results, with a brief review of published work.
Optical absorption of AlN thin films shows a ’’knee’’ structure at 6.2 eV and an intense band at 7.8 eV. The structure at 6.2 eV is interpreted as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV. Dichroism observed at the absorption edge indicates that the transition Γ1v–Γ1c (E∥c) is of lower energy than the transition Γ6v–Γ1c (E⊥c). Strong dichroism in the 7–8-eV region is thought to cause the birefringence of AlN.
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