Exciton Spectra of An AlN Epitaxial Film on Sapphire Substrate Grown by Low-Pressure Metalorganic Vapor Phase Epitaxy

 
 

Exciton resonance energies in an AlN epilayer on sapphire substrate grown by low-pressure metalorganic sapphire substratesvapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral line shape was fitted considering A (Γ7vu→Γ7c) and BC (Γ9v,Γ7vl→Γ7c) exciton transitions. The fitting gave the values of them at 0 K to be 6.211 and 6.266 eV, giving the crystal- field splitting (Δcr) of approximately 55 meV. The AlN film exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature ΘE was estimated to be 580 K.

A single‐crystalline aluminum nitride film is grown on a basal‐plane sapphire substrate and the c‐axis‐oriented films are grown on glass and gold‐film substrates at substrate temperatures as low as from 50 to 500 °C by using reactive rf planar magnetron sputtering. Surface acoustic waves are generated in both structures where interdigital transducers are located on the top of an aluminum nitride film and at the interface between the film and the substrate sapphire. The effective surface acoustic wave coupling factor k2 is 0.09 and 0.12%, respectively, for these interdigital transducer configurations. The aluminum nitride films sputtered on a gold film on a glass rod and on a glass sheet itself are also piezoelectric and used as bulk and surface acoustic wave transducers, respectively. These piezoelectric aluminum nitride films on glass and metal‐film substrates have become available for the first time because film growth at low temperature has become possible in the present study.


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