Abstract
Spectroscopy of photo-active centres in wide bandgap optical materials with absorption and emission bands in the range close to vacuum ultraviolet spectrum is complicated. In this work, the pulsed photo-ionization (PPI) transients, electron spin resonance (ESR) and proton induced luminescence spectroscopy techniques have been combined to evaluate the origin and parameters of deep centres in crystalline sapphire substrates. Additionally, the layered structures with MOCVD grown thin top layers of GaN, AlGaN and AlN on sapphire substrates were examined in order to clarify origin of emission bands related to the epilayers and sapphire. The sapphire assigned emission bands have been ascribed to the F+ centres, characterized by photo-activation energy of 4.8 eV. Prevailing of F+ centres has been confirmed by ESR spectroscopy results. The covering nitride layers of AlN, AlGaN and GaN led to appearance of the additional PPI spectral peaks ascribed to recombination on the interface between epitaxial material and sapphire substrate.
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