Influence of a sapphire substrate on the emission spectra of gallium nitride light-emitting diodes

The emission spectra of green light-emitting diodes based on InGaN/AlGaN/Ga N heterostructures revealed a weak thin doublet line at the long-wavelength edge. This line is ascribed to luminescence of residual Cr3+ impurity ions in the sapphire substrate (similar to ruby, Al2O3:Cr, doublet wavelengths 692.9 and 694.3 nm). The ions are excited by visible diode radiation which is close to the absorption bands of the Cr3+ ions. It is shown that ruby lu minescence may be excited by radiation from blue and green GaN light-emitti ng diodes. (C) 1999 American Institute of Physics. [S1063-7850(99)01307-5].