RADIATIVE ENERGY-TRANSFER IN GANMG/AL2O3CR3+ EPITAXIAL SYSTEMS

A photoluminescence study of undoped and Mg-doped GaN epitaxial layers grown by means of metalorganic vapor phase epitaxy (MOVPE) on sapphire (Al2O3) substrates is reported. In undoped n-type GaN the characteristic exciton emissions are observed near the band gap (E(g) = 3.47 eV). Mg-doped GaN shows a very strong blue donor-acceptor recombination band at about 3.2 eV. Only in these samples is a sharp line detected at 1.79 eV which is due to the characteristic R1,2 lines of Cr3+ (3d3) trace impurities in the Al2O3 substrate. An obvious explanation for this effect is the very efficient radiative energy transfer from the GaN:Mg layer emitting blue photons into the absorption band 4A2 --> 4T1 of Cr3+(3d3) trace impurities in the Al2O3 substrate.