Radiative energy transfer in GaN-Mg/Al2O3-Cr3plus epitaxial systems

A photoluminescence study of undoped and Mg-doped GaN epitaxial layers grown by means of metalorganic vapor phase eptiaxy (MOVPE) on sapphire (Alsub2Osub3) substrates is reported. In undoped n-type GaN the characteristic excition emissions are observed near the band gap (Esubg=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 Rsub1,2 lines of Crhigh3plus(3dhigh3) trace impurities in the Alsub2Osub3 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 high4Asub2-high4Tsub1 of Crhigh3plus(3dhigh3) trace impurities in the Alsub20sub3 substrate.