Epitaxial growth and time-resolved photoluminescence studies of AlN Epilayers

AJN epilayers with high optical qualities have been grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to probe the optical quality as well as optical transitions in the grown epilayers. Two PL emission lines associated with the donor bound exciton (D°X, or '2) and free exciton (FX) transitions have been observed, from which the binding energy of the donor bound excitons in A1N epilayers was determined to be around 16 meV. Time-resolved PL measurements revealed that the recombination lifetimes of the 12 and free exciton transitions in A1N epilayers were around 80 P5 and 50 p5, respectively. The temperature dependencies ofthe free exciton radiative decay lifetime and emission intensity were investigated, from which a value of about 80 meV for the free exciton binding energy in A1N epilayer was deduced. This value is believed to be the largest free exciton binding energy ever reported in semiconductors, implying excitons in A1N are an extremely robust system that would survive well above room temperature. The PL emission properties of A1N have been compared with those of GaN. It was shown that the optical quality as well as quantum efficiency of A1N epilayers is as good as that of GaN. It was shown that the thermal quenching ofPL emission intensity is greatly reduced in A1N over GaN, which suggests that the detrimental effect of impurities and dislocations or non-radiative recombination channels in A1N is much less severe than in GaN. The observed physical properties of AlN may considerably expand future prospects for the application of IIInitride materials.