Deep ultraviolet picosecond time-resolved photoluminescence studies of AlN epilayers.

A1N epilayers with high optical qualities have been obtained by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in A1N epilayers. Two PL emission lines associated with the donor bound exciton (D[sup 0]X, or I[sub 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 I[sub 2] and free exciton transitions in A1N epilayers were around 80 and 50 ps, respectively. The temperature dependencies of the 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. This together with other well-known physical properties of A1N may considerably expand future prospects for the application of III-nitride materials. [ABSTRACT FROM AUTHOR]