Acceptor-bound exciton transition in Mg-doped AlN epilayer

Mg -doped AlN epilayers grown by metalorganic chemical-vapor deposition have been studied by deep ultraviolet time-resolved photoluminescence (PL) spectroscopy. A PL emission line at 6.02eV has been observed at 10K in Mg-doped AlN, which is about 40meV below the free-exciton transition in undoped AlN epilayer. Temperature dependence of the PL intensity of this emission line also reveals a binding energy of 40meV. This transition line is believed to be due to the recombination of an exciton bound to neutral Mg acceptor (I1) with a binding energy of Ebx=40meV. This value is also about 10% of the energy level of Mg impurity in AlN satisfying Haynes’ rule. The recombination lifetime of the I1 transition in Mg-doped AlN has been measured to be 130ps, which is close to the expected value. The larger Ebx of the acceptor-bound exciton in AlN than that in GaN is due to large effective masses of the electrons and holes, as well as the energy level of Mg impurity.