Temperature-dependent photoluminescence and photoluminescence excitation of aluminum monodoped and aluminum-indium dual-doped ZnO nanorods

Abstract

The authors report fabrication of aluminum monodoped ZnO (AlZnO) and aluminum-indium dual-doped ZnO (AlInZnO) nanorods arrays. Optical properties of AlZnO and AlInZnO nanorods are studied through temperature-dependent photoluminescence (PL) and PL excitation (PLE). Compared to AlInZnO nanorods, AlZnO nanorods possess better PL properties, as evidenced by a higher ratio of intensity of band-edge emission to green emission at 10 K and a higher PL intensity at room temperature. As supported by x-ray diffraction patterns, AlZnO nanorods also have higher crystallinity than AlInZnO nanorods. Indium doping induces a pronounced donor-acceptor pair transition of ∼3.22 eV at 10 K, the mechanism of which is discussed. Temperature-dependent energies of the A free exciton (FXA) and neutral donor bound exciton (D0X) are analyzed and the Einstein temperature is deduced to be ∼310 K. An activation energy of ∼8 meV is determined from the quenching of D0X as a function of temperature in AlInZnO nanorods. It is interpreted that nonradiative centers caused by indium segregation result in the small activation energy. Moreover, temperature-dependent PLE of AlZnO and AlInZnO nanorods reveals that the donor levels of aluminum and indium are 75 and 102 meV, respectively. Considering that the donor level of Al is shallower than that of In and that the optical and crystal properties of AlZnO nanorods are better than those of AlInZnO nanorods, aluminum is a better n-type dopant than indium for ZnO nanorods.