The substrate effect on the in-plane orientation of vertically well-aligned ZnO nanorodsgrown on ZnO buffer layers

Abstract

Vertically well-aligned ZnO nanorods were synthesized without employing any metal catalysts onvarious substrates including glass, Si(111), 6H-SiC(0001) and sapphire (0001), which were pre-coatedwith c-oriented ZnO buffer layers, by simple physical vapour deposition. The alignments ofthe ZnO nanorods on the different substrates depend on the crystallographicalignments of the pre-coated ZnO buffer layers. The ZnO nanorods grown on glass andSi(111) are vertically aligned but randomly oriented in the in-plane direction. Incontrast, the vertically aligned ZnO nanorods on 6H-SiC(0001) and sapphire(0001) show an in-plane alignment with azimuthally sixfold symmetry, whichindicates the epitaxial relationship between ZnO and the substrate. Similarly,photoluminescence measurements show the distinct appearance of ZnO nanorods ondifferent substrates. Besides the UV band, which was attributed to the recombination offree excitons near the band edge, defect-related visible emissions were also observedfor the samples grown on both glass and Si(111) substrates. However, the ZnOnanorods exhibit only strong band edge emission peaks with no noticeable deep levelemissions when grown on the 6H-SiC(0001) and sapphire (0001) substrates, whichconfirms the good crystalline and optical quality of the epitaxial ZnO nanorods.