Growth Of ZnO Nano-Structures And Investigation Of Their Optical & Electrical Properties

Due to its excellent optical and electrical properties, wide applications and easy to synthesize, ZnO nanostructure has already become one of the most actively studied semiconducting nanomaterials in the nanotechnology world. Tremendous progress has been made in the fabrication and synthesis of ZnO nanostructures, but the controllability in preparation of ZnO nanostructures is still in the exploratory stage. According to the current controllable tendency in the nanostructure research, this thesis took the ZnO nanostructures by a hydrothermal method as the core subject and studied the controllability in preparation of ZnO nanostructures by the pre-conditions of ZnO seed layer. And we further combined the ZnO nanorods with the p-Si and p-GaN substrates to form the hybrid heterojuntions and investigated the electrical and optical properties. This thesis is divided into three main sections.The first section studied the controllability and characteristics of the obtained ZnO nanostructures. We started with the controllability in the growth orientation of the ZnO nanostructure. Results show that ZnO seed layer on the substrates can engineer the growth orientation of the ZnO nanorod array. The effect of pre-conditions, e.g. pre-annealing treatment and thickness, of the ion-beam sputtered seed layer on the growth of thereon ZnO nanostructures are investigated for the first time. XRD and SEM results indicate that better crystallinity of the seed layer will result in a greater growth rate of thereon ZnO nanorods; and thicker seed layer will induce a higher density of thereon nanorods and well-aligned ZnO nanorod array is obtained on the 1 nm ultrathin ion-beam sputtered seed layer. The XPS results further revealed that the ratio of O and Zn for the obtained ZnO nanostructures is slightly less than 1, still O deficient. The photoluminescent (PL) results show that the optical properties of the obtained ZnO nanostructure can be comparable to most the reported ZnO films'results and the well-aligned ZnO nanorods have better optical emission than the randomly aligned ZnO nanrods. In addition, a novel method for controlling the horizontal growth of the ZnO nanorod array is introduced.In the second section, the electrical properties of n-ZnO nanorods/p-Si heterojunctions were investigated. The experimental results show that under forward bias, theâ… -â…¤curve of this structure can be divided into three regions, linear ohmic region, exponential region and power-law region. And the result is consistent with the space charge limited current conductance model proposed by Lampert and Mark. The effect of post-annealing treatment on the electrical properties of this structure was further studied. PL and XPS results show that post-annealing treatment can reduce the adsorbed O element on the surface of the ZnO nanorods and improve the carrier injection of the n-ZnO nanorods/p-Si structure. In addition, the seed layer also has an effect on the transition voltage of the I-V curve. Results show that thicker seed layer will introduce more traps and result in higher trap-filled limit voltage in the n-ZnO nanorods/p-Si structure. Finally we studied the thermal stability of this structure from 300K to 450K and electrical properties of single ZnO nanorod. I-V results show that the grown ZnO nanorod is an n-type semiconductor.The electroluminescent (EL) properties of n-ZnO nanorods/p-GaN LED structure are presented in the third section. Experimental results show that the formed heterojunction can only work under reverse bias and the emission is centered at 550nm. Further results indicated that the parasitic'p-n'junction in the p-GaN substrate may be the origins of the emission of this structure under reverse bias. In addition, SEM results show that the ZnO nanostructures on the p-GaN can be improved by a seed layer. And the ZnO nanostructures on the ion-beam seed layer can even form a dense film. The n-ZnO nanorods/p-GaN structure with a Sol-gel seed layer showed a dominant ZnO-related emission centered at 600nm in the EL spectrum. So these results indicate that various ZnO seed layers will have an effect on the EL properties of n-ZnO nanorods/p-GaN structure, which is meaningful for the study of the LED based on ZnO nanostructures.