The Growth And Physical Characteristics Of Low-Dimensional ZnO Materials

In this thesis, we discuss the formation of hexagonal cross‐section, field emission of one‐dimensional ZnO materials and p‐type doping of ZnO thin films. On purpose to investigate the formation of hexagonal cross‐section, we fabricate large‐area and uniform ZnO 1D materials sucessfully by catalyst‐free chemical vapor deposition(CFCVD). It is found that almost all the ZnO microprisms have hexagonal cross‐section as well as other groups'. In order to illuminate the interesting phenomena, we build a model for simulating ZnO growth in a‐b lattice plane. Basing on the lowest energy theory, it is believed that in every saturation step, the counteratom will inhabit the position where it can saturate the dangling‐bonds farthest. As a result, the growth in a‐b plane will terminate with a hexagonal cross‐section.Randomly‐aligned ZnO hexagonal nanoprisms are fabricated by using catalyst‐free chemical vapor deposition (CFCVD) in a double‐tube system. The growth mechanism is attributed to vapor‐solid mechanism. The absence of metal catalyst nanoparticles on the top of nanoprisms ensures a real field emission from ZnO nanostructures. It is shown that the emission current density of 1 mA/cm2 is obtained at 6.6 V/μm macroscopic electric field. The field enhancement factor (γ= 3000) is far larger than the theoretical value(γ= 205). By comparing the discrepancy of experimental and estimated value of field enhancement factor, it is believed the actual emitters are just the salient instead of the whole tip part of ZnO hexagonal nanoprisms. It implies that the dominating contributions can be attributed to the pyramidal salients other than the whole crests of hexagonal nanoprisms. In order to investigate the influence of interface junction between the roots of ZnO micro‐prisms (ZOMPs) and the Si substrate on the field emission behaviour from ZOMPs, we synthesize the ZOMPs on p‐type and n‐type Si substrates, separately. The I‐V curves analyzed by AFM show that the interface junctions between the ZnO micro‐prisms and the p‐type substrate and between the ZnO micao‐prisms and the n‐type Si substrate exhibit p‐n junction behaviour and ohmic contact behaviour, respectively. The formation of the p‐n heterojunction and ohmic contact is ascribed to the intrinsic n‐type conduction of ZnO material. Better field emission performance(lower onset voltage and larger emission current)is observed from an individual ZnO micro‐prism grown on the n‐type Si substrate. It is suggested that the...