Fabrication And Performance Of ZnO Based Nanometer Field Effect Transistor

ZnO nanobelt/wire as an important qusi one-dimensional semiconductor, has promisingpotential for the applications in the field of photonics, piezotronics, sensor and transparentelectronics. There is especial value to research ZnO nanobelt/wire field-effect transistor,which acts as the basic building block to realize the above applications. In this dissertation,the back-gated ZnO nanobelt/wire field-effect transistors with top electrodes is fabricated bythe nanomechanical manipulation. Focusing on the two basic parameters, threshold voltageand mobility, we finished the following work：1. Threthold voltage instability in ZnO nanobelt field-effect transistor. With the smallthickness and single crystal nature of ZnO nanobelt, trapped charge near the interface isconfirmed by experiment. Combining the low channel defect density, long recover time oftherhold voltage and the bias stress data, we proved that the trapped charge comes from theelectron drift from the channel to dielectric under positive gate bias. Further, after replacingthe SiO2with polystyrene as dielectric, the above instability of threshold voltage can beavoided.2. Origin of field effect mobility difference in ZnO nanobelts and nanowires transistors.The result of finite element method reveals the large difference in ZnO nanobelt andnanowire transistor comes from the deviation in the parallel-plate capacitor (PPC) model andthe metallic cylinder on an infinite metal plate (MCIMP) model. The former underestimatesthe gate capacitance of nanobelt transistor, on the contrary, the latter overrates the gatecapacitance of nanowire transistor. The deviation in both sides causes the mean field effectmobility of ZnO nanobelt to be four times as high as that of ZnO nanowire. After revised bythe finite element method, the mean field effect mobility of nanobelt and nanowire arerespectively101and84cm2V-1s-1, which indicates the different cross sections, nanobelt andnanowire, have less influence on the field-effect mobility.3. The anisotropy of field effect mobility in ZnO nanobelt transistors. At first, wefabricate transistors based on ZnO nanobelts, which have the same large facet （2110）buttwo different growth directions,[0110] and[044n](n=2~5). The two kinds of ZnO nanobelttransistors show similar mean conductivity but different mean field effect mobilities,101and68cm2V-1s-1. The anisotropy of field effect mobility may originate from the two factors: Oneis the surface vibration modes near （2110）facet, which enhance the piezoelectric potentialand piezoelectric scattering along [044n]. The other is because the anisotropy of Zn atomarrangement makes the electron effective mass along [044n] larger than that along [0110]. On the crystal surface, as the greater scattering probability than bulk, make the difference ineffective mass larger.