Preparation Of Metail Oxide Semiconductor By Wet Chemical Methods

As a inexhaustible clean energy, development of solar energy is one of the most effective way to solve the energy crisis and environmental problems. Among the materials for photovoltaic applications, silicon has disadvantages of high cost, high energy consumption and high pollution. CdTe and CdS are highly toxic, which may cause severe pollution. CuInSe2 thin film solar cells are highly restricted by the absence of In and Se. Therefore, developing new photovoltaic materials is necessary. Cuprous oxide and zinc oxide have advantages of abundant source materials, low cost, direct band structure and high theoretical conversion efficiency and are considered as promising candidates for photovoltaic applications.In this work, by adjusting the growth conditions of cuprous oxide and zinc oxide, the surface morphology and orientation of crystals are well controlled. Also, the growth mechanism is discussed and the effect of crystal orientation on the properties of cuprous oxide is studied. By using electro-deposition method and hydrothermal method, cuprous oxide and zinc oxide are prepared and results show:1. The density of oxygen on different crystallographic planes of cuprous oxide is different. By adjusting the solution pH, the orientation and surface morphology of the cuprous oxide films can be controlled. The film orientation transfers from (100) to (111) and surface morphology transfers from 4-sided pyramids to 3-sided pyramids with increasing pH values. As indicated by the capacitance-voltage measurements, the electrical properties of cuprous oxide changes with the film orientation: flat band potential varies from 0.157 V to -0.331 V and the carrier concentration shifts from 2.8×10¹⁸ cm^-3 to 5.5×10¹⁸ cm^-3. The UV-Vis transmittance characterization shows cuprous oxide has a direct band structure with a bang gap of 2.06 eV.2. Due to the different oxygen density on different crystallographic planes of cuprous oxide, the growth rate of different crystallographic planes of cuprous oxide can be affected by solution pH and addition of organic solvent. As indicated by the results: the preferred orientation of cuprous oxide crystal transfers from (100) to (111) and surface morphology transfers from branched structure to cubic structure with increasing pH values.3. Zinc oxide is grown by hydrothermal method and results show that the surface morphology does change with solution pH values. However, there is no obvious changing rule for the surface morphology as a function of pH, which may be ascribed to the complicated structure of zinc oxide.