Ground State Properties Of Exciton In ZnO Quantum Dots And The Effects Of Surface-modification On Optical Properties

ZnO is a new wide and direct band gapâ…¡-â…¥semiconductor material with a large exciton binding energy of 60meV at room temperature, much larger than the ionization energy of room temperature (26meV), so ZnO is a suitable high efficient ultraviolet material. ZnO quantum dots (QDs) has unique photoelectric properties, especial used in UV laser devices filed having extensively applied foreground and application values, It's photoelectric properties is closely related with the excitonic characteristic. Therefore, it is very important to study the ground state properties of exciton in ZnO QDs and the optic and electronic properties of dopped and modified ZnO QDs, that will have importance to the theory study and devices application of ZnO QDs. In this thesis, the ground state properties of exciton in ZnO QDs, the process of transform from amorphous ZnO to nanocrystalline ZnO, the optical and magnetic properties of Mn dopped and modified nanocrystalline ZnO and the optic properties of Carbon dopped nanocrystalline ZnO were detailed studied. The major results are as follows: 1. Introduced a new and simple trial wave function and studied the ground state properties of the exciton in ZnO QDs by variation methods based on effective mass approximation. The results indicate, the ground state energy increased quickly as the decrease of ZnO QD radius, when the radius decreased to the effective Bohr radius of ZnO exciton (aB=1.8nm), the ground state energy is 488meV higher than the conduction band bottom,about 8 times of binding energy of ZnO free exciton. When the radius is larger,the ground state energy inclined to a constant (under conductor bottom about 65meV), approximate the binding energy of the exciton in bulk crystal ZnO. Compared the calculation results with the experiment values and Y.Kayanuma's calculation results, the compared results illuminate the calculation is consistent very well with the the experiment values and Y.Kayanuma's calculation results, that make out the new trial wave function is simple and effective, and can applied to other semiconductor QDs. Mean while, the wave function of the exciton in ZnO quantum dots has a drastic change with decreasing the ZnO QDs radiu. That indicate the outer environment, surface of QDs and impurity in QDs will have affects on the exciton properties of ZnO QDs. So it is more essentially need to modified and effect dopped the surface of ZnO QDs. 2. Detailed studied the process of transform from amorphous ZnO to nanocrystalline ZnO. The results indicate amorphous ZnO effectively modified the surface of nanocrystalline ZnO, and forms three dimention confined quantum structure,greatly enhances the emission efficency of nanocrystalline ZnO,while a new visible emission band was observed, which was ascribed to the interface emission between nanocrystalline ZnO and amorphous ZnO, the emission intensity is correlate with the effects of amorphous ZnO act to nanocrystalline ZnO surface. Deposited high quality armorphous ZnO and nanocrystalline ZnO films by electrophoretic deposition, strong ultraviolet emission peak was observed at room temperature, can be expected to have wide application in materials research. 3,Prepared Mn dopped and modified nanocrystalline ZnO. Nanocrystalline ZnO has excellent emission properties, only ustraviolet photoluminescence was observed,no visible emission, which indicates Mn can effectively modify the surface of nanocrystalline ZnO, and nanocrystalline ZnO modified by Mn shows a clear quantum size effect. For potential application of spintronic devices of ZnO:Mn dilute magnetic semiconductor material. We mesured the magnetic property of ZnO:Mn at room temperture, and observed ferromagnetism of ZnO:Mn at room temperture. That indicates the Mn ions subsustitute the Zn ions in nanocrystalline ZnO, and spontaneously products ferromagnetism. 4,Firstly we prepared Carbon dopped nanocrystalline ZnO, in the sample only ultravioled photoluminescence was observed. This indicates Carbon modifies the nanocrystalline ZnO surface, and acts as a center of non-radiative recombination and non-radiative recombined with the carries on nanocrystallin ZnO surface. It is known newly developed C60 and Carbon nanotube exhibite P-type characteristics and have extensive applications in optoelectronic device, it is possible to joint P-type C60 and Carbon nanotube together N-type nanocrystalline ZnO, The new struture may be promissing for figuring new optoelectronics devices with good characteristics and for expanding the application of ZnO.