| In order to grow the high quality and large Zn O single crystals, the mechanism of Zn O chemical vapor growth was studied and the preparation technology was optimized. For one thing, the purification of Zn O raw material by graphite assisted chemical vapor phase transport method was studied. For another, the Zn O single crystal which shows the 001 face was grown by seeded chemical vapor transport method, and the formation mechanism of surface morphology was analyzed. Lastly, the vertical chemical vapor transport method was designed, and the large Zn O single crystal with high quality was grown. The sample was characterized by X-ray diffraction, Hall measurement, scanning electron microscopy, low temperature photoluminescence, Raman scattering and UV-Vis-IR spectrophotometer. The results of the study mainly include the following three points:(1) Purification of Zn O raw material by graphite assisted chemical vapor phase transport method was studied. According to the results of reaction mechanism and TG analysis, it is found that the Zn O-C system starting reaction temperature is about 1000 ℃, the reaction rate increased dramatically when temperature reach to 1200 ℃. A dense Zn O crystal ingot with faint yellow was obtained by reaction, transport and recrystallization in the vacuum-sealed quartz ampoule. X-ray diffraction spectrum without impurity peak and coincide well with the standard spectrum. ICP-MS test shows that the impurity ions of Zn O decreased significantly, especially for deep level and multiple levels of heavy metal ions, such as Ag, Cu, Pb, etc. The Zn O polycrystal obtained by chemical vapor phase transport method can be as high-purity raw materials for manufacturing various kinds of photoelectric component.(2) Zn O single crystals were grown by graphite assistant chemical vapor phase transport method. The structure and surface morphology of Zn O single crystals was analyzed by means of X-ray diffraction、metallographic microscope and scanning electronic microscope. The results show that crystals surface consist of many hexagon steps. The crystalline grain with hexagon umbrella structure always shows(001) surface. The size and Steep degree of steps in the same plane are different and the directions are parallel between the steps. The corrosion morphology of growth surface is flat-bottomed hexagon etch pit. Analysis of the mechanism indicates that the screw dislocation is main factor of step growth.(3) A new vertical chemical vapor transport method has been designed and a 12 millimeter Zn O single crystal has been obtained. The spontaneous nucleation was controlled by design of quartz ampoule and optimizing of the experimental process. And many evidences indicate that the quality of crystal is high, for example:(a) the strong X-ray diffraction peak and the narrow rocking curve reveal that the crystallinity of Zn O crystal is high.(b) The purity of Zn O single crystal can reach to as high as 5 N.(c) A prominent exciton UV emission can be observed in the PL spectrum at 77 K indicate the luminous efficiency of crystal is very high. According to the results of Hall effect measurement we propose that the dominant donor of our as-grown Zn O crystal is assigned to shallow donor impurities(Al and In) and ZnI. |
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