| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 101 === ZnO is a candidate for applications in optoelectronic devices like ultraviolet region light-emitting diodes due to its wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. It has also been investigated extensively because of its electrical and piezoelectric characteristics, which are suitable for applications such as transparent conductive films and surface acoustic wave filters. The film quality of ZnO is a key factor for above-mentioned characteristics. In addition, obtaining a stable p-type ZnO layer is another important issue for realizing ZnO based optoelectronic devices.
A polar mirror symmetrical contribution originated from the arrangement of grain boundaries existing in the ZnO film is detected by reflective second harmonic generation (RSHG) pattern. The ordering of ZnO grain boundary is dependent on the kinetic energy of deposited atoms and affects the quality of ZnO films. The net direction of the grain boundary in ZnO film trends toward the [1 ̅10] direction of Si(111) to reach the minimum grain energy for better quality ZnO film. The polar structure of the mirror-like boundaries under the optically macroscopic viewpoint presents a correlation with film quality.
The p-type ZnO film is obtained out of thermal diffusion of Phosphorus (P)/ Arsenic (As) atoms from the low-energy high-dose implanted Si substrate through annealing process. A lot of non-activated dopants atoms exist on the surface of the shallow implanted Si substrate and easily out-diffuse into ZnO films at proper annealing conditions. In addition, we modulate the implanting conditions, such as implanting dose or energy so that more non-activated dopants reside in the surface region of the substrate and and out-diffuse into ZnO films efficiently by this diffusion method. Moderate implanting dose or energy could make the ZnO films exhibit p-type conducting; increase the hole concentrations and preservation time in the air ambient. We also demonstrate that stable p-type conduction appears at a proper substrate temperature (TS). The best crystallinity and electrical properties of the p-type ZnO films were obtained at TS=400 °C. The maximum carrier concentration of the As dopant was 6.7×1018 cm-3 and the resistivity reached 1.1×10-1 Ω-cm. The reproducible As-doped ZnO films can be obtained by this diffusion method. The crystalline microstructure of the ZnO films was studied by X-ray diffraction (XRD). The composition of these films was measured by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The conduction type of the ZnO films was detected using Hall effect measurements. This diffusion method was not restricted by particular substrate and combined with popular silicon-based manufacturing process.
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