氧化鈥鋅/氧化亞鈷多層膜結構的螢光及磁光特性

Abstract

本論文利用脈衝雷射蒸鍍法製備在c-sapphire上三種不同鍍膜環境的單層ZnO摻雜Ho薄膜及三種不同類型夾雜著CoO層的多層膜，其中Ho摻雜比例分為0、1及3%，並研究其結構特性、光學特性及磁光特性。 結構特性方面，X光繞射和拉曼散射光譜觀察到纖鋅礦結構ZnO和岩鹽結構CoO的特徵峰，代表樣品為多層單晶薄膜。其中多層膜結構中較下層的薄膜會因熱退火效應而晶體結構較佳。拉曼散射光譜則從ZHO薄膜觀察到Ho3+ 4f軌域躍遷譜線。 光學特性方面，在所有樣品中皆有ZnO的近能隙發光，在樣品中發現由氧空缺、鋅空缺、鋅間隙或其複合缺陷造成的缺陷發光，但無CoO或Ho3+的螢光，亦無ZnO/CoO/ZnO量子井的譜線。溫度從300 K變化到20 K，因晶格收縮使發光峰值藍移，且因熱擾動減少使ZnO近能隙發光強度相對於缺陷發光上升。 磁光特性方面，由MOFE及MOKE得知，在室溫下量測所有樣品的磁滯曲線皆為順磁性，且磁矩無達到飽和。法拉第磁光效應較強的波長為400到540 nm。薄膜的等效Verdet常數值隨波長增長而減小。除了ZHO 3%的三層膜結構外，多層膜等效Verdet常數的估計值與測量值相近，而ZHO 3%三層膜測量值較低的原因是其ZHO層的法拉第磁光效應比單層薄膜弱。In this thesis, single-layer Ho -doped ZnO (ZHO) films with three different deposition conditions and three different types of ZHO/CoO multilayer films on c-sapphire were prepared by pulsed laser deposition. The doping percentage of Ho doping was 0, 1, and 3%, and their structural, optical, and magneto-optical properties were investigated. For the structural properties, the characteristic peaks of ZnO and CoO were observed in x-ray diffraction and Raman-scattering spectra, which represent that the multilayer films are single-crystalline without interdiffusion. The lower layer of the multilayer film structure had a better crystal structure due to the thermal annealing effect. In the Raman-scattering spectra, the Ho3+4f intra-subband emission lines were observed from the ZHO films. In photoluminescence (PL) spectra, the near-energy edge (NBE) emissions of ZnO was observed from all samples, and the defect emissions due to oxygen vacancies, zinc vacancies, zinc interstitials, or their combinations, were also identified. However, no emission characteristics of CoO, Ho3+ intra-subband, and ZHO/CoO/ZHO quantum wells were observed. The PL peak was blue-shifted due to the lattice shrinkage when the temperature was changed from 300 K to 20 K. Moreover, the intensity of ZnO NBE emission increases relative to that of defect luminescence due to the reduction of the thermal disturbance. For the magneto-optical properties, the MOFE and the MOKE showed only paramagnetic behavior at room temperature without saturation magnetization at the maximum magnetic field. The magneto-optical Faraday effect is stronger at wavelengths between 400 and 540 nm. The value of effective Verdet constant of the films decreases with increasing wavelength. The estimated values of the effective Verdet constant are close to the measured values for the multilayer films except for the ZHO3% trilayer structure, where the measured values are relatively lower due to the smaller contribution from the ZHO layer in the trilayer structure than its single-layer counterpart.