氧化釓鋅薄膜的法拉第磁光光譜

Abstract

本文為延續研究，主要在探討摻雜釓的氧化鋅薄膜在室溫的光致螢光光譜和法拉第磁光效應。釓的摻雜莫耳濃度0%到20%，光譜的測量範圍是340 nm至700 nm，磁場介於±900 mT之間。摻雜不同濃度釓元素的氧化鋅薄膜都會產生鋅空缺，發出Ec→VZn-能階躍遷的螢光，此外除5%薄膜外，各薄膜亦同時有鋅間隙及氧間隙。當摻雜比例上升超過5%時，非本質發光會主宰PL光譜且光譜外型明顯改變。各樣品的總法拉第旋轉角基板加上薄膜的總合，和外加磁場成負斜率的直線關係。單獨觀察基板薄膜亦是如此。基板及薄膜的韋爾代常數介於-0.01287至-0.00399及-5.96000到6.74000 rad/mT．m之間，且隨波長增長量值減小，多數皆為負值，唯5%摻雜薄膜於380 nm到540 nm間為正值。在波長380、420、480及640 nm之韋爾代常數對於摻雜比有先增後減的現象，並在5%時有最大值。此結果有助於找到薄膜對波長在法拉第效應上的最高敏感度。總合兩光譜結果，可發現除摻雜元素可造成磁性，進而改變法拉第磁光效應外，缺陷對薄膜的磁性及法拉第磁光效應亦有相當的影響。This thesis follows up previous study on Gd-doped ZnO thin films and it focused on photoluminescence (PL) and magneto-optical Faraday effect (MOFE). The mole fraction of gadolinium is from 0% to 20%. The spectral range for both PL and MOFE is from 340 nm to 700 nm. The magnetic field for MOFE ranged between ±900 mT.Clear defect emission were observed from PL spectra of all Gd-doped ZnO thin films, and the defects were identified as zinc vacancies, zinc interstitials, oxygen vacancies, and oxygen interstitials. For thin films of Gd mole fraction over 5%, defect emissions are dominant in the PL spectra. The total Faraday angle is the sum of substrate’s and thin films’. They were related to magnetic field with negative slope. Verdet constant of substrate was from -0.01287 to -0.00399 rad/mT．m, and films’ ranged from -5.96000 to 6.74000 rad/mT．m. Most Verdet constant were negative, except 5% film’s before 540 nm. The magnitude of Verdet constant decreased while wavelength of incident light increased. At near-band-edge emission and defect emission wavelengths, such as 380, 420, 480, and 640 nm, Verdet constant would grow first then shrink against doped mole fraction growth. Therefore, electron interband transition and defect sub-bands have clear response in magneto-optical Faraday effect. Our study enables us to tune MOFE spectral range and strength by changing Gd doping concentration.