氧化釓鋅薄膜在不同鍍膜氧壓下的結構、光學與磁性

Abstract

本論文以脈衝雷射蒸鍍法在c指向單晶藍寶石基板上製備150nm厚的ZnGdO薄膜，並探討薄膜鍍膜速率、薄膜的結構特性、光學性質及磁性與鍍膜氧壓的關係，其中單位面積雷射能量為2.6 J/cm2，鍍膜氧壓分別為0.3與0.08 mbar，Gd摻雜的原子比例為0~20 %，基板溫度為700℃。 ZnGdO薄膜鍍膜速率會隨著Gd比例的增加而上升，且在高氧壓(0.3 mbar)環境下製備的薄膜其鍍膜速率高於低氧壓(0.08 mbar)製備的薄膜。藉由X光光電子能譜測定的Gd摻雜比例皆略大於配方比例。X光繞射及拉曼散射光譜顯示所有薄膜皆無雜質或其他晶相產生，代表Gd成功取代Zn的位置。Gd比例增加時，c軸晶格常數先減少後增加，粒徑大小則持續下降，代表薄膜結晶品質變差。當Gd比例高於5%時，高氧壓製備的薄膜之結晶品質較低氧壓製備的薄膜差。光致螢光光譜顯示所有薄膜中都存在鋅空缺與鋅間隙，而在純氧化鋅中還有氧空缺。橢圓偏振儀測定的薄膜直接能隙隨著Gd比例的上升而增加。超導量子干涉磁量儀測定結果顯示所有純氧化鋅薄膜皆為超順磁性，氧化釓鋅薄膜皆為順磁性。在低溫下，高氧壓製備的薄膜其最大磁矩大於低氧壓製備的薄膜。

Pulsed-laser deposition(PLD) was applied to grow 150nm thick gadolinium(Gd)- doped ZnO(Gd:ZnO) thin films on c-sapphire substrate under two different oxygen partial pressures of 0.08 and 0.3 mbar. The Gd concentration ranges from 0 to 20 at.%, temperature of substrate is 700 degree Celsius, and laser fluence is 2.6 J/cm2. The relations bewteen oxygen partial pressure and deposition rate, structural properties, optical properties and magnetic properties of Gd:ZnO thin films were investigated in this study. Deposition rate of Gd:ZnO thin films were increase as Gd concentration increasing for both oxygen partial pressures, and the thin films grown under 0.3 mbar had higher deposition rate. Gd concentrations determined by the X-ray photoelectron spectroscopy(XPS) were slightly larger than the nominal concentration. X-ray diffraction(XRD) and Raman-scattering spectra revealed Gd incorporation into ZnO without secondary phase. As Gd density increased, the grain size of Gd:ZnO thin films decreased monotonically, while the c-lattice constant first decreased till 5 % of Gd doping and then increased monotonically. The thin films which grown under 0.08 mbar and Gd concentration larger than 5% have better crystal qualities. Photoluminescence(PL) spectroscopy showed that all the thin films had zinc interstitials and zinc vacancies. In addition, pure ZnO thin films had oxygen vacancies. From ellipsometry, the direct band gap of Gd-doped ZnO thin films was found to increase with increasing Gd concentration. Magnetic investigations with a superconducting quantum interference device(SQUID) magnetometer showed superparamagnetism for pure ZnO thin films and paramagnetism for all Gd-doped ZnO thin films. At T = 5K, the thin films which grown under 0.3 mbar have lager magnetic moment at = 40 kOe.