磁约束电感耦合等离子体增强溅射沉积Co掺杂ZnO薄膜及其光学特性

采用磁约束电感耦合等离子体增强溅射法(ICP-PVD)在Si(100)和石英玻璃衬底上沉积了Zn_0.95Co_0.05O薄膜。XRD谱显示薄膜具有较强的(002)衍射峰,表明Zn_0.95Co_0.05O薄膜为c轴择优取向生长;透过光谱显示Zn_0.95Co_0.05O薄膜具有良好的透过性,其在可见光和红外波段的平均透过率大于80%,吸收光谱表明Co²⁺取代了Zn²⁺处于四配位晶体场中;喇曼光谱证明Zn_0.95Co_0.05O薄膜具有良好的六方纤锌矿结构;室温PL谱测量发现在可见光的蓝光波段和绿光波段存在较宽的发光带,却没有发现本征的近紫外光发射,这是由于Co掺杂后引入较多的缺陷导致的。

Optical Properties of Co-doped ZnO Film Prepared by Sputtering Deposition in a Magnetic Inductively Coupled Plasma

The semiconductor ZnO has grained substantial interests in the research community in part because of its wide direct band gap (3.3 eV) and large exciton binding energy (60 meV). It is a well-known piezoelectric and electro-optic material with potential applications such as optoelectronic and luminescent devices as well as chemical sensors. Even though the research focusing on ZnO goes back to several decades, one of the renewed interests is fueled by the observation of ferromagnetic behavior in transition metals doped ZnO which is called diluted magnetic semiconductors (DMS). DMS could be served as ideal material for exploiting spin in addition to charge in semiconductor devices. Much attention has been paid to the magnetic properties of ZnO-based DMS. In this paper we focused on the optical properties of Co-doped ZnO films. Highly (002) orientated Zn_0.95Co_0.05O films were deposited on Si (100) substrate using inductively coupled plasma enhanced physical vapor deposition (ICP-PVD) with magnetic confinement. X-ray diffraction pattern and typical Raman spectrum show that Zn_0.95Co_0.05O film has a wurtzite structure. Transmittance spectrum indicates that the Zn_0.95Co_0.05O film has an average transparency of over 80% in the visible and infrared wavelength. The band gap of Zn_0.95Co_0.05O film (3.11 eV) is less than that of pure ZnO, which is due to sp-d exchange interactions between the band electrons in ZnO and the localized d electrons of the Co²⁺ ions. Three obvious absorption peaks around 660, 615 and 560 nm are found. They are ascribed to derive from d-d transitions of tetrahedrally coordinated Co²⁺ and attributed to the ⁴A₂(⁴F)→²E(²G), ⁴A₂(⁴F)→⁴T₁(⁴P), and ⁴A₂(⁴F)→⁴A₁(⁴G) transitions. The photoluminescence spectrum shows broad blue and green emission from the Zn_0.95Co_0.05O film at room temperature. On the other hand, no luminescence is found in the ultraviolet region near 380 nm.