摘要
CuAlO_2(CAO)p型透明导电薄膜是1997年Kawazoe等人基于价带化学修饰(CMVB)理论,首次制备出的铜铁矿结构p型直接带隙透明氧化物薄膜。它的成功开发为实现半导体全透明光电器件,如透明二极管、透明晶体管提供了可能性,也推动了传统意义上透明导电氧化物(TCO)薄膜到透明氧化物半导体(TOS)薄膜的发展。CuAlO_2已经成为当前透明导电薄膜领域的研究热点之一。
本文采用Cu靶和Al靶直流共溅射法制备出p型透明导电Cu-Al-O薄膜,用原子力显微镜(AFM)、X射线衍射(XRD)仪、四探针测量仪、紫外-可见分光光度计等测试手段对沉积的薄膜进行了表征和分析。研究了退火温度、氧氩比和溅射功率对薄膜光电特性的影响。
XRD分析表明,制备的Cu-Al-O薄膜为多晶结构,适当的退火处理能使其结晶度提高。AFM表明,样品表面较平整,粗糙度较小,且晶粒较致密。XPS分析表明:Cu元素主要是以+1价的形式存在;Al元素仅是以+3价的形式存在,与CAO中Cu,Al价态吻合。
薄膜的电学性能分析结果表明,Cu-Al-O薄膜的电阻率受退火温度、氧氩比和Al靶溅射功率的影响较大。随着退火温度和氧氩比的升高,电阻率减小。随着Al靶溅射功率的增大,电阻率先减小后增大。
薄膜的光谱分析结果表明:薄膜样品的可见光透过率可达72%,随着氧氩比和Al靶溅射功率的增大,薄膜的透过率逐渐增大。计算结果显示薄膜的光学带隙在3.0-3.8 eV范围内变化。
根据对Cu-Al-O薄膜的组织结构和光电性质的研究,得出了双靶直流共溅射法制备Cu-Al-O薄膜的最佳工艺条件为:氧氩比2:3,衬底温度300℃,工作压强3 Pa,溅射功率Cu靶:20 W,Al靶:60 W,退火温度1000℃。
Based upon the theory of "the chemical modulation of the valence", the delafossite structure,p-type and directly band-gap electrical conductivity transparent oxide thin film of CuAlO_2 was designed by Kawazoe etc.in 1997 for the first time.The discovery of p-type TCO made possible the fabrication of transparent oxide optoelectronic devices such as transparent p-n junction diodes and transistors using an appropriate combination of p- and n-type TCO films,which also led TCO material to the frontier of transparent oxide semiconductor(TOS). CuAlO_2 has become one of the research hotspots in transparant conductive films fields.
In this paper,p-type transparent conducting Cu-Al-O films were prepared by using direct current(dc)magnetron reactive co-sputtering deposition with Cu and Al metallic targets.The samples were characterized by atomic force microscopy(AFM),X-ray diffraction (XRD),4-point probe,UV-VIS spectrophotometer,respectively.The influence of the annealing temperature,Oxygen argon(O_2/Ar)ratio and sputtering power on the optical and electrical properties were studied.
XRD analyses indicate that Cu-Al-O films are polycrystalline structure and the crystallinity is improved by appropriate annealing treatment.AFM results show that the surfaces morphology of the films was smooth and the surface roughness was small.The films are composed of some excellent columnar crystallites.The XPS results indicate that the Cu mostly exist as + 1 valence charge and Al exist as +3 valence charge,this is the same with CAO.
The analysis of the electrical properties indicate that annealing temperature,oxygen argon ratio and sputtering power of the Al target have strong influence on the properties of Cu-Al-O films.With the increase of the annealing temperature and oxygen argon ratio,the resistivity of the films decreased.With the increase of the sputtering power of the Al target,the resistivity are decreased,and then increased.
The spectral analysis results indicate that the transmission rate of the thin film in visible region can reach 72%.With the increase of the oxygen argon ratio and sputtering power of the Al target,the transmission rate are gradually increased.The calculation results indicate that films' band gaps changed in range of 3.0-3.8 eV.
Based on the studies of the structural,optical and electrical properties of Cu-Al-O thin films,it can be obtained the optimal deposition conditions of Cu-Al-O thin films by direct current reactive magnetron co-sputtering with Cu and Al metallic targets.The oxygen argon ratio,deposition temperature,gas pressure,sputtering power and annealing temperature were 2:3,300℃,3 Pa,Cu target:20 W,Al target: 60 W,1000℃,respectively.
引文
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