正电子湮没谱学研究半导体材料微观结构的应用进展

Advances in applications of positron annihilation spectroscopy to investigating semiconductor microstructures

正电子湮没谱学技术在研究材料微观缺陷、微观结构方面有着独特的优势,尤其是在针对阳离子空位等负电性空位型缺陷的研究中,可以获取材料内部微观缺陷的种类与分布的关键信息.正电子湮没寿命和多普勒展宽能谱是正电子湮没谱学的最基本的分析方法,在半导体材料的空位形成、演化机理以及分布等研究方面能够发挥独特的作用;此外,慢正电子束流技术在半导体薄膜材料的表面和多层膜材料的界面的微观结构和缺陷的深度分布的研究中有广泛的应用.通过正电子技术所得到的微观结构和缺陷、电子密度和动量分布等信息对研究半导体微观结构、优化半导体材料的工艺和性能等方面有着指导作用.本文综述了正电子湮没谱学技术在半导体材料方面的应用研究进展,主要围绕正电子研究平台在半导体材料微观缺陷研究中对材料的制备工艺、热处理、离子注入和辐照情况下,各种缺陷的微观结构的表征及其演化行为的研究成果展开论述.

Positron annihilation spectroscopy has unique advantage for detecting the micro-defects and microstructures in materials, especially for investigating the negatively charged defects such as cation vacancies in semiconductors. It is a powerful tool to characterize the important features for vacancy-type defects localized electron states within the forbidden energy gap and cation vacancy which provides the key information about the type and distribution of microdefects. Positron annihilation lifetime and Doppler broadening spectroscopy are the major methods of analyzing the vacancy formation, evolution and distribution mechanism. Importantly, the slow positron beam technique can provide the dependences of surface, defect and interface microstructure information on depth distribution in semiconductor thin film. Vacancy and impurity elements can change the ambient electron density in material. They also induce the middle band, which will have dramatic effects on optical and electrical performance. And the variation of electron density will exert furtherinfluences on the positron-electron annihilation mechanism and process. For the fundamental experiments in semiconductors, fabrication technology, thermal treatment, ion implantation/doping, irradiation etc,positron annihilation spectroscopy technology has been extensively applied to detecting the detailed electron density and momentum distribution, and gained the information about microstructure and defects. It can guide the fundamental researches in experiment and give optimal design of the technology and properties about semiconductors. In principle,defect concentrations can be derived and an indication can be obtained about the nature of the defect. Results are presented showing that cation vacancies can be easily detected. Also charge states and defect levels in the band gap are accessible. By combining the positron annihilation spectroscopy with optical spectroscopies or other experimental methods, it is possible to give detailed identifications of the defects and their chemical surroundings. The positron annihilation spectroscopy technology is a very special and effective nuclear spectroscopy analysis method in studying semiconductor microstructure. In this review, the research progress in applications of positron annihilation spectroscopy technology to semiconductors is reported, which focuses on the experimental results from the Positron Research Platform located in Institute of High Energy Physics, Chinese Academy of Sciences. Under different growth modes and ways of treating semiconductors, the experimental results about the internal micro-defect formation mechanism of material,evolution mechanism, and defect feature research progress are reviewed Future challenges including the analysis of electropositivity vacancy（i.e. oxygen vacancy） and of multi-ion implantation phenomena are also presented new technologies such as digitization and new theory will make the positron annihilation spectroscopy portable and reliable.