The two origins of p-type conduction in transparent conducting Ga-doped SnO 2 thin films
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The two origins of p-type conduction in transparent conducting Ga-doped SnO2 thin films Huan-hua Wang *, Tieying Yang †, Baoyi Wang, Kurash Ibrahim and Xiaoming Jiang Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China Keywords: tin oxide, net hole conduction, doping, oxygen adsorption, grain boundary PACS: 81.05.Hd; 68.55.Ln; 68.55.-Nq; 81.15.Cd * Correspondence author: [email protected] Present address: Shanghai Synchrotron Radiation Facility, Shanghai 201204, China
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Abstract The p-type conduction in transparent Ga-doped SnO2 thin films was realized and its two origins were discerned through comparison experiments associated with growth conditions, Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy analysis. All the experiment results suggest that the adsorbed oxygen both in the grain boundaries and at the surfaces is another origin of the net hole conduction in the polycrystalline thin films. This mechanism provides a fairy well explanation for the growth temperature dependence of the p-type conductivities of the films. It also offers a useful guide to better the properties of p-type conducting oxide thin films.
INTRODUCTION p-Type transparent conducting oxide (p-TCO) thin films have very great potentials in applications such as multiple-junction solar cells used in outer space, ultraviolet light emitting diodes, shortwavelength laser devices and so on. Many p-TCOs were successfully synthesized and intensely studied in past decade [1-8]. But by and large speaking, this material family are neither well understood in their fundamental material sciences nor sophisticatedly controlled in their material engineering. The former is embodied by our poor understanding of their defect structures and defect dynamics [9-11]. The latter is demonstrated by the low reproducibility and unsatisfying uniformity of p-TCO thin films and devices. Contrary to the situation of n-type TCOs that have been widely applied in industries like the famous ITO, most p-type TCOs currently are not suitable for practical applications either due to their poor photoelectric properties or due to our inability to solve the problem of their instability or short lifetime. Their instability has to be controlled and their conductivity, hole concentration and mobility must be improved before any industrial application is realized. Therefore, understanding their fundamental microstructure-property relationship is a critical step to improve the fabrication technology and to better the material properties. Among various p-TCOs, p-type SnO2 is an excellent candidate for potential industrial applications with many attractive characteristics. It is of simple structure with few components, relatively low growth temperature, low cost, stable thermal and mechanical properties. Compared with p-type ZnO it is more stable in performance. One of its most attractive characteristics is that it can use the alreadycommercialized n-type SnO2:F conducting glass as substrate for device applications. Scientists have
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