Oxygen partial pressure dependence of surface space charge formation in donor-doped SrTiO3
Oxygen partial pressure dependence of surface space charge formation in donor-doped SrTiO3
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DOI：
10.1063/1.4983618
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发表时间：
2017-05-01
期刊：
影响因子：
6.1
通讯作者：
Waser, Rainer
中科院分区：
文献类型：
--
作者：
Andrae, Michael;Dvorak, Filip;Waser, Rainer
在这项研究中，我们研究了供体掺杂钛酸锶的电子表面结构。在 770 K 的温度和高达 5 mbar 的氧气压力下，通过原位近环境压力 X 射线光电子能谱分析了同质外延 0.5 wt.% 供体掺杂的 SrTiO3 薄膜。在高温下暴露于氧气气氛时，我们观察到随着氧气压力的增加，所有 SrTiO3 核心能级峰值和价带最大值在真空条件下发生高达 0.6 eV 的刚性结合能向较低结合能的转变。刚性偏移归因于费米能向价带的相对偏移，同时伴随着表面负电荷的积累，导致在近表面区域形成补偿电子耗尽层。仅仅基于碳污染物的电荷捕获效应不太可能，因为它们在给定的实验条件下不可逆解吸。此外，由于高铌掺杂剂浓度主导了材料的电子特性，因此可以排除氧空位的简单再氧化。相反，负表面电荷可以通过在表面形成阳离子空位或形成带电氧吸附物来提供。我们的结果清楚地表明，在氧化条件下，施主掺杂的 SrTiO3 中存在与 pO(2) 相关的表面空间电荷形成。 (C) 2017 年作者。
In this study, we investigated the electronic surface structure of donor-doped strontium titanate. Homoepitaxial 0.5 wt.% donor-doped SrTiO3 thin films were analyzed by in situ near ambient pressure X-ray photoelectron spectroscopy at a temperature of 770 K and oxygen pressures up to 5 mbar. Upon exposure to an oxygen atmosphere at elevated temperatures, we observed a rigid binding energy shift of up to 0.6 eV towards lower binding energies with respect to vacuum conditions for all SrTiO3 core level peaks and the valence band maximum with increasing oxygen pressure. The rigid shift is attributed to a relative shift of the Fermi energy towards the valence band concomitant with a negative charge accumulation at the surface, resulting in a compensating electron depletion layer in the near surface region. Charge trapping effects solely based on carbon contaminants are unlikely due to their irreversible desorption under the given experimental conditions. In addition, simple reoxygenation of oxygen vacancies can be ruled out as the high niobium dopant concentration dominates the electronic properties of the material. Instead, the negative surface charge may be provided by the formation of cation vacancies or the formation of charged oxygen adsorbates at the surface. Our results clearly indicate a pO(2)-dependent surface space charge formation in donor-doped SrTiO3 in oxidizing conditions. (C) 2017 Author(s).