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arXiv 0811.1924cond-mat.mtrl-sci
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掺杂和场致载流子密度对纳米晶ZnO电子输运的影响

Effect of doping-- and field--induced charge carrier density on the electron transport in nanocrystalline ZnO

Maria S Hammer, Daniel Rauh, Carsten Deibel, Vladimir Dyakonov

摘要:

研究了溶胶-凝胶法制备的掺杂浓度在0.8at%~ 10at%之间的未掺杂和Al掺杂氧化锌纳米粒子的薄膜的电荷输运性质。X射线衍射研究表明,在高掺杂样品的平均晶粒尺寸的减少。我们提供的电导率和由此产生的载流子密度相对于掺杂水平的估计。将由于非本征掺杂引起的载流子密度的增加与场效应晶体管结构中的载流子的积累进行比较。这允许评估由于非本征掺杂对电子迁移率的散射效应。随着掺杂密度的增加,后者从4.6*10^-3 cm ^2/Vs降低到4.5*10^-4 cm ^2/Vs。与此相反,积累导致迁移率增加到1.5*10^-2 cm ^2/Vs。与微晶之间的晶界相关的势垒高度来自温度相关的迁移率测量。非本征掺杂最初导致晶界势垒高度降低,随后由于掺杂引起的结构缺陷而增加。我们的结论是,溶胶-凝胶处理纳米ZnO:Al的导电性是由增强的载流子密度和掺杂诱导的载流子散射效应的相互作用,在我们的情况下,在0.8原子%达到最大值。

英文摘要:

Charge transport properties of thin films of sol--gel processed undoped and Al-doped zinc oxide nanoparticles with variable doping level between 0.8 at% and 10 at% were investigated. The X-ray diffraction studies revealed a decrease of the average crystallite sizes in highly doped samples. We provide estimates of the conductivity and the resulting charge carrier densities with respect to the doping level. The increase of charge carrier density due to extrinsic doping were compared to the accumulation of charge carriers in field effect transistor structures. This allowed to assess the scattering effects due to extrinsic doping on the electron mobility. The latter decreases from 4.6*10^-3 cm^2/Vs to 4.5*10^-4 cm^2/Vs with increasing doping density. In contrast, the accumulation leads to an increasing mobility up to 1.5*10^-2 cm^2/Vs. The potential barrier heights related to grain boundaries between the crystallites were derived from temperature dependent mobility measurements. The extrinsic doping initially leads to a grain boundary barrier height lowering, followed by an increase due to doping-induced structural defects. We conclude that the conductivity of sol--gel processed nanocrystalline ZnO:Al is governed by an interplay of the enhanced charge carrier density and the doping-induced charge carrier scattering effects, achieving a maximum at 0.8 at% in our case.

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