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Carrier accumulation near electrodes in ferroelectric films due to polarization boundary conditions

机译：由于极化边界条件，铁电薄膜中电极附近的载流子积累

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摘要

We study the effect of surface polarization on the distribution of free carriers in a wide bandgap semiconductor ferroelectric (FE) film using a thermodynamic approach. We show that free carriers, namely, holes and electrons from ionizable impurities or atomic vacancies can accumulate near the film-electrode interface, if FE polarization profile has a very steep change near the surface that is specified by the extrapolation length. Such an outcome is just the opposite of what happens in a Schottky junction in a partially or fully depleted film. This is also an entirely different effect than what has been often studied in similar structures, where the work function and screening length of the electrode metal determines the electronic character of the interface. Even for low-to-moderate densities of ionizable defects with states within the bandgap close to the band edges, high densities of carriers can localize close to the electrodes in a single domain state FE film when above a critical thickness. For very low densities of such ionizable defects, short extrapolation lengths cause electrical domain formation with minimal carrier accumulation because of the already weak depolarizing fields. This is also true for films below a critical thickness with low-to-moderate densities of ionizable impurities, i.e., electrical domains get stabilized regardless of defect density. The implications of our findings for polarization controlled Schottky to Ohmic-like transition of an interface and experimental results are discussed. It is also found that interfaces of an n-type FE heterostructure can behave like a p-type depending on the barrier heights and impurity density. We conclude that, for low-to-moderate ionizable impurity densities, it is the rate of change of polarization at the interface with position rather than solely its presence that leads to carrier accumulation and that both interfaces can become Ohmic-like with opposite signs of carriers.
机译：我们使用热力学方法研究了表面极化对宽带隙半导体铁电（FE）薄膜中自由载流子分布的影响。我们表明，如果FE极化轮廓在由外推长度指定的表面附近具有非常陡峭的变化，则自由载流子（即，来自可电离杂质或原子空位的空穴和电子）会聚集在膜电极界面附近。这种结果与部分或完全耗尽的薄膜中肖特基结发生的情况恰好相反。这与在类似结构中经常研究的效果完全不同，在类似结构中，电极金属的功函数和屏蔽长度决定了界面的电子特性。即使对于带隙内状态接近带边缘的可电离缺陷的中低密度，当高于临界厚度时，高密度的载流子也可以位于单畴态FE膜中靠近电极的位置。对于这种电离缺陷的密度非常低，由于去极化场本来就很弱，所以短的外插长度会导致形成带有最小载流子累积的电畴。对于低于临界厚度且具有低至中等密度的可电离杂质的薄膜，也是如此，即，无论缺陷密度如何，电畴均得以稳定。讨论了我们的发现对偏振控制的肖特基到类似欧姆的界面过渡和实验结果的影响。还发现，取决于势垒高度和杂质密度，n型FE异质结构的界面可以表现得像p型。我们得出的结论是，对于低至中度的可电离杂质密度，是导致界面处极化的变化率，而不是仅因其存在而导致载流子积累，并且两个界面都可能变成类似欧姆的，并具有相反的符号。运营商。

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  • 来源
    《Journal of Applied Physics》 |2014年第2期|024102-024102|共1页
  • 作者

    Misirlioglu I.B.; Yildiz M.;

  • 作者单位

    Faculty of Engineering and Natural Sciences, Sabanci University, Tuzla/Orhanli, 34956 Istanbul, Turkey|c|;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
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