Building up a solid-state material from quantum dots (QD), which are often referred to as artificial atoms, offers the potential to create new materials with unprecedented macroscopic properties. The investigation of the electronic properties of such QD assemblies has attracted attention due to the increasing applications of QD solids in both electronics and optoelectronics. In the past, charge transport in QD assemblies has been explained by a variety of mutually exclusive theories, with the Mott and Efros-Shklovskii variable range hopping models being most common. However, these theories fall short in explaining the anomalous exponents of the temperature-dependent conductivity ∝ exp (− (T₀/T)^α) observed in various QD materials. Here, we measure the temperature-dependent conductivity of semiconducting ZnO QDs under different UV illumination intensity. Regulating the UV intensity allows us to systematically change the effective diameter of the ZnO QDs without having to rely on cumbersome size control by synthesis. Instead, the UV level controls the width of the QD depletion shell and therefore the size distribution in the overall material. We observe exponents that systematically increase from α = 0.25 to α = 0.62 with increasing illumination intensity, which we interpret in terms of a charge transport being limited by the (size-dependent) charging energy of the QDs.

中文翻译：

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尺寸依赖性的充电能量决定了 ZnO 量子点固体中的电荷传输


从量子点 （QD）（通常被称为人造原子）构建固态材料，有可能创造出具有前所未有的宏观特性的新材料。由于 QD 固体在电子和光电子学中的应用越来越多，对这种 QD 组件的电子特性的研究引起了人们的关注。过去，QD 组件中的电荷传输由各种相互排斥的理论来解释，其中 Mott 和 Efros-Shklovskii 可变范围跳变模型是最常见的。然而，这些理论无法解释在各种 QD 材料中观察到的温度依赖性电导率 ∝ exp （− （T₀/T）^α） 的异常指数。在这里，我们测量了半导体 ZnO 量子点在不同紫外照射强度下随温度变化的电导率。调节紫外线强度使我们能够系统地改变 ZnO QD 的有效直径，而不必依赖通过合成进行繁琐的尺寸控制。相反，UV 级别控制 QD 耗尽壳的宽度，从而控制整个材料中的尺寸分布。我们观察到随着照明强度的增加，指数从 α = 0.25 系统地增加到 α = 0.62，我们将其解释为电荷传输受 QD 的（尺寸依赖性）充电能量的限制。