透明石墨烯纳米电容器中的反向光电效应
Reversed Photoeffect in Transparent Graphene Nanocapacitors
摘要：
介电薄膜的电学性质一直受到人们的关注，因为它们在各种电子器件中起着重要的作用，例如场效应晶体管和存储元件。晶体管中栅氧化层的绝缘特性是限制摩尔定律的关键因素。绝缘膜的介电强度限制了纳米电容器中可以存储多少能量。纳米级绝缘屏障中电流的来源仍然无法解释。在这里，我们提出了一种光学透明的Al-Al 2 O 3-石墨烯纳米电容器，适用于研究高电场和光照下校准的纳米电介质薄膜中的电子输运。可控的光子流提供了一个额外的强大的探针，有助于解决这些高质量绝缘膜中的导电性难题。采用原子层沉积技术沉积了介电氧化铝Al 2 O3。用这个装置，我们观察到一个光子辅助场致发射效应，其中的有效势垒高度减少了一个数量等于光子能量。我们的主要发现是一种反向光效应。即，在足够高的偏置电压下，通过电介质膜的电流随着光强度的增加而减小。此外，较高的光子能量与电流的较强减小相关。为了解释这种反向的光效应，我们提出了一个定性模型的基础上的猜想，电子泄漏到电介质和形成带电的沙堆状分支模式，这有利于运输，并可以分散的光。
英文摘要：
Electronic properties of ultrathin dielectric films consistently attract much attention since they play important roles in various electronic devices, such as field effect transistors and memory elements. Insulating properties of the gate oxide in transistors represent the key factor limiting Moore's law. The dielectric strength of the insulating film limits how much energy can be stored in nanocapacitors. The origin of the electric current in the nanometer-scale insulating barrier remains unexplained. Here we present an optically transparent Al-Al2O3-graphene nanocapacitor suitable for studying electronic transport in calibrated nanoscale dielectric films under high electric fields and with light exposure. The controllable flow of photons provides an additional powerful probe helping to resolve the puzzle of the electric conductivity in these high-quality insulating films. The dielectric alumina, Al2O3, is deposited by atomic layer deposition technology. With this device we observe a photon-assisted field emission effect, in which the effective barrier height is reduced by a quantity equal to the photon energy. Our main finding is a reversed photoeffect. Namely, at sufficiently high bias voltages the current through the dielectric film decreases as the light intensity increases. Moreover, higher photon energies correlate with stronger decreases of the current. To explain this reversed photoeffect, we present a qualitative model based on a conjecture that electrons leak into the dielectric and form charged sandpile-like branching patterns, which facilitate transport, and which can be dispersed by light.
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