Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576.
ACS Nano. 2010 Dec 28;4(12):7221-8. doi: 10.1021/nn101950n. Epub 2010 Nov 3.
Graphene field effect transistors commonly comprise graphene flakes lying on SiO(2) surfaces. The gate-voltage dependent conductance shows hysteresis depending on the gate sweeping rate/range. It is shown here that the transistors exhibit two different kinds of hysteresis in their electrical characteristics. Charge transfer causes a positive shift in the gate voltage of the minimum conductance, while capacitive gating can cause the negative shift of conductance with respect to gate voltage. The positive hysteretic phenomena decay with an increase of the number of layers in graphene flakes. Self-heating in a helium atmosphere significantly removes adsorbates and reduces positive hysteresis. We also observed negative hysteresis in graphene devices at low temperature. It is also found that an ice layer on/under graphene has a much stronger dipole moment than a water layer does. Mobile ions in the electrolyte gate and a polarity switch in the ferroelectric gate could also cause negative hysteresis in graphene transistors. These findings improved our understanding of the electrical response of graphene to its surroundings. The unique sensitivity to environment and related phenomena in graphene deserve further studies on nonvolatile memory, electrostatic detection, and chemically driven applications.
石墨烯场效应晶体管通常由石墨烯薄片覆盖在 SiO2 表面上构成。栅极电压相关的电导表现出与栅极扫描速率/范围有关的滞后现象。本文表明，这些晶体管在其电特性方面表现出两种不同类型的滞后现象。电荷转移导致最小电导的栅极电压发生正移，而电容门控可以导致电导相对于栅极电压的负移。正滞后现象随着石墨烯薄片层数的增加而衰减。在氦气气氛中的自加热会显著去除吸附物并减少正滞后。我们还在低温下观察到石墨烯器件中的负滞后现象。此外，我们还发现，石墨烯上/下的冰层的偶极矩比水层强得多。电解质门中的可移动离子和铁电门中的极性转换也会导致石墨烯晶体管中的负滞后现象。这些发现提高了我们对石墨烯对周围环境的电响应的理解。石墨烯对环境的独特敏感性及其相关现象值得进一步研究非易失性存储器、静电检测和化学驱动应用。
