石墨烯的量子电容

Quantum capacitance in graphene

量子电容在半导体纳米材料和器件中是一个日趋重要的参数,测量和提取石墨烯的量子电容,不仅可以得到石墨烯的重要物理性质,而且对石墨烯晶体管的尺寸缩减行为具有重要指导意义.文章中采用简单工艺在石墨烯上制备出均匀超薄的高质量Y2O3栅介质,其等效栅氧厚度(EOT)可缩减至1.5nm,通过控制栅介质厚度的变化,精确测量并提取了石墨烯量子电容,其电容值在远离狄拉克点时与理论计算相符合;在此基础上,文章作者提出了基于电势涨落的量子电容微观模型,通过采用单一参数——电势涨落δV,可以定量地描述Dirac点附近的量子电容行为,从而在全能量范围内实现对石墨烯量子电容测量值的完美拟合,并得到了石墨烯的相关重要参数.进而,作者从量子电容的角度,探索了石墨烯晶体管的性能极限,并比较其相对于Ⅲ-Ⅴ族场效应晶体管的潜在优势.

Quantum capacitance is an increasingly important parameter in semiconducting nanomaterials and devices. By measuring and extracting the quantum capacitance of graphene, we can infer important physical properties of graphene, and it is also a useful guide for the vertical scaling of graphene field-effect transistors. In this work, a new simple method has been used to fabricate ultrathin, high-quality Y2 O3 gate dielectric on graphene with an equivalent oxide thickness as low as 1.5 nm. By changing the thickness, the quantum capacitance has been accurately measured and extracted, with results that agree well with the the- oretical calculation when far away from the Dirac point. Furthermore, a microscopic model of the quantum capacitance based on potential fluctuations has been developed which can quantitatively describe the meas- ured values near the Dirac point through use of the single parameter-potential fluctuation. Our model fits the experimental results excellently throughout the whole energy range. In addition, we have explored the performance limits and potential advantages of graphene transistors compared with Ⅲ-Ⅴ field-effect tran- sistors from the perspective of quantum capacitance.