Norhakim Nadia, Gunasilan Thaachayinie, Kesuma Zayyan Rafi, Hawari Huzein Fahmi, Burhanudin Zainal Arif
Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, Seri Iskandar, Malaysia.
Centre of Innovative Nanostructure and Nanodevices, Universiti Teknologi PETRONAS, Seri Iskandar, Perak, Malaysia.
Nanotechnology. 2024 Oct 1;35(50). doi: 10.1088/1361-6528/ad7b42.
The charge neutrality point (CNP) is one of the essential parameters in the development of graphene field-effect transistors (GFETs). For GFET with an intrinsic graphene channel layer, the CNP is typically near-zero-volt gate voltage, implying that a well-balanced density of electrons and holes exists in the graphene channel layer. Fabricated GFET, however, typically exhibits CNP that is either positively or negatively shifted from the near-zero-volt gate voltage, implying that the graphene channel layer is unintentionally doped, leading to a unipolar GFET transfer characteristic. Furthermore, the CNP is also modulated in time, indicating that charges are dynamically induced in the graphene channel layer. In this work, understanding and mitigating the CNP shift were attempted by introducing passivation layers made of polyvinyl alcohol and polydimethylsiloxane onto the graphene channel layer. The CNP was found to be negatively shifted, recovered back to near-zero-volt gate voltage, and then positively shifted in time. By analyzing the charge density, carrier mobility, and correlation between the CNP and the charge density, it can be concluded that positive CNP shifts can be attributed to the charge trapping at the graphene/SiOinterface. The negative CNP shift, on the other hand, is caused by dipole coupling between dipoles in the polymer layer and carriers on the surface of the graphene layer. By gaining a deeper understanding of the intricate mechanisms governing the CNP shifts, an ambiently stable GFET suitable for next-generation electronics could be realized.
电荷中性点（CNP）是石墨烯场效应晶体管（GFET）发展中的关键参数之一。对于具有本征石墨烯沟道层的GFET，CNP通常处于接近零伏的栅极电压附近，这意味着在石墨烯沟道层中存在电子和空穴的良好平衡密度。然而，制造出的GFET通常表现出CNP相对于接近零伏的栅极电压正向或负向偏移，这意味着石墨烯沟道层被无意掺杂，导致了单极GFET的转移特性。此外，CNP还会随时间调制，这表明电荷在石墨烯沟道层中被动态诱导。在这项工作中，通过在石墨烯沟道层上引入由聚乙烯醇和聚二甲基硅氧烷制成的钝化层来尝试理解和减轻CNP偏移。发现CNP先负向偏移，恢复到接近零伏的栅极电压，然后随时间正向偏移。通过分析电荷密度、载流子迁移率以及CNP与电荷密度之间的相关性，可以得出结论，CNP的正向偏移可归因于石墨烯/二氧化硅界面处的电荷俘获。另一方面，CNP的负向偏移是由聚合物层中的偶极与石墨烯层表面的载流子之间的偶极耦合引起的。通过更深入地理解控制CNP偏移的复杂机制，可以实现适用于下一代电子器件的环境稳定型GFET。
