HfO{sub 2} dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

• Published in: Journal of applied physics 2015-10, Vol.118 (14)
• Main Authors: Zhang, Cheng, Xie, Dan, Xu, Jian-Long, Sun, Yi-Lin, Dai, Rui-Xuan, Li, Xian, Li, Xin-Ming, Zhu, Hong-Wei, Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084
• Format: Article
• Language: English
• Subjects: CARRIER MOBILITY; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DIELECTRIC MATERIALS; ELECTRICAL PROPERTIES; FIELD EFFECT TRANSISTORS; GRAPHENE; HAFNIUM OXIDES; HOLE MOBILITY; IMPURITIES; LAYERS; SILICON OXIDES; THICKNESS
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4932645

We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO{sub 2} dielectric and different thickness of high-k HfO{sub 2} dielectric. The results show that transform characteristic (I{sub ds}–V{sub gs}) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO{sub 2} and HfO{sub 2} dielectric (SiO{sub 2}-GFETs and HfO{sub 2}-GFETs). The gate voltage reduces drastically in HfO{sub 2}-GFETs compared with that in SiO{sub 2}-GFETs, and it becomes much smaller with the decline of HfO{sub 2} thickness. The left charge neutrality point in I{sub d}–V{sub g} curves of all HfO{sub 2}-GFETs is negative, compared to the positive ones in SiO{sub 2}-GFETs, which means that there exists n-doping in graphene with HfO{sub 2} as bottom dielectric. We speculate that this n-doping comes from the HfO{sub 2} layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO{sub 2}-GFETs contrast to that in SiO{sub 2}-GFETs. In a series of HfO{sub 2}-GFETs with different HfO{sub 2} dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO{sub 2} film from atomic layer deposition process, the concentration of which varies from the thickness of HfO{sub 2} layer.