Dielectric thickness dependence of carrier mobility in graphene with HfO2 top dielectric

Abstract

We investigate the carrier mobility in mono-and bi-layer graphene with a top HfO 2 dielectric, as a function of the HfO 2 film thickness and temperature. The results show that the carrier mobility decreases during the deposition of the first 2-4 nm of top dielectric and remains constant for thicker layers. The carrier mobility shows a relatively weak dependence on temperature indicating that phonon scattering does not play a dominant role in controlling the carrier mobility. The data strongly suggest that fixed charged impurities located in close proximity to the graphene are responsible for the mobility degradation.

Charged impurity scattering in top-gated graphene nanostructures

“…This has been attributed to the roughening of the graphene surface. However, using atomic layer deposition (ALD), Fallahazad and co-workers [5,8] have been able to deposit ultrathin high-κ dielectric materials on SLG with much less roughness and observe a significant improvement in the carrier mobility. Hollander and co-workers were also able to see an increase of the Hall mobility in epitaxial graphene with thinner top gate dielectrics [15].…”

“…We consider three top gate dielectrics, SiO 2 (κ=3.9), Al 2 O 3 (κ=12.5) [8] and HfO 2 (κ=22.0) [5]. The bottom dielectric is assumed to be SiO 2 .…”

“…However, their theory is limited to the simple geometry of SLG supported by a substrate. In more realistic graphene heterostructures, the SLG is encapsulated between the substrate and the top gate [5,8,9], an arrangement which offers better local electrostatic control than the bottom gate and is probably required for large scale integration. On the other hand, top gates modify the dielectric environment of the SLG by introducing image charges along the various interfaces.…”

Formation of Diamond-Like Carbon Films by Photoemission-Assisted Plasma-Enhanced Chemical Vapor Deposition

“…Oxide gate dielectrics like SiO 2 , aluminum oxide (Al 2 O 3 ), and hafnium oxide (HfO 2 ) are difficult to apply to the graphene channel because the carbon atoms are subject to oxidization, forming a poor interface. [18][19][20][21][22] Consequently, graphene devices require a non-oxide gate dielectric material.…”

Effect of ferroelectric substrate on carrier mobility in graphene field-effect transistors

“…The highest reported room-temperature mobility values in graphene field-effect transistors (G-FETs), utilizing different dielectric materials, including Al 2 O 3 , Y 2 O 3 , HfO 2 , BN, SiC, SiO 2 , and polymers, are below 24 000 cm 2 /V s. [4][5][6][7][8][9] A reason is the Coulomb scattering caused by charged impurities. 1,10 In a simple model, the charged impurities are located either inside the substrate or created near the graphene-substrate interface during the processing and induce a spatially inhomogeneous screened Coulomb potential.…”