Bilayer Insulator Tunnel Barriers for Graphene-Based Vertical Hot-electron Transistors

摘要

Vertical graphene-based device concepts that rely on quantum mechanicaltunneling are intensely being discussed in literature for applications inelectronics and optoelectronics. In this work, the carrier transport mechanismsin semiconductor-insulator-graphene (SIG) capacitors are investigated withrespect to their suitability as the electron emitter in vertical graphene basetransistors (GBTs). Several dielectric materials as tunnel barriers arecompared, including dielectric double layers. Using bilayer dielectrics, weexperimentally demonstrate significant improvements in the electron injectioncurrent by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST)while suppressing defect mediated carrier transports. High injected tunnelingcurrent densities approaching 10$^3$ A/cm$^2$ (limited by series resistance),and excellent current-voltage nonlinearity and asymmetry are achieved using a 1nm-thick high quality dielectric, thulium silicate (TmSiO), as the firstinsulator layer, and titanium dioxide (TiO$_2$) as a high electron affinitysecond layer insulator. We also confirm the feasibility and effectiveness ofour approach in a full GBT structure which shows dramatic improvement in thecollector on-state current density with respect to the previously reportedGBTs. The device design and the fabrication scheme have been selected withfuture CMOS process compatibility in mind. This work proposes a bilayer tunnelbarrier approach as a promising candidate to be used in high performancevertical graphene-based tunneling devices.