Improving the electrical properties of InAs nanowire field effect transistors by covering them with Y ₂ O ₃ /HfO ₂ layers

Quasi-one-dimensional semiconducting materials have attracted increasing attention due to their excellent ability to downscale the size of transistors. However, in quasi-one-dimensional nanowire (NW) transistors, their surface and interface properties play a very important role mainly due to the large surface-to-volume ratio of NWs and surface scattering, which degrade their carrier mobility. Herein, we developed a new method to cover the channel surface of InAs NW field effect transistors (FETs) with Y₂O₃/HfO₂ layers to improve their electrical properties. We successfully fabricated nine FETs and measured their electrical properties, which improve after depositing the Y₂O₃/HfO₂ layers, including an increase in on-state current, decrease in off-state current, increase in transconductance, increase in electron mobility and decrease in subthreshold swing. By comparing the properties of Y₂O₃/HfO₂-covered devices with that of the FETs fabricated without the Y₂O₃ covering or without annealing, we prove that it is the combined Y₂O₃/HfO₂ layers instead of only the Y₂O₃ or HfO₂ layer that improve the electrical properties of the FETs. The Cs-corrected high-resolution scanning transmission electron microscopy study demonstrates that Y can actually diffuse through the native oxide layer (confirmed to be InO_x) and reach the surface of the InAs NWs. Our results indicate that the desirable characteristics of Y₂O₃ and the surface passivation by HfO₂ improve the electrical properties of the InAs NW FETs, in which Y₂O₃ plays an important role to modify and stabilize the interface between the InAs NWs and the outside dielectric layer. Furthermore, this method should also be applicable to other III-V materials.