Modeling Radiation-Induced Degradation in Top-Gated Epitaxial Graphene Field-Effect-Transistors (FETs)

Ivan Esqueda,Michael Bajura,Travis Anderson,Michael Fritze,Jonathan Ahlbin,Jeong-S Moon,Cory Cress

doi:10.3390/electronics2030234

Abstract

This paper investigates total ionizing dose (TID) effects in top-gated epitaxial graphene field-effect-transistors (GFETs). Measurements reveal voltage shifts in the current-voltage (I-V) characteristics and degradation of carrier mobility and minimum conductivity, consistent with the buildup of oxide-trapped charges. A semi-empirical approach for modeling radiation-induced degradation in GFETs effective carrier mobility is described in the paper. The modeling approach describes Coulomb and short-range scattering based on calculations of charge and effective vertical field that incorporate radiation-induced oxide trapped charges. The transition from the dominant scattering mechanism is correctly described as a function of effective field and oxide trapped charge density. Comparison with experimental data results in good qualitative agreement when including an empirical component to account for scatterer transparency in the low field regime.

Highlights

Graphene field effect transistors (GFETs) have received significant interest from the electron-device community in the past few years due to the novel electronic properties of graphene, such as ambipolar field effect, high carrier mobilities and high thermal conductivity [1,2,3]
In [4,7] it was reported that chemical doping (p-type) that results from oxygen adsorption and/or reactions with the graphene layer during X-ray exposure resulted in positive shifts in the current-voltage (I-V) characteristics of devices irradiated in air
We have investigated total ionizing dose (TID) effects in top-gated epitaxial graphene field-effect-transistors (GFETs)

Summary

Introduction

Graphene field effect transistors (GFETs) have received significant interest from the electron-device community in the past few years due to the novel electronic properties of graphene, such as ambipolar field effect, high carrier mobilities and high thermal conductivity [1,2,3]. Initial investigations of total ionizing dose (TID) effects on graphene-based devices were done using back-gated GFETs and performed under different conditions (e.g., irradiated and characterized under vacuum or in air) resulting in a different radiation response [4,5,6]. We present evidence of TID effects in top-gated epitaxial GFETs. Oxide trapped charge near the SiO2/graphene channel interface is identified as the main contributing mechanism to radiation-induced degradation. The buildup of oxide-trapped charges results in negative voltage shifts in the I-V characteristics and degradation in carrier mobility. These effects are determined experimentally by in situ characterization of GFETs exposed to Co-60 gamma rays. The modeling approach is verified through the comparison with GFET effective electron mobility and its radiation response extracted from the degraded I-V characteristics

Experimental Section

Current-Voltage Characteristics

Experimental Ambient Conditions

Mobility Degradation

Modeling

Conclusions