Quantum Tunneling in Graphene Devices with TiOx Barriers : Experimental Investigation of IV Characteristics in Graphene-Based Tunneling Barriers

Sammanfattning

This project investigates the current-voltage (IV) characteristics of graphene-based tunneling devices, with a focus on optimizing tunneling barrier performance for spintronics. Devices using chemical vapor deposition (CVD) graphene and titanium oxide (TiOx) tunneling barriers were fabricated and studied. Electrical measurements were performed and the resulting IV curves were plotted using OriginLab and analysed using theoretical models of transport mechanisms. The effects of contact size and substrate material — silicon dioxide (SiO2) and polyethylene naphthalate (PEN) — on tunneling behaviour were examined. Curve fitting was then used to extract key parameters such as barrier height, barrier thickness, and effective electron mass. The results suggest that tunneling is elastic, indicating that energy is conserved during the process, with possible contributions from inelastic effects. A larger contact area was found to reduce contact resistance. Transport was characterized by direct tunneling at low bias, transitioning to Fowler-Nordheim tunneling around 0.7—0.8 V. The barrier height (ΦB ≅ 0.546 V) and effective electron mass (m* ≅ 0.744 me) were consistent with values reported in the literature. An observed asymmetry between positive and negative bias voltages is consistent with the presence of a trapezoidal potential barrier in TiOx. The barrier thickness is not reported due to unreliable values, likely arising from implicit assumptions made during parameter determination. Substrate material was found to affect tunneling behaviour by changing the barrier parameters and transport mechanism regimes. However, low data quality, likely due to poor contacts, affects the reliability of the results. Time constraints and barrier degradation further restricted analysis. Despite these limitations, the findings support the viability of tunnelling in both electronic and spintronic applications. However, further study is necessary for definitive conclusions and optimization strategies.