Engineering of electrical contacts on 2D-semiconductor field-effect transistors
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Physics (MPPHS), MSc
Publicerad
2024
Författare
Ullman, Patrik
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Two-dimensional (2D) semiconductor materials, such as the transition metal dichalcogenides (TMDC), have attracted great attention in the last decade due to their
excellent electronic properties, thin nature, free of surface dangling bonds, and
ability to retain high carrier mobility down to atomic thickness. TMDCs such as
Molybdenum disulfide (MoS2) have the potential to be integrated into and augment
conventional silicon complementary metal-oxide semiconductor (Si-CMOS) technology for post-Moore’s law technology. However, the performance of 2D field-effect
transistors (FETs) are largely limited by poor charge carrier injection at the metalsemiconductor (M-S) interface, owing to a large Schottky barrier due to metalinduced gap states (MIGS) and fermi-level pinning (FLP). In this work, exfoliated
MoS2-FETs were fabricated and various contact engineering approaches were proposed to mitigate MIGS, to achieve efficient carrier injection. The M-S junction
of gadolinium and bismuth has been investigated using state-of-the-art fabrication
methods and electrical measurement techniques. Semi-metal Bi has the ability
to suppress MIGS due to its near-zero density of states (DOS) near the chargeneutrality point (CNP), while gadolinium is in theory able to lower the Schottky
barrier by work function tuning. Key parameters were extracted by performing
temperature-dependent I-V measurements, as well as height profile analysis by AFM.
It was found that both bismuth and gadolinium have the potential to be considered
as good ohmic contacts to MoS2, owing to their low SBH of ϕ ≈ 43 meV and ϕ ≈
56 meV, respectively. This thesis work sheds light on the challenges of contact en gineering and fabrication methods for 2D-FETs.
Beskrivning
Ämne/nyckelord
FET, contacts, 2DMs, TMDC, MIGS, MoS2, FLP, SBH