ETD

Digital archive of theses discussed at the University of Pisa

 

Tesi etd-09262020-150108


Thesis type
Tesi di laurea magistrale
Author
BUONI, LUCA
URN
etd-09262020-150108
Thesis title
CVD MoS2 Field Effect Transistors with multiple low-resistance graphene contacts
Department
FISICA
Course of study
FISICA
Supervisors
relatore Roddaro, Stefano
relatore Pitanti, Alessandro
Keywords
  • tmd
  • fet
  • graphene
Graduation session start date
26/10/2020;
Consultabilità
Secretata d’ufficio
Release date
26/10/2090
Summary
In this thesis we propose a procedure that allows fabricating a large number of flexible, ultrathin back gated field-effect transistors based on 2D-TMD channel material and graphene contacts. In particular, we fabricated FETs with MoS2 as channel material and regular arrays of single-crystal graphene flakes grown by chemical vapor deposition (CVD) as ohmic contacts. The CVD-grown large area MoS2 single layer flakes, consisting of a monolayer of molybdenum atoms sandwiched between two layers of sulfur atoms in a hexagonal lattice, allow creating multiple contacts on a single flake. Our device geometry is particularly valuable for studying the role of contact resistances. In particular, it contains a large number of contacts that allow performing four-probe measurements and distinguishing resistance linked to the contacts from the one due to the TMD channel. In addition, each individual graphene stripe can have multiple contacts which allow monitoring how the TMD junction and field-effect gating affect conduction in the graphene layer. During the various fabrication steps, the materials properties are tracked by photoluminescence (PL), atomic-force microscopy (AFM), and micro-Raman spectroscopy. In the final device, back-gated enabled transport measurements produced an estimated resistance of the order of 100 kΩ in the vacuum and at room temperature conditions. The effect of gating on the TMD and on the graphene-TMD stack is used to estimate the band alignment at the interface. Experimental results are also compared with a simulation of the field effect on the junction region, taking into account reciprocal screening effects between TMD and graphene.
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