טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKafri Alonit
SubjectLaser Assisted Mask-Less Device Fabrication and its Impact
on Electronic Properties of 2D Materials
DepartmentDepartment of Materials Science and Engineering
Supervisor Dr. Elad Koren
Full Thesis textFull thesis text - English Version


Abstract

The successful isolation of graphene in 2004, has created massive research interest in graphene and other two-dimensional (2D) materials from both the academia and semiconductor industry. Beyond graphene, transitions metal dichalcogenides (TMDCs) become the most investigated 2D family, where MoS2 is in the focus of attention due to its relatively high stability and semiconducting nature. Due to their extremely large surface-to-volume ratio, 2D materials are extremely sensitive to surface interactions and contaminants, which can dramatically influence the material quality. This holds great potential in the tunability of materials properties, which can be engineered by introducing or reducing surface disorders.

In the present study, we present a unique lithography-based fabrication method that holds excellent design flexibility which is essential for proto-typing research and development in which, the obviation of fabrication mask and development steps are of great advantage. To this end, we developed a novel mask-less lithography process by leveraging a green laser (532 nm) beam, of our Raman microscope, and a relatively low ceiling temperature of - cyclic polyphthalaldehyde (c-PPA) based resist. The laser beam locally heats this self-developed resist above its ceiling temperature, resulting in a perfectly removed pattern for following metallization. The direct interaction between a laser beam and a 2D material is also utilized to control the metal-2D material contact electronic properties, which is experimentally studied by charge transport measurements and Kelvin Probe Force Microscopy. It is found that the electronic nature of MoS2 is greatly influenced by intrinsic disorders that can form either donor, acceptor or trap states depending on the laser intensity. Electrical performance measurements of CVD MoS2 monolayer devices demonstrate a thinning of the metal induced Schottky barrier and low effective contact resistance induced by the local change in MoS2 work function.