The central hypothesis of this proposal is that quantum well based tunable energy filters can be used as building blocks for novel (opto)electronic devices. The envisioned devices to demonstrate the concept is an energy filter field effect transistor (EFFET). The conventional semiconductor driven technologies used nowadays in the electronics industry approach the limits of what is technically possible, this is especially true for logic devices based on field effect transistors (FET). Investigation of novel concepts/paradigms is of crucial importance. In an EFFET the transmission probability of carriers will vary according to the changes in the height and width of the potential barrier of the created quantum well(s). Conceptually, this electrostatic control can be achieved through modulation of the chemical potential of the material by a perpendicular field. Graphene is a very interesting material given the high mobility of the carriers and the controllable tuning of its electrochemical potential by a perpendicular field. Furthermore, a local selective opening of the band gap of up to 0.4eV can be achieved by covalent surface functionalization (Steven De Feyter group). Due to these advantages the device to be demonstrated will be a graphene based energy filtering filed effect transistor (Gr-EFFET). The deployment and understanding of the energy filtering and valleytronic concepts in a 2D material will require area controlled manipulation and/or surface functionalization of these materials. For the EFFET device concept, graphene will be used. At imec, there is an extensive research activity in the group of Prof. Stefan De Gendt to produce synthetic graphene through reaction on metal catalytic surfaces. These graphene films will be functionalized in the De Feyter group with covalently bonded aryl groups. By the covalent bond formation, the sp2 hybridization of the graphene carbons is changed to sp3 hybridization and thus a band gap of up to 0.4eV can be achieved with high-density random covalent grafting. Conventional field effect transistors have been the backbone of modern electronics for more than 30 years. With this proposal we want to advance forward by considering new materials allowing new concepts and paradigms. With the Gr-EFFET, the possibility to turn off the device without concerns about the limitations imposed by thermal charge injection (60mV/dec at room temperature) opens the door for more energy efficient devices that could operate at very low drain biases (power consumption), which is of utmost importance for many of the ‘Internet of Everything Applications’. Additionally, in these devices, novel materials (graphene) can be used relying on their intrinsic properties and without trying to modify these properties to emulate those of conventional semiconductors.
The following individual goals will be pursued:
- Evaluate the concept feasibility and optimal process parameters for high performance of the Gr-EFFET through theoretical understanding of the underlying mechanisms.
- Identify and develop the required pieces of technology for the device concepts and implementation, specifically related to selective surface modification of 2D materials.
- Demonstration and characterization of the novel concept devices based on 2D materials and area selective surface modification.
Required background: candidate should have a broad interest and knowledge, ranging from electrical engineering to chemistry, be creative, able to work independently as well as in a team, and very communicative.
Type of work: 10% literature, 30% modeling, 60% experimental work
Supervisors: Stefan De Gendt, Steven De Feyter
Daily advisors: Cesar Lockhart de la Rosa, Geoffrey Pourtois
The reference code for this PhD position is STS1712-44. Mention this reference code on your application form.