Department(s): Physics and Astronomy
Research Interests: High performance single-crystal organic field-effect transistors (OFETs). Understanding the fundamentals of charge carrier transport and photo-physical properties of organic semiconductors
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Organic electronics is an emergent interdisciplinary research field focusing on technologies that rely on organic (carbon-based) semiconductors, as opposed to traditional inorganic semiconductors usually based on silicon. Organic electronic devices with unique capabilities include, for instance, organic field-effect transistors (OFET), light emitting displays (OLED) and organic photo-voltaic (OPV) cells. Organic electronics will help us address a number of important problems of modern society, such as renewable energy and green chemistry. It might also help to overcome the limitations of modern semiconductor nanostructures. This field may result in technologies, such as flexible or wearable electronics (e.g., rollable computer and TV screens, electronic paper and solar cells), energy efficient solid-state lighting, photo-detectors and molecular sensors. These kinds of technologies are becoming increasingly important in modern World, but yet they are difficult to tackle using conventional inorganic semiconductors. In addition, enormous possibilities of synthetic chemistry and compatibility with inexpensive solution-based or printing fabrication techniques make organic semiconductors an extremely viable novel technology of the future.
Inspite of the progress in applied research, such fundamental aspects of organic semiconductors as charge (polaron) and energy (exciton) generation and transport remain poorly understood. Therefore, our interests lie in the basic physics of organic semiconductors that determine the operation of organic transistors and solar cells. With the recent development of single-crystal OFETs, we can study the intrinsic charge transport and optical properties of organic semiconductors without limitations imposed by disorder present in amorphous and polycrystalline organic films. Owing to a great reproducibility and a very low density of defects (traps) in our single-crystal devices, the experimental observations of a band-like polaronic transport, Hall effect, and novel photo-induced phenomena became possible in OFETs. The availability of well-characterized single-crystal OFETs opens new exciting opportunities for research on charge carrier transport, photo-physics and novel device applications. Furthermore, new nanoscale surface functionalization techniques using self-assembled monolayers can be explored for organic electronics.
Some of the projects we are working on:
- High-performance single-crystal OFETs.
- Molecular self-assembly.
- Optics of organic semiconductors (excitons, photo-conductivity, photo-voltaics).
- Charge transport in conjugated polymers.
- Surfaces and interfaces in organic semiconductor devices.
Layered inorganic semiconductors is a large class of materials composed of layers of covalently or ionically bonded atoms, with a week van der Waals bonding between the layers. This specific structure allows individual layers of these materials to be peeled off, exposing clean, dangling-bond-free surfaces. These materials include graphene (single and multi-layered), graphite (HOPG) and transition metal dichalcogenides (MoS2, MoSe2, WS2, WSe2, etc).
The 1-st paper reporting field-effect transistors based on this class of materials has been published by us in 2004 after a lengthy delay partially caused by the Rutgers-Lucent lawyers patenting this discovery (V. Podzorov et al., "High mobility ambipolar field-effect transistors based on transition metal dichalcogenides", Appl. Phys. Lett. 84, 3301 (2004)). In the end, the patent was won by the Rutgers-Lucent team, our paper got published and appeared before the first paper on graphene. Our patent covers transition metal dichalcogenides, as well as graphene. The irony is that only a handful of people are actually aware of this fact. Our original work, although largely unnoticed by the community, had been apparently revolutionary at that time.
The remarkable fact is that novel inorganic FETs like these could be produced by such a simple fabrication technique as parylene deposition to form a high-quality semiconductor-dielectric interface (that is, out of clean room environment and w/o using expensive facilities typically used in Si technology). In addition, these devices exhibit a great performance: electron and hole mobilities in the range 100-500 cm2V-1s-1 and in many cases ambipolarity. These characteristics are easily comparable to or even better than those of commercial single-crystal Si MOSFETs that took decades to develop. The FETs based on layered materials perform so well due to their specific chemical structure: a strong in-plain bonding ensures a good delocalization of charge carriers and a high in-plain carrier mobility, while week van der Waals out-of-plane bonding ensures saturated surfaces free from dangling bonds, that would otherwise result in overwhelming deep-trap densities and dysfunctional devices.