Iue Annual Review 2009

Biography:
Neophytos Neophytou received the BSc degree in electrical and computer engineering in 2001 from Purdue University, West Lafayette IN. He received the MSc and the PhD degrees in 2003 and 2008 respectively in the area of microelectronics and nanotechnology, both from Purdue University. He is currently a post doctoral researcher at the Institute for Microelectronics at the Technische Universität Wien. His research interests include computational modeling of quantum mechanical electron transport through new channel materials such as carbon nanotubes, nanowires, graphene based channels and III-V materials. He is currently working on the effects of bandstructure on the electronic properties of nanoscale devices electronic and thermoelectric device applications.

Modeling of Nanoscale Devices for Electronic and Thermoelectric Applications

As devices scale towards atomistic sizes, research in silicon electronic device technology investigates alternative structures and materials. As predicted by the International Roadmap for Semiconductors (ITRS), structures will evolve from planar devices into devices that include 3D features, strong channel confinement, strain engineering, and gate all around placement for better electrostatic control on the channel. Alternative channel materials such as Carbon NanoTubes (CNT), NanoWires (NW), and III-V based channel materials are considered as possible candidates for future device technology nodes. For nanoscale dimensions, both atomistic and quantum effects become important in determining the electronic structure and transport properties of the devices.
We use the Non-Equilibrium Green's Function (NEGF) formalism for quantum transport simulations and real space atomistic tight-binding techniques (pz, sp3d5s*-SO) to investigate transport properties in CNT, NW and III-V HEMT field-effect transistors. We investigate the effect of physical quantization on the electronic structure of NW field-effect transistors and identified the main electronic structure factors that influence their performance. It was found that structural and quantization below 10nm can severely affect the electronic properties of NW channels by changing the effective masses and altering degeneracies through valley splitting. In addition, different wire orientations can provide different transport properties. We also analyze recent experimental data for III-V HEMT devices using the NEGF formalism and address several issues related to the operation of HEMT devices. Interestingly, to first order, a 60nm HEMT device can be thought as a ballistic channel connected to two series resistances.
The properties of nanoscale devices can be engineered to some degree since the length scale degree of freedom enters the design space. Specifically, the electron and phonon mean free path and scattering length can be altered and new properties can emerge. We use this concept to design new low dimensional thermoelectric devices for more efficient energy conversion.

The charge spectrum density in a HEMT device at ON-state extracted from the NEGF simulation.

The charge distribution in the cross section of a Si NW at ON-state extracted from atomistic tight-binding calculations.