Events Calendar

EE-EP Seminar

Speaker: Rajib Rahman, Purdue University

Talk Title: Atomistic modeling of solid-state devices: from qubits to transistors

Abstract: Due to aggressive scaling, today’s transistors have reached sizes of tens of nanometers and are fast approaching the ultimate limits of scaling, as predicted by Moore’s Law. At the nanoscale, the atomic granularity of the devices and the associated quantum mechanical effects strongly influence device operation and need to be considered in theoretical models. To ensure continued progress in computing in the post Moore’s Law era, novel device concepts need to be developed utilizing quantum phenomena at the nanoscale. I will present an atomistic modeling technique for solid-state devices that combine material and device level description of electronic structure and transport from a full quantum mechanical treatment. This framework helps to model a variety of systems ranging from solid-state qubits to field-effect-transistors, and can help in designing the next generation of electronic devices.

In particular, I will show several applications of this method to model silicon qubits hosted in quantum dots and donors. 1) The method captures the precise electric field control of electronic and nuclear spins in donor qubits through the hyperfine and spin-orbit interactions [1], and helps in the first experimental realization of the Kane A-gate [2]. 2) Spin-lattice relaxation times are computed from an atomistic electron-phonon Hamiltonian to interpret experimental measurements, and design guidelines are presented to enhance the relaxation times by an order of magnitude [3]. 3) Electron-electron interaction is captured from a full configuration interaction technique in the tight-binding basis, and is used to obtain two-qubit exchange energy as a function of detuning electric field and qubit separation. Design considerations are presented to improve the electric-field tunability of exchange by several orders of magnitude in donor qubits. The computed single and multi-electron wavefunctions are also compared with tunneling probability measurements in scanning tunneling microscopy experiments to identify signatures of conduction band valley quantum interference in silicon [4].

I will also show atomistic quantum transport simulations of tunnel field-effect transistors (FET) in the emerging class of two-dimensional transition metal dichalcogenides. The simulations elucidate the material choice and design principles needed to achieve a steep sub-threshold slope transistor with large on-currents and high on/off ratio, which may help to scale down the power supply voltage and thus reduce the power consumption [5].

References:
[1] R. Rahman et. al., Phys. Rev. Lett. 99, 036403 (2007).
[2] B. E. Kane, Nature 393, 133 (1998).
[3] Y. Hsueh et. al., Phys. Rev. Lett. 113, 246406 (2014).
[4] J. Salfi et. al., Nature Materials 13, 605 (2014).
[5] H. Ilatikhameneh et. al., arXiv: 1502.01760 (2015).


Biography: Rajib Rahman obtained his PhD degree in Electrical and Computer Engineering from Purdue University in 2009 in the area of computational nanoelectronics. Subsequently, Rajib spent three years in Sandia National Laboratories, New Mexico, as a postdoctoral fellow in the Silicon Quantum Information Science and Technology group. Both in his PhD and postdoc, Rajib developed large-scale computational techniques in the NEMO3D tool to investigate the properties of quantum bits in silicon based on quantum dots and impurities. In 2012, Rajib joined Purdue University as a Research Assistant Professor in the Network for Computational Nanotechnology (NCN). Rajib currently leads the device modeling effort of the Australian Centre for Quantum Computer and Communication Technology (CQC2T), and investigates silicon qubits and their interaction with a solid-state environment. At Purdue, Rajib also works on novel low energy field-effect transistors in emerging materials such as 2D transition metal dichalcogenides, graphene, and polarization engineered Nitride devices.

Host: EE-Electrophysics

Location: Olin Hall of Engineering (OHE) - 122

Audiences: Everyone Is Invited

Contact: Marilyn Poplawski