UC Berkeley

2-D Materials: Low Power Electronics and Novel Device Possibilities

by

Varun Mishra

Doctor of Philosophy in Engineering – Electrical Engineering and Computer Sciences

University of California, Berkeley

Professor Sayeef Salahuddin, Chair

Semiconductor modeling assumes a critical role in understanding the physics of nanoscale devices as semi-classical approaches start breaking down for highly scaled devices. In this thesis, a quantum transport simulator is designed within the non-equilibrium Greens function (NEGF) formalism to explore the application of layered materials in low-power electronic and novel spintronic devices.

The quantum transport simulator is used to calculate the optimal performance of transition metal dichalcogenides (TMD) field effect transistors at the ultimately scaled limit of 5 nm gate lengths. MoS2 based transistors are studied in further detail using a rigorous tight binding Hamiltonian in order to include the effects of non-parabolicity of the electronic structure on the transistor performance. Large band gaps and effective masses were shown to result in excellent switching performance with ON/OFF ratios of 10 5 even at 5 nm gate lengths showing potential applicability in low power electronics, while screening effects were found to affect the drive current in few-layer devices. Possibility of a one-dimensional spin channel is also discussed at the junction of a lateral heterostructure of two dimensional TMDs when the system is in non-equilibrium in the absence of any external magnetic field. The one-dimensional spin channel arises out of spin-orbit splitting in conjunction with the in-plane electric field that exists in the heterojunction of two materials with a conduction band offset. A spin polarization of 0.1 % was calculated at the junction of MoS2 /WSe2 , while the effect of effective mass and spin diffusion on the above is discussed. Such one dimensional spin channel could open up the possibility to probe spin dynamics in confined phase spaces while contributing to spintronics applications.