Hong-Hyun Park

NEMO5: A Parallel Multiscale Nanoelectronics Modeling Tool

The development of a new nanoelectronics modeling tool, NEMO5, is reported. The tool computes strain, phonon spectra, electronic band structure, charge density, charge current, and other properties of nanoelectronic devices. The modular layout enables a mix and match of physical models with different length scales and varying numerical complexity. NEMO5 features multilevel parallelization and is based on open-source packages. Its versatility is demonstrated with selected application examples: a multimillion-atom strain calculation, bulk electron and phonon band structures, a 1-D Schrödinger-Poisson simulation, a multiphysics simulation of a resonant tunneling diode, and quantum transport through a nanowire transistor.

Material Selection for Minimizing Direct Tunneling in Nanowire Transistors

When the physical gate length is reduced to 5 nm, direct channel tunneling dominates the leakage current for both field-effect transistors (FETs) and tunnel FETs. Therefore, a survey of materials in a nanowire geometry is performed to determine their ability to suppress the direct tunnel current through a 5 nm barrier. The materials investigated are InAs, InSb, InP, GaAs, GaN, Si, Ge, and carbon nanotubes. The tunneling effective mass gives the best indication of the relative size of the tunnel currents when comparing two different materials of any type. The indirect-gap materials, Si and Ge, give the largest tunneling masses in the conduction band, and they give the smallest conduction band tunnel currents within the range of diameters considered. Si gives the lowest overall tunnel current for both the conduction and valence bands, and therefore, it is the optimum choice for suppressing tunnel current at the 5 nm scale. A semianalytic approach to calculating tunnel current is demonstrated, which requires considerably less computation than a full-band numerical calculation.

Contact modeling and analysis of InAs HEMT transistors

Novel device concepts and better channel materials than Si are required to improve the performance of conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). The exploration of III–V semiconductors is mainly driven by the extremely high electron mobility of the materials. Recently, several researches have demonstrated that III–V high electron mobility transistors (HEMTs) can achieve high-speed operation at low supply voltage for applications beyond Si-CMOS technology. While the intrinsic device performance looks promising, current prototypes are dramatically influenced by high contact resistances. From a modeling point of view the understanding of the intrinsic device performance is now quite advanced, while the understanding of the contacts remains quite limited. Hence, a precise theoretical approach is required to model the contact characteristics. This work investigates the contact resistance physics of InAs HEMT transistors. The Nano-Electronic Modeling Tool (NEMO5) is used to solve the non-equilibrium Greens function (NEGF) formalism which embeds Schrödinger and Poisson equations self-consistently. For this study a real-space effective mass approximation with a simple phonon scattering is utilized.