Contact Resistance Modeling in HEMT Devices M. Salmani-Jelodar, S. H. Park, H.-H. Park, S. Steiger, G. Klimeck Network for Computational Nanotechnology (NCN), Purdue University Towards III-V MOSFET Why III-V HEMTs? Towards realistic contact modeling Explore effective parts for resistances in contact-to-channel region. Acknowledgement: Robert Chau, Intel 2015-2019 Research Channel doping S/D doping Strained channel New gate dielectrics: HfO2 and Al2O3 Device geometries Channel materials High-k dielectrics and metal gates III-V channel devices Low-power & high-speed III-V: Extraordinary electron transport properties and high injection velocities HEMTs: Similar structure to MOSFETs except high-κ dielectric layer Excellent to Test Performances of III-V material (strain, band gap, effective masses, band-to-band tunneling, contacts, …) without interface defects Short Gate Length HEMTs are Introduced by del Alamo’s Group at MIT Channel region Contact 1 Contact 2 Lead 1 channel Lead 2 Contact-to-channel region channel channel Device Pie Regular compact model features: Uses a virtual source and drain. Need to fit I-V characteristic with series resistances RS and RD. Simulation Domain 2007: 40nm 2008: 30nm Simulation domain of compact model (IEDM 2009, N. Kharche et al.) D.H. Kim et al., EDL 29, 830 (2008) Contact resistance of HEMT device Contact resistance of HEMT device 2D simulations setting Objective: Guide III-V InAs experimental device design through simulation Challenge: 2D geometries, and confinement New materials, strain, disorder Gate leakage Contacts – scattering, disorder, and curved shape. Approach: NEMO5 quantum simulator Quantum transport simulations using realistic geometries Includes phonon scattering Parallel computing region of interest 40nm 90nm In53Ga47As Virtual Source In52Al48As InP InAs virtual drain 2D sim. domain Si δ-doping Source Drain N+ Cap In0.53Ga0.47As N+ Cap In0.53Ga0.47As 25nm Hetero-structures represented in 2D Ohmic contacts for virtual source/drain NEGF/Poisson self-consistent simulation Intra- and inter-valley phonon scattering mechanisms VDS = 0~0.15V for experimental VDD = 0.5V  Considered the channel and series resistances measured experimentally In0.52Al0.48As In0.52Al0.48As InP InP In0.52Al0.48As Gate In0.52Al0.48As In0.52Al0.48As In0.53Ga0.47As InAs In0.53Ga0.47As In0.52Al0.48As Contact Pad Rpad 35nm N+ Cap InGaAs Rcap 15 nm In0.52Al0.48As Y 6 nm InP etch stop Source spacing = 2 μm* Series resistance = 240 Ωμm In0.52Al0.48As Rbarrier X 11 nm 2 nm In0.53Ga0.47As Rside InAs 5 nm Virtual Drain 3 nm In0.53Ga0.47As In0.52Al0.48As *D.-H. Kim, J. D. A. del Alamo, IEEE Trans. Elec. Dev. 57, 1504 (2010) 500nm 2D simulation results: electron density and current flow 2D simulation results: electron density spectrum Methodology Real-space non-equilibrium Green’s function (NEGF) formalism with single-band effective-mass basis Self-consistent Born approx. for phonon self-energy functions1 Bulk phonon parameters based on deformation potential theory2 Limitations of phonon model : local in real and k spaces --- Conduction Band --- Electron Density Electron density spectrum Electron density profile Electron flux vectors δ-doped Layer EF EF n+ cap InGaAs InAlAs InP InAs ( /cm3) InAlAs barrier 0 nm 100 nm Plot Line ( a.u.) n+ cap channel Corner effect Preliminary results with single-band effective-mass model Electrons are thermalized at source/drain regions due to electron-phonon interactions Electrons pass the barrier NEMO5 simulator: Atomistic tight-binding / effective-mass basis Self-consistent NEGF-Poisson Solver 4-level MPI parallelization Thick InAlAs barrier is the main element of resistance [1] S. Jin et al., JAP 99, 123719 (2006) [2] M. Lundstrom, Fundamentals of carrier transport (Cambridge Univ. Press) 2D simulation results: current and resistance Summary Future work EF Quantum transport modeling of the contact-to-channel region Achievements: - 2D L-shaped simulation domain - Phonon scattering - Resistive behavior Limitations: - Parabolic effective-mass model  inaccurate for high energy electrons - Scattering model not fully calibrated Experimental resistance and model are at the same order of magnitude The InAlAs barrier plays the main role in the series resistance Current density spectrum at the source/drain contacts  thermal injection + tunneling Include nonparabolic band structure effects Improving phonon scattering model – calibrate against experimental mobility models Include alloy disorder effects, impurity / doping disorder Surface roughness effects Extend spatial region of the device sections Predict higher performance HEMT devices Explore more realistic modeling including: Process variation Dopant and surface randomness with atomistic simulations More elaborate phonon scattering models Preliminary model – parabolic effective-mass model conduction band too low  working on nonparabolic band model Series resistance vs. applied bias  resistive characteristic