Contact Resistance Modeling and Analysis of HEMT Devices S. H. Park, H Contact Resistance Modeling and Analysis of HEMT Devices S. H. Park, H.-H. Park, M. Salmani-Jelodar, S. Steiger, M. Povolotsky, T. Kubis, G. Klimeck Network for Computational Nanotechnology (NCN), Purdue University Towards III-V MOSFET Why III-V HEMTs? Towards realistic contact modeling Contact Resistance of HEMT 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 without interface defects Short Gate Length HEMTs are Introduced by del Alamo’s Group at MIT 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 Source Drain N+ Cap In0.53Ga0.47As N+ Cap In0.53Ga0.47As Channel region In0.52Al0.48As In0.52Al0.48As Contact 1 Contact 2 InP InP Lead 1 channel Lead 2 In0.52Al0.48As Gate In0.52Al0.48As Contact-to-channel region In0.52Al0.48As channel In0.53Ga0.47As channel InAs Device Pie In0.53Ga0.47As In0.52Al0.48As Simulation Domain Contact Pad 2007: 40nm 2008: 30nm Regular compact model features: Uses a virtual source and drain. Need to fit I-V characteristic with series resistances (RS and RD) from experimentalists or ITRS Rpad 35nm N+ Cap InGaAs Rcap 15 nm In0.52Al0.48As Y 6 nm InP etch stop In0.52Al0.48As Rbarrier X 11 nm 2 nm In0.53Ga0.47As Rside InAs 5 nm Virtual Drain 3 nm In0.53Ga0.47As Simulation domain of compact model (IEDM 2009, N. Kharche et al.) D.H. Kim et al., EDL 29, 830 (2008) In0.52Al0.48As 500nm 2D Simulation Results: electron density and current flow Methodology Contact Resistance of HEMT 2D Simulations Setting 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 Region of interest 40nm 90nm In53Ga47As Virtual Source In52Al48As InP InAs virtual drain 2D simulation domain Si δ-doping Electron density profile Electron flux vectors 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 n+ cap InGaAs InAlAs InP InAs ( /cm3) 0 nm 100 nm Plot Line ( a.u.) Corner effect NEMO5 simulator: Atomistic tight-binding / effective-mass basis Self-consistent NEGF-Poisson Solver MPI parallelization Source spacing = 2 μm* Series resistance = 240 Ωμm [1] S. Jin et al., JAP 99, 123719 (2006) [2] M. Lundstrom, Fundamentals of carrier transport (Cambridge Univ. Press) *D.-H. Kim, J. D. A. del Alamo, IEEE Trans. Elec. Dev. 57, 1504 (2010) 2D Simulation Results: electron density spectrum 2D Simulation Results: current and resistance Summary Future Work Quantum transport modeling of the contact-to-channel region Achievements: - 2D L-shaped simulation domain - Phonon scattering - Resistive behavior Limitations: - Parabolic effective-mass model  over predict the Fermi level - 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 Include nonparabolic band structure effects Improving phonon scattering model – Calibrate against experimental mobility models Include alloy disorder effects, impurity / doping disorder Surface roughness effects Predict higher performance HEMT devices Explore more realistic modeling including: Process variation Dopant and surface randomness with atomistic simulations --- Conduction Band --- Electron Density Electron density spectrum EF Current density spectrum at the source/drain contacts  Thermal injection + Tunneling δ-doped Layer EF EF InAlAs barrier Preliminary model – parabolic effective-mass model  Conduction band too low  Working on nonparabolic band model n+ cap channel Preliminary results with single-band effective-mass model Electrons are thermalized at source/drain regions due to electron-phonon interactions Electrons pass the hetero-barriers Series resistance vs. applied bias  Resistive characteristic Thick InAlAs barrier is the main element of resistance TECHCON Sept 11-14, 2011