1. 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
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, (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