Transcript sicdiodeposter - University of Maryland

ISDRS 2003
Numerical and Experimental
Characterization
of 4H-SiC Schottky Diodes
Xiaohu Zhang, N.Goldsman, J.B.Bernstein,
J.M.McGarrity and S. Powell
Dept. of Electrical and Computer Engineering
University of Maryland, College Park, MD 20742
[email protected] [email protected]
Introduction
4H-SiC appears to be the structure that
seems especially promising for the
development of Schottky Diodes:
Wide bandgap (3.26eV)
High critical electric field (2.2×106V)
Thermal conductivity (3.2-3.8W/cm·K)
Saturated electron drift velocity (2.0×107cm/sec).

Introduction
A methodology was developed to extract key
physical parameters for 4H-SiC Schottky
diode operation including:
•Temperature dependent mobility
•Mobility versus position and doping
•Schottky barrier height versus temperature
•Device performance dependence on geometry and
doping
Methodology
Combined simulation and experimental
methods to extract the key parameters.
•Simulations were achieved by developing a
drift-diffusion based CAD tool tailored for SiC
Schottky diode analysis
•Experiments involved measuring currentvoltage characteristics under different controlled
external temperatures.
•Coordinated use of simulation and experiment
facilitated the parameter extractions.
Device Structure
Schottky contact
Metal
Epitaxial n Drift Layer
Epitaxial n+ Layer
The schematic cross section of
the Simulated SiC Schottky diode
Simulation and Physical Models
A. Drift-diffusion model
n
div  grad 
q

n  p  C  0
divJ n  q
J n  q n  n  grad  Dn  gradn
t
divJ p  q
 q( Rn  Gn )
p
 q( Rn  Gn )
t


J p  q  p  p  grad  D p  gradp
B. Intrinsic
Carriers
and
Band
Gap
Narrowing
dE


 KT 

ni (T )  2
2
 2 
3/ 2
  E g (T ) 

mc mv 3 / 4 exp
 2 KT 


T  n, p
)
  nmin
,p
300
C 
1  ( ref ) n , p
Cn, p
 n, p (
C. Mobility
Modeling


 nLF
, p (T , C )
 nmin
,p
E g (T )  E go 
 nHF
, p (T , C )
g
dT
(T  300)
 nLF
,p


(1  (
 nLF
,p E
nsat
,p
)
 n , p 1/  n , p
)
Results
The experiment (dot curve) and simulation results (solid curve) of the forward current-voltage
(IV) characteristics of the Ti/4H-SiC Schottky diode under four different temperatures
show a very good agreement.
Results
The simulation result shows a much more accurate result than the analytical analysis
Mobility
A T-2.4 variation of 4H-SiC mobility was obtained.
Mobility variation from n+ epilayer to ndrift epilayer under different temperature
Average mobility for different doping
density under different temperature
Barrier Height
Simulation results indicate that the barrier height displays negative temperature dependence.
Temperature(K)
Barrier
Height(eV)
Temperature(K)
Barrier
Height(eV)
298.15
1.14
373.15
0.97
323.15
1.06
423.15
0.91
Device improvement
Better IV characteristic of 4H-SiC Schottky diodes can be shown in this simulation
program by changing the length and doping density in two epilayers.
It shows clearly that the current can be increased more than five times by changing the
length of the n-drift epilayer from 4µm to 1µm
Device improvement
The doping density of n-epilayer changing
from 1×1015 cm-3 to 1×1018 cm-3
The doping density of n+ epilayer
Changing from 1×1015 cm-3to 1×1018 cm-3
Summary and Conclusion
• High temperature 4H-SiC Schottky Barrier Diode
measurements were performed
•A 4H-SiC Schottky diode device simulator was
developed
•Simulations and experiments were performed in
conjunction to extract key diode parameters.
•Results show mobility values ranging from 1000 to
200cm2/Vsec temperatures ranging from 273 to 573K
for doping of 1015/cm3
Summary and Conclusion
•Results show mobility values ranging from 250 to
50cm2/Vsec temperatures ranging from 273 to 573K
for doping of 1018/cm3
•Schottky barrier height ranged from 1.14 to 0.91eV
for temperatures ranging from 298 to 423K
•Shorter drift regions give rise to larger diode forward
currents.