Novel Physics of Nitride Devices

Novel Physics of Nitride Devices
M. S. Shur
CIE and ECSE Department, RPI, Troy, 12180, US
Tutorial
ICPS 2004
July 25, 2004
Flagstaff, Arizona, USA
[email protected]
1
Outline
• Potential applications
• Polarization effects
– Piezo –Pyro -Movable Quantum Dots and THz
• Electron transport
•
•
•
•
•
– Low field - High field
– Ballistic and overshoot transport
Trapping
Noise
New FET physics – MOSHFET and Current Collapse
Plasma wave electronics
Conclusions
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2
Device Universe Is Both Infinite and Expanding
1200
1100
Number of Publications
1000
900
New Nitride Galactic
INSPEC search query:
Gallium Nitride
or Indium Nitride
or Aluminum Nitride
800
700
600
500
400
300
200
100
0
1970
1975
1980
1985
1990
1995
2000
Year
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3
“The Universe is full of magical things patiently waiting for our wits
to grow sharper”
Eden Phillpott
Isa Genzken (born 1948)
Basic research
Lembach Villa, Munich
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4
Potential and Existing Applications of Nitride Devices
• Blue, green, white light, and UV emitters
•
•
•
•
•
•
•
•
•
– Traffic lights
– Displays
– Water, food, air sterilization and detection of biological
agents
– Solid state lighting
Visible-blind and solar-blind photodetectors
High power microwave sources
High power and microwave switches
Wireless communications
High temperature electronics
SAW and acousto-optoelectronics
Pyroelectric sensors
Terahertz electronics
Non volatile memories
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5
White and UV applications (for 250 nm – 340 nm).
Sensing and beyond
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Environmental protection
Homeland security
Plant growth
Surgery lighting
Visual stimuli
Capillaroscopy
Monitoring of arterial oxygen
Phototherapyherapy of Seasonal
Affective Disorder
Water and air purification
Solid-state white lighting
Dense data storage
Ballistic missile defense
Photopolymerization of Dental
Composites
Photobioreactors
UV-LED Based Fluorimeter with Integrated
Lock-in Amplifier (after Prof. Zukauskas, U of V.)
Applications of U of V/RPI/SET quadrichromatic
Versatile Solid-State Lamp: Phototherapy of
seasonal affective disorder at Psychiatric Clinic of
Vilnius University
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6
Nitrides: New Symmetry, New Physics
Zinc Blende Structure (GaAs)
Diamond Structure (Si, Ge)
Wurtzite Structure (SiC, GaN)
Si boule
GaAs boule
AlN boule (Courtesy Crystal IS
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7
Crystal symmetry of pyroelectric crystals
Crystal system
Crystal class
Crystal class
(Schönflies)
(Hermann-Mauguin)
Triclinic
C1
1
Monoclinic
Cs
m
C2
2
Orthorhombic
C2v
2mm
Tetragonal
C4
4
C4v
4mm
C3
3
C3v
3m
Rhombohedral
Hexagonal
HEXAGONAL
C6
C6v
C6
C6V
6
6mm
6
6mm
?
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8
Wide Gap Semiconductors
Enabling Technology for Piezoelectronics and
Pyroelectronics
GaAs
• Zinc blende structure
• No PE or SP effect in
<100> direction
• PE coefficient <111>
~0.15 C/m2
• No PE/SP ‘doping’ reported
GaN/AlN
• Wurtzite structure
• c-axis growth direction
• PE coeficient in cdirection ~1 C/m2
• PE/SP ‘doping’
demonstrated
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9
Nitride Heterostructures:
Polarization Induced Electron and Hole 2D Gases
AlGaN on GaN
C
From A. Bykhovski, B. Gelmont, and M. S. Shur,
J. Appl. Phys.74, p. 6734-6739 (1993)
4
6v
P6 3 mc
From O. Ambacher et al
JAP 87, 334 (2000)
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10
Polarization signs
Ga face
P sp
AlG aN
P sp
GaN
N face
Relaxed
P sp
AlG aN
Relaxed
P sp
GaN
P pe Tensile
Strain
+σ
Relaxed
P sp
AlG aN
P pe
P sp
GaN
-σ
GaN
P pe
+σ
2D holes
-σ
2D electrons
P sp
AlG aN
P sp
GaN
2D holes
GaN
AlG aN
P peCom pressive
Strain P sp
-σ
Relaxed P sp
AlG aN
+σ
[0001]
[0001]
2D electrons
After O. Ambacher et al. J.Appl. Phys. 85, 3222 (1999)
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11
Spontaneous polarization
After F.
AlN
Bernardini et al.
Phys Rev. 56,
10024(1997)
GaN
InN
Spontaneous
polarization
(C/m2)
(cm-2)
-0.029
2.23 1014
-0.032
-0.057
-0.045
2.46 1014 4.39 1014 3.47 1014
-0.081
6.24 1014
ZnO
BeO
For comparison, in BaTiO3, Ps = 0.25 C/m2 (1.93x1015cm-2)
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12
Pyroelectric effect
-4
0
4
8
12
16
20
50
0
2
4
6
8
10
12
0
2
4
6
8 10 12
Time, s
100
a
0
50
-50
0
-100
b
0
50
-40
-80
01
3
0.7
c
2
0.4
1
0.1
0
-0.2
-1
-4
0
4
8
12
16
20
Time, s
Pyroele ctr ic
m ate rial
Ip
(after A. D. Bykhovski, V. V. Kaminski, M. S. Shur, Q. C. Chen, and M. A. Khan
"Pyroelectricity in gallium nitride thin films", Appl. Phys. Lett., 69, 3254 (1996)).
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13
)
C
o(
er 40
ut
ar
e 20
p
m
et
0
ht
a
B)
20
u.
a(
x
0
ul
f
t
a
e -20
H
)
V 0.4
m
(
e
g
0
at
l
o
V
-0.4
(a)
Pyroelectric voltage for primary
pyroelectric effect (changing flux magnitude
and direction)
Two time constants:
Sample cooling and
Charge relaxation
-4
0
4
8
12
16
20
50
a
0
-50
-100
(b)
-40
Ga N
)
C
o( 200
T
b
0
a.
300
-80
3
c
2
100
(c )
)
V
m
(
e
g
at
l
o
V
1
0
0
12
-1
b.
-4
10
20 30
Tim e (s )
4
8
12
16
20
Time, s
8
4
0
0
0
40
0
10
20
30
40
Primary pyroelectric
effect at 300o C
(High Temperature
Operation!)
Tim e (s )
(after A. D. Bykhovski, V. V. Kaminski, M. S. Shur, Q. C. Chen, and M.
A. Khan "Pyroelectricity in gallium nitride thin films", Appl. Phys.
Lett., 69, 3254 (1996)).
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14
Strain from the lattice mismatch
• uxx = (aGaN -aAlGaN)/aGaN
• Ppe = 2 uxx (e31-e33 C13/C33)
How Piezoelectric constants are determined?
•Electromechanical coefficients (difficult)
•Optical experiments (indirect)
•Estimate from transport measurements (very indirect)
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15
Effect of Strain on
Dislocation-Free Growth
Critical thickness as a function of Al
mole fraction
in AlxGa1-xN/GaN:
superlattice (solid line), SIS structure
(dashed line).
From A. D. Bykhovski, B. L.
Gelmont, and M. S. Shur, J. Appl.
Phys. 81 (9), 6332-6338 (1997)
Hall Mobility (cm /Vs)
60
2
•
Thickness, nm
50
40
30
20
10
Effect of Critical Thickness
on Electron Mobility
3,000
2,000
77K
300K
1,000
0
0
0.2
0.4
0.6
0.8
Al Mole Fraction
1
100 200 300 400 500 600
AlGaN Thickness (A)
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16
Twice as large
as in SiC
SIS sensor
Top Contact
n - GaN 0.4 µm
AlN 30 Å - 100 Å
Bottom
Contact
F
GaN
n
AlN GaN
n
u
B A B AB A
(1)
(2)
(3)
n - GaN 1.0 µm
i - GaN 1.0 µm
Ec
AlN Buffer
Sapphire
L
Ef
45.3
45.2
Resistance, Ω
• Piezoelectric sensors
• Pyroelectric sensors
Short range
superlattice
is four times
larger than in
SiC
45.1
45
44.9
44.8
44.7
44.6
44.5
Ev
44.4
0
0.5
1
1.5
2
2.5
3
Strain (compression), 10-4
After R. Gaska, J. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, S. M. Soloviev,
Appl. Phys. Lett. 71(26), 3817 (1997)
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17
Polarization domain structure
Surface
Surface
Surface
Ga
N
Ga
Ga
N
Ga
N
N
N
N
N
N
Ga
Ga
Ga
Ga
N
N
Ga
Ga N
Ga Ga
N
After A. D. Bykhovski, V. V. Kaminskii, M. S. Shur, Q. C. Chen, and M. Asif Khan,
Piezoresistive Effect in Wurtzite n-type GaN, Appl. Phys. Lett., 68 (6), pp. 818-819 (1996)
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18
Superlattice Band Diagram and resistance
change in SRSL
25
1 SRSL
-3
δR/R (10 )
En erg y (eV)
20
e ffec tive
A B AB AB A B
band gap
AB
15
2 SiC
1
10
2
5
3 GaN
3
(000 1)
0
y
0.0
0.5
1.0
1.5
2.0
2.5
3.0
-4
Strain (10 )
After A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, Elastic Strain Relaxation in GaN-AlN, GaN-AlGaN,
and GaN-InGaN Superlattices, J. Appl. Phys. Vol. 81, No. 9, pp. 6332, May (1997)
Relative change in resistance under applied strain. (o) - correspond to [(AlN)6-(GaN)3]150 SRSL ;
( ) - [(AlN)3-(GaN)8]150 SRSL; solid line 1 shows dependence measured for GaN-AlN-GaN SIS 1;
dashed line 2 - SiC p-n junction 1 ; 3 - GaAs 2. The GF for the measured samples was in the 30 to 90 range.
The larger GF (higher sensitivity to strain) was measured in SRSLs with higher Al content.
1
J. S. Shor, L. Bemis, and A. D. Kurtz, IEEE Trans. Electron Dev. , 41 (5), 661 (1994).
2 A. Sagar, Phys. Rev., 112, 1533 (1958); 117, 101 (1960).
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19
High Temperature p-GaN Pressure Sensor
0 .1 2
p -G a N
0 .1 0
δR/R
0 .0 8
0 .0 6
G a N /A lN /G a N
0 .0 4
S iC
0 .0 2
0 .0 0
Si
0
1
2
3
4
S tr a in , 1 0
5
-4
From R. Gaska, M. S. Shur, A. D. Bykhovski, J. W. Yang, M. A. Khan, V. V. Kaminski and S. M. Soloviov, Piezoresistive Effect
in Metal-Semiconductor-Metal Structures on p-type GaN, Appl. Phys. Lett., vol. 76, No. 26, pp. 3956-3958, June 26 (2000)
Static Gauge factors (GF)
(measured under longitudinal mechanical deformation)
GaN
n-type GF=10
p-type GF > 200
GaN/AlN/GaN Sapphire AlGaN/GaN Heterostructures
GF = 50
GF = 10-15
AlN/GaN Short Range
Superlattices
GF = 30-80
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20
Polarization effects in undoped and doped
channel GaN/AlGaN HFETs
)
Ve
(
yg
er
n
E
Undoped
2
1
Nd = 5x1017 cm-3
.
-20
20
0
Distance (nm)
40
)
V
e(
y
g
r
e
n
E
-20
0
20
40
-2
-4
Distance (nm)
0.01
••••
•
•
•
20 nm (100% s trained)
•
•••
40 nm (60%)
••••
•
••
60 nm (30%)
•••
••
•
•
100 nm (0%)
••
•
•
•••
••
•••
•
•
•
•
••
•
•
•
••• •
10 nm (100% s trained)
0.008
0.006
0.004
0.002
0
-16
-12
-8
After M. S. Shur, GaN and related materials for high power applications,
Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998) and From
A. D. Bykhovski, R. Gaska, and M. S. Shur, Appl. Phys. Lett. 73 (24)
(1998).
-4
0
Voltage, V
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21
Piezoelectric and Pyroelectric
Doping in AlGaN/GaN
6
5
4
3
State-of-the-art
2
1
0
0
0 .2
0 .4
0 .6
A l M o la r
0 .8
1
F r a c t io n
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22
Strain and Energy Band Engineering
Dc (Angstroms)
•Graded composition profile and quaternary AlGaInN
0.035
•Superlattice buffers for strain relief
0.030
•PALE and MEMOCVD epitaxial growth
0.025
•Homoepitaxial substrates
0.020
•Non-polar substrates
0.015
70
0.000
40
0.25
30
20
10
0
0.0
Al - 9%
0.005
50
DEg (eV)
Thickness (nm)
60
0.010
Al - 17%
0.20
0.15
0.2
0.4
0.6
Al molar fraction
0.8
1.0
A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, Elastic
Strain Relaxation in GaN-AlN Superlattices, Proceedings of
International Semiconductor Device Research Symposium,
Vol. II, pp. 541-544, Charlottesville, VA, ISBN 1-880920-04-4,
Dec. 1995
0.10
0.0
0.5
1.0
1.5
2.0
In Molar Fraction (%)
M. Asif Khan, J. W. Yang, G. Simin, R. Gaska, M. S.
Shur, Hans-Conrad zur Loye, G. Tamulaitis, A.
Zukauskas, David J. Smith, D. Chandrasekhar, and R.
Bicknell-Tassius, Lattice and Energy Band Engineering in
AlInGaN/GaN Heterostructures, Appl. Phys. Lett 76 (9)
pp. 1161-1163 (2000)
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23
New Screening Mechanism in Multilayer Pyroelectrics
d e p le tio n
p y ro e le c tric ( 2 )
a c c u m u la tio n
Screening the
polarization
induced dipole
involves smaller
charges than the
charges in
polarization dipole
Screening dipole – smaller changes
but at larger separation
r e g io n ( 3 )
re g io n (1 )
P
o
s e m ic o n d u c to r
m a trix
0
L
L
d
z
+
New screening length (larger than Debye Polarization dipole
but smaller than depletion)
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24
Electronic island at the surface of
semiconductor grain in pyroelectric matrix
(MQDs -Moveable Quantum Dots)
Inversion electron and hole islands at the surface of
pyroelectric grain in semiconductor matrix
Pyroelectric
Po
Po
Semiconductor
Semiconductor
Hole inversion island
Pyroelectric
Electronic island
Electronic inversion island
Control by external field – Zero dimensional Field Effect (ZFE)
V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)
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25
Basic Equations
4 π P0
E =
ε + 2ε p
N=
polarization induced
electric field
4π
nd R 3
3
nd
total number of
electrons in the grain
donor concentration
The size of the island should be
determined by the minimum of
the total energy
QEa 2 Q 2
W =
+
R
εa
Potential energy
in the field E
Coulomb repulsion
energy
W should be minimal provided that the total charge
of the island, Q=eN , is constant
eN 4π end R
Ec = 2 =
screening field
εR
3ε
E >> Ec
P0 >> end R
Electrons cannot screen polarization induced
field. Strong field push electrons into small
2D island
1/ 3
 QR 
a~

 E 
1/ 3
 end R 
 R
~ 
 P0 
For typical values of polarization the size
of electron island is small compared to R
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26
Terahertz oscillations
2D island might oscillate as a whole over grain surface. The
oscillations can be exited by ac field perpendicular to P0
Oscillation frequency
w0 =
4p eP0
( e+ 2 ep ) mR
MOVABLE QUANTUM DOTS (MQD)
Oscillation frequency is of the order of a terahertz
w0 p/2~ 1 THz to 30 THz
SWITCH OR SHIFT FREQUENCY
BY EXTERNAL FIELD OR BY LIGHT
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27
New Physics of Movable Quantum Dots
•
•
•
•
Self-assembled quantum dot arrays
Coulomb blockade
Light concentration in quantum dots
Left handed materials
New Potential Applications
•
•
•
•
•
•
•
Terahertz detectors
Terahertz emitters
Terahertz mixers
Photonic terahertz devices
Photonic crystals
Plasmonic crystals
Solar cells and thermo voltaic cells
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28
New features of electron transport in nitrides
•
Large polar optical phonon energy leads to two step
scattering optical photon absorption and re-emission
resulting in an elastic scattering process [1]
•
In high electric fields, an electron runaway plays a key
role [2]. The runaway effects are enhanced in 2D
electron gas [3]
•
In very short GaN-based structures, ballistic and
overshoot effects are very pronounced [4]
1. B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
2. B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, Solid State Communications. 118, 79(2001)
3. A. Dmitriev, V. Kachorovskii, M. S. Shur, and M. Stroscio, International Journal of High Speed
Electronics and Systems, 10, 103 (2000)
4. B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, J. Appl. Phys. 85, 7727 (1999)
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29
Consequence of high polar optical energy:
two step optical polar scattering process
Active region
1,000
h w0
m obility (cm 2 /Vs)
K=0
K = 0.3
100
0
Passive region
1017
K = 0.6
1018
1019
Doping (cm-3)
From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
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30
Temperature dependencies
2000
Ga A s
8000
No impurit y
sc at t er in g
6000
4000
T o t al
2000
Mobility (cm2/V-s)
Mobility (cm2/V-s)
10000
1500
500
500
T o t al
n = 5 x1 0 1 7 cm -3
0
400
No impurit y
sc at t er in g
1000
n = 5 x1 0 1 7 cm -3
300
Ga N
600
0
300
Temperat ure ( K)
( a)
400
500
600
Temperat ure ( K)
(b)
Weaker contribution of impurity scattering for GaN because of heavier mass
After M. S. Shur, Solid State Electronics, 42, 2131 (1998)
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31
Evidence of penetration into AlGaN
or 2D-3D transition
2,5
VT = -5.6 V
60
2
10 CG (F/cm )
2,0
RDS (Ω)
1,5
7
1,0
40
20
0,5
0
0
0,0
-8
10
15
20
L (µm)
-6
-4
-2
0
2
4
Gate voltage, VG (V)
1600
1200
8
Gch (mA/V)
2
Mobility, µ (cm /Vs)
5
800
400
6
4
2
0
-6
0
0.0
0.2
0.4
-4
0.6
13
-2
0
VG (V)
0.8
2
1.0
1.2
X. Hu, J. Deng, N. Pala, R. Gaska,
M. S. Shur, C. Q. Chen, J. Yang,
S. Simin, and A. Khan, C. Rojo,
L. Schowalter, AlGaN/GaN Heterostructure Field Effect Transistor on
Single Crystal Bulk AlN, Appl. Phys.
Lett, 82, No 8, pp. 1299-1302,
24 Feb (2003)
-2
ns / 10 (cm )
From R. Gaska, M. S. Shur, A. D. Bykhovski, A. O. Orlov, and G. L.
Snider, Appl. Phys. Lett. 74, 287 (1999)
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32
Effect of Substrates: Bulk GaN on GaN
Ga N on b ul k
GaN/saphire
GaN/6H-SiC
5x10
SiC
bulk GaN
Sapphire
4
Al0.13Ga0.87N : 20 nm
4x10 4
n-type GaN : 1 µm
3x10
160
4
Mg-doped
GaN crystal
150 µm
2x10 4
140
120
g m (m S/m m)
2
Hall mobility µH(cm /Vs)
6x10 4
100
80
60
Vd s= + 10V
40
20
1x10 4
(a)
0
-10
-8
-6
-4
-2
0
2
12
-2
carrier density nH*10 (cm )
24
V gs (V)
22
20
110 µm
18
16
150 µm
14
After M. Asif Khan and J. W. Yang, W. Knap, E. Frayssinet, X.
Hu and G. Simin, P. Prystawko, M. Leszczynski, Grzegory, S.
Porowski, R. Gaska, M. S. Shur, B. Beaumont, M. Teisseire, and
G. Neu, GaN-AlGaN Heterostructure Field Effect Transistors
Over Bulk GaN Substrates, Appl. Phys. Lett. 76, No. 25, pp.
3807-3809, 19 June (2000)
10 µm
630 µm
12
10
8
6
4
2
(b)
0
1
10
Temperature (K)
100
From E. Frayssinet, W. Knap, P. Lorenzini,
N. Grandjean and J. Massies,
C. Skierbiszewski, T. Suski, I. Grzegory,
S. Porowski, G. Simin, X. Hu, M. Asif Khan,
M. Shur, R. Gaska, and D. Maude,
Applied Physics Letters, 77, 2551 (2000)
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33
Shubnikov de Hass (SdHO) and magnetoresistance
results
• Parallel conduction model
yields the roomtemperature 2D carrier
mobility exceeded 2,650
cm2/Vs
High mobility channel
Low mobility channel
Ec
GaN
AlGaN
2D electrons
After E. Frayssinet, W. Knap, P. Lorenzini,
N. Grandjean and J. Massies, C.
Skierbiszewski, T. Suski, I. Grzegory, S.
Porowski, G. Simin, X. Hu, M. Asif Khan, M.
Shur, R. Gaska, and D. Maude, Applied
Physics Letters, 77, 2551 (2000)
Distance
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34
Cryogenic low field transport:
Acoustic Scattering
Inverse Linear Dependence at Low Temperatures
-5
9.0x10
Sample D Ns~5.4x10
-5
8.0x10
Extracted
Deformation potential
ac=8.1 0.2 eV
12
-5
2
1/µ (Vs/cm )
7.0x10
-5
6.0x10
12
sample C Ns~5.7x10
-5
5.0x10
-5
4.0x10
-5
3.0x10
12
12
Sample A&B Ns~2.4x10 & Ns~2.7x10
-5
2.0x10
-5
1.0x10
0
5
10 15 20 25 30 35 40 45 50 55
Temperature (K)
1
1
= αT +
µ0
µ
From W. Knap, E. Borovitskaya, M. S. Shur, L. Hsu, W. Walukiewicz, E. Frayssinet,
P. Lorenzini, N. Grandjean, C. Skierbiszewski, P. Prystawko, M. Leszczynski,
I. Grzegory, Appl. Phys. Lett., 80, 1228 ( 2002)
[email protected]
35
New Features of Low Field Transport
• “Quasi-elastic” optical polar scattering
• 2D electron wave function penetration into
AlGaN in undoped GaN channels
• 2D-3D electron transition in doped GaN
channels
• Limiting role of acoustic scattering at
cryogenic temperatures
[email protected]
36
High field transport in Nitrides
Drift Velocity at Room and Elevated Temperatures
GaN
3
GaAs
3
2
3 00 K
5 00 K
1,00 0 K
2
3 00 K
5 00 K
1 ,00 0 K
1
0
0.1
Elect ric
0.2
field
( a)
1
0 .3
( MV/ cm)
0
5
Elect ric
10
field
15
20
( kV/ cm)
( b)
From: M. S. Shur, GaN and related materials for high power applications,
Mat. Res. Soc. Symp. Proc., vol. 483, pp. 15-26 (1998)
[email protected]
37
Intervalley Transition
From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
[email protected]
38
Velocity-field characteristics of GaN:
effect of doping and compensation
3.5
Electron Velocity [107 cm/s]
3
2.5
2
1e17
1e18
1e19
1.5
1
0.5
0
0
50
100
150
200
250
300
Electric Field [kV/cm]
After B. E. Foutz, L. F. Eastman, U. V. Bhapkar, M. S. Shur, Appl. Phys. Lett., 70, No 21, pp. 2849-2851 (1997)
[email protected]
39
Velocity-Field Curves for Nitride Family
InN is the fastest
nitride material
From B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, J. Appl. Phys. 85, 7727 (1999)
[email protected]
40
Ballistic and Overshoot Effects in GaN
Velocity (105 m/s)
GaN 600 kV/cm
GaAs 30 kV/cm
8
6
4
2
After B. E. Foutz, L. F. Eastman,
U. V. Bhapkar, M. S. Shur, Comparison
of High Electron Transport in GaN and
GaAs, Appl. Phys. Lett., 70, No 21,
pp. 2849-2851, 1997
0
0.1 0.2 0.3 0.4 0.5
Distance (micron)
[email protected]
41
More on the overshoot
InN – higher
overshoot at
smaller fields
From B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman,
J. Appl. Phys. 85, 7727 (1999)
[email protected]
42
High Field Breakdown.
Breakdown field measurement
-7.5
ln (Ig/Id)
-8
Gate -
-8.5
o
experiment, T=23
-9
ln(I
ln(I
-9.5
C, Vg=-4.75 V
/I d )
leakage
hole
ln(I
+
/I d )
hole
Drain
High Field Region
/I d ), approximation
-10
-10.5
-11
0.014
0.016
0.018
1/(Vds-Vds sat)
0.02
0.022
After N. V. Dyakonova, A. Dickens, M. S. Shur, R. Gaska, J. W. Yang,
Temperature dependence of impact ionization in AlGaN-GaN
Heterostructure Field Effect Transistors, Applied Physics Letters,
72 (20), pp. 2562-2564, May 18 (1998)
[email protected]
43
Higher Breakdown Field in
Heterostructures?
AlGaN
GaN
Quantum Well
AlGaN
Breakdown field might be determined
by cladding layers
(see M. Dyakonov and M. S. Shur, Consequences of Space
Dependence of Effective Mass in Heterostructures,
J. Appl. Phys. Vol. 84, No. 7, pp. 3726-3730, October 1 (1998))
[email protected]
44
3D and 2D Velocity-Field Characteristics
2D peak velocity and peak field in compound
semiconductors are smaller than for 3D
electrons because of
Vdr
VC3
3D
VC2
•Subband shift
•Runaway effect
2D
•Runaway is an unstable situation when
•the electron energy loss as a result of the
•collision is smaller then the average
E
•energy gain in the electric field during
•the free light time
Both EC and VC are smaller for 2D case than for 3D case:
EC2 < EC3
VC2 < VC3
EC2
EC3
!
[email protected]
45
Shift of Valley Bottoms in 2D Case
2
Energy
1
m1 << m2
h2
δ2 ∝
m2 a 2
1 >>
2
h2
δ1 ∝
m1a 2
Wave vector
The bottom of the upper valley (2) with heavy mass rises less than the
bottom of the central valley (1) with light mass.
[email protected]
46
Comparison of Runaway in 2D and 3D Systems
3D Case
•Deformation scattering on
acoustic and optical
phonons does not lead to
runaway
•Polar optical scattering
(forward!) leads to runaway
2D Case
•Even deformation scattering
leads to runaway
[email protected]
!
47
Experimental data
After V.T. Masselink,
Applied Physics Letters,
vol. 67(6), 801-805, 1995
Comparison of electron velocity in lightly doped In0.53Ga0.47As with
that in a InGaAs/InAlAs modulation-doped heterostructure
[email protected]
48
New physics of 2D transport
Vdr
– High field velocity is smaller
than in bulk (because of
runaway)
– Impact ionization in quantum
well is determined by cladding
layers
VC3
3D
VC2
2D
EC2 EC3
E
Experimental date after V.T. Masselink,
Applied Physics Letters,
vol. 67(6), 801-805, 1995
[email protected]
49
Trapping in Nitrides:
Reverse Gate Leakage Modeling
Direct tunneling and trap-assisted tunneling
From S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaN
HEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)
[email protected]
50
Comparison with Experiment
From S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaN
HEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)
[email protected]
51
MOSHFET Gate Leakage
Traps and
leakage:
Complexities of
highly non-ideal
systems
Gate Current Density (A/cm^2)
1. E- 01
1. E- 02
o
150 C
1. E- 03
o
100 C
1. E- 04
o
75 C
1. E- 05
50oC
1. E- 06
o
25 C
1. E- 07
1. E- 08
- 10
-5
0
5
Voltage ( V )
From F. W. Clarke, Fat Duen Ho, M. A. Khan, G. Simin, J. Yang, R. Gaska, M. S. Shur, J. Deng, S. Karmalkar,
Gate Current Modeling for Insulating Gate III-N Heterostructure Field-Effect Transistors,
Mat. Res. Symp. Proc. Vol. 743, L 9.10 (2003)
[email protected]
52
GaN 1/f Noise surprises
1.E+01
10
GaN HFET
on Sapphire [8-9]
1.E+00
1
1.E-01
10-1
1.E-02
10-2
1.E-03
10-3
GaN[8] GaAs[1-2]
Si [1-2]
GaAs
HEMTs [5]
GaN
HFET
on SiC [9]
GaN
MOS-HFET [10]
1.E-04
10-4
SiC [3-4]
1.E-05
10-5
1.E-06
10-6
Si
NMOS [6-7]
-7
10
1.E-07
Device noise is smaller than materials noise!!!
[email protected]
53
Data from
•
•
•
•
•
•
•
•
•
[1] R.H. Clevers, Volume and temperature dependence of the 1/f noise parameter
alpha in Si, Physica B Vol.154, pp. 214-224, (1989)
[2] F.N. Hooge, M. Tacano, Experimental studies of 1/f noise in n-GaAs Physica
B Vol.190, pp. 145-149, (1993)
[3] M. Levinshtein, S. Rumyantsev, J. Palmour, and D. Slater, Low frequency
noise in 4H Silicon Carbide, Journ. Appl. Phys. Vol. 81, No.4, 1758-1762,
(1997))
[4] M. Tacano and Y. Sugiyama, Comparison of 1/f noise of AlGaAs/GaAs HEMTs
and GaAs MESFETs, Solid State Elect. Vol.34. No 10, pp. 1049-53,(1991).
[5] D. Fleetwood, T.L. Meisenheimer, J. Scofield, 1/f noise and radiation effects
in MOS devices IEEE Trans. Electron Dev. Vol. 41, No 11, pp. 1953-1964 (1994)
[6] L.K. J Vandamme, X. Li, D. Rigaud, 1/f noise in MOS devices, mobility or
number fluctuations? IEEE Trans. Electron Dev. Vol. 41, No:11, pp. 1936-1945
(1994)
[7] A. Balandin, S. Morozov, G. Wijeratne, C. Cai, L. Wang, C. Viswanathan,
Effect of channel doping on the low-frequency noise in GaN/AlGaN
heterostructure field-effect transistors, Appl. Phys. Lett. V. 75, No 14 pp.
2064-2066 (1999)
[8] S. Rumyantsev, M.E. Levinshtein, R. Gaska, M. S. Shur, J. W. Yang, and M.
A. Khan, Low-frequency noise in AlGaN/GaN heterojunction field effect
transistors on SiC and sapphire substrates" Journal of Applied Physics, Vol. 87,
No4, pp. 1849-1854 (2000)
[9] N. Pala, R. Gaska, S. Rumyantsev, M. S. Shur M. Asif Khan, X. Hu, G.
Simin, and J. Yang, Low frequency noise in AlGaN/GaN MOS-HFETs, Electronics
Lett. Vol.36,No.3, pp. 268-270, (2000)
[email protected]
54
A relatively low level of noise in GaN-based HFETs
is related to a very high density of channel carriers
S
n
0 is the bottom
of the conduction band
1,000
10
0.1
-10
-5
0
ΕF /kT
3
5
10
Dependence of noise on the Fermi level position in bulk semiconductor
from E. Borovitskaya, M. Shur, On theory of 1/f nose in semiconductors Solid-State Electronics Vol. 45, No. 7, 1067 (2001)
[email protected]
55
Drain voltage, arb. units
Correlation between current slump
and 1/f noise in GaN transistors
1.0
0.5
HF ET
0.0
MOS-H FET
0
D rain voltage, arb. units
a
-3
α=(0.8-2) x 10
5x10
-8
-7
-7
1x10
1x10
Time t, s
2x10
-7
Longer transient – higher
Hooge constant
1.0
b
0.5
α=0.1-0.4
0.0
α=(5-8) x 10
0
-3
-3
-2
1x10
5x10
Time t, s
2x10
-2
From S. L. Rumyantsev, M. S. Shur, R. Gaska, M. Asif Khan,
G. Simin, J. Yang, N. Zhang, S. DenBaars, and U. Mishra,
Transient Processes in AlGaN/GaN Heterostructure Field
Effect Transistors, Electronics Letters, vol. 36, No.8, p. 757759 (2000)
[email protected]
56
In devices with relatively high noise
no correlation between
1/f noise and gate leakage
-80
SI/I2, dB/Hz
-90
HFETs
No leakage in MOSHFETs
Gate leakage in HFETs
-100
-110
After S. L. Rumyantsev, N. Pala, M. S. Shur, R. Gaska,
M. E. Levinshtein, M. Asif Khan, G. Simin, X. Hu,
and J. Yang, Effect of gate leakage current on noise
properties of AlGaN/GaN field effect transistors",
J. Appl. Phys., Vol. 88, No. 11, pp. 6726-6730, (2000)
MOSHFETs
-120
-130
-140 -5
10
Vg=0
10
-4
-3
10
10
Drain current I d, A
-2
10
-1
[email protected]
57
AlGaN barrier layer is main source of
generation-recombination noise
Arrhenius plots for several samples.
diamonds—HFET, Fig. 1(b); crosses—MOS-HFET,
Fig. 1(c). All other symbols represent HFETs.
The slope of the lines determines
activation energies of local level E 0:8–1.0 eV.
S. L. Rumyantsev, N. Pala, M. S. Shur, E. Borovitskaya, A. P.
Dmitriev, M. E. Levinshtein, R. Gaska, M. A. Khan, J. Yang, X. Hu,
and G. Simin, Generation-Recombination Noise in GaN/ GaAlN
Heterostructure Field Effect Transistors, IEEE Trans. Electron Dev.
Vol. 48, No 3, pp. 530-533 (2001)
[email protected]
58
Where the traps are (from GR noise)
AlGaN
thin films
0.0
[30]
1-3 meV
[42]
0.24 eV
[37]
0.42 eV
-0.5
Energy E (eV)
-1.0
AlGaN/GaN
heterostructures
1 eV
[33]
AlGaN/InGaN/GaN
heterostructures
GaN
photodetectors
[38]
EC
0.2 eV
[36,38]
0.35-0.36 eV
0.85 eV
1 eV
-1.5
[38]
1 eV
[4]
1.6 eV
[54]
[41]
-2.0
-2.5
-3.0
-3.5
From S. L. Rumyantsev, Nezih Pala, M. E. Levinshtein, M. S. Shur, R.
Gaska, M. Asif Khan and G. Simin, Generation-Recombination Noise in
GaN-based Devices, from GaN-based Materials and Devices: Growth,
Fabrication, Characterization and Performance, M. S. Shur and R. Davis,
Editors, World Scientific, 2004
[email protected]
59
Nitride-based FETs – promises and problems
Promises
• 30 W/mm at 10 GHz versus 1.5 W/mm
• > 150 W per chip
Problems
• Gate leakage
• Gate lag and current collapse
• Reliability
• Yield
Solutions
• Strain energy band engineering
M. A. Khan, M. S. Shur, Q. C.
• MEMOCVDtm
Chen, and J. N. Kuznia, CurrentVoltage Characteristic Collapse in
• Insulated gate designs
AlGaN/GaN Heterostructure
Insulated Gate Field Effect
• Gate edge engineering
Transistors at High Drain Bias,
Electronics Letters, Vol. 30, No.
25, p. 2175-2176, Dec. 8, 1994
[email protected]
60
High Electron Sheet Density Allows
for a New Approach: AlGaN/GaN MISFET
M. A. Khan, M. S.
Shur, Q. C. Chen,
and J. N. Kuznia,
Current-Voltage
Characteristic Collapse
in AlGaN/GaN
Heterostructure
Insulated Gate Field
Effect Transistors at
High Drain Bias,
Electronics Letters,
Vol. 30, No. 25, p.
2175-2176, Dec. 8,
1994
[email protected]
61
Resolving the issues: AlGaInN,
gate dielectrics, InGaN channel
SiO2
S
G
D
Pd/Ag/Au
Pd/Ag/Au
AlInGaN
GaN
AlN
Reducing the gate leakage
current (104 - 106 times)
MOSHFET (SiO2 )
Si3N4
S
Reducing current collapse,
Improving carrier confinement
D
Pd/Ag/Au
Pd/Ag/Au
AlInGaN
GaN
AlN
MISHFET Si3N4
I-SiC
G
I-SiC
Combining the advantages
Si3N4 /SiO2
S
G
D
S
G
D
AlInGaN
Pd/Ag/Au
InGaN
GaN
AlN
AlInGaN
Pd/Ag/Au
InGaN
GaN
AlN
I-SiC
I-SiC
AlGaN/ InGaN GaN DHFET
MISDHFET
[email protected]
62
Unified charge control model (UCCM)
MOSFETs and HFETs
2.5
σs (mS)
VGT
 ns 
− αVF = a ( ns − n0 ) + ηVth ln 
 n0 
VDS = 0.5 V
Real space
transfer
2.0
HFET Exp.
HFET Sim.
1.5
MOSHFET Exp.
MOSHFET Sim.
1.0
0.5
0.0
-12 -10
-8
-6
-4
-2
0
2
4
6
Vg ( V )
www.aimspice.com
[email protected]
63
Gate Lag and Current collapse in AlGaN/GaN HFETs:
Pulsed measurements of “return current”
VG
60
Idc(VG= 0)
50
Current collapse
Time
40
Id (return @ VG= 0)
VT
IDS
30
Current collapse
20
10
Id (VG)
0
“Return” current
-10
Time
-8
VG(t)
-6
-4
-2
VG= 0
Tarakji, G. Simin, N. Ilinskaya, X. Hu, A. Kumar, A. Koudymov, J. Zhang,
and M. Asif Khan, M.S. Shur and R. Gaska, Appl. Phys. Lett., 78, N 15, pp.
2169-2171 (2001)
G. Simin, A. Koudymov, A. Tarakji , X. Hu, J. Yang and
M. Asif Khan, M. S. Shur and R. Gaska APL October 15 2001
[email protected]
64
Nearly Identical Gate Lag Current Collapse was observed
in:
SiO
2
G
S
G
S
D
n-GaN
Pd/Ag/Au
GaN
AlN
I-SiC/Sapphire
D
S
G
AlGaN
Pd/Ag/Au
GaN
AlN
I-SiC/Sapphire
GaN MESFET
AlGaN/GaN HFET
R, kΩ
LG
GTLM pattern
(LG variable, LGS= LGD =const)
D
Pd/Ag/Au
AlGaN
GaN
AlN
I-SiC
AlGaN/GaN MOSHFET
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
R(0)
R(τ)
0
20
40
60
80
100
120
140
LG , µm
• AlGaN cap layer is not primarily responsible for CC
• Only the gate edge regions contribute to the CC
[email protected]
65
Dynamic I-V characteristics
of AlGaN-GaN HFETs
60
DC I-V (VG = 0)
Drain bias:
30 V
20 V
10 V
50
40
60
50
40
30
20
10
0
0.0
-1.0
RD
0
10
RL
20
30
RL = 50 Ω....1kΩ
30
RL
20
Measured @ 2GHz
-0.5
RF Power, dB
Drain Current,
mA (@ max V )
Peak drain
current
G
Load impedance scan @ constant VD = 10 V… 30 V
-1.5
-2.0
-2.5
-3.0
-3.5
Calculated from dynamic I-Vs
2
P RF ~ R L/(R D+R L)
-4.0
10
-4.5
-5.0
0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30
Drain Voltage, V
0
200
400
600
800
Load Impedance, Ω
A. Koudymov, G. Simin and M. Asif Khan, A. Tarakji, M. S. Shur, and R. Gaska,
Dynamic I-V Characteristics of III-N Heterostructure Field Effect transistors, IEEE EDL,
Vol. 24, No. 11, pp. 680-682, November (2003)
[email protected]
66
InGaN channel DHFET Design – 2D simulations
G-Pisces (VG= -1; VD = 20 V)
• Better
G
S
D
AlGaNPd/Ag/Au
(x=0.25,250 A)
InGaN (x ≤ 5%, 50 A)
S
2DEG confinement and Partial strain compensation
• Significantly reduced carrier spillover
•No current collapse
G
D
G
S
D
GaN
~0.1 mm
AlN
1014
I-SiC
1017
1016
~0.05
mm
1014
Regular HFET
InGaN channel DHFET
G. Simin et.al. Jpn. J. Appl. Phys.
Vol.40 No.11A pp.L1142 - L1144 (2001)
[email protected]
67
Two Dimensional Simulation (ISE)
ISE 2D GaN device simulator
From N. Braga, R. Gaska, R. Mickevicius, M. S. Shur, M. Asif Khan, G. Simin, Simulation of Hot
Electron and Quantum Effects in AlGaN/GaN HFET, submitted to JAP
[email protected]
68
Band Diagrams
(a)
(b)
From N. Braga, R. Gaska, R. Mickevicius, M. S. Shur, M. Asif Khan, G. Simin, Simulation of Hot
Electron and Quantum Effects in AlGaN/GaN HFET, accepted in JAP
[email protected]
69
Electron temperature contour map
VD = 10V and VS = VG = 0V
Importance of gate
edge engineering
confirmed
From N. Braga, R. Gaska, R. Mickevicius, M. S. Shur, M. Asif Khan, G. Simin, Simulation of Hot
Electron and Quantum Effects in AlGaN/GaN HFET, submitted to JAP
[email protected]
70
Mechanism of current collapse in GaN FETs
• Current collapse is not related to AlGaN layer
alone
• Current collapse is caused by trapping at gate
edges
• Current collapse can be eliminated by using
DHFET structures
• Current collapse time delay correlates with
1/f noise spectrum
• SOLVE THE CURRENT COLLAPSE ISSUE BY
CHANNEL AND GATE EDGE ENGINEERING
[email protected]
71
RF Power of collapse free DHFET
and MISHFET RF Power stability
[email protected]
72
Plasma Wave THz Devices
Deep submicron FETs can operate in a new PLASMA regime at frequencies
up to 20 times higher than for conventional transit mode of operation
5
A
4
3
B
2
1
C
14
12
1.0
InSb-bulk
a)
b)
f (THz)
16
1.0
0.8
0.5
0.6
0.4
0.0
0
1
f (THz)
10
2
8
3
0.2
0.4
0.6
Usd (V)
0.8
InGaAs-HEMT
6
4
2
0
0
-600 -500 -400 -300 -200 -100
Gate Voltage(mV)
18
Emission (a.u.)
Emission Intensity (a.U.)
Resonant Peak (a.u.)
20
0
0
2
4
6
8
10
12
Detection Frequency (THz)
Resonant detection THz emission from 60 nm InGaAs HEMT
W. Knap, J. Lusakowski, T. Parenty, S. Bollaert, A. Cappy, V. Popov, and
Of sub-THz and THz From
M. S. Shur, Emission of terahertz radiation by plasma waves in sub-0.1 micron
AlInAs/InGaAs high electron mobility transistors,
Appl. Phys. Lett. , March 29 (2004)
[email protected]
73
8.0
T=8 K, GaN HEMT
600 GHz
5.0
6.0
Intensity (a.u.)
Induced Vs-Vd (mV) (Lock-In X Output)
Plasma Wave Electronics
4.0
2.0
8 GHz cutoff
4.0
3.0
2.0
1.0
0.0
0.0
-4
-2
0
Vg (V)
2
4
50
75
100
125
150
175
200
225
250
Frequency (GHz)
600 GHz radiation response Radiation intensity from 1.5
of GaN HEMT at 8 K
micron GaN HFET at 8 K.
[email protected]
74
Conclusions
•New device physics of nitride based materials
requires new designs and new modeling approaches
• Polarization devices
•Pyroelectric sensors
•Piezoelectric sensors
• Electron runaway and overshoot effects
determine high field transport
• Traps can be easier filled because of high
electron densities
• Noise determined by tunneling into traps
• Strain control: Strain Energy Band Engineering
• FETs – MOSHFET, DHFET, MOSDHFET
• Terahertz applications – plasma wave devices
[email protected]
75