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Novel Physics of Nitride Devices
M. S. Shur CIE and ECSE Department, RPI, Troy, 12180, US
Tutorial
ICPS 2004July 25, 2004
Flagstaff, Arizona, USA
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
Device Universe Is Both Infinite and Expanding
1970 1975 1980 1985 1990 1995 20000
100
200
300
400
500
600
700
800
900
1000
1100
1200 INSPEC search query: Gallium Nitrideor Indium Nitrideor Aluminum Nitride
Num
ber o
f Pub
licat
ions
Year
New Nitride Galactic
“The Universe is full of magical things patiently waiting for our wits to grow sharper”
Eden Phillpott
Lembach Villa, MunichIsa Genzken (born 1948)Basic research
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
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
Applications of U of V/RPI/SET quadrichromatic Versatile Solid-State Lamp: Phototherapy of seasonal affective disorder at Psychiatric Clinic of Vilnius University
UV-LED Based Fluorimeter with IntegratedLock-in Amplifier (after Prof. Zukauskas, U of V.)
Nitrides: New Symmetry, New Physics
Zinc Blende Structure (GaAs)Diamond Structure (Si, Ge) Wurtzite Structure (SiC, GaN)
GaAs bouleSi boule AlN boule (Courtesy Crystal IS)
Crystal symmetry of pyroelectric crystals Crystal system Crystal class
(Schönflies)
Crystal class
(Hermann-Mauguin)
Triclinic C1 1
Monoclinic Cs
C2
m
2
Orthorhombic C2v 2mm
Tetragonal C4
C4v
4
4mm
Rhombohedral C3
C3v
3
3m
Hexagonal C6
C6v
6
6mm
?
HEXAGONAL6
6mm
C6
C6V
Wide Gap SemiconductorsEnabling Technology for Piezoelectronics and
Pyroelectronics
• Zinc blende structure• No PE or SP effect in
<100> direction• PE coefficient <111>
~0.15 C/m2
• No PE/SP ‘doping’ reported
• Wurtzite structure• c-axis growth direction • PE coefficient in c-
direction ~1 C/m2
• PE/SP ‘doping’demonstrated
GaAs GaN/AlN
Nitride Heterostructures: Polarization Induced Electron and Hole 2D Gases
From A. Bykhovski, B. Gelmont, and M. S. Shur, J. Appl. Phys.74, p. 6734-6739 (1993)
AlGaN on GaN
From O. Ambacher et alJAP 87, 334 (2000)
46vC mcP 36
Polarization signs
GaN
GaN
GaN
AlGaN
AlGaN
AlGaN
Relaxed
Relaxed
TensileStrain
CompressiveStrain
Relaxed
Relaxed
GaN
GaN
GaN
AlGaN
AlGaN
AlGaN
Psp
Psp
Psp
Psp
Ppe
Ppe
Psp
Psp
Ppe
Ppe
Psp
Psp
PspPsp
+σ
+σ
-σ +σ
-σ
-σ
[0001] [0001]
Ga face N face
After O. Ambacher et al. J.Appl. Phys. 85, 3222 (1999)
2D electrons
2D holes
2D holes
2D electrons
Spontaneous polarization
For comparison, in BaTiO3, Ps = 0.25 C/m2 (1.93x1015cm-2)
-0.0453.47 1014
-0.0574.39 1014
-0.0322.46 1014
-0.0292.23 1014
-0.0816.24 1014
Spontaneous polarization(C/m2)(cm-2)
BeOZnOInNGaNAlNAfter F. Bernardini et al. Phys Rev. 56, 10024(1997)
Pyroelectric effect
b
-100-50
050
-4 0 4 8 12 16 20
Time, s
-1
0
1
2
3
-4 0 4 8 12 16 20
0
-40
-80
a
c
-0.2
0.1
0.4
0.7
1
0 2 4 6 8 10 12Time, s
0
50
1000 2 4 6 8 10 120 2 4 6 8 10 12
50
0
(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)).
IpPyroelectr icm aterial
Pyroelectric voltage for primarypyroelectric effect (changing flux magnitude
and direction)
0 20
0
0.4 (c )
0
20
(a)
-20
0
(b)
Bat
h te
mp
erat
ure
(oC
)H
eat
flux
(a
.u)
Tim e (s )10 30 40
-0.4Vo
ltage
(m
V)
20
40
(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)).
b
-100-50
050
-4 0 4 8 12 16 20
Time, s
-1
0
1
2
3
-4 0 4 8 12 16 20
0
-40
-80
a
c
Two time constants:Sample cooling andCharge relaxation
0
0
4
8
b .
0
a .Ga N
T(o
C)
300
200
100
12
Vol
tag
e (m
V)
10 20 30 40
Tim e (s )
Primary pyroelectric effect at 300o C(High Temperature Operation!)
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)
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)
0
10
20
30
40
50
60
0 0.2 0.4 0.6 0.8 1
Al Mole Fraction
Thickness, nm
100 200 300 400 500 600
1,000
2,000
3,000
300K
77K
Hal
l Mob
ility
(cm
2 /Vs)
AlGaN Thickness (A)
Effect of Critical Thickness on Electron Mobility
SIS sensor
• Piezoelectric sensors• Pyroelectric sensors
After R. Gaska, J. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, S. M. Soloviev,
Appl. Phys. Lett. 71(26), 3817 (1997)
n - GaN 0.4 µm
AlN 30 Å - 100 Å
n - GaN 1.0 µm
i - GaN 1.0 µm
AlN Buffer
Sapphire
Top ContactBottomContact
Twice as largeas in SiC
Short range superlatticeis four timeslarger than inSiCGaN
n
F
(1) (2) (3)
GaNn
Ef
Ev
Ec
L
AlNu
B A B A B A
44.4
44.5
44.6
44.7
44.8
44.9
45
45.1
45.2
45.3
0 0.5 1 1.5 2 2.5 3
Res
ista
nce,
Ω
Strain (compression), 10-4
Polarization domain structure
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)
N
GaGa
GaSurface
N
GaGa
N N
GaGa
NSurface
NGaGaN
Surface
NGaGaN
N
N N
Ga
Superlattice Band Diagram and resistance change in SRSL
y
A A A A AB B B BBeffec tiveband gap
(000 1)En
erg
y (e
V)
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)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
5
10
15
20
25
3
21
δR/R
(10-3
)
Strain (10-4 )
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).
1 SRSL
2 SiC
3 GaN
Static Gauge factors (GF)(measured under longitudinal mechanical deformation)
GaNn-type GF=10
p-type GF > 200
GaN/AlN/GaN SapphireGF = 50
AlN/GaN Short Range Superlattices
GF = 30-80
AlGaN/GaN HeterostructuresGF = 10-15
0 1 2 3 4 50 .0 0
0 .0 2
0 .0 4
0 .0 6
0 .0 8
0 .1 0
0 .1 2
p -G a N
S iS iC
G a N /A lN /G a NδR/R
S tra in , 1 0 -4
High Temperature p-GaN Pressure Sensor
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)
Polarization effects in undoped and doped channel GaN/AlGaN HFETs
.
2
-20 20 40
0
Ener
g y (e
V)
Distance (nm)
Undoped
Nd = 5x1017 cm-3 1
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
Ener
gy (e
V)
Distance (nm)
-20
-2
20 40
••••••••
•••••••••••••
••••••••••••••••••••••••••••••
••••••••••••••••••••••••••
0
0.002
0.004
0.006
0.008
0.01
-16 -12 -8 -4 0Voltage, V
10 nm (100% strained)
20 nm (100% strained)
40 nm (60%)60 nm (30%)100 nm (0%)
Piezoelectric and Pyroelectric Doping in AlGaN/GaN
A l M o la r F r a c t io n
0
1
2
3
4
5
6
0 0 .2 0 .4 0 .6 0 .8 1
State-of-the-art
0
5
10
15
20
25
30
35
GaA
s/A
lGa A
s
InG
aAs/
AlG
a As
GaN
/Al G
a N
GaN
/AlIn
GaN
Al - 9%
Al - 17%
0.0 0.5 1.0 1.5 2.00.10
0.15
0.20
0.25
∆c (A
ngst
rom
s)∆E
g(e
V)
In Molar Fraction (%)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
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)
Strain and Energy Band Engineering
•Graded composition profile and quaternary AlGaInN •Superlattice buffers for strain relief•PALE and MEMOCVD epitaxial growth•Homoepitaxial substrates•Non-polar substrates
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
50
60
70
Thic
knes
s (n
m)
Al molar fractionA. 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
New Screening Mechanism in Multilayer Pyroelectrics
Screening the polarization induced dipole involves smaller charges than the charges in polarization dipole
0 L z
p y r o e l e c t r i c ( 2 )
s e m i c o n d u c t o r
m a t r i x
a c c u m u l a t i o n
r e g i o n ( 1 )
d e p l e t i o n
r e g i o n ( 3 )
L d
P o
Polarization dipole
+
Screening dipole – smaller changesbut at larger separation
New screening length (larger than Debye but smaller than depletion)
Electronic island at the surface of semiconductor grain in pyroelectric matrix
(MQDs -Moveable Quantum Dots)
Control by external field – Zero dimensional Field Effect (ZFE)
Po
Semiconductor
Electronic island
PyroelectricPo
Semiconductor
Electronic inversion island
Pyroelectric
Hole inversion island
Inversion electron and hole islands at the surface of pyroelectric grain in semiconductor matrix
V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)
Basic Equations04
2 p
PE πε ε
=+ 2
43
dc
en ReNER
πε ε
= =
3(4 3) dN n Rπ= /
polarization inducedelectric field
total number of electrons in the grain 0 dP en R>>
Electrons cannot screen polarization induced field. Strong field push electrons into small 2D island
Coulomb repulsionenergy
W should be minimal provided that the total charge of the island, Q=eN , is constant
For typical values of polarization the size of electron island is small compared to R
dn donor concentrationThe size of the island should be determined by the minimum of the total energy
screening field
Potential energy in the field E
Terahertz oscillations
MOVABLE QUANTUM DOTS (MQD)
SWITCH OR SHIFT FREQUENCY BY EXTERNAL FIELD OR BY LIGHT
1 THz to 30 THz
2D island might oscillate as a whole over grain surface. The oscillations can be exited by ac field perpendicular to P0
00
4( 2 )p
ePmR
=+
πωε ε
Oscillation frequency is of the order of a terahertz
0 2~ω π/
Oscillation frequency
New Physics of Movable Quantum Dots• Self-assembled quantum dot arrays• Coulomb blockade• Light concentration in quantum dots• Left handed materials
• Terahertz detectors• Terahertz emitters• Terahertz mixers• Photonic terahertz devices• Photonic crystals• Plasmonic crystals• Solar cells and thermo voltaic cells
New Potential Applications
New features of electron transport in nitrides
• Large polar optical phonon energy leads to two step scattering optical photon absorption and re-emissionresulting 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)
Consequence of high polar optical energy: two step optical polar scattering process
Active region
Passive region
From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
hω0 K = 0.6
K = 0K = 0.3
mob
il ity
(cm
2 /V
s)0
100
1,000
1017 1018 1019
Doping (cm-3)
Temperature dependencies
300 400 500 6000
500
1000
1500
2000
300 400 500 6000
2000
4000
6000
8000
10000Ga A s Ga N
Temperat ure ( K) Temperat ure ( K)
To t al To t al
No impurit yscat t er ing
No impurit yscat t er ing
n = 5 x10 1 7 cm-3 n = 5x10 1 7 cm-3
(a) (b)
Mob
ility
(cm
2 /V
-s)
Mob
ility
(cm
2 /V
-s)
After M. S. Shur, Solid State Electronics, 42, 2131 (1998)
Weaker contribution of impurity scattering for GaN because of heavier mass
Evidence of penetration into AlGaN or 2D-3D transition
From R. Gaska, M. S. Shur, A. D. Bykhovski, A. O. Orlov, and G. L. Snider, Appl. Phys. Lett. 74, 287 (1999)
0 5 10 15 200
20
40
60
RD
S (Ω
)
L (µm)
-8 -6 -4 -2 0 2 4
0,0
0,5
1,0
1,5
2,0
2,5 VT = -5.6 V
107 C
G (
F/cm
2 )
Gate voltage, VG (V)
-6 -4 -2 0 20
2
4
6
8
0.0 0.2 0.4 0.6 0.8 1.0 1.20
400
800
1200
1600
Gch
(mA
/V)
VG (V)
Mob
ility
, µ (c
m 2/V
s)
ns / 1013 (cm-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 Hetero-structure Field Effect Transistor on Single Crystal Bulk AlN, Appl. Phys. Lett, 82, No 8, pp. 1299-1302, 24 Feb (2003)
Effect of Substrates: Bulk GaN on GaN
1x104
2x104
3x104
4x104
5x104
6x104
1 10 1000
2
4
6
8
10
12
14
16
1820
22
24
Al0.13
Ga0.87
N : 20 nm
n-type GaN : 1 µm
Mg-doped GaN crystal
150 µm
(a)
Hal
l mo b
ility
µ H(cm
2 /Vs )
630 µm
10 µm
110 µm
150 µm
(b)
GaN/saphire GaN/6H-SiC
carri
er d
ensi
ty n H*
1012
(cm
-2)
Temperature (K)
GaN on bulk
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)
Vds= +10V
0
20
40
60
80
100
120
140
160
-10 -8 -6 -4 -2 0 2
Vgs(V)
g m(m
S/m
m)
SiCbulk GaNSapphire
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)
Shubnikov de Hass (SdHO) and magnetoresistance results
• Parallel conduction model yields the room-temperature 2D carrier mobility exceeded 2,650 cm2/Vs
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)
High mobility channel
Low mobility channel
Ec
Distance
GaNAlGaN
2D electrons
Cryogenic low field transport:Acoustic Scattering
Inverse Linear Dependence at Low Temperatures
0 5 10 15 20 25 30 35 40 45 50 551.0x10-5
2.0x10-5
3.0x10-5
4.0x10-5
5.0x10-5
6.0x10-5
7.0x10-5
8.0x10-5
9.0x10-5
Sample D Ns~5.4x1012
sample C Ns~5.7x1012
Sample A&B Ns~2.4x1012& Ns~2.7x1012 1/µ
(Vs/
cm2 )
Temperature (K)
ExtractedDeformation potential
ac=8.1 0.2 eV
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)
0
11µ
T += αµ
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
High field transport in NitridesDrift Velocity at Room and Elevated Temperatures
From: M. S. Shur, GaN and related materials for high power applications,Mat. Res. Soc. Symp. Proc., vol. 483, pp. 15-26 (1998)
3
2
1
0
300 K500 K1,000 K
0 . 1 0 . 2 0 . 3
Elect ric field (MV/ cm)
GaN 3
2
1
0 5 1 0 1 5 2 0
300 K500 K1,000 K
GaAs
Elect ric field ( kV/ cm)
( a) (b)
Intervalley Transition
From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
Velocity-field characteristics of GaN:effect of doping and compensation
0
0.5
1
1.5
2
2.5
3
3.5
0 50 100 150 200 250 300
Electric Field [kV/cm]
Elec
tron
Vel
ocity
[107 c
m/s
]
1e171e181e19
After B. E. Foutz, L. F. Eastman, U. V. Bhapkar, M. S. Shur, Appl. Phys. Lett., 70, No 21, pp. 2849-2851 (1997)
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)
Ballistic and Overshoot Effects in GaN
246
8
GaN 600 kV/cmGaAs 30 kV/cm
Velocity (105 m/s)
Distance (micron)0 0.1 0.2 0.3 0.4 0.5
After B. E. Foutz, L. F. Eastman,U. V. Bhapkar, M. S. Shur, Comparison
of High Electron Transport in GaN andGaAs, Appl. Phys. Lett., 70, No 21,
pp. 2849-2851, 1997
More on the overshoot
From B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, J. Appl. Phys. 85, 7727 (1999)
InN – higherovershoot atsmaller fields
High Field Breakdown.Breakdown field measurement
1/(Vds-Vds sat)
-11
-10.5
-10
-9.5
-9
-8.5
-8
-7.5
0.014 0.016 0.018 0.02 0.022
ln (I
g/Id
)
experiment, T=23 oC, Vg=-4.75 V
ln(I leakage /I d )
ln(I hole /I d )
ln(I hole /I d ), approximation
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)
Gate
High Field Region
+
-
Drain
Higher Breakdown Field inHeterostructures?
AlGaN
AlGaN
GaN Quantum Well
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))
E
EC2 EC3
!Both EC and VC are smaller for 2D case than for 3D case:EC2 < EC3VC2 < VC3
Vdr
VC3
VC2 3D2D
3D and 2D Velocity-Field Characteristics2D peak velocity and peak field in compound semiconductors are smaller than for 3D electrons because of•Subband shift•Runaway effect
•Runaway is an unstable situation when •the electron energy loss as a result of the •collision is smaller then the average •energy gain in the electric field during •the free light time
The bottom of the upper valley (2) with heavy mass rises less than the bottom of the central valley (1) with light mass.
21
2
1 amh
∝δ
22
2
2 amh
∝δ
m1 << m2 ⇒ δ1 >> δ 2
2
1
Shift of Valley Bottoms in 2D Case
Wave vector
Energy
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
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
New physics of 2D transport
– High field velocity is smaller than in bulk (because of runaway)
– Impact ionization in quantum well is determined by cladding layers
Experimental date after V.T. Masselink, Applied Physics Letters, vol. 67(6), 801-805, 1995
EEC2 EC3
Vdr
VC3
VC2 3D
2D
EEC2 EC3
Vdr
VC3
VC2 3D
2D
Trapping in Nitrides:Reverse Gate Leakage Modeling
Direct tunneling and trap-assisted tunnelingFrom S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaNHEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)
Comparison with Experiment
From S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaNHEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)
MOSHFET Gate Leakage
1. E- 08
1. E- 07
1. E- 06
1. E- 05
1. E- 04
1. E- 03
1. E- 02
1. E- 01
- 10 - 5 0 5Voltage ( V )
Gat
e Cu
rrent
Den
sity
(A/c
m^2
)
25oC
50oC
75oC100oC
150oC
Traps and leakage:Complexities of highly non-ideal systems
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)
GaN 1/f Noise surprises
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+0110
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
GaN[8]
Si [1-2]
GaAs[1-2]
SiC [3-4]
GaN HFETon Sapphire [8-9]
GaAsHEMTs [5]
GaN HFETon SiC [9]
Si NMOS [6-7]
GaN MOS-HFET [10]
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+0110
10-7
10-6
10-5
10-4
10-3
10-2
10-1
110
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
GaN[8]
Si [1-2]
GaAs[1-2]
SiC [3-4]
GaN HFETon Sapphire [8-9]
GaAsHEMTs [5]
GaN HFETon SiC [9]
Si NMOS [6-7]
GaN MOS-HFET [10]
Device noise is smaller than materials noise!!!
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)
A relatively low level of noise in GaN-based HFETsis related to a very high density of channel carriers
0.1
10
-5 0 5 10
3
Sn
ΕF /kT
1,000
-10
Dependence of noise on the Fermi level position in bulk semiconductorfrom E. Borovitskaya, M. Shur, On theory of 1/f nose in semiconductors Solid-State Electronics Vol. 45, No. 7, 1067 (2001)
0 is the bottom of the conduction band
Correlation between current slump and 1/f noise in GaN transistors
0 5x10-3 1x10-2 2x10-2
0.0
0.5
1.0
b
α=0.1-0.4
α=(5-8) x 10-3
Dra
in v
olta
ge, a
rb. u
nits
Time t, s
0 5x10-8 1x10-7 1x10-7 2x10-7
0.0
0.5
1.0
a
MOS-HFET
HFET
α=(0.8-2) x 10-3
Time t, s
Dra
in v
olta
ge, a
rb. u
nits
Longer transient – higher Hooge constant
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. 757-759 (2000)
In devices with relatively high noise no correlation between
1/f noise and gate leakage
10-5 10-4 10-3 10-2 10-1-140
-130
-120
-110
-100
-90
-80
Vg=0
HFETs
MOSHFETs
S I/I2 , d
B/H
z
Drain current I d, A
No leakage in MOSHFETsGate leakage in HFETs
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)
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 determinesactivation 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)
Where the traps are (from GR noise)
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.24 eV [42]
AlGaN thin films
1 eV [54]
1.6 eV [41]
0.2 eV [38]1-3 meV [30]
0.35-0.36 eV [36,38]
0.42 eV [37]
0.85 eV [38]
1 eV [4]1 eV [33]
EC
AlGaN/InGaN/GaN heterostructures
AlGaN/GaN heterostructures
GaNphotodetectors
Ene
rgy
E (
eV)
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
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• YieldSolutions• Strain energy band engineering• MEMOCVDtm
• Insulated gate designs• Gate edge engineering
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
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
MOSHFET (SiO2 )
I-SiC
Pd/Ag/AuGaN AlN
Pd/Ag/AuAlInGaN
S G D
SiO2
AlGaN/ InGaN GaN DHFET
I-SiC
Pd/Ag/AuGaN AlN
InGaN AlInGaN
S G D
Si3N4 /SiO2
I-SiC
Pd/Ag/AuGaN AlN
InGaN AlInGaN
S G D
MISDHFET
MISHFET Si3N4 I-SiC
Pd/Ag/AuGaN AlN
Pd/Ag/AuAlInGaN
S G D
Si3N4Reducing the gate leakage current (104 - 106 times)
Reducing current collapse, Improving carrier confinement
Combining the advantages
Resolving the issues: AlGaInN, gate dielectrics, InGaN channel
Unified charge control model (UCCM)
V V a n n V nnGT F s th
s− = − +⎛⎝⎜
⎞⎠⎟α η( ) ln0
0
MOSFETs and HFETs
www.aimspice.com
-12 -10 -8 -6 -4 -2 0 2 4 60.0
0.5
1.0
1.5
2.0
2.5
σ s (mS)
Vg ( V )
HFET Exp. HFET Sim.
MOSHFET Exp. MOSHFET Sim.
Real space transfer
VDS = 0.5 V
0
10
20
30
40
50
60
-10 -8 -6 -4 -2
Idc(VG= 0)
VG(t)
Id (return @ VG= 0)
VG= 0
Id (VG)
Current collapse
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
VG
Gate Lag and Current collapse in AlGaN/GaN HFETs:Pulsed measurements of “return current”
Time
Time
IDS
VT
“Return” current
Current collapse
Nearly Identical Gate Lag Current Collapse was observed in:
I-SiC/Sapphire
Pd/Ag/AuGaN AlN
AlGaN S G D
I-SiC/Sapphire
Pd/Ag/AuGaN AlN
n-GaN S G D
GaN MESFET AlGaN/GaN HFET AlGaN/GaN MOSHFET
I-SiC
Pd/Ag/AuGaN AlN
AlGaN
S G D
SiO2
0 20 40 60 80 100 120 1400.00.20.40.60.81.01.21.41.61.82.02.22.4
R, k
Ω
LG, µm
R(0) R(τ)
LG
• AlGaN cap layer is not primarily responsible for CC
• Only the gate edge regions contribute to the CC
GTLM pattern (LG variable, LGS= LGD =const)
Load impedance scan @ constant VD = 10 V… 30 V
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300
10
20
30
40
50
60
RL = 50 Ω....1kΩ
DC I-V (VG = 0)
RL
Drain bias: 30 V 20 V 10 V
Dra
in C
urre
nt, m
A
Drain Voltage, V
Peak
dra
in c
urre
nt (@
max
VG
)
0 10 20 300
102030405060
RLRD
0 200 400 600 800-5.0-4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.0
Calculated from dynamic I-VsPRF ~ RL/(RD+RL)
2
Measured @ 2GHz
RF
Pow
er, d
B
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)
Dynamic I-V characteristics of AlGaN-GaN HFETs
G. Simin et.al. Jpn. J. Appl. Phys. Vol.40 No.11A pp.L1142 - L1144 (2001)
• Better 2DEG confinement and Partial strain compensation• Significantly reduced carrier spillover
•No current collapse
I-SiC
Pd/Ag/Au
GaN
AlN
InGaN (x ≤ 5%, 50 A) AlGaN (x=0.25,250 A)
S G D
I-SiC
Pd/Ag/Au
GaN
AlN
InGaN (x ≤ 5%, 50 A) AlGaN (x=0.25,250 A)
S G DS G D S G D
1017
1016
1014
~0.1 µm
Regular HFET InGaN channel DHFET
1014
~0.05 µm
InGaN channel DHFET Design – 2D simulationsG-Pisces (VG= -1; VD = 20 V)
Two Dimensional Simulation (ISE)
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
ISE 2D GaN device simulator
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
Electron temperature contour map VD = 10V and VS = VG = 0V
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
Importance of gate edge engineeringconfirmed
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
Plasma Wave THz DevicesDeep submicron FETs can operate in a new PLASMA regime at frequencies up to 20 times higher than for conventional transit mode of operation
-600 -500 -400 -300 -200 -100 0
0
1
2
3
4
5
C
B
A
Res
onan
t Pea
k (a
.u.)
Gate Voltage(mV)
THz emission from 60 nm InGaAs HEMTResonant detectionOf sub-THz and THz
0 2 4 6 8 10 1202468
101214161820
0 1 2 30.0
0.5
1.0
0.2 0.4 0.6 0.8
0.4
0.6
0.8
1.0
InGaAs-HEMT
f (TH
z)
Usd (V)f (THz)
Em
issi
on (a
.u.)
Emis
sion
Inte
nsity
(a.U
.)
Detection Frequency (THz)
InSb-bulka)
b)
From W. Knap, J. Lusakowski, T. Parenty, S. Bollaert, A. Cappy, V. Popov, and 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)
Plasma Wave Electronics
-4 -2 0 2 4
0.0
2.0
4.0
6.0
8.0 T=8 K, GaN HEMT600 GHz
Indu
ced
V s-Vd (m
V) (L
ock-
In X
Out
put)
Vg (V)
50 75 100 125 150 175 200 225 250
0.0
1.0
2.0
3.0
4.0
5.0
Inte
nsity
(a.u
.)
Frequency (GHz)
Radiation intensity from 1.5 micron GaN HFET at 8 K.
600 GHz radiation response of GaN HEMT at 8 K
8 GHz cutoff
•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
Conclusions
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