GaN Microwave Transistors
Michael S. Shur
Rensselaer Polytechnic Institute
Presented at NJIT on 11/09/05
http://nina.ecse.rpi.edu/shur/
shurm@rpi.edu
1
TNT
0.12
0.09
0.06
TNT
0.03
0.00
– GaN Microwave Transistors
• THz plasma wave electronics
• Modeling and simulation
–
–
–
–
–
–
–
600 500 400 300 200 100
-1
Wavenumber (cm )
Photoresponse (arb. units)
– Deep UV LEDs
– SAW acousto optoelectronics
– Solid State Lighting
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.0
x 60
Photoresponse(a.u.)
• Wide band gap electronics/photonics
Absorbance
Research Topics
0.15
1.0
0.8
0.6
0.4
0.2
0.0
6 THz
30 nm
0.5
1.0
1.5
2.0
Vg(V)
120 GHz
3 THz
0.3
Lg=30 nm
0.6
Vg (V)
0.9
1.
Si THz 300 K
Unified Charge Control Model
Monte Carlo
2D Circuit CAD (AIM-Spice)
HEMTs
TFTs
CMOS
HBTs
• Remote Internet Lab
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2
GaN-based Microwave and MM Wave
Field Effect Transistors
Michael S. Shur
Rensselaer Polytechnic Institute
Troy, NY 12180, USA
1200
Number of Publications
1100
1000
900
INSPEC search query:
Gallium Nitride
or Indium Nitride
or Aluminum Nitride
800
700
600
500
400
300
200
100
0
1970
1975
1980
1985
Year
http://nina.ecse.rpi.edu/shur/
1990
1995
2000
shurm@rpi.edu
3
Motivation: silicon is becoming a commodity
$6,000
$5,000
$4,000
China
$3,000
India
$2,000
Bangladesh
$1,000
$0
Annual salary
Value added
Profit
Data for 2001 textile industry from Time, December 13 (2004). Page A16
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4
Outline
• New physics of GaN-based FETs
• Problems and solutions
–
–
–
–
–
Gate lag and current collapse
2D modeling
Field plates
MEMOCVD
MOSHFETs, MISHFETs, MISDHFETs
• High power and microwave switches
• GaN FETs at THz frequencies
• Conclusions
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5
Nitride Advantages
Properties
Advantages
•High mobility
High power
•High saturation velocity
•High sheet carrier concentration
•High breakdown field
•Decent thermal conductivity
•Growth on SiC substrate
•Chemical inertness
•Good ohmic contacts
•No micropipes
•SiO2/AlGaN and SiO2/GaN
good quality interfaces
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Heat handling capability
Reliability should
be possible
Insulated
Gate
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6
Combined Figure of Merit
Figure of Merit
for high frequency/high power
400
CFOM =
200
0
(
χε o µv s E B2
χε o µv s EB2
)silicon
χ is thermal conductivity
EB is breakdown field
4H6HGaAs
Si
GaN µ is low field mobility
SiC
SiC
vs is saturation velocity
εo is dielectric constant
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7
Nitride Disadvantages
Blue emitters:
NONE
UV emitters – low
efficiency
Electronics:
Reproducibility,
Reliability
Yield
Hence $130 M DARPA
program
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8
GaN Device History
• 1932 – Roosevelt wins Presidential Election.
First GaN crystal synthesized (W. C. Johnson et al)
• 1961 – Yuri Gagarin becomes the first man in space. First
p-type GaN (A. G. Fischer)
• 1969 – First Moon walk by Armstrong and Aldrin. First
monograph on nonmetallic nitrides (G. V. Samsonov)
• 1971- Bangladesh Independence. First GaN LED
(J. I. Pankove and Paul Maruska)
• 1987- Dow Jones plunges 508 points (22.6%) on October
19 p-type activation via e-beam irradiation (Obyden S.K et
al) RPI FRESHMEN conceived
(from Paul Maruska, A Brief History Of GaN Blue Light-Emitting Diodes,
http://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/gan/maruskastory.asp)
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9
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
Applications of U of V/RPI/SET
Terahertz electronics
quadrichromatic
Versatile Solid-State Lamp: Phototherapy of
Non volatile memories
seasonal affective disorder at Psychiatric
Bioelectronics
Clinic of Vilnius University
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10
Nitrides: New Symmetry, Hence New Physics
Zinc Blende Structure (GaAs)
Diamond Structure (Si, Ge)
Wurtzite Structure (SiC, GaN)
Si boule
GaAs boule
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AlN boule (Courtesy Crystal IS)
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11
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)
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4
6v
P6 3 mc
From O. Ambacher et al
JAP 87, 334 (2000)
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12
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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13
Spontaneous polarization
After F.
Bernardini et al.
Phys Rev. 56,
10024(1997)
AlN
GaN
InN
ZnO
BeO
Spontaneous
polarization
(C/m2)
(cm-2)
-0.081
6.24 1014
-0.029
2.23 1014
-0.032
-0.057
-0.045
2.46 1014 4.39 1014 3.47 1014
For comparison, in BaTiO3, Ps = 0.25 C/m2 (1.93x1015cm-2)
Carrier density in AlGaAs/GaAs is ~ 1012 cm-2
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14
Both Spontaneous and Piezo
Polarizations are Important
Ga face
P sp
P sp
AlG aN
GaN
2D holes
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
-σ
2D electrons
P sp
AlG aN
P sp
GaN
GaN
2D holes
AlG aN
[0001]
P peCom pressive
Strain P sp
-σ
Relaxed P sp
AlG aN
+σ
[0001]
2D electrons
After O. Ambacher et al. J.Appl. Phys. 85, 3222 (1999)
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15
Polarization Doping in AlGaN/GaN Heterostructures
6
From M. S. Shur, A. D. Bykhovski, R. Gaska,
and A. Khan, GaN-based Pyroelectronics
and Piezoelectronics, in Handbook of Thin Film Devices,
Volume 1: Hetero-structures for High Performance Devices,
Edited by Colin E.C. Wood, pp. 299-339,
5
Academic Press, San Diego, 2000
1.2
4
••
1
0.8
3
graded interface
•
0.6
2
0.4
•
0.2
1
•
abrupt interface
0
0
20
40
60
80
100 120
Thickness, nm
0
0
0 .2
0 .4
0 .6
A l M o la r
0 .8
1
F r a c t io n
R. Gaska, A. D. Bykhovski, M. S. Shur, Piezoelectric Doping
and Elastic Strain Relaxation in AlGaN/GaN HFETs,
pp. 435-458, Appl. Phys. Lett. Vol. 73, No. 24, 3577 (1998)
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16
Effect of Strain on
Dislocation-Free Growth
2
Hall Mobility (cm /Vs)
• 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.
60
Appl. Phys. 81 (9), 6332-6338
50
Thickness,
nm
(1997)
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
1
Al Mole Fraction
http://nina.ecse.rpi.edu/shur/
100 200 300 400 500 600
AlGaN Thickness (A)
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17
New physics of electron/hole transport
•Large polar optical phonon energy
(x 3 GaAs) - Quasi-elastic polar
optical scattering
Vdr
VC3
3D
VC2
2D
•Ultra dense 2D gas (x 20)
EC2 EC3
E
•Electron “runaway” dominant
•Strange holes/ strange acceptors
After V.T. Masselink,
Applied Physics Letters,
vol. 67(6), 801-805, 1995
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18
New physics of electron transport
•Large polar optical phonon energy
(x 3 GaAs) - Quasi-elastic polar
optical scattering
•Ultra dense 2D gas (x 20)
•Electron “runaway” dominant
Vdr
2
VC3
3D
VC2
1
2D
EC2 EC3
E
=2
δ2 ∝
m2 a 2
m1 << m2 ⇒
=2 δ1 >> δ 2
δ1 ∝ 2
After V.T. Masselink,
Applied Physics Letters,
vol. 67(6), 801-805, 1995
m1a
From A. Dmitriev, V. Kachorovskii, M. S. Shur, and M. Stroscio,
Electron Drift Velocity of Two Dimensional Electron Gas in Compound Semiconductors
International Journal of High Speed Electronics and Systems, Invited, Volume 10, No 1, pp. 103-110, March 2000
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Consequence of high polar optical energy:
two step optical polar scattering process
Active region
=ω0
mobility (cm 2 /Vs)
1,000
K=0
K = 0.3
100
0
Passive region
1017
K = 0.6
1019
1018
Doping (cm-3)
From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)
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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
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2D Case
•Even deformation scattering
leads to runaway
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21
High Drift Velocity and high mobility
> 2,000 cm2/V-s (300 K)
see R. Gaska, J. W. Yang, A. Osinsky, Q. Chen,M. Asif
Khan, A. O. Orlov, G. L. Snider, M. S. Shur, Appl. Phys.
Lett., 72, 707, 1998
3
10
Velocity (100,000 m/s)
GaN
2
GaN
3
SiC
GaAs
GaAs
3
2
300 K
500 K
1,000 K
2
1
300 K
500 K
1,000 K
1
Si
0
0
0
100
200
300
Electric Field (kV/cm)
Velocity [107 cm/s]
.
0.2
0.1
1
600 kV/cm
8
200 kV/cm
6
150 kV/cm
4
2
0
75 kV/cm
0
0.3
Electric field (MV/cm)
(a)
0
5
10
20
0.2
0.3
Distance[micron]
Electric field (kV/cm)
(b)
Fig. 1 a is from U. V. Bhapkar, and M. S. Shur, Monte Carlo Simulation of Electron
Transport in Wurtzite GaN, J. Appl. Phys., 82 (4), pp. 1649-1655,August 15 (1997)
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15
0.1
After B. E. Foutz, S. K. O'Leary, M. S. Shur,
and L. F. Eastman. Appl. Phys., vol. 85,
. 7727 (1999)
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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)
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23
Hall M obility (cm 2/V-s)
Electron mobility (over 2,000 cm2/V-s)
2 ,1 00
1 ,8 0 0
Al0 .2 Ga 0. 8 N -GaN
1 ,5 0 0
1 ,2 0 0
9 00
60 0
0
1
2
3
4
2D Electron Density (x 10 1 3 cm -2 )
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24
7
Velocity [10 cm/s]
Overshoot in GaN
Below 150 kV/cm
little or no
overshoot occurs
600 kV/cm
10
8
200 kV/cm
6
150 kV/cm
At 200 kV/cm
modest overshoot
occurs over 0.3
micron
4
2
75 kV/cm
0
0
0.1
0.2
0.3
At 600 kV/cm high
velocity occurs
below 0.1 micron
Distance [micron]
After B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, Transient Electron Transport in Gallium Nitride, Indium Nitride,
and Aluminum NitrideJ. Appl. Phys., vol. 85, No. 11, pp. 7727-7734 (1999
)
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25
Higher Breakdown Field in Heterostructures?
Large current carrying capabilities are combine
with large voltage blocking capabilities
AlGaN
Wavefunction
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)
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26
Thermal Conductivity (W cm-1 K-1)
Thermal Conductivity versus Temperature
100
Si
Si data after Glassbrenner and Slack (1964)
10
GaN data after Sichel and Pankove (1977)
GaN
1
Thick red line - theoretical expectations for pure
GaN based on Pankove data and anharmonicity
mechanism
0.1
10
1000
100
Temperature (K)
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27
Nitride-based FETs – promises and problems
Promises
• 30 W/mm at 10 GHz versus 1.5 W/mm for GaAs
• 150 W – 240 W per chip
• Highest cutoff frequency so far 152 GHz
Problems
• Gate leakage
• Gate lag and current collapse
• Reliability
• Yield
Solutions
• Strain energy band engineering
• MEMOCVDtm
M. A. Khan, M. S. Shur, Q. C.
• Insulated gate designs
Chen, and J. N. Kuznia, Current• Gate edge engineering
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
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28
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
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29
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
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MISDHFET
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30
Unified charge control model (UCCM)
and Real Space Transfer
VGT
⎛ ns ⎞
− αVF = a ( ns − n0 ) + ηVth ln⎜ ⎟
⎝ n0 ⎠
MOSFETs and HFETs
From S. Saygi, A. Koudymov, S. Rai, V. Adivarahan, J. Yang, G. Simin, M. Asif Khan, J. Deng, M.S. Shur, and R. Gaska,
Real Space Electron Transfer in III-Nitride Metal-Oxide-Semiconductor-Heterojunction (MOSH) Structures, Appl. Phys. Lett.,
accepted for publication
www.aimspice.com
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31
Real Space Transfer in MOSHFETs
From S. Saygi, A. Koudymov, S. Rai, V. Adivarahan, J. Yang, G. Simin, M. Asif Khan, J. Deng, M.S. Shur, and R. Gaska,
Real Space Electron Transfer in III-Nitride Metal-Oxide-Semiconductor-Heterojunction (MOSH) Structures, Appl. Phys. Lett.,
accepted for publication
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32
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)
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33
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)
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34
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)
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35
.
Energy (eV)
Doped channel GaN/AlGaN HFETs for Higher Power
2
1
-20
Undoped
Nd = 5x1017 cm-3
20
0
Distance (nm)
40
After M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483,
pp. 15-26 (1998)
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36
MOSHFET Switch
20
2
R ON = 75 mOhm-mm
• 75 mOhm×mm2
Vg = + 6 V
2
Current, A/mm
• 2 - 3 times less than that
reported for buried channel
SiC FETs
15
• 25-100 times less than
that for SiC induced channel
MOSFETs
+3V
10
2
PON/OFF = 7.5 kW/mm
0V
-3V
5
-6V
0
0
100
200
300
400
500
600
Drain Voltage, V
15 µm source-drain spacing
After G. Simin, X. Hu, N. Ilinskaya, A. Kumar, A. Koudymov, J. Zhang, M. Asif Khan, R. Gaska and M. S. Shur
A 7.5 kW/mm2 current switch using AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors
on SiC Substrates, Electronics Letters. Vol. 36 Issue: 24, pp. 2043 –2044, Nov. 2000
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37
MOSHFET Technology for Power Electronics
2
10
RONsp =
0
10
8.725 × 10 −3V B2 EG−7.5
µ eε r
Si
From J.L Hudgins, G.S. Simin
E. Santi, and M.A. Khan,
IEEE Transactions on Power
Electronics, vol. 18, no. 3, May 2003
-2
RONsp (Ω
2
)
10
SiC
-4
10
GaN
-6
10
-8
10
2
10
3
10
Breakdown Voltage (V)
4
10
9Switching speeds1,000 times higher than
for Si IGBTs can be achieved (up to GHz
range
9Commensurate decrease in power supply
weight, cost and reliability due to dramatic
decrease in size and weight of reactive
components
9Big improvement in power quality
9Energy markets: “future energy”
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38
Applications
10 3
HD V C
AlGaN-UF
10 0
Power
Supplies
Current (A)
10 2
Au to
mo tive
10 1
10 0
GaN
region
S p ec ific R es istan c e (o h m -c m 2 )
T ra c tio n
Mo to r
Co n t ro l
F a c to ry
A u to m at io n
Lam p
B a l la s t
T e le c o m m u ni c a tio ns
10 -1
D is p la y
d ri ve s
10 -2
10
100
1,0 00
GaN-UF
10 -1
GaN-Caltech
10 -2
Data from B. J. Baliga, IEEE Trans., ED-43, p. 1717 (1996)
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SiC-Purdue
GaN-UF
SiC-NCSU
6H-SiC
10 -3
4H-SiC
SiC-RPI
AlGaN
10, 000
B lo c k in g vo lta g e ( V )
SiC-ABB
GaN-UF
GaN
10 -4
10 1
10 2
M G-M OSHFET
10 3
10 4
Brea k do w n Vo lta ge (V )
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39
Design Example
G1
G2
+-
+G4
L
+-
MOSHFET Switch,
x10 voltage x3 current
Dramatic improvement
in yield and reliability
+-
G3
After G. Simin and M. Asif Khan, M. S. Shur, R. Gaska, High-power switching using III-Nitride Metal-Oxide Semiconductor
Heterostructures, International Journal of High Speed Electronics and Systems, Vol. XX, No. X 1-14 (2005)
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40
Field Plate
0.5 µm
1 µm
Vg
Ldg
2 µm
2 µm
Silicon nitride, 0.3 µm
n-AlGaN 1 x 1016 / cm3
0.02 µm
1 x 1015 / cm3
0.03 µm
n-GaN
tp
p-GaN, 1.5 x 1016 / cm3
2-DEG, 1x1013 / cm2
1 x 1018 / cm3 0.05 µm
http://nina.ecse.rpi.edu/shur/
From S. Karmalkar, M. S.
Shur, and R. Gaska, GaNbased power high
mobility
Velectron
d
transistors, in 'Wide
Energy Bandgap
Electronic Devices”, pp.
173-216, Fan Ren and
John Zolper, Editors,
World Scientific (2003),
ISBN 981-238-246-1
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41
No Field Plate, One Field Plate
Two Field Plates
Gate FP
3
3
Drain FP
30
Drain Current ( mA/mm )
A
2
20
C
1
10
Electric Field (MV / cm)
B
2
A
1
C
B
0
0
0
200
400
600
800
1000
0
1200
0
2
4
6
8
10
Distance from Source (µm)
Drain Bias ( V )
From S. Karmalkar, M. S. Shur, and R. Gaska, GaN-based power high
electron mobility transistors, in 'Wide Energy Bandgap Electronic
Devices”, pp. 173-216, Fan Ren and John Zolper, Editors, World Scientific
(2003), ISBN 981-238-246-1
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42
RESURF Effect
Ideal
Breakdown voltage, Vbr (V)
1200
Grounded
substrate
1000
Floating
substrate
800
Field plates and
p-n junction
600
400
Field plates only
200
0
0
2
4
6
8
10
12
Drain to gate separation, Ldg (µm)
From S. Karmalkar, M. S. Shur, and R. Gaska, GaN-based power high electron mobility
transistors, in 'Wide Energy Bandgap Electronic Devices”, pp. 173-216, Fan Ren and John
Zolper, Editors, World Scientific (2003), ISBN 981-238-246-1
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43
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!!!
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44
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
[38]
1 eV
[4]
-1.5
1.6 eV
[54]
[41]
-2.0
-2.5
-3.0
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
-3.5
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45
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
30
Current collapse
IDS
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
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46
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
Pd/Ag/Au
AlGaN
GaN
AlN
I-SiC
AlGaN/GaN HFET
R, kΩ
LG
GTLM pattern
(LG variable, LGS= LGD =const)
D
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
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47
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
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48
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
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49
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 µm
AlN
1014
I-SiC
1017
1016
~0.05 µm
1014
Regular HFET
InGaN channel DHFET
G. Simin et.al. Jpn. J. Appl. Phys.
Vol.40 No.11A pp.L1142 - L1144 (2001)
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50
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
70
Thickness (nm)
60
50
40
30
20
10
0
0.0
0.2
0.4
0.6
Al molar fraction
0.8
1.0
From 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
http://nina.ecse.rpi.edu/shur/
From R. Gaska, M. Asif Khan, and M. S. Shur, III-nitride
based UV light emitting diodes, pp. 59-76
in UV Solid-State Light Emitters and Detectors. Proc.
NATO ARW, Series II, Vol. 144, ed. By M. S. Shur and A.
Zukauskas, Kluwer, Dordrecht, 2004
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51
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
1
Al Mole Fraction
http://nina.ecse.rpi.edu/shur/
100 200 300 400 500 600
AlGaN Thickness (A)
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52
Conventional MOCVD
gas-phase reaction and
low surface migration
MOs
Pre-reaction!!!
NH3
Growth steps
Surface
roughening
Growth front
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53
MEMOCVDTM
allowing V/III separation hence reducing
gas-phase reaction &
enhancing surface migration
Minimized pre-reaction
MOs
NH3
Growth steps
Enhanced migration
Growth front
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54
AlInGaN HFETs on 4” Substrates
PL Intensity (a.u.)
MEMOCVD™
5
6000
1
2
3
4000
4
2000
0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
Photon Enenrgy (eV)
Room temperature PL mapping of
4” diameter AlGaN/GaN HFET wafer
Al%
22 22
Al0.25Ga0.75N/GaN
4” sapphire
8 mm edge exclusion
23 23 24
Al- variation < 2% over 4” wafer
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55
HEMT structure design on Bulk AlN
substrate
Source
Gate
Drain
Makes surface smoother
Pd/Ag/Au
Pd/Ag/Au
AlGaN (22 nm)
GaN (0.3 µm)
Epitaxial AlN (0.3 µm)
Bulk AlN (400 µm)
Substrate from Crystal IS
Al molar fraction 29%
AlGaN/ GaN HFET
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56
DC characteristics of AlGaN/GaN HEMT device
Lg ~ 1.5 mm, Lgs ~ 1 mm,
Ldg ~ 4 mm
Drain Current, A/mm
1.0
0.9 Max. VGS=+5V;
0.8 1V step
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-2
0
2
4
6
8
10 12 14 16 18
VDS, V
Large positive Vgs > 5 V
applied
Much larger than for
HEMTs on SiC
Devices on AlN comparable to those on semi-insulating SiC
Devices with W = 1 mm (multi finger) have been fabricated
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57
POut, dBm ; Gain, dB ; PAE, %
RF characteristics of AlGaN/GaN HEMT device
28
26 Dev. Eff. Width = 100 µm4.1 W/mm
24
POut
22
VDS=25 V
2.2 W/mm
20
VDS=45 V
18
16
PAE
14
12
10
8
6
Gain
4
2
0
-2
-10
-5
0
5
10
15
20
25
4 GHz
Delivered Input Power, dBm
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58
Inverted channel design to be explored
Source
Gate 1
Drain
InGaN
n-type AlGaInN
AlN
Source
Gate 1
Drain
InGaN
n-type modulation doped AlGaInN
AlN
SET, patent pending
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shurm@rpi.edu
59
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
16
14
12
1.0
InSb-bulk
a)
1.0
b)
f (THz)
18
Emission (a.u.)
Emission Intensity (a.U.)
Resonant Peak (a.u.)
20
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)
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)
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60
GaN Microwave Detector
20
GaN HFET
(b)
Measured Data
15
R ( V/W )
(a)
300
Calculated (x0.25)
200
10
5
100
0
0
0
5
10
15
20 0.0 0.5 1.0 1.5 2.0
f ( GHz )
From J. Lu, M. S. Shur, R. Weikle, and M. I. Dyakonov, Detection of Microwave Radiation by Electronic Fluid in
AlGaN/GaN High Electron Mobility Transistors, in Proceedings of Sixteenth Biennial Conference on Advanced
Concepts in High Speed Semiconductor Devices and Circuits, Ithaca, New York, Aug. 4-6 (1997), pp. 211-217
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61
8.0
T=8 K, GaN HEMT
600 GHz
5.0
6.0
Intensity (a.u.)
Induced Vs-Vd (mV) (Lock-In X Output)
GaN-based 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
2
4
Vg (V)
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.
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62
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)
After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)
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63
Terahertz oscillations
2D island might oscillate as a whole over grain surface.
The oscillations can be exited by AC field perpendicular to Po
Oscillation frequency
ω0 =
4π eP0
( ε + 2εp ) mR
MOVABLE QUANTUM DOTS (MQD)
Oscillation frequency is of the order of a terahertz
ω0π/2~ 1 THz to 30 THz
CAN SWITCH OR SHIFT FREQUENCY
BY EXTERNAL FIELD OR BY LIGHT
After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)
http://nina.ecse.rpi.edu/shur/
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64
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
http://nina.ecse.rpi.edu/shur/
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65
Sponsors
Humboldt
Foundation
http://nina.ecse.rpi.edu/shur/
NATO
shurm@rpi.edu
66
I owe a debt of gratitude to my students, postdocs, and
collaborators around the Globe
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shurm@rpi.edu
67
Conclusions
¾New device physics of nitride based materials
ƒ Enables new applications
ƒ Requires new designs and new modeling approaches
¾GaN based microwave devices
ƒ Factor of 10 to 30 advantage in power
ƒ Insulated gate has an advantage
¾THz plasma wave electronics devices
ƒ GaN has an advantage
ƒ Both resonant detectors and emitters are possible
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68