Advantages of Blue InGaN Light-Emitting Diodes with Slightly-Doped Step-Like Electron-Blocking Layer Tsun-Hsin Wang Tsun-Hsin Wang Ph.D. Candidate, Department of Ph.D. Candidate, Department of Physics, National Changhua Physics, National Changhua University of Education University of Education Advisor: Prof. Yen-Kuang Advisor: Prof. Yen-Kuang
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Advantages of Blue InGaN Light- Emitting Diodes with Slightly-Doped Step-Like Electron-Blocking Layer Tsun-Hsin Wang Ph.D. Candidate, Department of Physics,
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Advantages of Blue InGaN Light-Emitting Diodes with Slightly-Doped Step-Like Electron-Blocking Layer
Tsun-Hsin WangTsun-Hsin WangPh.D. Candidate, Department of Physics, Ph.D. Candidate, Department of Physics, National Changhua University of EducationNational Changhua University of Education
Advisor: Prof. Yen-Kuang KuoAdvisor: Prof. Yen-Kuang Kuo
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OutlineIntroduction and Motivation
Device Structure
Simulation Results
Conclusion
Reference
Tsun-Hsin Wang/BLL/NCUE
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Introduction S. Pimputkar, J. S. Speck, S. P. DenBaars, and S.
Nakamura, Nat. Photonics 3, 180 (2009). More than one-fifth of US electricity is used to power artificial
lighting. Light-emitting diodes (LEDs) based on group III/nitride
semiconductors are bringing about a revolution in energy-efficient lighting.
Tsun-Hsin Wang/BLL/NCUE
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Introduction E. F. Schubert and J. K. Kim, Science 308, 5276 (2005). Energy savings and environmental benefits Spectral power distribution Spatial distribution Color temperature Temporal modulation Polarization properties
Spontaneous polarization
=>Asymmetric wurtzite Piezoelectric polarization
=>Lattice mismatch
Tsun-Hsin Wang/BLL/NCUE
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Motivation
Tsun-Hsin Wang/BLL/NCUE
Development of InGaN LEDsGaN-InGaN-GaN barriers
InGaN-AlGaN-InGaN barriers
Slightly-doped step-like electron blocking layer (EBL)
Shallow first well
Kuo et al., Appl. Phys. Lett. 99, 091107 (2011).
Kuo et al., Appl. Phys. Lett. 100, 031112 (2012).
Wang et al., IEEE Photonics Technol. Lett. (2012).
Kuo et al., IEEE Photonics Technol. Lett. 24, 1506 (2012).
Ene
rgy
(eV
)
quasi-Fermi level
p-side
GaN barriers (original)@ 300 mA
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Device Structure
Tsun-Hsin Wang/BLL/NCUE
sapphire
i-GaN
n-GaN
n-GaN
i-InGaN/GaN
p-AlGaN
p-contact
n-contact
p-GaN
Kuo et al., Appl. Phys. Lett. 95, 011116 (2009).
Ene
rgy
(eV
)
quasi-Fermi level
p-side
GaN barriers (original)@ 300 mA
0
10
20
30
40
50
60
70
0 60 120 180 240 300
Current (mA)
IQE
(%
)
7Tsun-Hsin Wang/BLL/NCUE
sapphire
i-GaN
n-GaN
n-GaN
i-InGaN/GaN
p-AlGaN
p-contact
n-contact
p-GaN
Ene
rgy
(eV
)
quasi-Fermi level
p-side
GaN barriers (original)@ 300 mA
0
10
20
30
40
50
60
70
0 60 120 180 240 300
Current (mA)
IQE
(%
)
Device Structure
8Tsun-Hsin Wang/BLL/NCUE
sapphire
i-GaN
n-GaN
n-GaN
i-InGaN/GaN
p-AlGaN
p-contact
n-contact
p-GaN
Ene
rgy
(eV
)
quasi-Fermi level
p-side
GaN barriers (original)@ 300 mA
0
10
20
30
40
50
60
70
0 60 120 180 240 300
Current (mA)
IQE
(%
)
Device Structure
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Device Structure Drawbacks of polarization electric field:
– Serious tilting of energy band – Severe leakage current of electrons – Insufficient injection efficiency of holes – Nonradiative Auger recombination induced by
non-uniform distribution of carriers
=> Efficiency droop!
Tsun-Hsin Wang/BLL/NCUE
10Tsun-Hsin Wang/BLL/NCUE
Device Structure
sapphire
i-GaN
n-GaN
n-GaN
i-InGaN/GaN
p-AlGaN
p-contact
n-contact
p-GaN compositiondoping (1018 cm–3)
conventional EBL (original)
Al0.15Ga0.85N 1.2
slightly-doped EBL Al0.15Ga0.85N 0.6
slightly-doped step-like EBL
Al0.15Ga0.85N
Al0.075Ga0.925N
GaN
Al0.075Ga0.925N
Al0.15Ga0.85N
0.6
Impact ionization– Hole concentration is conventionally 1% of dopant concentration.
with slight-doped step-like EBL are studied numerically.
According to the simulation results, the LED has enhanced carrier concentrations in the QWs due to appropriately modified energy band diagrams which are favorable for the injection of holes without the price of confinement of electrons.
Tsun-Hsin Wang/BLL/NCUE
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Reference
1. T.-H. Wang and Y.-K. Kuo, IEEE Photonics Technol. Lett. accepted (2012).
2. Y.-K. Kuo, T.-H. Wang, J.-Y. Chang, and J.-D. Chen, IEEE Photonics Technol. Lett. 24, 1506 (2012).
3. Y.-K. Kuo and T.-H. Wang, IEEE J. Quantum Electron. 48, 946 (2012).
4. Y.-K. Kuo, T.-H. Wang, and J.-Y. Chang, Appl. Phys. Lett. 100, 031112 (2012).
5. Y.-K. Kuo, T.-H. Wang, J.-Y. Chang, and M.-C. Tsai, Appl. Phys. Lett. 99, 091107 (2011).
Tsun-Hsin Wang/BLL/NCUE
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Acknowledgement: This work was supported by the National Science Council under grant NSC-99-2119-M-018-002-MY3.
Thank you for your attention!
Tsun-Hsin Wang/BLL/NCUE
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Q & A – Physical modelsPoisson equation: ∇2V=−ρ /ε, where ρ: volume charge density, ε: dielectric constant.Continuity equation: J+∂ρ/∂t=0, where J: ∇current density, t: time.Complex wave equation: ∇2W+k2(ε−β2)W=0, where W: optical wave function, k: wave vector, β: real eigen-value.Rate equation: ∂S/∂t=c(g−α)/n, where c: speed of light, n: refractive index, g: gain, α: loss, S: photon number.Gain equation: g=α+[ln(1/R1R2)]2L, where R: reflectance of mirrors, L: cavity length.
Tsun-Hsin Wang/BLL/NCUEAPSYS by Crosslight Software Inc.
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Q & A – Physical models
Equations ParametersPoisson equation: V, n, p, S, W, gContinuity equation: V, n, pComplex wave equation: n, p, S, W, gRate equation: n, p, W, lambda, gGain equation: n, p, lambda, g
V: potential, n and p: electron and hole concentration, S: photon number, W: optical field intensity, lambda: wavelength, g: gain.
Tsun-Hsin Wang/BLL/NCUEAPSYS by Crosslight Software Inc.
Polarization
1
2
( )
( ) (1 ) ( ) (1 ) ( )
0.042 0.034 (1 ) 0.038 (1 )[ / ]
sp x x
sp sp sp
P In Ga N
x P InN x P GaN x x B InGaN
x x x x C m
1 1 1( ) ( ) ( )total x x sp x x pz x xP In Ga N P In Ga N P In Ga N
1
2
( )
( ) (1 ) ( ) (1 ) ( )
0.090 0.034 (1 ) 0.021 (1 )[ / ]
sp x x
sp sp sp
P Al Ga N
x P AlN x P GaN x x B AlGaN
x x x x C m
Vurgaftman et al., J. Appl. Phys. 94, 3675 (2003).
1 1 1( ) ( ) ( )total x x sp x x pz x xP Al Ga N P Al Ga N P Al Ga N
21Tsun-Hsin Wang/BLL/NCUE
Q & A – Parameters
Polarization
0xx yy
a a
a
13
33
2zz xx
C
C
1( ) ( ) (1 ) ( ) ( )pz x x pz pz pzP Al Ga N x P AlN x P GaN x P AlN 2 2( ) 1.27 7.56 [ / ]pzP InN C m
2 2( ) 1.81 7.89 [ / ]pzP AlN C m
1( ) ( ) (1 ) ( ) ( )pz x x pz pz pzP In Ga N x P InN x P GaN x P InN
Wu, J. Appl. Phys. 106, 011101 (2009).
2 2( ) 0.918 9.541 [ / ]pzP GaN C m
22Tsun-Hsin Wang/BLL/NCUE
Q & A – Parameters
Energy band gap
Wu, J. Appl. Phys. 106, 011101 (2009).
2 20.91( , ) ( ,0) 3.5 [ ]
830GaN
g gGaN
T TE GaN T E GaN eV
T T
2 20.41( , ) ( ,0) 0.69 [ ]
454InN
g gInN
T TE InN T E InN eV
T T
2 21.8
( , ) ( ,0) 6.3 [ ]1462
AlNg g
AlN
T TE AlN T E AlN eV
T T
23Tsun-Hsin Wang/BLL/NCUE
Q & A – Parameters
Energy band gap
1( )
( ) (1 ) ( ) (1 ) ( )
0.69 3.5 (1 ) 1.4 (1 )[ , 0 ]
g x x
g g g
E In Ga N
x E InN x E GaN x x B InGaN
x x x x eV T K
1( )
( ) (1 ) ( ) (1 ) ( )
6.3 3.5 (1 ) 0.6 (1 )[ , 0 ]
g x x
g g g
E Al Ga N
x E AlN x E GaN x x B AlGaN
x x x x eV T K
Wu, J. Appl. Phys. 106, 011101 (2009).
24Tsun-Hsin Wang/BLL/NCUE
Q & A – Parameters
Mobility
2
2
( ) 2
:
[ / ]
( ) 10[ / ]
h
h
InGaN cm V s
Ho
AlGaN cm V s
le
Kuo et al., IEEE J. Quantum Electron. 46, 1214 (2010).
max minmin
2
1.3717
2
0.2917
( )1 ( )
298( , ) 386 [ / ]
1 ( )1.0 10
174( , ) 132 [ / ]
1 ( )1.0
:
10
e
ref
e
e
NN
N
InGaN N cm V sN
AlGaN N cm V sN
Electron
25Tsun-Hsin Wang/BLL/NCUE
Q & A – Parameters
Recombination rate
Kuo et al., IEEE J. Quantum Electron. 46, 1214 (2010).