博士論文口試-Ph.D. Defense (2013-06-19)-TH Wang.ppt

Numerical investigation of polarization
effects and dual-wavelength
emission in InGaN light-emitting diodes
Student: Tsun-Hsin Wang
Advisor: Prof. Yen-Kuang Kuo
Date: 2013-06-22
Ph.D. Defense

Tsun-Hsin Wang/BLL/NCUE 2
Outline
1. Introduction
2. Literature review
3. Polarization effects
4. Dual-wavelength emission
5. Conclusion
6. Q&A

Outline
1. Introduction
5. Conclusion
6. Q&A

1. Introduction
1.1 Dissertation proposal
1.2 Physical models and applied
equations
1.3 Material parameters
1.4 Free parameters
1.5 Limit and criteria of
numerical simulation

1. Introduction
(1.1 Dissertation proposal)
Research motivation
Proposed approaches
InGaN light-emitting diodes (LEDs) with
GaN-InGaN-GaN barriers
Monolithic white InGaN LEDs
Proposed future works
Publication list
(2011-10-01)

1. Introduction
(1.2 Physical models and applied equations)
( / )
( )
( )
( ) ( )
D A f
p
n
p p p B
n n n B
e p n N N N
p
e J e R G
t
n
e J e R G
t
J e p k T p
J e N n N k T n
 
  
  
 
      

   


   

    
    
Models
Poisson’s equation
Current continuity equations
Drift and diffusion models
Chen et al., Appl. Phys. B- Lasers Opt. 98, 779 (2010).

1. Introduction
Green InGaN LEDs
Mobility in cm2/V-s
max min
min
1.37
17
0.29
17
( )
1 ( )
298
( , ) 386
1 ( )
1.0 10
174
( , ) 132
1 ( )
1.0 1
:
0
n
ref
n
n
N
N
N
InGaN N
N
AlGaN N
Elec
N
tron

 
 



 

 


 

 Wu, J. Appl. Phys. 106, 011101 (2009).
Caughey, Proc. IEEE 55, 2192 (1967).
( ) 10
:
( )
p p
Ho
InGaN A
le
lGaN
 
 

1. Introduction
Polarization in C/m2
1
( )
( ) (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

        
         
1 1 1
( ) ( ) ( )
total x x sp x x pz x x
P In Ga N P In Ga N P In Ga N
  
 
1
( )
( ) (1 ) ( ) (1 ) ( )
0.090 0.034 (1 ) 0.090 (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

        
        
1 1 1
( ) ( ) ( )
total x x sp x x pz x x
P Al Ga N P Al Ga N P Al Ga N
  
 
Wu, J. Appl. Phys. 106, 011101 (2009).
Fiorentini et al., Appl. Phys. Lett. 80, 1204 (2002).

1. Introduction
Polarization in C/m2
0
xx yy
a a
a
 

 
13
33
2
zz xx
C
C
 
 
1
( ) ( ) (1 ) ( )
pz x x pz pz
P Al Ga N x P AlN x P GaN
     
2
( ) 1.347 7.559
pz
P InN  
    
2
( ) 1.808 7.888
pz
P AlN  
    
1
( ) ( ) (1 ) ( )
pz x x pz pz
P In Ga N x P InN x P GaN
     
Wu, J. Appl. Phys. 106, 011101 (2009).
2
( ) 0.918 9.541
pz
P GaN  
    

1. Introduction
Bandgap energy (binary) in eV
Wu, J. Appl. Phys. 106, 011101 (2009).
2 3 2
1.799 10
( , ) ( ,0) 6.25
1462
AlN
g g
AlN
T T
E AlN T E AlN
T T



 
   
 
Varshni, Physica 34, 149 (1967).
2 3 2
0.909 10
( , ) ( ,0) 3.51
830
GaN
g g
GaN
T T
E GaN T E GaN
T T



 
   
 
2 3 2
0.414 10
( , ) ( ,0) 0.69
454
InN
g g
InN
T T
E InN T E InN
T T



 
   
 

1. Introduction
Bandgap energy (ternary) in eV
1
( , )
( , ) (1 ) ( , ) (1 ) ( )
0.69 3.51 (1 ) 2.1 (1 ) [ 0 ]
g x x
g g g
E In Ga N T
x E InN T x E GaN T x x B InGaN
x x T
x K
x

        
       
 
1
( , )
( , ) (1 ) ( , ) (1 ) ( )
6.25 3.51 (1 ) 0.24 (1 ) [ ]
0
g x x
g g g
E Al Ga N T
x E AlN T x E GaN T x x B AlGaN
x x x x T K

        
        

Wu, J. Appl. Phys. 106, 011101 (2009).

1. Introduction
Recombination rate
2 3
2
2 3
3
2 3
Recombination=Radiative+Nonradiative
Nonradiative=Shockley-Read-Hall (SRH)+Auger
1
SRH Radiative Auger
C
SRH
C C C
C
Radiative IQE
C C C
C
Auger
C C C
A n
A n B n C n
B n
A n B n C n
C n
A n B n C n
  

 

  


    

 
    


    
Cho et al., Laser Photonics Rev. 7, 408 (2013).

1. Introduction
Efficiency
External quantum efficiency (EQE)
=Internal quantum efficiency (IQE) Extraction efficiency (EE)
Injection efficiency (IE)
(max) (min)
Efficiency droop 100%
(max)
EQE IQE EE IE
IQE IQE
IQE
   
 



  

 

1. Introduction
(1.3 Material parameters)
6 × 6 k∙p model
6 6
0
0
H
L
H
H
H

 
  
 
t t
H
t t
t t
F K iH
H K G iH
iH iH 

 
 
  
 
 
 
 
t t
L
t t
t t
F K iH
H K G iH
iH iH 
 
 
  
 
 
  
 
1 2
F  
     
1 2
G  
     
2
2 2 2
1 2 1 2
0
[ ( )] ( )
2
z x y zz xx yy
Ak A k k D D
m
   
     
2
2 2 2
3 4 3 4
0
[ ( )] ( )
2
z x y zz xx yy
A k A k k D D
m
   
     
2
2 2
5
0
( )
2
t x y
K A k k
m
 
2
2 2
6
0
2
t z x y
H A k k k
m
 
3
2
  
Zhao et al., IEEE J. Quantum Electron. 45, 66 (2009).

1. Introduction
Parameters Symbol (unit) GaN InN AlN
Lattice constant a0 (Å) 3.189 3.533 3.112
Lattice constant (c-axis) c0 (Å) 5.185 5.693 4.982
Lattice mismatch to GaN template ε 0 2.47% –9.74%
Bandgap energy (0 K) Eg(0) (eV) 3.51 0.69 6.25
Varshni parameter α (meV/K) 0.909 0.414 1.799
Varshni parameter β (K) 830 454 1462
Spontaneous polarization PSP (C/m2) –0.034 –0.042 0.090
Piezoelectric polarization PPZ (C/m2) 0 –0.451 0.205
Crystal-field split energy Δcr (eV) 0.010 0.040 –0.169
Spin-orbit split energy Δso (eV) 0.017 0.005 0.019
Hole effective mass parameter A1 –7.21 –8.21 –3.86
A2 –0.44 –0.68 –0.25
A3 6.68 7.57 3.58
A4 –3.46 –5.23 –1.32
A5 –3.40 –5.11 –1.47
A6 –4.90 –5.96 –1.64
Hydrostatic deformation potential (c-axis) az (eV) –7.1 –4.2 –3.4
Hydrostatic deformation potential (transverse) at (eV) –9.9 –4.2 –11.8
Shear deformation potential D1 (eV) –3.6 –3.6 –2.9
D2 (eV) 1.7 1.7 4.9
D3 (eV) 5.2 5.2 9.4
D4 (eV) –2.7 –2.7 –4.0
Elastic stiffness constant c13 (GPa) 106 92 108
c33 (GPa) 398 224 373
Electron effective mass (c-axis) 0.20 0.07 0.30
Electron effective mass (transverse) 0.21 0.07 0.32
z
e 0
m m
t
e 0
m m
Wu, J. Appl. Phys. 106, 011101 (2009).

1. Introduction
Parameters Symbol (unit) InGaN AlGaN
Minimum dopant dependent electron
mobility
(cm2/V-s) 386 132
Maximum dopant dependent electron
mobility
(cm2/V-s) 684 306
Referenced doping density of
impurity
Nref (1/cm3) 1.0 × 1017 1.0 × 1017
Slope of mobility versus logarithmic
doping density for electron
γ 1.37 0.29
Hole mobility (cm2/V-s) 10 10
Bowing parameter of bandgap energy BEG (eV) 2.1 0.24
Bowing parameter of spontaneous
polarization
BSP (C/m2) 0.038 0.09
min

max


Wu, J. Appl. Phys. 106, 011101 (2009).

1. Introduction
(1.4 Free parameters)
Parameters Value (unit)
Band offset ratio 0.67 : 0.33
SRH lifetime 10 (ns)
Auger coefficient 0.55 × 1017 (cm6/s)
Radiative coefficient 2.0 × 10‒11 (cm3/s)
Internal loss 20 (cm‒1)
Percentage of polarization charges 50%
Extraction efficiency 60%

1. Introduction
(1.5 Limits and criteria of numerical simulation)
 It is time-saving and cost-saving to evaluate the
fabrication process by way of technology
computer-aided design (TCAD) based on the well-
established physical models and carefully-verified
material parameters.
 However, the simulation results can’t exceed the
limits and criteria of the physical models. In other
words, it is not suitable to tune free parameters
roughly to fit any condition of the LEDs as well as
experimental data can’t be gotten beyond the
accuracy.

Outline
1. Introduction
5. Conclusion
6. Q&A

2.1 Landmark
developments
2.2 Recent progress
2.3 Industrial survey
2.4 Efficiency droop
2.5 Referenced device
structures Schubert et al., Science 308, 1274 (2005).

(2.1 Landmark developments)
Pimputkar et al., Nat. Photonics 3, 180 (2009).

(2.2 Recent progress)
Lee et al., Appl. Phys. Lett. 100, 061107 (2012).
Hwang et al., Appl. Phys. Lett. 99, 181115 (2011). Chen et al., Appl. Phys. Lett. 100, 241112 (2012).

(2.3 Industrial survey)
Epistar Inc. in 2013.5. (http://www.epistar.com.tw)

(2.4 Efficiency droop)
Current droop mechanisms
1. Defect-related mechanisms
2. Auger recombination
3. Electron leakage

(2.4 Efficiency droop)
Kioupakis et al., Appl. Phys. Lett. 98, 161107 (2011).

(2.5 Referenced device structures)
Blue InGaN LEDs
sapphire
u-GaN
n-GaN 5×1018 cm3 4500 nm
i-In0.21Ga0.79N/GaN 2 nm / 15 nm
p-Al0.15Ga0.85N 1.2×1018 cm3 20 nm
p contact
n contact
p-GaN 1.2×1018 cm3 500 nm
Kuo et al., Appl. Phys. Lett. 95, 01116 (2009).

(2.5 Referenced device structures)
Green InGaN LEDs
sapphire
u-GaN
n-GaN 5×1018 cm3 3000 nm
i-In0.32Ga0.68N/GaN 2 nm / 10 nm
p-Al0.13Ga0.87N 5×1017 cm3 20 nm
p contact
n contact
p-GaN 5×1017 cm3 200 nm

Outline
1. Introduction
5. Conclusion
6. Q&A

3.1 GaN-InGaN-GaN barriers
3.2 Tailored configuration
3.3 InGaN-AlGaN-InGaN barriers
3.4 Shallow first well
3.5 Slightly-doped step-like electron blocking
layer (EBL)
3.6 Polarization-reversed EBL
3.7 Other approaches
3.8 Summary
More nonradiative
recombination
More radiative
recombination

(3.1 GaN-InGaN-GaN barriers)

(3.2 Tailored configuration)
Kuo et al., IEEE J. Quantum Electron. 48, 946 (2012).
Location

Numbers

Indium composition

(3.3 InGaN-AlGaN-InGaN barriers)

(3.4 Shallow first well)
Wang et al., IEEE Photonics Technol. Lett. 24, 2084 (2012).

(3.4 Shallow first well)

(3.5 Slightly-doped step-like EBL)
Kuo et al., IEEE Photonics Technol. Lett. 24, 1506 (2012).

(3.5 Slightly-doped step-like EBL)

(3.6 Polarization-reversed EBL)

Comparing the operation
of the reversed AlGaN-
GaN-InGaN EBL LEDs,
one can see that the IQE
of the LEDs is higher at
350 K at 300 mA than at
300 K because of the lower
electron current leakage.

(3.7 Other approaches)

(3.8 Summary)
In this chapter, effective approaches toward the solution of efficiency
droop with
• GaN-InGaN-GaN barriers
• InGaN-AlGaN-InGaN barriers
• shallow first well
• slightly-doped step-like EBL
• polarization-reversed AlGaN-GaN-InGaN EBL
are discussed and compared.
1. With such designs, the progress of blue InGaN-based LEDs is
extensively improved in solid-state lighting under different
circumstances of epitaxial condition such as low-pressure or
atomic-pressure.
2. The physical origins of improved opto-electrical performance and
suppressed efficiency droop can be attributed to reduced electron
leakage and enhanced hole injection efficiency.

Outline
1. Introduction
5. Conclusion
6. Q&A

4.1 Effects of polarization state
4.2 Spectral competition
4.3 Nonradiative competition
4.4 Summary

(4.1 Effects of polarization state)

(4.2 Spectral competition) Wang et al., Appl. Phys. Lett. 102, 171112 (2013).

(4.3 Nonradiative competition)

(4.4 Summary)
In conclusion, in addition to the issue
of crystalline quality that is generally
desired for good LED performance,
the efficient suppression of
piezoelectric polarization effect and
Auger recombination also play
important roles toward the
commercial realization of effective
dual-wavelength broad-band LEDs.

Outline
1. Introduction
5. Conclusion
6. Q&A

5. Conclusion
5.1 Conclusion
5.2 Future works
5.3 Simulated input files
5.4 Publication list

5. Conclusion
(5.1 Conclusion)
In this dissertation, the spontaneous and piezoelectric
polarizations in InGaN LEDs leads to severe electron
leakage, insufficient efficiency of hole injection, serious
Auger recombination and other effects.
Therefore, InGaN LEDs with
• GaN-InGaN-GaN barriers,
• InGaN-AlGaN-InGaN barriers,
• shallow first well,
• slightly-doped step-like EBL, and
• polarization reversed AlGaN-GaN-InGaN EBL
are beneficial for improvement of optical and electrical
performance compared with conventional device
structures.

5. Conclusion
(5.1 Conclusion)
Furthermore, for the commercial
realization of monolithic phosphor-free
white InGaN LEDs, broad-band LED with
shallow first well and tailored QW
configuration is suggested in order to
overcome
• detrimental polarization state,
• spectral competition, and
• obstructive Auger recombination
in dual-wavelength emission.

5. Conclusion
(5.2 Future works)
1. An overall solution of efficiency droop and a
generally accepted model are still on demand. Multi-
functionally integrated device structure which has
better and better performance such as
• optical,
• electrical,
• thermal,
• spectral,
• spatial,
and other characteristics remains desirable.

5. Conclusion
(5.2 Future works)
2. Monolithic phosphor-free white InGaN LEDs are
still possible candidates of future generation in solid-
state lighting. The widely-ranged bandgap energies
of nitrides can be very advantageous if the issues of
• polarization effects and
• epitaxial processes
will be overcome in the future.

5. Conclusion
(5.3 Simulated input files)
*.sol
*.layer
*.plt
APSYS
Band
Carrier
Field
…

5. Conclusion
(5.4 Publication list)
1. Y.-K. Kuo, T.-H. Wang, J.-Y. Chang, and M.-C. Tsai,
“Advantages of InGaN light-emitting diodes with GaN-InGaN-
GaN barriers, ” Appl. Phys. Lett. 99, 091107 (2011). (APL's monthly
top 20 most-downloaded articles in September 2011. )
2. Y.-K. Kuo, T.-H. Wang, and J.-Y. Chang, “Advantages of blue
InGaN light-emitting diodes with InGaN-AlGaN-InGaN barriers,”
Appl. Phys. Lett. 100, 031112 (2012). (APL's monthly top 20 most-
downloaded articles in January and February 2012. ) (One of the most notable
APL articles published in 2012.)
3. Y.-K. Kuo, T.-H. Wang, and J.-Y. Chang, “Blue InGaN light-
emitting diodes with multiple GaN-InGaN barriers,” IEEE J.
Quantum Electron. 48, 946 (2012).
4. Y.-K. Kuo, T.-H. Wang, J.-Y. Chang, and J.-D. Chen, “Slightly-
doped step-like electron blocking layer in InGaN light-emitting
diodes,” IEEE Photonics Technol. Lett. 24, 1506 (2012).

5. Conclusion
(5.4 Publication list)
5. T.-H. Wang and Y.-K. Kuo, “Efficiency enhancement
of blue InGaN light-emitting diodes with shallow first
well,” IEEE Photonics Technol. Lett. 24, 2084 (2012).
6. Y.-A. Chang, Y.-R. Lin, J.-Y. Chang, T.-H. Wang, and
Y.-K. Kuo, “Design and characterization of
polarization-reversed AlInGaN based ultraviolet light-
emitting diode,” IEEE J. Quantum Electron. 49, 553
(2013).
7. T.-H. Wang and Y.-K. Kuo, “Spectral competition of
chirped dual-wavelength in monolithic InGaN
multiple-quantum well light-emitting diodes,” Appl.
Phys. Lett. 102, 171112 (2013).

Thank you for your attention!

Outline
1. Introduction
4. Dual-wavelength
5. Conclusion
6. Q&A

Q&A
1. Overall academic contribution
2. Physical models
3. Free parameters
4. Macro
5. Recent progress on LEDs
6. Curve fitting
7. Polarization charges

Overall academic contribution
Effective solutions to suppress polarization
problems in nitride optoelectronic devices
Possible solutions on carrier balance and
spectral competition for dual-wavelength
InGaN LEDs
Better comprehension of efficiency droop in
InGaN LEDs
Possible relationships of polarization effects
and thermal effects in InGaN LEDs
BACK TO Q&A

Physical models
Equations Parameters
Poisson equation: φ, n, p, S, W, g
Continuity equation: φ, n, p
Complex wave equation: n, p, S, W, g
Rate equation: n, p, W, λ, g
Gain equation: n, p, λ, g
φ: potential, n and p: electron and hole
concentration, S: photon number, W: optical
field intensity, λ: wavelength, g: gain.
APSYS by Crosslight Software Inc.

Physical models
Poisson equation: ∇2V=−ρ /ε, where ρ: volume charge
density, ε: dielectric constant.
（a）∇V 為電場。
（b）εdc 為相對介電常數。
（c）n、p 為電子與電洞濃度。
（d）ND(NA)為淺層donor(acceptor)摻雜的密度，fD(fA)為介面中
donor(acceptor)淺層能階的佔有率。（此項會造成介面結合的電子濃
度產生影響，NAfA 前面的負號為接收電子濃度產生）
（e）δj 為delta function 當作acceptor 時其值為0 當作donor 時其值為1，
Ntj 為介面中第j 個深層能階的密度，ftj 為第j 個深層能階的佔有率。(
此項和前兩項比較下其意義為相似) APSYS by Crosslight Software Inc.

Physical models
Continuity equation: ∇J+∂ρ/∂t=0, where J: current
density, t: time.
（a）電子的電流密度Jn = n×μn×∇Efn（其中μn 為電子的mobility，Efn 為電
子的Fermi-level），而電洞的電流密度Jp = n×μp×∇Efp 。
（b）Rn
tj 為通過邊界上第j 個能階時，每單位體積的電子結合律，而Rp
tj
為通過邊界上第j 個能階時，每單位體積的電洞結合律。(SRH)
（c）Rsp 為自發輻射率，Rst 為受激放射率。
（d）Rau=(Cnn+Cpp)(np-ni
2)；Cn 和Cp 均為常數取決於材料本身，ni 指純
質的載子密度。(Auger recombination rate)

Physical models
Complex wave equation: ∇2W+k2(ε−β2)W=0, where W:
optical wave function, k: wave vector, β: real eigen-
value.
（a）W為光子的波函數，|W|2為每單位體積找到光子的機率。
（b）k0 為波向量，ε為介電常數，β為real eigenvalue 實數本
徵值。

Physical models
Rate equation: ∂S/∂t=c(g−α)/n, where c: speed of light,
n: refractive index, g: gain, α: loss, S: photon number.
（a） ng 為材料的折射率，gm 為增益模式(model
gain)，αint 為初始的損失(loss)， α em 為發射光子
產生的損失，S 為光子數。
（b） cm 為小部份自發輻射的常數。

Physical models
Gain equation: g=α+[ln(1/R1R2)]2L, where R:
reflectance of mirrors, L: cavity length.
（a）γ為intra-band 的散射時間
（b）L(Ex-Eij
0)為Lorentzian shape function
（c）gij 為第i 能階到第j 能階的local gain，Eij 為第i 能階到
第j 能階的能差
（d）gij 內有包含輕電洞和重電洞的TE 和TM 模式
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Free parameters
 In order to access the recent and common
consensuses, only the papers published at Appl.
Phys. Lett. and J. Appl. Phys., first two most-
cited journals in applied physics, in 2010-2011
are discussed herein.
 Bowing parameters of Eg
 Band offset ratio
 Current density
 SRH
 Auger
 Loss
 Extraction efficiency

Free parameters
 Bowing parameter of
InGaN:
 M. César, Y. Ke, W. Ji, H. Guo, and Z.
Mi, Appl. Phys. Lett., 98, 202107, 2011.
 R. R. Pelá, C. Caetano, M. Marques, L. G.
Ferreira, J. Furthmüller, and L. K. Teles,
Appl. Phys. Lett., 98, 151907, 2011.
 I. Gorczyca, T. Suski, N. E. Christensen,
and A. Svane, Appl. Phys. Lett., 98,
241905, 2011.
 Conclusion: Set to be
1.4 eV in my macro.

Free parameters
 Band offset ratio of AlGaN:
0.65 : 0.35
 M. F. Schubert, Appl. Phys. Lett., 96, 031102,
2010.
 K. S. Kim, J. H. Kim, S. J. Jung, Y. J. Park, and
S. N. Cho, Appl. Phys. Lett., 96, 091104, 2010.
 Y. Liao, C. Thomidis, C. Kao, and T. D.
Moustakas, Appl. Phys. Lett., 98, 081110, 2011.

Free parameters
 Band offset ratio of AlGaN: 0.5 : 0.5
 W. Lee, M.-H. Kim, D. Zhu, A. N. Noemaun, J. K. Kim, and E. F. Schubert, J. Appl. Phys., 107,
063102, 2010.
 L. Zhang, K. Ding, N. X. Liu, T. B. Wei, X. L. Ji, P. Ma, J. C. Yan, J. X. Wang, Y. P. Zeng,
and J. M. Li, Appl. Phys. Lett., 98, 101110, 2011.

Free parameters
 Current density:
 D. Zhu, A. N. Noemaun, M. F. Schubert,
J. Cho, E. F. Schubert, M. H. Crawford,
and D. D. Koleske, Appl. Phys. Lett., 96,
121110, 2010.

Free parameters
 SRH lifetime:
 W. G. Scheibenzuber, U. T. Schwarz, L. Sulmoni, J. Dorsaz, J.-F. Carlin, and N.
Grandjean, J. Appl. Phys., 109, 093106, 2011.
 A. David and M. J. Grundmann, Appl. Phys. Lett., 96, 103504, 2010.
 Conclusion: 1 ns ~ 100 ns

Free parameters
 Auger coefficient:
 E. Kioupakis, P. Rinke, K. T. Delaney, and C. G.
Van de Walle, Appl. Phys. Lett., 98, 161107, 2011.
 Q. Dai, Q. Shan, J. Cho, E. F. Schubert, M. H.
Crawford, D. D. Koleske, M.-H. Kim, and Y. Park,
Appl. Phys. Lett., 98, 033506, 2011.
 Conclusion: 1028 ~ 31 cm6s1

Free parameters
 Internal loss:
 Y. Zhang, T.-T. Kao, J. Liu, Z.
Lochner, S.-S. Kim, J.-H. Ryou, R. D.
Dupuis, and S.-C. Shen, J. Appl. Phys.,
109, 083115, 2011.
 J. H. Zhu, S. M. Zhang, H. Wang, D.
G. Zhao, J. J. Zhu, Z. S. Liu, D. S.
Jiang, Y. X. Qiu, and H. Yang, J. Appl.
Phys., 109, 093117, 2011.
 Conclusion: 103 ~ 7 m1

Free parameters
 Extraction efficiency:
 S. Chhajed, W. Lee, J. Cho, E. F.
Schubert, and J. K. Kim, Appl. Phys.
Lett., 98, 071102, 2011.
 E. Matioli, E. Rangel, M. Iza, B.
Fleury, N. Pfaff, J. Speck, E. Hu, and
C. Weisbuch, Appl. Phys. Lett., 96,
031108, 2010.
 Conclusion: 25% ~
95%
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Macro
Macro
Optical
Index
Absorption
Auger
SRH
Radiative
Thermal Kappa
Electrical
Mobility
Affinity
k.p
Bandgap

Macro
Crosslight.mac
APSYS
ingan
algan
InGaN/
InGaN
…
More.mac
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Recent progress on LEDs
Patterned sapphire substrate , Nanodisks …
Graded superlattice EBL, graded EBL, w/o
EBL, …
Thermal Auger…
Blue and green, low-In + high-In, …
Structure
Droop
White
LEDs
Device

Y. Li, S. You, M. Zhu, L. Zhao, W. Hou, T. Detchprohm, Y. Taniguchi, N.
Tamura, S. Tanaka, and C. Wetzel, “Defect-reduced green GaInN/GaN
light-emitting diode on nanopatterned sapphire,” Appl. Phys. Lett. 98,
151102 (2011).

J. Hader, J. V. Moloney, and S. W. Koch,
“Temperature-dependence of the internal
efficiency droop in GaN-based diodes,”
Appl. Phys. Lett. 99, 181127 (2011).
 With increasing temperature, a strongly
decreasing strength of the loss
mechanism responsible for droop is
found which is in contrast to the usually
assumed behavior of Auger losses.
 However, the experimental observations
can be well reproduced assuming density
activated defect recombination with a
temperature independent recombination
time.

Y.-J. Lu, H.-W. Lin, H.-Y. Chen, Y.-C. Yang, and S.
Gwo, “Single InGaN nanodisk light emitting diodes
as full-color subwavelength light sources,” Appl. Phys.
Lett. 98, 233101 (2011).
 Subwavelength electroluminescent sources with
spatial, spectral, and polarization controlling
capabilities are critical elements for optical
imaging and lithography beyond the diffraction
limit.

Y. Y. Zhang and Y. A. Yin, “Performance enhancement of
blue light-emitting diodes with a special designed AlGaN/GaN
superlattice electron-blocking layer,” Appl. Phys. Lett. 99,
221103 (2011).

N. Zhang, Z. Liu, T. Wei, L. Zhang, X. Wei, X. Wang, H. Lu,
J. Li, and J. Wang, “Effect of the graded electron blocking
layer on the emission properties of GaN-based green light-
emitting diodes,” Appl. Phys. Lett. 100, 053504 (2012).

D.-Y. Lee, S.-H. Han, D.-J. Lee, J. W. Lee, D.-J. Kim, Y. S.
Kim, and S.-T. Kim, “Effect of an electron blocking layer on
the piezoelectric field in InGaN/GaN multiple quantum well
light-emitting diodes,” Appl. Phys. Lett. 100, 041119 (2012).

H. Long, T. J. Yu, L. Liu, Z. J. Yang, H. Fang, and G. Y. Zhang, “Different
exciton behaviors in blue and green wells of dual-wavelength InGaN/GaN
MQWs structures,” J. Appl. Phys. 111, 053110 (2012).
 Staggered structures with blue and green quantum wells (QWs) were grown by
metal organic vapor phase epitaxy (MOVPE) and characterized by
photoluminescence (PL) and time resolved photoluminescence (TRPL) at various
temperatures from 10K to 300 K.
 High efficiency green light was observed, accompanying with decreased intensity
of blue light.
 Efficiency of the green band was lower than that of the blue band below 100 K,
but became two times greater than the efficiency of blue when temperature
increased to room temperature.
 Three-dimensional and two-dimensional exciton behaviors were observed by
TRPL measurements corresponding to blue and green bands, respectively.
 It is considered that carrier tunneling from blue wells is a key process for high
efficiency luminescence in green QWs.

L. Liu, L. Wang, N. Liu, W. Yang, D. Li, W. Chen, Z. C. Feng,
Y.-C. Lee (NTU), I. Ferguson, and X. Hu, “Investigation of the
light emission properties and carrier dynamics in dual-
wavelength InGaN/GaN multiple-quantum well light emitting
diodes,” J. Appl. Phys. 112, 083101 (2012).
 Three dual-wavelength InGaN/GaN multiple quantum well (MQW) light
emitting diodes (LEDs) with increasing indium content are grown by
metal-organic chemical vapor deposition, which contain six periods of
low-In-content MQWs and two periods of high-In-content MQWs.
 For the low-In-content MQWs of three studied samples, their internal
quantum efficiency (IQE) shows a rising trend as the emission wavelength
increases from 406 nm to 430 nm due to the suppression of carriers escape
from the wells to the barriers.

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Curve fitting
0
50
100
150
200
250
3.2
3.4
3.6
Auger/10
Original LED
Auger×10
Auger/10
Original LED
Auger×10
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)
0
50
100
150
200
250
3.2
3.4
3.6
SRH/10
Original LED
SRH×10
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)
0
50
100
150
200
250
3.2
3.4
3.6
Radiative/10
Original LED
Radiative×10
Radiative/10
Original LED
Radiative×10
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)
0
50
100
150
200
250
3.2
3.4
3.6
Loss/10
Original LED
Loss×10
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)

Curve fitting
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0
50
100
150
200
250
3.2
3.4
3.6
Extraction－10%
Original LED
Extraction+10%
Extraction－10%
Original LED
Extraction+10%
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)
0
50
100
150
200
250
3.2
3.4
3.6
Screening－10%
Original LED
Screening+10%
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)
0
50
100
150
200
250
3.2
3.4
3.6
Offset－10%
Original LED
Offset+10%
Offset－10%
Original LED
Offset+10%
0 50 100 150 200 250
Output
power
(mW)
Voltage
(V)
Current (mA)

Polarization charges
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Interface (top/bottom) Green LEDs (1/m2)
p-GaN/p-EBL –2.63×1016
p-EBL/GaN +2.63×1016
GaN/In0.32Ga0.68N +1.67×1017

Macro
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博士論文口試-Ph.D. Defense (2013-06-19)-TH Wang.ppt

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