1. Introduction of Master's thesis of Jih-Yuan Chang and Wen-Wei Lin
Speaker:Meng-Lun Tsai
National Changhua University of Education
2019/1/16
National Changhua University of Education

2. National Changhua University of Education
Electronic Current Overflow and Inhomogeneous Hole Distribution of the InGaN Quantum Well Structures
Master's thesis of Jih-Yuan Chang
2019/1/16
National Changhua University of Education

3. National Changhua University of Education
Outline
Introduction
Electronic Current Overflow of the InGaN SQW Structures
Inhomogeneous Hole Distribution of the InGaN Quantum Well Structures
Conclusion
2003/3/31
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4. National Changhua University of Education
Introduction
The InGaN materials have important application in visible light-emitting diodes (LED) and short-wavelength laser diodes. In this work Jih-yuan investigate the electronic current overflow and the inhomogeneous hole distribution of the blue InGaN quantum well structures with a LASTIP (abbreviation of LASer Technology Integrated Program) simulation program.
2003/3/31
National Changhua University of Education

5. Reasons to electron current overflow
There are several causes for the electron current overflow of III-V Nitrides：
high threshold current
narrow quantum well width
small conduction band-offset
poor hole injection to the active region
These four causes have important influence on the degree of current overflow.
2003/3/31
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6. Schematic diagram of the preliminary laser diode structure
The reflectivities of the two end mirrors are 85 % and 90 % respectively.
2003/3/31
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7. The current distribution and L-I curves for the preliminary structure
 = 462 nm
The laser threshold current is mA.
2003/3/31
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8. Current distribution curves at various
p-doping levels
p-doping：11017 cm-3
p-doping：31017 cm-3
p-doping：51017 cm-3
p-doping：71017 cm-3
p-doping：11018 cm-3
The higher the p-doping level, the lower the percentage of the electronic overflow current.
2003/3/31
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9. L-I curves at various p-doping levels
p-doping：11017 cm-3
p-doping：31017 cm-3
p-doping：51017 cm-3
p-doping：71017 cm-3
p-doping：11018 cm-3
The higher the p-doping level, the better the performance of InGaN laser diode.
2003/3/31
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10. Current distribution curves at various Al mole fractions
The higher the Al mole fraction, the lower the percentage of the electronic overflow current.
2003/3/31
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11. L-I curves at various Al mole fractions
The higher Al mole fraction, the better performance of InGaN laser diode.
2003/3/31
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12. The current distribution and L-I curves of the improved structure
The modified structure：  Al mole fraction : 10 %
 p-doping level : 11018 cm-3
2003/3/31
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Laser output power as a function of input electric power for the original and improved structures
The improved structure has a better power conversion efficiency.
2003/3/31
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Threshold current as a function of temperature for the original and improved structures
Initial Structure
（ T0 = K ）
Improved Structure
（ T0 = K ）
The improved structure is more stable, especially for high-temperature operation.
2003/3/31
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L-I curves of the InGaN laser structures of different quantum well numbers.
Single QW
Double QWs
Triple QWs
With the increase of the quantum well number, the performance of the InGaN laser diodes decreases.
2003/3/31
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16. Energy band diagram of the triple-QW structure
The quasi-Fermi level in the valance band is not quite continuous  inhomogeneity of hole distribution among quantum wells.
2003/3/31
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17. Carrier concentration distribution of the
triple-QW structure
It is obvious that the hole distribution among quantum wells is quite inhomogeneous.
2003/3/31
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Spontaneous and stimulated emission diagrams of the triple-QW structure
The right quantum well has the most spontaneous emission.
The right quantum well is the only quantum well that possesses positive stimulated emission.
2003/3/31
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Carrier concentration and stimulated diagrams when the barriers have a p-doping level of 2.3  1019 cm-3
Hole Concentration
Electron Concentration
The distribution of hole concentration is much more homogeneous.
All three quantum wells contribute to stimulated emission.
2003/3/31
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20. L-I curves for various doping concentration of the barriers
p-doping：2.31019 cm-3
p-doping：2.51019 cm-3
p-doping：2.71019 cm-3
p-doping：3.01019 cm-3
p-doping：3.31019 cm-3
When the doping level is at 31019 cm-3, the threshold current is mA and the slope efficiency is 25.74%.
2003/3/31
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21. L-I curves for SQW and Triple-QW structures
The triple-QW structure has better laser performance.
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Conclusion
It is found that this electronic current overflow is severe in the single quantum well InGaN laser structure at room temperature, especially when the p-doping is low. Increasing the p-doping level and using an AlGaN stopper layer in the p-side can resolve this problem. In addition to the improvement of laser performance at room temperature, the improved InGaN laser structure has a higher characteristic temperature and hence is less sensitive to temperature.
Jih-Yuan have also investigated the deterioration of the laser performance of the multiple quantum well InGaN lasers caused by the inhomogeneous distribution of the holes inside the active region. It happens due to the difficulty for the holes to transport from one quantum to another. Jih-Yuan have proposed to p-dope the barriers between wells to help the holes to transport and thus help solve the problem of inhomogeneous hole distribution.
2003/3/31
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23. National Changhua University of Education
Theoretical Investigation on Band Structure of the BAlGaInN Semiconductor Materials
Master's thesis of Wen-Wei Lin
2019/1/16
National Changhua University of Education

24. National Changhua University of Education
Content
The band-gap energy-gap bowing parameter of the wurtzite InGaN,AlGaN,AlInN alloys are investigated numerically with the CASTEP simulation program by Wen-Wei Lin
2003/3/31
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25. Simulation for the WZ-InGaN
In this simulation , Indium will be constricted between and And the lattice constants of the unstrained InGaN layer depend linearly on the indium composition.
a(x) = (x) (1-x)
b(x) = (x) (1-x)
c(x) = (x) (1-x)
2003/3/31
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26. WZ-InxGa1-xN band gap energy
Eg(x) = x · Eg,InN + (1-x) ·Eg,GaN - b · x · (1-x)
To use this formula to fit the results, and obtain bowing parameter of eV
2003/3/31
National Changhua University of Education

27. Simulation for the WZ-AlGaN
Since AlGaN have large energy band gap , so it is usually used as barrier of active layer or DBR material.
Since the energy band gap structure of the AlGaN is direct in the whole
range of the aluminum composition, wen-wei study the characteristics of
the AlGaN for the aluminum composition to be between zero and one.
The lattice constants of the unstrained AlGaN layer depend linearly on the
aluminum composition.
a(x) = (x) (1-x)
b(x) = (x) (1-x)
c(x) = (x) (1-x)
2003/3/31
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28. WZ-AlxGa1-xN band gap energy
Aluminum Composition, x
Band-Gap Energy (eV)
Eg(x) = x · Eg,AlN + (1-x) ·Eg,GaN - b · x · (1-x)
To use this formula to fit the results, and obtain bowing parameter of eV
2003/3/31
National Changhua University of Education

29. Simulation for the WZ-AlInN
Compared to the InGaN and AlGaN alloys, the third ternary nitride alloy ,AlInN ,is less investigated.This alloys exhibits the largest variation in band gap and it is a candidate for lattice matched confinement layers in optical devices.
Wen-wei study the characteristics of the AlInN for the aluminum composition
to be between zero and one.
The lattice constants of the unstrained AlGaN layer depend linearly on the
aluminum composition.
a(x) = (x) (1-x)
b(x) = (x) (1-x)
c(x) = (x) (1-x)
2003/3/31
National Changhua University of Education

30. WZ-AlGaInN band gap energy
Composition, x
Band-Gap Energy (eV)
Eg(x) = x · Eg,AlN + (1-x) ·Eg,InN - b · x · (1-x)
To use this formula to fit the results, and obtain bowing parameter of eV
2003/3/31
National Changhua University of Education

31. National Changhua University of Education
WZ-AlGaInN
Band-gap energy and corresponding wavelength of the InGaN,AlGaN, and AlInN as a function of the lattice constant
Band-Gap Energy (eV)
Lattice Constant (Angstrom)
Wavelength (nm)
2003/3/31
National Changhua University of Education