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

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

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 National Changhua University of Education

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

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 National Changhua University of Education

Schematic diagram of the preliminary laser diode structure The reflectivities of the two end mirrors are 85 % and 90 % respectively. 2003/3/31 National Changhua University of Education

The current distribution and L-I curves for the preliminary structure  = 462 nm The laser threshold current is 103.4 mA. 2003/3/31 National Changhua University of Education

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 National Changhua University of Education

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 National Changhua University of Education

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 National Changhua University of Education

L-I curves at various Al mole fractions The higher Al mole fraction, the better performance of InGaN laser diode. 2003/3/31 National Changhua University of Education

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 National Changhua University of Education

National Changhua University of Education 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 National Changhua University of Education

National Changhua University of Education Threshold current as a function of temperature for the original and improved structures Initial Structure （ T0 = 63.40 K ） Improved Structure （ T0 = 208.60 K ） The improved structure is more stable, especially for high-temperature operation. 2003/3/31 National Changhua University of Education

National Changhua University of Education 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 National Changhua University of Education

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 National Changhua University of Education

Carrier concentration distribution of the triple-QW structure It is obvious that the hole distribution among quantum wells is quite inhomogeneous. 2003/3/31 National Changhua University of Education

National Changhua University of Education 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 National Changhua University of Education

National Changhua University of Education 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 National Changhua University of Education

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 43.22 mA and the slope efficiency is 25.74%. 2003/3/31 National Changhua University of Education

L-I curves for SQW and Triple-QW structures The triple-QW structure has better laser performance. 2003/3/31 National Changhua University of Education

National Changhua University of Education 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 National Changhua University of Education

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

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 National Changhua University of Education

Simulation for the WZ-InGaN In this simulation , Indium will be constricted between 0 and 0.375.And the lattice constants of the unstrained InGaN layer depend linearly on the indium composition. a(x) = 3.501 (x) + 3.162 (1-x) b(x) = 3.501 (x) + 3.162 (1-x) c(x) = 5.669 (x) + 5.142 (1-x) 2003/3/31 National Changhua University of Education

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 1.210 eV 2003/3/31 National Changhua University of Education

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) = 3.082 (x) + 3.162 (1-x) b(x) = 3.082 (x) + 3.162 (1-x) c(x) = 4.948 (x) + 5.142 (1-x) 2003/3/31 National Changhua University of Education

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 0.353 eV 2003/3/31 National Changhua University of Education

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) = 3.082 (x) + 3.501 (1-x) b(x) = 3.082 (x) + 3.501 (1-x) c(x) = 4.948 (x) + 5.669 (1-x) 2003/3/31 National Changhua University of Education

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 3.326 eV 2003/3/31 National Changhua University of Education

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