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«A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Approved November 2014 by the Graduate ...»

-- [ Page 1 ] --

Structural Properties of III-Nitride Semiconductors

by

Yong Wei

A Dissertation Presented in Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy

Approved November 2014 by the

Graduate Supervisory Committee:

Fernando Ponce, Chair

Andrew Chizmeshya

Martha McCartney

JoséMené ndez

Hongbin Yu

ARIZONA STATE UNIVERSITY

December 2014

ABSTRACT

Group III-nitride semiconductors have been commercially used in the fabrication of light-emitting diodes and laser diodes, covering the ultraviolet-visible-infrared spectral range and exhibit unique properties suitable for modern optoelectronic applications.

InGaN ternary alloys have energy band gaps ranging from 0.7 to 3.4 eV. It has a great potential in the application for high efficient solar cells. AlGaN ternary alloys have energy band gaps ranging from 3.4 to 6.2 eV. These alloys have a great potential in the application of deep ultra violet laser diodes. However, there are still many issues with these materials that remain to be solved. In this dissertation, several issues concerning structural, electronic, and optical properties of III-nitrides have been investigated using transmission electron microscopy. First, the microstructure of InxGa1-xN (x = 0.22, 0.46, 0.60, and 0.67) films grown by metal-modulated epitaxy on GaN buffer /sapphire substrates is studied. The effect of indium composition on the structure of InGaN films and strain relaxation is carefully analyzed. High luminescence intensity, low defect density, and uniform full misfit strain relaxation are observed for x = 0.67. Second, the properties of high-indium-content InGaN thin films using a new molecular beam epitaxy method have been studied for applications in solar cell technologies. This method uses a high quality AlN buffer with large lattice mismatch that results in a critical thickness below one lattice parameter. Finally, the effect of different substrates and number of gallium sources on the microstructure of AlGaN-based deep ultraviolet laser has been studied. It is found that defects in epitaxial layer are greatly reduced when the structure is deposited on a single crystal AlN substrate. Two gallium sources in the growth of i multiple quantum wells active region are found to cause a significant improvement in the quality of quantum well structures.

ii To my parents, my wife, and my daughter.

iii

ACKNOWLEDGEMENTS

I would like to gratefully thank my advisor, Prof. Fernando Ponce, for offering me the great opportunity in study of the III-nitrides as well as his academic guidance and supportduring my attendance at Arizona State University. I would also like to thank my committee members, Prof. Andrew Chizmeshya, Prof. Martha McCartney, Prof. José Menéndez, and Prof. Hongbin Yu.

I want to express my special thanks and appreciation to Dr. Alec Fischer, for his enthusiastic and effective help in my research, in the writing of reports and papers, and in the writing of this dissertation. I have spent a wonderful time working with my knowledgeable and friendly colleagues, and I thank their generous help during my Ph. D studies, they are: Mr. Hongen Xie, Mr. Shuo Wang, Mr. Hanxiao Liu as well as former group members Dr. Qiyuan Wei, Dr. Kewei Sun, Dr. Yu Huang, Dr. Ti Li, Dr. Jingyi Huang, and Dr. Reid Juday. I would like to thank Mr. Karl Weiss, Dr. Zhenquan Liu, Dr.

John Mardinly and Dr. Toshihiro Aoki of LeRoy Erying Center for Solid State Science at Arizona State University for their excellent facilities and technical help with TEM.

I sincerely thank my parents for their support throughout my education. I deeply appreciate my wife Yifang Chen for her constant love.

–  –  –

LIST OF FIGURES

LIST OF TABLES

CHAPTER

1. INTRODUCTION TO GROUP-III NITRIDES

1.1. III-Nitride Materials

1.2. III-Nitrides Structures

1.3. III-Nitride Growth

1.4. InGaN for Solar Cell

1.5. Chanllenges in realization of high quality InGaN Alloy

1.6. AlGaN for Deep Ultraviolet Laser

1.7. Organization of this Dissertation

References

2. LATTICE MISMATCH AND PLASTIC RELAXATION

2.1. Lattice Mismatch in Heteroepitaxial structures

2.2. Critical Thickness for the Formation of Misfit Dislocation

2.3. Plastic Relaxation in Cubic Material System

2.4. Plastic Relaxation in Hexagonal Material System

References

3. EXPERIMENTAL TECHNIQUES

3.1. Electron Diffraction Pattern

3.2. Diffraction-contrast Imaging

–  –  –

3.3. High-Resolution TEM

3.4. Scanning Transmission Electron Microscopy

3.5. TEM Sample Preparation

3.5.1. Sectioning

3.5.2. First Side Polishing

3.5.3. Second Side Polishing

References

4. MICROSTRUCTURE OF InxGa1-xN (x = 0.22 - 0.67) FILMS GROWN BY METALMODULATED EPITAXY

4.1. Introduction

4.2. Experimental Techniques

4.2.1. Growth

4.2.2. Determination of Alloy Composition





4.2.3. Structural Characterization

4.2.4. Optical Characterization by Photoluminescence

4.3. Results

4.3.1. InGaN Epilayers with [In] ~ 22%

4.3.2. InGaN Epilayers with [In] ~ 46%

4.3.4. InGaN Epilayers with [In] ~ 67%

4.4. Discussion

4.4.1. Critical Thickness for Misfit Strain Relaxation in Thin Film Epitaxy............ 65 4.4.2. InxGa1-xN Thin Film Microstructure Evolution with Indium Composition.... 67

–  –  –

4.4.3. Misfit Strain Relaxation and High Luminescence Characteristics.................. 70

4.5. Conclusions

References

5. MICROSTRUCTURE OF HIGH-QUALITY HIGH-INDIUM-CONTENT InGaN

LAYERS GROWN BY MODIFIED MOLECULAR BEAM EPITAXY WITH AlN

BUFFER

5.1. Introduction

5.2. Experimental Techniques

5.3. Microstructure of InGaN Epilayer with [In] ~ 100%

5.5. Microstructure of InGaN Epilayer with [In] ~ 78%

5.6. Microstructure of InGaN Epilayer with [In] ~ 60%

5.7. Microstructure of InGaN Epilayer with [In] ~ 54%

5.8. Microstructure of InGaN Epilayer with [In] ~ 48%

5.9. Discussion

5.10. Conclusions

References

6. MICROSTRUCTURE OF DEEP UV AlGaN-BASED HETEROSTRUCTURES..... 97

6.1. Introduction

6.2. Microstructure of AlGaN/AlN Heterostructure on AlN Substrate with a Stimulated Emission at 257 nm

6.2.1. Microstructure Characterization of UV Laser Devices

–  –  –

6.3. The Effect of Different Number of TMG Sources on the Active Region of Sub 300 nm DUV Lasers

6.3.1. Microstructure on the Active Region of DUV Lasers Grown by One and Two TMG Sources

6.3.2. Optical Properties of DUV Lasers Grown by One and Two TMG Sources. 108

6.4. Conclusions

References

7. SUMMARY AND FUTURE WORK

7.1. Summary

7.2. Future Work

REFERENCES

APPENDIX

A LIST OF PUBLICATIONS DURING THE STUDY TOWARDS THE DOCTORAL

DEGREE

–  –  –

1.1. Bandgap Energy Vs. Chemical Bond Length for Compound Semiconductors that Emit in the Visible Range of the Electromagnetic Spectrum.

1.2. Fundamental Lattice Vectors of Basal Plane in Hexagonal Structure.

1.3. The Fields Present in Wurtzite Materials. (A) Spontaneous Fields Due to Natural Charge Separation; (B) Piezoelectric Fields Due to Induce Strain in Material......... 5

1.4. Different Polarities (Ga- And N-Faced) of Wurtzite GaN

1.5. Calculated Phase Diagram for Binary Alloys of GaN And InN, Showing the Binodal (Green Filled Circles), Spinodal (Filled Triangles) Curves, and the Critical

–  –  –

2.1. Schematic Diagrams Showing (a) Compressive Strain State (when as af) and (b) Tensile Strain (when as af), where as and af Are In-Plane Lattice Constant for Substrate and Epitaxial Film.

2.2. Schematic Diagram Showing the Geometry of the Slip System in a Heteropeitaxial Structure.

2.3. Schematic Diagram Illustrating Geometric Consideration for Strain Relaxation Via Glide of Dislocations along Slip Planes in Heteroepitaxy.

2.4. A Segement of Misfit Dislocation Is Generated with the Help of Pre-Existing Threading Dislocaiton Bending to the Film/Substrate Interface when Film Thickness h hc.

–  –  –

2.5. A Dislocation Half Loop Nucleates at the Growth Surface and Glides Down along the {111} Slip Planes to Form a Segment of Misfit Dislocation along with Two Threading Arm.

2.6. Hexagonal Slip Systems. Slip Plane and Slip Directions Are Indicated..................26

–  –  –

is Weaker than the (0002) Diffraction Spots. This Can Be Understood as the Result of Double Diffraction.

3.3. Bright-Field Image (Left) And Dark-Field Image of GaN at the Same Region.......34

3.4. Comparison of BF Image and g/3g Dark-Field Image.

–  –  –

3.7. Configuration of Detectors for ADF and ABF Imaging in a TEM (JEMARM200F)...

3.8. TEM Cross-Section Sample Preparation Procedures.

4.1. Cross-Section TEM Bright-Field Images of the In0.22Ga0.78N Epilayer, Taken along

–  –  –

Satellite Peaks, Indicating Presence of Stacking Faults along the Growth Direction.

Enlargement in the Lower Right Corresponds to a Higher-Order Diffraction Spot Showing Separation of GaN and InGaN Diffraction Spots.

4.3. High-Resolution Electron Micrographs Showing the Atomic Stacking Sequence in the In0.22Ga0.

78N Epilayer. (a) Overall Structure of the In0.22Ga0.78N Film. (b) Cubic Regions in the GaN Capping Layer. (c) Region near the GaN Underlayer with High Density Of BSFs.

4.4. High-Resolution Electron Micrographs Showing the In0.22Ga0.78N/GaN Interface. A Schematic Representation below Shows the Initial Growth of the In0.22Ga0.78N Layer. The Horizontal Lines Represent Stacking Faults Formed during Growth... 52

–  –  –

The Vertical Lines in the Schematic Representation below Are Domain Boundaries.

Notice that the Patterns at the Interface Are also Observed at the top Surface....... 53

4.6. Composition Determination for the InxGa1-xN Film with x ~ 0.60 using: (a) XRD  Scan And (b) RBS Spectrum. Red Lines Represent Corresponding Simulations.

4.7. (a) X-Ray Rocking Curve for the (002) GaN Peak. The Green and Red Gaussian Curves with A FWHM of 6.15 and 13.07 arcmin Correspond to the GaN Underlayer and The GaN Capping Layer. (b) X-Ray Rocking Curve for (002)

–  –  –

Spots

4.9. Photoluminescence Spectrum at 10 K for the In0.60Ga0.40N Film.

4.10. Indium Composition Determination for the In0.67Ga0.33N Film by XRD  Scan.

4.11. Crystal Structure Characteristics of the In0.67Ga0.33N Film. (a) X-ray rocking Curve for GaN: The GaN Underlayer Has a FWHM of 5.8 arcmin (Dashed Gaussian Curve), while the GaN Capping Layer has a FWHM of 11.6 arcmin (Dotted Curve).

(b) X-Ray Rocking Curve Corresponding to the In0.67Ga0.33N Film, with a FWHM of 8.5 arcmin.

4.12. Cross-Section Bright-Field TEM Image of In0.67Ga0.33N Film with (a) g

–  –  –

4.15. Photoluminescence Spectra at 10 K for the In0.67Ga0.33N Film. The Dashed Line Has Been Obtained by Removing the Thickness Interference Produced by the 4m-thick GaN Underlayer.

4.16. Critical Thickness vs. Indium Content x for the InxGa1-xN/GaN System Using Three Different Models. The Critical Thickness of One Lattice Period c (Horizontal Dotted Line) Happens at x = 0.55.

4.17. Calculated Lattice Mismatch and Misfit Dislocation Separation vs. Indium Composition for the InxGa1-xN/GaN System with x = 0.22, 0.46, 0.60, and 0.67.

Black Dots Are Experimental Data

5.1. Cross-Section TEM Images Depict the Different Dislocation Types Based on Diffraction Condition. The Image on the left, Fig. 5.1(a), (g = 0002) Highlights

–  –  –

InGaN/AlN Interface.

5.4. Cross-Section TEM of In0.84Ga0.16N Epilayers (a) HAADF Image, (b) EDS Profile Taken from Segment Shown in (b)

–  –  –

MoiréFringes Is Observed at InGaN/AlN Interface

5.7. (a) Annular Bright-Field Image of InGaN Epilayer near Surface. CBED Were Taken near the Surface Region. (b) Experimental CBED Disks. (c) Simulated CBED Disks with 40 nm Thickness..

5.8. Cross-Section TEM Bright-Field Image of In0.6Ga0.4N Epilayers with (a) g = 0002, (b) g =.

5.9. Selected-Area Diffraction Patterns and Cross-Section TEM Dark-Field Images of

–  –  –

Diffraction Pattern and Periodic MoiréFringes at the Interface

5.10. High-Resolution HAADF image of In0.6Ga0.4N/AlN Interface at Projection with the Intensity of bottom right AlN Underlayer Enhanced. The Interface Is Smooth with about One Atomic Layer Roughness.

5.11. Z Contrast Imaging of Thick InGaN Layer at (a) Lower Magnification and at (b) Higher Magnification of the Selected Squared Region.

–  –  –

Overall Structure of InGaN film. Horizontal Striations May Be due to Indium Segregated Layers.

–  –  –

5.15. Cross-Section TEM Bright-Field Image of InGaN Epilayers with (a) g = 0002, (b) g =. High Density of Defects Is Observed in the Epilayer.

5.16. Critical Thickness vs. Indium Content x for the InxGa1-xN/AlN System Using Three Different Models. The Critical Thickness of One Lattice Period c (Horizontal Dotted Line) Happens at x = 0.45.



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