Title Page
Contents
Abstract 14
1. Introduction 16
2. Experimental 24
2.1. Materials 24
2.2. Fabrication of Nano-Dot LED 24
2.3. Fabrication of Electrode 29
2.4. Assembly of Nano-Dot LED on the patterned electrode 32
2.5. Fabrication of Nano-Dot LED EL device 36
3. Result and Discussion 38
3.1. Simulation of Nano-Dot LED displacement on interdigitated electrode 38
3.1.1. Gravity 38
3.1.2. Dielectrophoresis 39
3.1.3. Brownian motion 40
3.1.4. ACEO 41
3.1.5. Displacement simulation graph 42
3.2. Optimization of ACEO assembly condition 45
3.2.1. Frequency 47
3.2.2. Voltage 50
3.2.3. Solvent 53
3.3. Optimization of Nano-Dot LED structure for selective assembly 58
3.3.1. ITO and Shell 58
3.3.2. Shell material variation 64
3.3.3. Aspect ratio variation 67
3.4. Luminescence properties of Nano-Dot LED EL device 71
3.5. Optical characteristics of Nano-Dot LED 74
3.5.1. Temperature-dependent Photoluminescence properties of Nano-Dot LED array in wafer scale 77
3.5.2. PL and CL properties for individually separated Nano-Dot LED 79
4. Conclusion 83
Reference 85
국문초록 87
Table 1. Comparison of Nano-Rod LED and Nano-Dot LED. 21
Table 2. Parameter table using in solvent variation to optimize ACEO assembled condition. It shows dielectric constant and viscosity from PEG 200 to PGMEA. 55
Table 3. Conductivity table of Nano-Dot LED used as material of structure. It shows the conductivity of SiO₂, GaN and ITO. 61
Table 4. Conductivity table of Nano-Dot LED used as material of shell. It shows Conductivity of SiO₂, Al₂O₃ and SiNx.[이미지참조] 65
Figure 1. Images of neutral body and DEP force. When a non-uniform electric field is applied to a particle, If it can be polarization, DEP force can work on... 22
Figure 2. When the dielectric constant of a medium is bigger than the particle's and the conductivity of the particle is bigger than the medium, Re[CM] direction... 22
Figure 3. Illustration of DEP force including ACEO to nDEP according to real part of CM factor. (a) ACEO (b) p-DEP and (c) n-DEP. 23
Figure 4. Illustration of Alternating Current Electroosmosis flow. It shows direction and applied force to the particle when the ACEO power is working. 23
Figure 5. Schematic images of the Dot LED according to fabrication step. (a) On the GaN wafer deposited ITO, SiO₂, and Al were deposited in order. (a)... 26
Figure 6. SEM images of the cross-sectional view of the Dot LED according to the fabrication step. (a) Nano-imprinted using SOG on the wafer deposited ITO,... 27
Figure 7. SEM images of Nano-Dot LED ink ITO / SiO₂ shell structure dispersed in acetone. (a) is magnified to 2,000 and (b) is magnified to 50,000. 28
Figure 8. Schematic fabrication images of electrodes. (a) negative photo resist coated on the substrate, (b) Alignment of mask pattern on PR-coated substrate,... 30
Figure 9. SEM and Optical Microscope images of interdigitated finger-pattern electrode. (a) SEM image of an electrode and (b) OM image of an electrode. 31
Figure 10. Schematic images of the assembly method. (a) Fabricated electrode in Figure 8 using n-PR and lift-off process, (b) Nano-Dot LED ink droplet... 33
Figure 11. Illustration showing how the Nano-Dot LED is aligned when the ACEO force is applied within the solvent. 34
Figure 12. SEM images of Dot classification by contact layer. The n-GaN contact can view the ITO layer, p-GaN contact can view electrochemical etched... 35
Figure 13. Schematic illustration of nano-Dot LED EL device fabrication. (a) is assembly process, (b) Image of Assembled Dot LED, (c) Insulator coating... 37
Figure 14. Illustration of ACEO simulation of a homogeneous GaN sphere particle. 43
Figure 15. Integrated simulation graph when 10 Vpp was applied, electrode spacing 2 μm.[이미지참조] 44
Figure 16. When a DEP force is applied, it shows the hot spot of a DEP force. 46
Figure 17. Counting standard ACEO and DEP force. ACEO is assembled on an electrode, the Dot that falls off the side of the electrode is counted as DEP. 46
Figure 18. Simulation of the ACEO and DEP forces tendency according to frequency increasing. 48
Figure 19. SEM images of Dot LED displacement tendency according to frequency variation (a) 1 Hz, (b) 10 Hz, (c) 100 Hz, (d) 1k Hz, (e) 10k Hz and... 49
Figure 20. Counting of graph of Dot LED according to frequency variation. 49
Figure 21. Applied voltage variation in acetone from 5 Vpp to 40 Vpp. (a) 5 Vpp, (b) 10 Vpp, (c) 20 Vpp and (d) 40 Vpp.[이미지참조] 51
Figure 22. SUM of ACEO force from 5 Vpp to 40 Vpp. According to increase of applied voltage, ACEO MAX value arose.[이미지참조] 51
Figure 23. OM images of Dot LED displacement tendency according to applied voltages (a) 5 Vpp, (b) 10 Vpp, (c) 20 Vpp and (d) 40 Vpp.[이미지참조] 52
Figure 24. Counting of graph of Dot LED according to applied voltages from 5 Vpp to 40 Vpp.[이미지참조] 52
Figure 25. Solvent variation from PEG 200 to PGMEA. (a) PEG 200, (b) EtOH (c) IPA and (d) PGMEA. 56
Figure 26. SUM of ACEO force from PEG to PGMEA. 56
Figure 27. SEM images of Dot LED displacement tendency according to solvent materials. (a) PEG 200, (b) EtOH, (c) Acetone, (d) IPA and (f) PGMEA. 57
Figure 28. Counting of graph of Dot LED according to solvent materials PEG, EtOH, Acetone, IPA and PGMEA. 57
Figure 29. Illustration of various types of Nano-Dot LED. (a) No ITO and No Shell, (b) ITO and No Shell, (c) No ITO and Shell and (d) ITO and Shell structures. 62
Figure 30. SEM images of Dot LED displacement tendency according to Nano-Dot structure variation. (a) No ITO and No Shell, (b) ITO and No Shell,... 63
Figure 31. Counting of graphs of Dot LED according to Nano-Dot structure variation. 63
Figure 32. SEM images of Dot LED displacement tendency according to Nano-Dot shell material variation (a) SiNx, (b) Al₂O₃ and (c) SiO₂.[이미지참조] 66
Figure 33. Counting of graphs of Dot LED according to Nano-Dot shell material variation (a) SiNx (b) Al₂O₃ and (c) SiO₂.[이미지참조] 66
Figure 34. Illustration of various aspect ratio types of Nano-Dot LED (a) 1:1.1 (b) 1:1.4 and (c) 1:1.7. 69
Figure 35. SEM images of Dot LED displacement tendency according to Nano-Dot aspect ratio variation of (a) 1:1.1, (b) 1:1.4 and (c) 1:1.7. 70
Figure 36. Counting of graphs of Dot LED according to Nano-Dot aspect ratio variation (a) 1:1.1, (b) 1:1.4 and (c) 1:1.7. 70
Figure 37. Images of Luminous light applied 10 V to Nano-Dot LED EL device assembled at optimum conditions. 72
Figure 38. (a) Luminescence graph of Nano-Dot LED EL device according to applied voltages. (b) EL intensity of Nano-Dot EL device at 10 V. 73
Figure 39. The graphic images and SEM images of various structures of Nano-Dot LED. (a) no ITO, no SiO₂ shell, (b) ITO, SiO₂ shell, (e) No ITO, SiO₂... 75
Figure 40. TEM images of ITO and SiO₂ shell individual Nano-Dot LED. 76
Figure 41. PL spectrum of Nano-Dot LED array on the wafer-scale according to each structure. (a) No ITO and No Shell, (b) ITO and No Shell, (c) No ITO... 78
Figure 42. PL spectrum of separated individual Nano-Dot LEDs according to each structure. (a) No ITO and No Shell, (b) ITO and No Shell, (c) No ITO and Shell and (d) ITO and Shell, (c) No ITO... 80
Figure 43. CL spectrum and CL images of separated individual Nano-Dot LED according to each structure. (a) No ITO and No Shell, (b) ITO and No Shell,... 81
Figure 44. Comparison of CL intensity of various Nano-Dot LED. 82