1. GaN based blue LED Joonas Leppänen Emma Kiljo Jussi Taskinen
Niklas Heikkilä
Alexander Permogorov
Photonics
School of Electrical Engineering
Group 3
LED

2. Content Introduction Theoretical Background Manufacturing Applications
Future Prospects
Conclusions
Photonics
Group 3: LED

3. Introduction First LEDs from late 50’s to early 60’s
Expensive at first, nowadays quite cheap
Green and red LEDs easier to create than blue ones
Higher energy (gap) needed
By combining red, green and blue LEDs, it is possible to create white light
Nobel prize for blue LED in 2014
Phosphorus coating of blue-LED also provides white light
By replacing incandecent lighting with LEDs, energy can be saved
Photonics
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4. Theoretical Background
The operation princible of LED is based on semiconductor pn- junction
Heterojunction structure is a typical structure used in LEDs
Confinement of the charge carriers in active layer
Reduction of reabsorption
Manipulation of bandgaps by alloying compound semiconductors
Photonics
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5. Theoretical Background
The most important materials for blue LEDs are currently GaN based compound semiconductors
Zinc compounds and silicon carbide may also be utilized but they are indirect bandgap semiconductors
GaN is direct band gap semiconductor, which provides better efficiency.
GaN and most substrates have a large lattice mismatch, sapphire is often used as substrate
P-type GaN can be produced by doping with Mg or Zn, and n-type by doping with silicon
Photonics
Group 3: LED

6. Manufacturing On foreign substrate
MOVPE (Metal-Organic Vapour Phase Epitaxy)
Poor quality (TDD = cm-2)
MBE (Molecular Beam Epitaxy)
Better quality (TDD = cm-2)
Pros
Cons
MBE
Control of doping
Slower growth
Good crystalline quality
Expensive
Composition at the monolayer level
Ultra high vacuum required
MOVPE
Poisonous precursor gases
Faster growth ~ 2µm/h
C and H from precursors are incorporated into layers
Easier maintenance
Widely used in industry
Photonics
Group 3: LED

7. Manufacturing Bulk Growth
MOVPE and MBE are not cost effective since they are slow when compared to Czochralski for Si
Quality is not that good due to lattice mismatch and other things related to the growth on top of foreign material
Low luminous flux
Bulk growth of GaN may overcome these issues using GaN seeds which may be grown on foreign substrates
Possibility of higher growth rates for cost effective growth
Photonics
Group 3: LED

8. Manufacturing Bulk Growth
HVPE (Hydride Vapour Phase Epitaxy)
High quality (TDD = cm-2)
Extremely high growth rate (300 µm/h)
Can be used to grow GaN seeds on sapphire or silicon, which can be removed by a lift-off technique after the growth
Seeded growth is possible but requires high quality seed
the quality is seed quality dependent
HVPE-GaN can itself be used as a seed
Wafer bow/bending causes difficulties for larger wafers
Widely used for bulk GaN growth at the moment
Process
FEOL (Front-End of line) process
1000 ◦C
Based on a reaction between GaCl and NH3 to form GaN crystals
GaCl is provided via reaction between solid Ga and HCl
Photonics
Group 3: LED

9. Manufacturing Bulk Growth
Ammonothermal growth
Higher quality (TDD = cm-2)
Difficult to handle safely!
Growth rate only 20 µm/h
No bending or cracking issues
Process
BEOL (Back-End of line) process ◦C
3500 atm pressure
Grown from polycrystalline GaN grains in a supercritical ammonia solution
Can be grown on HVPE seeds but the quality depends on the seed quality
Photonics
Group 3: LED

10. Manufacturing Bulk Growth
Sodium (Na) Flux
Extremely high quality (TDD = cm-2)
High growth rate of 100 µm/h
No cracking
Still on its early stages!
Process
FEOL process
800 ◦C
Grown in Ga-Na melt on top of seed
MOCVD-GaN or HVPE-GaN on sapphire, which can be removed afterwards
Necking technique decreases the TDD even if the seed is poor quality!
Reason behind this are unknown
Photonics
Group 3: LED

11. Why LED chosen Incandescent: 17 lm/W Fluorescent: 90 lm/W
LED: up to 425 lm/W
Photonics
Group 3: LED

12. LED in illumination

13. Blue LED to white light: phosphors
Ce3+:YAG
Excited by LED radiation
Blue + Yellow = White
Highest efficiency – 425 lm/W
Reasonable Color Rendering Index (CRI)

14. Blue LED to white light: color mixing
Efficiency lower than for phosphors – 300 lm/W
Highest CRI
Possibility of color changing

16. Driving Forces of the blue-LED technology
Future Prospects
Driving Forces of the blue-LED technology
US DOE plan that 70 % of public lights will be replaced by LED’s til 2030
Pressure to lower price and increasing efficiency and lumens.
Photonics
Group 3: LED

17. Conclusions First LEDs in the 60’s Blue LEDs enabled white light
Current manufacturing methods can be used
A need for better quality and more cost-effective wafers
Bulk growth may be the answer
HVPE+MOVPE-seed is currently used but the TDD must be decreased
Na-flux seems most promising in the future but size must be increased
Superior lumen per watt production
Major possibilities for energy saving
Photonics
Group 3: LED

18. Thanks!
Photonics
Group 3: LED