1. High-efficiency green light-emitting diodes P
High-efficiency green light-emitting diodes
by InGaN/GaN pyramidal structures
Son Phuong Le
The Department of Physics, Chemistry, and Biology IFM
Linköping University, SWEDEN
Stockholm, December 5th 2018

2. Effective lighting by light-emitting-diodes and issues
Light-emitting-diodes (LEDs)
high efficiency, long lifetime…
Lighting by LEDs (by 2020)…
saves more than 50% of lighting energy
( 20 % of today global energy)
 reducing hundreds TWh elec. plants
 reducing 200M tons of CO2/year
S. Nakamura, 2016
J. Jamestad, 2014
White light from LEDs by
 Blue+Yellow
Phosphor coating: 50% light loss
Low color rendering
 Blue+Green+Red
Efficiency drop in green LEDs
To realize the effective lighting, high-efficiency green LEDs are urgently required!

3. InGaN/GaN pyramidal structures and LEDs
p-GaN cap
2 m
InGaN layer
SiC substrate
n-doped GaN
SiNx
n-GaN base
InGaN/GaN pyramidal structures…
 small size: advantageous to relax the strain
 possible for incorporation of high In contents for longer wavelengths emission
 semi-polar facets: effective to reduce the electric field
 possible for increase of emission efficiency by reducing quantum Stark effects
InGaN/GaN pyramidal structures: possible to realize high-efficiency green LEDs…
This project
 high-efficiency: compatible to blue LEDs…
 long wavelength: up to red regime

4. Present progress (after 4 months granted)
1. Development of InGaN/GaN LED structures by hot-wall MOCVD
n-doped GaN
1.11014 cm2
253 /sq
Good
p-doped GaN
1.41013 cm2
75 k/sq OK
2. Development of InGaN/GaN LED devices
Blue-UV for low In content
Green for high In content
under investigation and optimization
3. Employment of new personel
Dr. Kamran Rajabi (Tsinghua Univ.),
expertised on device optical characterization

5. Thank you for your kind attention!

7. Why green InGaN/GaN light-emitting diodes?

8. Lighting technologies
R. Haitz et al., 1999
To realize white-color light,
a combination of red, green, and blue (RGB) light sources are required.
1962 N. Holonyak Jr.
GaAsP red light-emitting diodes (LEDs)
…..
1994 S. Nakamura, H. Amano, and I. Akasaki
GaN blue LEDs

9. Light-emitting diodes
Quantum dots (QDs) offer optical emission…
 narrow spectrum due to quantum confinement
 frequency tunability by size control
 potential for LED applications, providing any colors expected
1994 V. L. Colvin
CdSe QD-LEDs (the first, low efficiency)
2007 P. O. Anikeeva
ITO QD-LEDs with broad emission spectra (RGB)
2015 Y. Yang
QD-LEDs with full range RGB and high efficiency
…..
Advance in QD synthesis and device fabrication improves device efficiency!

10. Green gap of light-emitting diodes
Quantum dots (QDs) offer optical emission…
 narrow spectrum due to quantum confinement
 frequency tunability by size control
 potential for LED applications, providing any colors expected
1994 V. L. Colvin
CdSe QD-LEDs (the first, low efficiency)
2007 P. O. Anikeeva
ITO QD-LEDs with broad emission spectra (RGB)
2015 Y. Yang
QD-LEDs with full range RGB and high efficiency
…..
Advance in QD synthesis and device fabrication improves device efficiency!

11. InGaN/GaN pyramidal quantum structures
Quantum dots (QDs) offer optical emission…
 narrow spectrum due to quantum confinement
 frequency tunability by size control
 potential for LED applications, providing any colors expected
1994 V. L. Colvin
CdSe QD-LEDs (the first, low efficiency)
2007 P. O. Anikeeva
ITO QD-LEDs with broad emission spectra (RGB)
2015 Y. Yang
QD-LEDs with full range RGB and high efficiency
…..
Advance in QD synthesis and device fabrication improves device efficiency!

12. This work: LEDs by InGaN/GaN pyramidal quantum structures
InGaN with energy gap in between 0.7 eV and 3.4 eV
is promising for full visible range LEDs.
InGaN QDs on GaN pyramids should be promisingly applied to LEDs.

13. Emission by InGaN/GaN pyramidal quantum structures

14. Crystal growth of InGaN/GaN pyramidal quantum structures

15. Advantages of InGaN/GaN pyramidal quantum structures

16. Photoluminescence of InGaN/GaN pyramidal quantum structures

17. Development of green light-emitting diodes
by InGaN/GaN pyramidal structures

18. Fabrication of LEDs: crystal growth

19. Fabrication of LEDs: isolation
p-type
n-type
InGaN
substrate
patterning
- Cleaning: acetone, isopropanol, DIW 3 min for each
- S1818: 2000 rpm, 60 s, (doubled), 110 oC in 2 min
- Mesa patterning: 30 sec exposure
- Development: 2 min in developer
p-type
n-type
InGaN
substrate
etching
- ICP etching: Cl2 (50 sccm)+H2(15 sccm),
400/500 W in 90 sec (1.5 min)
- Resist removal: acetone, isopropanol, DIW 3 min for each
- Optical microscopy, profile measurement
p-type
n-type
InGaN
substrate

20. Fabrication LEDs: metallization
p-type
n-type
InGaN
substrate
patterning
- Cleaning: acetone, isopropanol, DIW 3 min for each
- S1818: 2000 rpm, 60 s, (doubled), 110 oC in 2 min
- Mesa patterning: 30 sec exposure
- Development: 2 min in developer
n-type
InGaN
substrate
p-type
Ni/Au for anode, Ti/Al/Ti/AU for cathode
surface treating
- HCl:H2O 1:1 5 min, DIW 3 min
electrode formation
- n-pad: Ti(10 nm)/Au(300 nm) by sputter
- p-pad: Ni(3 nm)/Au(5+300 nm) by evaporator
- Lift-off: acetone 1-2 hr, and 5 min in ultrasonic, DIW
- Optical microscopy
p-type
n-type
InGaN
substrate

21. Characterization of LEDs: I-V properties

22. Characterization of LEDs: emission properties

23. Characterization of LEDs: micro-LEDs behaviors

24. Characterization of LEDs: emission by quantum dots

25. Characterization of LEDs: emission polarization

26. Thank you for your kind attention!