High-efficiency green light-emitting diodes P46671-1 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

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!

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

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.), 2019.02- expertised on device optical characterization

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Why green InGaN/GaN light-emitting diodes?

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

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!

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!

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!

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.

Emission by InGaN/GaN pyramidal quantum structures

Crystal growth of InGaN/GaN pyramidal quantum structures

Advantages of InGaN/GaN pyramidal quantum structures

Photoluminescence of InGaN/GaN pyramidal quantum structures

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

Fabrication of LEDs: crystal growth

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

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

Characterization of LEDs: I-V properties

Characterization of LEDs: emission properties

Characterization of LEDs: micro-LEDs behaviors

Characterization of LEDs: emission by quantum dots

Characterization of LEDs: emission polarization

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