Design of Monolithic White LED with InGaN/GaN/InGaN MQWsShreyas DmelloMaster of Engineering, Electrical Engineering

▪ White light generation

– RGB LED

– High energy + phosphor coating

▪ “White” LEDs have poor Color Rendering

Index

– Green Gap

– Phosphor emission is limiting

▪ Applications favor high luminosity + CRI

– Safety considerations

– Aesthetics

▪ Goal: Want 6000K “White” LED

Problem & Motivation

Source: Westinghouse Lighting CRI-Color Rendering Index

Source: ADV Pulse Cyclops Headlights

▪ Monolithic Device

– MQW Structure

– Blue + Yellow = White!

▪ GaN/InGaN structures

– Wide emission range

– Similar lattice constants (3.54-

InN vs 3.19-GaN)

▪ Band Engineering

– Control barrier height

– Control color temperature!

Device Structure

3

Source: Light Emitting Diodes, E. F. Schubert

▪ Maintains basic LED physics

– High efficiency

– IV curve is standard

▪ Confirms hypothesis

– Barrier height is linked with

carrier filling

– Changing one barrier layer,

changes output emission

Simulation Results

4

5

▪ CIE 1931 Color Space

– Visual representation of spectrum

– Takes into account human eye responses

▪ 6000 K is perfect sunlight

– Actual temperature is opposite

descriptors

– Bluer emission is “cooler”

– Reddish emission is “warmer”

▪ Monolithic structure was close!

– 0% In comp. – cool (8372 K)

– 1% In comp. – neutral (5914 K)

– 2% In comp. – warm (4649 K)

Color Accuracy

6

Source: mat.univie.ac.at –CIE Chromaticity Diagram

▪ Monolithic “White” LED is possible!

– Research groups investing in this tech

– Design constrains limited emission

– Slight blue shift in current design

▪ Pros vs. Cons:

– Pro - No phosphor

– Pro - Single structure

– Con - Costly to manufacture

– Con - Efficiency vs. color balance

▪ LED devices are becoming cheaper

– 50 years prior vs. 50 years to the future

– Manufacturing process improvements

Conclusions

7

Source: White Emission from InGaN MQW on c-planes and nano-pyramid hybrid structures, Kim et al.

Source: LEDinside – LED Price Trends

8