Colin Humphreys

Department of Materials

University of Cambridge, UK

Lighting, power electronics, communications and health

New Technologies for off-grid villages – a look ahead Cambridge Workshop, Moller Centre, 15 January 2014

Gallium nitride (GaN) and off-grid villages

• GaN is a new manmade material.

• Important for off-grid:

• Low-energy lighting (now + next 10 years)

• Health: water purification (2-10 years)

• Low-energy power electronics (3-10 years)

• Communications (3-10 years)

• Also for super-efficient solar cells (5-10 years)

Main light-emitting semiconductors

How to make white light

US DoE Report

• By 2025 Solid-State Lighting using GaN-based

LEDs could reduce the global amount of

electricity used for lighting by 50%

• No other consumer of electricity has such a

large energy-savings potential as LED lighting

LEDs

• Light emitting diodes (d)

• Made from solids (e.g. GaN) that emit light

• LEDs last 100,000 hours (electronics 50,000)

• Light bulbs (incandescent) last 1,000 hours

• LEDs fail by slow intensity decrease

• Light bulbs fail totally and suddenly

Efficiency of light sources

Incandescent light bulb = 5% (15 lm/W)

Fluorescent tube (long) = 25% (80 lm/W)

Fluorescent lamp (CFL) = 20% (60 lm/W)

White LEDs (350 mA) = 30% (100 lm/W)

White LEDs (in lab) = 60% (200 lm/W)

Sodium lamp (high P) = 40% (130 lm/W)

Lighting in the Developing World

• White LED + solar cell + battery

• Off-grid -- No electricity costs

• Light to study when it is dark

• Light to work when it is dark

• Help people get out of poverty

• Take care with choice of LED – no standards yet

Off-grid lighting

• GaN LEDs have been available for several years

for off-grid lighting (+ solar panel + battery)

• LEDs recently become so efficient can be used

for off-grid street lighting (+ solar + battery)

• LED efficiency will continue to increase for next

10 years

What is preventing widespread use of

LED lighting in developing countries

• Problem: Cost

• Low-power LEDs cheap: a few pence

• High-power LEDs for lighting: expensive

• Philips 60 W equivalent LED costs £15

Solving the GaN LED cost problem

• All commercial GaN LEDs grown on small-diameter (2”, 3”, 4”) sapphire or SiC wafers

• Reduce costs: grow on large-diameter Si wafers

• Will substantially reduce cost of LEDs

• Will enable LED lighting in homes and offices

• In UK, save £2 billion pa electricity costs

• Close (or not build) 8 large power stations

• My group (Dandan Zhu) pioneered growth of GaN LEDs on 6-inch Silicon

Why grow GaN on 6-inch Si?

• Compatibility with Si processing techniques using a Si foundry

– Should give improved automation and yield

– Compare with “hand” processing with sapphire

• Cost substrates (6” Si costs 30x < sapphire)

• Growing on 6”, 8” and larger substrates will offer increasing cost reductions

• Ease of removal of Si substrate

• Lower cost LEDs and other devices

Commercial Exploitation

• My group set up CamGaN (2010) and Intellec (2011) to exploit Cambridge GaN on 6” Si LEDs

• Plessey acquired both companies in February 2012. Hired 3 post-docs from my group

• Plessey is now manufacturing low-cost GaN on 6” Si LEDs at their factory in Plymouth, UK (d)

• The first manufacture of LEDs in the UK

• First order: 20 million LEDs from China

• Will enable widespread GaN LED lighting

Plessey exhibit with Lewis Liu, Barry Dennington and Vince Cable

Lack of Drinkable Water

• Over half of the hospital beds in the developing world are occupied by people with water related diseases (BMJ)

• 3 million die each year from impure water (WHO)

– Mainly Africa, India

• Probably more people will die this century from the lack of drinking water than from any other cause

A Scientific Approach to Purifying Water

• Need to destroy bacteria, viruses, mosquito larvae, etc., in water

• Preferably without chemicals

– Giardia resistant to chlorine

– Chlorine reacts with organic acids in soil to produce carcinogens

• Earth’s atmosphere completely blocks deep-UV radiation from the Sun

• Biological organisms on Earth never developed a tolerance for deep-UV radiation

Effects of Deep-UV Radiation

• Deep-UV radiation damages nucleic acids in

DNA, RNA

• Bacteria, viruses, unicellular organisms,

cannot reproduce

• Fungi, mosquito larvae, etc., killed

• Deep-UV radiation purifies water

• WHO states that UV light is best treatment to

purify water

Deep-UV for water purification

• Mercury (Hg) vapour lamp used today.

– Emits 254 nm deep-UV

– Purifies water

– Needs high voltage supply, hence grid electricity

• UV LED AlGaN-based

– Wavelength flexible

– 280 nm the best: kills every micro-organism

– Power off-grid with solar + battery

– Point-of-use the best treatment (WHO)

AlGaN LEDs for Water Purification

• Emission at 280 nm achievable now

• BUT efficiency is too low to purify flowing water

• More research required: 2-10 years timescale

• Needs specific research funding

• If we can achieve we will help to solve the major problem in the developing world and save millions of lives

GaN power electronics

• Power electronic devices in power supplies for mobile phones, computers, power inverters for photovoltaics

• GaN has low power consumption for both lighting and electronics: very energy efficient

• GaN power electronics 40% more efficient than Si

• Power electronics: replace Si devices by GaN – grow GaN on large-area Si to reduce the cost

• Enable easier off-grid charging and use of mobile phones, computers, etc., using solar plus batteries

Li-Fi for Wi-Fi in developing world

• Two-thirds of world lacks good Internet access

• Wi-Fi equipment expensive and energy inefficient

• Use light as carrier instead of radio frequencies

• Use LEDs for Wi-Fi, videos, data communication

• Li-Fi in every room in house, office, street lights

• Li-Fi for off-grid low-cost energy-efficient Wi-Fi in developing countries

• Details to be worked out (3-10 years)

InGaN for super-efficient solar cells • Most solar cells made from Si

– Bandgap 1.1 eV -- in the infra-red

– About 20% efficient (theoretical max. ~ 25%)

• Organic solar cells ~ 10% efficient (max)

• Bandgap of InN is 0.7 eV and of GaN is 3.4 eV

– Covers most of the solar spectrum

• Multi-junction InGaN solar cells in theory can

be 80% efficient. Difficult (5-10 years)

How do we get to where we want to be?

• GaN LEDs for lighting

– Important for developed world – it will pay research

– Some extra research needed for optimising LED

design for off-grid power by battery/solar cell?

• UV AlGaN LEDs for water purification

– Research funding needed to accelerate research

• GaN power electronic devices

– Important for developed world – it will pay research

– Extra research needed for optimising for solar power

How do we get there (2)

• Li-Fi using GaN LEDs

– Useful for developed world. It will fund research

– Extra research needed for optimising using solar

• Super-efficient InGaN solar cells

– Difficult long-term project

– Needs specific funding to accelerate progress

What is needed (tentative!) • New Research Centre, or network of Centres,

focussed on specific problems

• Strongly linked to developing countries

• Funded for 10 years

• Go from basic research through to real prototype

devices

• To solve the GaN problems (purifying water, etc)

need, say, £5 m start plus £2 m pa + building

Funding source(s)

• Would the Department for International

Development (DFID) fund this out of its

existing resources?

• Or in partnership with EPSRC, etc?

Conclusions

• The new material GaN has huge potential for

use in developing countries

• Bring light to the world

• Purify water: save millions of lives

• Save energy in charging computers, mobile

phones

• Bring Wi-Fi with LED Lighting (Li-Fi)

• Promises ultra-efficient solar cells