Presentation by Colin Humphreys, Cambridge University, Smart Villages Technology Workshop, Cambridge 14 January 2014 The purpose of the workshop was to bring together leading UK researchers to discuss emerging technologies for the sustainable production and use of energy in rural communities in developing countries, and to take a ‘look ahead’ at scientific developments and technologies that might be influential over the next 10 - 20 years. It was held under the auspices of the ‘smart villages’ initiative, a three - year project to advance sustain able energy provision for development in off - grid villages in Africa, Asia and Latin America.

1. 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

2. 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)

3. Main light-emitting semiconductors

4. How to make white light

5. 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

6. 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

7. 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)

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Plessey exhibit with Lewis Liu, Barry Dennington and Vince Cable

15. 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

16. 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

17. 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

18. 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)

19. 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

20. 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

21. 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)

22. 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)

23. 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

24. 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

25. 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

26. Funding source(s)
• Would the Department for International
Development (DFID) fund this out of its
existing resources?
• Or in partnership with EPSRC, etc?

27. 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