High-efficiency low-cost LEDs
Submitting InstitutionUniversity of Cambridge
Unit of AssessmentElectrical and Electronic Engineering, Metallurgy and Materials
Summary Impact TypeTechnological
Research Subject Area(s)
Physical Sciences: Atomic, Molecular, Nuclear, Particle and Plasma Physics, Other Physical Sciences
Engineering: Materials Engineering
Summary of the impact
Research on the growth of gallium nitride (GaN) light-emitting diode
(LED) structures has led to the creation of two spin-out businesses
(subsequently sold), has assisted Forge Europa Ltd in expanding
its sales of LED-lighting products, has helped AIXTRON to achieve
sales of related GaN-growth equipment [text removed for publication],
& has enabled Plessey Semiconductors Ltd to manufacture the
world's first commercially available LEDs on 6-inch Si (& the first
LEDs to be manufactured in the UK).
Sir Colin Humphreys, Professor in the Dept of Materials
Science & Metallurgy (DMSM) at the University of Cambridge (UCAM)
since 1990, has a long record of research (grants listed in Section
3) on GaN LEDs, in which the light-emitting layers are quantum wells (QWs)
of InGaN sandwiched between GaN barriers. The QWs emit blue light & a
covering phosphor converts this to white. Bright emission is obtained for
dislocation densities as high as 109 cm-2, while for
all other light-emitting semiconductors the dislocation density has to be
less than 103 cm-2, or dislocations, as
non-radiative recombination centres, quench light emission. It was thought
that nm-sized In-rich clusters in the QWs localized the carriers
(electrons & holes) & prevented them from diffusing to the
dislocations. Such clusters, observed in electron microscopy, were shown
by Humphreys' group to be an artefact of electron-beam damage ,
changing the accepted understanding of why GaN LEDs are so efficient with
high dislocation densities, & underpinning the group's subsequent work
on high-efficiency GaN LEDs.
In collaboration with Manchester University (performing optical studies),
Humphreys' group showed that carriers in the InGaN quantum wells are
localized within a few nanometres, & suggested a localization
mechanism : monolayer-height QW thickness fluctuations, which the group
observed in high-resolution electron microscopy in device structures grown
Although the efficiency of GaN LEDs is not highly sensitive to the
dislocation density, the efficiency is reduced if the dislocation density
is very high. To study this, Humphreys' group invented a novel, fast
method for assessing dislocation densities in GaN , followed by a
breakthrough  on how to reduce the dislocation density of GaN grown on
sapphire, using porous silicon nitride interlayers. The group was able to
transfer this method to growth of GaN LEDs on 6-inch Si substrates — very
difficult, compared to growth on smaller-diameter sapphire or SiC
substrates. The large (54%) difference in the thermal expansion
coefficients of GaN & Si leads to wafer bowing on cooling from the
growth temperature (~1000°C); the GaN is in tension & cracks.
Humphreys' group inserted four graded AlGaN layers, carefully tailored so
that their compressive stress compensates the tensile stress upon cooling,
crucially ending with a flat, crack-free LED. The large (17%) lattice
mismatch between GaN & Si would result in an unacceptably high
dislocation density, & Humphreys' group solved this problem using a
sub-monolayer SiN mask with natural holes; epitaxial lateral overgrowth
from these reduces the dislocation density by two orders of magnitude.
To protect know-how, only a little (eg  & a patent pending )
has so far been published on the commercially important processing to
achieve GaN LED growth on 6-inch Si.
Humphreys' group members taking up specialist roles drawing on their
Tim Smeeton (PhD student), 2001-4. Joined Sharp Europe in 2004.
Lixia Zhao (PDRA), 2006-8. Joined Forge Europa in 2008.
Matt Charles (PhD ), 2002-5. Joined AIXTRON in 2007.
Clifford McAleese (PhD student, then PDRA), 2001-9. Joined AIXTRON
Dandan Zhu (PhD then PDRA), 2003-12. Joined Plessey in 2012.
Lewis Liu (PhD student), 2007-11. Joined Plessey in 2012.
David Wallis (PDRA), 2011-12. Joined Plessey in 2012.
Other key researchers in Humphreys' group:
Rachel Oliver (Royal Comm for 1851 Exhibition Fellow, then Royal Society
URF, Univ Lecturer in DMSM, & now Reader in DMSM), 2002-present. Menno
Kappers (Senior Research Associate in DMSM), 2000-present.
References to the research
1*. TM Smeeton, MJ Kappers, JS Barnard, ME Vickers & CJ
Humphreys: Electron-beam-induced strain within InGaN quantum wells: False
indium `cluster' detection in the transmission electron microscope, Applied
Physics Letters 83 (2003) 5419; DOI: 10.1063/1.1636534. [129
citations as of October 2013]
2*. DM Graham, A Soltani-Vala, P Dawson, MJ Godfrey, TM Smeeton,
JS Barnard, MJ Kappers, CJ Humphreys & EJ Thrush: Optical and
microstructural studies of InGaN/GaN single-quantum well structures, Journal
of Applied Physics 97 (2005) 103508; DOI: 10.1063/1.1897070.
3*. RA Oliver, MJ Kappers, J Sumner, R Datta & CJ Humphreys:
Highlighting threading dislocations in MOVPE-grown GaN using an in-situ
treatment with SiH4 and NH3, Journal of Crystal
Growth 289 (2006) 506; DOI: 10.1016/j.jcrysgro.2005.12.075.
4. MJ Kappers, R Datta, RA Oliver, FDG Rayment, ME Vickers & CJ
Humphreys: Threading dislocation reduction in (0001) GaN thin films using
SiN interlayers, Journal of Crystal Growth 300 (2007) 70;
DOI: 10.1016/j.jcrysgro.2006.10.205. [64 citations]
5. D Zhu, C McAleese, KK McLaughlin, M Haeberlin, CO Salcianu, EJ Thrush,
MJ Kappers, WA Phillips, P Lane, DJ Wallis, T Martin, M Astles, S Thomas,
A Pakes, M Heuken & CJ Humphreys, GaN based LEDs grown on 6-inch
diameter Si (111) substrates by MOVPE, in `LEDs: Materials and Devices for
Solid-State Lighting XIII', Proc. SPIE 7231 (2009) 723118;
DOI: 10.1117/12.814919. [9 citations]
6. UK Patent Application Number 1019301.9: "Semiconductor wafer
comprising gallium nitride layer having one or more silicon nitride
interlayers therein", filed 15/11/2010; application now in public domain,
application now in progress to grant. International (PCT) application,
PCT/GB2011/001474, filed 12/10/2011. International searches by European
Patent Office received and citations assessed. Liaising with patent agents
& inventors to best determine in which countries to file under an
International Patent Application.
*references best indicating the quality of the underpinning
research. The distinction of Humphreys' research in this area has
been widely recognised: since 2008, he has been invited to give 10
Plenary, 4 Keynote & 33 Invited talks at international conferences. He
was awarded the Platinum Medal (IOM3) in 2013. He has given 4 named
lectures (Kelly, 2013; Finniston, 2012; Winegard, 2012; Cowley, 2011).
Key Research Grants (all to Humphreys as PI, or as Cambridge PI):
1. "Exploratory proposal to grow and characterise gallium nitride on
silicon", EPSRC, 01/02/2003-30/04/2003, £53,664.
2. "Next generation GaN-based materials", EPSRC, 01/05/2003-30/06/2006,
3. "Materials challenges in GaN-based light emitting structures", EPSRC,
4. "A low-cost manufacturing route for gallium nitride based solid-state
lighting", DTI, 01/04/2007-30/06/2010, £582,665.
5. "Nitrides for the 21st Century", EPSRC Platform Grant,
6. "Lighting the Future", EPSRC Programme Grant, 01/12/2010-30/11/2015,
£3,166,773 (UCAM part of a total of £6.3M shared with Bath, Manchester
Details of the impact
The research of the Humphreys' group has had impact on three companies: Forge
Europa Ltd, AIXTRON Ltd and Plessey Semiconductors Ltd.
The impact on Forge Europa has been from the Humphreys' group
research on LED reliability, & it was highlighted in the EPSRC Annual
Report 2010-2011  under the heading "Economic Success for Gallium
Nitride LEDs": "Professor Sir Colin Humphreys and his team at Cambridge
University... have delivered positive outcomes for businesses in the
lighting industry... For example, Forge Europa, an SME in Cumbria...
received the Queens Award for Innovation in 2009. Its Managing Director
Peter Barton writes, `The excellent work of the Cambridge group has
proved to be of great benefit to Forge Europa and assisted our business
to grow by over 100% in a 3-year period... A great deal of our knowledge
is directly attributed to our links with Cambridge.'..." Of the
impact on AIXTRON, its Managing Director, Tony Pearce (in October
2013), writes "Our collaboration with Professor Humphreys' group in
Cambridge has been hugely valuable to AIXTRON. The research carried out
by the Cambridge group not only advances understanding of the material
technology, but helps us build deposition systems to meet these demands.
AIXTRON remains in a dominant position, with significant revenues
generated by this technology of [text removed for publication]. Furthermore,
AIXTRON continues to develop next-generation products that will serve
the future semiconductor material challenges, and our collaboration with
the team at the University of Cambridge will continue to help us steer
Humphreys & two colleagues (Dandan Zhu & Lewis Liu) set up
spin-offs to exploit their research, CamGaN in 2010 & Intellec
in 2011, to which UCAM transferred the patent noted in Sections 2 & 3,
that provides a framework for a considerable amount of know-how that was
deliberately not patented. The patent & know-how provide a method for
growing low-cost high-efficiency GaN LEDs on 6-inch Si. Plessey
acquired CamGaN & Intellec in February 2012 for [text
removed for publication] & hired Zhu & Liu (Fig. 1), & another
Humphreys group member, David Wallis. Plessey raised funds to permit this
acquisition of patent & know-how, to purchase a commercial-scale GaN
growth reactor from AIXTRON & other equipment, & to revive
a mothballed 6-inch Si processing line in its factory in Plymouth. Zhu
& Wallis successfully transferred the UCAM recipe for growing GaN LED
structures to the new reactor at Plessey in December 2012. This
has enabled Plessey to sustain ~12 manufacturing jobs, & it is
currently in the process of hiring additional staff to support the
production of GaN LEDs on 6-inch Si. Plessey is addressing a
global market: this is a clear indication of the cost savings the UCAM
technology brings. The LEDs are already on the market (Fig. 2; product
data sheet at: [www.plesseysemiconductors.com/doc/?id=292040]).
Sales of [text removed for publication]. Until now, all the LEDs in the UK
are manufactured in China or Taiwan. Plessey has recently raised
additional funding to purchase nine more commercial-size GaN growth
The impact of Humphreys' group research on Plessey has been
highlighted in: Inside: Technology ; The Economist ;
& Ingenia . The Economist  states: "Plessey's
other big venture is light-emitting diodes (LEDs) for lighting homes and
offices... Plessey is up against mighty competitors like GE, Philips,
Samsung and Siemens. Mr LeGoff (Managing Director, Plessey) says Plessey
has an edge. It can make LED lights at a fraction of the cost of rivals,
thanks to a unique process developed at Cambridge University."
David Willetts, the Universities & Science Minister, writes in Eight
Great Technologies : "The team led by Professor Sir Colin
Humphreys at Cambridge has developed a new cost-effective way of growing
gallium nitride on silicon, which in turn increases the cost effectiveness
and energy efficiency of LED lighting. Since lighting accounts for today
20% of all electricity generated in the UK, widespread adoption of LED
lighting would reduce electricity consumption by 10-15%. And moreover,
these are being manufactured in the UK (using the technology) by Plessey.
Plessey acquired this technology in 2012 and plan to produce 500 million
LEDs a year in Plymouth — the first manufacturer of LEDs in the UK".
Electronics Weekly  states: "Plessey got into white LEDs by
buying University of Cambridge GaN-on-Si spin-out CamGaN... this
is the first production of GaN-on-Si LEDs from any company, and Plessey
has gone from never having made an LED to manufacturing with this advanced
technology in 15 months."
The research of the Humphreys' group has revolutionized the
manufacturing of low-cost high-efficiency LEDs and we expect that the
impact of this work will continue to grow.
Main types of impact
Economic — Performance of existing business improved
through new products & processes (Plessey, establishing the
UK's first manufacture of LEDs); Spin-out business created (CamGaN
& Intellec, now bought by Plessey with financial benefit for
UCAM & the inventors); Business sector adopted new or
significantly changed technology or process (AIXTRON, market
leader through innovation in GaN-growth technologies); Performance
improved through highly skilled people taking up specialist roles that
draw on their research (members of Humphreys' group joining AIXTRON,
Forge Europa and Plessey).
Society — Research has contributed to community regeneration
(Forge Europa investment, creating jobs in Cumbria; Plessey
investment, sustaining & creating jobs in Devon).
Environment — Improved through introduction of new products or
processes (much broader use of LED lighting will significantly
reduce electricity consumption & CO2 emissions).
Sources to corroborate the impact
AIXTRON (headquartered at Herzogenrath, Germany) — claims
about the impact on this company can be verified by the Managing Director
at AIXTRON Ltd, Swavesey, Cambridgeshire (see also http://www.aixtron.com/en/home/).
Forge Europa Ltd — claims about the impact on this company
can be verified by its Managing Director (see also http://www.forge-europa.co.uk/).
Plessey Semiconductors Ltd — claims about the impact on
this company can be verified by its CEO (see also http://www.plesseysemiconductors.com/index.php).
EPSRC Annual Report 2010-2011, p. 20
Inside:Technology, journal of The Technology Partnership: 3
linked articles in Issue 8
- "Chips with everything" The Economist, 13 October 2012
- "Changing Lightbulbs" by Richard Stevenson, in the journal of The
Royal Academy of Engg: Ingenia, iss 54, March 2013 (http://www.ingenia.org.uk/ingenia/articles.aspx?index=820).
- David Willetts, Eight Great Technologies, Policy Exchange,
Electronics Weekly, 8 April 2013 (http://www.electronicsweekly.com/news/components/led-lighting/plessey-gan-on-silicon-led-sampling-2013-04/).
- More media linked articles in (http://www.gan.msm.cam.ac.uk/media/).