LED Lighting for the 21st Century

Lead Research Organisation: University of Cambridge
Department Name: Materials Science & Metallurgy

Abstract

A major factor preventing the acceptance of LED lighting in our homes and offices is cost. The Cambridge part of this proposal focuses on reducing the cost by growing LED structures on silicon substrates which are much deeper than the sapphire substrates normally used. Our industrial partner, PhotonStar LED, plans to use ultra-thin flip-chip LEDs, which means that the substrate has to be removed. A major challenge is for Cambridge to incorporate a novel interlayer in the growth process which facilitates the removal of the substrate.Initially Cambridge will use sapphire substrates to test our ideas for interlayers. For example, it is proposed to grow n-GaN on sapphire, followed by an AlGaN interlayer, followed by further growth of n-GaN, and then multi-quantum-wells of InGaN/GaN. The plan is for the AlGaN interlayer to facilitate the removal of the sapphire substrate plus some of the n-GaN.Having developed a suitable interlayer for growth on sapphire we will then move to growth on silicon with an interlayer. Possible candidates are AlN or SiN. Because of the higher dislocation densities in growth on silicon we will need to introduce additional interlayers of other materials to reduce the dislocation density. We will then deliver to PhotonStar LED an ultra-thin, low-cost, GaN LED structure emitting at 450 nm.

Publications

10 25 50

publication icon
Jiang B (2010) Combined structure-factor phase measurement and theoretical calculations for mapping of chemical bonds in GaN. in Acta crystallographica. Section A, Foundations of crystallography

publication icon
Massabuau F (2017) Carrier localization in the vicinity of dislocations in InGaN in Journal of Applied Physics

 
Description A major factor preventing the acceptance of LED lighting in our homes and offices is cost. Hence we focused on reducing the cost by growing LED structures on silicon substrates which are much cheaper than the sapphire substrates normally used. Our industrial partner, PhotonStar LED, planned to use ultra-thin flip-chip LEDs, which means that the substrate had to be removed. A major challenge was for us to incorporate a novel interlayer in the growth process which facilitated the removal of the substrate.

Initially we used sapphire substrates to test our ideas for interlayers. For example, it was proposed to grow n-GaN on sapphire, followed by an AlGaN interlayer, followed by further growth of n-GaN, and then multi-quantum-wells of InGaN/GaN. The plan was for the AlGaN interlayer to facilitate the removal of the sapphire substrate plus some of the n-GaN. This was successful.

Having developed a suitable interlayer for growth on sapphire we then moved to growth on silicon with an interlayer. Possible candidates were AlN or SiN. Because of the higher dislocation densities in growth on silicon we needed to introduce additional interlayers of other materials to reduce the dislocation density. We delivered to PhotonStar LED an ultra-thin, low-cost, GaN LED structure emitting at 450 nm.

The above was successful. In particular we developed suitable interlayers for growth on both sapphire and silicon substrates and then for removal of these substrates. We also developed additional interlayers of other materials (SiN and AlN) to reduce the dislocation density. The work in this project also contributed towards the filing of a patent on dislocation reduction in GaN LEDs on Silicon.
Exploitation Route The fiondings were taked forward and pur to use by PhotonStar LED. When we started this project in 2008, PhotonStar LED had 5 employees, 3 part-time. When this project ended, in 2010, it had over 90 employees. We do not claim credit for all of this! However, it is consistent with our successful project.
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology

URL http://www.gan.msm.cam.ac.uk
 
Description A major factor preventing the acceptance of LED lighting in our homes and offices is cost. Hence we focused on reducing the cost by growing LED structures on silicon substrates which are much cheaper than the sapphire substrates normally used. Our industrial partner, PhotonStar LED, planned to use ultra-thin flip-chip LEDs, which means that the substrate had to be removed. A major challenge was for us to incorporate a novel interlayer in the growth process which facilitated the removal of the substrate. Initially we used sapphire substrates to test our ideas for interlayers. For example, it was proposed to grow n-GaN on sapphire, followed by an AlGaN interlayer, followed by further growth of n-GaN, and then multi-quantum-wells of InGaN/GaN. The plan was for the AlGaN interlayer to facilitate the removal of the sapphire substrate plus some of the n-GaN. This was successful. Having developed a suitable interlayer for growth on sapphire we then moved to growth on silicon with an interlayer. Possible candidates were AlN or SiN. Because of the higher dislocation densities in growth on silicon we needed to introduce additional interlayers of other materials to reduce the dislocation density. We delivered to PhotonStar LED an ultra-thin, low-cost, GaN LED structure emitting at 450 nm. The above was successful. In particular we developed suitable interlayers for growth on both sapphire and silicon substrates and then for removal of these substrates. We also developed additional interlayers of other materials (SiN and AlN) to reduce the dislocation density. The work in this project also contributed towards the filing of a patent on dislocation reduction in GaN LEDs on Silicon.
First Year Of Impact 2010
Sector Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Societal,Economic

 
Description Science Policy (Round Table meetings at No. 10 and BIS)
Geographic Reach National 
Policy Influence Type Participation in advisory committee
Impact Increased funding for materials research has resulted. This will have economic impacts and on the quality of life
 
Description Nitrides for the 21st century (Platform Grant)
Amount £826,500 (GBP)
Funding ID EP/H019324/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2009 
End 10/2014
 
Description Programme Grant: Lighting the Future
Amount £6,361,650 (GBP)
Funding ID EP/I012591/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2010 
End 11/2015
 
Description Aixtron 
Organisation Aixtron Limited
Country United Kingdom 
Sector Private 
PI Contribution We grew world class GaN device structures on our Aixtron reactor(s), thus increasing Aixtron sales.
Collaborator Contribution They donated to us a senior scientist for 25% of his time. They provided free servicing and maintenance of our growth reactor.
Impact Increased sales of Aixtron growth reactors.
 
Description Forge Europa (International Headquarters 
Organisation Forge Europa
Country United Kingdom 
Sector Private 
PI Contribution Expertise. Solving a major problem with the reliability of some Forge Europa LEDs
Collaborator Contribution Advice. Testing. Market forecasts.
Impact Improved reliability and lifetimes of Forge Europa LED based products.
 
Description PhotonStar LED 
Organisation PhotonStar LED
Country United Kingdom 
Sector Private 
PI Contribution This was a jointly funded project by the TSB and the EPSRC, with the EPSRC funding the Cambridge University part of the project and the TSB funding PhotonStar LED. We optimized GaN epitaxial growth on both sapphire and silicon using novel interlayers that enable rapid removal of the sapphire or silicon substrate. We also developed dislocation reduction techniques. This research was successful and we supplied ultra-thin device structures to PhotonStar LED
Collaborator Contribution The main contribution was the staff time of Dr Majd Zoorob, the CTO of PhotonStar LED. He spend a lot of time working with us. This was valuable to us and we learned a lot from him. Photon Star were a partner in a 2016 application (unsuccessful) for a manufacturing hub in GaN.
Impact We produced ultra-thin flip-chip LEDs using novel interlayers. Multi-disciplinary: Materials science, physics, chemistry, electronics
Start Year 2008
 
Title GaN on Si device substrate with GaN layer including sub-10nm SiNx interlayers that promote crystal growth with reduced threading dislocations 
Description The present invention relates to a semiconductor material and the use of a semiconductor material in wafer form as a support for forming a light emitting diode (LED) or other optoelectronic device. Further, the present invention relates to a method of constructing high quality optoelectronic devices using the wafer. In particular, the present invention relates to an improved LED having a silicon substrate that minimises the dislocation-defects that occur when larger support wafers are used. A gallium nitride (GaN) semiconductor substrate for grown of nitride semiconductor devices comprises an underlying wafer that carries a first GaN layer that has one or more very thin silicon nitride SiNx inter-layers therein. These Si N x inter-layer(s) are 0.5nm to 10nm thick and the GaN penetrates through one or more portions of the inter-layer preferably to form discrete crystalline structures (3D GaN). Preferably these crystalline structures help reduce threading dislocations when the GaN layer is grown, by MOVPE for example. Additionally, below the GaN layer, an aluminium nitride AlN nucleation layer may lie on the underlying wafer with an aluminium gallium nitride AlGaN buffer layer above the AlN and below the GaN layer. The underlying wafer may be silicon Si.; The AlGaN layer may have a graded alloy content so the amount of aluminium decreases from the Si wafer towards the GaN layer. The GaN layer may be undoped and a second, doped, GaN layer may be formed on top, the dopant concentration of Si or Ge increasing with increasing distance from the first undoped GaN layer. Devices may be formed including MQW structures which may comprise LED or Solar (photovoltaic) devices. The substrate may be from 6 inches (15cm) to 12 inches (30cm) in diameter. 
IP Reference WO2012066269 
Protection Patent granted
Year Protection Granted 2010
Licensed Yes
Impact This patent was transferred to a Cambridge spin-out, CamGaN Ltd, for commercial exploitation of the technology described in the patent. CamGaN was later acquired by Plessey semiconductors in 2012. A portfolio of products based on the CamGaN technology has been launched by Plessey and has generated positive market feedback.
 
Description BBC Breakfast TV and BBC Radio "You and Yours" 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interview of Prof Humphreys on BBC Breakfast TV, and on the BBC Radio "You and Yours" on low-cost LEDS sparked a lot of discussions

Increased public awareness of LEDs
Year(s) Of Engagement Activity 2009
 
Description Big Bang Fair (London) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Schools
Results and Impact Encouraged school pupils to study science

Schools reported increased interest in science and increased numbers studying science
Year(s) Of Engagement Activity 2013,2014
 
Description Chelterham Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Schools
Results and Impact More school pupils studying science

Schools reported greater interest in science.
Year(s) Of Engagement Activity 2013,2014