Materials Challenges in GaN-based Light Emitting Structures
Lead Research Organisation:
University of Cambridge
Department Name: Materials Science & Metallurgy
Abstract
Gallium nitride (GaN) is an amazing material that can emit brilliant light. GaN light emitting diodes (LEDs) first became available about ten years ago, and are already used in a wide range of applications, including interior lighting in cars, buses and planes; traffic lights, large full-colour displays and backlighting in mobile phones. GaN blue lasers are about to be sold for next-generation DVD players, in which the DVDs will contain up to ten times the amount of music or pictures as existing DVDs. Looking to the future, GaN may make possible high-quality, high efficiency white lighting which will produce major energy savings. Another exciting development could be high-efficiency deep ultra-violet LEDs for water purification, particularly in the developing world.Unfortunately, we are currently unable to make the high-efficiency white lighting and deep-UV LEDs referred to above because there are some key scientific problems that remain to be solved. To successfully surmount these challenges requires a detailed understanding of the complex processes involved in the fabrication of the light emitting regions of the LED. These consist of thin layers of an alloy called InGaN, which are sandwiched between thicker layers of GaN to make structures called quantum wells. These quantum wells are 50,000 times thinner than a human hair. We must also understand the processes that limit light emission and optimise the electrical conductivity of the many other semiconductor layers in an LED. Following on our highly successful work on GaN of the last five years which has put us into an internationally competitive position, we have put together a team of leading researchers from different universities and industry to attack the critical factors that limit the performance of GaN-based LEDs.One key limitation to our understanding is the reason why GaN blue LEDs emit brilliant light even though they are full of defects called dislocations that should quench the light emission arising from the quantum wells. This is hotly debated and in 2005 two major international conferences had special sessions devoted to discussing this topic. Our theory is that the light-emitting InGaN quantum wells have atomic scale thickness fluctuations on a nanometre lateral scale, and thus the light emission is mainly localised in tiny nanometre-scale regions away from the dislocations. However, this localisation is much weaker for UV LEDs, and so unfortunately dislocations strongly quench the light emission in these devices.A major thrust of our research is to understand how the electrical carriers whose interaction is responsible for the light emission are localised, and kept away from defects which would otherwise quench the light emission, and then to optimise this localisation. This may be achieved by engineering the growth of the quantum wells. To understand the quantum wells we will not only examine the light they emit, but use microscopes that allow us to visualise objects far smaller than the wavelength of light to image detailed, atomic-scale variations within the light emitting regions. Quantum structures made from GaN also have strong internal electric fields which can reduce the light emission. We will use specialist microscopy techniques to measure these fields, and study ways of reducing them.Another focus is to develop new methods of reducing the density of defects in crystals called dislocations. Additionally, we will study the electrical properties of the GaN material which surrounds the quantum wells in an LED, in order to understand what defects prevent electrical conduction and reduce their occurrence. Our research involves crystal growers, electron microscopists, experts in optical and electrical characterisation techniques, theoretical and experimental physicists, chemists, and materials scientists. Only this type of integrated approach can solve the challenging problems in GaN-based technology.
Publications
Watson-Parris D
(2010)
Energy landscape and carrier wave-functions in InGaN/GaN quantum wells
in physica status solidi c
Schulz S
(2010)
Electronic and optical properties of nonpolar a -plane GaN quantum wells
in Physical Review B
Zhu D
(2010)
InGaN/GaN LEDs grown on Si(111): dependence of device performance on threading dislocation density and emission wavelength
in physica status solidi c
Badcock T
(2011)
The effect of indium concentration on the optical properties of a -plane InGaN/GaN quantum wells grown on r -plane sapphire substrates
in physica status solidi (a)
Watson-Parris D
(2011)
Carrier localization mechanisms in In x Ga 1 - x N/GaN quantum wells
in Physical Review B
Badcock T
(2011)
The Effect of Dislocation Density and Surface Morphology on the Optical Properties of InGaN/GaN Quantum Wells Grown on r-Plane Sapphire Substrates
in Japanese Journal of Applied Physics
Holec D
(2011)
Towards predictive modeling of near-edge structures in electron energy-loss spectra of AlN-based ternary alloys
in Physical Review B
Moram M
(2011)
The effects of Si doping on dislocation movement and tensile stress in GaN films
in Journal of Applied Physics
Fu W
(2011)
Dislocation Climb in c -Plane AlN Films
in Applied Physics Express
Bennett SE
(2011)
Atom probe tomography and transmission electron microscopy of a Mg-doped AlGaN/GaN superlattice.
in Ultramicroscopy
Amari H
(2011)
Accurate calibration for the quantification of the Al content in AlGaN epitaxial layers by energy-dispersive X-ray spectroscopy in a Transmission Electron Microscope
in Journal of Physics: Conference Series
Badcock T
(2011)
Properties of surface-pit related emission in a -plane InGaN/GaN quantum wells grown on r -plane sapphire
in physica status solidi c
Hao R
(2011)
Defect reduction processes in heteroepitaxial non-polar a-plane GaN films
in Journal of Crystal Growth
Humphreys C
(2011)
Solid-State Lighting
in MRS Bulletin
Bennett S
(2011)
Atom probe tomography assessment of the impact of electron beam exposure on InxGa1-xN/GaN quantum wells
in Applied Physics Letters
Petrov M
(2011)
Strain-induced effects on the electronic structure and N K-edge ELNES of wurtzite A1N and Al x Ga 1- x N
in Journal of Physics: Conference Series
Hammersley S
(2011)
Study of efficiency droop and carrier localisation in an InGaN/GaN quantum well structure
in physica status solidi c
Zhu D
(2011)
Efficiency measurement of GaN-based quantum well and light-emitting diode structures grown on silicon substrates
in Journal of Applied Physics
Zhu T
(2012)
Unintentional doping in GaN.
in Physical chemistry chemical physics : PCCP
Radtke G
(2012)
Structure and chemistry of the Si(111)/AlN interface
in Applied Physics Letters
Chan C
(2013)
Optical studies of the surface effects from the luminescence of single GaN/InGaN nanorod light emitting diodes fabricated on a wafer scale
in Applied Physics Letters
Meneghini M
(2013)
Electroluminescence Analysis and Simulation of the Effects of Injection and Temperature on Carrier Distribution in InGaN-Based Light-Emitting Diodes with Color-Coded Quantum Wells
in Japanese Journal of Applied Physics
Oliver R
(2013)
High resolution transmission electron microscopy and three-dimensional atom probe microscopy as complementary techniques for the high spatial resolution analysis of GaN based quantum well systems
in Materials Science and Technology
Davies M
(2014)
High excitation density recombination dynamics in InGaN/GaN quantum well structures in the droop regime
in physica status solidi c
Davies M
(2014)
Effects of an InGaN prelayer on the properties of InGaN/GaN quantum well structures
in physica status solidi c
Sutherland D
(2014)
An investigation into defect reduction techniques for growth of non-polar GaN on sapphire
in physica status solidi c
Rodenburg C
(2014)
Helium ion microscopy and energy selective scanning electron microscopy - two advanced microscopy techniques with complementary applications
in Journal of Physics: Conference Series
Davies M
(2014)
The effects of varying threading dislocation density on the optical properties of InGaN/GaN quantum wells
in physica status solidi c
Naresh-Kumar G
(2014)
Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN.
in Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
Han Y
(2015)
Toward defect-free semi-polar GaN templates on pre-structured sapphire
in physica status solidi (b)
Caliebe M
(2015)
Growth and coalescence studies of oriented GaN on pre-structured sapphire substrates using marker layers
in physica status solidi (b)
Han Y
(2015)
Origin of faceted surface hillocks on semi-polar ( 1 1 2 ¯ 2 ) GaN templates grown on pre-structured sapphire
in Journal of Crystal Growth
Kakanakova-Georgieva A
(2016)
n-Type conductivity bound by the growth temperature: the case of Al 0.72 Ga 0.28 N highly doped by silicon
in Journal of Materials Chemistry C
Schulz S
(2016)
Theoretical and experimental analysis of the photoluminescence and photoluminescence excitation spectroscopy spectra of m -plane InGaN/GaN quantum wells
in Applied Physics Letters
Muhammed MM
(2016)
High-quality III-nitride films on conductive, transparent (2¯01)-oriented ß-Ga2O3 using a GaN buffer layer.
in Scientific reports
Caliebe M
(2016)
Influence of trench period and depth on MOVPE grown ( 11 2 ¯ 2 ) GaN on patterned r-plane sapphire substrates.
in Journal of Crystal Growth
Presa S
(2016)
Combined electrical and resonant optical excitation characterization of multi-quantum well InGaN-based light-emitting diodes
in AIP Advances
Gîrgel I
(2016)
Investigation of indium gallium nitride facet-dependent nonpolar growth rates and composition for core-shell light-emitting diodes
in Journal of Nanophotonics
Pristovsek M
(2016)
Comparative study of (0001) and InGaN based light emitting diodes
in Japanese Journal of Applied Physics
Hibberd M
(2016)
Dielectric response of wurtzite gallium nitride in the terahertz frequency range
in Solid State Communications
Hammersley S
(2016)
Effect of electron blocking layers on the conduction and valence band profiles of InGaN/GaN LEDs
in physica status solidi c
Qian H
(2016)
Characterization of p-GaN 1- x As x /n-GaN PN junction diodes
in Semiconductor Science and Technology
Dunn A
(2016)
Investigating efficiency droop in InGaN/GaN quantum well structures using ultrafast time-resolved terahertz and photoluminescence spectroscopy
in physica status solidi c
Novikov S
(2016)
Molecular beam epitaxy of free-standing bulk wurtzite Al x Ga 1-x N layers using a highly efficient RF plasma source
in physica status solidi c
Dawson P
(2016)
The nature of carrier localisation in polar and nonpolar InGaN/GaN quantum wells
in Journal of Applied Physics
Hocker M
(2016)
Determination of axial and lateral exciton diffusion length in GaN by electron energy dependent cathodoluminescence
in Journal of Applied Physics
Description | We have discovered that GaN LEDs can be grown on large area Silicon substrates. We were the first group in the world to demonstrate fully processed GaN LEDs on a 6-inch Si substrate |
Exploitation Route | They have been taken forward and Plessey is now manufacturing LEDs based on our technology at its factory in Plymouth. This year so far it has made 1.8 million LEDs |
Sectors | Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology |
URL | http://www.gan.msm.cam.ac.uk |
Description | This was a key grant which enabled us to file our first patent for the growth of low-cost GaN LEDs on large area Si substrates and to set up a spin-off company, CamGaN, in 2010. |
First Year Of Impact | 2010 |
Sector | Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology |
Impact Types | Societal,Economic |
Description | EPSRC |
Amount | £6,330,270 (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 | EPSRC |
Amount | £1,447,635 (GBP) |
Funding ID | EP/G042330/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 03/2009 |
End | 10/2012 |
Description | EPSRC |
Amount | £6,330,270 (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 | EPSRC |
Amount | £826,111 (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 | EPSRC |
Amount | £148,698 (GBP) |
Funding ID | TS/G001383/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2008 |
End | 02/2011 |
Description | EPSRC |
Amount | £826,111 (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 | EPSRC |
Amount | £1,447,635 (GBP) |
Funding ID | EP/G042330/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 03/2009 |
End | 10/2012 |
Description | Sharp Laboratories Of Europe Ltd |
Amount | £27,000 (GBP) |
Funding ID | RG50526 |
Organisation | Sharp Laboratories of Europe Ltd |
Sector | Private |
Country | United Kingdom |
Start | 11/2006 |
End | 09/2010 |
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 | QinetiQ |
Organisation | Qinetiq |
Country | United Kingdom |
Sector | Private |
PI Contribution | We supplied GaN-on-Si LED structures to QinetiQ for processing into devices |
Collaborator Contribution | They processed Cambridge grown device structures. |
Impact | Joint publications. A major EU grant. Multi-disciplinary: physics, materials, electronics. |
Description | Thomas Swan Scientific Equipment Ltd |
Organisation | Thomas Swan and Co Ltd |
Country | United Kingdom |
Sector | Private |
Start Year | 2006 |
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 |