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
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
Moram M
(2009)
The Spatial Distribution of Threading Dislocations in Gallium Nitride Films
in Advanced Materials
De?Sousa?Pereira S
(2008)
Controlled Integration of Nanocrystals in Inverted Hexagonal Nano-Pits at the Surface of Light-Emitting Heterostructures
in Advanced Materials
Presa S
(2016)
Combined electrical and resonant optical excitation characterization of multi-quantum well InGaN-based light-emitting diodes
in AIP Advances
Fu W
(2011)
Dislocation Climb in c -Plane AlN Films
in Applied Physics Express
Badcock T
(2007)
Low threshold current density and negative characteristic temperature 1.3µm InAs self-assembled quantum dot lasers
in Applied Physics Letters
Hollander J
(2008)
Improvements in a-plane GaN crystal quality by a two-step growth process
in Applied Physics Letters
Galtrey M
(2007)
Three-dimensional atom probe studies of an InxGa1-xN/GaN multiple quantum well structure: Assessment of possible indium clustering
in Applied Physics Letters
Badcock T
(2008)
Optical properties of GaN/AlGaN quantum wells grown on nonpolar substrates
in Applied Physics Letters
Van Der Laak N
(2007)
Role of gross well-width fluctuations in bright, green-emitting single InGaN/GaN quantum well structures
in Applied Physics Letters
Spencer B
(2016)
Terahertz cyclotron resonance spectroscopy of an AlGaN/GaN heterostructure using a high-field pulsed magnet and an asynchronous optical sampling technique
in Applied Physics Letters
Moram M
(2010)
Dislocation movement in GaN films
in Applied Physics Letters
Jarjour A
(2007)
Cavity-enhanced blue single-photon emission from a single InGaN/GaN quantum dot
in Applied Physics Letters
Moss D
(2009)
Coherent terahertz acoustic vibrations in polar and semipolar gallium nitride-based superlattices
in Applied Physics Letters
Sahonta S
(2009)
Mechanism of compositional modulations in epitaxial InAlN films grown by molecular beam epitaxy
in Applied Physics Letters
Radtke G
(2012)
Structure and chemistry of the Si(111)/AlN interface
in Applied Physics Letters
Rizzi F
(2007)
( In , Ga ) N / Ga N microcavities with double dielectric mirrors fabricated by selective removal of an (Al,In)N sacrificial layer
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
Charash R
(2009)
Carrier distribution in InGaN/GaN tricolor multiple quantum well light emitting diodes
in Applied Physics Letters
Jarjour A
(2008)
Electrically driven single InGaN/GaN quantum dot emission
in Applied Physics Letters
Radtke G
(2010)
Scanning transmission electron microscopy investigation of the Si(111)/AlN interface grown by metalorganic vapor phase epitaxy
in Applied Physics Letters
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
Rossetti M
(2008)
Degradation of InGaN/GaN laser diodes analyzed by microphotoluminescence and microelectroluminescence mappings
in Applied Physics Letters
Moram M
(2007)
Dislocation reduction in gallium nitride films using scandium nitride interlayers
in Applied Physics Letters
Bennett S
(2011)
Atom probe tomography assessment of the impact of electron beam exposure on InxGa1-xN/GaN quantum wells
in Applied Physics Letters
Galtrey M
(2008)
Compositional inhomogeneity of a high-efficiency InxGa1-xN based multiple quantum well ultraviolet emitter studied by three dimensional atom probe
in Applied Physics Letters
Zhang Y
(2007)
Misoriented domains in (0001)-GaN/(111)-Ge grown by molecular beam epitaxy
in Applied Physics Letters
Davies M
(2016)
Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells
in Applied Physics Letters
Johnston C
(2009)
Defect reduction in (112¯2) semipolar GaN grown on m-plane sapphire using ScN interlayers
in Applied Physics Letters
Fraser I
(2007)
Compositional contrast in AlxGa1-xN/GaN heterostructures using scanning spreading resistance microscopy
in Applied Surface Science
Ketteniss N
(2008)
The role of strain in controlling the surface morphology of AlxGa1-xN following in situ treatment with SiH4 and NH3
in Applied Surface Science
Galtrey M.
(2007)
Atom probe provides evidence to question InGaN cluster theory
in Compound Semiconductor
Holec D
(2008)
A theoretical study of ELNES spectra of Al x Ga 1 - x N using Wien2k and Telnes programs
in Computational Materials Science
Kurniawan O
(2010)
A Direct Method for Charge Collection Probability Computation Using the Reciprocity Theorem
in IEEE Transactions on Electron Devices
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
Pristovsek M
(2016)
Comparative study of (0001) and InGaN based light emitting diodes
in Japanese Journal of Applied Physics
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
Sumner J
(2009)
Scanning capacitance microscopy studies of unintentional doping in epitaxial lateral overgrowth GaN
in Journal of Applied Physics
Moram M
(2009)
On the origin of threading dislocations in GaN films
in Journal of Applied Physics
Moram M
(2009)
Understanding x-ray diffraction of nonpolar gallium nitride films
in Journal of Applied Physics
Moram M
(2011)
The effects of Si doping on dislocation movement and tensile stress in GaN films
in Journal of Applied Physics
Van Der Laak N
(2007)
Characterization of InGaN quantum wells with gross fluctuations in width
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
Zhu T
(2010)
Characterization of unintentional doping in nonpolar GaN
in Journal of Applied Physics
Zhao L
(2008)
Degradation of GaN-based quantum well light-emitting diodes
in Journal of Applied Physics
Founta S
(2007)
Anisotropic strain relaxation in a-plane GaN quantum dots
in Journal of Applied Physics
Johnston C
(2009)
Microstructural evolution of nonpolar (11-20) GaN grown on (1-102) sapphire using a 3D-2D method
in Journal of Applied Physics
Dawson P
(2016)
The nature of carrier localisation in polar and nonpolar InGaN/GaN quantum wells
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 | 04/2009 |
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 | 10/2008 |
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 | 04/2009 |
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 |