Optimising GaN light emitting structures on free-standing GaN substrates
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 more than five 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.A major problem with GaN materials and devices is understanding the role of defects called dislocations. GaN devices are normally grown on sapphire or SiC. Because GaN has different atomic spacings from the atoms in sapphire or SiC, a very high number of dislocations are formed when GaN is grown on these materials. Recently free-standing bulk GaN with far fewer dislocations has become available in limited quantities. Because it is very difficult to grow, it is expensive. However, two producers of this material, Samsung Corning and Lumilog, have offered us some of this material free-of-charge, so that we can optimise the growth of GaN light-emitting structures: both blue and green. This is a wonderful opportunity to do this. As far as we are aware, no one in the world has grown green LEDs on GaN substrates. This research will not only produce blue and green LEDs, it will also help us to understand the role of dislocations in GaN LEDs.
Publications
Badcock T
(2012)
Recombination mechanisms in heteroepitaxial non-polar InGaN/GaN quantum wells
in Journal of Applied Physics
Cerezo A
(2007)
Atom probe tomography today
in Materials Today
Costa P
(2006)
Misfit dislocations in In-rich InGaN/GaN quantum well structures
in physica status solidi (a)
Datta R
(2006)
Mechanisms of bending of threading dislocations in MOVPE-grown GaN on (0001) sapphire
in physica status solidi c
De?Sousa?Pereira S
(2008)
Controlled Integration of Nanocrystals in Inverted Hexagonal Nano-Pits at the Surface of Light-Emitting Heterostructures
in Advanced Materials
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
Galtrey M.
(2007)
Atom probe provides evidence to question InGaN cluster theory
in Compound Semiconductor
Graham D
(2007)
High photoluminescence quantum efficiency InGaN multiple quantum well structures emitting at 380nm
in Journal of Applied Physics
Graham D
(2006)
Resonant photoluminescence excitation studies of InGaN/GaN single quantum wells
in physica status solidi c
Graham D
(2006)
The effect of a Mg-doped GaN cap layer on the optical properties of InGaN/AlGaN multiple quantum well structures
in physica status solidi c
Graham D
(2006)
High quantum efficiency InGaN/GaN structures emitting at 540 nm
in physica status solidi c
Holec D
(2007)
Critical thickness calculations for InGaN/GaN
in Journal of Crystal Growth
Hollander J
(2007)
Epitaxial lateral overgrowth of off-basal GaN thin-film growth orientations
in Physica B: Condensed Matter
Humphreys C
(2007)
Does In form In-rich clusters in InGaN quantum wells?
in Philosophical Magazine
Hylton N
(2007)
Excitation energy dependence of the photoluminescence spectrum of an In x Ga 1 - x N / GaN single quantum well structure
in Physical Review B
Kappers M
(2007)
Threading dislocation reduction in (0001) GaN thin films using SiNx interlayers
in Journal of Crystal Growth
Kappers M
(2007)
Growth and characterisation of semi-polar InGaN/GaN MQW structures
in Journal of Crystal Growth
Kappers M
(2007)
Interlayer methods for reducing the dislocation density in gallium nitride
in Physica B: Condensed Matter
Kazemian P
(2007)
Quantitative secondary electron energy filtering in a scanning electron microscope and its applications
in Ultramicroscopy
Moldovan G
(2006)
Temperature current-voltage characterisation of MOCVD grown InGaN/GaN MQW LEDs
in physica status solidi c
Moldovan G
(2006)
Effects of KOH etching on the properties of Ga-polar n-GaN surfaces
in Philosophical Magazine
Moram M
(2007)
Dislocation reduction in gallium nitride films using scandium nitride interlayers
in Applied Physics Letters
Moram M
(2007)
Growth of dislocation-free GaN islands on Si(111) using a scandium nitride buffer layer
in Journal of Crystal Growth
Moram M
(2007)
Accurate experimental determination of the Poisson's ratio of GaN using high-resolution x-ray diffraction
in Journal of Applied Physics
Moram M
(2007)
Growth of low dislocation density GaN using transition metal nitride masking layers
in Journal of Crystal Growth
Oehler F
(2013)
Surface morphology of homoepitaxial c-plane GaN: Hillocks and ridges
in Journal of Crystal Growth
Oliver R
(2008)
The origin and reduction of dislocations in Gallium Nitride
in Journal of Materials Science: Materials in Electronics
Oliver R
(2007)
Intentional and unintentional localization in InGaN
in Philosophical Magazine
Oliver R
(2006)
Highlighting threading dislocations in MOVPE-grown GaN using an in situ treatment with SiH4 and NH3
in Journal of Crystal Growth
Oliver R
(2007)
Materials challenges for devices based on single, self-assembled InGaN quantum dots
in Journal of Physics: Conference Series
Oliver R
(2006)
Three methods for the growth of InGaN nanostructures by MOVPE
in physica status solidi c
Sumner J
(2007)
Practical issues in carrier-contrast imaging of GaN structures
in physica status solidi c
Van Der Laak N
(2006)
Towards a better understanding of nano-islands formed during atmospheric pressure MOVPE
in physica status solidi c
Von Pezold J
(2006)
The effect of Si on the growth mode of GaN
in physica status solidi c
Zhu D
(2007)
Optical and micro-structural properties of high photoluminescence efficiency InGaN/AlInGaN quantum well structures
in Journal of Crystal Growth
Zhu T
(2010)
The impact of ScO x N y interlayers on unintentional doping and threading dislocations in GaN
in Journal of Physics: Conference Series
| 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 | Science Bridge Award USA: Harnessing Materials for Energy |
| 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 | 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 |