Non-polar nitride quantum dots for application in single photon sources

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

Abstract

Physicists understand that light can be thought of as either a wave, or a stream of tiny particles called "photons". A photon is the smallest amount of light which can exist. Using single photons, we can encode information for cryptography and computing. Quantum cryptography using photons offers the ultimate in data security, and linear optical quantum computation provides the opportunity for massively parallel data processing. However, progress towards these applications is limited by the current performance of single photon sources. Such a device can reliably provide one - and only one - photon on demand. Using a dim conventional light source in place of a true single photon source always risks the possibility of emission of multiple photons, compromising the security of quantum cryptography and corrupting the performance of quantum computers.

True single photon sources can be made using semiconductor quantum dots: tiny crystals with atom-like properties, whose very nature means that they emit a single photon upon optical or electrical excitation. Different semiconductor materials are being explored, including families of materials based on compounds of arsenic (the "arsenides") and on compounds of nitrogen (the "nitrides"). Of the two, the arsenides have been fairly widely studied, and can be used to produce efficient single photon sources, but with one major disadvantage: these devices only operate at very low temperatures: typically, 250 degrees below zero, or lower. The nitrides, on the other hand, have been used to demonstrate single photon emission at room temperature, which would obviously be much more convenient for real-world applications. However, this family of materials has been studied much less, and current devices are not very efficient and have a low rate of photon emission compared to the arsenides. Another difference between the arsenides and the nitrides is that whilst the former give red or infra-red light, the latter are currently most useful at the other end of the colour spectrum: in the green, blue and ultra-violet. (However, the nitrides do have potential for emission of almost any colour of light depending on the exact composition of the material used.)

A team of researchers at Oxford and Cambridge Universities have recently invented a new way to grow nitride quantum dots which may help to overcome some of the disadvantages of the nitrides. By changing the orientation of the substrate crystal on which the quantum dots are grown, we have shown that the rate of photon emission could be increased by a factor of ten or more. Furthermore, initial studies suggest that these more efficient quantum dots also retain sufficiently good temperature stability that devices could be designed which can operate with on-chip cooling, which would be a practical solution for real applications. In this project, we aim to explore the properties of quantum dots grown in this new orientation, and develop the crystal growth techniques which allow them to be incorporated into practical devices, which we will then test. We hope to develop a practical quantum technology based on the discoveries we have made about these exciting nitride materials.

Planned Impact

The aim of this project is to develop non-polar nitride quantum dots for application in single photon sources. An inherent feature of such devices is that a single photon state cannot be amplified, so the devices need to be bright with a high repetition frequency from the outset. Such developments in quantum information science form the basis of a disruptive technology, with structures such as these having the potential to achieve efficient single photon emission at room temperature - or at least at temperatures accessible by on-chip Peltier cooling. Such apparently esoteric devices might be initially commercialised for use in the laboratory context, providing a compact and convenient single photon source for use in experiments concerning quantum key distribution and non-linear quantum computation. In the longer term, we would envisage this technology being transferred into the wider world, where it would be used in free-space quantum cryptography. Such quantum cryptographic applications might be short-range (involving communication between a mobile electronic device and an ATM for example), or long range (involving communication between satellites outside the earth's atmosphere). In the long-range situation, using blue or UV wavelengths, conveniently accessible using nitride materials, would give the lowest beam divergence for the currently available, weight-limited telescopes, minimizing losses from the quantum key distribution system. Looking beyond quantum cryptography, blue-emitting single photon sources have wider applications in high resolution quantum imaging and improved quantum sensing, which are of particular interest to our industrial partners at Toshiba.
In order to achieve economic impact based on our work towards devices for these applications, we plan to (1) exploit pre-existing contacts with relevant industries including Toshiba and Plessey Semiconductor Ltd., (2) utilise know-how within the Cambridge GaN Centre concerning patenting and spin-out companies to develop new companies or licence IP if appropriate, and (3) safeguard public expectations of such nanotechnologies by pursuing opportunities for two-way engagement with the public. Further societal impact will then arise if these new technologies are commercialised, since they could provide opportunities for improved security of data transfer to the general populace. Paradigms already exist for the use of single photon sources in "Quantum ATMs" which any mobile phone user could utilise in order to totally securely download a supply of secret "keys" (binary numbers used in encoding) which would then be used in securing their internet transactions, or other cashless payments. This could allow all of us to protect ourselves more effectively against internet fraud.
Furthermore, we anticipate that our work on nitride crystal growth for single photon sources will also generate knowledge relevant to other societally important projects such as the development of white light emitting diodes (LEDs) for low energy solid state lighting, the development of ultraviolet LEDs for water purification and the development of high efficiency power electronics. (Work on defect reduction, doping of non-polar materials and the impact of growth parameters on quantum dot array formation will be particularly relevant in this context.) Impact in these sectors will be ensured by strong communications links both within the Cambridge Centre for GaN which has a diverse portfolio of nitride research and also by our close interaction with the UK Nitride Consortium, which provides regular fora for the discussion of nitride research results within the UK academic and industrial community.
Lastly, we anticipate that students and post-doctoral research associates involved in the project will receive a broad training including vital technical knowledge and transferrable skills and will contribute to the people pipeline for the emerging quantum technologies industry and for other sectors.

Publications

10 25 50
 
Description We have demonstrated that when non-polar nitride quantum dots are pumped by a laser to cause them to emit light, they act as single photon emitters at temperatures up to 220 K. This temperature is significant since it is achievable by on chip cooling. We have further shown that the quantum dot emission maintains its polarisation properties up to this temperature.
We have developed the first non-polar nitride single photon light emitting diode and demonstrated the single photon nature of the emission and the fact that the quantum dot electroluminescence is highly polarised.
We have developed a new method of growing non-polar quantum dots integrated with self-assembled nanorods and shown that the emission from these quantum dots is single photon in nature.
We have developed a new method for making reflector structures which allow more of the photons generated by a single photon emitter to be sent in the desired direction.
We have also shown that the quantum dots we are studying maintain a fixed polarisation at temperatures up to 150 K and have linked this property to a model of the quantum dot structure.
Exploitation Route We plan to take these findings forward ourselves at this stage into the development of a temperature stable, efficient, polarised electrically-pumped single photon source, which could be used in the laboratory context for experiments on quantum key distribution.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description Working in collaboration with Dr Vasant Kumar, the Cambridge Centre for GaN has invented a facile method for the fabrication of mesoporous gallium nitride structures and devices across whole GaN wafers with controlled pore size and porosity using a one-step electrochemical etching method which requires no lithographic processing. The unique vertical etching mechanism achieves the formation of sub-surface porosity through a top undoped GaN layer leaving the properties and morphology of that top layer largely unchanged. Single or multiple sub-surface porous layers may be fabricated and device structures then overgrown on the resulting pseudo-substrate. This technology, which has a range of potential applications in photonic, optoelectronics and electronics has been patented (PCT/GB2017/052895) and potential routes to commercialisation were initally being explored under an IAA grant (LJAG/927) in collaboration with local technology development and investment advisory business, Elucidare. A further patent application (UK Patent application no: 1801337.5) was then filed for a related technology which allows the nanoengineering of nitride quantum wells using electrochemical etching, which may have applications particularly in the development of efficient ultra-violet LEDs for water purification, a huge potential market in the developing world. A second IAA grant will demonstrate the feasibility of ultra-violet LED improvements using this technology. The original patented porosification technology underpins our new spinout company, Poro Technologies. This spinout company won the University of Cambridge's Postdoc Business Plan Competition with a prize of £20,000 investment from Cambridge Enterprise (CE) in November 2018. Thereafter, the post-doc involved in the invention, Dr Tongtong Zhu, won an Enterprise Fellowship from the Royal Academy of Engineers to develop the techology towards commercialisation (https://www.raeng.org.uk/grants-prizes/grants/enterprise-hub-support-for-entrepreneurs/enterprise-fellowships/current-and-recent-awards). During the course of his Fellowsip, Dr Zhu raised £1.5M in seed funding to allow Poro Technologies to set up a pilot plant in Cambridge. Poro Technologies now has three employees, and plans to employ eight people by the end of 2020. The company is working with a range of UK and internatioanl industries to exploit porous GaN in improving electronic and optoelectronic devices. Current large industrial collaborators include IQE and Plessey.
First Year Of Impact 2017
Sector Digital/Communication/Information Technologies (including Software),Electronics,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description IoP Photonics Roadmapping Workshop
Geographic Reach National 
Policy Influence Type Participation in a national consultation
URL http://www.iopblog.org/roadmapping-the-photonics-sector/
 
Description RAEng/Leverhulme Senior Research Fellowship
Amount £50,276 (GBP)
Organisation Royal Academy of Engineering 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2015 
End 08/2016
 
Title Research data supporting "Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence" 
Description Research data in support of the publication "Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence". We have included the original data (tab-separated text files) as plotted for the quantum wells, measured by spatially- and time-resolved cathodoluminescence. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
 
Title Research data supporting "Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence" 
Description Research data in support of the publication "Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence". We have included the original data (tab-separated text files) as plotted for the quantum wells, measured by spatially- and time-resolved cathodoluminescence. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
 
Title Research data supporting "Wafer-scale Fabrication of Non-polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification" 
Description Research data in support of the publication "Wafer-scale Fabrication of Non-polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification". We have included all the figures and the original data (tab-separated text files) as plotted for the micro-reflectivity and C-V curves. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Research data supporting"Nanoscopic insights into the effect of silicon on core-shell InGaN/GaN nanorods: Luminescence, composition, and structure" 
Description Research data in support of the publication" Nanoscopic insights into the effect of silicon on core-shell InGaN/GaN nanorods: Luminescence, composition, and structure". We have included all the figures. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Description Anvil 
Organisation Anvil Semiconductors
Country United Kingdom 
Sector Private 
PI Contribution Growth of material
Collaborator Contribution Provision of substrates
Impact Ongoing - outputs not yet complete
Start Year 2015
 
Description Harvard 
Organisation Harvard University
Country United States 
Sector Academic/University 
PI Contribution Supply of samples
Collaborator Contribution Processing and characterisation of samples
Impact Multiple publications.
Start Year 2006
 
Description IQE Collaboration 
Organisation IQE Europe Limited
Country United Kingdom 
Sector Private 
PI Contribution Electrochemical etching and characterisation of distributed Bragg reflectors
Collaborator Contribution Provision of materials for etching, overgrowth, characterisation
Impact Ongoing work.
Start Year 2019
 
Description Investigating opportunities for commercialization of porous nitrides 
Organisation Elucidare
Country United Kingdom 
Sector Private 
PI Contribution We are working with Elucidare on an EPSRC Impact Acceleration Account Follow-On Fund project to explore commercialisation opportunities for the porous GaN technologies arising from this project. We are providing access to a range of research data to facilitate this.
Collaborator Contribution Elucidare are using our research data to liaise with a range of companies internationally to explore commercialisation opportunities for our technology.
Impact No specific impacts yet.
Start Year 2018
 
Description Quantopticon collaboration 
Organisation Quantopticon Ltd
Country United Kingdom 
Sector Private 
PI Contribution Quantopticon are a startup company developing software to predict the performance of quantum systems. Based on the outputs of this grant, they have asked us to partner with them on a new InnovateUK grant. We have been involved so far in writing the grant proposal which has recently been funded, and will in future provide data to Quantopticon as an input to their model to test its effectiveness.
Collaborator Contribution Quantopticon are leading the InnovateUK project mentioned above.
Impact New funding.
Start Year 2017
 
Description Toshiba 
Organisation Toshiba Research Europe Ltd
Country United Kingdom 
Sector Private 
PI Contribution Provision of samples and microstructural data
Collaborator Contribution Clean room processing
Impact Publication: DOI: 10.1021/acs.cgd.5b01560
Start Year 2015
 
Description Tyndall 
Organisation University College Cork
Department Tyndall National Institute
Country Ireland 
Sector Academic/University 
PI Contribution Provision of data on the structural and optical properties of non and semi-polar quantum wells
Collaborator Contribution Theoretical modelling of non- and semi-polar quantum wells
Impact Publication: DOI: 10.1063/1.4868692
Start Year 2010
 
Title METHOD FOR POROSIFYING A MATERIAL AND SEMICONDUCTOR STRUCTURE 
Description A method for porosifying a Ill-nitride material in a semiconductor structure is provided, the semiconductor structure comprising a sub-surface structure of a first Ill-nitride material, having a charge carrier density greater than 5 x 1017 cm-3, beneath a surface layer of a second Ill-nitride material, having a charge carrier density of between 1 x 1014 cm-3 and 1 x 1017 cm-3. The method comprises the steps of exposing the surface layer to an electrolyte, and applying a potential difference between the first Ill-nitride material and the electrolyte, so that the sub-surface structure is porosified by electrochemical etching, while the surface layer is not porosified. A semiconductor structure and uses thereof are further provided. 
IP Reference WO2019063957 
Protection Patent application published
Year Protection Granted 2019
Licensed Yes
Impact Patent has been licenced to Poro Technologies Ltd, a University of Cambridge Spinout Company which currently has 3 employees and plans to hae 8 by the end of the year. Poro Technologies are setting up a pilot plant in Cambridge.
 
Title X-ray modelling code for porous GaN DBRs 
Description A modelling code to simulate X-ray diffraction data from porous gallium nitride distributed Bragg reflectors. 
Type Of Technology Software 
Year Produced 2019 
Impact Very recently released open access software. No known impacts yet. 
URL https://aip.scitation.org/doi/suppl/10.1063/1.5134143
 
Company Name PORO TECHNOLOGIES LTD 
Description Poro Technologies is an early stage spinout from the Cambridge Centre for Gallium Nitride focussed on porous GaN technologies for performance enhancement in LEDs 
Year Established 2018 
Impact Poro Technologies won the 2018 Cambridge Enterprise Postdoc Business Plan competition and is currently in discussion with venture capatalists about seed funding.
Website https://www.enterprise.cam.ac.uk/news/poro-technologies-wins-2018-postdoc-business-plan-competition/
 
Description Alumni festival talk (Secrets and Lights) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact An interactive talk was delivered at the Cambridge Alumni Festival about single photon sources and their application in quantum cryptography
Year(s) Of Engagement Activity 2016
URL https://www.alumni.cam.ac.uk/events/alumni-festival-2016/secrets-and-lights
 
Description Cambridge Science Festival 2015 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Over 100 people attended an interactive talk which sparked questions and discussions afterwards. The science festival had positive feedback that attendees enjoyed the event and we have been asked to put on a larger event in 2016.
Year(s) Of Engagement Activity 2015
URL http://www.sciencefestival.cam.ac.uk/about/past-festivals/2015-cambridge-science-festival
 
Description Cheltenham Science Festival 2019: Communication using Liht 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Three separate school groups attended a workshop on light-based communications, covering fibre optics, LiFi and single photon sources.
Year(s) Of Engagement Activity 2019
 
Description Chesterton Science Club (Communication using Light) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact An interactive talk on "Communication using Light" was delivered to the Chesterton Community College Science Club, incorporating elements on LiFi using LEDs and quantum communication using single photon sources.
Year(s) Of Engagement Activity 2016
 
Description Communication using light - Hatchend School 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact A workshop on the uses of light in communications, delviered to multiple classes in thee 14-16 age group and their teachers.
Year(s) Of Engagement Activity 2018
 
Description Little Light Sources With Big Ideas (#RobinSTEM) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact A short talk on quantum dots and single photon sources as part of the Robinson College Women in Science Festival, which I organise.
Year(s) Of Engagement Activity 2018
URL https://www.robinson.cam.ac.uk/news/women-stem-festival-2018
 
Description RealSci Nano - Twitter curation and podcast 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Rachel Oliver curated the @realscinano twitter account for a week, describing her research on nitride materials at the nanoscale and taking questions from the general public. She was interviewed for an accompanying podcast.
Year(s) Of Engagement Activity 2019
URL https://www.realscientistsnano.org/rachel-oliver
 
Description Researcher profiles website 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact A website has been set up with career profiles for members of the Cambridge Gallium Nitride Centre as a resource for school and University students considering a career in research.
Year(s) Of Engagement Activity 2016,2017
URL http://www.gan.msm.cam.ac.uk/resources/profiles
 
Description Robinson College Women in Science Festival Talk (Little light sources with big ideas) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact As part of the Robinson College Women in Science Festival, an interactive talk was delivered on single photon sources.
Year(s) Of Engagement Activity 2016
 
Description Robinson Science Residential 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Approximately 40 sixth formers took part in a 2 day even at Robinson College to which I contributed a talk, tutorial content and a practical session. Robinson reported increased student applications in related subject areas.
Year(s) Of Engagement Activity 2015
URL https://www.robinson.cam.ac.uk/access-and-outreach
 
Description Robinson Women in Science Festivale 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Over 120 female sixth formers took part in a day festival aimed at encouraging participation in the Physical Sciences. In addition to organising the day, I gave a presentation on my research, chaired a student talk session and organised a practical session. Feedback from the sixth formers was very positive, several have been influenced to apply to study science at University and a second event is being organised.
Year(s) Of Engagement Activity 2015
URL https://www.robinson.cam.ac.uk/access-and-outreach
 
Description School visit (Hackney) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Two workshops were held at a primary school in Hackney and a whole school assembly was delivered. The workshops were titled "Communications in Lights" (for an older group of children) and "Lots and lots of Light Bulbs" (for a younger group of children).
Year(s) Of Engagement Activity 2017
 
Description Science festival talk (How Can GaN Change Your Life?) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact An interactive talk was delivered to a large audience at the Cambridge Science Festival, outlinging a number of different uses for Gallium Nitride from lighting to quantum communications.
Year(s) Of Engagement Activity 2016
 
Description Secrets and Lights - Cafe Scientifique Bishops Stortford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact A lecture on single photon sources and quantum cryptography
Year(s) Of Engagement Activity 2018
 
Description Talk to visiting school group (Communications using light) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact An interactive talk on "Communication using Light" was delivered to a group of sixth formers visiting the department, incorporating elements on LiFi using LEDs and quantum communication using single photon sources.
Year(s) Of Engagement Activity 2016