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

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


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.


10 25 50
Description We have been successful in producing single photon sources pumped optically in InGaN a-plane quantum dots systems that emit single photons with a lifetime of 1ns at temperatures up to 220K. These emitters are strongly polarised and very bright. We have further succeeded in pumping a p-i-n structure with embedded InGaN quantum dots electrically to produce an electrically driven single photon source.
Exploitation Route The next stage in the production of single photons in the blue on demand is to take our planar p-i-n structure and incorporate it in a microcavity, which we can then contact electrically and produce bright, single blue photons on demand at a high repetition rate with got spatial modes. This will require further funding and development over 3 - 5 years.
Sectors Digital/Communication/Information Technologies (including Software)

Description The quantum dots and the optical techniques used to investigate them came to the attention of the company Quantopticon, who wished to develop and test their modelling software product, This led to an Innovate UK application entitled "Simulation Software for Modelling Quantum Light Sources", which was for 1 year and was successful and will commence on 1st March 2018. This has now produced a saleable product and further funding is being sought by the company to develop the product further. A new company has been spun out in Cambridge, partly as a result of this project as well as other EPSRC funded programmes, called Poro Technologies by Prof. Rachel Oliver and Dr. Tontong Zhu making high reflectivity mirrors as an integral part of GaN wafers for optoelectronic applications.
First Year Of Impact 2017
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Economic

Description Innovate UK
Amount £364,675 (GBP)
Funding ID EP/R044554/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2018 
End 02/2019
Description Produced an animation for use on the Oxford Sparks public engagement website on single photon sources 
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 The Oxford Sparks website hosts animations on science generated by researchers in Oxford. This animation deals with single photon sources and is aimed at informing the general public and schoolchildren about the research field and also refers to quantum computing. There are school materials for use by teachers available which supplement the animation and add impact through education.
Year(s) Of Engagement Activity 2016