GaSb/GaAs quantum rings as single photon sources

Lead Research Organisation: Lancaster University
Department Name: Physics


Quantum technologies are those which exploit the exotic properties of nature described by quantum mechanics to deliver
devices with unprecedented speed or accuracy compared with conventional technology, or even generate completely novel
technologies with new functionalities, which simply do not exist at present. Quantum cryptography is one such technology:
communication whose security is guaranteed by fundamental laws of quantum mechanics. The implementation of quantum
cryptography relies on the ability to generate single photons of light on demand. Several different physical systems have
been used to generate single photons, but very few of them are suitable for commercial production as they are impractical
and inconvenient. An ideal single photon source should be fast, cheap, operate at room temperature, and emit photons at
the wavelengths used in existing optical-fibre based telecommunications systems. In fact, a practical single photon source
is expected to look very like a type of semiconductor laser diode called a vertical cavity surface emitting laser (VCSEL). In
this year-long project we will assess the feasibility of mass-producing low-cost, room-temperature single photon sources
with telecom-wavelength emission by developing novel VCSEL devices whose active regions incorporate tiny
semiconductor nanostructures called self-assembled quantum rings. This will allow us to leap-frog a stage in the
development of practical, i.e. commercial, single photon sources, and to make a realistic assessment of their commercial

Planned Impact

The exploitable results of this project are: (i) LED devices with GaSb/GaAs active material, (ii) VCSEL devices with
GaSb/GaAs active material, (iii) Academic IP relating to fundamental properties of GaSb/GaAs optical properties and
device design, and (iv) A UK supply chain from research to product feasibility in an important emerging technology. After a successful outcome of this project, the consortium intends to continue development into a fully realised commercial
product in the form of a packaged semiconductor chip. The most obvious form factor for this would be a TO-header-type
package typical of VCSEL devices currently used in datacoms applications. The current consortium embodies a full UK
supply chain for this product with CST Global ltd being the partner intending to manufacture and directly market and sell the
product. CST already has an existing supply chain for T0-header laser products. After the end of this programme the
consortium will require a further two year co-funded development project into which an end user or system integrator will be
added. CIP/Huawei have expressed an interest in this role. A further year of pre-production is envisaged before the
commercial product will be launched. The consortium intends to disseminate scientific advances in high impact journals
including Nature Photonics, Nature Communications and Applied Physics Letters, and will target talks at national and
international conferences such as UK Semiconductors, Photonics West [OPTO] and QD2016.
Direct economic benefit to the industrial members of the consortium is expected from the marketing and sales of the
resultant single photon source devices. Manufacturing of this product will be exclusively carried out in the UK until volumes
are high enough to justify to subcontracting the assembly stages. The top-line forecast revenue total of £5 million by 2020
split between IQE and CST at a projected return on investment of ~300%. A successful commercialisation of the
fundamental academic research at Lancaster University will have a positive impact on the research impact status
(REF2020) allowing it to attract enhanced funding. The UK technology community as a whole will be supported by the
generation of a quantum device supply chain.
Direct production of these high value quantum devices will result in safeguarding existing employment in the UK III-V
component manufacturing industry, a vital enabling high technology capability vital to many UK companies, of which CST
and IQE play a unique and critical part. Increased employment at CST would be needed to set up the product
manufacturing line.


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Description The idea behind the project was to explore the feasibility of using self-assembled GaSb quantum rings (QRs) in GaAs for commercial production of single photon sources. Single photon sources are a key component in fundamentally secure communications using the quantum key distribution technique. However, rather than taking the traditional method of trying to isolate the emission from a single ring at low temperature in a lab, and then working towards a device, our approach was to see if we could make a device first, using established industrial techniques that would be needed for mass production of single photon sources. The target device we chose was not a single photon LED, but a different (classical) device with a similar structure. Vertical-cavity surface-emitting lasers (VCSELs) are a cheap, but fast, type of laser diode. They are widely used for many applcations, e.g. datacoms, but are not commercially available at telecoms wavelengths (1260 to 1675 nm), which is where our QRs emit. This was thus an additional motivation behind the research.

We started off by investigating the effect of placing the GaSb QRs in GaAs quantum wells (QW) of different thicknesses. Rather surprisingly, photoluminescence (2 to 380 K) and time-resolved photoluminescence (room temperature) measurements showed a negligible effect of the QW width. This was unexpected because the electrons are not confined by the GaSb QRs (only the positive-charge carriers, i.e. holes, are: the system is type-II). However, it meant that this would not restrict the device design in terms of GaAs QW thickness.

In the next stage, and in collaboration with CST Global Ltd., we produced some GaSb QR LEDs. All the LEDs tested showed good current-voltage characteristics and electroluminescence from 2 to 380 K. At room temperature and above the emission overlapped with the telecoms band.

In the latter part of the project we concentrated on the development of the world's first GaSb QR VCSELs. In the first instance this involved developing the growth of the distributed Bragg reflectors (DBRs) that form the mirrors for the laser cavity. These are made by growth of alternating of GaAs and AlGaAs layers. Layer thickness analysis using the technique of beam-exit cross-sectional polishing (BEXP) combined with atomic force microscopy (commercialised by spin-out Lancaster Material Analysis Ltd.) was absolutely essential in the rapid development of VCSEL material growth in Lancaster. The VCSEL material growth was easily the most ambitious ever attempted in Lancaster, with the growth of ~100 layers taking a period of 24 hours.

The VCSEL material was sent to CST Global Ltd. for processing into devices with ring-shaped contacts and 100-micron diameter mesas. Due to a lack of time, current guiding was not incorporated into the process (typically steam oxidation or proton bombardment are used), which is known to significantly decrease the efficiency of the device. Nevertheless, all devices tested lased in a single mode (unique wavelength), with lasing persisting to 110 C: the highest available temperature in our set-up. This is a very significant result, and consistent with the underlying physics of charge-carrier confinement in this system. Room temperature threshold currents were extremely low, <20 microAmps. Again, this impressive result is believed to be a direct consequence of the underlying physics of this system: GaSb QRs are intrinsically good active elements for a laser, because so-called population inversion is easily achieved. The lasing wavelength was also 10x more temperature stable then the LED emission wavelength.
Exploitation Route We are continuing to work with our industrial partners to take the research forward. The objective remains to produce classical and quantum light sources based on self-assembled quantum rings, and for these to be exploited in communications, as well as other sectors.

The original idea behind the research was to test the suitability of GaSb quantum rings (QR) as a means of mass-producing low-cost, room-temperature single photon sources by first trying to make conventional classical devices using standard industrial production methods. Having achieved this with remarkable success in a short time, we worked with industrial partners on the development of single photon LEDs, with EPSRC/Innovate UK funding.

Meanwhile, the very successful demonstration of QR VCSELs has generated a 'spin-off' activity which has very high value in its own right. We subsequently grew a second iteration of VCSEL material. Cross sectional analysis shows that the material quality has dramatically improved, and we adjusted the size of the cavity to get emission at ~1300 nm (the first VCSELs lased at 1140 nm: short of telecoms band). Devices were processed at Sheffield University, and emission was indeed 1324 nm at room temperature. We continue to work with industrial partners to further develop the technology, principally via (I)CASE and Innovate UK projects.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics,Healthcare,Security and Diplomacy

Description CASE award for Tom Wilson
Amount £26,000 (GBP)
Organisation IQE Europe Limited 
Sector Private
Country United Kingdom
Start 10/2016 
End 09/2019
Description Commercialisation of quantum technologies feasibility studies and collaborative research and development
Amount £211,354 (GBP)
Funding ID EP/P034233/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2017 
End 02/2018
Description GaAs-based vertical-cavity surface-emitting lasers with GaSb quantum rings (QRVCSELs)
Amount £255,470 (GBP)
Funding ID 103444 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 03/2018 
End 09/2019
Description Collaboration with Hitachi Cambridge 
Organisation Hitachi Cambridge Laboratory
Country United Kingdom 
Sector Private 
PI Contribution Proposing a problem of interest to the partner, expertise.
Collaborator Contribution Theoretical calculations/modelling.
Impact No outputs or outcomes.
Start Year 2016
Description Industrial partners in projects 'GaSb/GaAs quantum rings as single photon sources' and 'GaSb/GaAs quantum ring single photon LEDs (QR_SPLEDs)' 
Organisation Compound Semiconductor Technologies Global
Country United Kingdom 
Sector Private 
PI Contribution These are the two industrial partners for the EPSRC/Innovate UK and the foillowing Innovate project. We grew the semiconductor material for the CST to process and characterised the devices they made.
Collaborator Contribution CST was the project coordinator and processed the LED and laser devices. IQE's main contribution was single photon source specification.
Impact The outputs and outcomes are those of the projects 'GaSb/GaAs quantum rings as single photon source' and 'GaSb/GaAs quantum ring single photon LEDs (QR_SPLEDs)'
Start Year 2015
Description Industrial partners in projects 'GaSb/GaAs quantum rings as single photon sources' and 'GaSb/GaAs quantum ring single photon LEDs (QR_SPLEDs)' 
Organisation IQE Europe Limited
Country United Kingdom 
Sector Private 
PI Contribution These are the two industrial partners for the EPSRC/Innovate UK and the foillowing Innovate project. We grew the semiconductor material for the CST to process and characterised the devices they made.
Collaborator Contribution CST was the project coordinator and processed the LED and laser devices. IQE's main contribution was single photon source specification.
Impact The outputs and outcomes are those of the projects 'GaSb/GaAs quantum rings as single photon source' and 'GaSb/GaAs quantum ring single photon LEDs (QR_SPLEDs)'
Start Year 2015
Description A photon source is disclosed. The photon source comprises a semiconductor device comprising a first nanostructure and a second nanostructure, and control circuitry operable to apply an electric pulse to the semiconductor device so as to cause the first nanostructure to emit one single photon. The photon source is configured such that when the electric pulse is applied to the semiconductor device, only a single electron or only a single hole is provided to the first nanostructure via the second nanostructure. 
IP Reference WO2018162894 
Protection Patent application published
Year Protection Granted 2018
Licensed No
Impact The patent application has lapsed.
Title Vertical-cavity surface-emitting laser 
Description The present invention is a vertical-cavity surface-emitting laser ("VCSEL") comprising at least a substrate (104), electrical contacts (116), a first mirror region (106), a second mirror region (112) and an active region (108) between the mirror 5 regions; where the mirror regions (106,112) comprise distributed Bragg reflectors formed of a plurality of layers; laser emission is from at least one gallium arsenide antimonide nanostructure in the active region; and each said nanostructure contains more antimony atoms than arsenic atoms. 
IP Reference GB1503498.6 
Protection Patent granted
Year Protection Granted 2020
Licensed No
Impact The European patent (EP3266080B1) has been granted. Noification of intention to grant has been given by US (US20180054041A1) and Japan (JP2018507564A). The patent is pending in S. Korea (KR20180011063A). The search for a licensee for the knowledge is currently in progress.   
Description 2nd National Quantum Technologies Showcase 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact The event was the 2nd National Quantum Technologies Showcase, which was held as the QE-II Conference Centre, Westminster on 3rd November 2016. The technoogy we developed during the project was exhibited.
Year(s) Of Engagement Activity 2016
Description Lancaster University Community Day May 2017 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact The activity was part of Lancaster University Community Day, aimed at the general public from the city. The intended purpose was to strengthen links with the local community & communicate some of the research undertaken on campus. We had a stand with demonstration of infrared vertical-cavity surface-emitting lasers, pull-up banner, glossy leaflets etc. In excess of 100 people of a wide variety of ages visited the stand and learnt about (mini) lasers and sending light down optical fibres.
Year(s) Of Engagement Activity 2017