Room Temperature Terahertz Quantum Cascade Lasers on Silicon Substrates

Lead Research Organisation: University of Glasgow
Department Name: School of Engineering

Abstract

The THz part of the electromagnetic spectrum has a number of potential applications which include oncology (skin cancer imaging), security imaging, THz bandwidth photonics, production monitoring and astronomy. The U.K. has been one of the pioneering countries in THz research but also in the exploitation of the technology with a number of companies including TeraView, QMC Instruments and Thruvision. At present most commercial imaging and spectroscopy systems use expensive femtosecond lasers with photoconductive antenna which fundamentally limits the power output to the microWatt level. Virtually all the applications referenced above require room temperature sources with over 10 mW of output power if parallel, fast, high performance imaging and/or spectroscopy systems are to be developed.While interband recombination of electrons and holes in Si and Ge are inefficient due to the indirect bandgap of the semiconductors, intersubband transitions provide an alternative path to a laser for low energy radiation such as THz frequencies. Intersubband unipolar lasers in the form of quantum cascade lasers have been demonstrated using III-V materials. Powers up to 248 mW at 10 K have been demonstrated at THz frequencies but due to polar optical phonon scattering and the associated reduction in intersubband lifetimes as the temperature is increased, such devices only operate at cryogenic temperatures. Previous work has been undertaken on p-type Si/SiGe quantum cascade lasers but due to large non-parabolicity and large effective mass (0.3 to 0.4 m_0) in the valence band, significant gain above 10 cm^-1 is difficult to engineer.In this proposal, we propose to use pure Ge quantum well designs and L-valley electrons for the first experimental demonstration of a n-type Si-based quantum cascade laser grown on top of a Si substrate. We demonstrate that the low effective of 0.118 m_0 and long non-polar lifetimes in the Ge/SiGe system potentially provide gain close to values demonstrated in GaAs THz quantum cascade lasers at 4 K and also potentially allow 300 K operation. Further the cheap and mature available Si process technology will allow at least a x100 reduction in the cost of THz quantum cascade lasers compared to GaAs devices. Such devices could be further developed into vertical cavity emitters (i.e. VCSELs) for parallel imaging applications or integrated with Si photonics to allow THz bandwidth telecoms. Finally we propose optically pumped structures which have the potential for broadband tunability, higher output powers and higher operating temperatures than THz quantum cascade lasers.This programme has brought together the modelling and design toolsets at Leeds University with the CVD growth expertise at Warwick University combined with the fabrication and measurement expertise of SiGe devices at Glasgow University to deliver internationally leading research. We have a number of industrial partners (AdvanceSis, Kelvin Nanotechnology and TeraView) who provide direct exploitation paths for the research. Successful room temperature quantum cascade lasers are an enabling technology for many new markets for THz applications including oncology (skin cancer imaging), security imaging, production monitoring, proteomics, drug discovery and astronomy.

Planned Impact

Work has shown that THz has potential applications in medical imaging (oncology and dental areas), security imaging, explosives and narcotics detection and identification, drug discovery, proteomics, manufacturing quality control, gas sensing, pollution monitoring and astronomy. Present THz imaging systems cost >250k, use mirrors for optics and mechanically raster a single pixel using a <1 microWatt source. The success of this proposal would result in 300 K, high power (>10 mW) arrays of sources which could be used for parallel imaging systems. A tunable optically pumped source (using a MIR GaAs QCL pump) would also have a large number of applications where spectroscopic identification (molecular fingerprinting) is important. Such sources could be manufactured at extremely low cost compared to present photoconductive sources which require expensive femtosecond laser pumps and III-V QCLs. The achievement of fast, parallel imaging and spectroscopic systems would open up many new markets for THz systems and applications which previous have been unavailable due to slow, serial imaging and poor power-detector performance resulting in poor signal to noise. We will exploit successful results with the industrial partners AdvanceSis, Kelvin Nanotechnology and TeraView, providing IP and know-how to aid their economic growth and provide return to the U.K. investment in this research. Companies who purchase THz systems will benefit through new technology and increased productivity. The healthcare market requires far cheaper THz parallel imaging systems which could be significantly helped by the success of this proposal. At present all skin cancer detection requires an appointment with a consultant at a hospital and significant savings could be made if a safe and reliable diagnosis technique could be employed at GP surgeries. This is especially important as early detection is key for high survival rates. Also any 3D detection technique would significantly reduce trauma and patient time in hospital compared to present biopsy techniques thereby significantly reducing the costs for treatment for the NHS (see http://www.teraview.com/). Skin cancer imaging systems for GP surgeries would require a complete imaging system for less than 10k with source powers > 10 mW at room temperature for parallel imaging which could be achieved with the sources in this proposal. The success of this proposal could therefore have significant benefits to UK society by increasing the quality of living by fast detection of skin cancers and in doing so also significantly reduce the treatment costs in the NHS. From the security side, room temperature THz QCLs would be an enabling technology for the use of THz technology in portal security screening systems (i.e. walk through portals) for airports, civil buildings and public places. The technology would be enabling to allow safe screening through clothing at video rates for short stand-off distances compatible with portal systems. As the probability of terrorist attacks in the U.K. is higher than ever before, such fast detection using safe non-ionising radiation in public spaces could potentially save many lives. Also the detection of suicide bombers before detonation will not only save lives but also significant reduce the costs of first responders, the cost of medical care of victims and the cost of the clear up operation. While the Home Office through HOSDB is responsible for testing equipment, the potential beneficiaries in government include the Home Office (Police but also first responders at incidents i.e. Fire and Ambulance) and the Borders Agency. For the private U.K. airports, it is the operators who are responsible for security e.g. BAA. We will disseminate successful research to contacts in these agencies. In addition, any tunable source would be useful for spectroscopy systems for chemical and materials anaylsis. Hence the DH, NHS, HPA and DEFRA would all benefit through new analytical tools.
 
Description THz intersubband transitions require low doping levels in Ge heterolayers to be observed. In an EC project we have now measured the doping segregation by SIMS and are redesigning structures to account for these issues. This work is with the Germany companies IHP and Nextnano.
Exploitation Route Solid source MBE would allow the structures to be grown. The problems are all with chemical vapour deposition of the SiGe and Ge heterolayers where n-type doping segregates. We are attempting to use LPCVD techniques to design structures where the dopant segregation is included in the design of the bottom contact.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description Knowledge has been used to aid a two UK companies in developing manufacturable processes for semiconductor material and devices. Also a new EC grant "Far-infrared Lasers Assembled using Silicon Heterostructures (FLASH)" for 3.22 MEuros has been funded and started in November 2017. This grant includes two Germany companies Nextnano and IHP. Nextnano is developing simulation software for quantum cascade lasers (QCLs) and IHP has the aim of taking group IV QCL devices to market.
First Year Of Impact 2014
Sector Electronics,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description Cabinet Office: Scientific Advisory Group for Emergencies
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
URL https://www.gov.uk/government/groups/scientific-advisory-group-for-emergencies-sage
 
Description Home Office Chemical Biological Radiological and Nuclear Scientific Advisory Committee
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Impact I was involved in advising the Home Secretary on a wide range of counter terrorism and national security related activities. This was during the period of the 7/7 bombing, the shoot to kill policy, the Litvinenko event and many other affairs not in the public domain.
URL https://www.gov.uk/government/groups/home-office-science-advisory-council
 
Description MOD Defence Scientific Advisory Council
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Impact I have reviewed a number of the Uk defence policies and made a ranger of recommendations, most of which have been implemented.
URL https://www.gov.uk/government/organisations/defence-scientific-advisory-council
 
Description MOD report "Urgent Operation Requirements into Core"
Geographic Reach National 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Impact This material is restricted as it has national security importance.
 
Description UK Counter Terrorism Capability Review
Geographic Reach National 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Impact Details are restricted due to national security implications.
 
Description Centre for Doctoral Training
Amount £4,884,594 (GBP)
Funding ID EP/L016753/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 05/2014 
End 10/2022
 
Description EC Horizon 2020 Future Emerging Technologies
Amount £512,000 (GBP)
Funding ID 613055 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 02/2014 
End 01/2017
 
Description EPSRC Quantum Technology
Amount £23,061,154 (GBP)
Funding ID EP/M01326X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 11/2019
 
Description EPSRC Quantum Technology
Amount £7,796,554 (GBP)
Funding ID EP/M013294/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 11/2019
 
Description EPSRC Supergen
Amount £2,455,231 (GBP)
Funding ID EP/K022156/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 11/2013 
End 10/2017
 
Description EPSRC Supergen
Amount £568,271 (GBP)
Funding ID EP/M025012/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 08/2015 
End 07/2018
 
Description Equipment award
Amount £550,000 (GBP)
Funding ID EP/L021129/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 09/2014 
End 09/2018
 
Description Horizon 2020 Future Emerging Technologies
Amount € 3,225,547 (EUR)
Funding ID 766719 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 11/2017 
End 10/2020
 
Description Programme Grant
Amount £6,196,718 (GBP)
Funding ID EP/K014471/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 03/2013 
End 02/2018
 
Description Programme Grant
Amount £850,000 (GBP)
Funding ID EP/L024020/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2014 
End 06/2019
 
Description Quantum Technology Fellowships
Amount £1,512,465 (GBP)
Funding ID EP/N003225/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 07/2015 
End 06/2020
 
Description BBC news 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact I was interviewed on BBC Scotland news and a 3 minute broadcast of the interview was on BBC1 Scotland on the 15th October 2014. This is available on the BBC news webpages.
Year(s) Of Engagement Activity 2014
URL http://www.bbc.co.uk/news/uk-scotland-29629779
 
Description Energy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact I give a 1 hour lecture to school children three times a year on "Energy: Can renewables save the planet?"
Year(s) Of Engagement Activity 2009,2010,2011,2012,2013