MBE-LEEM: A UK facility for the ultimate control of complex epitaxy

Lead Research Organisation: Cardiff University
Department Name: School of Physics and Astronomy

Abstract

This first grant project will develop an MBE-LEEM system, combining in-situ state-of-the-art Molecular Beam Epitaxy and a Low Energy Electron Microscope. The project will increase capabilities in sample exchange between institutions, enabling the analysis of nucleation on complex samples, increase reproducibility and accuracy of flux measurements, increase reproducibility and accuracy of temperature control, increase the number of material sources, enabling the growth of new materials, increase safety, reduce down-time of the system and increase control during surface preparation. The development of the MBE-LEEM will enable close collaboration between Cardiff University and EPSRC National Centre for III-V Technologies and with IQE, a world leading semiconductor wafer company. The system will be used for basic research, providing a wealth of data on nucleation dynamics and key epitaxial processes for theorists across UK, and providing industrial and academic partners with a unique characterization technique to determine optimum growth parameters in complex epitaxial processes by analysing growth dynamics.

The extended capabilities of the MBE-LEEM will be tested by studying the nucleation of MnAs on InAs, determining the conditions for nucleation of Zinc-Blende MnAs. The nucleation of half-metallic MnAs on an InAs buffer layer with thickness below 2 monolayers was shown by Kim et al. in 2006, but the process has not been reproduced and no explanation on the mechanism leading to Zinc-Blende MnAs has been provided. MBE-LEEM will produce videos of the nucleation of MnAs on InAs with different thicknesses, highlighting the evolution of MnAs crystal structure and morphology during nucleation.

The fabrication of half-metallic semiconductors can be key for the development of spintronics. Follow-up research is projected after this first grant development project in order to analyse magnetic properties of half-metallic MnAs, and to apply MBE-LEEM to other key research on epitaxial processes, such as the integration of GaAs on Silicon, or the nucleation of nanostructures.

Planned Impact

The development of MBE-LEEM system addresses the need of real-time, in-situ monitoring of thin film growth dynamics. MBE-LEEM increases thin film and nanostructure growth control and provides data that complements current characterization techniques to underpin growth mechanisms e.g. mechanisms behind the nucleation of nanostructrures, the nucleation of particular crystalline phases of a material or the nucleation and dynamics of defects.

MBE-LEEM will benefit academic and industrial R&D groups across UK, and contribute to the progress of a wide range of technologies such as nanoelectronics, nanotechnology, advanced materials, and photonics, defined as Key Enabling Technologies by the European Comission, and such as, Epitaxy on Silicon, VCELS, QD lasers, InGaAs and InAs transistors, Spintronics, Bismides and quantum information devices, technologies specified in the III-V roadmap elaborated by the National Centre for III-V technologies. During this development project the capabilities of the new MBE-LEEM will be demonstrated by applying it to study the epitaxial processes of III-V semiconductors and magnetic semiconductors. MBE-LEEM will contribute to consolidate the leading status of UK's III-Vs R&D, providing world leading capabilities on monitoring of growth dynamics of As-containing compounds.

The project includes the liaison with the EPSRC National Centre for III-V Technologies (See LOS) and IQE, global leader in the design and manufacture of advanced semiconductor wafer products (see LOS), to set the procedures for epitaxial analysis and upscaling of the growth conditions defined with the MBE-LEEM. We will also collaborate with Warwick University, to study the epitaxial dynamics of MnAs and the possibility of stabilizing the half metallic phase of this compound. The collaboration between the Welsh government, Cardiff University and IQE has crystallized in the creation of the Institute for Compound Semiconductors, which will enable us to rapidly transfer the growth conditions defined by real-time in-situ monitoring in the MBE-LEEM to industrial MBE systems. Development of an IP portfolio on the nanoscale control of epitaxial processes will be carried out in collaboration with University College Cardiff Consultants Limited. IQE has committed to provide advice, training and materials (see letter of support), providing a unique opportunity for PhD students.

During this project the MBE-LEEM system will be developed and its capabilities demonstrated obtaining preliminary data that will serve to fuel further research projects and encourage collaboration. An important component of the project will be to communicate the new possibilities of the system to the III-V community.

The wide range of potential collaborations with academic and industrial partners offers a unique opportunity for development of future researchers, engineers and technologists, who will have a unique perspective of the field, while participating in research involving theoretical studies, basic research, experiment design, hands-on work on thin film growth and microscopy, and industrial development of III-V semiconductors. The unique capabilities of the MBE-LEEM also provide them with an exceptional opportunity to publish in high impact journals such as Science, Nature or Physical Review Letters.

The plans include significant effort in outreach activities, to disseminate our results, but also to reach to the public and obtain attention on III-Vs research, show how important semiconductors are in everyday life and the benefits that UKs III-V research can provide. The efforts include the collaboration with 3rd and 4th year students to build physics demos and show them in scientific events, and the editing of videos showing research results and their potential implications to society.

Publications

10 25 50
 
Description Semiconductors are the basis of current electronics. We use semiconductor devices to operate computers, phones, cars, etc. Most electronic devices are based on Silicon, a material that has been used in computing for over 50 years. The development of Silicon based devices is currently saturating, and new materials are being tested to develop new technologies that enable us to fabricate faster and more efficient devices. Electronics that use light (photonics) or magnetic properties of atoms (spintronics) are currently being used and developed.
Most semiconductor devices are based on thin layers of crystalline materials that are combined in order to exploit their properties. These layers are "grown" on top of each other using epitaxial techniques. These techniques enable us to arrange the atoms with a desired structure and combine thin layers of different materials.
Epitaxial techniques are "blind", we cannot see what is happening on the surface of our semiconductors while we are growing them, and most of the characterization is done after the process is finished. We have developed a system that enables us to observe epitaxial processes in real time with 5 nm resolution in x/y plane and atomic resolution on z-plane. The work carried out during this project has enabled us to increase the functionality of the system and study nucleation mechanisms in complex samples.
We have used this system to develop a method that allow us to observe the dynamics of the physical surface, but also of the atomic structure of the surface during a process, and we are currently applying this technique to develop our understanding of the growth of III-As materials. III-As are key materials for the development of photonics.
Exploitation Route The MBE-LEEM system we have developed to observe epitaxial processes is already producing results that complete our knowledge of the surface dynamics of the semiconductor during growth. We have developed a method that allow us to directly observe all the different atomic structures occurring on the surface of the semiconductor under different conditions and the transitions between them. Our observations also indicate that surfaces are not as stable as we currently assume. Surface stability is key, because the atomic structure of the surface of the semiconductor determines how the new material will grow on them, therefore how good our structures are.
Our current findings will be useful for the semiconductor community (Academic and Industry). It completes the knowledge of the processes, helps understanding current results and provides guidance on the conditions that produce optimum material quality. The connection between our observations and the electronics we use may seem distant, but there is a very direct connection between our ability to grow high quality materials and device performance.
The new system enable us to collaborate with a wider community. During this project we have established collaborations with groups across Europe, e.g. Sheffield National Epitaxy facility, Warwick University, Paul Drude Institute(Berlin, Germany), Universidad Politectica de Madrid - ISOM (Madrid, Spain), Universidad Autonoma de Madrid (Madrid, Spain). Complex samples are sent to us to study III-As epitaxial dynamics to understand the growth processes and determine growth conditions.
The work carried out during this first grant has improved control over growth conditions and increased our ability to collaborate. The system new capabilities of the system have been tested by direct observation of nanostructure formation and growth of III-As within the microscope. During the next few weeks Mn containing materials will be grown and growth dynamics will be recorded. This step is key for the development of spintronics, a new kind of electronics based on the magnetic properties of atoms.
The modification of the LEEM has enabled further collaborations with University of Bremen, Lund University which were planned at the beginning of lockdown and carried out whenever travel normalises. Current activity at the LEEM laboratory associated to the imaging of growth of III-As on GaAs and Silicon have also been facilitated by the instrument development carried out during the grant period.
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Energy,Manufacturing, including Industrial Biotechology

URL https://www.cardiff.ac.uk/news/view/1716639-scientists-spy-unstable-semiconductors
 
Description A press release of some of the results produced during the project was reproduced by several sources devoted to non-academic audiences. We have been contacted by several publishers of scientific dissemination to provide a description of our work, our experimental set-up for popular audiences. Some examples of internet sources reproducing the press release: https://www.cardiff.ac.uk/news/view/1716639-scientists-spy-unstable-semiconductors https://compoundsemiconductor.net/article/109274/GaAs_not_as_stable_as_thought https://www.electronicsweekly.com/news/business/instabilities-gaas-surfaces-discovered-2019-11/ https://scitechdaily.com/scientists-spy-unstable-compound-semiconductors-could-have-profound-consequences/ http://www.semiconductor-today.com/news_items/2019/nov/cardiff-041119.shtml https://www.sciencedaily.com/releases/2019/11/191104112849.htm https://www.nanowerk.com/nanotechnology-news2/newsid=53954.php https://phys.org/news/2019-11-scientists-spy-unstable-semiconductors.html
First Year Of Impact 2019
Impact Types Cultural

 
Title Development of MBE-LEEM 
Description We have modified the Low Energy Electron Microscopy at Cardiff, in order to enable in-situ characterization of growth conditions, as well as growth on complex samples. The development is ongoing. One article describing the system is expected to be submitted to Review of Modern Instruments or similar journal. Several elements have been developed. We are currently exploring the development of a patent. 
Type Of Material Improvements to research infrastructure 
Year Produced 2019 
Provided To Others? No  
Impact The MBE-LEEM allows the monitoring of growth dynamics of III-As compounds on real time with atomic resolution on z-axis and 5 nm lateral resolution. The modifications we have included enable us to determine growth conditions more accurately, therefore facilitating collaborations with academic and industrial partners involved on MBE growth of III-As compounds. The goal is to understand the basic mechanisms behind surface dynamics observed during growth and provide solutions to key problems for semiconductor industry. 
 
Title Selected energy dark-field imaging using low energy electrons for optimal surface phase discrimination 
Description We propose a general strategy for surface phase discrimination by dark-field imaging using low energy electrons, which maximizes contrast using diffraction spots, at selected optimal energies. The method can be automated to produce composite phase maps in real space and study the dynamics of complex phase transformations in real-time. To illustrate the capabilities of the technique, surface phases are mapped in the vicinity of liquid Ga droplets on the technologically important GaAs (001) surface. The data is in .dat format, each file corresponds with a photogram of a movie taken with the Low Energy Electron Microscope. 3 types of data can be found: Photograms from Low Energy Electron Diffraction profiles. In this cases the x/y plane corresponds to coordinates in the reciprocal space taken at given electron energies. Photograms from real space movies taken with the Low Energy Electron Microscope at given electron energies. In this case the x/y plane corresponds to real space coordinates, where the total size of the image varies between 20 microns and 6 microns. Each file is labelled a,b,c,d depending on the diffracted beam we are selecting, being a.diffracted beam from c(8x2), b. diffracted beam from 6x6 pattern, c. diffracted beam from 3x6 pattern, d. diffracted beam from 2x4 pattern. IV curves: Data extracted from the total intensity of a particular diffracted beam of a certain pattern. The Y axis represents the total intensity, and the X-axis represents the energy. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Description Formation of Ga nanoparticles 
Organisation Autonomous University of Madrid
Department The Department of Physics of Materials
Country Spain 
Sector Academic/University 
PI Contribution We will use the MBE-LEEM to observe the formation of Ga nanoparticles on nanostructured substrates.
Collaborator Contribution Nanostructured substrates will be sent from Universidad Autonoma de Madrid.
Impact The collaboration is ongoing. We expect to receive the substrates in March 2019
Start Year 2018
 
Description Nanostructure evolution under annealing. Surface evaporation dynamics in Nitride nanocolumns. 
Organisation Paul Drude Institute for Solid State Electronics
Country Germany 
Sector Academic/University 
PI Contribution We will use the LEEM-MBE system to observe the evolution of the facets of the nanocolumns during annealing. It has been observed that the width of the nanostructures can be further reduced by annealing. We expect to observe the surface dynamics during evaporation in order to develop a procedure to produce GaN nanostructures with any width. This procedure will simplify current nanostructure fabrication processes.
Collaborator Contribution We have received 4 samples from Paul Drude Insitut.
Impact The collaboration is currently ongoing. The measurements will be carried out in the next few months.
Start Year 2018
 
Description Protecting GaAs substrates. Development of As capped GaAs substrates. 
Organisation Technical University of Madrid
Department Institute of Optoelectronic Systems and Microtechnology
Country Spain 
Sector Public 
PI Contribution As-capped samples enable us to observe growth dynamics in complex samples. ISOM-UPM has sent us 4 As-capped samples for us to test. We will be able to test the quality of the samples and study growth dynamics of thin films and nanostructures. We expect the collaboration to continue in order to facilitate further collaboration on the study of growth dynamics on complex heterostructures.
Collaborator Contribution ISOM-UPM have 4 MBE systems. They have currently provided simple As-capped MBE grown samples. We expect the collaboration will continue in order to explore more complex structures.
Impact The project will allow us to understand the growth dynamics on complex heterostructures, therefore enabling us to implement the growth procedures and the design of complex semiconductor devices.
Start Year 2018
 
Description University of Bremen - Ruthenium, Graphene, Arsenene and Diamond 
Organisation University of Bremen
Country Germany 
Sector Academic/University 
PI Contribution Cardiff group will make the unique capabilities of the LEEM in Cardiff available to understand As intercalation in graphene and growth of GaAs and As monolayers on Ruthenium.
Collaborator Contribution Cardiff's LEEM group has established a collaboration with Prof. Jens Falta's group. The collaboration encompasses mainly 4 separate projects: 1. CBLEED - The project aims at developing convergent beam low energy electron microscopy experimentally. Initial testing has been done by our previous post-doctoral research associate (currently in MAXIV in Lund, Sweden). Lens configuration is not yet optimal and significant beam damage was observed. Several strategies have been proposed to optimise the lenses, the collaboration consists of testing complementary configurations in Bremen and Cardiff in different material systems with strong strain gradients across the surface (Dislocation network on Ge/Si system, InAs/GaAs system close to critical thickness, GaN surface and GaN wires). David Jesson will provide his experience on the sensitivity to strain of the technique based on his own simulations. This project should lead to preliminary results for funding proposals and at least one publication. 2. Intercalation of As on Ruthenium - Prof. Jens Falta's group has strong experience on preparing graphene on Ruthenium via high temperature annealing of the samples. Cardiff's LEEM has the unique capability of enabling imaging under high As flux. The goal of this project is to observe the behaviour of As atoms on Graphene on Ruthenium and study possible intercalation of Arsenic between Graphene monolayers. 3. Growth of As or GaAs monolayers on Ruthenium: This experiment is complementary to the previous one. It is based on the study of the growth dynamics of Arsenene or monolayer GaAs on Ruthenium. Both experiments take advantage of the strength of Bremen's group preparing Ruthenium substrates and the unique capabilities of Cardiff's system. We expect these experiments to provide preliminary results for future funding proposals and at least one publication in common. 4. Study of burning Diamond thin films and graphitization of Diamond: The experiment takes advantage of the Cardiff's experience in diamond thin film growth (Prof. Oliver Williams) and the compatibility of two LEEM systems with unique characteristics in Cardiff and Bremen. The project aims at observing the dynamics of the phase transformation of diamond into graphite and the reaction of diamond with oxygen at high temperatures. Bremen's LEEM has been chosen to perform the experiments due to the capability to expose the sample to oxygen flux, which reduces the complications associated to Carbon contamination. Funding from the Cardiff-Bremen alliance will be sought for in order for Dr. J. Pereiro to travel to Bremen to carry out the experiment. Two publications in common are expected from this experiment. Experiments 1 and 4 will be scheduled within the next month.
Impact Not outcomes yet. Several common publications and funding proposals are expected.
Start Year 2020
 
Description Demonstration of LEEM laboratory in visit of First Secretary of State and Minister for the Cabinet Office. 
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 demonstrated the MBE-LEEM instrument to the First Secretary of State and Minister for the Cabinet Office and the media.
Year(s) Of Engagement Activity 2017
URL https://www.walesonline.co.uk/news/politics/carwyn-jones-made-major-threat-13572822
 
Description Development of Cardiff LEEM lab webpage 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Development of the webpage associated to the LEEM laboratory group at Cardiff University.
Year(s) Of Engagement Activity 2018
URL https://leemlab.cf.ac.uk/
 
Description Development of Physics demonstrations 
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 I develop physics demonstrations with undergraduate students. These demonstrations are used in open days and have also been used by Science Made Simple in some of their shows at schools across the UK.
Year(s) Of Engagement Activity 2017,2018
URL http://www.sciencemadesimple.co.uk/
 
Description Innovation in Isolation - Dissemination talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Dissemination talk through youtube live.
Year(s) Of Engagement Activity 2020
URL https://www.youtube.com/channel/UCXuEKKD55k05QVrn1rbrFlA
 
Description Presentation at LEEM/PEEM international conference, Chongqin (China), October 30th-November 3rd (2018) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk summarizing our work on "Time Resolved and Selected Energy Dark Field LEEM Imaging for Optimal Surface Phase Discrimination on GaAs(001)" at LEEM/PEEM international conference, Chongqin (China), October 30th-November 3rd (2018). The talk was given by Y.Niu who was working in the group as a post-doctoral fellow at the time of the conference.
Year(s) Of Engagement Activity 2018
 
Description Press release: A press release for one of our publications was written by Cardiff University press office and distributed by several internet outlets 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact The initial press release and websites that distributed the news are listed below. A couple of outlets for scientific dissemination has contacted the group to write a piece on our instrument.

https://www.cardiff.ac.uk/news/view/1716639-scientists-spy-unstable-semiconductors
https://compoundsemiconductor.net/article/109274/GaAs_not_as_stable_as_thought
https://www.electronicsweekly.com/news/business/instabilities-gaas-surfaces-discovered-2019-11/
https://scitechdaily.com/scientists-spy-unstable-compound-semiconductors-could-have-profound-consequences/
http://www.semiconductor-today.com/news_items/2019/nov/cardiff-041119.shtml
https://www.sciencedaily.com/releases/2019/11/191104112849.htm
https://www.nanowerk.com/nanotechnology-news2/newsid=53954.php
https://phys.org/news/2019-11-scientists-spy-unstable-semiconductors.html
Year(s) Of Engagement Activity 2019
 
Description Science Cafe - Cardiff 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Public talk describing my research and current progress on semiconductor physics at Cardiff University. The talk started a debate on the future of electronics and current progress at Cardiff University. The talk also sparked interest from Welsh government workers.
Year(s) Of Engagement Activity 2018
URL https://twitter.com/scicafecardiff?lang=en