Nanoscale characterisation of nitride semiconductor thin films using EBSD, ECCI, CL and EBIC.

Lead Research Organisation: University of Strathclyde
Department Name: Physics

Abstract

The aim of this project is to produce a step change in the performance of the scanning electron microscopy techniques of electron backscatter diffraction (EBSD), and electron channelling contrast imaging (ECCI), and exploit these relatively new techniques together with cathodoluminescence imaging (CL) and electron beam induced current (EBIC) for the characterisation and hence the improvement of nitride semiconductor thin films. Such materials are used in the manufacture of UV/blue laser diodes, UV/visible LEDs and white LEDs. Nitride laser diodes are presently dictating the development of next generation DVDs and developments in printing and colour copying. Present applications of nitride LEDs extend from street lighting, to back lighting in mobile phones, to traffic lights. Future use of nitride-based LEDs promises to revolutionise lighting in the home and office. Nitrides are also being developed for the production of high frequency, high power electronic devices.

EBSD is an attractive technique with which to interrogate the crystallographic properties of materials because it can provide information on crystal orientation, polytype and strain with a resolution of tens of nanometres. In EBSD an electron beam is incident on a sample which is tilted at an angle of typically 70 degs. The impinging electrons are scattered inelastically through high angles forming a diverging source of electrons that can be diffracted. A simple description for the formation of an electron backscatter diffraction pattern (EBSP) presumes that electrons that satisfy the Bragg condition for a given plane emanate in diffraction cones from both the upper and lower surfaces of that plane. When these cones intersect a phosphor screen Kikuchi lines are observed. An EBSP consists of a large number of overlapping Kikuchi bands and is a 2-D projection of the crystal structure. Rotation of a crystal will produce a rotation of the EBSP; a tilt of a crystal will produce a shift in the EBSP, strain will produce distortion of the EBSP. EBSPs acquired from a mesh of points on a sample will produce a map of tilt, rotations or strain in that sample. In the course of our research we aim to attain much improved levels of sensitivity (less than 1 part in 10,000) to changes in tilt, rotation and strain to obtain detailed high resolution information on the crystallographic texture and strain distribution in nitride semiconductors.

ECCI can be used to reveal single crystallographic defects such as dislocations in semiconductor thin films. In ECCI the intensity of electrons backscattered from a suitably oriented sample depends on the relative orientation of planes in a crystal. Changes in crystallographic orientation or changes in lattice constant due to strain are revealed by changes in grey scale of an image constructed by monitoring the intensity of backscattered electrons as an electron beam is scanned over the sample. Defects are imaged due to lattice plane tilting and strain they produce. Our aim is develop the ECCI technique so that it may be used to fully characterise all defects present in our films.

We plan to apply these powerful techniques to optimise the quality of nitride semiconductor thin films, including: (i) non-polar and semi-polar nitride thin films, (ii) epitaxially overgrown nitride thin films and nitride thin films grown on native substrates, (iii) high aluminium content nitride thin films (including films grown on silicon), (iv) high indium content nitride thin films, and (v) zinc blende nitride thin films. Such novel nitride semiconductor structures will allow the production of higher power LEDs and extend their wavelength range to the red and infrared. They will also open up new applications for nitride-based devices - solar cells for example.

Throughout the project we will also establish with industrial partners the best routes for development and commercialisation of new instrumentation, and nitride thin film growth processes.

Planned Impact

The aim of our project is to develop and apply novel, rapid, high resolution and non-destructive characterisation techniques to the optimisation of III-nitride semiconductors. We envisage a step change in the identification and the subsequent reduction of defects in these materials. We envisage a tenfold improvement in the time required to obtain quantitative information on defects compared to presently available techniques. This is due to the minimal sample preparation required for materials characterisation using the EBSD, ECCI, CL and EBIC techniques. Our project will have a major impact on the time taken to optimise new nitride materials such as those to be studied in this project, namely semi-polar and non-polar nitride thin films, high aluminium and high indium concentration nitride thin films. Reducing the defect densities in such materials is fundamental to the optimisation of a multiplicity of III-N devices. These include laser diodes operating across the visible, in particular in the green (filling in the 'green gap') and high aluminium content AlInGaN semiconductor thin films from which high efficiency UV LEDs could be manufactured. UV LEDs are of use in a wide range of applications, in particular biomedical, pharmaceutical and germicidal/sterilisation. Reduction in defect densities should also benefit visible LEDs, particularly at the very high drive current densities needed for high efficiency lighting. Minimising defects in AlInGaN semiconductor thin films is critical to development of nitride based high power electronics with applications ranging from electric cars to high power distribution.
We are collaborating with three UK based SMEs that are well placed to exploit advances we produce in the EBSD, ECCI, CL and EBIC techniques, i.e., BLG Productions, Aunt Daisy Scientific and K.E. Developments. Collaboration between AJW and BLG Productions has already produced Cross Court 2 a commercially available Strain Measurement software package. Cross Court 2 is presently in use in academic and commercial research and development environments around the world. We envisage that our collaborative research with Aunt Daisy Scientific and K.E. Developments will lead to new and improved instrumentation and software and open up new markets for their products. Collaborative work to date has already led to improvements to K.E.'s new backscattered electron detector and the development of software to analyse ECP patterns (by Aunt Daisy Scientific). The markets for the EBSD and ECCI techniques are presently mainly confined to the geosciences and to metallurgy, our research will expand this market to the world of semiconductor research and industry.

Publications

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Naresh-Kumar G (2016) Electron channelling contrast imaging for III-nitride thin film structures in Materials Science in Semiconductor Processing

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Naresh-Kumar G (2014) Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN. in Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada

 
Description Our project investigated technologically important GaN-based semiconductor materials. Such materials underpin highly successful and growing technologies, such as LED lighting and high power, high frequency transistors, and also have great potential in developing technologies, such as UV emitters and solar energy converters. However, deeper understanding of the materials is needed to ensure progress. We have expanded the capabilities of the advanced scanning electron microscope based techniques of electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) and combined the use of these techniques with cathodoluminescence (CL) imaging and electron beam induced current (EBIC) imaging. For example, we can now use cross-correlation based high resolution electron backscatter diffraction (HR-EBSD) and ECCI to quantitatively map the strain variation and lattice rotation and determine the density of structural defects such as dislocations and stacking faults in nitride semiconductor thin films. We can acquire EBSD maps and ECCI micrographs from both the top and the side of a sample, i.e., acquire both plan-view and cross-sectional images. We can compare ECCI micrographs, CL and EBIC maps and explore the influence of structural defects on the sample's luminescence and electrical properties. Experiments are guided and data interpreted through use of imaging tools, statistical analysis and theoretical simulations. We have also explored new detector development, demonstrating the advantages of energy filtered direct electron detection for the acquisition of EBSD patterns. In all our endeavours we collaborated with a wide range of academic and industrial partners.
Exploitation Route Ourselves and researchers world-wide are using the techniques we have developed to characterise nitride semiconductors and other material systems.
Sectors Aerospace, Defence and Marine,Electronics,Energy,Manufacturing, including Industrial Biotechology

URL http://ssd.phys.strath.ac.uk/
 
Title Data for Diffractive triangulation of radiative point sources 
Description This dataset contains detector diffraction patterns and electron backscatter diffraction patterns acquired using the digital hybrid pixel detector Timepix. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Not recorded 
 
Title Data for: "Design and fabrication of enhanced lateral growth for dislocation reduction and strain management in GaN using nanodashes" 
Description This dataset contains the results of scanning electron microscopy (SEM) secondary electron (SE) images, panchromatic cathodoluminescence (CL) imaging and Electron Channelling Contrast Imaging (ECCI) and Raman spectroscopy on GaN epitaxial layers. These techniques were used to assess the morphology of the GaN crystal growth, and the dislocation density and strain in planar layers. Dataset held at University of Bath Research Data Archive 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact
 
Title Data for: "Scanning electron microscopy as a flexible technique for investigating the properties of UV-emitting nitride semiconductor thin films" 
Description Scanning electron microscope images, electron channelling contrast micrographs, Electron backscatter diffraction data and cathodoluminescence data 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact
 
Title Electron channelling contrast and cathodoluminescence images obtained from III-nitride layer structures 
Description "Electron channelling contrast imaging (ECCI) performed in a scanning electron microscope (SEM) is a rapid and non-destructive structural characterisation technique for imaging, identifying and quantifying extended defects in crystalline materials. This dataset provides examples of applying the ECCI technique to GaN-based structures, including: - Comparing ECCI using forescatter and backscatter geometries; - Applying ECCI to GaN thin films, GaN-based high electron mobility transistor (HEMT) structures and GaN-based distributed Bragg reflectors (DBRs); - Comparing ECCI from GaN grown on different substrates and different crystal planes; - Correlating ECCI with cathodoluminescence (CL) imaging. The text file Data_description.txt provides further experimental details, and more in-depth analysis is presented in G. Naresh-Kumar et al. (2016) Materials Science in Semiconductor Processing and G. Naresh-Kumar et al. (2014) Microscopy and Microanalysis 20 55-60." 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Not recorded 
 
Title Energy filtered electron backscatter diffraction patterns obtained using direct electron imaging 
Description This dataset contains electron backscatter patterns (EBSPs) using a Medipix direct electron array detector. The figure numbers refer to those in the Physical Review B paper by Vespucci et al. associated with this dataset. Note that the images in Figures 1, 3 and 4 are saved in a 32-bit floating-point TIFF format, which may only be opened by scientific imaging software (such as ImageJ). 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Not recorded 
 
Description Joint research with SHEFFIELD UNIVERSITY 
Organisation University of Sheffield
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from SHEFFIELD UNIVERSITY
Start Year 2012
 
Description Joint research with University of Bath 
Organisation University of Bath
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Bath
Start Year 2012
 
Description Joint research with University of Nottingham 
Organisation University of Nottingham
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Nottingham
Start Year 2012
 
Description Joint research with University of Oxford 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Oxford
Start Year 2012
 
Description Project partnership with Aunt Daisy Scientific, Glouster, England 
Organisation Aunt Daisy Scientific
Country United Kingdom 
Sector Private 
PI Contribution Aunt Daisy Scientific, Glouster, England worked with the research team and assisted/contributed to the project outcomes
Start Year 2012
 
Description Project partnership with KE Developments, Cambridge, England 
Organisation K E Developments Ltd
Country United Kingdom 
Sector Private 
PI Contribution KE Developments, Cambridge, England worked with the research team and assisted/contributed to the project outcomes
Start Year 2012
 
Description Invited Talk: 12th International Conference on Nitride Semiconductors, Strasbourg, France, July, 2017 Title: Novel scanning electron microscopy techniques for rapid structural characterisation of III-N films. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Invited Talk: 12th International Conference on Nitride Semiconductors, Strasbourg, France, July, 2017 Title: Novel scanning electron microscopy techniques for rapid structural characterisation of III-N films.
Year(s) Of Engagement Activity 2017
 
Description Invited Talk: International Workshop on UV Materials and Devices 2017, Fukuoka, Japan, November 2017 Title: Nanocharacterisation of the structural and luminescence properties of UV light-emitting materials in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Invited Talk: International Workshop on UV Materials and Devices 2017, Fukuoka, Japan, November 2017 Title: Nanocharacterisation of the structural and luminescence properties of UV light-emitting materials in the scanning electron microscope
Year(s) Of Engagement Activity 2017
 
Description Invited talk: 21st International Conference on Microscopy of Semiconducting Materials (MSM-XXI), UK, April 2019 Title: Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Invited talk: 21st International Conference on Microscopy of Semiconducting Materials (MSM-XXI), UK, April 2019 Title: Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope
Year(s) Of Engagement Activity 2019
 
Description Invited talk: Gordon Research Conference on Defects in Semiconductors, New London, US, August 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk: Gordon Research Conference on Defects in Semiconductors, New London, US, August 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope
Year(s) Of Engagement Activity 2018
 
Description Invited talk: International Workshop on Nitride Semiconductor, Japan, November 2018 Title: Visualization and investigation of defects using electron channeling (electron diffraction) in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk: International Workshop on Nitride Semiconductor, Japan, November 2018 Title: Visualization and investigation of defects using electron channeling (electron diffraction) in the scanning electron microscope
Year(s) Of Engagement Activity 2018
 
Description Invited talk: State-of-the-art trends of scientific research of artificial and natural nanoobjects (STRANN), Russia, October 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk: State-of-the-art trends of scientific research of artificial and natural nanoobjects (STRANN), Russia, October 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope
Year(s) Of Engagement Activity 2018
 
Description Invited talk: The Royal Microscopical Society Electron Backscatter Diffraction Conference, UK, April 2019 Title: Visualisation and investigation of defects using electron channelling (electron diffraction) in the scanning electron microscope. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talk: The Royal Microscopical Society Electron Backscatter Diffraction Conference, UK, April 2019 Title: Visualisation and investigation of defects using electron channelling (electron diffraction) in the scanning electron microscope.
Year(s) Of Engagement Activity 2019
 
Description Invited talk: mmc2019 EMAG, UK, July 2019 Title: Electron backscatter diffraction - exploring the structural properties of materials in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Invited talk: mmc2019 EMAG, UK, July 2019 Title: Electron backscatter diffraction - exploring the structural properties of materials in the scanning electron microscope
Year(s) Of Engagement Activity 2019
 
Description Invited talk:CAM-IES Workshop: Multi-Modal Characterisation of Energy Materials, UK, November 2019 Title: Investigating crystal structure, defects and luminescence from optoelectronic materials in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Invited talk:CAM-IES Workshop: Multi-Modal Characterisation of Energy Materials, UK, November 2019 Title: Investigating crystal structure, defects and luminescence from optoelectronic materials in the scanning electron microscope
Year(s) Of Engagement Activity 2019
 
Description Invited talk:EMAS 2019 - 16th European Workshop on Modern Developments and Applications in Microbeam Analysis, Norway, May 2019 Title: Advances in electron channelling contrast imaging and electron backscatter diffraction for imaging and analysis of structural defects in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Invited talk:EMAS 2019 - 16th European Workshop on Modern Developments and Applications in Microbeam Analysis, Norway, May 2019 Title: Advances in electron channelling contrast imaging and electron backscatter diffraction for imaging and analysis of structural defects in the scanning electron microscope
Year(s) Of Engagement Activity 2019
 
Description Lecture Series in India as part of "Science and Beyond" organised by the British Council, January 2016. Gave talks on - "Studying structure and light emission in the scanning electron microscope" and "Engaging the Public with Science and Technology - from statues to rainbows" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Lecture Series in India as part of "Science and Beyond" organised by the British Council, January 2016. Gave talks on - "Studying structure and light emission in the scanning electron microscope" and "Engaging the Public with Science and Technology - from statues to rainbows"
Year(s) Of Engagement Activity 2016
 
Description Lecture at the Birla Industrial and Technological Museum (BITM), Kolkata, India, January 2015 "Nitrides - The Rainbow Material" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Third sector organisations
Results and Impact Lecture at the Birla Industrial and Technological Museum (BITM), Kolkata, India, January 2015 "Nitrides - The Rainbow Material"
Year(s) Of Engagement Activity 2016
 
Description Maxwell Lecture at King's College London, March 2015 "Nitrides - The Rainbow Material" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact Maxwell Lecture at King's College London, March 2015 "Nitrides - The Rainbow Material"

To improve understanding of others thinking
Year(s) Of Engagement Activity 2015
 
Description Plenary Lecture: International Workshop on Advance Materials and Device Technology, Chennai, India, November 2017 Title: Characterisation of the structural and luminescence properties of nitride materials in the scanning electron microscope 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Plenary Lecture: International Workshop on Advance Materials and Device Technology, Chennai, India, November 2017 Title: Characterisation of the structural and luminescence properties of nitride materials in the scanning electron microscope
Year(s) Of Engagement Activity 2017