Nanoscale and Atom-scale Characterization of Novel Functional Nanostructures for Photonics and Photovoltaics Atif Alam Khan ESR Cádiz INNANOMAT GROUP (MATERIALS and NANOTECHNOLOGY for INNOVATION) Department of Material Science, Metallurgical Engineering and Inorganic Chemistry, IMEYMAT Faculty of Science University of Cádiz 11510 Puerto Real, Cádiz, Spain. Date: December 8, 2016

Outline Personal Background The Project Project Background Methodology and Instrumentation Present Results and Analysis Summary Future Works

Personal Background MSc. in Micro- and Nanotechnology BSc. in Electrical and Electronic Engineering Research on Microphotolumincesce of Nanostructures

The Project Process Flow Aims Materials for Energy (CPV): WP3 Identification of optimum design parameters for antimony (Sb) based energy saving high efficient mid-infrared (MIR) III-V solar cells (SCs), light emitting diodes (LEDs) and gas sensors (GSs) using various transmission electron microscopy (TEM) techniques. Motivation 3.6 million GWh electric usage by 2020 High efficient SC Cheaper III-V photonic materials Solutions III-Sb quantum dot (QD) IBSC and LEDs III-Sb/Si hybrid tandem structures Optimization Modelling Growth Processing Characterization Morphological and Compositional analyses TEM CPV: Concentrated Photovoltaics IBSC: Intermediate Band Solar Cell

Project Background InSb sub-monolayer QDs for LEDS QRs: Quantum Rings Materials InSb sub-monolayer QDs for LEDS InxAl1-xAsySb1-y for SCs/GSs GaxIn1-xAs/III-Sb for SCs/GSs GaSb QRs for SCs Si InAs GaAs (Al)GaSb AlSb/GaSb QD formation wetting layer dependent Low QD density Functionality barrier layer dependent: AlSb Differences in lattice constants and thermal expansion coefficients QRs shapes, density and dimensions control device performace TEM Analyses Structural quality and dimensions Barrier based influences Defect type and density Compositional distribution Designing high efficient MIR photonic devices

Methodology and Instrumentation JEOL 2100 JEOL 2010F FEI Titan Cubed Themis Double Aberration Corrected CTEM: Diffraction contrast based morphological analysis HRTEM: Cross-sectional measurements of nano-structures HAADF-STEM: Atomic level compositional mapping EDX: Material identification InSb QDs EELS: Material identification at nano-scale InxAl1-xAsySb1-y GaxIn1-xAs GaSb QRs CTEM: Conventional TEM HRTEM: High Resolution TEM HAADF-STEM: High Angle Annular Dark Field-Scanning TEM EDX: Energy –dispersive X-ray EELS: Electron Energy Loss Spectroscopy

Present Results and Analysis: GaSb/GaAs QRs DIFFRACTION CONTRAST GaSb QR Low QR density (0.004-0.02/nm) Large barrier prevents vertical stacking GaSb WL GaSb WL GaAs GaSb QR No structural defect/dislocation QR induced strain observed GaAs 220 bright field image 002 dark field image HAADF-STEM nanocup QR Average QR diameter = 25±3 nm Average lobe diameter = 5±2 nm Average lobe height = ~ 3 nm HAADF images show that the QRs have the shape of nanocups HAADF-STEM image

Present Results and Analysis: InSb/InAs QDs DIFFRACTION CONTRAST InAs (200 nm) InAs (200 nm) The diffraction contrast images ensure the presence of 10 InSb QDs layers with good quality. InSb QDs layers InAs (100 nm) HAADF images are sensitive to the average Z number in the atomic columns. A new methodology based in HAADF experimental images and simulations is in progress in order to quantify the Sb distribution at atomic column resolution. This will allow analyzing the QDs characteristics, in order to be correlated to their functional properties. 002DF 220BF InAs (100 nm) CTEM images HAADF-STEM Intensity profiles from column 10 of the HAADF-STEM image In In Sb InAs As Group III Group V InSb In: Z-> 49 Sb: Z-> 51 HAADF-STEM image of a QD layer region As: Z-> 33 Simulated intensity profile at ideal case InAs

Present Results and Analysis: InSb/(Al)GaSb QDs DIFFRACTION CONTRAST The analysis by diffraction contrast shows that the InSb/(Al)GaSb QDs layers have good structural quality. QDs layers ATOM PROBE TOMOGRAPHY Atom probe tomography (APT) analysis is in progress in order to obtain 3-dimensional (3D) information on the composition distribution of the material. First analyses failed because of the difficulties in specimen preparation by focused ion beam (FIB) of Sb containing materials. The optimization of the preparation process is in progress. 220BF 002DF CTEM images HAADF-STEM In this case, the existence of more than one group III elements complicate the correlation intensity-composition from HAADF images. Scanning Electron Microscope (SEM) image of a FIB micro-needle sample for APT HAADF-STEM image of a QD layer region

Summary GaSb/GaAs QRs: the analysis by diffraction contrast shows low QR density of 0.004-0.02/nm with no vertical stacking in the SC structure, with an overall good structural quality. The QRs have “nanocup” shape with an average diameter of ~ 25 nm. These shape and dimension based information will help finding high optical quality associated design parameters from fabrication point of view. InSb/InAs QDs: the development of a new methodology based in HAADF-STEM experimental images and simulations is in progress in order to quantify the Sb distribution at atomic column scale, what will allow the study of the QDs size and shape. InSb/(Al)GaSb QDs: the analysis by diffraction contrast ensures a good structural quality. APT analysis are in progress in order to obtain 3D compositional information from the material, and for this the optimization of the sample preparation by FIB is being carried out.

Skills acquired Operating JEOL 2100 microscope to do diffraction contrast. Interpretation of diffraction contrast images Interpretation of HAADF-STEM images with qHAADF and MATLAB software Conventional electron transparent TEM sample preparation techniques Outputs Poster presentation in European Microscopy Conference (EMC) in Lyon, France in August, 2016. Poster presentation in Molecular Beam Epitaxy (MBE) conference in Montpellier, France in September, 2016.

Future Works Analysis of InSb/InAs QDs using HAADF-STEM experimental images and MATLAB simulated data to obtain Sb composition, followed by low loss EELS experimentation for comparative analysis Analysis of InSb/(Al)GaSb QDs samples by APT to determine In composition and hence, generating complete compositional map Analysis of InxAl1-xAsySb1-y quaternary alloy with the help of qHAADF software and MATLAB simulations Analysis on GaxIn1-xAs/III-Sb/Si samples Involvement in various outreach programs Set up a robust network platfrom that should help me advancing my career as a future expert either in industry or academy.

Thanks for your attention ¿QUESTIONS? Daniel Fernández de los Reyes 12 Cádiz