0. 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

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

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

3. 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

4. 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

5. 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

6. Present Results and Analysis: GaSb/GaAs QRs
DIFFRACTION CONTRAST
GaSb QR
Low QR density ( /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

7. 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

8. 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

9. Summary
GaSb/GaAs QRs: the analysis by diffraction contrast shows low QR density of /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.

10. 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.

11. 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.

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