0. ESR : Shumithira Gandan
WP2
Characterisation of Novel Materials for Avalanche Photodiodes
PROMIS Mid-term Review Meeting, London
ESR : Shumithira Gandan
Supervisors : Dr. Tomasz Ochalski & Dr. David Williams
Tyndall National Institute, Ireland
7th December 2016

1. Personal background
Beng (Hons) Electrical and Electronics Engineering, Malaysia
MSc Electrical and Electronics majoring in Photonics, Malaysia

2. Project title
Optical characterization of novel Avalanche Photodiode (APD) samples.
Aim
To obtain information from APD samples with various spectroscopy techniques such as photoluminescence (PL), time resolved photoluminescence (TRPL), modulation spectroscopy and spectral elipsometry
Deliverables
Carrier dynamics and bandgap structure of the quartenary alloy.
Identification of possible defects and their activation energy to define the non-radiative recombination channels.

3. Photonics – Physics of interaction of light with matter
Background of project
Incident light ray
Matter
Photonics – Physics of interaction of light with matter
Reflection
Transmission
Scattering
Photoluminescence
Absorption
-- Sample --
Converts incident photons
to different wavelength
-- Filter --
Passes part
of the spectrum
Energy
Electrical energy
(laser)
--Detector--
Spectroscopy – Experimental techniques to measure the interaction of light with matter
Novel quartenary materials for Avalanche Photodiodes -
AlGaAsSb
Samples tested

4. Photoluminescence spectroscopy
Involves photoexcitation of the sample using a laser source so that the emission from the sample can be read and interpreted.
Temperature dependent PL experiments for four samples of Al1-xGaxAsSb, x = 0, 5, 10, 15
Samples are placed in a cryostat and cooled to very low temperatures (7-10K) and heated slowly with measurements taken at each interval
Information: wavelengths at which radiative recombination occurs
Intensity (a.u)
Wavelength (nm)
Wavelength (nm)
Temperature (K)

5. Wavelength (nm)
Intensity (a.u)
Power dependence of Ga 15% at 7K
Power dependent PL measurements are done to determine the most suitable power for sample excitation.
Setup for PL and TRPL

6. Time resolved photoluminescence spectroscopy
Involves spectral and temporal evolution of the emission of a sample following its
illumination by a short pulse of light.
Low
High
Laser repetition
rate
Laser repetition
rate

7. Information: transition energies, carrier lifetimes
Intensity of emission proportional to the number of photo-generated carriers
Information: transition energies, carrier lifetimes
Decay times reflect recombination rates and reveals quality of crystalline structure
Presence of impurities and defects significantly reduce decay times
Wavelength(nm)
Time(ps)
Streak image of measured AlGaAsSb at 830nm and 7K
Decay times of temperature dependent TRPL

8. Photoreflectance & Electroreflectance spectroscopy
A spectroscopy technique that allows probing of the electric field of the sample through electromodulation
Information: bandgap structure and alloy composition particularly in quartenary compounds
Setup for PR

9. Collaboration with other WPs
1. WP1 - GaAsN/GaAsN:H Quantum dots - Sapienza Universita’ di
Roma
2. WP3 - GaSbN Quantum dots in intermediate band semiconductors for solar cells - Lancaster University
3. WP4 - InAsSb/GaSb and plasmonics for high sensitivity chemical and bio-sensing - Universitè Montpellier 2
GaAsN:H
GaAs
GaAsN
GaAs: cap 100nm
GaAs: spacing Layer “0,3,5,40nm”
GaAs: buffer nm
n doping GaAs (Si) substrate QD
stack (x10)
QD GaSb
GaSb

10. Summary
Different optical characterization techniques have been used to investigate the physical parameters and quality of the grown APD samples.
Continued characterization will provide a complete understanding of the Al1- x Gax AsSb layers and allow feedback to University of Sheffield for optimizing growth of the sample layers for APD fabrication.
TRPL, PL and autocorrelation characterization of GaAsN/GaAsN:H quantum dot samples from Sapienza Universita’ di Roma was also done to provide feedback on quality of samples.

11. Skills acquired
Advanced optical techniques in photoluminescence, time-resolved
photoluminescence, and modulation spectroscopy
Ridge waveguide laser fabrication process
Cryogenics and vacuum technology
2 week secondment in University of Sheffield;
Basic electrical characterization of avalanche photodiode samples,
including IV, CV and X-ray absorption spectrum analysis.
Analysis of the rationale behind choosing specific parameters for the
APD materials
Courses : Key Enabling Technologies (KETs) workshop, Photonic Devices and
Materials, Advanced Characterization of Materials, Laser safety, Cryogenics
safety training

12. Outputs Poster presentation Oral presentation
Effect of Gallium composition in AlGaAsSb alloys for APDs
S. Gandan, J.S.D. Morales, X. Zhou, C.H. Tan, J.S. Ng and T.J. Ochalski, 19th International Conference on Molecular Beam Epitaxy, Montpellier (2016)
Oral presentation
Optical characterization of natural and CVD diamonds and diamond nano-particles; emission dynamics studies
Tomasz J. Ochalski, H.Ye, D. Saladukha, J. Morales, S. Gandan
33rd International Conference on the Physics of Semiconductors, Beijing (2016)
Optical spectroscopy of P-GaAs nanopillars on Si for monolithically- integrated light sources
J.S.D Morales, S. Gandan, D. Ren, D. L. Huffaker, T. J. Ochalski,
SPIE, Photonics West Conference & Exhibition, San Francisco, California (Jan 2017)

13. Future work
N umerical analysis of PR/ER spectra with Third Derivate Lineshape (TDLS) and Airy function line shape fitting to derive accurate bandgap information and broadening parameters of APD samples.
Spectroscopy and analysis of samples from collaborations.
Hosting of planned secondments
28th November – 3rd December 2016
ESR 14 from Universitè Montpellier 2 (Mario Bomers)
Within the next month
ESR 9 from Lancaster University (Denise Montesdeoca Cardenes)
Planned secondments
Universitè Montpellier 2 (May 2017)
University of Sheffield (2017)

14. Aspirations
Industry position in photonics sector related to optical characterization techniques.
Academic position in a topic to further investigate physics related to spectroscopy.