1. Confinement of Excitons in Strain-engineered InAs/InGaAs/GaAs Metamorphic Quantum Dots
By Shaukat Ali Khattak1,2
Manus Hayne1, Luca Seravalli3, Giovanna Trevisi3 and Paola Frigeri3
1Department of Physics, Lancaster University, Lancaster LAI 4YB, UK,
2Department of Physics, Abdul Wali Khan University Mardan, Pakistan, 3CNR-IMEM Institute, Parco delle Scienze 37a, I Parma, Italy

2. Why InAs/InGaAs/GaAs QDs?
Telecom-wavelength emission (1.3 – 1.5 µm)
low attenuation in optical fibres.
InAs/InGaAs/GaAs strain-engineered (tuning of emission wavelength)

3. Structure of the sample
Base diameter and height of InAs QDs are 21 ± 4 nm and 4 ± 1 nm respectively. AFM measurements confirm that they are independent of X
InAs QDs
InGaAs upper confining layer (UCL)
InGaAs colower nfining layer (LCL)
GaAs substrate
QDs self-assemble due to strain from lattice mismatch

4. How to control emission wavelength?
Changing In composition in CLs:
Affects conduction and valence band discontinuities between QDs and CLs.
changes strain
Changing LCL thickness “d”:
Affects only mismatch between QDs and LCL
InAs QDs
InGaAs upper confining layer (UCL)
InGaAs lower confining layer (LCL)
GaAs substrate

5. What are we looking for? Exciton confinement: Whether confined or not?
How much?
What do we mean by ‘strongly’ confined?
We do this by measuring exciton properties
(like reduced mass and radius)

6. Strong and weak confinement?
Strong confinement: when ΔEL and ΔEQ is large
ΔEL
ΔEQ
Energy level of the dot
Energy level of the exciton
InAs QD
Wave function of exciton
InGaAs

7. Strong and weak confinement?
Weak confinement, Case 1: when ΔEL (exciton localization energy) is small,
ΔEL
ΔEQ
Energy level of the dot
Energy level of the exciton
InAs QD
Wave function of exciton
InGaAs

8. Strong and weak confinement?
Weak confinement, Case 2: when ΔEQ (exciton quantization energy) is small,
ΔEL
ΔEQ
Energy level of the dot
Energy level of the exciton
InAs QD
Wave function of exciton
InGaAs

9. Tool used Magneto-photoluminescence at Low Temperature (2K)
Excitonic Model:
where aB and µ are the Bohr
radius and reduced mass of
exciton respectively.
Transition from Eq-1 to Eq-2
occurs when magnetic length  becomes smaller
than the spatial confinement.
for
Eq- 1
Eq- 2

10. Our results & analysis

11. Our results & analysis

12. Our results & analysis
The mass increases with increase in mismatch up to 6 % and then suddenly drops down

13. Our results & analysis
No clear trend in radius with increasing mismatch

14. Further Work & Conclusion:

15. Further Work & Conclusion:
As We want to probe the exciton confinement.
Therefore these results lead us towards:
1- Determination of exciton confinement by finding reduced mass of exciton and diamagnetic shift coefficient.
2- Evidence that the trend in data is the effect of two parameters x & d.
3- Need of more samples to probe the confinement

16. Thanks for attention