Discovery of Topological States in InN Quantum Dots

Student: Malak Refaei

Degree: Ph.D., December 2022

Major Professor: Dr. Morgan Ware

Research Area(s):

Microelectronics & Photonics

Nanoscience & Engineering

View Research Quadslide

Background/Relevance

  • The prediction that InN thin films may become a two dimensional (2D) topological insulator results in increasing the research interest of InN.
  • Topological insulator can be utilized as quantum bits “qubits” in order to manage quantum information which would provide a potential improvement of quantum computing.

Innovation

  • Explore a novel growth technique of InN QDs.
  • Investigate the topological state in InN QDs.

Approach

  • Growing InN QDs using MBE.
  • Grow a low temperature GaN layer to cap InN QDs either through MME or conventional growth techniques in order to protect the InN QDs.
  • Photoluminescence is used to probe the QDs.
  • Atom Force Microscope (AFM) measurements is used to understand of QD size and distribution
  • Fabricate sub-micrometer metal apertures on the surface of the InN/GaN QDs using electron-beam lithography.

Key Results

  • Simulated the band structure of GaN/InN/GaN using Nextnano software for different QW thicknesses with and without strain.

Conclusions

  • The application of strain by the GaN substrate resulting from coherent growth results in the bandgap narrowing and inverting due to the large strain and deformation potentials of InN. The resulting piezoelectric polarization results in a substantial quantum-confined Stark effect, which ultimately causes the confined electron-hole states to become inverted at ~4 MLs.

Future Work

  • Grow InN/GaN QDs using MBE using droplet technique.
  • Find good growth conditions for capping InN with epitaxial GaN.
  • Measure photoluminescence emission from InN QDs.