In 2023, the Nobel Prize in Chemistry was awarded for the discovery and development of quantum dots. Quantum dots are very luminescent nanoparticles used for various optoelectronic, photonic, quantum, and sensing applications. Using MBE, I grow InAs QDs emitting at 1.3 micron and quantum dashes emitting at 2.0 micron.

The 2 micron wavelength is promising for telecommunication, gas sensing, medical imaging, spectroscopy, lidar, and even gravitational wave observation!

There are so many alloys we can grow using MBE, but only few kinds of substrates available. The most coveted substrate is silicon. Unfortunately, due to mismatches in lattice, polarity, and thermal properties, growing III-V materials on Si introduces defects and dislocations, which kill the device. We develop sophisticated buffer designs to minimize these defects.

We have grown GaAs on Si, InAs on Si, InAsSb0.6 on GaAs, GaSb on Si, and In0.53AlGaAs on Si.

While the materials science of QD growth and mismatch epitaxy are interesting, a device needs to be eventually made. After growing p-i-n or n-i-n epitaxial layers, we fabricate the materials into various emitting (laser, LED) and photodetecting (solar cell, PD, QWIP) devices. We also transferred some of the PD and solar cells to flexible substrates. I specialize in fabricating narrow-ridge waveguide lasers with ridge widths below 6 um.

Graphene/QD heterostructures exhibit properties that are otherwise unobtainable from either material alone. We grow the QD using MBE and transfer CVD-grown graphene. We have shown that this mixed-dimensional heterostructure shows up to 8x enhancement in photoluminescence.