Using molecular-beam epitaxy (MBE), I explored the mechanisms behind the formation of GaN quantum dots (QDs) through the nitridation of Ga droplets. Substrate type and temperature influence the size, density, and polytype (zincblende or wurtzite) of QDs. There are two competing mechanisms when it comes to self-assembly GaN QDs: 

• QD formation at pre-existing Ga droplets 

• QD formation at other surface locations via Ga surface diffusion

Substrate greatly impacts diffusion and nucleation processes. Tailoring QD properties for III-N semiconductor applications is possible through careful consideration of the impact of substrates (i.e. native oxide, crystal orientation, etc).  

For the full study, see: Mechanisms of GaN quantum dot formation during nitridation of Ga droplets, H. Lu, C. Reese, S. Jeon, Y. Fan, E. E. Rizzi, Y. Zhuo, L. Qi, and R. S. Goldman, Applied Physics Letters.116, 062107 (2020);  https://doi.org/10.1063/1.5133965

During molecular-beam epitaxy (MBE), the transition between zinc blende (ZB) and wurtzite (WZ) GaN structures is possible. Gallium (Ga) surface saturation, Ga diffusion, and SixNy interlayer formation greatly impact NW and thin film morphology selection. A nested type-I band alignment at the ZB/WZ interface is observed, impacting optical properties. Understanding how to tailor polytype selection and nanowire growth mechanisms can enable and improve CMOS-compatible GaN-based optoelectronics.

For the full study, see: Influence of gallium surface saturation on GaN nanowire polytype selection during molecular-beam epitaxy, H. Lu, S. Moniri, C. Reese, S. Jeon, A. Katcher, T. Hill, D. Hui, and R. Goldman, Applied Physics Letters. 119, 031601 (2021) https://doi.org/10.1063/5.0052659