Lattice matched epitaxial shell growth on InZnP quantum dots

Abstract

Quantum dots are semiconductor nanocrystals that exhibit size specific photophysical properties. Therefore, they can be applied as phosphors in LED lighting and television screens. The main issue regarding currently used quantum dots is that most of them are cadmium based (e.g. cadmium selenide). Because cadmium is highly toxic and carcinogenic, its use is restricted from most commercial applications.
As solution to this problem is an indium based quantum dot, which is far less toxic. The main problem with indium based quantum dots, is a lower photoluminescence quantum yield, a lower stability and a lower color purity. For this reason, in this thesis we aimed to improve the photoluminescence quantum yield by a better quantum dot surface passivation, to reduce the number of non-emitting recombination sites (dangling bonds). To passivate the surface, zinc magnesium selenide was chosen as a shell material that has an improved lattice match compared to currently used materials (such as zinc sulfide and zinc selenide). Furthermore, this zinc magnesium selenide shell should protect the quantum dot from the outside, therefore increasing its stability to air and moisture. Also, the bandgap energy of this material is higher compared to currently used shell materials, so the electron and hole are more confined in the quantum dot core. This automatically should improve the color purity.

The research performed showed that the synthesis of zinc magnesium selenide is quite difficult and cannot be approached the same way as a zinc selenide shell is usually synthesized. Therefore, a method using organometallic precursors was developed to synthesize this material. Results showed that zinc magnesium selenide as a shell material has an improved effect on the photoluminescence quantum yield, stability and color purity of indium phosphide quantum dots, compared to a zinc selenide shell. The synthetic method needs to be optimized before the indium phosphide quantum dots with a zinc magnesium selenide shell are able to compete with cadmium selenide quantum dots.