Optoelectronic Applications of Quantum Dots

In the large nanomaterials family, zero-dimensional (0D) materials are key building blocks of exotic artificial materials that have significant technological impact on a myriad of applications. Such materials demonstrate totally different properties at their nanoscale when compared to bulk form. At nanoscale, quantum effects govern the properties and behaviour of particles. Hence, properties of materials rely on their size in this scale range. Quantum dots (QDs) are nanometer sized (~2-10 nm) 0D semiconducting materials that confine charge carriers in three dimensions. The confinement of charge carriers is a quantum phenomenon. The density of states for the confined particles is totally different from the density of states for particles in a larger part of the material. Discrete energy levels exist for an ideal isolated quantum dot corresponding to a deltashaped density of states devoid of states in between the delta peaks. This is a characteristic behaviour of atoms. Hence, quantum dots can be considered as a type of artificial atoms that can change energy levels depending on their design. This can be done either by controlling the material composition or dimensions of the quantum dots. Since the discovery of cadmium based QDs in the 1980s, a variety of cadmium and non-cadmium based QDs have been synthesized and investigated. Significant improvements in the electrical and optical properties of QDs have been made by adjusting their shape and size and they have emerged as an important class of material with applications extending from light emitting diodes (LEDs), to photovoltaics, photodetectors, and quantum computing. This paper highlights some of such novel QD-based devices and device concepts.