Perpustakaan Digital ITB

Quantum dots (QD) materials have unique properties due to the formation of discrete energy levels and tunable electronic energy bandgap originated from the quantum confinement effect that occurs in nano-sized materials. These arising properties are totally different from what usually possessed by their bulk form. In bulk, the electronic energy states are continuous. Therefore, QDs are prospective for many applications, such as solar cell, photodetector, light emitting devices, and optoelectronic devices. On the other hand, nowadays chemical processing can produce nanocrystalline materials in colloidal form with high uniformity of particle size with a diameter small enough to reach quantum confinement regime. However, in functionalizing colloidal QD as active materials for electronic devices, there are several important issues to carefully scrutinized. One of the issues is related to the interaction between individual QDs to enable charge carriers to move from one QD to another. This interaction is affected by complex roles of molecular ligands that stabilize the QD, and the formation mechanism of the QD assemblies themselves. Here in this study, the roles of QD assembly formation to enhance their corresponding electronic transport is investigated. Lead sulfide (PbS) QD is utilized as the model system. The assembly is controlled by several deposition techniques that spin-, dip-coating, and liquid-air interfacial assembly method, together with ligand exchange process to enhance the coupling between the QDs. The variations of QD assemblies are characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM) to probe their morphology. UV-VIS-NIR spectroscopy is used to clarify the optical absorption of the assembly, specifically to check the preservation of the excitonic peak existence. Electrical transport properties of the corresponding assemblies were investigated by using field effect transistor (FET). Besides it is a functional device, a FET is one of the best tools to characterize the intrinsic transport properties of a semiconductor. Both solid-gated FETs and electrolyte-gated FETs were used to provide us the capability to measure the electrical transport characteristics at different charge carrier density regimes to alleviate the fact that that the large surface area of QDs made them possess large number of carrier trap density. We observed strong proportionality between the superlattice assembly quality and the corresponding electronic transport properties. FETs with QDs deposited using liquid-air interface assembly demonstrate the highest carrier mobility values, which are orders of magnitude larger than those demonstrated by the state-of-the-art spin-coated devices. Furthermore, we found that different deposition method will have significant influence on the interaction between the substrate and QD assembly that in the end affects the electron transport of the fabricated FETs. These results will become guidelines for developing diverse electronic devices based on colloidal QD assemblies that relies strongly on controllable assembly.