Ligand Exchange Optimization for Quantum Dot Based Infrared Thin-film Photodetectors

• Autor(a) principal: Sanches, Tomás Correia
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/117486
• topic: infrared; image sensor; colloidal quantum dots; ligands; thin-film; photodiode; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

Image in the infrared wavelength range offers several advantages when compared with the visible range. The information that is impossible to acquire with our naked eyes can be used for different industries such as quality control, surveillance, augmented and virtual reality, medical diagnostics, and others. Colloidal quantum dots (QDs) have been gathering increased attention and becoming one of the most promising candidates for infrared optoelectronic devices, being praised for their size-dependent bandgap tunability, low-cost manufacturing when comparing to III-V semiconductors, and suitability for deposition on large and flexible substrates. However, the main challenge to accomplish is precise control over their material properties through surface passivation. The work performed in this thesis is focused on exploring the effect of different strategies of surface ligand treatments to colloidal QDs for further integration as an active layer of thin-film photodetectors. Therefore, thin-films made from solution-phase ligand exchange lead sulfide (PbS) QDs deposited on glass substrates were analyzed in terms of their optical and morphological properties through multiple characterization techniques. Full processing and fabrication of thin-film photodiode detectors were then carried out, pursuing the highest devices performance according to their electrical characterization. In the end, the developed PbS QD-based photodiode stack successfully completed the proposed optimization by reaching dark currents values close to 10-5 A/cm2 at -3 V and external quantum efficiency of 29% at 1450 nm.