Photodetectors based on colloidal quantum dots

Abstract

Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices (QD-LEDs), we set out to develop thin-film, layered photodetectors in which the active layer is a chemically annealed QD solid. This thesis reports initial steps in this development. Chapters 1 and 2 contain introductory material. In Chapter 3, we demonstrate a layered QD photodetector (QD-PD) in which the active layer is a 200-nm thick film of CdSe QDs annealed with n-butylamine. These "thick-slab" devices, active in the visible spectrum, represent a minimal transformation from the transverse channel test structures employed for more fundamental studies to a layered, sandwich geometry. The thick-slab design exhibits a number of desirable characteristics, including near-unity internal quantum efficiency and a 50-kHz bandwidth. More complex QD-PD designs, allowing the successful incorporation of much thinner QD solids, are discussed in Chapter 4, and these devices provide insight into the zero-bias operation of thick-slab QD-PDs.

(cont.) The final three chapters of the thesis focus on PbSe QDs, this group's initial material of choice for accessing the short-wavelength-IR spectral window. Initial study of PbSe QDs as a material for QD-PDs is described in Chapter 5. Chapter 6 discusses an 31P-based NMR investigation of the mechanism of PbSe monomer formation, allowing for rational "doping" of syntheses to increase chronically low yields. Finally, Chapter 7 discusses a brief assessment of the suitability of PbSe QDs for in vivo imaging.