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Abstract

The deposition of functional semiconducting materials from solution and processing under mild conditions can lower manufacturing costs and expand device versatility. In this document, we examine three classes of solution-processable inorganic semiconductors to gain a better understanding of these materials and plan a route for their optimization. Chapters 2 and 3 focus on the characterization and applications of chalcogenidocadmates, soluble precursors for II-VI semiconductors. Single crystal x-ray diffraction and extended x-ray absorption fine structure (EXAFS) measurements allow us to elucidate the molecular structure of Na2Cd2Se3 in its solid state and in hydrazine solution. We explore cation exchange of this species to expand its solubility from hydrazine to more benign solvents and use the cation exchanged selenocadmate to stabilize CdSe nanocrystals in NMF. In Chapter 3, we modify the chalcogenidocadmate structure through interaction with micelle-forming organic cations to create templated mesostructures of CdSe and CdTe. We also show that the reaction of selenocadmate with Cd2+ creates a stoichiometric CdSe gel which can be annealed under mild conditions to form photoconductors or field effect transistors. In the final chapters of the document, we shift our focus away from molecular semiconductor precursors and instead explore colloidal semiconductor nanocrystals, or quantum dots (QDs). HgTe QDs have tunable absorbance across the infrared and can be used as the active layer in mid-infrared photodetectors. In Chapter 4, we use precise synthesis, chemical control of ensemble doping, optical characterization, and electrochemical studies to show that the intraband absorbance of electron-doped HgTe QDs has three peaks, which correspond to transitions between the 1Se state and three nondegenerate Pe states. In Chapter 5, we study several parameters in the molten salt synthesis of In1-xGaxP QDs. The emission energy of these QDs can be tuned by both QD size and alloy composition. We show that the QD surface chemistry can be designed to improve the QD phase stability at elevated temperature. Additionally, we explore a variety of reaction conditions to show that indium-to-gallium cation exchange is diffusion controlled and is accompanied by surface recrystallization. These insights will be useful in designing cation exchange conditions to achieve a desired alloy composition.

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