ORCID
https://orcid.org/0000-0002-3573-0156
Date of Award
3-13-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Metal chalcogenides exhibit perovskite, chiral, and layered structures, and accommodate many atoms from periodic table, providing abundant properties such as ferroelectricity, circular dichroism, and anisotropic carrier transport. Those various physical properties make metal chalcogenides promising for the applications from electronics to optoelectronics, such as thermoelectrics, photovoltaics, and photodetectors. The upper limit of carrier mobility, termed as intrinsic carrier mobility, is the key factor that determine the performance of the semiconductor-based applications. However, either experiments or first-principle calculations are challenging to obtain the intrinsic carrier mobility over a wide class of materials. I found a descriptor that have a good correlation with the carrier mobility compared to other descriptors. Traditional synthesis methods for high-quality metal chalcogenide semiconductors typically require expensive operating conditions such as a vacuum environment, gasification of precursors, protective gas, and single-crystal growth substrates. As an alternative to those processes, I developed solution-based approaches at near-ambient conditions to synthesize metal chalcogenide semiconductors on polycrystalline substrates. To support this experimental work, I used density-functional theory to predict the functionality of metal chalcogenide semiconductors and reveals their growth mechanisms. My work not only identifies the usefulness of metal chalcogenides, but also provide the synthesis strategy to grow metastable metal chalcogenides with desired functionalities. Chalcogenide perovskites have been claimed as defect-tolerant materials that can retain the electronic properties of their pristine form even in the presence of defects. I used density-functional-theory calculations to investigate the tolerance of BaZrS3, a prototypical chalcogenide perovskite, to various native point defects. Our calculations reveal that the dominant sulfur vacancy in perovskites BaZrS3 is a deep-level defect, which matches with the experimentally measured photocurrent decay time exceeding 20 seconds. By contrast, the Ruddlesden-Popper phase of BaZrS3, Ba3Zr2S7, possesses shallow-level vacancy defects, indicating a defect-tolerant material and fewer carrier trapping states. While defects influence the electronic carrier transport, the ultimate limit of carrier mobility is dictated by the coupling of electrons and polar-optical phonons. Thus, I calculated the intrinsic carrier mobility for a variety of semiconductors using the linearized Boltzmann transport equation. Through this work, I demonstrated the Fröhlich coupling constant, which is used to quantify the electron-phonon interaction, serves as a universal descriptor of carrier mobility in a wide class of materials such as semiconductors, ferroelectrics, and insulators. By controlling the Fröhlich coupling constant, I identified that the chalcogenide perovskite, BaZrS3, can exhibit both ferroelectricity and semiconductivity, which potentially serves as a platform to integrate ferroelectrics on semiconductors for non-volatile memory devices. To compliment these computational efforts, I demonstrated synthesis methods to grow metastable metal chalcogenides on polycrystalline substrates at near-ambient conditions. To achieve high crystallinity during the electrochemical growth of semiconductors with polar covalent bonding, a single-crystalline substrate is typically required that provides epitaxial matching between the substrate surface and the structure of the desired phase. This requirement restricts the versatility of electrodeposition for growing metal chalcogenide semiconductors. I developed a seeded electrochemical growth mechanism that enables the deposition of metastable Bi2Se3 on both single- and poly-crystalline growth substrates. Nanoscale seed crystals composed of cubic BiSe can be deposited onto a variety of conductive substrates, including polycrystalline fluorine-doped tin oxide and polycrystalline gold, to establish an epitaxial relationship with the desired phase. The technique avoids using expensive single-crystal growth substrates and facilitates the integration of metal chalcogenide semiconductors for energy and information storage and conversion. We hypothesize that seeded electrochemical growth, using nanoscale seed particles, can be used to synthesize other metastable phases of metal chalcogenides such as the metastable phase of SnS with a chiral structure. Chiral metal chalcogenide semiconductors with distinct chiroptical activity can generate dissymmetric photocurrent based on the differential absorption of left- and right-circularly polarized light. π-SnS features an intrinsically chiral structure, a high absorption coefficient, and a band gap in the near-infrared, making it a promising candidate for polarization-sensitive photodetectors. To date, there are no reports demonstrating the enantioselective growth, or chiroptical activity of π-SnS particles or films. By selecting L-ascorbic acid as a complexing agent during chemical bath deposition, I successfully synthesized π-SnS films that demonstrate circular dichroism over the full spectrum of visible light. I identified that the π-SnS films exhibit authentic isotropic circular dichroism by excluding the influence of linear dichroism and linear birefringence. Furthermore, the sign and the spectral position of circular dichroism exhibited by the π-SnS films depends on the morphology and composition of the film. Due to its accessible solution-phase growth, absorption across the visible spectrum, and composition of earth-abundant elements, chiral π-SnS films are a promising candidate for advanced optoelectronic devices based on circularly polarized light.
Language
English (en)
Chair and Committee
Bryce Sadtler Sadtler, Rohan Mishra
Committee Members
Richard Loomis, Bryce Sadtler, Rohan Mishra, Elijah Thimsen, Robert Wexler
Recommended Citation
Luo, Jiang, "Synthesis and Functional Properties of Metal Chalcogenide Semiconductors" (2024). Arts & Sciences Electronic Theses and Dissertations. 3241.
https://openscholarship.wustl.edu/art_sci_etds/3241