Theory Of Electronic And Optical Properties Of Atomically Thin Films Of Indium Selenide

This thesis provides the first comprehensive theoretical overview of the electronic and optical properties of two dimensional (2D) Indium Selenide: atomically thin films of InSe ranging from monolayers to few layers in thickness. The thesis shows how the electronic propertes of 2D InSe vary significantly with film thickness, changing from a weakly indirect semiconductor for the monolayer to a direct gap material in the bulk form, with a strong band gap variation with film thickness predicted and recently observed in optical experiments. The proposed theory is based on a specially designed hybrid k.p tight-binding model approach (HkpTB), which uses an intralayer k.p Hamiltonian to describe the InSe monolayer, and tight-binding-like interlayer hopping. Electronic and optical absorption spectra are determined, and a detailed description of subbands of electrons in few-layer films and the influence of spin-orbit coupling is provided. The author shows that the principal optical excitations of InSe films with the thickness from 1 to 15 layers broadly cover the visible spectrum, with the possibility of extending optical functionality into the infrared and THz range using intersubband transitions.

Among the 2D layered metal chalcogenide materials is tin selenide (SnSe), which belongs to group IV--VI that has attracted considerable attention due to its interesting structural and optical properties, hence it has potential applications in optoelectronics, photovoltaics, memory, energy storage, and catalysis. To date, SnSe films have been produced by exfoliation or chemical vapor deposition that produces flaky films. In this research, uniform, smooth and high quality SnSe thin films were grown over large area (5cm x 5cm) Si/SiO2 substrates using Atomic Layer Deposition (ALD). Films were grown over a temperature range of 350°C to 450°C, which exhibit p- type semiconductor characteristics. ALD is perfect for the growth of layered materials due to its precise controllability of film composition and thickness as the growth proceeds layer by layer. Structural and optical properties of the as-grown films were investigated using X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). These analyses show growth of 2 dimensional, orthorhombic phase films. Magnetic analysis shows a paramagnetic behavior. Back-gated transistors were fabricated for electrical characterization which showed p-type conductance, with an average hole mobility of 10 cm2/V.s and Ion/Ioff ratio of ~105.

This dissertation, "Preparation and Post-annealing Effects on the Optical Properties of Indium Tin Oxide Thin Films" by Rongxin, Wang, 王榮新, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled PREPARATION AND POST-ANNEALING EFFECTS ON THE OPTICAL PROPERTIES OF INDIUM TIN OXIDE THIN FILMS Submitted by WANG Rong Xin for the degree of Doctor of Philosophy at The University of Hong Kong in April 2005 Many opto-electronic devices, such as III-V compound devices, liquid crystal displays, solar cells, organic and inorganic light emitting devices, and ultraviolet photodetectors, demand transparent electrode materials simultaneously having high electrical conductance. To meet the requirements for particular applications, a great deal of basic research and studies have been carried out on the electrical and optical properties of these materials. As a most promising candidate for such materials, indium tin oxide (ITO) has attracted interest in recent years. Furthermore, ITO has many unique properties such as excellent adhesion on the substrate, thermal stability and ease of patterning. The deposition of high-quality ITO thin films is a key step for successful application of ITO thin films as transparent electrode materials. To obtain optimal electrical and optical properties of ITO films, the growth parameters and conditions must be determined. Moreover, the optical and electrical properties of ITO contact layers, which can either be on the top side or the bottom side of a device, are influenced by various post-deposition treatments. For the present work, ITO thin films were deposited on glass and quartz substrates using e-beam evaporation with different deposition rates. The influence of substrate material, deposition rate, deposition gas environment and post-deposition annealing on the optical properties of the films was investigated in detail. Atomic force microscopy, X-ray diffraction and X-ray photoemission spectroscopy was employed to obtain information on the chemical state and crystallization of the films. Analysis of these data suggests that the substrate material, deposition rate, deposition gas environment and post-deposition annealing conditions strongly affect the chemical composition and the microstructure of the ITO films and these in turn influence the optical properties of the film. Oxygen incorporation transfers the In O phase to the In O phase and removes metallic In to form both indium oxide 2 3-x 2 3 phases. Both of these reactions are beneficial for the optical transmittance of ITO thin films. Moreover, it was found that the incorporation and decomposition reactions of oxygen can be controlled so as to change the optical properties of the ITO thin films reversibly. DOI: 10.5353/th_b3154617 Subjects: Thin films - Optical properties Indium compounds Annealing of metals

The advent of graphene and, more recently, two-dimensional materials has opened new perspectives in electronics, optoelectronics, energy harvesting, and sensing applications. This book, based on a Special Issue published in Nanomaterials – MDPI covers experimental, simulation, and theoretical research on 2D materials and their van der Waals heterojunctions. The emphasis is the physical properties and the applications of 2D materials in state-of-the-art sensors and electronic or optoelectronic devices.

This volume provides a broad overview of the fundamental materials science of thin films that use silicon as an active substrate or passive template, with an emphasis on opportunities and challenges for practical applications in electronics and photonics. It covers three materials classes on silicon: Semiconductors such as undoped and doped Si and SiGe, SiC, GaN, and III-V arsenides and phosphides; dielectrics including silicon nitride and high-k, low-k, and electro-optically active oxides; and metals, in particular silicide alloys. The impact of film growth and integration on physical, electrical, and optical properties, and ultimately device performance, is highlighted.

A comprehensive account of the properties, growth and applications of semiconducting transparent thin films, this book provides a single source reference for researchers in the field. It discusses the underlying physics of such films, and their commercial applications in such areas as gas sensors and temperature control coatings in the aerospace industry. It is clearly written, with sections on the different materials, different growth techniques, electrical properties, optical properties, and selected applications, for coatings, sensors, detectors and display devices. It is a valuable reference tool for the established researcher, and provides a comprehensive introcution to the subject for graduates of electrical and electronic engineering. The international team of authors, under the leadership of one of the world's authorities on the subject have written a book which has become the standard work in the field.