Nanostructured Semiconductor Oxides for the Next Generation of Electronics and Functional Devices

Properties and Applications

Serge Zhuiykov

• Publisher: Woodhead Publishing
• Year: 2014
• Print ISBN: 9781782422204
• eBook ISBN: 9781782422242
• Topic: Technology & Engineering
• Subtopic: Quantum Theory
• Index: Technology & Engineering

Nanostructured Semiconductor Oxides for the Next Generation of Electronics and Functional Devices focuses on the development of semiconductor nanocrystals, their technologies and applications, including energy harvesting, solar cells, solid oxide fuel cells, and chemical sensors. Semiconductor oxides are used in electronics, optics, catalysts, sensors, and other functional devices. In their 2D form, the reduction in size confers exceptional properties, useful for creating faster electronics and more efficient catalysts. After explaining the physics affecting the conductivity and electron arrangement of nanostructured semiconductors, the book addresses the structural and chemical modification of semiconductor nanocrystals during material growth. It then covers their use in nanoscale functional devices, particularly in electronic devices and carbon nanotubes. It explores the impact of 2D nanocrystals, such as graphene, chalcogenides, and oxide nanostructures, on research and technology, leading to a discussion of incorporating graphene and semiconductor nanostructures into composites for use in energy storage. The final three chapters focus on the applications of these functional materials in photovoltaic cells, solid oxide fuel cells, and in environmental sensors including pH, dissolved oxygen, dissolved organic carbon, and dissolved metal ion sensors. Nanostructured Semiconductor Oxides for the Next Generation of Electronics and Functional Devices is a crucial resource for scientists, applied researchers, and production engineers working in the fabrication, design, testing, characterization, and analysis of new semiconductor materials. This book is a valuable reference for those working in the analysis and characterization of new nanomaterials, and for those who develop technologies for practical devices fabrication. - Focuses on the development of semiconductor nanocrystals, their technologies and applications, including energy harvesting, solar cells, solid oxide fuel cells, and chemical sensors - Reviews fundamental physics of conductivity and electron arrangement before proceeding to practical applications - A vital resource for applied researchers and production engineers working with new semiconductor materials

1

Electrons and holes in a semiconductor

Abstract

The chapter begins with the general theory of semiconductors. It then reviews the science of the mechanism of n- and p-type conductivity, factors influencing conductivity. It continues with an explanation of electrons and holes in semiconductors. The chapter includes some aspects of band theory and state-of-the-art characterization techniques for nanostructured semiconductors.

Key words

semiconductor

nanostructures

n- and p-type conductivity

characterization techniques

1.1 Order and disorder in semiconductor crystals

1.1.1 Types of defects

Identification of native (or intrinsic) defects during preparation and/or modification of semiconductor materials is of primary importance since so many electronic and structural properties critically depend on the presence of such defects. On the one hand, it is preferable to use ordered nanocrystalline semiconductors. However, many practical applications, for example, microelectronics technology, use such materials that are weakly or strongly disordered by careful doping. On the other hand, many of the challenging problems within solid-state physics and nanochemistry today are in some way or other connected to disorder. Therefore, all the macroscopic properties of semiconductor crystals can be grouped into two main classes. The first represents all characteristics which are determined by the periodicity of the semiconductor crystal, and for which the small defects accumulated in any real lattice play a negligible role. These properties can be considered as structure-independent. The second class contains features determined by local violations of the periodicity of the semiconductor crystal lattice. In this case, the defects are of significant importance, as the functional properties of the semiconductor have been manipulated through deliberate introduction of defect and grain boundaries, as well as through the partitioning of very low concentration of dopant species to these localized regions of semiconductors.^1,2 These properties are known as structure-sensitive. The electrical conductivity of a semiconductor crystal containing small traces of impurities within the moderate temperature range is a clear example of a structure-sensitive aspect. As temperature increases towards the higher range, the conductivity loses its sensitivity to impurities and structural defects and becomes a structure-independent property (intrinsic conductivity).

Another example is the absorption spectrum of a semiconductor crystal. Absorption bands at relatively low frequencies are structure-sensitive (impurity absorption), while absorption bands in the high-frequency region have proven to be structure-independent (intrinsic absorption).³ Adsorption is always accompanied by a reduction of the free energy ΔG, and therefore it is an exothermal process: ΔG = ΔH – TΔS,⁴ where H is enthalpy (J/mol), T is absolute temperature (K) and S is entropy (J mol⁻ K⁻¹). Adsorption continues up to the point when the equilibrium between the gaseous (liquid) phase and the surface of the semiconductor crystal is established. Chemisorptive and catalytic properties of semiconductors constitute another typical example of structure-sensitive properties. They depend on the pre-history of the sample and can be chang...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• About the author
• Woodhead Publishing Series in Electronic and Optical Materials
• Introduction
• Acknowledgements
• Dedication
• 1: Electrons and holes in a semiconductor
• 2: Structural and chemical modification of semiconductor nanocrystals
• 3: Electronic devices and functional structures based on nanostructured semiconductors
• 4: Two-dimensional semiconductor nanocrystals: new direction in science and technology
• 5: Composite graphene/semiconductor nanostructures for energy storage
• 6: Nanostructured semiconductor composites for solar cells
• 7: Nanostructured semiconductor composites for solid oxide fuel cells (SOFCs)
• 8: Semiconductor nanocrystals in environmental sensors
• Index