Preface

A heterostructure is a sandwich of two dissimilar semiconductors (or other materials) with different bandgaps and lattice constants. The junction between two different materials is known as heterojunction. Nanostructures are structures that range between 1 nm and 100 nm in at least one dimension. In the case of semiconductor nanostructures, the carriers can be confined in one, two, or all three dimensions, and the structures are known as quantum wells, quantum wires, and quantum dots, respectively. The aforementioned structures, as well as many others, are of interest for various electronic and optoelectronic device applica‐ tions such as diodes, lasers, spintronic devices, and dissipationless transistors for quantum computers, among others. Molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), and some other micro-fabrication techniques are used to create highquality heterostructures. Computational methods such as numerical integration and partial differential schemes have been mainly used to describe, among others, the carrier confine‐ ment, as well as the relaxation and dephasing rates.

A collection of research topics related to heterojunctions and nanostructures is presented in the current book. The first part of the book includes chapters related to topological insula‐ tors. A few presented topics are, among others, the topological phases of matter, the band topology of insulators and also of Weyl semimetals, transport properties of 3D topological insulator quantum wires and the influence of disorder, transport properties of quasi-1D (and 2D) topological surface states, quantum coherence, and the topological insulator thinfilm Hall bar device. The second part of the book includes chapters related to the nanostruc‐ ture devices for light emission. Topics such as semiconductor quantum nanowire laser diodes, solutions of Schrodinger equation in nanostructures, numerical methods, light-toelectricity conversion devices, photoexcited carrier transportation process in quantum wells and quantum dots, growth mode and characterization of heterostructure of large lattice mis‐ match, and photoionization cross section are included in the second section, among others.

As an editor of this book, I would like to thank all the authors for their contribution, their high-research standards, and their constructive feedback. Lastly, I would like to express my thanks and gratitude to the InTech team for their support during the preparation of this book.

> **Dr. Vasilios N. Stavrou** Hellenic Naval Academy Piraeus, Greece

**Section 1**

**Topological Insulators**
