Laser Diodes and Their Applications to Communications and Information Processing

Takahiro Numai

• Publisher: Wiley-IEEE Press
• Year: 2011
• ISBN:
  9781118074428
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

In order to develop excellent photonic devices, we have to fully understand the physics behind operations of photonic devices. This book thoroughly teaches the fundamental physics currently applied to the development of photonics devices such as energy bands of semiconductors, optical transitions, optical waveguides, and semiconductor junctions. The book also reviews the characteristics of laser diodes, optical filters, and optical functional devices, which have been developed based on the above physics. These photonic devices have been demonstrated in system applications, and several experimental results are described.

PART I

PHYSICS REQUIRED TO DESIGN LASER DIODES

CHAPTER 1

ENERGY BANDS IN BULK AND QUANTUM STRUCTURES

1.1 INTRODUCTION

Transitions of Electrons

The emission and absorption of light are generated by the transitions of electrons. Light is emitted because electrons transit from high-energy states to lower-energy states, and light is absorbed in the reverse process. When electrons transit from high-energy states to lower-energy states, nonradiative transitions, which do not emit light, may exist as well as radiative transitions, which accompany light emissions.

Energy Bands

When the atomic spacing is so large that mutual interactions of atoms may be neglected, the electron energies are discrete and energy levels are formed. With a decrease in the atomic spacing, the positions of the electrons of neighboring atoms start to overlap. Therefore, the energy levels begin to split to satisfy the Pauli exclusion principle. With a further decrease in atomic spacing, the number of electrons whose positions overlap with each other increases. As a result, the number of split energy levels goes up, and the energy differences in the adjacent energy levels are reduced. In semiconductor crystals, the number of atoms per cubic centimeter is on the order of 1022, where the atomic spacing is about 0.2 nm. As a result, the spacing of energy levels is much narrower than the bandgap energy, on the order of electron volts. Therefore, the constituent energy levels are considered to be almost continuous, and energy bands are formed.

1.2 BULK STRUCTURE

Bulk

Semiconductors in which constituent atoms are placed periodically at a sufficiently long range compared with lattice spacing are called bulk semiconductors. In this section, the energy bands in bulk semiconductors are calculated.

k·p Perturbation

Semiconductors have free electrons and holes only in the vicinity of band edges. As a result, the band shapes and effective masses of carriers near band edges often give us sufficient information about optical transitions. To analyze the energy bands in the neighbor of band edges, k·p perturbation theory [1–4] is often employed. The wave functions and energies of the bands are calculated with Δk = k–k0 as a perturbation parameter, where k is a wave vector near a band edge and k0 is a wave vector at a band edge. For simplicity, k0 = 0 is selected in the following.

Schrödinger Equation

The Schrödinger equation in the steady state is given by [5,6]

(1.1)

where

is Dirac’s constant, h = 6.6261 × 10−34 J · s is Planck’s constant, m = 9.1094 × 10−31 kg is the electron mass in vacuum, Vr) is a potential,

is a wav...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright
• Dedication
• Preface
• Part I: Physics Required to Design Laser Diodes
• Part II: Conventional Laser Diodes
• Part III: Advanced Laser Diodes and Related Devices
• Part IV: System Demonstrations Using Advanced Laser Diodes and Related Devices
• Appendix A: Density of States
• Appendix B: Density-of-States Effective Mass
• Appendix C: Conductivity Effective Mass
• Index