Fiber Optic Tutorials

This is a continuation from the previous tutorial - semiconductor junctions. The general characteristics of electron-hole recombination processes in a semiconductor are discussed in the carrier recombination tutorial. The net result of any recombination process is the transition of an electron from an occupied state at a higher energy to an empty state at a lower energy, accompanied by the release of the energy that is the difference between these two states. An electron-hole recombination process in a semiconductor can be either radiative or nonradiative. In a radiative recombination process, the released energy is emitted as electromagnetic radiation. In a...

This is a continuation from the previous tutorial - current density in semiconductors.   Useful semiconductor devices are made of inhomogeneous semiconductors that have either spatially nonuniform doping distribution or spatially varying bandgaps or both. There are two categories of semiconductor junctions: homojunctions and heterojunctions. A homojunction is formed by different doping in the same semiconductor, whereas a heterojunction is formed between two different semiconductors. In addition, a metal-semiconductor junction can be formed between a metal and a semiconductor. The immense possibilities of such structures are witnessed by the existence of the great variety of semiconductor devices and by the...

This is a continuation from the previous tutorial - carrier recombination.   An electric current in a semiconductor results from the flow of electrons and holes. The current density flowing in a semiconductor is the current flowing through a unit cross-sectional area of the semiconductor; its unit is amperes per square meter. There are two mechanisms that can cause the flow of electrons and holes: drift, in the presence of an electric field, and diffusion, in the presence of a spatial gradient in the carrier concentration. The electron current density, \(\pmb{J}_\text{e}\), and the hole current density, \(\pmb{J}_\text{h}\), can be expressed...

This is a continuation from the previous tutorial - electron and hole concentrations.   In a semiconductor, electrons in the conduction bands and holes in the valence bands can be generated through many mechanisms, including thermal excitation, current injection, and optical excitation. Meanwhile, an electron in a conduction band and a hole in a valence band can be eliminated together through a recombination process. In an equilibrium state, electron-hole generation is exactly balanced by electron-hole recombination.   Recombination Processes There are many different electron-hole recombination processes. Based on the mechanisms responsible for these processes, they are classified into three general...

This is a continuation from the previous tutorial - introduction to semiconductors.   The electron concentration in a semiconductor is the number of conduction electrons in the conduction bands per unit volume of the semiconductor, and the hole concentration is the number of holes in the valence bands per unit volume of the semiconductor. The concentrations of electrons and holes in a semiconductor are determined by many factors, including the bandgap and band structure of the semiconductor, the types and concentrations of the impurities doped in the semiconductor, temperature, and any external disturbances to the semiconductor.   Density of States...