Electron Device

a device that converts electromagnetic energy of one form into electromagnetic energy of another through the interaction of electromagnetic fields and electrons moving in a vacuum, a gas, or a semiconductor. Electron devices may be divided into electron-tube devices (incandescent lamps excepted) and semiconductor devices.

The processes that occur in electron devices are extremely varied. In vacuum tubes, including such microwave tubes as klystrons, magnetrons, and traveling-wave tubes, electrons emitted by the cathode interact with stationary and variable electric fields. The interaction with a stationary field results in an increase in the kinetic energy of the electrons. The interaction with a variable field transforms constant electron flow into a variable flow and converts part of the kinetic energy of the electrons into the energy of electric oscillations.

In vacuum-tube indicators and in cathode-ray devices, electrons accelerated by a stationary electric field bombard a target, for example, a phosphor screen. When the electrons interact with the target, part of their kinetic energy is converted into a form of electromagnetic energy, such as light energy. In photoelectric vacuum-tube devices, including phototubes and photomultipliers, the electrons emitted by a photocathode exposed to light are accelerated by a stationary electric field toward the anode. Consequently, the light energy is converted into an electric current flowing in the anode circuit. In X-ray tubes, the energy of electrons accelerated while traveling from the cathode toward the anode, or anticathode, is partially converted into X-radiation when the electrons strike the anode.

In gas-discharge, or ion, devices, electrons accelerated by a stationary electric field collide with gas molecules and either ionize them or raise them to an excited state. Such gas-discharge devices as mercury-arc rectifiers, hot-cathode gas tubes, thyratrons, and tacitrons are similar to vacuum-tube diodes and triodes in the way energy is converted. The primary difference between the gas-tube and vacuum-tube devices is that the gas ions in the gas-discharge devices neutralize the space charge of the electron flow, making high currents possible (up to thousands of amperes, for example, in mercury-arc rectifiers) at comparatively low anode voltages of 15–20 volts.

In gas-discharge lamps and indicators, every excited gas molecule emits light when it enters the equilibrium state. Light is emitted in fluorescent lamps by phosphor molecules that are excited by the ultraviolet radiation of a discharge. In quantum gas devices, such as gas lasers and quantum frequency standards, excited gas molecules interacting with electromagnetic oscillations amplify the oscillations upon entering the unexcited state.

Energy conversion in semiconductor devices, as in vacuum-tube devices, is based on the creation of stationary electric fields and on the control of charge-carrier mobility. Among the electronic processes and phenomena that underlie the operation of semiconductor devices are unilateral conductivity during current flow across the depletion layer at a p-n junction or across the potential barrier at a metal-semiconductor interface (seeSCHOTTKY EFFECT); the avalanche effect, or cumulative multiplication of carriers in strong electric fields; the tunnel effect; and the acousto-electric, electrooptical, and thermoelectric effects in dielectric and semiconductor materials.

The effect of unilateral conductivity is made use of in semiconductor diodes. The transistor effect—that is, the control of the current of a reverse-biased junction by means of a forward-biased junction current—is made use of in transistors to amplify electric oscillations. In Gunn diodes and avalanche transit time diodes, cumulative multiplication at p-n junctions as a result of the impact ionization of atoms by carriers is used to generate electric oscillations. In light-emitting diodes, electric energy is converted into optical radiation through injection electroluminescence.

Used in virtually all fields of science and technology, electron devices find particular application in radio engineering, automation, communications, computer technology, astronomy, physics, and medicine. More than 10 billion electron devices were manufactured annually throughout the world in the 1970’s.