In Physics, What Is a Phonon?

Phonons are "normal mode energy quanta of lattice vibration". English is phonon.

Phonon

(Physical noun)

The phonon is "

English name: Acoustic Emission, AE

Chinese name:

Phonon is an unreal

Phonon concept

When the acoustic wave (longitudinal wave) propagates in the crystal, it will cause a sparse and dense change in the atomic density of the crystal-the sparse wave, and thus generate an additional periodic potential field wave (the period of Sound waves are the same). In atomic semiconductors such as Si and Ge, the potential field wave generated by sound waves is the periodic potential field of distortion potential (the potential field wave has a smaller amplitude); while in piezoelectric semiconductors, the potential field wave generated by sound waves is Piezoelectric periodic potential field (this potential field wave has a large amplitude). Because the acoustic wave in the crystal is essentially the same as the long acoustic wave of the lattice vibration, it can also be quantized into a phonon (the energy phonons of the lattice vibration can be called "hot phonons") . Therefore, the potential field wave generated by the acoustic wave in the crystal can be considered as the effect of the phonon-the phonon potential field wave. When a phonon potential field wave exists in the crystal, if the average free path of the crystal electron is smaller than the wavelength of the acoustic wave ( = 2 / q ) ( q is the wave number of the phonon), the electron will continue to suffer from phonon scattering and loss Energy so that electrons will be captured by the troughs of the phonon potential field waves. In the case where electrons are captured by the phonon potential field wave, when the sound wave propagates in the crystal, the electron is pulled forward by the phonon potential field wave, which is the so-called phonon drag effect. as the picture shows. Because the larger the amplitude of the phonon potential field wave, the stronger the phonon traction effect, so the phonon traction effect in the piezoelectric semiconductor is more significant. At the same time, ultrasonic waves can also generate large periodic potential field waves, so the role of ultrasonics in drawing electrons is also strong.

Phonon effect

Acoustoelectric effect: In a semiconductor, if a phonon drag effect occurs, that is, the electron is pulled by the phonon

Leading forward movement will inevitably cause electrons to concentrate more to one side, and as a result, an electromotive force is generated. This phenomenon of generating electromotive force by sound waves is the so-called sonoelectric effect. If it is a piezoelectric semiconductor, and it is ultrasonically used for traction, then the phonon traction effect and the corresponding acoustoelectric effect will be stronger. Therefore, in the acousto-electric device that uses the acousto-electric effect to work, it is mostly made of piezoelectric semiconductors, while using ultrasound to work. Amplification and attenuation of sound waves: If a phonon-drawing effect occurs, an electric field is added to the semiconductor to accelerate the electron's drifting motion. At this time, two opposite effects will occur: If the electron's drifting speed Greater than the speed of sound waves, the electrons will propel the phonon potential field waves to move forward. At this time, the sound waves will obtain energy from the electrons, that is, the sound waves are amplified. This is the physical basis of the operation of the ultrasonic amplifier. If the drift speed of the electron is less than the speed of the acoustic wave, the electron will be pulled forward by the phonon potential field wave. At this time, the acoustic wave will transfer part of the energy to the electron. As a result, the amplitude of the acoustic wave decreases, that is, the acoustic wave is attenuated. The physical basis of the attenuator's work.