Effects of charge carriers on elastic waves in piezoelectric semiconductors

The performance of piezotronic devices is primarily governed by the interaction between elastic waves and charge carriers. Therefore, understanding the underlying mechanisms of this interaction in piezoelectric semiconductors is crucial for the research and development of piezotronic devices. Unlike in purely elastic or piezoelectric media, an elastic wave propagating in a piezoelectric semiconductor involves two interdependent physical processes: the evolution process of thermodynamic state, and the vibration state of elastic wave-front. The former is from the evolution of carrier behavior and the latter is related to the dynamic characteristics of polarization electric field. The mutual competition between two dynamic processes stimulates the interaction between electric field and charge carriers, i.e., appearing a field-particle coupling wave (FPCW). This coupling wave is useful in remaking elastic wave-front characteristics to develop new acoustoelectric devices or to prompt performance of piezoelectric semiconductor devices. Thus, a multi-field coupling dynamic model is established to analyze the relationship between polarized electric field and charge carriers at the elastic wave-front. Furthermore, the distinct coupling mechanisms of these processes at varying vibration frequencies are examined. It is found that a vibration state of an elastic wave-front was altered by the corresponding thermodynamic state most severely at a low-frequency situation, significantly at a medium-frequency one and almost none at a highfrequency one. Correspondingly, a FPCW becomes most pronounced due to strong competition between two dynamic processes in a medium-frequency situation, and very weak in the other two ones. Furthermore, it is revealed in the paper that the nonlinear behavior in drift current is to transfer energy to higher order vibration modes instead of being consumed as claimed from the harmonic analysis technique. These findings are of great significance for designing passive delay line filters, amplifiers, and circulators, etc.