Origin of the High Field Domains in Piezoelectric Semiconductors (A phenomenological Theory)

Abstract

The current oscillations which are observed in piezoelectric semiconductors, such as CdS, are often accompanied by a high field domain which moves through the sample at the velocity of sound. A phenomenological explanation of the high field domains is given by in the following manner: Voltage pulses applied on a piezoelectric semiconductor drift carriers gifting a gain to acoustic waves. A train of the pulses is expanded in Fourier series. The Fourier components of the series generate sound waves at the surface of the sample contacting with electrodes, because a discontinuity in the piezoelectric stress is produced at the boundary surfaces between the sample and electrodes. The sound waves excited at one of the electrodes can propagate to the other in a coherent manner, if the sound waves are amplified by drifting carriers, otherwise the sound waves are damped away. When the sound wave of frequency ω exists continuously in the sample, the frequency component of conductivity σ(ω) is negative under the condition of the acoustic traveling-wave amplification. The frequency component of electric field E(ω) should be, therefore, localized at a position because of σ(ω)<0. As a number of frequency components of the electric field are included in the sample as the Fourier components of applied voltage pulses, all the components of the field are localized to a high field domain as a results of summation of the Fourier components.