Site of signal generation in electron-acoustic microscopy using an Si Tr-chip under bias application

The junction between the base and collector of an npn Si Tr chip was exposed to a microscopic field by drilling and etching. The spread of depletion layer of the junction in the Tr chip thus prepared was observed in-situ by scanning electron microscopy (SEM) and electron-acoustic microscopy (EAM) under various bias conditions. The site of the electron acoustic (EA) signal generation stays unchanged under varying bias voltage. The amplitude of the EA signal increases under reverse and decreases under forward bias voltage. The site of EA signal generation nearly corresponds to the junction. The EA and electron beam induced current signals nearly correspond to each other but are clearly different. The EA signal is generated when recombination of the injected carriers occurs and is directly generated simultaneously. The mechanism of EA signal generation is discussed