Performance of piezoelectric semiconductor bipolar junction transistors and the tuning mechanism by mechanical loadings

Abstract

A coupling model is established on piezoelectric semiconductor bipolar junction transistors (PS-BJT) subjected to mechanical loadings by abandoning depletion layer approximation and low injection assumption. Effect of base region on device performance and interaction between emitter/base junction (E/B) and base/collector junction (B/C) are investigated. It is found that too small a base width will cause B/C to extract electrons directly from emitter region, implying that an electron passageway will be excited to link from collector- to emitter-region by striding over base-region (abbreviated as “EP-CE” hereafter). We particularly clarify that the current produced by electrons flowing across EP-CE is independent of electron-hole recombination in E/B, which means that this current has not yet been bestowed on the information of base current. “Information of base current” refers to dispatching information of base current on the electrons in emitter region. Thus, a current from EP-EC cannot be reckoned in the amplification effect of base current. Our investigations show that base width should not be designed too small to avoid EP-CE, which has not been revealed before. As regards to tuning PS-BJT performance by mechanical loadings, we revealed the mechanism as follows: 1) raising electron-hole recombination rate inside E/B to reduce resistivity such that more electrons can be driven from emitter- to base-region; 2) elevating electron conductivity in base-region for easier pass of electrons; 3) promoting attractive ability of B/C on electrons such that more electrons cross the interface. Numerical results show that transmission characteristics can be greatly increased as expected by mechanical tuning.