Giant piezoresistance in silicon-germanium alloys

Abstract

We use first-principles electronic structure methods to show that the piezoresistive strain gauge factor of single-crystalline bulk $n$-type silicon-germanium alloys at carefully controlled composition can reach values of $G=500$, three times larger than that of silicon, the most sensitive such material used in industry today. At cryogenic temperatures of 4 K we find gauge factors of $G=135\phantom{\rule{0.16em}{0ex}}000$, 13 times larger than that observed in Si whiskers. The improved piezoresistance is achieved by tuning the scattering of carriers between different ($\ensuremath{\Delta}$ and $L$) conduction band valleys by controlling the alloy composition and strain configuration.