Pressure effects on self-diffusion in silicon

Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

The formation of abrupt Si/Ge heterointerfaces in nanowires presents useful possibilities for bandgap engineering. We grow Si nanowires containing thick Ge layers and sub-1 nm thick Ge "quantum wells" and measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial compressive strains of several percent, while stress at the Si/Ge interface causes lattice rotation. High strains can be achieved in these heterostructures, but we show that they are unstable to interdiffusion.

Gettering of metals by voids in silicon

The gettering efficiency of copper and platinum by cavities formed in silicon after high dose helium implantation and thermal processing has been investigated. The formation of helium bubbles and their evolution into cavities has been investigated by transmission electron microscopy; the measured values of void density, diameter and the width of the void layer can be interpreted by assuming a simple coalescence model. Metal impurities intentionally introduced in silicon by ion implantation are efficiently gettered inside these cavities, probably due to the large amount of unsatured bonds at the void internal surface. Processing at temperatures higher than 1000oC causes a release of the trapped metal atoms which can be gettered again by repeating the process. The method is demonstrated on real devices such as large area diodes (a particle detector) and bipolar transistors. The capability to localize in depth and across the wafer surface on the gettering sites allows the development of a new gettering engineering.