Local vibrations on hydrogen dimers in dilute SiGe crystalline solutions

Atomic hydrogen is a concomitant impurity in semiconductors. Its presence in Si, Ge and SiGe alloys has been established by means of paramagnetic resonance, optical, electrical and theoretical modeling studies. Hydrogen self-trapping is known to occur in Si and Ge, resulting in the formation of molecular hydrogen and H2* interstitial dimers. Here we report on the properties of H2* complexes in dilute SiGe alloys, by using an ab initio density functional method. It is found that these complexes form preferentially within Si-rich regions. H2* dimers in Si-rich alloys show vibrational properties similar to those in pure Si. On the other hand, in Ge-rich material the minority Si atoms act as nucleation sites, with the consequent formation of at least one preferential H2*−Si defect variant, showing a distinct vibrational activity.