Effects of crystal disorder on the molecular hydrogen formation in silicon

We have investigated quantitatively the effect of crystal disorder on the formation of hydrogen molecule in crystalline silicon. Disordered crystalline silicon was obtained by implanting crystalline silicon with 200 keV Si+ with doses ranging from 1013 to 1016 Si cm−2. The optical phonon line broadened and downshifted with increasing ion dose, corresponding to an increase in crystal disorder and decrease in phonon correlation length. The implanted samples were then treated with a remote downstream hydrogen plasma at 250°C. The vibrational Raman line of hydrogen molecule at around 4160 cm−1 decreased monotonically in its intensity with decreasing phonon correlation length. The results suggest that hydrogen molecules are formed preferably in well-ordered parts of Si lattice.