Dipole moments of H2, D2, and HD molecules in Czochralski silicon

Measurements show that the effective charge eta(nu(3DD)) (dipole moment per unit displacement) of the infrared (IR) active stretch mode of isolated interstitial D-2 molecules is smaller than eta(nu(3HH)) for H-2 molecules in Si crystals. This may relate to differences in the orientations of the molecular axes that are not in general parallel to the direction of the dipole moments. For molecules paired with an interstitial oxygen atom in Czochralski Si, i.e., (D-2(H-2)-O-i) (two configurations of each), the effective charges eta(nu(1DD)) and eta(nu(2DD)) are essentially equal to eta(nu(1HH)) and eta(nu(2HH)) respectively. No information has been obtained for the effective charges of the three nu(HD) modes. For samples heated in a mixture of [H-2]=[D-2], the ratios of the concentrations of [H-2]:[HD]:[D-2] are expected to be 1:2:1 but the derived concentrations of [HD] are always too small, although [H-2] is essentially equal to [D-2]. Measurements show that the solubilities of hydrogen and deuterium at 1300 degrees C are equal and both vary as p(0.56), where p is the partial pressure of the gas that is mixed with argon. It is inferred either (a) that the dipole moments of HD molecules in the three locations are all anomalously small or (b) that the concentrations of [HD] are significantly smaller than expected from random pairing of H and D atoms during cooling following the heat treatment. A proposal that similar to 70% of the hydrogen and deuterium is introduced into the Si in the form of correlated H-H and D-D pairs at 1300 degrees C removes the discrepancy (b) but is unlikely as there is then conflict with the measured pressure dependencies of the hydrogen and deuterium solubilities. [S0163-1829(99)00542-1].