Hydrogen in semiconductors studied by vibrational spectroscopy

This dissertation reports experimental studies of hydrogen in Si. The ortho-para transition of interstitial H2 in crystalline Si has been observed in a recent Raman study. In order to address issues that are difficult to study by Raman spectroscopy, we have performed IR-absorption experiments to further investigate this ortho-para transition. We find that when a Si sample containing H2 that has been equilibrated at room temperature is subsequently held at 77 K, the 3618.4 cm-1 IR line assigned to ortho-H2 is reduced in intensity with a single exponential time constant of 229 h as the system relaxes to the para-H 2 state. We have also investigated the para-ortho transition of interstitial D2 and have found decay rates similar to those for the ortho-para transition of H2.;Hydrogen and carbon are important impurities in the silicon materials used to fabricate solar cells. The defects that are formed where H and C interact have been studied by infrared (IR) absorption spectroscopy. A defect structure known as H2*(C) in which two H atoms are trapped by C has been investigated so that this defect could be used as a probe of hydrogenation processes used to fabricate solar cells. The vibrational properties of an unidentified defect that involves C and H that gives rise to a vibrational line at 2183.4 cm-1 have also been studied. The rich vibrational spectrum that appears in samples that contain both H and D reveals that this defect is a vacancy that has been trapped by a C impurity and whose four dangling bonds are terminated by H.