Thermally induced changes in the hydrogen microstructure of amorphous hydrogenated silicon films, analyzed using in situ real time infrared spectroscopy

Changes in the hydrogen content and bonding in amorphous hydrogenated silic on (a-Si:H) films during stepwise thermal annealing are measured using in s itu real time infrared spectroscopy The experimental spectra are fit using previously identified SiH stretching modes for hydrogen bonded at isolated network sites, hydrogen in platelet-like configurations-and hydrogen at sur faces. Based on this mode separation, the release of hydrogen from surfaces and platelet configurations is found to occur at similar to 320-370 degree s C. By 470 degrees C, these groups are completely released from the sample , whereas isolated SiH network sites are still present. This thermal anneal ing of the sample also irreversibly changes the microstructure and thereby the distribution of available hydrogen bonding sites in the amorphous netwo rk. Re-hydrogenation experiments Show that isolated bonding sites are creat ed and platelet and surface bonding sites are removed from the hydrogen den sity of states. This structural transformation during annealing is interpre ted as the release of hydrogen from platelet like configurations and the re formation of Si-Si bonds in a-Si:H.