The nanostructural analysis of hydrogenated silicon films based on positron annihilation studies

Due to the complex nature of hydrogenated amorphous and microcrystalline silicon (a-Si:H; μc-Si:H) a profound understanding of the Si:H nanostructure and its relation to the Staebler–Wronski effect (SWE) is still lacking. In order to gain more insight into the nanostructure we present a detailed study on a set of Si:H samples with a wide variety of nanostructural properties, including dense up to porous films and amorphous up to highly crystalline films, using Doppler broadening positron annihilation spectroscopy (DB-PAS) and Fourier Transform infrared (FTIR) spectroscopy. The results obtained from these material characterisation techniques show that they are powerful complementary methods in the analysis of the Si:H nanostructure. Both techniques indicate that the dominant type of open volume deficiency in device grade a-Si:H seems to be the divacancy, which is in line with earlier positron annihilation lifetime spectroscopy (PALS), Doppler broadening (DB) PAS and FTIR studies.