engleski

Analysis of amorphous-nanocrystalline Si thin films by Time-of-Flight Elastic Recoil Detectoin Anlaysis and High Resolution Electron Microscopy

The in-depth distribution of hydrogen atoms in 100 nm thick amorphous-nano-crystalline silicon films (a-nc-Si) with 10 nm resolution was estimated by Time-of-Flight Elastic Recoil Detection Analysis (TOF ERDA) using previously described setup [1]. Samples were deposited by plasma enhanced chemical vapour deposition, using silane gas highly diluted with hydrogen. As seen by high resolution transmission electron microscopy (HRTEM), the films contained nano-crystals of silicon embedded in amorphous Si: H matrix. The size of crystals and crystal to amorphous fraction increased starting from substrate towards surface of the film. Amorphous matrix looked uniform except in the area close to substrate where spots brighter than average appeared. These areas can be attributed to les density material, presumably voids. It is assumed that the surface of voids is “decorated” with hydrogen that saturates silicon “dangling bonds” [2]. That is why distribution of hydrogen should indicate density fluctuation in material. Consistent with this assumption, TOF ERDA showed non uniform distribution of hydrogen across the depth with maximum close to substrate that coincidence with less density material seen by HRTEM. This supports the idea about important influence of voids in crystal formation, in particularly in nucleation phase. After heat treatment at 400oC, the distribution of hydrogen remained the same, while total hydrogen concentration decreased. This indicated that the type of hydrogen bonding was the same across the amorphous network and assumed that areas of less density materials consist of agglomerates of smaller voids. [1] Z.Siketić, I.Bogdanović Radović, Milko Jakšić, Thin Solid Films 518, 2617 (2010). [2].S. D.Gracin, U.V.Desnica nd M.Ivanda, J.Non- Cryst. Solids 149, 257 (1992)

TOF-ERDA; amorphous-nanocrystalline silicon; thin films; hydrogen distribution

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