hrvatski

Utjecaj grijanja na optička svojstva amorfno-nano-kristalnog silicija

In this work, we study the correlation between optical and structural properties of hydrogenated amorphous - nanocrystalline silicon (a-nc-Si:H) thin films. The samples were deposited on a soda lime glass substrate using plasma enhanced chemical vapor deposition (PECVD) and radio-frequency discharge (13.6 Mhz) in hydrogen-diluted silane. Two discharge rates were used, 12 mW/cm2 (sample set 011) and 15 mW/cm2 (sample set 04). Transmission electron microscopy shows that samples created in this way consist of an amorphous matrix into which crystals of nanometric dimensions, separate from each other, are built. Greater discharge rate results in somewhat larger nanocrystals, a more porous structure and lower hydrogen concentration. After deposition, the samples were heated in a vacuum at 100, 200, 300 and 400°C over the period of 1 hour. The samples were studied by following methods: transmittance measurements (400 – 1000 nm), Fourier Transform Infrared (FTIR) spectroscopy (450 – 3000 cm-1) and Raman spectroscopy (250 – 850 cm-1). From transmittance measurements we estimated the spectral absorption, optical energy gap (Eoptg) and Urbach parameter (EU). From FTIR spectroscopy we estimated the concentration of SiH and SiH2 bonds. With Raman spectroscopy we estimated the structural properties of amorphous matrix and size of nanocrystals. It is shown that the optical energy gap decreases with the increase of the annealing temperature which is most probable a consequence of dangling bonds formation due to effusion of hydrogen from the material. This is confirmed by decrease of Si-H bonds concentration, as determined from FTIR spectroscopy. The increase of the Urbach parameter, , and the changes of transversal optical (TO) mode of a-Si and nc-Si peak (centered around 480 and 520 cm-1 , respectively) with the increase of the annealing temperature indicate enhancement of structural disorder in amorphous matrix and structural relaxation in nano-crystals.

amorfno-nano-kristalinični silicij; optička svojstva; Ramanova spektroskopija

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