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Heliuminduced structural disorder in hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared by HW-CVD method

Nabeel A.Bakr

Structural, optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) films, deposited from silane (SiH4) and helium (He) gas mixture without hydrogen by hot wire chemical vapor deposition (HWCVD) method were investigated as a function of helium dilution of silane (RHe). We observed that the deposition rate is much higher (4-33 Å/s) compared to conventional plasma enhanced chemical vapour deposited (PE-CVD) nc-Si:Hfilms. Raman spectroscopy revealed that the crystalline volume fraction decreases with increasing He dilution of silane whereas the crystallite size remains almost constant (~ 2 nm) for the entire range of He dilution of silane studied. Furthermore, an increase in the structural disorder in the nc-Si:H films has been observed with increasing He dilution of silane. The hydrogen content was ~ 9 at. %in the filmdeposited at 60%RHe and decreases rapidly as RHe increases further. The photoresponse decreases by order of 1 with increasing heliumdilution of silane from60 to 97 %. It has been concluded that adding helium gas to the silane induces the structural disorders in the hydrogenated nanocrystalline silicon (nc- Si:H) thin films prepared byHW-CVDmethod.