The properties of a-SiGe:H films deposited by 55 kHz PECVD

The optoelectronic properties and microstructure of a-SiGe:H films deposited by 55 kHz plasma enhanced chemical vapor deposition (PECVD) method were investigated. The growth rate of a-SiGe:H deposited by this method is larger in comparison to the commonly used 13.56 MHz PECVD and does not change with the variation of GeH4 content from 0% to 44.5% in the gas mixture. The optical bandgap of 55 kHz a-SiGe:H depends linearly on the GeH4 content and is not affected by the variation of the total hydrogen content in the films. On the other hand the specific features of the hydrogen-related microstructure affect the electronic properties such as dark conductivity, ημτ product, defect density and Urbach slope. The decrease of Si–H bond concentration and increase in the number of Ge–H bonds lead to a deterioration of the electronic properties. The results of the measurements of optoelectronic properties and Staebler–Wronski (SW) effect measurements of 55 kHz a-SiGe:H films demonstrated an increased stability in comparison with a-Si:H.