The growth mechanism of Ge1−x-Cx:H films deposited by PECVD method

Abstract

In the current study, the Ge1−x-Cx:H films were deposited on silicon and glass substrates by a plasma-enhanced chemical vapor deposition (PECVD) process with a gas mixture of GeH4 and CH4 as the precursors. For characterizing the films, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry, elastic recoil detection analysis, and adhesion test were used. Based on the results, the growth mechanism of Ge1−x-Cx:H films by PECVD process was suggested as three separate steps including 1) the removal of surface H and the formation of dangling bonds, 2) insertion of germanium and methane radicals into the dangling bonds and 3) removal of inter-atomic H and the formation of GeGe, CC and GeC transverse bonds, respectively. If in the growth environment the radicals XH3 (X = Ge, C) be the dominant radicals, a two-dimensional growth occurs. On the other hand, the presence of a variety of radical species (XH3, XH2, XH) results in a preferred three-dimensional growth. With increasing the CH4: GeH4 flow rate ratio, the surface homogenization mechanism by H ions becomes more prevalent and consequently, the three-dimensional growth tends to the two-dimensional growth.