Increasing sp³ hybridized carbon atoms in germanium carbide films by increasing the argon ion energy and germanium content

We have prepared germanium carbide (Ge_1-xC_x) films on Si(0 0 1) by radio frequency (RF) reactive sputtering a pure Ge(1 1 1) target in a CH₄/Ar mixture discharge, and found that the sp³ hybridized carbon atoms in the Ge_1-xC_x film can be significantly increased in two ways. One is by increasing the Ge content via increasing the RF power during the film deposition, which can lead to a transition from sp² C-C to sp³ C-Ge bonding in the film. Another is by increasing the Ar ion energy in a discharge Ar/CH₄ gas by applying the negative bias voltage, which plays an important role in inducing the compressive stress in film. We find that when the compressive stress increases above a critical value of 2.2 GPa, an abrupt transition from sp ² C-C to sp³ C-C bonding occurs in the Ge _1-xC_x film, which is a consequence of energy minimization.