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

Abstract

We have prepared germanium carbide (Ge1−xCx) 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 Ge1−xCx 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 sp2 C–C to sp3 C–C bonding occurs in the Ge1−xCx film, which is a consequence of energy minimization.