The efficiency of carbon adsorption as a diffusion barrier in Ge/Si heterostructures

Silicon (Si), germanium (Ge) and Si1−xGex alloys are currently used as active layers in microprocessors. Si and Ge are fully miscible and their interdiffusion can occur even at room temperature. Thus, well-controlled Ge/Si interdiffusion is crucial to insure the performance of electronic devices. During the course of our experiments to synthesize tensile-strained and n-doped Ge/Si films for optoelectronic applications, we notice that Ge/Si interdiffusion could affect the optical properties of Ge/Si films. We report here an approach to use carbon (C) adsorption on Ge to minimize Ge/Si interdiffusion. Since carbon atoms have a small atomic radius, deposited carbon can occupy vacancies and interstitial sites in Ge. This allows to greatly reduce Ge/Si interdiffusion because diffusion mechanisms via vacancies and interstitial sites are known to have the lowest activation energy. In addition, by optimizing the deposited C amount, one can maintain the epitaxial growth process of Ge/Si heterostructures.