Suppressing phosphorus diffusion in germanium by carbon incorporation

Introduction: The low effective mass and higher mobility of carriers in germanium (Ge) compared to silicon (Si) (two times higher mobility for electrons and four times for holes) has prompted renewed interest in Ge-based devices for high-performance logic, especially as it becomes increasingly difficult to enhance Si CMOS performance through traditional device scaling. However, it has been difficult to fabricate high-quality Ge MOSFETs owing to the lack of a devicequality gate dielectric (stable with low interface state density). In particular, the Ge native oxide is water soluble. Since this makes processing difficult and stability unlikely, other dielectrics have been tried, such as GeON dielectric [1], and high-k materials [2]. For n-channel Ge MOSFETs, there is an additional fabrication challenge, namely, owing to the fast phosphorus diffusion during activation [3], the nþ S=D is very difficult to control. In this Letter, we present a study of phosphorus diffusion in Ge, and demonstrate for the first time that the carbon incorporated in Ge can suppress the phosphorus diffusion effectively during the annealing process.