KCS

Recently, germanium nanowires (GeNWs) have attracted much attention due to their unique one dimensional nanostructure, the advanced electrical properties such as high carrier mobilities, and compatibility with existing IC process. Various growth mechanisms for single crystalline GeNWs until now. Among them, VLS growth method by transition metal catalyst has been much widely used because it provides a facile route for synthesis and allows to control the morphology and doping ratio during the growth process. However, conventional GeNW growth by VLS method has many problems, such as metal impurities contamination, and ununiform dopant and Ge adsorption on NW side wall. In addition, more fundamental issue is that Ge easily forms unstable oxides on the surfaces. Compared with chemically and electronically stable Si/SiO₂interface, the Ge/GeO_xinterface has considerably high surface states and is trouble with unfavorable electrical properties and poor chemical instability. Herein, we present single crystalline germanium nanowire growth with protective carbon shell by low-pressure chemical vapor deposition (LPCVD) process. Carbon shell has amorphous nanostructure with very thin thickness of 2-3nm. It can be acted as not only the passivation layer preventing the oxidation at even high temperature, but also barrier for metal diffusion during GeNW growth process. In addition, the simultaneous shell growth prevents the uncatalyzed Ge deposition. These carbon shell effects on NW growth were investigated using field emission scanning electron microscopy (FE-SEM), raman spectroscopy, and high resolution transmission electron microscopy (HR-TEM).