Despite a renewed interest in germanium (Ge) as a material for beyond the silicon (Si) era for electronic and photonic applications, the GeO2/Ge interface remains to be controlled for making the best of Ge's advantages. Not only electrical challenges but also structural challenges must be considered. The crystallization of GeO2 on Ge without the desorption of GeO is clearly demonstrated. This demonstration means that the desorption of GeO observed in a GeO2/Ge stack is not the sole indicator of deterioration of the GeO2/Ge gate stack. Moreover, a study using atomic force microscopy demonstrates that a nonuniform reaction at the GeO2/Ge interface [with root mean square (rms) roughness of 2.3 nm] is observed on the initially flat Ge surface (rms: 0.3 nm). Furthermore, a reaction at the GeO2/Si interface is experimentally investigated in comparison with the GeO2/Ge case, and crystalline Ge islands are demonstrated to form on Si. These findings are of fundamental interest as well as of technical importance from the viewpoint of Ge-based electronics and photonics.
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