Formation of Pyramidal Etch Pits Induced by Metallic Particles on Ge(100) Surfaces in Water

We demonstrate that pyramidal etch pits composed of (111) micro facets are formed on single-crystalline Ge(100) surfaces when the Ge samples with metallic particles are immersed into water. The mechanism behind this anisotropic etching is the enhanced oxidation of Ge around metallic particles by the catalytic activity of noble metals to reduce dissolved oxygen (O2) to water molecules, and the subsequent removal of the oxide in water due to the soluble nature of Ge oxides. This enhanced etching of Ge surfaces is observed not only with metallic particles but also with a metallic thin film. The results insist that remaining metallic contaminants can roughen Ge surfaces during a rinse process with water, which will be important to design wet cleaning processes for Ge wafers.