Abstract
We propose the metal-assisted chemical etching of Ge surfaces in water mediated by dissolved oxygen molecules (O2). First, we demonstrate that Ge surfaces around deposited metallic particles (Ag and Pt) are preferentially etched in water. When a Ge(100) surface is used, most etch pits are in the shape of inverted pyramids. The mechanism of this anisotropic etching is proposed to be the enhanced formation of soluble oxide (GeO2) around metals by the catalytic activity of metallic particles, reducing dissolved O2 in water to H2O molecules. Secondly, we apply this metal-assisted chemical etching to the nanoscale patterning of Ge in water using a cantilever probe in an atomic force microscopy setup. We investigate the dependences of probe material, dissolved oxygen concentration, and pressing force in water on the etched depth of Ge(100) surfaces. We find that the enhanced etching of Ge surfaces occurs only when both a metal-coated probe and saturated-dissolved-oxygen water are used. In this study, we present the possibility of a novel lithography method for Ge in which neither chemical solutions nor resist resins are needed.
Highlights
Germanium (Ge) is considered to be a substitute for Si for future complementary metal-insulator-semiconductor devices because of its higher carrier mobility than silicon (Si) [1]
We showed that noble metal particles such as Ag and Pt induce anisotropic etching
The mechanism of this formation is the catalytic activity of noble metals to reduce O2 molecules in water, which promotes preferential oxidation around metallic particles
Summary
Germanium (Ge) is considered to be a substitute for Si for future complementary metal-insulator-semiconductor devices because of its higher carrier mobility than silicon (Si) [1]. Wet-chemical treatments are essential for the fabrication of Ge-based devices, they have not been well established yet. Ge oxide (GeO2) is permeable and soluble in water, unlike the more familiar silicon oxide (SiO2). Ge surfaces are not resistant to various chemical solutions. A piranha solution (a mixture of H2SO4 and H2O2) is commonly used in removing metallic and organic contaminants on the Si surface. We cannot use it for Ge because it damages Ge surfaces very . In several earlier works, the etching property of Ge surfaces has been investigated [2,3], the unique chemical nature of Ge prevents researchers from developing surface treatment procedures for Ge using solutions
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