Shallow V-Shape Nanostructured Pit Arrays in Germanium Using Aqua Regia Electroless Chemical Etching

Abstract

Due to its high refractive index, reflectance is often a problem when using Germanium for optoelectronic devices integration. In this work, we propose an effective and low-cost nano-texturing method for considerably reducing the reflectance of bulk Germanium. To do so, uniform V-shape pit arrays are produced by wet electroless chemical etching in a 3:1 volume ratio of highly-concentrated hydrochloridric and nitric acids or so-called aqua regia bath using immersion times ranging from 5 to 60 min. The resulting pit morphology, the crystalline structure of the surface and the changes in surface chemistry after nano-patterning are all investigated. Finally, broadband near-infrared reflectance measurements confirm a significant reduction using this simple wet etching protocol, while maintaining a crystalline, dioxide-free, and hydrogen-passivated surface. It is important to mention that reflectance could be further reduced using deeper pits. However, most optoelectronic applications such as photodetectors and solar cells require relatively shallow patterning of the Germanium to allow formation of a pn-junction close to the surface.

Wet Chemical Processing of Ge in Acidic H2O2 Solution: Nanoscale Etching and Surface Chemistry

“…[22][23][24][25][26][27] In the past, wet-chemical etching of Ge utilizing hydrogen peroxide based etchants have been explored. [27][28][29][30][31][32][33][34][35][36][37] Cerniglia et al 32 have reported on the etching of Ge in aqueous H 2 O 2 with concentrations ranging from 3% to 30% using a mass balance difference method and proposed an electroless dissolution mechanism for Ge (100). Later, an electrochemical study by Gerischer and co-workers 38 suggested a purely chemical mechanism for the acidic H 2 O 2 etchant, which was also supported by the work of Huygens via profilometry and electrochemical experiments for electrolytes of various pH.…”