Nano-indented Ge surfaces by metal-assisted chemical etching (MacEtch) and its application for optoelectronic devices

Surface reflection is one of the major limiting factors to determine light absorption performance of optoelectronic devices. In recent years, light management using various types of nanostructures has gained much attention [1]. However, fabricating the nanostructures by conventional dry etching results in damage within the crystal structures attributed to high energy ions. Metal assisted chemical etching (MacEtch) is an alternative method to produce the nanostructures [2]. Because MacEtch is fundamentally a wet etch which does not involve high energy ions, structural defects can be avoided [3,4]. Therefore, the technique has been widely used to create surface texturing for the optoelectronic and photonic applications. However, the MacEtch enabled nanostructures have been mainly formed on Si and III-V compounds [5,6]. In this report, we present a novel MacEtch based technique to create nano-indentations on Ge and the enhanced responsivity and reduced dark current of Ge photodiodes.