Crystal Structure Preserving Electron-Beam Etching For Functional Ge-Nanodevices ***Motivation & Background New materials like Ge-nanowires (Ge-NWs) and Germanium-on-insulator (GOI) enable innovative devices such as nanowire-transistors with small subthreshold leakage and GOI transistors with short cycle-times. As geometrical channel dimensions are crucial for the electrical properties, fine-tuning of critical dimensions by locally confined etching is the key to optimize Ge-based devices. Unfortunately, processing with a focused ion beam (FIB) leads to Ga implantation and destruction of the crystalline structure whether focused electron beam induced etching (FEBIE) is damage- and contamination-free. FEBIE of Si was demonstrated with XeF2 as etch gas but (i) suffers from spontaneous etching and (ii) is blocked by surface contaminants. Recently we have developed a process for controlled etching of Ge-substrates with the use of chlorine as etch gas. ***Objectives This project comprises 2 development objectives: (i) the etch process, (ii) Ge-devices development. (i) ¿Development of the chlorine based etching process for Ge¿ has the goal to provide insights in surface mechanisms (adsorption, diffusion and desorption) of beam induced etching. Process optimization will provide improved etch rates, lower surface roughness, and an application for the 3 dimensional modification of Ge-nanowire structures. The etching process will enable damage-free removal of FIB-amorphized layers while maintaining full crystalline integrity of Ge-devices. (ii) ¿Device fabrication and characterization¿ will utilize the previously developed FEBIE process for structuring and fine-tuning of nanodevices. The aim is the fabrication and electrical characterization of gated Ge-nanowire devices and of a GOI-MOSFET. Moreover, in-situ electrical analysis in the SEM during ongoing FEBIE etching and cryo-measurements down to 4 K will be performed. ***Method Using a chlorine-based etch gas mixture high-resolution nanostructuring of germanium can be performed in only those areas exposed to the electron beam. Yet, chlorine FEBIE fully maintains the crystalline structure of the sample but evades spontaneous etching. Project activities will align along 2 simultaneous activity lines ¿ each conducted by one PhD student. (1) Etching of Ge-nanodevices with an focused electron beam using chlorine as etch gas : Etching of bulk Ge, Ge-NWs and GOI will be performed in a LEO 1530 electron microscope with chlorine gas injection. Vertical and horizontal thinning of Ge-NWs and MOSFET channels. (2) Analysis and Electrical Characterization of Ge-nanodevice: Processed surfaces will be investigated by TEM. Electrical properties of Ge-FETs will be investigated by C-V and I-V measurements. Electrical in-situ measurement during etching will be performed as well as structural (AFM), crystallographic and chemical (AES, SIMS) analysis. ***Relevance For the first time fine-tuning of device characteristics will be performed on Ge-NW and GOI devices as well as damage-free removal of amorphized surfaces for preparation of cross-sectional samples. Together with achieved new insights on the surface physics of adsorbed etchants and on their interaction with electrons aided by in-situ electrical monitoring during processing this project will reveal new insights beneficial both for industry and research.