In-situ propagation of a Cu phase in germanium nanowires observed by transmission electron microscopy

Semiconductor nanowires (NWs) are promising candidates for many device applications ranging from electronics and optoelectronics to energy conversion and spintronics. However, typical NW devices are fabricated using electron beam lithography and therefore source, drain and channel length still depend on the spatial resolution of the lithography. In this work we show fabrication of NW devices in a transmission electron microscope (TEM) where we can obtain atomic resolution on the channel length using in‐situ propagation of a metallic phase in the semiconducting NW. The corresponding channel length is independent on the lithography resolution. We show results on semiconducting NW devices fabricated on two different electron transparent Si 3 N 4 membranes: a calibrated heater chip from DENs solution [1] and homemade membranes where the NW‐metal contact is locally heated by Joule heating [2]. We demonstrate a real‐time observation of the metal diffusion in the semiconducting NW. First we present results on in‐situ propagation of a copper‐germanium phase in Ge NWs while monitoring the system temperature [3] and by Joule heating while measuring the current through the device. We study the kinetics and rate limiting step by monitoring the position of the reaction front as a function of time. Second we will show characterization of the formed phase at atomic length scales with different (S)TEM techniques (electron diffraction tomography, energy dispersive X‐ray spectroscopy, HR(S)TEM) to understand how the metal atoms diffuse and incorporate into the germanide phase at the reaction front and how these parameters relate to the electrical properties of the same interface. Using EDX and diffraction characterization we find that an orthorombic Cu 3 Ge phase is created in the reacted NW part, see Fig. 2,3. Furthermore, both Cu and Ge are diffusing in opposite directions. Both EDX and diffusion studies indicate that the reaction proceeds via surface diffusion along the Cu 3 Ge segment.