Type of presentation: Oral

MS-8-O-1963 In-situ propagation of a metal-semiconductor phase in silicon and germanium nanowires observed by transmission electron microscopy

El hajraoui K.1, Den hertog M. I.1, Zeiner C.3, Mongillo M.2, Prager A.2, Lugstein A.3, Rouvière J. L.2
1Institut Néel-CNRS, Grenoble, France, 2CEA-Grenoble, Grenoble, France, 3Vienna University of Technology, Vienna, Austria
khalil.el-hajraoui@neel.cnrs.fr

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 Si3N4 membranes: a planar membrane and a membrane where devices are suspended over holes and we demonstrate a real-time observation of the metal diffusion in the semiconducting NW. First we describe the process of making lithographically defined reliable electrical contacts on individual NWs dispersed on a membrane. Second we present first results on in-situ propagation of a metal-semiconductor phase in Ge NWs by joule heating [1] while measuring the current through the device. Three different metals are used as contacts: platinum, copper and aluminum. Different phenomena can occur in PtSi, AlGe and CuGe [2] NWs during phase propagation. Furthermore we study the crystalline structure of the different phases and the diffusion mechanisms of the different metals.
[1] M. Mongillo, P. Spathis, G. Katsaros, P. Gentile, M. Sanquer and S. De Franceschi, ACS Nano, 5, 7117-7123 (2011).
[2] T. Buchhart, A. Lugstein, Y. J. Hyun, G. Hochleitner and E. Bertagnolli, Nano. Lett, 9, 3739-3742 (2009).

Financial support from the French ANR for the ̎ COSMOS ̎ project is acknowledged. We thank J-L. Thomassin, B. Fernandez and T. Fournier for their technical support.

Fig. 1: TEM image of suspended Ge NW device connected by Cu pads showing the procedure of the joule heating for the in-situ propagation.

Fig. 2: TEM image of Ge NW after the in-situ propagation showing the progression of the CuxGey phase.