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J. Sama, S. Barth, A. Romano-Rodriguez:
"Novel Gas Sensors Based on Germanium Nanowires";
Vortrag: 2014 MRS Fall Meeting, Boston; 30.11.2014 - 05.12.2014; in: "2014 MRS Fall Meeting - Program", (2014), S. LL12.07.

Germanium (Ge), a classical semiconducting material, is sparsely used in electronics due to its low abundance at the earth crust. Ge finds some applications in photodetectors and, alloyed with Si, in high-speed bipolar transistors. However, recently, there has been a growing interest on Ge nanowires (NWs) because they show improved electrical and optical properties as compared to silicon.
NWs, due to their large surface to volume ratio, are very interesting material geometries for their introduction in applications where surface phenomena take place, as is the case of gas sensors. This justifies that in the last 15 years there has been a huge number of papers dealing with NWs of several different materials as efficient gas sensors. However there has been no report on Ge NWs employed as gas sensors, and only few papers show some gas sensitivity of bulk Ge.
Here we will present the synthesis of Ge nanowire based on the VLS method, the fabrication of chemoresistive gas sensors based on them and their gas response towards different gases. The Ge have been grown either on Si or alumina substrates or either on the top of bulk or suspended micromembranes, equipped with surface interdigitated electrodes and a buried heater. Similarly to other chemiresistors, the Ge NW surface reacts with the presence of gases, what causes a change in its resistance. The results have shown good response towards the presence of hundreds ppb´s of NO2 and CO at low temperatures, below 1000C.
The behaviour of the Ge NW gas sensor will be presented and discussion about their sensing mechanism, which differs from that of Si or metal oxides, will be presented. For this, the fact that Ge NWs are covered by a non uniform and non stoichiometric GeOx layer will be of capital importance.