Germanium nanowires grown on Ge bulk crystals

Germanium nanowires grown on Ge bulk crystals Giovanni Attolini, Giovanna Trevisi, Francesca Rossi, Davide Calestani, IMEM-CNR Institute, Parco Area delle Scienze 37A, 43124 Parma (Italy) giovanni.atolini@imem.cnr.it Germanium is a semiconductor material with an indirect bandgap at 0.66 eV and a diamond cubic crystal structure. Due to its excellent opto-electronic properties such as high carrier mobility and high dielectric constant, germanium is interesting for the realization of many electronic devices. Nanowires (NWs) exhibit unique electronic, optical and mechanical properties resulting from their low-dimensionality and shape, many applications have been demonstrated in which they are used as active elements in nanodevices. In particular, germanium nanowires are attractive because their properties (high electronic and hole mobility, quantum confinement effect) have potential application in high speed field effect transistors [1]. Many methods have been developed to grow germanium nanowires: laser ablation, thermal evaporation, metal organic chemical vapour deposition (MOCVD) and chemical vapour deposition (CVD) [2]. Ge-NWs are usually grown on silicon and germanium wafers using gold as a catalyst that, forming an eutectic at low temperatures, allows the NWs growth with the VLS mechanism (vapour-liquid-solid). In this communication we report on the VLS growth of germanium nanowires (after optimization of the growth parameters on Si and Ge (100) surfaces) on germanium bulk crystal obtained by Chemical Vapour Transport (CVT). The germanium bulk crystal prepared to be used in this work confirms a cubic structure (131) oriented [3]. As catalyst a gold layer of nanoparticles was deposited on the substrates previously cleaned in hydrochloric acid to remove the native oxide. Ge powder as starting material was added in a quartz boat and inserted in a quartz tube with the substrates upstream in a tubular furnace, purged with argon. Temperature was 900 °C for the source and 550 °C for substrates and kept for 1h. This method exploits the thermal evaporation of the powder (Ge vapour) in the range of temperature used in this preparation, the Ge vapour is transported in the deposition zone by nitrogen flow, leading to the nucleation of the nanowires. The morphology of the NWs was characterized by Scanning Electron Microscopy (SEM) that showed a dense network of thin NWs with diameter in the range of 50-100 nm Transmission Electron Microscopy (TEM) has been used to observe their structural properties, showing uniform diameter without defects, such as dislocations and stacking faults with cubic structure. References __________________ [1] Li Z. Pei and Zheng Y. Cai, A Review on Germanium Nanowires, Review Patents on Nanotechnology 6 (2012) 44-59 [2] Chuanbo Li, Hiroshi Mizuta and Shunri Oda, Growth and Characterization of Ge Nanowires by Chemical Vapour Deposition, chapter 22 pag. 487-508 Nanowires - Implementations and Applications Edited by Dr. Abbass Hashim Interchopem 2011. ISBN 978-953-307-318-7 [3] To be published Acknowledgements The authors are grateful to Mr. Tullo Besagni for his technical support.