GaN nanorod assemblies on self-implanted (1 1 1) Si substrates H.W. Seo a , Q.Y. Chen a, * , L.W. Tu b , M. Chen b , X.M. Wang a , C.L. Hsiao b , Y.J. Tu b , L. Shao c , O. Lozano a , Wei-Kan Chu a a Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX, USA b Physics Department and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC c Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA Available online 3 March 2006 Abstract Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si substrates. Nanocapillary condensation is found to be an effective catalytic process fostering the formation of epitaxially aligned GaN nanorods in company with the thin film matrix. Changes of Si substrate surface morphology prior to deposition as a result of ion bombardments are responsible for the enhanced nanorod growth. This is attributed to the nanocapillary condensation of Ga droplets that serve as a medium to the vapor– liquid–solid growth of nanorods out of its supporting matrix. Ó 2006 Elsevier B.V. All rights reserved. Keywords: GaN; Nanostructure; Nanotrench; Nanorod; Surface modification; Self-implantation; Silicon In order for functional nanostructures to have practical device-application values, one must first be able to fabri- cate them in a controllable fashion, e.g., by lithography. Many nanostructures of alluring geometries have been reported in the literature, ranging from flexible and often entangled nanowires to epitaxial spikes of nanorods stand- ing on supporting base materials [1,2]. For these nanostruc- tures to form, very thin metallic layers were often used as a catalyst [2]. These catalytic metals act as the seeds for nucleation. They can also foster nanostructure growth. Use of metal catalysts depresses a material’s melting-point due to the alloying effect. This enables metal droplets to form on top of the fledgling nanostructures, be they the better-aligned nanorods or entangled nanowires and whis- kers. As nanostructure growth commences, the nanodro- plets continue to stay on top. The alloyed droplets are the source that provides what is needed for the continuing growth of the nanostructures. Such mechanism of nano- structure formation is known as vapour–liquid–solid (VLS) growth [3]. In VLS growth, traces of catalysts unavoidably would contaminate the growing material and alter its electronic band structure. Therefore, we believe that, if one can replace such extrinsic seeding procedure with an intrinsic means, say by use of the same atomic constituents, the con- tamination problems can then be solved. To this end, we introduced in an earlier publication a concept of nanocap- illary condensation and elucidated its effects on the nano- rod growth out of a supporting matrix [4,5]. Essentially, it uses nanocapillaries as a seed in lieu of the extrinsic cat- alytic seeding based on foreign elements. In this work, we envisage a method to produce such cap- illary effects by ion beam surface engineering [6]. Through self-implantation of Si into Si substrates, we were able to control the growth of nanorod arrays. Periodic patterns were realized first by traditional UV lithography, then followed by Si ion self-implantations. The defects, especially vacancies generated as a result of self-implantation, under the influence of a heating process, provide the necessary driving force for nucleation and growth in the implanted area. The density of nanorods in the patterned arrays can be controlled by the energy and dosage of the self-implantation that determines the vacancy concentration near the free surface. 0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.258 * Corresponding author. Tel.: +1 713 743 8253; fax: +1 713 743 8201. E-mail address: Qchen@uh.edu (Q.Y. Chen). www.elsevier.com/locate/mee Microelectronic Engineering 83 (2006) 1714–1717