Direct-gap photoluminescence from germanium nanowires

Yoko Kawamura,3 Kevin C. Y. Huang,1 Shruti V. Thombare,1 Shu Hu,1 Marika Gunji,1 Toyofumi Ishikawa,3 Mark L. Brongersma,1,2 Kohei M. Itoh,3 and Paul C. McIntyre1,2,* 1Materials Science and Engineering, Stanford University, Stanford, California 94305 2Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 3School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan (Received 15 March 2012; published 6 July 2012)