Scientific Reports 3, Article number: 1876 (2013); Published: 23 May 2013; Updated: 20 December 2013

This Article contains a typographical error in the Introduction section. “1 × 1014 carriers/cm2” was incorrectly given as “11014 carriers/cm2” and “1 × 1014 carriers/cm2” in the HTML and PDF versions of this Article respectively.