Influence of grain size and surface condition on minority-carrier lifetime in undoped n-BaSi2 on Si(111)

We have fabricated approximately 0.5-mu m-thick undoped n-BaSi2 epitaxial films with various average grain areas ranging from 2.6 to 23.3 mu m(2) on Si(111) by molecular beam epitaxy, and investigated their minority-carrier lifetime properties by the microwave-detected photoconductivity decay method at room temperature. The measured excess-carrier decay curves were divided into three parts in terms of decay rate. We characterized the BaSi2 films using the decay time of the second decay mode, tau(SRH), caused by Shockley-Read-Hall recombination without the carrier trapping effect, as a measure of the minority-carrier properties in the BaSi2 films. The measured sSRH was grouped into two, independently of the average grain area of BaSi2. BaSi2 films with cloudy surfaces or capped intentionally with a 3 nm Ba or Si layer, showed large tau(SRH) (ca. 8 mu s), whereas those with mirror surfaces much smaller tau(SRH) (ca. 0.4 mu s). X-ray photoelectron spectroscopy measurements were performed to discuss the surface region of the BaSi2 films. (C) 2014 AIP Publishing LLC.