We have recently developed an epitaxial growth technique for Ge1-xSnx layers with an especially high Sn content, and we investigated the crystalline properties of the Ge1-xSnx epitaxial layers. In this report, we describe our recent achievements for improving the crystalline quality of the epitaxial growth of Ge1-xSnx layers on various substrates. We also demonstrate the impacts of Sn incorporation on the defect and dopant behaviors and electrical properties of Ge1-xSnx epitaxial layers. Sn incorporation improves on the. issue of unintentional hole generation due to vacancy defects and enhances the dopant activation of Ga atoms in the Ge matrix. In addition, we introduce a recent study of the optical properties of Ge1-xSnx epitaxial layers with very high Sn contents. (c) 2013 Elsevier Ltd. All rights reserved.