Amorphous Si1-xGex films were prepared by co-sputtering on an oxidized Si wafer, followed by rapid thermal annealing to form nanocrystal films. The formation of Ge nanocrystals was not at thermodynamic equilibrium formed in the amorphous Si1-xGex matrix. High-resolution transmission electron microscopy was used to characterize the increase in the size of the grains in the Ge nanocrystals as the Ge content increased. The Ge nanocrystals have a greater absorption in the near-infrared region and higher carrier mobility than SiGe crystals, and the variation in their grain sizes can be used to tune the bandgap. This characteristic was exploited herein to fabricate n-Si1-xGex/p-Si1-xGex p-n diodes on insulating substrates, which were then examined by analyzing their current-voltage characteristics. The rectifying property became stronger as the fraction of Ge in the Si1-xGex films increased. The Si1-xGex diodes are utilized as photodetectors that have a large output current under illumination. This paper elucidates the correlations between the structural, optical and electrical properties and the p-n junction performance of the film. (C) 2015 Elsevier B.V. All rights reserved.