Enhancement of IR photoluminescence of [beta]-FeSi2 nanocrystals by Cu-doping and study of its mechanism

We have investigated the IR photoluminescence (PL) behavior of Cu-doped [beta]-FeSi2 nanocrystals ([beta]-NCs) embedded in Si layers. The diffusion rate of Cu atom was controlled by annealing. The most appropriate condition brought the largest intensities of both the intrinsic A band emission at 0.803 eV by 214% and the acceptor related C band emission at 0.75 eV by 582% in comparison with those of non-doped [beta]-NCs. Rutherford backscattering spectrometry (RBS) revealed increase of Cu atoms in the Si layer with [beta]-NCs with increasing the anneal duration. The C band enhancement surely is originated from increase of a density of state at acceptor levels relating to increase of Cu in [beta]-lattice. Photocarrier injection PL measurements (PCI-PL) reveal that the enhancement of the A band emission may be attributed to a controlled migration process of holes with a repeated trap process due to Cu-doping into the Si phase. This dynamic condition leads to an increase of valence band offset at the [beta]-NCs/Si heterointerfaces where the migration of holes from the [beta]-NCs to Si is prevented, so that a radiative recombination rate can be enhanced. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)