Thermal diffusion studies of MBE-grown ZnSe/Fe/ZnSe and ZnS/Fe/ZnS structures

This study focused on the investigation of the thermal stability of Fe on ZnSe and ZnS matrix using secondary ion mass spectroscopy (SIMS). Sandwiched three layer source structures of ZnSe/Fe/ZnSe and ZnS/Fe/ZnS were grown on GaAs and GaP substrates, respectively, by the molecular beam epitaxy technique. The bottom II-VI layers and the Fe- sandwiched layers in these structures are single crystalline while the top II-VI layers are polycrystalline. Thermal annealing was conducted in a range covering from 320 to 550 °C. The SIMS depth profiles of the as-grown and annealed structures reveal that (1 0 0) oriented single crystalline Fe/ZnSe interface is thermally stable at temperature as high as 450 °C while its polycrystalline counterpart suffers from fast diffusion even at the growth temperature. In contrast, (1 0 0) oriented polycrystalline Fe/ZnS interface is quite stable at least up to 200 °C. For both ZnSe/Fe/ZnSe and ZnS/Fe/ZnS systems, (1 1 1) oriented structures were found to have lower thermal stability than (1 0 0) oriented ones. These results provide important findings towards the optimization of Fe-based tunneling magneto-resistance structures using a II-VI semiconductor barrier.