Annealing-related conductivity conversion in lightly Fe-doped n-type InP wafers

As-grown semiconducting InP wafers containing iron at a level between 5 and 8×10¹⁵ cm^-3 were seen to convert to semi-insulating, with high resistivity and good mobility, after a thermal treatment at 900°C. This fact is interesting since it allows the preparation of semi-insulating InP with Fe content substantially lower than in standard LEC material. In this paper we report the annealing parameters and the results of an extensive electro-optical characterization of the treated samples. The experimental results suggest that the conductivity drop is mainly due to a considerable loss of shallow donors