Irradiation enhanced diffusion of boron in delta-doped silicon

Abstract

Two kinds of silicon samples have been used in this work: one containing a sequence of boron spikes and one with a sequence of alternating boron and antimony spikes, both grown by molecular beam epitaxy. These samples were irradiated with 2.5 MeV protons at an elevated temperature ranging from 500 to 830 °C and characterized by secondary-ion-mass spectrometry. The energy of the proton beam was chosen such that the generation rate of point defects can be considered as uniform throughout the delta-doped Si samples. The influence of the sample surface and of the boron concentration (ranging from 5×1015 to 3.2×1018 B/cm3 in the different samples) on the diffusion of boron have been studied in detail. The effect of antimony on boron diffusion has also been analyzed. For each sample, the B diffusion coefficient is increased under irradiation as compared to the B diffusion coefficient in unirradiated areas. This enhancement is dependent on the irradiation temperature, on the position of the boron spike and on the boron concentration. Further, the presence of antimony enhances the boron diffusion during low-temperature proton irradiation.