Anisotropy of phosphorous electron donor state in strained clusters in silicon at low temperatures

An anisotropic EPR spectrum at T = 4 K was observed in silicon samples irradiated by phosphorus ions and subsequently annealed at 1000°C. Epitaxial silicon layers with a natural isotope composition and enriched by ²⁸Si isotope grown on a natural silicon wafer were investigated. The spectrum consisted of three lines corresponding to different g-factor components: g _x ,g _y , and g _z . The central line was overlapped by the isotropic line coinciding by its g-factor with the line of the conduction electrons in silicon. The shape of the spectral lines indicated that the spectrum was due to the paramagnetic centers which belong to the randomly oriented clusters with the anisotropic g-factor. The nature of the anisotropic EPR spectrum is due to the electrons localized on donors located in the strained phosphorous clusters. The strains were caused by either incompletely annealed defects after the phosphorous implantation (E = 40 keV, D = 2 × 10¹⁴ cm⁻², T _ann = 1000°C, 1 h) or phosphorous atoms in clusters. The distance between the components strongly depended on the temperature and microwave power and decreased as they increased.