The nature of electrically inactive antimony in silicon

Abstract

Supersaturated solutions of substitutional, electrically active Sb in 〈100〉 silicon single crystals have been obtained by ion implantation, followed by short-duration incoherent-light annealing. Substitutional and nonsubstitutional fractions have been studied as functions of implanted dose and anneal temperature by Rutherford backscattering and channeling techniques, transmission-electron microscopy, Hall-effect and resistivity measurements (combined with layer removal), and Mössbauer spectroscopy. The maximum electrically active concentration, which can be incorporated on undisturbed substitutional sites, is found to be 4.5×1020 Sb/cm3 for 700 °C annealing. Upon further annealing, the supersaturated solution is reduced and approaches the Trumbore solubility value at temperatures of about 1100 °C. The Sb going out of solution is shown for the first time to be created in two different surroundings: Sb is predominantly found in Sb-vacancy complexes for low doses and low annealing temperatures and in Sb precipitates for high doses and/or high annealing temperatures. Complete agreement is found between substitutional fractions derived from Mössbauer spectroscopy and electrically active fractions from Hall-effect measurements, whereas the substitutional fractions from channeling measurements are significantly higher. The experiments are not conclusive as to whether this difference is due to the fraction of Sb in Sb-vacancy complexes or in coherent Sb precipitates.