Carrier concentration, mobility, resistivity and impurity concentration of 400 keV channeled phosphorus ions in silicon

Abstract

High resistivity single crystals of p-type silicon have been implanted at room temperature in the (110) direction with 400 keV P-31 and P-32 ions, using total doses of 10¹³ and 10¹⁵ ions/cm². Hall effect measurements on samples annealed to 600 °C combined with peeling techniques have been used to determine the surface carrier concentration and effective mobility as a function of depth (in 0.2 μ steps), and also as a function of measurement temperature (300 °K to 88 °K). From these measurements the bulk carrier concentration and mobility have been computed. The conductivity and carrier concentration distributions for samples implanted with 10¹⁵ ions/cm² have a large ‘random’ peak at 0.5 μ depth and a ‘channeled’ peak at 1.6 μ. The distribution of radioactive P-32 atoms also shows the prominent random peak and extends as far as 1.6 μ. The carrier concentration of 10¹⁹ cm⁻³ at any temperature indicates that impurity banding is present in the random peak. A corresponding decrease in mobility is observed. From the temperature dependence of the carrier concentration at other depths, estimates of the donor density and compensating acceptor density are obtained. In the channeled region a donor density of 2·10¹⁷ cm⁻³ and a compensation ratio of 0.2 are estimated.