Effects of nitrogen on dislocation behavior and mechanical strength in silicon crystals

The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating-zone technique. These are compared with those in the usual floating-zone-grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600 °C. Dislocations in the nitrogen-doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski-grown silicon, nitrogen-doped silicon shows a much higher yield strength than usual floating-zone-grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.