Thermally Induced Deep Centers in Silicon Doped with Europium or Lanthanum

Melt-grown silicon crystals doped with europium or lanthanum were studied by capacitance spectroscopy and infrared absorption spectrophotometry. The Eu and La in the as-grown crystals were demonstrated to be electrically inactive. Annealing in the temperature range 900–1200°C produced a few deep levels in the band gap of both n-Si〈Eu〉 and n-Si〈La〉. These levels are likely related to the activation of the Eu and La impurities: Eu seems to be responsible for the levels at Ec– 0.40 eV and Ec– 0.46 eV, and La for the level at Ev+ 0.32 eV. Infrared absorption measurements indicate that heat treatment increases the concentration of optically active (interstitial) oxygen in the crystals by 15–20%.