Optical study of lithium-defect complexes in irradiated silicon

Abstract

Optical spectroscopy has been used to study the interaction of lithium impurity atoms with neutron-produced defects in silicon. In addition to the divacancy-associated defect absorption bands at 1.8, 3.46, and 3.61 μ, several additional radiation-produced infrared absorption bands at 1.36, 1.50, 1.6, 1.94, 2.05, 2.09, 2.14, and 2.4 μ are observed in lithium-doped silicon, irrespective of the oxygen concentration. In high oxygen concentration Si, a decrease of the (LiO)+ vibrational band (9.85 μ) accompanied by an increase of the oxygen interstitial vibrational band (9 μ) is observed after neutron irradiation (at ∼ 300 ∘K) and heat treatment (to ∼ 150 ∘C). This fact rules out the possibility of the formation of the Li–O-vacancy defect complex. The presence of Li decreases the production of the oxygen-vacancy complex. The intensity and the annealing temperature of the divacancy-associated bands strongly depend upon the Li concentration, and the intensity is found to be substantially lower than that observed for Si not containing Li. The Li defect bands exhibit a saturation in their intensity for (Li) ≈6×1016 cm−3. The bands increase in intensity after T ≳80 ∘C heat treatment. This is attributed to the dissociation of other simple Li-associated defects. The results indicate that higher-order defect complexes are responsible for the bands and the divacancy must be directly involved in the formation of at least one of them. Detailed annealing studies are presented.