Vibrational infrared-absorption bands related to the thermal donors in silicon

Abstract

Thermal donor formation in silicon at 390, 420, and 450 °C has been investigated and correlated with IR vibrational absorption bands observable at room temperature. It is suggested that oxygen is clustering in different structures giving rise to absorption bands at 975, 988, 1000, 1006, and 1012 cm−1. The bands at 975, 988, and 1000 cm−1 are related to the three first appearing double donors as studied by low-temperature infrared spectroscopy. The 1012 cm−1 band is related to the most frequently appearing type of structure and is suggested to correspond to a different type of donor, possibly the shallow thermal donors or the new thermal donors. The development of the new bands with heat treatment time shows a complex behavior. The early stages of thermal donor formation as studied at 390 °C are not governed by ordinary long-range oxygen diffusion but by a transformation process of pre-existing clusters corresponding to the 1012 cm−1 band. At 450 °C the cluster transformation process appears in parallel with an aggregation of oxygen atoms diffusing to the clusters. Another group of vibrational bands appears in the range 724–745 cm−1. These bands develop simultaneously with the 975–1012 bands and are suggested to be related to a different vibrational mode of the oxygen atoms in the clusters.