Thermal donor formation in aluminum doped silicon

Aluminum as a dopant has been reported to enhance thermal donor (TD) formation in silicon. We present results based upon infrared (IR) studies of a recently discovered group of vibrational absorption bands related to the TDs. According to these vibrational absorption bands three categories of TDs has been suggested to develop in the temperature range 350–500 °C. Our results reveal that in comparison with dopants such as B and P the first category appearing is suppressed in Al-doped samples while the second category is not affected. The formation of the third category is enhanced in moderately (≈ 1 × 1016 at. cm−3) Al-doped samples. A new IR absorptional at 992 cm−1 which is linearly correlated to the Al-doped concentration is found. It is suggested to originate from an oxygen vibration in a SiOAl center.