Nitrogen-containing point defects in multi-crystalline Si solar-cell materials

Abstract

The multi-crystalline Si used to fabricate solar cells contains nitrogen, with a concentration typically in the mid-1015 cm−3 range that was introduced by the Si3N4 liner of the crucible used for ingot growth. Low temperature infrared spectroscopy has been used to identify and determine the concentrations of the nitrogen-containing point defects in multi-crystalline samples with a range of nitrogen and oxygen concentrations. We find that the dominant nitrogen centers in multicrystalline Si are the NN and NNOn complexes that are well-known from studies of monocrystalline Si. In as-grown, multi-crystalline Si with an oxygen content of [O] = 3.2 × 1017 cm−3, 44% of the nitrogen was found to be present as NN-On complexes. We also found that near 1 × 1014 cm−3 NOn shallow donors can be present. The concentrations of nitrogen centers that also contain oxygen depend strongly on the concentration of oxygen in the multi-crystalline Si substrate.