FTIR studies of hydrogen-related defects in dilute III-nitrogen-V alloys and crystalline silicon photovoltaics

In this dissertation, hydrogen-containing defects in two semiconducting material systems are studied: dilute III-N-V alloys (GaAsN and GaPN), and crystalline silicon. In both material systems, H has a significant effect on electronic properties. In dilute III-N-V alloys, there has been tremendous interest due to a large bandgap reduction caused by the introduction of N. Hydrogenation of these materials increases the band gap energy to near the value of the N-free host. A defect called H*2 (N) was proposed by many theorists to be the cause of band gap recovery in GaAsN and GaPN. We used vibrationa spectroscopy to investigated GaAsN and GaPN alloys into which H and/or D had been introduced. Our results show that the N-H complex in the III-N-V alloys contains two weakly-coupled N-H(D) stretching modes. This conclusion is inconsistent with the H*2 (N) defect. Later, a new model consisting of a canted NH2 complex in GaAsN was proposed. We performed an IR absorption study with uniaxial stress to investigate the symmetry of the NH2 complex. Our results showed that the NH2 complex has C2v symmetry or lower. This conclusion is consistent with the canted NH2 complex. H is introduced into Si solar cells to increase their efficiency. Two common ways of introducing H are by the post-deposition annealing of a SiN x-coating that acts as an anti-reflection coating and by H-plasma exposure. We have studied the hydrogenation mechanisms of crystalline Si by using infrared spectroscopy. For these experiments, floating-zone Si that contained Pt impurities that act as traps for H was used as a model system in which H could be directly detected. In this model system, the concentration and indiffusion depth of H were determined for different hydrogenation methods so that their effectiveness could be compared. The post-deposition annealing of a hydrogen-rich SiN x surface layer was found to introduce H into the Si bulk with a concentration of ∼1015 cm3 under the best conditions investigated here.