A Novel Model for Boron Diffusion in SiGe Strained Layers Based on a Kinetics Driven Ge-B Pairing Mechanism
A new temperature dependant model for the Ge-B pairing mechanism has been established and implemented in a process simulator. The combination of both lattice strain effects and GeB clustering has been successfully applied to various anneals. The match with experimental SIMS profiles is excellent.
Boron diffusion across silicon–silicon germanium boundaries
Most boron diffusion studies in Si–Ge have been made in regions of uniform germanium content. In this paper diffusion is observed from a boron-doped epitaxial silicon layer across surrounding Si–Ge layers. Pileup of boron in the Si–Ge layers shows that the activity coefficient for boron in Si–Ge is lower than that for pure silicon. A simple pairing model for Si–B interaction fitted the pileup quite well, with the same equilibrium constant applying to both Si0.9Ge0.1 and Si0.97Ge0.03 layers. The effect of this was simply to immobilize a significant fraction of the boron while retaining its acceptor qualities, the ratio of immobile boron to normal substitutional boron being proportional to the germanium content. Quasielectric field effects at the Si–SiGe interface have a strong effect on the results obtained.
Soil organic matter and microbiological development of technosols in the South Wales Coalfield
Abstract Degraded land (formerly ‘reclaimed’) after surface-coal-mining is a serious problem in South Wales. This project uses forestation to foster soil development on opencast coal-mine spoil technosols. It compares records of humification and the soil microbiological system (microcoenosis) using paired data from the same plantings in 1998 and 2018. Statistical analysis finds no significant difference between samples collected under trees planted by the pit-planting versus trench planting method or trees planted using organic or mineral fertilizer. However, there are strong significant differences in both soil organic matter and microflora components and significant correlations with time since tree planting. Most components of the soil organic carbon (TOC) and the microflora increase, often significantly. However, compared to 2018, 1998 samples contain significantly greater maximum levels of Insoluble Carbon while the microflora had significantly more Ammonifying bacteria. Decreases in Insoluble Carbon explain the relatively small increase in TOC between 1998 and 2018. The % extracted with 0.1 N H2SO4 is significantly larger in 2018, suggesting active weathering. Similarly, both the maxima and minima of total Humic and Fulvic acids content, extracted with 0.1 M Na4P2O7 + 0.1 M NaOH, are significantly greater in 2018. Total microflora shows significant positive correlations with time-since-tree-planting as do the proportions of bacilli and actinomycetes but the correlation with ammonifying bacteria is negative. In 1998, the microflora was dominated by non-spore-forming bacteria while, in 2018, bacilli and actinomycetes prevail; both are involved in the transformation of complex organic compounds and humification. This indicates active transformation of more complex organic compounds and advancing humification. In sum, forestation of these degraded, formerly reclaimed, opencast coal-mine spoils has resulted in a massive increase in both the size and functioning of the soil organic system.