Silicon Chemical (United States)

A correction to this paper has been published: https://doi.org/10.1007/s12109-021-09819-4

To develop solar light-driven photocatalysts with high activity and structural stability, Ag3PO4/POM/GO heterojunction has been successfully prepared by a facile method at room temperature. Ag3PO4/POM/GO shows remarkably enhanced activity and stability for photocatalytic degradation and H2 production from water-splitting under simulated solar light. The degradation rate of Ag3PO4/POM/GO is 1.8 times and 1.2 times those of Ag3PO4 and Ag3PO4/POMs, respectively. H2 production using Ag3PO4/POM/GO is 2.0 times that of Ag3PO4/GO. The enhanced photocatalytic performance of Ag3PO4/POM/GO is attributed to the increased surface area, electronegativity and structure stability. The Z-scheme system of Ag3PO4/POM/GO effectively promotes charge separation, resulting in enhanced photocatalytic performance under simulated solar light.

Between 2006 and the end of 2009, the production capacity of the softwood lumber sector covered by this report in the United States and Canada has shrunk from 190.8 million m 3 (nominal) to 166.4 million m 3 .The corresponding number of mills slumped from 1,025 to 875 over the same time and from 1,322 recorded in 1995.The Canadian capacity went from 88.2 million m 3 to 71.6 million m 3 , a loss of 19%, while the U.S. capacity dropped from 102.6 million m 3 to 94.8 million m 3 , a loss of 8%.These losses are attributable to three unprofitable years of sawmilling caused by the contraction in construction.Construction and repair and remodeling of homes each accounted for about 35% of total lumber consumption in 2006.Their downturn has caused demand to lag substantially behind the capacity that was built up to supply the prior boom.The greater drop in Canadian capacity can be deduced from a number of factors including the imposition of tariffs of up to 15% on exports to the U.S. and the strengthening of the Canadian dollar.Based on underlying population growth, the demand for home building is expected to rebound but somewhat slowly until the overhang of unoccupied homes built in the former building surge is absorbed.Further attrition of capacity is likely, as profitability is unlikely to return until a combination of recovering demand and contracting supply due to further capacity attrition equalize in the market.

Local open-circuit voltage (Voc) distributions on amorphous and nanocrystalline mixed-phase silicon solar cells were measured using a scanning Kelvin probe microscope (SKPM) on the p layer of an n-i-p structure without the top ITO contact. During the measurement, the sample was illuminated with a laser beam that was used for the atomic force microscopy (AFM). Therefore, the surface potential measured by SKPM is the sum of the local Voc and the difference in workfunction between the p layer and the AFM tip. Comparing the SKPM and AFM images, we find that nanocrystallites aggregate in the amorphous matrix with an aggregation size of ~0.5 mum in diameter, where many nanometer-size grains are clustered. The Voc distribution shows valleys in the nanocrystalline aggregation area. The transition from low to high Voc regions is a gradual change within a distance of about 1 mum. The minimum V oc value in the nanocrystalline clusters in the mixed-phase region is larger than the Voc of a nc-Si:H single-phase solar cell. These results could be due to lateral photo-charge redistribution between the two phases. We have also carried out local Voc measurements on mixed-phase SiGe:H alloy solar cells. The magnitudes of Voc in the amorphous and nanocrystalline regions are consistent with the J-V measurements

Abstract We have developed a new type of ultra-high vacuum plasma-enhanced chemical vapor deposition (UHV/PECVD) system. According to high sensitivity secondary ion mass spectrometry, device quality hydrogenated amorphous silicon (a-Si:H) films deposited at 250°C at a deposition rate of 1 Å/s contains 1015 cm-3 of O, 1015 cm-3 of C, and 1014 cm-3 of N impurities, while low defect hydrogenated microcrystalline silicon (μc-Si:H) films deposited at 200°C at a very low rate of 0.1 Å/s include 1016 cm-3 of O, 1015 cm-3 of C and 1016 cm-3 of N. These are the lowest concentrations of atmospheric contaminants for these kinds of materials observed so far. The essential features of the present UHV/PECVD system are an extremely low outgassing rate of 8×10-9 Torr·s, extremely low partial pressure of contaminant gas species <10-12 Torn, and purification of feed gas SiH4 at “point of use”. These efforts are quite important not only for clarifying the microscopic mechanism of photo-induced degradation in a-Si:H, but also for enlarging the crystalline grain size in μc-Si:H. μc-Si:H with a grain size of ≍1000 Å as determined by Scherrer's formula can be obtained at the higher rate of 1.5 Å/s by utilizing a VHF (Very High Frequency) plasma. The specific origins of impurities in the films are also discussed.

ABSTRACTUltra clean plasma CVD process opens the doorway to clarify the role of impurities in the growth process of μc-Si:H. A reduction of impurity levels during the growth extends the temperature range for crystalline formation to lower side, i.e., high-crystallinity μc-Si:H formation even at room temperature, substantially reduces midgap defect density at 200°C, and enlarges crystalline grain size at 350°C. These results imply that impurities disrupt crystalline formation even on hydrogen covered surface. The crystalline-to-amorphous transition is induced by a loss of surface hydrogen coverage due to thermal hydrogen desorption at higher temperature of ∼450°C irrespective of the effect of oxygen impurity. Light-soaking experiments for the series of the films from a-Si:H to μc-Si:H films with different crystalline volume fraction indicate that the presence of small volume fraction of crystallite significantly suppresses light induced defect creation under the present light soaking condition of 3SUN 60°C 6hr. These results are explained in terms of preferential recombination of photo-excited carriers in the crystallite.

Electrical measurements were made on silicon on sapphire (SOS) before processing to the device stage. The objective was to determine process conditions for producing high-resistivity, high-mobility SOS. The phenomenological approach was used to study variations in electrical properties across a wafer. Conductivity-type measurements were made where large variations in the resistivity occurred. A p-type autodoping pattern was observed and traced to aluminum diffusion into the episilicon layer from sapphire substrate defect areas which were identified by scanning electron microscopy. Process parameters were adjusted to eliminate patterned autodoping. The average of point-to-point resistivity parameter values was then equal to the value determined for the whole wafer using peripheral contacts. The resistivity parameter was influenced both by carrier concentration and microstructure. The Hall mobility was highest for material where patterned autodoping was absent. If the silicon deposition temperature was lowered too much, the Hall mobility decreased significantly. Resistivity parameter mapping and mobility measurements were necessary to fix epigrowth parameters.