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a-Si:H p-layers doped by trimethylboron (TMB) were obtained by PECVD in a monochamber reactor with a rotating substrate holder. The influence of the substrate temperature (Ts) on the film properties was systematically studied for two different doping gas concentrations. The incorporation of boron, hydrogen and carbon was studied by Secondary Ion Mass Spectrometry (SIMS). Optical properties were determined by means of Photothermal Deplection Spectroscopy (PDS) and optical transmission. Dark conductivity (aj and activation energy (Eact) were measured electrically. Our results show that Σd has a marked dependence on substrate temperature, although boron atom concentration depends only slightly on Ts. The optical gap for samples obtained at the higher concentration also depends on Ts and its dependence is related to the hydrogen content, as boron content does not change. P-i-n diodes were obtained with the p-layer deposited from TMB.
Some 3×109 kg of phosphogypsum (PG) wastes are annually generated by two fertiliser-production factories in Huelva (south-western Spain). PG has relatively high concentrations of 226Ra and other radionuclides, with an special concern due to the 222Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226Ra. The drainage waters have 226Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. Our results are suggesting that the major uranium input comes from the application of phosphate-fertiliser. No significant levels of radionuclides were found in the vegetal tissues.
Amorphous Silicon p-i-nphotodiodes were obtained by PECVD in a reactor with a rotating substrate holder. Reverse currents as low as 5 × 10−11 A/cm2 at a bias of − 2V were measured using a guard ring electrode to minimize lateral edge currents. The devices were degraded by a Xenon flash lamp in open circuit conditions. The kinetics of the degradation process was evaluated by studying the long time dark current transient under reverse bias.
This paper deals with the electrical properties in the parallel direction of compositionally modulated amorphous silicon/amorphous silicon-carbon multilayers. Conductivity of three series of samples with varying well and barrier thicknesses is studied. The results show that dark conductivity decreases when reducing a-Si:H layer thickness. This is interpreted as an alloy effect at interfaces. The role of the a-Si1-xCx:H layers in the photoconductivity decrease observed in series with variable mean composition and constant well thickness is discussed
A straightforward analytical expression of the density-of-states (DOS) of a-Si:H valid in non-equilibrium steady state situation has been obtained. The model is based on a statistical-mechanical treatment of the hydrogen occupation for different defect sites. The broadening of available defect energy levels (defect pool) and the possibility of charged defects are taken into account. This leads to a new explanation of the Staebler-Wronski effect, based on the "conversion" of shallow charge centers to neutrals near the middle of the gap as a consequence of hydrogen redistribution induced by electron-hole recombination.
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