Hydrogen-Induced Metastability of Polycrystalline Silicon

1995 ◽  
Vol 378 ◽  
Author(s):  
N. H. Nickel
Keyword(s):  
Polycrystalline Silicon ◽  
Elevated Temperatures ◽  
Prolonged Exposure ◽  
Dark Conductivity ◽  
Type Conversion

AbstractThe presence of H in polycrystalline silicon gives rise to new and hitherto unexpected phenomena. In this paper two of the most recent observations are reviewed: (i) Hydrogen-induced metastable changes of the dark conductivity due to the formation and dissociation of an electrically active H complex and (ii) the generation of acceptor states during prolonged exposure of poly-Si to monatomic H at elevated temperatures. The observed type conversion is clearly due to the diffusion of excess H from the plasma since it does not occur during exposure to other species such as oxygen.

Metastable Defect Kinetics in Hydrogen Passivated Polycrystalline Silicon

1994 ◽  
Vol 336 ◽  
Author(s):  
N. H. Nickel ◽  
R. A. Street ◽  
W. B. Jackson ◽  
N. M. Johnson
Keyword(s):  
Temperature Dependence ◽  
Polycrystalline Silicon ◽  
Direct Evidence ◽  
Slow Cool ◽  
Dark Conductivity ◽  
Active Hydrogen ◽  
Thermally Activated ◽  
Rate Dependent ◽  
Si Films ◽  
Metastable Defect

ABSTRACTThe temperature dependence of the dark conductivity, σD, of unhydrogenated and hydrogen passivated polycrystalline silicon (poly-Si) films was Measured. While σD of unhydrogenated poly-Si did not exhibit any influence of thermal treatment prior to the measurement, striking effects were observed in hydrogenated poly-Si films. Below 268 K a cooling-rate dependent metastable change of σD is observed. The dark conductivity increases by more than 8 orders of magnitude. This frozen-in state is metastable: Annealing and a slow cool restore the temperature dependence of the relaxed state. The time and temperature dependence of the relaxation reveal that this process is thermally activated with 0.74 eV. The lack of the quenching metastability in unhydrogenated poly-Si is direct evidence that the metastable changes in σD are due to the formation and dissociation of an electrically active hydrogen complex, in the grain-boundary regions.

Microstructure and Mechanical Properties of a New Ni-Cr-Fe-W-Al Alloy for Advanced Ultra-Supercritical Power Plants

2015 ◽  
Vol 816 ◽  
pp. 586-593 ◽  
Author(s):  
Xian Chao Hao ◽  
Long Zhang ◽  
Xiu Juan Zhao ◽  
Tian Liang ◽  
Ying Che Ma ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Thermodynamic Calculation ◽  
Power Plants ◽  
Elevated Temperatures ◽  
Prolonged Exposure ◽  
Thermal Exposure ◽  
Average Diameter ◽  
Al Alloy ◽  
Microstructural Stability

Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic calculation were used to study the phase stability and precipitation in a Ni-Cr-Fe-W-Al alloy. Mechanical properties were also studied. The major precipitates after standard heat treatment or prolonged aging at 725 oC and 800 oC were M23C6 and γ′. M23C6 precipitated intergranularly. P-phase was not detected after thermal exposure, which was different from the results of thermodynamic calculation. The average diameter of γ′ increased with the increasing exposure temperature and time, and could be depicted by the LSW theory. Specimens in solution-annealed condition exhibited excellent ductility. During the prolonged exposure at 725 oC, tensile strength and ductility at room and elevated temperatures kept well, which means this alloy possessed good microstructural stability after a long time exposure.

Microstructural Characterization of Base Material and Welded Joints of Serviced and Non-Serviced Coke Drums

2018 ◽  
Author(s):  
S. A. Romo ◽  
D. Barborak ◽  
J. Bedoya ◽  
J. Penso ◽  
A. J. Ramirez
Keyword(s):  
Oil And Gas ◽  
Elevated Temperatures ◽  
Prolonged Exposure ◽  
Low Cycle Fatigue ◽  
Base Material ◽  
Microstructural Characterization ◽  
Oil And Gas Industry ◽  
Pressure Vessels ◽  
Carbide Formation ◽  
Circumferential Welds

Coke drums are massive pressure vessels used in the oil and gas industry, which are subjected to demanding cyclic thermomechanical loading. Such conditions generate severe plastic deformation that leads to bulging and cracking during service due to low-cycle fatigue. The cracks are often repaired in programed maintenance shutdowns, and the repair procedures can be significantly different depending on the organization and failure characteristics. In this work, two types of weld repairs are evaluated after six months of service: (1) a full-excavation crack weld repair, and (2) a partial-excavation crack weld overlay repair. The repair welds were executed on a 1.25Cr-0.5Mo steel coke drum after 20 years of service. This work evaluates the microstructure of the base material, the fabrication circumferential welds, and the weld repairs. The results show that, after prolonged exposure to elevated temperatures, the originally normalized and tempered heat-treated steel microstructure has undergone severe aging. Thermodynamic equilibrium and para-equilibrium calculations were used to determine the carbide formation sequence, and SEM analysis was used to characterize the carbides present on the as-fabricated and aged microstructures. Analysis of the repaired regions did not reveal new cracks.

Selective Laser Melting of Oxide Dispersion Strengthened Steels

2011 ◽  
Author(s):  
Thomas Boegelein ◽  
Ashwin Rao ◽  
Andrew R. Jones ◽  
Gordon J. Tatlock
Keyword(s):  
Selective Laser Melting ◽  
Elevated Temperatures ◽  
Prolonged Exposure ◽  
Steel Substrate ◽  
Oxide Dispersion Strengthened ◽  
Nickel Base Superalloy ◽  
High Temperature Strength ◽  
Oxide Dispersion ◽  
Laser Melting ◽  
Ods Alloys

Oxide Dispersion Strengthened (ODS) alloys are a long established class of materials manufactured using powder metallurgy techniques. These alloys can offer exceptional high temperature strength and resistance to radiation damage, thus are envisioned to be used in a number of future nuclear and fossil energy power applications. However, due to the manufacturing steps involved, the overall cost to build components with these materials can be high. This paper presents work conducted to assess the feasibility of applying Selective Laser Melting (SLM) techniques to either coat or direct build on substrates with Fe-based Oxide Dispersion Strengthened (ODS) alloys. SLM is a rapid prototyping technique which can be used to manufacture near net-shape solid components from layered metallic powder beds. Two different geometries were of interest in this study — a simple button configuration with a nickel-base superalloy (IN939) substrate and a more complex hexagonal shaped wall with a mild steel substrate. Powders of PM2000 (a FeCrAl based ODS alloy) were deposited in both cases. Heat treatments were subsequently conducted on these structures to investigate effects of temperature on the bond characteristics and secondary recrystallisation. Electron microscopy examination revealed significant amounts of diffusion between the nickel and the ODS powders which enhances the bond strength. The studies have revealed the existence of a strong bond between the substrate and the interface even after prolonged exposure at elevated temperatures.

Thermal Stability in HgCdTe IR Photodiodes

2002 ◽  
Vol 744 ◽  
Author(s):  
J. M. Dell ◽  
T. Nguyen ◽  
C. A. Musca ◽  
J. Antoszewski ◽  
L. Faraone ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Bulk Material ◽  
Surface Condition ◽  
Surface Recombination ◽  
Conversion Process ◽  
Doping Profile ◽  
Surface Recombination Velocity ◽  
Type Conversion ◽  
Photoconductive Decay ◽  
Before And After

ABSTRACTPackaging of HgCdTe photodiode detector arrays in a dewar involves degassing at elevated temperatures for several days so as to achieve vacuum integrity. This sustained exposure to relatively high temperatures can influence the HgCdTe bulk material properties, p-n junction integrity, and the passivant-HgCdTe interface. This work investigates the effects of bake-out treatment on the performance of HgCdTe based photodiodes formed using a new plasma induced type conversion process. Experimental results of a series of experiments in both long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) devices are presented.Bulk lifetime was used as an indicator of the change in the bulk material resulting from baking in vacuum and was measured by photoconductive decay. These measurements did not show any appreciable changes as a result of baking. Modification of the doping profile in the n-p junction may also result from high temperature baking. Doping profiles of the photodiodes were studied by measuring the junction capacitance-voltage relation before and after baking. The results of these tests after baking showed no changes to C-V measurements from those before bake.The effect of baking on the passivant/HgCdTe interface was also examined by carrying out surface recombination velocity measurements by photoconductive decay on samples with different passivation layers.Variable area HgCdTe photodiodes have also been fabricated and studied to understand the effect of the surface condition of the performance of the devices. Initial bake tests on LWIR devices show that the technology is stable when employing a double layer passivation technique. Bake tests on the more advanced MWIR technology indicates that the plasma induced type conversion process produces stable photodiodes with state of the art performance.

scholarly journals Изменения фотоэлектрических свойств нелегированных пленок аморфного гидрированного кремния под влиянием предварительного освещения при повышенных температурах

2020 ◽  
Vol 54 (4) ◽  
pp. 367
Author(s):  
Н.Н. Ормонт ◽  
И.А. Курова
Keyword(s):  
Conduction Band ◽  
Density Of States ◽  
Elevated Temperatures ◽  
Energy Levels ◽  
Dark Conductivity ◽  
Active Oxygen ◽  
Illumination Intensity ◽  
Oxygen Impurity ◽  
Photoelectric Properties ◽  
Bimolecular Recombination

Abstract The effect of preliminary weak illumination at elevated temperatures on the photoelectric properties of undoped α-Si:H films is investigated. It is found that the dark conductivity and photoconductivity of films increases with the preliminary-illumination intensity, and the parameter γ determining the dependence of the photoconductivity on the illumination intensity decreases due to an increasing fraction of the bimolecular recombination of electrons at energy levels of the tail of the density of states of the conduction band. It is assumed that this effect may be induced by the presence of an uncontrolled oxygen impurity and an increase in the concentration of electrically active oxygen as a result of preliminary illumination of the films at elevated temperatures.

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