Field dependent dopant deactivation in bipolar devices at elevated irradiation temperatures

Dopant deactivation at 100 C is measured in bipolar Si-SiO{sub 2} structures as a function of irradiation bias. The deactivation occurs most efficiently at small biases in depletion and is consistent with passivation and compensation mechanisms involving hydrogen

Field Dependent Dopant Deactivation in Bipolar Devices at Elevated irradiation Temperatures

Metal-oxide-silicon capacitors fabricated in a bi-polar process were examined for densities of oxide trapped charge, interface traps and deactivated substrate acceptors following high-dose-rate irradiation at 100 C. Acceptor neutralization near the Si surface occurs most efficiently for small irradiation biases in depletion. The bias dependence is consistent with compensation and passivation mechanisms involving the drift of H{sup +} ions in the oxide and Si layers and the availability of holes in the Si depletion region. Capacitor data from unbiased irradiations were used to simulate the impact of acceptor neutralization on the current gain of an npn bipolar transistor. Neutralized acceptors near the base surface enhance current gain degradation associated with radiation-induced oxide trapped charge and interface traps by increasing base recombination. The additional recombination results from the convergence of carrier concentrations in the base and increased sensitivity of the base to oxide trapped charge. The enhanced gain degradation is moderated by increased electron injection from the emitter. These results suggest that acceptor neutralization may enhance radiation-induced degradation of linear circuits at elevated temperatures

Space charge limited degradation of bipolar oxides at low electric-fields

Radiation-induced degradation of many types of bipolar transistors and circuits is more severe following low dose rate exposure than following high dose rate exposure. Since microelectronic devices in space are generally subjected to low dose rate irradiation, this complicates the hardness assurance testing of linear circuits and can lead to an overestimation of device lifetime in space. Previous work examining the physical mechanisms responsible for this dose rate effect has focused primarily on oxide trapped charge. Reduced net positive oxide trapped charge densities at high dose rates and zero bias have been attributed to space charge effects from slowly transporting holes trapped metastably at O vacancy complexes. Decreasing the dose rate or increasing the irradiation temperature leads to an increase in net positive oxide trapped charge near the Si-SiO{sub 2} interface by reducing these space charge effects. In this work, concentrations of hydrogen transport through two types of bipolar oxides are estimated from dopant passivation measurements in MOS capacitors. For unbiased irradiations, hydrogen passivation of substrate acceptors is greatly reduced at high dose rates compared to that at low dose rates or elevated temperatures. Consistent with other widely accepted models, it is argued that fewer interface traps are formed by high dose rate irradiation under zero bias, because fewer H{sup +} ions can drift to the Si-SiO{sub 2} interface and react with trap precursors. Similar to hole transport in these oxides, drift of the H{sup +} ions is inhibited at high dose rates by space charge accumulated in the oxide bulk

Pressure Effects in Hafnium Pentatelluride and Zirconium Pentatelluride

We have measured the effect of pressure (0 to 17) kbar) on the resistivity and the thermopower of HfTe/sub 5/ and ZrTe/sub 5/ as a function of temperature. Pressure affects these two materials in different ways. The resistance shows a greater effect than the thermopower. There is a larger effect in HfTe/sub 5/ than in ZrTe/sub 5/. Possible explanations in terms of a Fermi surface instability and a semi-metal are given

Role of pressure in understanding the anomalous superconductivity in europium (molybdenum)/sub 6/(sulfur)/sub 8/ and (TMTSF)/sub 2/FSO/sub 3/

Both the Chevrel phase compound EuMo/sub 6/S/sub 8/ and the organic material, (TMTSF)/sub 2/FSO/sub 3/ are superconducting only under moderate pressure. In both instances the absence of superconductivity at ambient pressure is directly attributed to a low temperature structural distortion that introduces a gap over all or part of the Fermi surface. The role of pressure is to suppress the transition and thus allow the electrons to condense into the superconducting state. In EuMo/sub 6/S/sub 8/, details of the pressure dependence of both the structural and superconducting transition have been explained on the basis of a competition between a charge density wave-type state and superconductivity. In the case of (TMTSF)/sub 2/FSO/sub 3/ an anion ordering giving rise to a metal-insulator transition is responsible for suppressing superconductivity. The critical magnetic fields of EuMo/sub 6/S/sub 8/ are extremely anomalous and are related to the magnetism of the Eu as well as the structure of the compound

Structural Studies at Elevated Pressure and Reduced Temperatures Using Synchrotron Radiation: Application Tocerium/sub 8/Lanthanum)/sub 1/Thorium)/sub 1/

A facility is described which has been developed at the Stanford Synchrotron Radiation Laboratory for the rapid acquisition of structural information from a sample pressurized in a diamond-anvil cell and cooled to cryogenic temperatures. The system employs a closed-cycle He-refrigerator which can be continuously operated, independent of any liquid cryogens, from a remote control station; the sample temperature can be maintained constant to better than 0.05 K. The compressive contact force between the diamond anvils, and hence the sample pressure, is also externally controlled, thereby providing remote control capabilities for both the pressure and the temperature. Preliminary data on the critical points and volume changes associated with the pressure/temperature induced isomorphic phase transition in Ce/sub 8/La/sub 1/Th/sub 1/ are presented