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An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices. [ABSTRACT FROM AUTHOR]

We have measured the temperature and field dependence of emission rates from five traps in electron damaged GaAs. Four of the traps have previously been identified as radiation defects. One of the traps, seen in higher doped diodes, has not been previously identified. We have fit the data to a multiphonon emission theory that allows recombination in GaAs to be characterized over a broad range of temperature and electric field. These results demonstrate an efficient method to calculate field-dependent emission rates in GaAs. [ABSTRACT FROM AUTHOR]

The positions of the electronic levels of an intrinsic bistable defect have been measured using deep level transient spectroscopy (DLTS) in n- and p-type damaged silicon bipolar transistor diodes after minority carrier injection and thermal annealing. The kinetic rates observed during conversion of this defect have been determined using both DLTS and transistor gain measurements on devices irradiated with electrons and neutrons. First order conversion kinetics are observed during both injection and thermal annealing of this defect in electron damaged transistors, but more complicated, stretched-out kinetics are seen in neutron irradiated devices. The latter behavior can be successfully modeled as a small spread in the energy barriers for atomic displacements of this defect probably due to strain or electrostatic variations expected in damage clusters. The measured injection bias dependence of the recombination-driven transition to the bistable state of this defect is unlike that seen for generation-recombination currents at deep trap levels, but it is consistent with Shockley-Read-Hall predictions for recombination at shallow states. This latter behavior is expected from the lone shallow peak seen in DLTS measurements of the stable state of this center. Some comparisons of the present results with existing models of this defect are made. [ABSTRACT FROM AUTHOR]

Isochronal anneal sequences have been carried out on pnp and npn transistors irradiated with fast neutrons at a variety of fluences. The evolution of base and collector currents was utilized to characterize the annealing behavior of defects in both the emitter-base depletion region and the neutral base. Various annealing biases, theoretical modeling, as well as previous deep level transient spectroscopy (DLTS) data, were used to assign the relative magnitude of each of the important defects to the total recombination current. We find that donor-vacancy pairs in the neutral n-type base of our pnp transistors are responsible for about 1/3 of the postdamage lifetime degradation, while the remaining recombination currents can be largely attributed to a cluster-related divacancylike defect which has no shallow state DLTS emission peak. This latter defect anneals gradually from 350 to 590 K. Generation/recombination currents in the base-emitter junctions in both types of devices were found to anneal in a similar, gradual fashion, suggesting that this same cluster-related intrinsic lattice defect is also responsible for the large, damage-induced base currents. [ABSTRACT FROM AUTHOR]

We find that fast neutron irradiated n- and p-GaAs diodes both show a broad feature in deep level transient spectroscopy (DLTS) previously studied primarily in n-GaAs and termed the “U-band.” The high temperature edge of the broad DLTS feature cuts off at the same temperature in both n- and p-GaAs suggesting that the cut off is due to the DLTS behavior expected for a continuous density of defect states that spans midgap. The band gap implied by the DLTS midgap cut off is 1.36 eV, as compared to the bulk GaAs band gap 1.52 eV. Band gap narrowing is consistent with previous measurements of lattice expansion in neutron irradiated GaAs. This leads to a model of defect cascades that are regions of narrowed band gap with defect levels that are inhomogeneously broadened. We observe, in addition, that the damage cascades are surrounded by large Coulomb barriers that prevent the complete filling of traps in the damaged regions. [ABSTRACT FROM AUTHOR]

We have explored defect annealing in radiation damaged silicon in a regime characterized by defect clusters and higher doping. Several types of pnp and npn Si bipolar transistors have been irradiated with ions and neutrons, then isochronally annealed from 300 to 600 K to study the evolution of deep level transient spectroscopy (DLTS) defect signatures. Variations in these data with radiation environment, Fermi level, annealing temperature, and doping density have been used to separate the contributions of three dominant defects to the DLTS defect spectra. We find that the normal Si divacancy and a divacancylike defect with similar properties make similar contributions to a DLTS peak normally associated with transitions from the single minus charge state of the divacancy. However the latter defect is clearly associated with the presence of defect clusters. The vacancy-donor center can also contribute to this high temperature DLTS signature, and its relative importance can be quantitatively assessed by varying doping density and the bias applied to the sample p/n junctions during annealing, and also by the observation that another, donor-related defect grows in as this center anneals. The ratio of vacancy-donor and vacancy-oxygen pairs appears to accurately follow that seen in earlier studies of gamma-irradiated Si. Discussions are presented concerning the effects of defect clustering on the structure, appearance, and evolution of the defects we have identified. [ABSTRACT FROM AUTHOR]

Two deep level transient spectroscopy (DLTS) electron emission signatures, previously labeled E4 and E5, have been shown to be bistable with respect to minority carrier injection at room temperature. These result from two charge state transitions of the same defect. We have performed DLTS measurements as function of annealing between 350 and 680 K, using minority carrier injection after each annealing stage to make E4 and E5 visible. We show that the E4–E5 pair is associated with defect clusters which dominate after neutron or ion damage with annealing characteristics that closely parallel to those of silicon divacancies found in damage clusters. At annealing temperatures above 500 K, the E4–E5 pair ceases to be bistable and exists after anneals in thermal equilibrium. We show that the stable E4 peak appears to be the same emission signature previously labeled the L center. The transformation of the E4–E5 bistable pair into the stable L center and a stable E5 companion level occurs at the same temperature, where it has been suggested that the divacancy becomes mobile. The similarity of the annealing of the E4–E5 pair to that of the divacancy, the dependence of the density of these defects on degree of clustering, and the insensitivity to common impurities combine to suggest that the E4–E5 pair is associated with primary defects located in the defect cluster and closely related to the familiar divacancy. [ABSTRACT FROM AUTHOR]

We have exposed silicon bipolar transistors to fast neutrons and characterized the properties of the resulting defects using capacitance-based spectroscopy of the n-type collector. We have performed low-temperature electron capture measurement of the divacancy (=/-) and vacancy-oxygen (-/0) defects after the samples were annealed from 350–500 K. We show from a simple rate equation analysis that one can define an unambiguous test for cluster-induced reductions of defect level occupation due to slow capture. This allows easy identification of deep level transient spectroscopy (DLTS) levels where the capture is inhibited due to band bending. Our measurements show extremely long, temperature-dependent capture times for the doubly charged state of the divacancy. We have modeled the capture dynamics as a function of annealing using a simple electrostatic band-bending approach coupled with a realistic simulation of the cluster size and shape distribution as estimated from computer simulation of the damage cascades. We find that our simulation of neutron damage combined with electrostatic modeling of the capture data, with only a limited number of adjustable parameters, fits the measured data very well. Our annealing studies indicate, however, that isolated divacancies (those with visible DLTS signals from two acceptor states) comprise only about 30% of the charge in the defect cluster. [ABSTRACT FROM AUTHOR]

Deuterated p-type GaN(Mg,2H) films were irradiated at room temperature with 1 MeV protons to create native point defects with a concentration approximately equal to the Mg doping (5×1019 cm-3). The samples were then annealed isothermally at a succession of temperatures while monitoring the infrared absorption due to the H local mode of the MgH defect. As the samples were annealed, the MgH absorption signal decreased and a new mode at slightly higher frequency appeared, which has been associated with the approach of a mobile nitrogen interstitial. We used the time dependence of the MgH absorption to obtain a diffusion barrier of the nitrogen interstitial in p-type GaN of 1.99 eV. This is in good agreement with theoretical calculations of nitrogen interstitial motion in GaN. [ABSTRACT FROM AUTHOR]

This work is a systematic study of carbon incorporation in Ta[sub 2]O[sub 5] and its effect on the material and electrical properties of Ta[sub 2]O[sub 5], a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta[sub 2]O[sub 5] performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta[sub 2]O[sub 5] films with carbon. In thick (70 nm) Ta[sub 2]O[sub 5] films, an optimal amount (0.8–1.4 at. %) of carbon doping reduced the leakage current to 10[sup -8] A/cm[sup 2] at +3 MV/cm, a four orders of magnitude reduction compared to a leakage current of 10[sup -4] A/cm[sup 2] in an undoped Ta[sub 2]O[sub 5] film grown in similar conditions without CO[sub 2] in the plasma. This finding suggests that carbon doping can further improve the dielectric leakage property at an optimal concentration. X-ray Photoemission Spectroscopy analysis showed the presence of carbonate (carbon bonded to three oxygen) in these electrically improved carbon-doped films. Analysis by high-resolution transmission electron microscopy and Nomarsky microscopy exhibited no morphological or structural changes in these carbon-doped thin films. Moreover, carbon doping showed no improvement in the leakage current in thin (10 nm) Ta[sub 2]O[sub 5] films. This phenomenon is explained by a defect compensation mechanism in which the carbon-related defects remove carriers at low concentrations but form a hopping conduction path at high concentrations. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Giant magnetoresistance effect is higher in alloyed superlattice films than in unalloyed Fe/Cr multilayer films due to antiferromagnetic coupling. Cr impurities induce stronger spin-dependent scattering of conduction electrons, improving the deltaR/R in Cr-alloyed superlattice films. Alloyed superlattice films exhibit reduced coercivity and saturation magnetization.

Presents a study that examined the magnetic structures of several single-crystal, magnetic rare-earth superlattice systems grown by molecular-beam epitaxy. Results of neutron diffraction investigations of long-range magnetic order in gadolinium (Gd)-yttrium (Y), dysprosium (Dy)-Y, Gd-Dy and holmium-Y periodic superlattices; Development of an antiphase domain structure in the Gd-Y system; Occurrence of helical moment configurations in the other systems.

Investigates the long-range helimagnetic order in synthetic rare-earth dysprosium-yttrium superlattices. Development of advanced metal molecular beam epitaxy techniques; Result of the magnetic measurements using the Faraday method.

Provides information on a study which discussed the finding that using flux grown single crystals and cooling through the Curie temperature, SmMn[sub2]Ge[sub2] becomes ferromagnetic. Function of pressure; Observations that indicate the sensitivity of the magnetic properties of SmMn[sub2] Ge[sub2] to interatomic spacing; Technique used in generating pressure.