A simple and inexpensive circuit for emission and capture deep level transient spectroscopy

A simple and inexpensive circuit for deep level transient spectroscopy is described, which allows rapid characterization of emission as well as capture activation energies of deep levels. This flexibility of making capture activation studies affords more information on defect morphology than the more standard emission activation studies. This is demonstrated by making a representative capture activation energy measurement on the EL6 level in undoped n-type GaAs of 0.484±0.005 eV. Also the spectrometer has shown better performance than earlier reported systems by its ability to resolve the side peaks of the EL6 level, for which emission activation energies of 0.29 and 0.4 eV are assigned. Constructed around a commercially available capacitance meter and pulse generator, the control circuitry is designed and developed using inexpensive and off-the-shelf integrated circuits. © 1996 American Institute of Physics.published_or_final_versio

The transformations of the EL6 deep level defect in n-GaAs: is EL6 a DX-like center?

Symposium Theme: Defect and impurity engineered semiconductors IIBased on the charge redistribution effect, as observed by the present authors, and the earlier reported large lattice relaxation and persistent photoconductivity phenomena associated with the EL6 defect seen in doped, undoped, semiinsulating(SI) and low temperature grown GaAs (LT-GaAs), it is suggested that this defect be classified as a DX-center. A tentative unified atomic model is proposed for all the native defects EL2, EL3, EL5, and EL6 observed in GaAs.published_or_final_versio

Inexpensive circuit for the measurement of capture cross section of deep level defects in semiconductors

A simple and inexpensive circuit to facilitate the direct measurement of capture cross section, when synchronized with a deep level transient spectroscopy system, is described. It avoids the most commonly encountered problem of loading and distortion of the bias (trap filling) pulses of nanosecond duration in the capture cross-section measurement. The capacitance meter, whose internal circuitry is responsible for the distortion, is connected and disconnected from the rest of the apparatus with the help of simple and low-cost reed relay switches featuring high operating speed and low contact resistance. Sharp bias pulses as small as 30 ns can successfully be applied to the sample with no observable distortion. Finally, a representative measurement is shown to demonstrate the simplicity and high performance of the circuit. © 1996 American Institute of Physics.published_or_final_versio

Nature of the bulk defects in GaAs through high-temperature quenching studies

Deep-level transient spectroscopy has been applied to n-type horizontal gradient freeze grown GaAs that has been subjected to thermal stressing (quenching) and varying degrees of arsenic outdiffusion during rapid thermal annealing. The concentrations and activation energies of the various deep donor levels have been monitored. As a result of the external excitations in the lattice due to the thermal stress (quenching), dramatic effects occur in the defect level structure that could be of importance to device technology. It is found that the native EL6 group of defects is nearly absent in rapid thermally annealed material, while the levels EL5 and EL8 appear with EL3 becoming a dominant level that could act as a recombination center. With the lengthening of annealing time and significant As outdiffusion, there is a general reduction of the EL2, EL3, and EL5 defect concentrations together with a complete removal of EL8. Moreover, the EL2 activation energy may be varied from 0.827 to 0.922 eV by controlling the level of As out-diffusion. These observations are discussed in terms of the As Ga-As i model of the EL2 defect and the V As-V Ga divacancy model for the EL6 group of defects. The EL3, EL5, EL8, and EL15 defect levels seen in samples subjected to rapid thermally quenching are attributed to the breakup of V As-As i Frenkel pair defects known to be present in the as-grown material.published_or_final_versio

DX-like properties of the EL6 defect family in GaAs

Capacitance-voltage characterization at different temperatures and emission and capture deep-level transient spectroscopy carried out on undoped n-type GaAs lend strong confirmation to the recent suggestion that the EL6 defect arises from a center that is DX-like in nature. The evidence comes from the observation of an anomalous filling pulse duration dependence of the peak intensities of three to four different EL6 sublevels, similar to that recently found for the DX center in Al xGa 1-xAs and attributed to the charge redistribution. In addition, capture transients reveal large capture barriers (0.2-0.3 eV), which are typical of a defect undergoing large lattice relaxation into a deep-lying state. These observations indicate that the EL6 defect center comprises of a center with three to four slightly different ground-state configurations, each one of which forms as a result of some bond-breaking atomic displacement on capture of a second electron at the defect site. The significance of this in understanding the microstructure for the EL6 center is briefly discussed.published_or_final_versio

Odontogenic Fibromyxoma of Maxilla: A Case Report

Odontogenic fibromyxoma (OM) is a rare locally invasive, non metastasizing benign neoplasm found exclusively in the jaws. It commonly occurs in the second and third decade,and the mandible is involved more commonly than the maxilla. The lesion often grows without symptoms and presents as a painless swelling. The radiographic features are variable so the diagnosis is not easy in many cases. It posesa diagnostic and therapeutic challenge due to its morphology and biological behaviour. A caseo f OM of the maxilla with unusual radiographic and histological features is described in a 27 year old female

Deep level traps in the extended tail region of boron-implanted n-type 6H-SiC

Deep traps in the boron extended tail region of ion implanted 6H-SiC pn junctions formed during annealing have been studied using deep level transient spectroscopy. Dramatically high concentrations of ∼1016 cm-3 of the D center have been observed through the unusual appearance of minority peaks in the majority carrier spectra. No evidence is found for any shallow boron acceptor in this region, but an induced hole trap Ih at EV+0.46 eV is found under cold implantation conditions. These results support the picture of the extended tail, rich in boron-vacancy complexes such as the D center, which forms as a result of vacancy enhanced indiffusion. The dominance of the electrically active D center in the depletion layer of the technologically important SiC pn junction diode suggests the need for further research in this area. © 1998 American Institute of Physics.published_or_final_versio

Preliminary Clinical Results of a Biphasic Waveform and an RV Lead System

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72921/1/j.1540-8159.1999.tb00500.x.pd

Dynamics of mechanical waves in periodic grapheme nanoribbon assemblies

We simulate the natural frequencies and the acoustic wave propagation characteristics of graphene nanoribbons (GNRs) of the type (8,0) and (0,8) using an equivalent atomistic-continuum FE model previously developed by some of the authors, where the C-C bonds thickness and average equilibrium lengths during the dynamic loading are identified through the minimisation of the system Hamiltonian. A molecular mechanics model based on the UFF potential is used to benchmark the hybrid FE models developed. The acoustic wave dispersion characteristics of the GNRs are simulated using a Floquet-based wave technique used to predict the pass-stop bands of periodic mechanical structures. We show that the thickness and equilibrium lengths do depend on the specific vibration and dispersion mode considered, and that they are in general different from the classical constant values used in open literature (0.34 nm for thickness and 0.142 nm for equilibrium length). We also show the dependence of the wave dispersion characteristics versus the aspect ratio and edge configurations of the nanoribbons, with widening band-gaps that depend on the chirality of the configurations. The thickness, average equilibrium length and edge type have to be taken into account when nanoribbons are used to design nano-oscillators and novel types of mass sensors based on periodic arrangements of nanostructures

Microstructural evolution and trace element mobility in Witwatersrand pyrite

Microstructural analysis of pyrite from a single sample of Witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation. Internal deformation associated with dislocation creep is heterogeneously developed within grains, shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the Central Rand conglomerates. In contrast, brittle deformation, manifest by grain fragmentation that transects dislocation-related microstructures, is spatially related to grain contacts and is interpreted to represent post-depositional deformation of the Central Rand conglomerates. Analysis of the low-angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of {100} slip systems. However, some orientation boundaries have geometrical characteristics that are not consistent with simple {100} deformation.These boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized {120} slip system. These boundaries are associated with order of magnitude enrichments in As, Ni and Co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast-diffusion pathways. The results confirm the importance of grain-scale elemental remobilization within pyrite prior to their incorporation into the Witwatersrand gold-bearing conglomerates. Since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite, the results have implications for the application of minor element geochemistry to ore deposit formation, suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing