1,692 research outputs found
Staley, Roberta
No full textcurrentAcademic Biography
BA (University of Calgary)
Diploma Journalism (Grant MacEwan)
MA Liberal Studies (Simon Fraser University)
Roberta Staley is an author, a magazine editor and writer, and a documentary filmmaker who has reported from such places as Afghanistan, Papua New Guinea, Kenya, El Salvador, Haiti, Colombia, Cambodia, South Africa, Israel, and New Zealand. She currently edits Enterprise magazine, and is a contributor to BC Business, the South China Morning Post Magazine, Ms. Magazine, Trek, the Canadian Chemical News, Corporate Knights, and Sculpture, among others. She is also a columnist for Just for Canadian Doctors/Dentists magazines. Roberta has published her first book, titled Voice of rebellion : how Mozhdah Jamalzadah brought hope to Afghanistan. It is a biography of Afghan-Canadian human rights activist Mozhdah Jamalzadah
Size effect on high temperature variable range hopping in Al+ implanted 4H-SiC
No full textThe hole transport properties of heavily doped 4H-SiC (Al) layers with Al implanted concentrations of 3 × 1020 and 5 × 1020 cm-3 and annealed in the temperature range 1950-2100 °C, have been analyzed to determine the main transport mechanisms. This study shows that the temperature dependence of the resistivity (conductivity) may be accounted for by a variable range hopping (VRH) transport into an impurity band. Depending on the concentration of the implanted impurities and the post-implantation annealing treatment, this VRH mechanism persists over different temperature ranges that may extend up to room temperature. In this framework, two different transport regimes are identified, having the characteristic of an isotropic 3D VRH and an anisotropic nearly 2D VRH. The latter conduction mechanism appears to take place in a rather thick layer (about 400 nm) that is too large to induce a confinement effect of the carrier hops. The possibility that an anisotropic transport may be induced by a structural modification of the implanted layer because of a high density of basal plane stacking faults (SF) in the implanted layers is considered. The interpretation of the conduction in the heaviest doped samples in terms of nearly 2D VRH is supported by the results of the transmission electron microscopy (TEM) investigation on one of the 5 × 1020 cm-3 Al implanted samples of this study. In this context, the average separation between basal plane SFs, measured along the c-axis, which is orthogonal to the carrier transport during electrical characterization, appears to be in keeping with the estimated value of the optimal hopping length of the VRH theory. Conversely, no SFs are detected by TEM in a sample with an Al concentration of 1 × 1019 cm-3 where a 3D nearest neighbor hopping (NNH) transport is observed
Al+ Ion Implanted 4H-SiC Vertical p+-i-n Diodes: Processing Dependence of Leakage Currents and OCVD Carrier Lifetimes
No full textThe reverse and forward currents of Al+ ion implanted 4H-SiC p+-i-n diodes have been compared for identically processed devices except for the implanted Al concentration in the emitter, 6×1019 cm-3 against 2×1020 cm-3, and the post implantation annealing treatment, 1600°C/30 min and 1650°C/25 min against 1950°C/5min. The diodes’ ambipolar carrier lifetime, as obtained by open circuit voltage decay measurements, has been compared too. The devices with lower annealing temperature show lower leakage currents and higher ambipolar carrier lifetime; they also show lower current in ohmic conduction
OCVD Lifetime Measurements on 4H-SiC Bipolar Planar Diodes: Dependences on Carrier Injection and Diode Area
No full textIn this paper, open-circuit voltage decay measurements of carrier lifetimes on 4H silicon carbide ion implanted planar p–i–n diodes of circular shape and different diameters are performed at increasing bias currents. The measured ambipolar carrier lifetimes have shown to be dependent on the carrier injection levels, quickly increasing at low-bias current up to reaching a saturation value, τHL, when the value of the average carrier density within the
base exceedsthe intrinsic-regiondoping. The τHLmeasured in diodes of different area also demonstrate a marked dependence on the diode dimension, with longer lifetimes being typical of larger-diameter diodes, suggesting that a great contribution of recombination comes from the diode periphery. A bulk ambipolar lifetime τHL_Vol = 320 ns has been extracted fromthe area-dependent measured lifetimes
Perimeter and Area Components in the I-V Curves of 4H-SiC Vertical p+-i-n Diode With Al+ Ion-Implanted Emitters
No full textThis paper describes the separation between the area and the perimeter current density components of 4H-SiC vertical p+-i-n diode with a circular Al+ implanted emitter of different diameters in the range 150-1000 μm and for temperatures of measurement in the range 30-290 °C. It is shown that before the diode series resistances become dominant, the forward current is given by the sum of an area plus a perimeter component, both of exponential trend with ideality factor 2; while toward high voltages, an area component with exponential trend and ideality factor 1 adds to the previous components. Moreover, this paper shows that forward area and perimeter current density components can be used for a straightforward identification of the parameters controlling the current transport, provided that they can be fit by the p-n junction equations in the frame of the abrupt junction approximation. Finally, this paper shows that the area reverse current density can be used for the identification of the electrically active defects in the drift layer
Al+ implanted vertical 4H-SiC p-i-n diodes: experimental and simulated forward current-voltage characteristics
No full textThe temperature dependence of the forward and reverse current voltage characteristics of circular Al+ implanted 4H-SiC p-i-n vertical diodes of various diameters, post implantation annealed at 1950 °C/5 min, have been used to obtain the thermal activation energies of the defects responsible of the generation and the recombination currents, as well as the area and the periphery current component of the current voltage characteristics. The former have values compatible with those of the traps associated to the carbon vacancy defect in 4H-SiC. The hypothesis that only these traps may justify the trend of the current voltage characteristics of the studied diodes has been tested by simulations in a Synopsys Sentaurus TCAD suite
High temperature variable range hopping in heavy Al implanted 4H-SiC
No full textIn this work, we confirm and extend the results of a previous study where a variable range hopping transport through localized impurity states has been found to dominate the electrical transport properties of 3×1020 cm-3 and 5×1020 cm-3 Al+ implanted 4H-SiC layers after 1950- 2000 °C post implantation annealing. In this study, samples with longer annealing times have been taken into account. The temperature dependence of these sample conductivity follows a variable range hopping law, consistent with a nearly two-dimensional hopping transport of non-interacting carriers that in the highest doped samples, persists up to around room temperature. This result indicates that the hole transport becomes strongly anisotropic on increasing the doping level. At the origin of this unusual electrical behavior, may be the presence of basal plane stacking faults, actually observed by transmission electron microscopy in one of the 5×1020 cm-3 samples
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