Recombination activity of iron-gallium and iron-indium pairs in silicon

The recombination activity of iron-gallium (FeGa) and iron-indium (FeIn) pairs in crystalline silicon is studied by means of injection-dependent carrier lifetime measurements on Fe-implanted, Ga- and In-doped p-type silicon wafers of different resistivities (0.3–15Ωcm). Compared to FeB pairs, FeGa and FeIn pairs are found to be much more effective recombination centers in p-type silicon. Using Shockley–Read–Hall statistics we determine the energy level Et of the FeGa-related center to be 0.20eV above the valence-band edge Eν. The strong recombination activity of FeGa is assigned to its large electron-capture cross section σn of 4×10⁻¹⁴cm². The hole-capture cross section σp is 2×10⁻¹⁴cm². For the FeIn-related recombination center, our measurements show that Et=Eν+0.15eV, σn=3.5×10⁻¹³cm², and σp=1.5×10⁻¹⁴cm². Strong illumination with white light is found to dissociate both types of pairs. Storage of the samples in the dark leads to a full repairing of FeGa and FeIn pairs. Lifetime changes measured before and after illumination can be used to determine the interstitialiron concentration in Ga- and In-doped silicon using calibration factors determined from the measured defect parameters.J.S. thanks A. Cuevas and A. Blakers for their hospitality during his research stay at ANU and acknowledges the financial support of the Alexander von Humboldt Foundation. D.M. acknowledges the financial support of the Australian Research Council

How do retail prices react to minimum wage increases?

Wages ; Prices

The minimum wage and restaurant prices

Using both store-level and aggregated price data from the food away from home component of the Consumer Price Index survey, we show that restaurant prices rise in response to an increase in the minimum wage. These results hold up when using several different sources of variation in the data. We interpret these findings within a model of employment determination. The model implies that minimum wage hikes cause employment to fall and prices to rise if labor markets are competitive but potentially cause employment to rise and prices to fall if labor markets are monopsonistic. Therefore, our empirical results appear to provide evidence against the hypothesis that monopsony power is important for understanding the small observed employment responses to minimum wage changes.Labor market ; Wages ; Wages - Restaurants

The Effects of Increasing the Minimum Wage on Prices: Analyzing the Incidence of Policy Design and Context

We analyze the price pass-through effect of the minimum wage and use the results to provide insight into the competitive structure of low-wage labor markets. Using monthly price series, we find that the pass-through effect is entirely concentrated on the month that the minimum wage change goes into effect, and is much smaller than what the canonical literature has found. We then discuss why our results differ from that literature, noting the impact of series interpolation in generating most of the previous results. We then use the variation in the size of the minimum wage change to evaluate the competitive nature of low-wage labor markets. Finally, we exploit the rich variation in minimum wage policy of the last 10 to 15 years— including the rise of state- and city-level minimum wage changes and the increased use of indexation—to investigate how the extent of price pass-through varies by policy context. This paper contributes to the literature by clarifying our understanding of the dynamics and magnitude of the pass-through effect and enriching the discussion of how different policies may impact that effect

Daniel MacDonald CD Summer 2018

Supports faculty to redesign or develop a course in ways that implement high-impact, evidence-based, and/or innovative teaching strategies to improve student learning

Temperature dependent carrier lifetime studies of Mo in crystalline silicon

The capture cross sections of both electronsσn and holes σp were determined for interstitialmolybdenum in crystalline silicon over the temperature range of −110 to 150 °C. Carrier lifetimemeasurements were performed on molybdenum-contaminated silicon using a temperature controlled photoconductance instrument. Injection dependent lifetime spectroscopy was applied at each temperature to calculate σp and σn. This analysis involved a novel approach that independently determined the capture cross sections at each temperature assuming a known defect density and thermal velocity. Since the energy state is in the lower half of the bandgap, the determination of σp is unaffected by the defect energy at all temperatures, and σp is found to decrease with temperature in a fashion consistent with excitonic Auger capture. At temperatures below 0 °C, the determination of σn is also unaffected by the defect energy due to the suppression of thermal emission, and σn decreases with temperature as well. It is shown that a projection of σn to higher temperature suggests the defect has an energy of 0.375 eV above the valance band edge of silicon.D.M. likes to thank the Australian Research Council for fellowship and G.C. likes to thank “CrystalClear Integrated Project” Contract No. SES6-CT_2003-502583 funded by the European Commission

Mixing processes and hydraulic control in a highly stratified estuary

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2003This thesis utilizes field data from the Fraser River Estuary, a highly stratified system located in southwestern British Columbia, Canada, to investigate the nature of mixing processes in a highly stratified environment, and to extend two-dimensional hydraulic theory to a three dimensional environment. During the late ebb, a stationary front exists at the Fraser mouth. Although densimetric Froude numbers in the vicinity of the front are supercritical in a frame of reference parallel to the local streamlines, the front itself is oriented such that the value of the Froude number is equal to the critical value of unity when taken in a frame of reference perpendicular to the front. This observation presents a robust extension of established two-dimensional, two-layer hydraulic theory to thee dimensions, and implies similarity with trans-sonic flows, in that a Froude angle can be used to identify critical conditions in a manner similar to the Mach angle. Mixing processes were evaluated at the mouth during the late ebb using a control volume approach to isolate mean vertical entrainment processes from turbulent processes, and quantify the vertical turbulent salt and momentum fluxes. Observed turbulent dissipation rates are high, on the order of 10-3 m2s.3, with vertical entrainment velocities on the order of 2x10-3 m's'l. Mixing efficiencies, expressed as flux Richardson numbers, are confined within a range from 0.15 to 0.2, at gradient Richardson number values between 0.2 and 0.25. These results are consistent with previous laboratory studies, but represent energetic conditions that are several orders of magnitude higher. In the estuarine channel, the variability of mixing processes was investigated through the tidal cycle using control volume and overturn scale methods. Spatially, mixing was observed to be more intense near a width constriction on the order of25%. Temporally, more dominant mixing was observed during ebbs, due to increases in both vertical shear and stratification. Mixing is active and important throughout the tidal cycle, and was found to be the dominant process responsible for removing salt from the estuarine channel during the ebb.This research was funded by Office of Naval Research grants N000-14-97-10134 and N000-14-97-10566, National Science Foundation grant OCE-9906787, a National Science Foundation graduate fellowship, and the WHOI Academic Programs Office