Formation of Strain-Induced Quantum Dots in Gated Semiconductor Nanostructures

Elastic strain changes the energies of the conduction band in a semiconductor, which will affect transport through a semiconductor nanostructure. We show that the typical strains in a semiconductor nanostructure from metal gates are large enough to create strain-induced quantum dots (QDs). We simulate a commonly used QD device architecture, metal gates on bulk silicon, and show the formation of strain-induced QDs. The strain-induced QD can be eliminated by replacing the metal gates with poly-silicon gates. Thus strain can be as important as electrostatics to QD device operation operation.Comment: 5 pages, 3 figures, plus supplementary informatio

Simulating Capacitances to Silicon Quantum Dots: Breakdown of the Parallel Plate Capacitor Model

Many electrical applications of quantum dots rely on capacitively coupled gates; therefore, to make reliable devices we need those gate capacitances to be predictable and reproducible. We demonstrate in silicon nanowire quantum dots that gate capacitances are reproducible to within 10% for nominally identical devices. We demonstrate the experimentally that gate capacitances scale with device dimensions. We also demonstrate that a capacitance simulator can be used to predict measured gate capacitances to within 20%. A simple parallel plate capacitor model can be used to predict how the capacitances change with device dimensions; however, the parallel plate capacitor model fails for the smallest devices because the capacitances are dominated by fringing fields. We show how the capacitances due to fringing fields can be quickly estimated.Comment: 4 pages, 3 figures, to be published in IEEE Trans. Nan

Electrostatic and Strain-Induced Quantum Dots in Silicon Nanostructures

Quantum dots (QDs) are nanometer scale regions that can trap charges. In this dissertation I describe my work on understanding the reproducibility of silicon QDs, and why unintentional QDs are so common. I studied both the reproducibility and predictability of gate capacitances to intentional QDs. I found that, in our devices, electrostatic QDs have gate capacitances that are reproducible to within 10% and predictable using a capacitance simulator to within 20%. I describe a technique that uses the gate capacitances to determine the locations of the unintentional QDs in a nanowire with a precision of a few nanometers. I do this by comparing the measured gate capacitances to simulated gate capacitances. I suggest that strain from the gates or contacts may be the cause of many of the observed unintentional QDs. Strain can cause QDs because it changes the band structure, thus changing the energy of the conduction band and the valence band. I discuss the effects of strain in three common device architectures: a mesa-etched nanowire with poly-silicon gates, metal-gated bulk silicon, and chemically grown nanowires with metal contacts. Because strain can affect these very different architectures, I suggest that the strain in a QD can be as important as the electrostatics to understanding how a device works

Determining the Location and Cause of Unintentional Quantum Dots in a Nanowire

We determine the locations of unintentional quantum dots (U-QDs) in a silicon nanowire with a precision of a few nanometers by comparing the capacitances to multiple gates with a capacitance simulation. Because we observe U-QDs in the same location of the wire in multiple devices, their cause is likely to be an unintended consequence of the fabrication, not random atomic-scale defects as is typically assumed. The locations of the U-QDs appear consistent with conduction band modulation from strain from the oxide and the gates. This allows us to suggest methods to reduce the frequency of U-QDs

La batalla de Simancas, del Al jandaq, o batalla del Foso

El motivo de este trabajo es la identificación geográfica del lugar en donde tuvo lugar la denominada batalla del Foso o del Al jandaq. Esta batalla aconteció en el año 939. En ella la retaguardia del gran ejercito de Abderramán III fue puesta en fuga por tropas castellanas, perdiendo los musulmanes toda la impedimenta.The reason for this work is the geographical identification of the place where the so-called Battle of Al Jandaq took place. This battle took place in the year 939. In her the rear guard of the great army of Abderramán III was put in flight by Castilian troops

Disinflationary Monetary Policy and the Distribution of Income

Inflation over the last 5 years has remained below 3 percent. Many economic observers applaud these results, arguing that inflation has ceased to matter much in the decisions of consumers and businesses. Others such as Martin Feldstein (1996), Lee Hoskins (1991), and Jerry Jordan (1993) advocate further gains on the inflationary front. Feldstein, for instance, argues that reducing the inflation rate to zero would ameliorate the tax distortions caused by inflation, producing substantial gains to the economy. He estimates that to achieve price stability the Federal Reserve would have to engineer a recession that reduces real gross domestic product by 5 percent. Feldstein holds that these costs are far outweighed by the benefits that would occur from reducing the misallocation of resources (in jargon, the deadweight losses) due to inflation. What he overlooks in his analysis is how the costs and benefits of such a policy would be shared. Who would bear the burdens from disinflationary monetary policy? Who would reap the benefits? Would such distributional consequences be desirable in the present economic environment? This working paper attempts to answer these questions first by considering based on economic principles how different sectors would be affected by disinflationary policy. The traditional "money" channel of monetary policy implies that employment in interest-sensitive industries should fall the most. The "credit" channel implies that small, financially-constrained firms should be hurt more than large, financially-stable firms. A slowdown in aggregate activity working through either channel would burden low-income workers more than high-income workers. Since minorities tend to have lower wages than whites, disinflationary policy should disproportionately affect them. Lenders such as bond holders would gain by an unanticipated decrease in inflation.

Historia medieval de la Villa de Portillo

The article summarizes the Medieval History of "Portillo" village where Pío del Río Hortega was born, from the Ramiro ll's victory over Abderramán Ill in year 939 until the reign of the Reyes Católicos.El artículo resume la historia medieval de la Villa de Portillo, lugar de nacimiento de Río Hortega, desde el año 939 -victoria de Ramiro II sobre Abderramán III- hasta el reinado de los Reyes Católicos