We have demonstrated symmetrically high levels of electrical activation of both p- and n-type dopants in germanium. Rapid thermal annealing of various commonly implanted dopant species were performed in the temperature range of 600–850 °C in germanium substrates. Diffusion studies were also carried out by using different anneal times and temperatures. T-SUPREM™ simulations were used to fit the experimental profiles and to extract the diffusion coefficient of various dopants.
High-k metal oxide gate dielectrics may be required to extend Moore’s law of semiconductor device density scaling into the future. However, growth of a thin SiO2-containing interface layer is almost unavoidable during the deposition of metal oxide films onto Si substrates. This limits the scaling benefits of incorporating high-k dielectrics in future transistors. A promising approach, in which oxygen-gettering metal overlayers are used to engineer the thickness of the SiO2-based interface layer between metal oxide and Si substrate after deposition of the metal oxide layer, is reported. Using a Ti overlayer with high solubility for oxygen on ZrO2 or HfO2 dielectrics, the effective removal of the low-k interface layer at 300K has been confirmed by electron microscopy and spectroscopy techniques. Significant enhancement of the gate capacitance density, while retaining low leakage current densities, has also been demonstrated for these interface-engineered high-k gate stacks.
A few of the recent unsatisfactory germanium n-channel metal-oxide-semiconductor field-effect transistor MOSFET experimentations are believed to stem from the poor source and drain n+-p junction formations. In order to explain the primary cause and suggest rectifying solutions, we have examined the activation of common n-type dopants in germanium and the related dependences. These dependences include thermal anneal budget, impurity species, and implantation dosage. Low thermal budgets are generally preferred to activate shallow junctions to simultaneously annihilate defects and suppress fast dopant diffusion. Injecting dopants over the solid-solubility limitation into shallow junctions would only generate more implantation damage but could not however lower the junction sheet resistance.
Electrostatic counter ion screening is a phenomenon that is detrimental to the sensitivity of charge detection in electrolytic environments, such as in field-effect transistor-based biosensors. Using simple analytical arguments, we show that electrostatic screening is weaker in the vicinity of concave curved surfaces, and stronger in the vicinity of convex surfaces. We use this insight to show, using numerical simulations, that the enhanced sensitivity observed in nanoscale biosensors is due to binding of biomolecules in concave corners where screening is reduced. We show that the traditional argument, that increased surface area-to-volume ratio for nanoscale sensors is responsible for their increased sensitivity, is incorrect.I n recent years, there has been a major drive to use field-effect transistor (FET)-based devices to detect biological molecules in electrolytic environments (1). These biosensors use the charge of biomolecules to gate the current through a transistor (2). Frequently, the transistor is based on a quasi-1D nanostructure, such as a nanowire (NW) or nanotube, and the biomolecules bind directly to the surface of the nanoscale structure (1, 3). The use of such nanostructures is justified by the belief that nanoscale biosensors are more sensitive, with sensitivity defined as the relative change in drain current or a shift in threshold voltage in response to a change in bound biomolecule density. A few experiments specifically studied the effect of shrinking nanowire radii on sensitivity, albeit with varying structures, analytes, and sensing circumstances, and found that shrinking a sensor's dimensions indeed improves its sensitivity (4-6). The enhanced sensitivity has been loosely attributed to the increase in the sensor's surface area-to-volume ratio, which is a direct result of shrinking its dimensions. This argument has been analytically justified in the context of gas sensors (7). However, there is a fundamental difference between gas and biomolecule sensing: biomolecule sensing is performed in an electrolyte, and the ions therein will screen the charge of bound biomolecules in a phenomenon known as Debye screening (8, 9). The direct application of the gas sensing result to the biosensing environment implicitly assumes that the screening effect does not change with shrinking dimensions, an assumption we believe to be false. There have been studies that included a rigorous treatment of screening in biosensors, but they studied neither the specific cause of increased sensitivity at the nanoscale, nor the effect of varying size on screening behavior (10). We believe the phenomenon responsible for the increased sensitivity of nanowires in particular, and nanostructured biosensors in general, have not yet been uncovered by the research community.We have previously dissected the operation of biosensors into two independent parts to better understand the underlying physics (11): first, biomolecule charges cause a change in the local electrostatic potential at the outer surface of the gate dielectri...
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