Monte Carlo study of multibarrier heterostructure switch

A multibarrier heterostructure GaAs/AlAs current switching diode has been investigated by Monte Carlo method. The switching phenomenon is based on electron tunnelling and thermoemission from the GaAs wells to the AlAs barriers, electron drift across the thin AlAs barriers followed by a subsequent impact ionisation in the undoped GaAs layers. The calculated switching voltage is close to 100 V for the diode involving four AlAs barriers at 300 K lattice temperature. The estimated switching time is in the order of 10 ps

Disclosing water-energy-economics nexus in shale gas development

Shale gas has gained importance in the energy landscape in recent decades. However, its development has raised environmental concerns, especially, those associated with water management. Thus, the assessment of water management aspects, which inevitably impact the economic aspects, is crucial in evaluating the merits of any project exploiting this energy source. This paper provides a review of the economic and environmental implications of shale gas development around the world. Furthermore, to demonstrate the interplay between the various technical, environmental and economic factors in concrete terms, we report on a specific set of case studies conducted using an integrated decision-support tool that has been implemented to model and optimize shale gas development projects. The case study results confirm that the gas breakeven price decreases with expansion in scale of the shale gas development, i.e. increasing the number of well-pads in the system. However, scale also increases the options for water re-use and recycle in drilling and fracturing operations, which can result in lower freshwater withdrawal intensity. Moreover, under water scarcity scenarios, the choice of well-pad designs that are inherently less water intensive was found to be more cost-effective than water re-use or/and recycle strategies at reducing net freshwater demand. Similar trends were observed when the impact of wastewater quality, i.e. total dissolved solids concentration, on the optimal development strategy of shale gas plays was investigated. The results of these case studies reveal that greater efforts are needed at characterizing freshwater availability and wastewater quality for the evaluation of both the economic and environmental aspects of shale gas development

Optical pump rectification emission: route to terahertz free-standing surface potential diagnostics

We introduce a method for diagnosing the electric surface potential of a semiconductor based on THz surface generation. In our scheme, that we name Optical Pump Rectification Emission, a THz field is generated directly on the surface via surface optical rectification of an ultrashort pulse after which the DC surface potential is screened with a second optical pump pulse. As the THz generation directly relates to the surface potential arising from the surface states, we can then observe the temporal dynamics of the static surface field induced by the screening effect of the photo-carriers. Such an approach is potentially insensitive to bulk carrier dynamics and does not require special illumination geometries