Physics of Nanostructure Design for Infrared Detectors

Infrared detectors and focal plane array technologies are becoming ubiquitous in military, but are limited in the commercial sectors. The widespread commercial use of this technology is lacking because of the high cost and large size, weight and power. Most of these detectors require cryogenic cooling to minimize thermally generated dark currents, causing the size, weight, power and cost to increase significantly. Approaches using very thin detector design can minimize thermally generated dark current, but at a cost of lower absorption efficiency. There are emerging technologies in nanostructured material designs such as metasurfaces that can allow for increased photon absorption in a thin detector architecture. Ultra-thin and low-dimensional absorber materials may also provide unique engineering opportunities in detector design. This chapter discusses the physics and opportunities to increase the operating temperature using such techniques

Spectral and temperature dependence of two-photon and free-carrier absorption in InSb

The nonlinear absorption spectrum of InSb was measured using a combination of tunable similar to 160 fs, similar to 10 ps, and similar to 150 ns IR sources along with a cryostat for controlling the sample temperature to vary the band gap energy from 0.17 to 0.23 eV. The measured nonlinear optical properties in InSb are consistent with those predicted by the models which include two-and three-photon absorption (2PA and 3PA), multiphoton generated free-carrier absorption (FCA) and various recombination mechanisms. Temperature-dependent Z-scan and nonlinear transmission measurements yield information on the temperature and spectral dependence of 2PA, FCA, and carrier recombination processes of Shockley-Read-Hall, and Auger mechanisms. We find good agreement between the measured and the modeled nonlinear properties is possible only when the recently predicted temperature dependence of the FCA is considered. The wavelength-and temperature-dependent 2PA and 3PA coefficients in InSb were experimentally obtained. The inferred values of the 2PA and 3PA are consistent with the scaling rules of a simple two-parabolic band model. We further determine recombination rates from nonlinear transmittance of nanosecond pulses of CO2 laser

The Competitive Consequences Of Size In Banking: Evidence From Megabank Mergers

Concerns over size in banking arise from the potential for a megabank to harm competition and extract safety net subsidies. With the worrisome increases in size having been achieved through megamergers, this paper examines whether gains in such mergers trace to efficiency improvements or market power vis-à-vis customers and regulators administering the government safety net. The findings indicate that as statutory restrictions on bank expansion faded over time, size-related efficiency gains receded, and as bank size continued to expand through market overlap mergers, market power gains emerged. When mergers produced extremely large banks that were perceived to be Too-Big-To-Fail, gains arose from the ability to shift risk onto the government safety net. These finding have implications for reform proposals that aim to restrict bank size in the interests of macroeconomic stability