Alexandria, VA, United States
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Baril N.,Corbin Company | Baril N.,U.S. Army | Billman C.,U.S. Army | Maloney P.,U.S. Army | And 4 more authors.
Applied Physics Letters | Year: 2013

Suppression of generation-recombination dark current and bias stability in long wavelength infrared (LWIR) strained layer superlattice (SLS) detectors, consisting of a lightly doped p-type absorber layer and a wide bandgap hole barrier, are investigated with respect to the wide bandgap barrier layer thickness and doping profile. Dark current IV, photoresponse, and theoretical modeling are used to correlate device performance with the widegap barrier design parameters. Decreased dark current density and increased operating bias were observed as the barrier thickness was increased. This study also identifies key device parameters responsible for optimal performance of heterojunction based SLS LWIR detector. © 2013 U.S. Government.


Woodka M.D.,U.S. Army | Shpil J.C.,U.S. Army | Schnee V.P.,U.S. Army | Polcha J.M.P.,Corbin Company
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

A sensor system has been constructed that is capable of detecting and discriminating between various explosives presented in ocean water with detection limits at the 10-100 parts per trillion level. The sensor discriminates between different compounds using a biologically-inspired fluorescent polymer sensor array, which responds with a unique fluorescence quenching pattern during exposure to different analytes. The sensor array was made from commercially available fluorescent polymers coated onto glass beads, and was demonstrated to discriminate between different electron-withdrawing analytes delivered in salt water solutions, including the explosives 2,4,6-trinitrotoluene (TNT) and tetryl, the explosive hydrolysis products 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene, as well as other explosive-related compounds and explosive simulants. Sensitivities of 10-100 parts per trillion were achieved by employing a preconcentrator (PC) upstream of the sensor inlet. The PC consists of the porous polymer Tenax, which captures explosives from contaminated water as it passes through the PC. As the concentration of explosives in water decreased, longer loading times were required to concentrate a detectable amount of explosives within the PC. Explosives accumulated within the PC were released to the sensor array by heating the PC to 190 C. This approach yielded preconcentration factors of up to 100-1000x, however this increased sensitivity towards lower concentrations of explosives was achieved at the expense of proportionally longer sampling times. Strategies for decreasing this sampling time are discussed. © 2012 SPIE.


Woodka M.D.,U.S. Army | Schnee V.P.,U.S. Army | Polcha M.P.,Corbin Company
Analytical Chemistry | Year: 2010

A fluorescent polymer sensor array (FPSA) was made from commercially available fluorescent polymers coated onto glass beads and was tested to assess the ability of the array to discriminate between different analytes in aqueous solution. The array was challenged with exposures to 17 different analytes, including the explosives trinitrotoluene (TNT), tetryl, and RDX, various explosive-related compounds (ERCs), and nonexplosive electron-withdrawing compounds (EWCs). The array exhibited a natural selectivity toward EWCs, while the non-electron-withdrawing explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) produced no response. Response signatures were visualized by principal component analysis (PCA), and classified by linear discriminant analysis (LDA). RDX produced the same response signature as the sampled blanks and was classified accordingly. The array exhibited excellent discrimination toward all other compounds, with the exception of the isomers of nitrotoluene and aminodinitrotoluene. Of particular note was the ability of the array to discriminate between the three isomers of dinitrobenzene. The natural selectivity of the FPSA toward EWCs, plus the ability of the FPSA to discriminate between different EWCs, could be used to design a sensor with a low false alarm rate and an excellent ability to discriminate between explosives and explosive-related compounds. © 2010 American Chemical Society.


Nallon E.C.,U.S. Army | Polcha M.P.,Corbin Company | Schnee V.P.,U.S. Army
Sensors and Actuators, B: Chemical | Year: 2014

In this paper, we present an organic light emitting diode (OLED) used as a sensor for the detection of 1,4-dinitrobenzene (1,4-DNB). The detection method relies on the attenuation of the emitted light due to interactions between the 1,4-DNB and the active organic layer. The mechanism responsible for this attenuation involves an electron transfer from the electron donating organic layer to the electron deficient nitroaromatic 1,4-DNB. Devices were fabricated and tested against various concentrations of 1,4-DNB to determine if a dependence on concentration exists and to reveal more detail about the internal quenching mechanism.© 2013 Published by Elsevier B.V.


Baril N.,U.S. Army | Bandara S.,U.S. Army | Hoeglund L.,Jet Propulsion Laboratory | Henry N.,Corbin Company | And 6 more authors.
Infrared Physics and Technology | Year: 2015

Minimization of operating bias and generation-recombination dark current in long wavelength infrared (LWIR) strained layer superlattice (SLS) detectors, consisting of a lightly doped p-type absorber layer and a wide band gap hole barrier, are investigated with respect to the band alignment between the wide band gap barrier and absorber layers. Dark current vs. bias, photoresponse, quantum efficiency, lifetime, and modeling are used to correlate device performance with the wide gap barrier composition. Decreases in dark current density and operating bias were observed as the conduction band of the wide gap barrier was lowered with respect to the absorber layer. The device achieved 95% of its maximum quantum efficiency at 0 V bias, and 100% by 0.05 V. This study demonstrates key device design parameters responsible for optimal performance of heterojunction based SLS LWIR detectors.


Brown A.E.,U.S. Army | Brown A.E.,University of Illinois at Chicago | Jaime-Vasquez M.,U.S. Army | Almeida L.A.,U.S. Army | And 7 more authors.
Journal of Electronic Materials | Year: 2013

Molecular beam epitaxy n-type long-wavelength infrared (LWIR) Hg 1-x Cd x Te (MCT) has been investigated using variable-field Hall measurement in the temperature range from 50 K to 293 K. A quantitative mobility spectrum analysis technique has been used to determine the role of multicarrier transport properties with respect to epilayer growth on lattice-matched cadmium zinc telluride, as well as lattice-mismatched silicon (Si) and gallium arsenide (GaAs) buffered substrates. Overall, after postgrowth annealing, all layers were found to possess three distinct electron species, which were postulated to originate from the bulk, transitional (or higher-x-value) regions, an interfacial/surface layer carrier. Further, the mobility and concentration with respect to temperature were analyzed for all carriers, showing the expected mobility temperature dependence and intrinsic behavior of the bulk electron. Electrons from transitional regions were seen to match expected values based on the carrier concentration of the resolved peak. At high temperature, the lowest-mobility carrier was consistent with the properties of a surface carrier, while below 125 K it was postulated that interfacial-region electrons may influence peak values. After corrections for x-value and doping density at 77 K, bulk electron mobility in excess of 10 5 cm2 V-1 s-1 was observed in all epilayers, in line with expected values for lightly doped n-type LWIR material. Results indicate that fundamental conduction properties of electrons in MCT layers are unchanged by choice of substrate. © 2013 TMS.


Lennon C.M.,Corbin Company | Almeida L.A.,U.S. Army | Jacobs R.N.,U.S. Army | Benson J.D.,U.S. Army | And 5 more authors.
Journal of Electronic Materials | Year: 2013

The surface kinetics of CdTe (211)B grown by molecular beam epitaxy (MBE) is investigated using spectroscopic ellipsometry (SE) during in situ cyclic annealing. A method of measuring sublimation rates from high-index surfaces without use of reflection high-energy electron diffraction is presented. The effect of Te2 overpressure on the activation energy of sublimation for the CdTe (211)B surface is reported. The sensitivity of SE to surface temperature and film thickness was leveraged to monitor sublimation rates of CdTe stabilized by a Te2 overpressure. The sublimation activation energy was found to increase from 0.45 eV to 2.94 eV under the Te2 beam pressure regime investigated. © 2013 TMS (outside the USA).


Jacobs R.N.,U.S. Army | Nozaki C.,U.S. Army | Almeida L.A.,U.S. Army | Jaime-Vasquez M.,U.S. Army | And 9 more authors.
Journal of Electronic Materials | Year: 2012

Large-area, low-cost substrates are envisioned for next-generation HgCdTe infrared focal-plane arrays (IRFPA). Si, GaAs, Ge, and InSb have been previously examined as potential candidates. Fabrication of IRFPAs based on these substrates is limited by fundamental materials properties that potentially lead to lower detector performance and operability. Lattice and thermal mismatch between the substrate and epilayer are just two of several material factors that must be considered. We have reviewed these factors in the context of more recent data, and determined it worthwhile to revisit the use of GaAs substrates for epitaxial growth of HgCdTe. Our study starts with an evaluation of the surface quality (epireadiness) of commercially available (211) B-oriented GaAs substrates. Molecular beam epitaxial growth of CdTe buffer layers and subsequent HgCdTe absorber layers are performed in separate vacuum-interconnected chambers. The importance of optimization of the CdTe buffer layer growth for high-quality HgCdTe is detailed through surface morphology and x-ray studies. x-Ray diffraction rocking-curve full-width at half-maximum values as low as 52 arcsec have been obtained. Long-wave infrared Hg 1-xCd xTe (x = 0.23) has been grown on these buffer layers, producing cross-hatch- dominated surface morphologies, with dislocation densities as low as ∼3 × 10 6 cm -2. We have also obtained (for optimized layers), 80-K Hall-effect n-type carrier concentration and electron mobility of approximately ∼1.5 × 10 15 cm -3 and 1 × 10 5 cm 2 V -1 s -1, respectively. Finally, we briefly compare GaAs and Si in light of our preliminary investigation. © 2012 TMS (outside the USA).


Lennon C.M.,Corbin Company | Lennon C.M.,U.S. Army | Almeida L.A.,U.S. Army | Jacobs R.N.,U.S. Army | And 6 more authors.
Journal of Electronic Materials | Year: 2012

We describe the growth of CdTe (211)B by molecular beam epitaxy on largearea epiready GaAs (211)B substrates. Prior to CdTe growth, GaAs substrates were thermally cleaned under an As 4 flux. Oxide desorption was verified by in situ spectroscopic ellipsometry (SE) and reflection high-energy electron diffraction. The use of in situ SE played a significant role in the study of CdTeon-GaAs growth and annealing processes. An effective medium approximation (EMA) was used to model the overlayer thickness variation of CdTe epilayers throughout growth and in situ annealing cycles. A correlation between SE-derived EMA thickness values and surface defect formation mitigation is discussed. All annealed samples (11.5 μm to 13 μm thick) exhibited excellent crystalline quality with average double crystal rocking curve full-width at half-maximum (FWHM) values of ∼60 arcsec. © 2012 TMS.


Williams K.S.,U.S. Army | Lenhart J.L.,U.S. Army | Andzelm J.W.,U.S. Army | Bandara S.V.,U.S. Army | And 5 more authors.
Surface Science | Year: 2014

We report a DFT/GGA study of water adsorption and charge transfer at the relaxed (110) surfaces of several III-V binary semiconductors: GaAs, GaSb, and InAs. Our calculations are the first to show that adsorption of dissociated water changes the (110) surface structure. The characteristic III-V bond rotation through an angle of 30 is reversed. The buckled III-V bond at the semiconductor/water interface rotates into the surface through a new angle, which we calculate to be approximately 11 on all three binaries. Only dissociation of water - as opposed to chemisorption or physisorption - leads to this pseudo-unrelaxed configuration. We calculate geometries and reaction energies for several different adsorption mechanisms and find that molecular adsorption is the most favorable. We are able to reproduce binding configurations and energies for known adsorption sites on GaAs(110), but we also show new calculations for water on GaSb(110) and InAs(110). Lastly, we calculate the shift in electronic work function and induced surface dipole moment due to adsorbed water. We show that shifts in work function maximize at 1 ML of water, consistent with previous experimental works. Analysis of the partial charges and electron density reveals that adsorption of water polarizes the (110) surface, leading to local charge transfer across the semiconductor/water interface. © 2013 Elsevier B.V.

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