Dr. Silviu Velicu Profile

Dr. Silviu Velicu

President at EPIR, Inc.

SPIE Involvement:

Author

Publications (29)

Proceedings Article | 10 October 2023 Presentation

Optimizing advanced integration technology for large format, small pixel IRFPAs

Sushant Sonde, Kiran Sasikumar, Yong Chang, Subramanian Sankaranarayanan, Silviu Velicu

Proceedings Volume PC12687, PC1268708 (2023) https://doi.org/10.1117/12.2677419

KEYWORDS: Reliability, Mercury cadmium telluride

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Proceedings Article | 10 October 2023 Presentation

fabrication and modeling study to reduce valence band offset in HgCdTe MWIR nBn photodetectors grown on silicon using superlattice barriers

Ryan Sellers, Peihong Man, Silviu Velicu, Sushant Sonde, Zahira El Khalidi, Zaheer Ahmad, Danial Zengeneh

Proceedings Volume PC12687, PC1268709 (2023) https://doi.org/10.1117/12.2677394

KEYWORDS: Superlattices, Silicon, Photodetectors, Modeling, Mid-IR, Mercury cadmium telluride, Fabrication, Semiconductors, Photoresistors, Optical testing

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Proceedings Article | 11 October 2022 Presentation

Material considerations for vertical integration of IRFPAs (Conference Presentation)

Sushant Sonde, Kiran Sasikumar, Yong Chang, Subramanian KRS Sankaranarayanan, Silviu Velicu

Proceedings Volume PC12234, PC122340A (2022) https://doi.org/10.1117/12.2633654

KEYWORDS: Staring arrays, Indium, Thermography, Thermal modeling, Superlattices, Sensors, Reliability, Mercury cadmium telluride, Infrared radiation, Finite element methods

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Proceedings Article | 13 May 2019 Paper

High energy neutron irradiation effects on molecular beam epitaxy HgCdTe-based focal plane arrays and cameras

Y. Chang, S. Velicu

Proceedings Volume 10980, 109800V (2019) https://doi.org/10.1117/12.2521311

KEYWORDS: Staring arrays, Mid-IR, Mercury cadmium telluride, Infrared cameras, Cameras, Readout integrated circuits, Long wavelength infrared, Sensors, Infrared imaging, Infrared ROIC, Directed infrared countermeasures, Infrared detectors, Far infrared, Infrared photodetector characterization techniques

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Proceedings Article | 18 September 2018 Presentation

Material and process development for high operating temperature LWIR PIN HgCdTe focal plane arrays (Conference Presentation)

Silviu Velicu

Proceedings Volume 10766, 107660G (2018) https://doi.org/10.1117/12.2323254

KEYWORDS: Mercury cadmium telluride, Long wavelength infrared, Materials processing, Staring arrays, Diffusion, Array processing, Heterojunctions, Doping, Annealing, Infrared detectors

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Higher operating temperatures can be provided by a system based on HgCdTe infrared detectors utilizing optimized material parameters (i.e. doping and defects) and non-equilibrium device architectures that suppress detector diffusion current. A PIN (P+/Intrinsic/N+) hetero-junction photodiode can eliminate Auger generated diffusion current, resulting in a diode dominated by Shockley-Read-Hall (SRH) depletion current. The limiting dark current in the PIN diode will be determined by the SRH lifetime of the HgCdTe material. We are optimizing processes for material growth and post-annealing, to improve in SRH lifetimes and hence depletion dark current and performance at higher operating temperatures. We report on the growth of high-quality n-type long wavelength infrared (LWIR) HgCdTe (cutoff wavelength 10 μm at 77 K) layers grown on CdTe/Si and CdZnTe substrates by molecular beam epitaxy (MBE). A low indium concentration in the absorber layer of ~1x10-14 is confirmed by secondary ion mass spectrometry (SIMS). In order to reduce potential SRH centers and enable low doping levels, we are applying gettering processes to reduce impurity levels below what is achievable by best practices in MBE growth. Concentration profiles of impurities such as Na and K are seen to getter to top surface and interface with the substrate, and are seen to be dramatically reduced in the absorber layer as annealing temperature is increased. We are also studying the effect of anneals on the sharpness of heterojunctions created by MBE growth. The potential benefits of heterojunction devices in suppressing dark current, particularly structures with lower thickness, can only be realized if interdiffusion can be controlled. We have successfully fit SIMS Cd profiles to a model that incorporates the temperature and composition dependence of the interdiffusion coefficient. These results, along with dependence of As diffusion coefficients vs. temperature and Hg pressure lead us to propose and test alternative annealing profiles that better preserve the heterojunctions while maintaining an appropriate amount of As diffusion for junction formation.

Proceedings Article | 19 September 2016 Presentation + Paper

Extended short wavelength infrared HgCdTe detectors on silicon substrates

D. Hansel, A. Mukhortova, Y. Chang, R. Kodama, J. Zhao, S. Velicu, F. Aqariden, J. Park

Proceedings Volume 9974, 99740H (2016) https://doi.org/10.1117/12.2238053

KEYWORDS: Infrared detectors, Mercury cadmium telluride, Diodes, Sensors, Short wave infrared radiation, Infrared radiation, Infrared sensors, Detector arrays, Silicon, Semiconducting wafers

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Proceedings Article | 1 September 2015 Paper

Proton irradiation of MWIR HgCdTe/CdZnTe

Stephen Fahey, Silviu Velicu, Ramana Bommena, Jun Zhao, Vincent Cowan, Christian Morath, Sivalingam Sivananthan

Proceedings Volume 9616, 96160E (2015) https://doi.org/10.1117/12.2189829

KEYWORDS: Diodes, Sensors, Mid-IR, Medium wave, Mercury cadmium telluride, Temperature metrology, Infrared sensors, Infrared radiation, Sensor performance, Diffusion

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Proceedings Article | 27 February 2015 Paper

Large size MOEMS Fabry-Perot interferometer filter for focal plane array hyperspectral imaging

J. Chee, J. Hwu, T. Kim, J. Kubby, S. Velicu, N. Gupta

Proceedings Volume 9375, 93750K (2015) https://doi.org/10.1117/12.2076615

KEYWORDS: Electronic filtering, Staring arrays, Microopto electromechanical systems, Silicon, Electrodes, Computer aided design, Fabry–Perot interferometry, Hyperspectral imaging, Optical filters, Long wavelength infrared

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Proceedings Article | 17 September 2014 Paper

Mid and long wavelength infrared HgCdTe photodetectors exposed to proton radiation

Jeremy Bergeson, Silviu Velicu, Ramana Bommena, Stephen Fahey, Vincent Cowan, Christian Morath

Proceedings Volume 9226, 92260P (2014) https://doi.org/10.1117/12.2064074

KEYWORDS: Long wavelength infrared, Mid-IR, Mercury cadmium telluride, Photodetectors, Staring arrays, Radiation effects, Silicon, Sensors, Diodes, Readout integrated circuits

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Proceedings Article | 24 June 2014 Paper

High-performance SWIR HgCdTe FPA development on silicon substrates

S. Ketharanathan, H. Schaake, H. Shih, R. Bommena, J. Bergeson, P. Wijewarnasuriya, N. Dhar, R. Kodama, J. Zhao, F. Aqariden, S. Velicu

Proceedings Volume 9070, 907009 (2014) https://doi.org/10.1117/12.2053020

KEYWORDS: Short wave infrared radiation, Mercury cadmium telluride, Sensors, Silicon, Staring arrays, Quantum efficiency, Indium gallium arsenide, Detector arrays, Data modeling, Antireflective coatings

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Proceedings Article | 21 May 2014 Paper

Miniaturized imaging spectrometer based on Fabry-Perot MOEMS filters and HgCdTe infrared focal plane arrays

S. Velicu, J. Bergeson, C. Buurma, Tae Sung Kim, J. Kubby, N. Gupta

Proceedings Volume 9100, 91000F (2014) https://doi.org/10.1117/12.2053902

KEYWORDS: Electronic filtering, Reflectivity, Spectroscopy, Semiconducting wafers, Infrared imaging, Infrared radiation, Interfaces, Staring arrays, Long wavelength infrared, Spectral resolution

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Imaging spectrometry can be utilized in the midwave infrared (MWIR) and long wave infrared (LWIR) bands to detect, identify and map complex chemical agents based on their rotational and vibrational emission spectra. Hyperspectral datasets are typically obtained using grating or Fourier transform spectrometers to separate the incoming light into spectral bands. At present, these spectrometers are large, cumbersome, slow and expensive, and their resolution is limited by bulky mechanical components such as mirrors and gratings. As such, low-cost, miniaturized imaging spectrometers are of great interest. Microfabrication of micro-electro-mechanicalsystems (MEMS)-based components opens the door for producing low-cost, reliable optical systems. We present here our work on developing a miniaturized IR imaging spectrometer by coupling a mercury cadmium telluride (HgCdTe)-based infrared focal plane array (FPA) with a MEMS-based Fabry-Perot filter (FPF). The two membranes are fabricated from silicon-oninsulator (SOI) wafers using bulk micromachining technology. The fixed membrane is a standard silicon membrane, fabricated using back etching processes. The movable membrane is implemented as an X-beam structure to improve mechanical stability. The geometries of the distributed Bragg reflector (DBR)-based tunable FPFs are modeled to achieve the desired spectral resolution and wavelength range. Additionally, acceptable fabrication tolerances are determined by modeling the spectral performance of the FPFs as a function of DBR surface roughness and membrane curvature. These fabrication non-idealities are then mitigated by developing an optimized DBR process flow yielding high-performance FPF cavities. Zinc Sulfide (ZnS) and Germanium (Ge) are chosen as the low and the high index materials, respectively, and are deposited using an electron beam process. Simulations are presented showing the impact of these changes and non-idealities in both a device and systems level.

SPIE Journal Paper | 13 March 2014

Design and fabrication of Fabry–Perot filters for infrared hyperspectral imagers

Michael Morley, Silviu Velicu, Yong Chang, Christoph Grein, Dmitry Kozak, Bautista Fernandez, Joel Kubby, Neelam Gupta

JM3, Vol. 13, Issue 01, 011116, (March 2014) https://doi.org/10.1117/12.10.1117/1.JMM.13.1.011116

KEYWORDS: Electronic filtering, Reflectivity, Infrared imaging, Hyperspectral imaging, Imaging systems, Optical filters, Infrared radiation, Semiconducting wafers, Image filtering, Surface roughness

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Proceedings Article | 24 September 2013 Paper

Two color high operating temperature HgCdTe photodetectors grown by molecular beam epitaxy on silicon substrates

S. Velicu, R. Bommena, V. Cowan, C. Morath, S. Fahey, M. Morley, J. Zhao

Proceedings Volume 8876, 887608 (2013) https://doi.org/10.1117/12.2025301

KEYWORDS: Sensors, Long wavelength infrared, Mid-IR, Mercury cadmium telluride, Infrared detectors, Photodiodes, Quantum efficiency, Photodetectors, Molecular beam epitaxy, Instrument modeling

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Proceedings Article | 5 March 2013 Paper

Hyperspectral Fabry-Perot filters for HgCdTe infrared detectors

Yong Chang, Christoph Grein, Silviu Velicu, Neelam Gupta, Michael Morley

Proceedings Volume 8613, 861316 (2013) https://doi.org/10.1117/12.2007508

KEYWORDS: Electronic filtering, Long wavelength infrared, Reflectivity, Spectral resolution, Mercury cadmium telluride, Interfaces, Optical filters, Sensors, Infrared detectors, Zinc

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Proceedings Article | 4 February 2013 Paper

High operation temperature of HgCdTe photodiodes by bulk defect passivation

C. Grein, P. Hagler, Paul Boieriu, S. Velicu, R. Bommena, C. Blisset, C. Buurma, S. Sivananthan

Proceedings Volume 8631, 86311J (2013) https://doi.org/10.1117/12.2004708

KEYWORDS: Mercury cadmium telluride, Hydrogen, Long wavelength infrared, Silicon, Diodes, Doping, Photodiodes, Plasmas, Mid-IR, Infrared radiation

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Proceedings Article | 21 January 2012 Paper

Theoretical and experimental investigation of MWIR HgCdTe nBn detectors

Jun Zhao, Michael Morley, Silviu Velicu, Jamie Phillips, Anne Itsuno

Proceedings Volume 8268, 82682X (2012) https://doi.org/10.1117/12.904916

KEYWORDS: Mercury cadmium telluride, Mid-IR, Doping, Sensors, Instrument modeling, Heterojunctions, Infrared detectors, Temperature metrology, Optical testing, Photodiodes

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Proceedings Article | 16 September 2011 Paper

Calculated performance of an Auger-suppressed unipolar HgCdTe photodetector for high temperature operation

Silviu Velicu, Angelo Gilmore, Anne Itsuno, Jamie Phillips

Proceedings Volume 8155, 81550J (2011) https://doi.org/10.1117/12.893732

KEYWORDS: Mercury cadmium telluride, Long wavelength infrared, Photodetectors, Doping, Infrared technology, Instrument modeling, Thermography, Sensors, Infrared radiation, Device simulation

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Proceedings Article | 14 February 2011 Paper

Fabrication and testing of MEMS-based optical filter combined with a HgCdTe detector

Dmitry Kozak, Silviu Velicu, Bautista Fernandez, Joel Kubby, Michael Morley

Proceedings Volume 7930, 79300L (2011) https://doi.org/10.1117/12.874345

KEYWORDS: Silicon, Semiconducting wafers, Etching, Optical filters, Sensors, Mid-IR, Oxides, Reflectivity, Germanium, Mercury cadmium telluride

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Proceedings Article | 24 January 2011 Paper

VLWIR high operating temperature non-equilibrium photovoltaic HgCdTe devices

C. Grein, J. Phillips, S. Velicu, A. Itsuno

Proceedings Volume 7945, 79451L (2011) https://doi.org/10.1117/12.873470

KEYWORDS: Mercury cadmium telluride, Doping, Sensors, Heterojunctions, Infrared detectors, Photovoltaics, Cadmium, Temperature metrology, Infrared radiation, Absorption

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Proceedings Article | 18 February 2010 Paper

Prototyping of MWIR MEMS-based optical filter combined with HgCdTe detector

Bautista Fernandez, Dmitry Kozak, Joel Kubby, Silviu Velicu

Proceedings Volume 7594, 75940W (2010) https://doi.org/10.1117/12.842700

KEYWORDS: Sensors, Mercury cadmium telluride, Silicon, Optical filters, Prototyping, Mid-IR, Fabry–Perot interferometry, Mirrors, Microelectromechanical systems, Oxides

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Proceedings Article | 23 January 2010 Paper

Non-cryogenic operation of HgCdTe infrared detectors

J. Phillips, A. Itsuno, S. Velicu, C. Grein, P. Emelie, P. Wijewarnasuriya

Proceedings Volume 7608, 760820 (2010) https://doi.org/10.1117/12.838381

KEYWORDS: Mercury cadmium telluride, Doping, Infrared detectors, Photodiodes, Diffusion, Sensors, Instrument modeling, Long wavelength infrared, Mid-IR, Infrared radiation

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High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 μm and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicability. Reducing cooling requirements and eventually operating at temperatures that could be reached with thermoelectric coolers can lead to lighter and more compact systems. However, at these elevated temperatures, the absorber layer becomes intrinsic, carrier concentrations are high and Auger processes typically dominate the dark current and noise characteristics. Auger processes can be suppressed by placing the absorber layer between an exclusion junction and an extraction junction at reverse bias. This reduces the minority carrier concentration in the absorber by several orders of magnitude below thermal equilibrium. The majority carrier concentration also drops significantly below thermal equilibrium to maintain charge neutrality, eventually reaching the extrinsic doping level. This device architecture produces a lower dark current density and lower noise at non-cryogenic temperatures than standard p-n junction photodiodes. Due to the precise control of the layer's thicknesses and compositions that could be achieved with molecular beam epitaxy (MBE), this technique is the method of choice for implementing these novel non-equilibrium devices. In this work, we analyze Auger suppression in HgCdTe alloy-based device structures and determine the operation temperature improvements expected when Auger suppression occurs. We identified critical material (absorber dopant concentration and minority carrier lifetime) requirements that must be satisfied for optimal performance characteristics. Experimental dark current-voltage characteristics between 120 and 300 K are fitted using numerical simulations. Based on this, the negative differential resistance (NDR) observed in experimental data is attributed to the full suppression of Auger-1 processes and the partial suppression of Auger-7 processes. We will also present an analysis and comparison of our theoretical and experimental device results in structures where Auger suppression was realized.

Proceedings Article | 12 September 2007 Paper

Hg1-xCdxTe mid-wavelength infrared (MWIR) avalanche photodiode (APD) grown on Si substrate

Jun Zhao, Silviu Velicu, Siddhartha Ghosh, Shubhrangshu Mallick

Proceedings Volume 6660, 66600Y (2007) https://doi.org/10.1117/12.736340

KEYWORDS: Avalanche photodetectors, Mid-IR, Mercury cadmium telluride, Cadmium, Avalanche photodiodes, Silicon, Diodes, Mercury, Tellurium, Infrared photography

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Proceedings Article | 14 May 2007 Paper

Pronounced Auger suppression in long wavelength HgCdTe devices grown by molecular beam epitaxy

Priyalal Wijewarnasuriya, Gregory Brill, Arvind D'Souza, John Reekstin, P. Y. Emelie, Maryn Stapelbroek, Yuanping Chen, HyeSon Jung, Chris Grein, Silviu Velicu, Nibir Dhar, Sivalingam Sivanathan

Proceedings Volume 6542, 65420G (2007) https://doi.org/10.1117/12.723162

KEYWORDS: Mercury cadmium telluride, Arsenic, Doping, Diffusion, Sensors, Molecular beam epitaxy, Annealing, Solids, Resistance, Quantum efficiency

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Proceedings Article | 14 May 2007 Paper

Uniformity studies of inductively coupled plasma etching in fabrication of HgCdTe detector arrays

C. Grein, P. Boieriu, T. S. Lee, K. Tedjojuwono, S. Velicu, R. Bommena

Proceedings Volume 6542, 65420J (2007) https://doi.org/10.1117/12.719350

KEYWORDS: Etching, Mercury cadmium telluride, Plasma, Scanning electron microscopy, Argon, Plasma etching, Photoresist materials, Chemistry, Ions, Surface roughness

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Proceedings Article | 30 August 2004 Paper

LWIR MBE HgCdTe photovoltaic detectors grown on Si composite substrates

Gregory Brill, Nibir Dhar, Silviu Velicu, Priyalal Wijewarnasuriya, Y. P. Chen

Proceedings Volume 5406, (2004) https://doi.org/10.1117/12.541606

KEYWORDS: Mercury cadmium telluride, Long wavelength infrared, Composites, X-rays, Silicon, Selenium, Sensors, Tellurium, Etching, Diffusion

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Proceedings Article | 8 December 2003 Paper

Monolithically integrated HgCdTe focal plane arrays

Silviu Velicu, John Dinan, Y. Chen, Dimitrios Lianos, Renganathan Ashokan, Tae-Seok Lee, Christoph Grein, Paul Boieriu

Proceedings Volume 5209, (2003) https://doi.org/10.1117/12.504038

KEYWORDS: Readout integrated circuits, Mercury cadmium telluride, Silicon, Staring arrays, Metals, Semiconducting wafers, Infrared radiation, Etching, Crystals, Sensors

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Proceedings Article | 10 October 2003 Paper

Composite substrate for large-format HgCdTe IRFPA

Paul Boieriu, Nibir Dhar, Silviu Velicu, Y. Chen, Paul Amirtharaj, Priyalal Wijewarnasuriya, Gregory Brill, Anthony Birdwell

Proceedings Volume 5074, (2003) https://doi.org/10.1117/12.487725

KEYWORDS: Silicon, Mercury cadmium telluride, Long wavelength infrared, Composites, Tellurium, Selenium, Semiconducting wafers, Zinc, X-rays, Sensors

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Proceedings Article | 12 November 2001 Paper

High-temperature HgCdTe/CdTe/Si infrared photon detectors by MBE

Don Rafol, Paul Boieriu, Christoph Grein, Renganathan Ashokan, Silviu Velicu, Sivalingam Sivananthan

Proceedings Volume 4454, (2001) https://doi.org/10.1117/12.448173

KEYWORDS: Mercury cadmium telluride, Infrared detectors, Doping, Infrared radiation, Silicon, Sensors, Diodes, Infrared photography, Photodetectors, Mid-IR

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Proceedings Article | 12 November 2001 Paper

Hg1-xCdxTe(112) nucleation on silicon composite substrates

Paul Boieriu, Nibir Dhar, G. Brill, Y. Chen, Silviu Velicu

Proceedings Volume 4454, (2001) https://doi.org/10.1117/12.448190

KEYWORDS: Mercury cadmium telluride, Long wavelength infrared, Mid-IR, Mercury, Tellurium, Information operations, Silicon, Composites, Diodes, Doping

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Showing 5 of 29 publications

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