CEA and Lynred develop very large focal plane arrays (FPA) in the short wave infrared range (SWIR... more CEA and Lynred develop very large focal plane arrays (FPA) in the short wave infrared range (SWIR) with ultra-low dark current for space and astronomy applications. The structure of such arrays is based on a HgCdTe sensitive layer flipchipped onto a Si ROIC. This ROIC is based on a source follower per detector input and output stage giving access to very high gains for very low flux (below 1ph/s) and very low noise (11.5e-) measurements. However, during previous characterisations, these FPAs appeared particularly sensitive to electro-luminescence emitted by ROIC source follower output stage transistors in the saturation regime. Indeed, the emitted photons are in the sensitive wavelength range of the HgCdTe layer (2.1 μm cut-off). They are then collected by the photodiodes thus degrading the measured dark current. This phenomenon, called ROIC glow, is the limiting mechanism of dark current at low temperature for such arrays. We describe here a solution to reduce to ground level this ...
In the last decade, IR imaging detector trend has gone for smaller pixels and larger formats. Mos... more In the last decade, IR imaging detector trend has gone for smaller pixels and larger formats. Most of the time, this scaling is carried out at given total sensitive area for a single focal plane array (FPA). As an example, QVGA 30µm pitch and VGA 15µm pitch exhibit the exact same sensitive area. SXGA 10µm pitch tends to be very similar as well. This increase in format is beneficial to image resolution. However, this scaling to even smaller pixels raises questions because the pixel size becomes similar to the IR wavelength but also to typical transport dimensions in the absorbing material. Hence, maintaining resolution for such small pixel pitches requires a good control of the modulation transfer function (MTF) and quantum efficiency (QE) of the array, while decreasing the pixel size. This might not be obtained just scaling the pixel dimensions. As an example, bulk planar structures suffer from excessive lateral diffusion length inducing pixel-to-pixel cross talk and thus degrading ...
ABSTRACT In this paper, we report on results obtained both at CEA/LETI and SOFRADIR on p-on-n HgC... more ABSTRACT In this paper, we report on results obtained both at CEA/LETI and SOFRADIR on p-on-n HgCdTe (MCT) grown by liquid phase epitaxy (LPE) Infra-Red Focal Plane Arrays (IR FPAs) for the Long-wave (LW) and the Very-long-wave (VLW) spectral ranges. For many years, p-on-n arsenic-ion implanted planar technology has been developed and improved within the framework of the joint laboratory DEFIR. Compared to n-on-p, p-on-n technology presents lower dark current and series resistance. Consequently, p-on-n photodiodes are well-adapted for very large FPAs operating either at high temperature or very low flux. The long wave (LW) spectral ranges have been firstly addressed with TV/4, 30 µm pitch FPAs. Our results showed state-of-the-art detector performances, consistent with "Rule 07" law [1], a relevant indicator of the maturity of photodiode technology. The low dark current allows increasing the operating temperature without any degradation of the performances. The subsequent development of p-on-n imagers has produced more compact, less energy consuming systems, with a substantial resolution enhancement. Space applications are another exciting but challenging domains and are good candidates for the p-on-n technology. For this purpose, TV/4 arrays, 30 µm pixel pitch, have been manufactured for the very long wave spectral range. For this detection range, the quality of material and reliability of technology are the most critical. Detectors with different cutoff wavelength have been manufactured to aim 12.5 µm at 78K, 12.5 µm at 40K and 15 µm at 78K. Electro-optical characterizations reveal homogeneous imagers with excellent current operabilities (over 99.9% at best). The results highlight the very good quality of p-on-n technology with carrier diffusion limited dark current, fitting the "Rule 07" law, and high quantum efficiency. Further process developments have been made to improve photodiodes performances. Especially the transition temperature where the dark current shifts from diffusion limited regime to another one, has been lowered by more than 10K. Extremely low dark current has been obtained, down to 50 e-/s/pixel.
ABSTRACT Recent advances in miniaturization of IR imaging technology have led to a burgeoning mar... more ABSTRACT Recent advances in miniaturization of IR imaging technology have led to a burgeoning market for mini thermalimaging sensors. Seen in this context our development on smaller pixel pitch has opened the door to very compact products. When this competitive advantage is mixed with smaller coolers, thanks to HOT technology, we achieve valuable reductions in size, weight and power of the overall package. In the same time, we are moving towards a global offer based on digital interfaces that provides our customers lower power consumption and simplification on the IR system design process while freeing up more space. Additionally, we are also investigating new wafer level camera solution taking advantage of the progress in micro-optics. This paper discusses recent developments on hot and small pixel pitch technologies as well as efforts made on compact packaging solution developed by SOFRADIR in collaboration with CEA-LETI and ONERA.
ABSTRACT In this paper recent developments made by the French Atomic Energies and Alternative Ene... more ABSTRACT In this paper recent developments made by the French Atomic Energies and Alternative Energies Commission (CEA) at the Electronics and Information Technology Laboratory (LETI) on the fabrication of planar p-on-n HgCdTe photodiodes are reported. Results obtained on long-wavelength infrared (LWIR) liquid-phase epitaxy (LPE) and mid- and short-wavelength infrared (MWIR/SWIR) molecular beam epitaxy (MBE) have been previously published. For these photodiodes, p-type doping is obtained by arsenic implantation followed by diffusion and activation under Hg-overpressure annealing. The active layer is n-type doped by indium incorporation during growth. Control of the p-on-n junctions is one of the key points of this technology, requiring good knowledge of the arsenic implantation and diffusion and the evolution of implantation-induced defects. Concerning implantation, the impact of dose (from 2 × 1014 at./cm2 to 2 × 1015 at./cm2) and energy (from 50 keV to 500 keV) on As profiles is considered. The profiles after implantation are modeled using Pearson IV moments. Realistic descriptions of arsenic distributions are obtained, and the evolution of moments with implantation conditions is fitted. In addition, implantation damage is examined by transmission electron microscopy (TEM) and the evolution of defects is studied depending on implantation conditions and Hg-overpressure annealing. Previous results obtained on 30-μm-pitch LPE LWIR and MBE MWIR/SWIR showed state-of-the-art detector performance. Since these first results, progress has been made to decrease the pixel pitch to 15 μm and increase the focal-plane array (FPA) format. In this way, 640 × 512 LPE LWIR FPAs have been processed and characterized. In addition we report results obtained on our first p-on-n very long-wavelength infrared (VLWIR) photodiode fabricated at CEA–LETI with λ c = 13.35 μm at 50 K. These latest results demonstrate the viability of our technology and materials.
Multicolor detection capabilities, which bring information on the thermal and chemical compositio... more Multicolor detection capabilities, which bring information on the thermal and chemical composition of the scene, are desirable for advanced infrared (IR) imaging systems. This communication reviews intra and multiband solutions developed at CEA-Leti, from dual-band molecular beam epitaxy grown Mercury Cadmium Telluride (MCT) photodiodes to plasmon-enhanced multicolor IR detectors and backside pixelated filters. Spectral responses, quantum efficiency and detector noise performances, pros and cons regarding global system are discussed in regards to technology maturity, pixel pitch reduction, and affordability. From MWIR-LWIR large band to intra MWIR or LWIR bands peaked detection, results underline the full possibility developed at CEA-Leti.
ABSTRACT The purpose of this paper is to present the latest developments in Defir (LETI / Sofradi... more ABSTRACT The purpose of this paper is to present the latest developments in Defir (LETI / Sofradir joint laboratory) in the field of bi-color and dual band infrared focal plane arrays (FPA) made with HgCdTe. The npn structure is achieved using the Molecular Beam Epitaxy (MBE) technique, planar ion implantation, and both dry and wet etching steps. This back to back diode architecture that allows a perfect spatial coherence with a high field factor and large quantum efficiencies needs only one indium bump connection per pixel. This makes it possible to achieve small pitches (below 25μm) and opens the way to the fabrication of large FPAs (TV/4 to TV) with reasonable wafer sizes. In this paper we present electro optical characterizations of 256x256 prototypes fabricated in Defir operating in two MWIR bands (3.1 and 5μm) with a pitch of 25μm that exhibit background limited performances together with a very high operability (above 99.9%) and NEDT below 22mK for integration time of only 0.5ms. In parallel an industrial product soon available from Sofradir has been developed with a 320x256 format and with a 30μm pitch operating in the same bands. This product exhibits the same operability and NETD as low as 15mK for an integration time as short as 1 ms. Finally, last results regarding 256x256 prototypes operating in MWIR/LWIR bands are presented, together with preliminary APD operating mode for the MWIR photodiodes of this last dual band detector.
Quantum Sensing and Nano Electronics and Photonics XV, 2018
SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, mil... more SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. This is the result of strong and continuous development efforts to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. On one hand the advanced performances of Sofradir product rely on a strong partnership with CEA-LETI materialized in a common laboratory named DEFIR. On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.
High Energy, Optical, and Infrared Detectors for Astronomy VIII, 2018
CEA and Sofradir have been involved for 7 years in studies related to a large format detector dev... more CEA and Sofradir have been involved for 7 years in studies related to a large format detector development for science and astronomy applications. These studies are linked with ESA's Near Infrared Large Format Sensor Array roadmap which aims to develop a 2Kx2K large format low flux low noise device. The ALFA (Astronomical Large Focal plane Array) detector is currently at design, manufacturing and validation phase at CEA and Sofradir. This paper will present the very last achievements of the ALFA development with a specific focus on the readout integrated circuit design itself. Features and specification of the 2048x2048 15μm pitch with Source Follower Detector (SFD) input stage will be described. Apart from ESA development, European Commission is also contributing to the large detector development thanks to ASTEROID (AStronomical TEchnology EuROpean Infrared detector Development) program founded by REA (Research European Agency). ASTEROID main objectives are to develop very large raw materials (CdZnTe substrate, HgCdTe epilayer…) compatible with the manufacturing of very large detectors in volume keeping the same level of performance. Organization and status of this program will be presented where high synergy with 2K² ALFA detector are included.
X-Ray, Optical, and Infrared Detectors for Astronomy IX, 2020
Linked by ESA’s Astronomy Large Format Array for the near-infrared ("ALFA-N") technolog... more Linked by ESA’s Astronomy Large Format Array for the near-infrared ("ALFA-N") technology development program, CEA and Lynred aim at setting up the fabrication of very large IR focal plane arrays (FPA) for astronomy needs. Prior to this project, dark current and image persistence are under investigation for achieving the high level of performance needed by astronomers. During previous characterization of this kind of detector, the FPA appeared particularly sensitive to ROIC electro-luminescence, preventing to observe fainter effects such as persistence. With the mitigation of the glow, the first measurements showed that dark current was dominated by persistence instead of classical diffusion, Auger or ShockleyRead-Hall mechanisms. We propose a dedicated test protocol in order to electrically characterize persistence and an empirical modelling tool to describe it in terms of amplitude and characteristic time constant. The first step consists in removing the residual persistence, allowing to characterize the intrinsic photodiode’s dark current, down to 0.03e-/s at 90K on four tested devices. From this reference, the persistence contribution is dramatically minimized and experimental conditions are reproducible, enabling further investigation on persistence to be carried out. Applied on detectors manufactured in the CEA-LETI clean rooms, this protocol aims at a better understanding of the phenomenon. Using an array containing different diode flavours (ie variations in the technological parameters such as diode geometry, passivation…), the characterization scheme described above should bring information about technological contributions on persistence.
Infrared Sensors, Devices, and Applications VIII, 2018
We report on the development of short wave infrared (SWIR) imaging arrays for astronomy and space... more We report on the development of short wave infrared (SWIR) imaging arrays for astronomy and space observation in Europe. LETI and Sofradir demonstrated 640×480 SWIR HgCdTe (MCT) arrays geared at low flux, low dark noise operation. Currently, we are developing 2048×2048 arrays mated to a newly developed ROIC. In parallel, the European Space Agency and the European Commission are funding the development and industrialization of 4" CdZnTe substrates and HgCdTe epitaxy. These large wafers are needed to achieve the necessary economies of scale and address the need for even larger arrays. HgCdTe SWIR detector performance at LETI/Sofradir is known from previous programs and will be discussed here. However, we will only be able to summarize the features and specifications of the new 2048×2048 detectors which are still at a prototype stage.
CEA and Lynred develop very large focal plane arrays (FPA) in the short wave infrared range (SWIR... more CEA and Lynred develop very large focal plane arrays (FPA) in the short wave infrared range (SWIR) with ultra-low dark current for space and astronomy applications. The structure of such arrays is based on a HgCdTe sensitive layer flipchipped onto a Si ROIC. This ROIC is based on a source follower per detector input and output stage giving access to very high gains for very low flux (below 1ph/s) and very low noise (11.5e-) measurements. However, during previous characterisations, these FPAs appeared particularly sensitive to electro-luminescence emitted by ROIC source follower output stage transistors in the saturation regime. Indeed, the emitted photons are in the sensitive wavelength range of the HgCdTe layer (2.1 μm cut-off). They are then collected by the photodiodes thus degrading the measured dark current. This phenomenon, called ROIC glow, is the limiting mechanism of dark current at low temperature for such arrays. We describe here a solution to reduce to ground level this ...
In the last decade, IR imaging detector trend has gone for smaller pixels and larger formats. Mos... more In the last decade, IR imaging detector trend has gone for smaller pixels and larger formats. Most of the time, this scaling is carried out at given total sensitive area for a single focal plane array (FPA). As an example, QVGA 30µm pitch and VGA 15µm pitch exhibit the exact same sensitive area. SXGA 10µm pitch tends to be very similar as well. This increase in format is beneficial to image resolution. However, this scaling to even smaller pixels raises questions because the pixel size becomes similar to the IR wavelength but also to typical transport dimensions in the absorbing material. Hence, maintaining resolution for such small pixel pitches requires a good control of the modulation transfer function (MTF) and quantum efficiency (QE) of the array, while decreasing the pixel size. This might not be obtained just scaling the pixel dimensions. As an example, bulk planar structures suffer from excessive lateral diffusion length inducing pixel-to-pixel cross talk and thus degrading ...
ABSTRACT In this paper, we report on results obtained both at CEA/LETI and SOFRADIR on p-on-n HgC... more ABSTRACT In this paper, we report on results obtained both at CEA/LETI and SOFRADIR on p-on-n HgCdTe (MCT) grown by liquid phase epitaxy (LPE) Infra-Red Focal Plane Arrays (IR FPAs) for the Long-wave (LW) and the Very-long-wave (VLW) spectral ranges. For many years, p-on-n arsenic-ion implanted planar technology has been developed and improved within the framework of the joint laboratory DEFIR. Compared to n-on-p, p-on-n technology presents lower dark current and series resistance. Consequently, p-on-n photodiodes are well-adapted for very large FPAs operating either at high temperature or very low flux. The long wave (LW) spectral ranges have been firstly addressed with TV/4, 30 µm pitch FPAs. Our results showed state-of-the-art detector performances, consistent with "Rule 07" law [1], a relevant indicator of the maturity of photodiode technology. The low dark current allows increasing the operating temperature without any degradation of the performances. The subsequent development of p-on-n imagers has produced more compact, less energy consuming systems, with a substantial resolution enhancement. Space applications are another exciting but challenging domains and are good candidates for the p-on-n technology. For this purpose, TV/4 arrays, 30 µm pixel pitch, have been manufactured for the very long wave spectral range. For this detection range, the quality of material and reliability of technology are the most critical. Detectors with different cutoff wavelength have been manufactured to aim 12.5 µm at 78K, 12.5 µm at 40K and 15 µm at 78K. Electro-optical characterizations reveal homogeneous imagers with excellent current operabilities (over 99.9% at best). The results highlight the very good quality of p-on-n technology with carrier diffusion limited dark current, fitting the "Rule 07" law, and high quantum efficiency. Further process developments have been made to improve photodiodes performances. Especially the transition temperature where the dark current shifts from diffusion limited regime to another one, has been lowered by more than 10K. Extremely low dark current has been obtained, down to 50 e-/s/pixel.
ABSTRACT Recent advances in miniaturization of IR imaging technology have led to a burgeoning mar... more ABSTRACT Recent advances in miniaturization of IR imaging technology have led to a burgeoning market for mini thermalimaging sensors. Seen in this context our development on smaller pixel pitch has opened the door to very compact products. When this competitive advantage is mixed with smaller coolers, thanks to HOT technology, we achieve valuable reductions in size, weight and power of the overall package. In the same time, we are moving towards a global offer based on digital interfaces that provides our customers lower power consumption and simplification on the IR system design process while freeing up more space. Additionally, we are also investigating new wafer level camera solution taking advantage of the progress in micro-optics. This paper discusses recent developments on hot and small pixel pitch technologies as well as efforts made on compact packaging solution developed by SOFRADIR in collaboration with CEA-LETI and ONERA.
ABSTRACT In this paper recent developments made by the French Atomic Energies and Alternative Ene... more ABSTRACT In this paper recent developments made by the French Atomic Energies and Alternative Energies Commission (CEA) at the Electronics and Information Technology Laboratory (LETI) on the fabrication of planar p-on-n HgCdTe photodiodes are reported. Results obtained on long-wavelength infrared (LWIR) liquid-phase epitaxy (LPE) and mid- and short-wavelength infrared (MWIR/SWIR) molecular beam epitaxy (MBE) have been previously published. For these photodiodes, p-type doping is obtained by arsenic implantation followed by diffusion and activation under Hg-overpressure annealing. The active layer is n-type doped by indium incorporation during growth. Control of the p-on-n junctions is one of the key points of this technology, requiring good knowledge of the arsenic implantation and diffusion and the evolution of implantation-induced defects. Concerning implantation, the impact of dose (from 2 × 1014 at./cm2 to 2 × 1015 at./cm2) and energy (from 50 keV to 500 keV) on As profiles is considered. The profiles after implantation are modeled using Pearson IV moments. Realistic descriptions of arsenic distributions are obtained, and the evolution of moments with implantation conditions is fitted. In addition, implantation damage is examined by transmission electron microscopy (TEM) and the evolution of defects is studied depending on implantation conditions and Hg-overpressure annealing. Previous results obtained on 30-μm-pitch LPE LWIR and MBE MWIR/SWIR showed state-of-the-art detector performance. Since these first results, progress has been made to decrease the pixel pitch to 15 μm and increase the focal-plane array (FPA) format. In this way, 640 × 512 LPE LWIR FPAs have been processed and characterized. In addition we report results obtained on our first p-on-n very long-wavelength infrared (VLWIR) photodiode fabricated at CEA–LETI with λ c = 13.35 μm at 50 K. These latest results demonstrate the viability of our technology and materials.
Multicolor detection capabilities, which bring information on the thermal and chemical compositio... more Multicolor detection capabilities, which bring information on the thermal and chemical composition of the scene, are desirable for advanced infrared (IR) imaging systems. This communication reviews intra and multiband solutions developed at CEA-Leti, from dual-band molecular beam epitaxy grown Mercury Cadmium Telluride (MCT) photodiodes to plasmon-enhanced multicolor IR detectors and backside pixelated filters. Spectral responses, quantum efficiency and detector noise performances, pros and cons regarding global system are discussed in regards to technology maturity, pixel pitch reduction, and affordability. From MWIR-LWIR large band to intra MWIR or LWIR bands peaked detection, results underline the full possibility developed at CEA-Leti.
ABSTRACT The purpose of this paper is to present the latest developments in Defir (LETI / Sofradi... more ABSTRACT The purpose of this paper is to present the latest developments in Defir (LETI / Sofradir joint laboratory) in the field of bi-color and dual band infrared focal plane arrays (FPA) made with HgCdTe. The npn structure is achieved using the Molecular Beam Epitaxy (MBE) technique, planar ion implantation, and both dry and wet etching steps. This back to back diode architecture that allows a perfect spatial coherence with a high field factor and large quantum efficiencies needs only one indium bump connection per pixel. This makes it possible to achieve small pitches (below 25μm) and opens the way to the fabrication of large FPAs (TV/4 to TV) with reasonable wafer sizes. In this paper we present electro optical characterizations of 256x256 prototypes fabricated in Defir operating in two MWIR bands (3.1 and 5μm) with a pitch of 25μm that exhibit background limited performances together with a very high operability (above 99.9%) and NEDT below 22mK for integration time of only 0.5ms. In parallel an industrial product soon available from Sofradir has been developed with a 320x256 format and with a 30μm pitch operating in the same bands. This product exhibits the same operability and NETD as low as 15mK for an integration time as short as 1 ms. Finally, last results regarding 256x256 prototypes operating in MWIR/LWIR bands are presented, together with preliminary APD operating mode for the MWIR photodiodes of this last dual band detector.
Quantum Sensing and Nano Electronics and Photonics XV, 2018
SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, mil... more SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. This is the result of strong and continuous development efforts to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. On one hand the advanced performances of Sofradir product rely on a strong partnership with CEA-LETI materialized in a common laboratory named DEFIR. On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.
High Energy, Optical, and Infrared Detectors for Astronomy VIII, 2018
CEA and Sofradir have been involved for 7 years in studies related to a large format detector dev... more CEA and Sofradir have been involved for 7 years in studies related to a large format detector development for science and astronomy applications. These studies are linked with ESA's Near Infrared Large Format Sensor Array roadmap which aims to develop a 2Kx2K large format low flux low noise device. The ALFA (Astronomical Large Focal plane Array) detector is currently at design, manufacturing and validation phase at CEA and Sofradir. This paper will present the very last achievements of the ALFA development with a specific focus on the readout integrated circuit design itself. Features and specification of the 2048x2048 15μm pitch with Source Follower Detector (SFD) input stage will be described. Apart from ESA development, European Commission is also contributing to the large detector development thanks to ASTEROID (AStronomical TEchnology EuROpean Infrared detector Development) program founded by REA (Research European Agency). ASTEROID main objectives are to develop very large raw materials (CdZnTe substrate, HgCdTe epilayer…) compatible with the manufacturing of very large detectors in volume keeping the same level of performance. Organization and status of this program will be presented where high synergy with 2K² ALFA detector are included.
X-Ray, Optical, and Infrared Detectors for Astronomy IX, 2020
Linked by ESA’s Astronomy Large Format Array for the near-infrared ("ALFA-N") technolog... more Linked by ESA’s Astronomy Large Format Array for the near-infrared ("ALFA-N") technology development program, CEA and Lynred aim at setting up the fabrication of very large IR focal plane arrays (FPA) for astronomy needs. Prior to this project, dark current and image persistence are under investigation for achieving the high level of performance needed by astronomers. During previous characterization of this kind of detector, the FPA appeared particularly sensitive to ROIC electro-luminescence, preventing to observe fainter effects such as persistence. With the mitigation of the glow, the first measurements showed that dark current was dominated by persistence instead of classical diffusion, Auger or ShockleyRead-Hall mechanisms. We propose a dedicated test protocol in order to electrically characterize persistence and an empirical modelling tool to describe it in terms of amplitude and characteristic time constant. The first step consists in removing the residual persistence, allowing to characterize the intrinsic photodiode’s dark current, down to 0.03e-/s at 90K on four tested devices. From this reference, the persistence contribution is dramatically minimized and experimental conditions are reproducible, enabling further investigation on persistence to be carried out. Applied on detectors manufactured in the CEA-LETI clean rooms, this protocol aims at a better understanding of the phenomenon. Using an array containing different diode flavours (ie variations in the technological parameters such as diode geometry, passivation…), the characterization scheme described above should bring information about technological contributions on persistence.
Infrared Sensors, Devices, and Applications VIII, 2018
We report on the development of short wave infrared (SWIR) imaging arrays for astronomy and space... more We report on the development of short wave infrared (SWIR) imaging arrays for astronomy and space observation in Europe. LETI and Sofradir demonstrated 640×480 SWIR HgCdTe (MCT) arrays geared at low flux, low dark noise operation. Currently, we are developing 2048×2048 arrays mated to a newly developed ROIC. In parallel, the European Space Agency and the European Commission are funding the development and industrialization of 4" CdZnTe substrates and HgCdTe epitaxy. These large wafers are needed to achieve the necessary economies of scale and address the need for even larger arrays. HgCdTe SWIR detector performance at LETI/Sofradir is known from previous programs and will be discussed here. However, we will only be able to summarize the features and specifications of the new 2048×2048 detectors which are still at a prototype stage.
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Papers by Olivier Gravrand