Residual fixed pattern noise and random telegraph signal noise of a MWIR T2SL focal plane array

International audienceStability over time has recently become a figure of merit of major importance to compare the performances of infrared focal plane arrays (FPA) of different technologies. Indeed, this parameter dictates how often the calibration of operational electro-optical systems has to be done, and thus reflects the availability of the system during an operational mission. The stability over time is generally estimated through fixed pattern noise (FPN) and residual fixed pattern noise (RFPN) measurements after a two-point correction. However, each laboratory or industrial has its own protocols and criteria, such that published results cannot be easily compared. Recent studies also showed that random telegraph signal (RTS) noise, which leads to flickering pixels, can strongly affect the image quality, so the question arises as to wether these RTS pixels have an effect on RFPN. In this paper, we describe our experimental protocol to evaluate the stability over time of an FPA and to count up/classify flickering pixels. We then present the results obtained on a T2SL MWIR Integrated Detector Dewar Cooler Assembly (IDDCA) provided by IRnova. Our measurements show that the stability over time of the T2SL MWIR IDDCA are excellent: first, in terms of FPN/RFPN; then, in terms of RTS noise with only a few blinking pixels. We also show that the RTS pixels having an effect on the RFPN are fully detected by the algorithm used to rule out defective pixels before calculating RFPN

New architectures for infrared superlattices detector

Cette thèse effectuée au sein de l’équipe DOTA de l’ONERA Palaiseau, en collaboration étroite avec l’IES de l’Université de Montpellier, porte sur l’étude et la caractérisation électro-optique de détecteurs infrarouge à super-réseaux (SR).L’objectif était d’améliorer la compréhension du fonctionnement de l’architecture à « bariode » qui permet de réduire le courant d’obscurité du photodétecteur comparée à l'architecture classique PIN. Mes travaux se sont d’abord portés sur la viabilité de la filière pour le fonctionnement à haute température, par l’évaluation de deux critères essentiels sur un détecteur SR commercial refroidi à 80K : les pixels clignotants et leur impact sur la stabilité temporelle. L’étude montre un faible nombre de pixels clignotants et un impact limité. J’ai ensuite développé un banc cryogénique de caractérisation électro-optique pour des monoéléments SR InAs/GaSb LWIR 80K et SR InAs/InAsSb MWIR 150K. L’étude des monoéléments LWIR a montré des performances encourageantes, mais l’évaluation de son rendement quantique a été rendue difficile à cause d’une gravure particulière (dite « shallow-etch ») qui nécessite de prendre en compte une surface supplémentaire due à la diffusion latérale des porteurs photogénérés. C’est pourquoi, une démarche plus fine a été mise en place pour l’étude du SR InAs/InAsSb. Cette démarche m’a ensuite permis d’extraire les longueurs de diffusion des porteurs et d’en déduire les mobilités associées. Les valeurs extraites montrent que le transport par minibande, caractéristique fondamentale des SR, ne se fait pas à cause de mécanismes de diffusion élastiques. L’ensemble des résultats nous a permis d’établir une méthodologie standard d’étude et d’optimisation des bariodes SR et de confirmer la potentialité de la filière à haute température.This thesis, carried out in the DOTA team of ONERA Palaiseau, in close collaboration with the IES of the University of Montpellier, deals with the study and the electro-optical characterization of superlattices infrared detectors (SL).The objective was to improve the understanding of the operation of the "bariode" architecture (instead of the PIN diode) in order to reduce the dark current of the photodetector. My work first focused on the reliability for high temperature operation, by evaluating two key criteria on a commercial SL detector cooled at 80K: blinking pixels and their impact on the temporal stability. The study shows a low number of blinking pixels and a limited impact. I then developed a cryogenic bench for electro-optical characterization for the SL InAs/GaSb LWIR 80K and the SL InAs/InAsSb MWIR 150K monoelements. The study of LWIR monoelements showed encouraging performances, but the evaluation of its quantum efficiency was made difficult because of a particular etching (called "shallow-etch") which requires to take into account an additional surface due to the lateral diffusion of the photogenerated carriers. This is why a more detailed approach was implemented for the study of the SL InAs/InAsSb. This approach allowed me to extract the diffusion lengths of the carriers and to deduce the associated mobilities. The extracted values show that the miniband transport, a fundamental characteristic of SLs, does not occur because of elastic scattering mechanisms. All the results allowed us to establish a standard methodology for the study and optimization of SL bariodes and to confirm their potentiality for high temperature operation

Nouvelles architectures de détecteurs infrarouge à super-réseaux

This thesis, carried out in the DOTA team of ONERA Palaiseau, in close collaboration with the IES of the University of Montpellier, deals with the study and the electro-optical characterization of superlattices infrared detectors (SL).The objective was to improve the understanding of the operation of the "bariode" architecture (instead of the PIN diode) in order to reduce the dark current of the photodetector. My work first focused on the reliability for high temperature operation, by evaluating two key criteria on a commercial SL detector cooled at 80K: blinking pixels and their impact on the temporal stability. The study shows a low number of blinking pixels and a limited impact. I then developed a cryogenic bench for electro-optical characterization for the SL InAs/GaSb LWIR 80K and the SL InAs/InAsSb MWIR 150K monoelements. The study of LWIR monoelements showed encouraging performances, but the evaluation of its quantum efficiency was made difficult because of a particular etching (called "shallow-etch") which requires to take into account an additional surface due to the lateral diffusion of the photogenerated carriers. This is why a more detailed approach was implemented for the study of the SL InAs/InAsSb. This approach allowed me to extract the diffusion lengths of the carriers and to deduce the associated mobilities. The extracted values show that the miniband transport, a fundamental characteristic of SLs, does not occur because of elastic scattering mechanisms. All the results allowed us to establish a standard methodology for the study and optimization of SL bariodes and to confirm their potentiality for high temperature operation.Cette thèse effectuée au sein de l’équipe DOTA de l’ONERA Palaiseau, en collaboration étroite avec l’IES de l’Université de Montpellier, porte sur l’étude et la caractérisation électro-optique de détecteurs infrarouge à super-réseaux (SR).L’objectif était d’améliorer la compréhension du fonctionnement de l’architecture à « bariode » qui permet de réduire le courant d’obscurité du photodétecteur comparée à l'architecture classique PIN. Mes travaux se sont d’abord portés sur la viabilité de la filière pour le fonctionnement à haute température, par l’évaluation de deux critères essentiels sur un détecteur SR commercial refroidi à 80K : les pixels clignotants et leur impact sur la stabilité temporelle. L’étude montre un faible nombre de pixels clignotants et un impact limité. J’ai ensuite développé un banc cryogénique de caractérisation électro-optique pour des monoéléments SR InAs/GaSb LWIR 80K et SR InAs/InAsSb MWIR 150K. L’étude des monoéléments LWIR a montré des performances encourageantes, mais l’évaluation de son rendement quantique a été rendue difficile à cause d’une gravure particulière (dite « shallow-etch ») qui nécessite de prendre en compte une surface supplémentaire due à la diffusion latérale des porteurs photogénérés. C’est pourquoi, une démarche plus fine a été mise en place pour l’étude du SR InAs/InAsSb. Cette démarche m’a ensuite permis d’extraire les longueurs de diffusion des porteurs et d’en déduire les mobilités associées. Les valeurs extraites montrent que le transport par minibande, caractéristique fondamentale des SR, ne se fait pas à cause de mécanismes de diffusion élastiques. L’ensemble des résultats nous a permis d’établir une méthodologie standard d’étude et d’optimisation des bariodes SR et de confirmer la potentialité de la filière à haute température

Temperature Dependence Study of Electrical and Electro-Optical Performances of Midwave Infrared Ga-Free T2SL Barrier Photodetector

In this paper, we report on temperature dependence performances of a midwave infrared (MWIR) Ga-free InAs/InAsSb type-II superlattice (T2SL) barrier (XBn) photodetector grown by molecular beam epitaxy on n-type GaSb substrate. The T2SL structure, with a 3 µm thick active region, was processed in a mesa device in order to perform dark current measurements and spectral photoresponse as a function of temperature. Analyses of these temperature dependence characterizations help us to improve the design of Ga-free T2SL MWIR XBn detectors

Electro-optical performance and anisotropic transport study of a Ga-free type-II superlattice barrier structure

In the past ten years, InAs/InAsSb type-II superlattice has emerged as a promising technology for high-temperature mid-wave infrared photodetector. Nevertheless, transport properties are still poorly understood in this type of material. In this paper, optical and electro-optical measurements have been realised on InAs/InAsSb type-II superlattice midwave infrared photodetectors. Quantum efficiency of 50% is measured at 150 K, on the front side illumination and simple pass configuration. Absorption measurement, as well as lifetime measurement are used to theoretically calculate the quantum efficiency thanks to Hovel’s equation. Diffusion length values have been extracted from this model ranging from 1.55 μm at 90 K to 7.44 μm at 200 K. Hole mobility values, deduced from both diffusion length and lifetime measurements, varied from 3.64 cm²/Vs at 90 K to 37.7 cm²/Vs at 200 K. The authors then discuss the hole diffusion length and mobility variations within temperature and try to identify the intrinsic transport mechanisms involved in the superlattice structure

Influence of Pixel Etching on Electrical and Electro-Optical Performances of a Ga-Free InAs/InAsSb T2SL Barrier Photodetector for Mid-Wave Infrared Imaging

International audienceIn this paper, the influence of etching depth on the dark current and photo-response of a mid-wave infrared Ga-free T2SL XBn pixel detector is investigated. Two wet chemical etching depths have been considered for the fabrication of a non-passivated individual pixel detector having a cut-off wavelength of 5 µm at 150 K. This study shows the strong influence of the lateral diffusion length of a shallow-etched pixel on the electro-optical properties of the device. The lowest dark current density was recorded for the deep-etched detector, on the order of 1 × 10−5 A/cm2 at 150 K and a bias operation equal to −400 mV. The corresponding quantum efficiency was measured at 60% (without anti-reflection coating) for a 3 µm thick absorbing layer. A comparison of experimental results obtained on the two kinds of etched pixels demonstrates the need for a deep-etching process combined with efficient passivation for FPA manufacturing