Today, one of the main challenges in the quantum infrared detection field is to increase the operating temperature in order to reduce size, weight and power-cost (SWAP). However, this leads to two major issues: an increase in the number of random telegraph signal (RTS) pixels and a residual fixed pattern noise (RFPN) instability. To identify these noise sources and assess the performance of a component, numerous measurements at the operating temperature are necessary, which can be laborious. Nevertheless, there exists a noise quality indicator for detectors at high temperatures known as the Tobin factor. In this paper, our objective is to investigate and understand the relationship between random telegraph signal (RTS) pixels and the Tobin factor. The aim of this study is to evaluate the relevance of the Tobin factor extracted at high temperatures to forecast noise performance at operating temperatures.

The well-known Rule07 is a simple thus efficient way to compare available technologies for IR imaging detectors in terms of dark current. The noise is then often estimated using a shot noise approximation on the dark current. Both II-VI and III-V communities use this rule of thumb as a reference for well-performing IR photodiodes. For HOT applications, a dark current close to this rule07 is considered a necessary condition but not a sufficient one to obtain a high-performance IR imager. Indeed, when limited by shot noise, rule07 describes well the noise behavior of the considered device. However, when considering low-frequency noise, it fails to describe the expected performances. In this paper, we focus on another figure-of-merit, dedicated to detector low-frequency noise rather than dark current. Systemic 1/f noise investigation in an IR detector was first reported by Tobin et al. in 1980. There is today a relative consensus on the fact that measured 1/f noise is proportional to the dark current. The ratio between the amplitude of the 1/f noise and the dark current of the same devices may therefore be used as a figure-of-merit for a given technology. This ratio (called the Tobin factor alpha(T)) therefore appears adequate to compare different technologies as a figure-of-merit qualifying 1/f noise properties. This dimensionless ratio can also be very useful for optimizing a particular technology or process. However, in order to be relevant, this figure-of-merit must be estimated carefully as it appears, for instance, pixel pitch-dependent. Different examples of Tobin coefficient extraction are presented in this paper. We show that, depending on the technologies, the values of the Tobin coefficient can spread over several orders of magnitude. However, only low values result in high-quality IR imagers. Today, the best results we obtained show that alpha(T)=10-5 is a state-of-art value to be compared with.

LYNRED is a leading global provider of high-quality II-VI, III-V and bolometers infrared detectors for the aerospace, defence and commercial markets. Our vision is to preserve and protect, and provide the right technology to customers' needs. To consolidate our position among infrared detector manufacturer leaders and to enable us to respond to growing market demand for next-generation infrared technologies, a new state of the art industrial facility is breaking ground. This new industrial site named Campus will double the current cleanroom footprint and increase production capacity with optimal cleanliness classification for new high-performance products. Among these next generations technologies, Campus will serve the ongoing developments of sub-10 mu m pitch cooled infrared detectors, MCT HOT technology, for extended MW band and III-V HOT MW blue band technology. We will discuss in this paper the true figures of merit that have to be addressed during technology development and optimization to meet field mission requirements. We will then review latest results on II-VI and III-V HOT IDDCA (Integrated Detector Dewar Cryocooler Assembly) with 7.5 mu m pitch SXGA format focal plane array in terms of low frequency noise defects, stability and reproducibility of residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations while maintaining high quantum efficiency to keep highest possible range.

In this work, metal contacts are fabricated on a p-type Hg1−xCdxTe semiconductor, with composition x = 0.30 and acceptor mercury vacancy concentration in the range of 1016 cm−3, by two different technological processes. Depending on the fabrication process, either non-ohmic contacts, with highly nonlinear current–voltage I(V) characteristics, or ohmic contacts are obtained. Different test patterns are measured at variable temperatures down to 77 K. Isolated small-area contacts, comparable to those in focal plane arrays (FPAs), are used to characterize the metal/semiconductor Schottky barrier energy, while transfer length method (TLM) structures are used to estimate the contact specific resistivity of the ohmic contacts. Classical circular TLM (CTLM) patterns are studied and, in addition, new patterns, referred to as variable-width closed TLM (VW-CTLM), are proposed. The linear I(V) characteristics, measured at variable temperatures down to 77 K, demonstrate that high-performance true ohmic contacts on p-type Hg1−xCdxTe can be obtained. To our knowledge, the contact specific resistivity values for these contacts, in the range 0.7–1.8 × 10−4 ohms cm2 at 77 K, are lower than the published state-of-the-art values. The very stable values of contact resistance over the whole temperature range is coherent with a dominant pure tunnel conduction mechanism through the metal/Hg1−xCdxTe barrier. TLM is used to analyze the ohmic contacts, and in some cases is used to obtain useful information even on some of the non-ohmic contacts, which is somewhat unusual and possibly innovative.

One limitation of dark current for HOT HgCdTe MWIR detector is diffusion current related to Auger generation mechanisms. However, this limit can be overcame using a fully depleted P-i-N diode structure. On the way toward PIN structures, we discuss on the impact of Auger suppression on partially fully-depleted photodiodes. Indeed, we report dark current evolution with temperature following a diffusion trend line but also a dark current decreasing when increasing the applied voltage in the temperature range 120-180K on the same detector. If the SRH current in the space charge region is very low, an Auger suppression mechanism should result in a decrease of the total dark current when depleting a larger volume of the pixel on such detector. This hypothesis could match with the reported dark current data obtained on detectors manufactured at CEA LETI and Lynred. They are based on p/n diodes, 7.5μm pitch arrays connected as 2x2 super-pixels to a 15μm pitch ROIC (640x512 VGA format).

LYNRED is oriented towards excellence in II-VI, III-V and bolometers technologies, covering all Society’s needs in term of infrared detection. Our vision is to preserve and protect, and more than ever, our goal is to provide the right technology to the field missions, spatial and industrial applications, and more generally the right technology to customers’ needs. For this purpose we are developing for the next generation pitch, MCT HOT technology, for extended MW band as well as III-V HOT MW blue band technology. Many challenges have to be addressed for future small pitch, large format and HOT detectors. Electrical and optical crosstalks as well as image quality and stability, are one of the prime concern for detectors with pixel pitch below 10μm. We will discuss about the trade-off between the different material properties and detector performances to ensure mandatory minimization of Minimum Resolvable Temperature Difference (MRTD) for range optimization. We will then review latest 7.5μm pitch development at LYNRED, with SXGA formats, based on II-VI and III-V HOT materials, in terms of operability, residual fixed pattern noise (RFPN) and Modulation Transfer Function (MTF) optimizations.

— HgCdTe avalanche photodiode focal plane arrays (FPAs) and single element detectors have been developed for a large scope of photon starved applications. The present communication present the characteristics of our most recent detector developments that opens the horizon for low infrared (IR) photon number detection with high information conservation for imaging, atmospheric lidar and free space telecommunications. In particular, we report on the performance of TEC cooled large area detectors with sensitive diameters ranging from 30- 200 µm, characterised by detector gains of 2- 20 V/µW and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz.

SWAPc (Size, Weight And Power-cost) is a strong trend in IR imaging systems. It requires focal plane arrays with smaller pixels, operating at high temperatures. For MW systems, the full spectral band (up to 5μm) shows a strong advantage over the blue band (4.1µm) as it maximizes the number of incoming photons from a room temperature scene. Few years ago, LETI and Lynred have been developing 7.5μm pitch MCT arrays in MW full band. The first version of this technology was based on n/p diodes operating at 110K maximum temperature. Switching to p/n using extrinsic doping allows today an important gain in dark current, enabling operating temperature up to 130K or even higher. This paper will describe our latest results in the design and fabrication of such HOT small pitch arrays, starting with test chip arrays, followed by the full the characterization of 1280×1024 7.5μm pitch arrays. First order figure of merit (dark current, QE…) are of course considered, but second order figure of merit will also be discussed such as noise tails.

Infrared detectors based on II–VI semiconductors are cooled from room temperature (RT) to cryogenic temperatures between 80 K and 150 K in order to operate with strong requirements regarding sensor performances for infrared detection. At these cryogenic temperatures, the mechanical properties of II–VI alloys have to be known in detail to improve handling, use and lifetime of infrared sensors. We have developed a cryogenic indentation tool and in situ measured the mechanical properties of CdZnTe alloys at both RT and 90 K. CdZnTe hardness increases by a factor of about 3 when cooling from RT to 90 K, from 0.6 GPa to 1.6 GPa. The plastic flow driving mechanism shows at least two different domains with activation energies around 0.01 eV at low temperatures and around 0.05 eV at RT, showing an increase by a factor of about 5. These two domains might be ‘connected’ by an intermediate domain in the 235 K–290 K temperature range. Radial cracks can be in situ detected. Toughness of CdZnTe alloys also increases dramatically by a factor of about 2 with cooling down to cryogenic temperature from 0.13 MPa.m1/2 at RT to 0.25 MPa.m1/2 at 90 K.

HgCdTe (MCT) is a widely used semiconductor material used for manufacturing high-quality infrared detectors. At Sofradir, HgCdTe is grown by liquid phase epitaxy on lattice-matched CdZnTe substrates. Low threading dislocation densities (TDD) in the low 1 × 104 dislocations/cm2 are routinely obtained. Despite these low TDD levels, these dislocations are known to affect the electrical properties of photodiodes. Dislocation electrical behavior needs a deeper understanding in order to improve the manufacturing technology and the photodiode performance. In this study, we use Vickers micro-indentations to inject extra dislocations into dedicated areas of n on p mid-wave infrared photodiodes. The photodiodes were then characterized and analyzed theoretically thanks to I(V) and I(t) measurements under F/3 flux conditions (typical focal plane array illumination) at 110 K. Microindentations were performed close to the photodiodes in order to inject controlled high to very high dislocation densities. The effect of such an injection was then studied in depth on photodiodes. The electrical results have shown that the temporal variation of the current I(t) is mostly affected by the generation of extra dislocations. The same type of degradation of I(t) was observed in focal plane arrays, which confirms that dislocations play an important role in the generation of noise defects.

(111)-oriented CdZnTe semiconductor material exhibits a crystal polarity and hence, a face terminated by Cd atoms, conventionally called (111) A face with an opposite face terminated by Te atoms, called (111) B face. These A and B faces have different properties. Their mechanical properties have been studied by mechanical indentation. Sample surfaces were carefully prepared and mechanically and chemically polished, while the crystalline orientation and material defectivity was monitored on both faces using x-ray rocking curve measurements around the (222) orientation in order to evaluate faces with similar quality. The elastic moduli and hardness values of the A and B faces of CdZnTe were similar. Hardness increased from 0.60 GPa to 0.90 GPa with Zn concentration on the B face as a result of solution strengthening. Crack formation and propagation was carefully studied. Both toughness value and crack resistance were affected by polarity. A model involving plastic dislocation flow is proposed to interpret the results.

Rule07 is very convenient for dark current estimation of high-quality HgCdTe P-on-n photodiodes used in focal-plane arrays for science imaging, in which the diode behavior is dominated by the n-type absorption layer. Its popularity is partly due to the fact that it is very easy to use, while giving an accurate description of the evolution of the dark current with both temperature and cutoff. This modeling is actually the result of an empirical fit to experimental data from Teledyne Imaging Systems (TIS), short-wave infrared (SWIR) data between 300K and 160K, middle-wave infrared (MWIR) data around 80K, and long-wave infrared (LWIR) data above liquid-nitrogen temperature (78K). P-on-n diodes processed at CEA-LETI and SOFRADIR also follow this rule at high temperature and low cutoffs. However, at higher cutoffs (LWIR and very LWIR) and temperatures below 78K, the measured dark current deviates from this rule. Indeed, in this wavelength range, the observed activation energy tends to be lower than the value given by Rule07, closer to the semiconductor gap, which is more physically meaningful. This effect is also consistent with TIS data taken for the first characterizations of LWIR diodes for NEOCam at low temperatures. In this communication, the measured dataset is first presented and then discussed. Then, a new empirical rule describing the dark current of P-on-n HgCdTe diodes is proposed. This relation seems more suitable for this kind of wavelength and temperature (LWIR and VLWIR below 79K) than the well-known Rule07. Hence, Rule07 represents a rough overestimation of the dark current for this range of wavelengths. The new expression should describe the low-temperature dark current in the LWIR and VLWIR regions more accurately.

Extended electrically active defects have been investigated in Short Wave InfraRed (SWIR) HgCdTe n on p photodiodes, using the Deep Level Transient Spectroscopy (DLTS) technique. Three localized defects have been found in the dislocations core or in their close environment. DLTS studies have also been performed before and after indentation, a technique which generates dislocations in the material. DLTS spectra are discussed and dislocations generated by indentation have been found to be electrically active only after annealing.

The Shockley–Read–Hall (SRH) mechanism might be a limiting factor of an infrared (IR) photodiode's dark current. This limitation is twofold. SRH generation might occur in the depletion region of the photodiode. In that case, the corresponding current is usually limiting the low-temperature dark current. Moreover, SRH generation might also occur in the diffusion volume, close to the space charge region, resulting in an increase of the diffusion dark current, usually limiting the high-temperature behavior of the photodiode. Hence, the determination of the SRH lifetime of IR materials is of first importance and has to be measured (or at least estimated) to define upcoming trends in future high-performance IR detectors. During the last few years, a lot of papers have been published about SRH lifetime in III–V materials (InSb, superlattices, InAsSb) and a few other communications have been more focused on comparing different material systems including III–V and II–VI materials. Those latter communications proposed very long SRH lifetimes (longer than ms) for HgCdTe, instead of the classical 10–100 μs usually admitted until now. This paper aims at investigating this SRH lifetime in HgCdTe based on experimental measurements carried out at the Laboratoire d’électronique des technologies de l’information (LETI) on HgCdTe grown in-house. Direct lifetime measurement (photoconductive or photoluminescence decay) as well as indirect estimations from photodiode dark currents are discussed in order to clarify this question of SRH lifetime and its consequences in upcoming advanced IR detection structures. In the end, it appeared that except for p/n extrinsic heterojunctions (for which the narrow gap depleted volume is not well known), most of the devices tested seemed limited by SRH lifetimes in the 10–100-μs range.

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 in-house. 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, 10 mu m pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15 mu m pitch MW at 160K.

Photoluminescence decay (PLD) measurements have been performed on mid-wave infrared (MWIR) Hg-vacancy p-doped HgCdTe samples at temperatures ranging from 85 K to 330 K. The doping level is \(p_{0} = 6 \times 10^{15} \;{\hbox{cm}}^{ - 3}\) at 80 K and the cut-off wavelength is \(\lambda_{\rm{c}} = 4.2\;\upmu{\hbox{m}}\) at 300 K. The PLD signal has been fitted with a photo-injection level dependent model in order to estimate the contributions from the different recombination mechanisms to the total minority carrier lifetime. Shockley–Read–Hall centers lying in the bandgap at 25 meV from the conduction or the valence band has been found to limit the minority carrier lifetime from 85 to at least 200 K. The value of the Auger 1 lifetime coefficient is extracted from the first instants of signal decay for each temperature and reaches \(G_{\rm{eei}} n_{i}^{ - 3} = 5 \times 10^{ - 26} \;{\hbox{cm}}^{6} \;{\hbox{s}}^{ - 1}\) at 85 K. The temperature evolution of the different contributions to the lifetime are in accordance with dark current density measurements in HgCdTe photodiodes.

HgCdTe avalanche photodiode focal plane arrays (FPAs) and single element detectors have been developed for a large scope of photon starved applications. The present communication present the characteristics of our most recent detector developments that opens the horizon for low infrared (IR) photon number detection with high information conservation for imaging, atmospheric lidar and free space telecommunications. In particular, we report on the performance of TEC cooled large area detectors with sensitive diameters ranging from 30-200 mu m, characterised by detector gains of 2-20 V/mu W and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz.

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. As a result, strong and continuous development efforts are deployed 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. The actual trend in quantum IR detector development is the design of very small pixel, with the higher achievable operating temperature whatever the spectral band. Moreover maintaining the detector operability and image quality at higher temperature moreover for long wavelength is a major issue. This paper presents the recent developments achieved at Sofradir to meet this challenge for LW band MCT extrinsic p on n technology with a cut-off wavelength of 9.3μm at 90K. State of the art performances will be presented in terms of dark current, operability and NETD temperature dependency, quantum efficiency, MTF, and RFPN (Residual Fixed Pattern Noise) stability up to 100K.

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. As a result, strong and continuous development efforts are deployed 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.The actual trend in quantum IR detector development is the design of very small pixel, with the higher achievable operating temperature whatever the spectral band. Moreover maintaining the detector operability and image quality at higher temperature moreover for long wavelength is a major issue. This paper presents the recent developments achieved at Sofradir to meet this challenge for LW band MCT extrinsic p on n technology with a cut-off wavelength of 9.3 mu m at 90K. State of the art performances will be presented in terms of dark current, operability and NETD temperature dependency, quantum efficiency, MTF, and RFPN (Residual Fixed Pattern Noise) stability up to 100K.

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. Strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, low excess noise and high operability. The actual trend in quantum IR detector development is the design of very small pixel, with high operating temperature.To maintain the detector performances and operability at high temperature, the number of pixels exhibiting extra noise like 1/f and RTS noise must be limited. This paper presents the recent developments achieved in Sofradir in terms of HOT MCT extrinsic p on n technology, blue MW band (cut-off wavelength of 4.2pm at 150K) and extended MW band (cut-off wavelength of 5.3 mu m at 130K). Comparison between optimized and non-optimized technology will be presented in terms of NETD temperature dependency, MTF, 1/f noise and the corresponding impact on RFPN (Residual Fixe Pattern Noise) and its stability up to 170K will be shown.