Type-II Superlattice (T2SL) detectors have revolutionized the field of infraredimaging, establishing themselves as the forefront technology in defense, space,and industrial applications. These detectors enable larger formats and higheroperating temperatures (HOT) that minimize the need for bulky and energyconsumingcryogenic cooling, paving the way for imaging systems with reducedSize, Weight, and Power (SWaP).Their versatility across various IR wavebands—long-wavelength, midwavelength,and extended short-wavelength—combined with the intrinsicscalability characteristic of III-V detectors, positions T2SL technology as the idealchoice for next-generation HOT and high-resolution (HD) detectors.This thesis focuses on improving the manufacturing process for T2SL arrays toreduce surface leakage currents induced during pixel etching. This challengebecomes more pronounced with smaller pixels and directly affects the maximumoperating temperature.The investigation into T2SL detector performance provides comprehensiveinsights into the detectors' electrical characteristics. This includes 1/f noiseanalysis and a detailed experimental and quantitative modeling of surface leakagecurrents, proposing strategies for their reduction. Furthermore, the study delvesinto light-matter interactions within focal plane arrays (FPAs) to describe opticalconcentration effects to increase the sensitivity and provides Modulation transferfunction measurements and simulations to discuss the resolution of T2SL arrays.Employing diverse Sb-based T2SL detector photodiode structures, this thesisreports significant progress in the fabrication process, leading to remarkableachievements. These include the demonstration and industrial production of a640 × 512 – 15 μm format FPA operating at 150 K; the production of 10, 7.5,and 5 μm pitch arrays, all capable of functioning at 150 K; and the demonstrationof small-pitch HD FPAs, with the capability of operating at 150K.

Typ-II Supergitter (T2SL) detektorer har revolutionerat fältet för infraröd (IR)avbildning och etablerat sig som spetsteknologi inom försvar, rymd ochindustriella tillämpningar. Dessa detektorer möjliggör större format och högrearbetstemperaturer (HOT) som minskar behovet av plats- och energikrävandekryogen kylning, vilket banar väg för IR-kameror med minskad Storlek, Vikt ochEnergiåtgång (SWaP).Deras mångsidighet över olika IR-våglängdsband—långvåg, mellanvåg ochkortvåg—kombinerat med den inneboende skalbarheten som är karakteristisk förIII-V material, positionerar T2SL-teknologin som det ideala valet för nästagenerations HOT och högupplösta (HD) detektorer.Denna avhandling fokuserar på att förbättra tillverkningsprocessen för T2SLdetektormatriserför att minska ytströmmar som uppstår vid pixeletsning. Dennautmaning växer med minskad pixelstorlek och påverkar direkt en detektorsmaximala arbetstemperatur.Genom att betrakta T2SL-detektorernas prestanda ges omfattande insikter idetektorernas elektriska egenskaper. Detta inkluderar analys av 1/f-brus och endetaljerad experimentell och kvantitativ modellering av ytströmmar, samt förslagpå strategier för att reducera dessa. Vidare går studien in på fenomenet av optiskkoncentration som uppstår i fokalplansmatriser (FPAer) och resulterar i ett ökatsignal-brusförhållande. Slutligen analyseras graden av optiska och elektriskaläckage mellan närliggande pixlar genom mätning och simulering avmoduleringsöverföringsfunktionen.Denna avhandling presenterar betydande framsteg i tillverkningsprocessen hosflera olika T2SL-detektorstrukturer vilket resulterat i anmärkningsvärda stegframåt för IR-detektorteknologin. Dessa inkluderar industriell produktion avFPAer med 640 × 512 pixlar med 15 μm:s pixelstorlek och med enarbetstemperatur på 150 K; produktionen av detektormatriser med 10, 7.5, och 5μm pixel-till-pixelavstånd, alla kapabla att fungera vid 150 K; och demonstrationav HD FPAer, med förmåga att fungera vid 150 K.

The modulation transfer function (MTF) in fully delineated 15 μ m pitch type-II superlattice (T2SL) mid-wave infrared (IR) detectors is studied theoretically and experimentally. Theoretically, a 2-D model to simulate the spot scan (SS) profile is presented and used to compute the MTF as a function of the wavelength and the array geometry (pitch size, trench width). The dependence of the detector trench on the MTF is also evaluated experimentally by the edge spread function (ESF) method according to the ISO12233 standard. The experimental results show an excellent agreement with the theoretical model, reporting an MTF of 0.61 and 0.60 at the Nyquist frequency for 1 and 2 μ m trench, respectively. With the simulation model, the effect of the increased optical crosstalk for smaller pixel pitch is discussed as a function of the trench width (0.5, 1, and 2 μ m) and incidence angle up to ± 30 ∘ . Simulation results show MTF values at the Nyquist frequency between 0.61–0.62, 0.58–0.60, and 0.55–0.57 with an average degradation of 1%, 2%, and 7% at an angle of ± 30 ∘ compared to normal incidence for the 10, 7.5, and 5 μ m pitch, respectively.

This work investigates the potential of InAs/GaSb superlattice detectors for the short -wavelength infrared spectral band. A barrier detector structure was grown by molecular beam epitaxy and devices were fabricated using standard photolithography techniques. Optical and electrical characterisations were carried out and the current limitations were identified. The authors found that the short diffusion length of similar to 1.8 mu m is currently limiting the quantum efficiency (double-pass, no anti-reflection coating) to 43% at 2.8 mu m and 200 K. The dark current density is limited by the surface leakage current which shows generation-recombination and diffusion characters below and above 195 K, respectively. By fitting the size dependence of the dark current, the bulk values have been estimated to be 6.57 center dot 10(-6)A/cm(2) at 200 K and 2.31 center dot 10(-6) A/cm(2) at 250 K, which is only a factor of 4 and 2, respectively, above the Rule07.

The dependence of quantum efficiency (QE) on fill factor and pixel pitch is studied theoretically and experimentally in fully delineated type-II superlattice (T2SL) detectors. Theoretically, a 2-dimensional simulation model is used to compute the absorption in the array geometry, which shows an insensitivity of the optical response to the fill factor. This is a result of the photodiode array (PDA) geometry concentrating the light in the pixel area. QE measurements on PDAs with varying pixel pitch (from 225 to 10 μm) and fill factors (from 98% to 64%) confirm this independence of the QE on the fill factor and results in a 50% increase in the photocurrent density in 10 μm pitch PDAs compared to 225 μm pitch PDAs. Furthermore, measurements of the dark current density vs pixel size revealed an absence of surface leakage in these PDAs, which, combined with the increased photocurrent density results in an improved signal-to-noise ratio when reducing the pitch in these T2SL detectors. Finally, this result resolves the QE-modulation transfer function trade-off, as the electrical isolation of the pixel is carried out without impacting the QE of the array.

This work investigates the potential of p-type InAs/GaSb superlattice for the fabrication of full mid-wave megapixel detectors with n-on-p polarity. A significantly higher surface leakage is observed in deep-etched n-on-p photodiodes compared to p-on-n diodes. Shallow-etch and two-etch-step pixel geometry are demonstrated to mitigate the surface leakage on devices down to 10 mu m with n-on-p polarity. A lateral diffusion length of 16 mu m is extracted from the shallow etched pixels, which indicates that cross talk could be a major problem in small pitch arrays. Therefore, the two-etch-step process is used in the fabrication of 1280 x 1024 arrays with a 7.5 mu m pitch, and a potential operating temperature up to 100 K is demonstrated.

The surface leakage in InAs/GaSb type-II superlattice (T2SL) is studied experimentally and theoretically for photodiodes with small sizes down to 10 x 10 mu m(2). The dependence of dark current density on mesa size is studied at 110 and 200 K, and surface leakage is shown to impact both generation-recombination (GR) and diffusion dark current mechanisms. A quasi-3-dimensional model to simulate the fabrication process using surface traps on the pixel's sidewall is presented and is used to accurately represent the dark current of large and small pixels with surface leakage in the different temperature regimes. The simulations confirmed that the surface leakage current has a GR and diffusion component at low and high temperature, respectively. Finally, the surface leakage current has been correlated with the change in minority carrier concentration at the surface due to the presence of donor traps.

Herein, results from noise and dark current density studies on InAs/GaSb type-II superlattice IR detectors are presented. The activation energy of the dark current density is used to identify the dominating dark current mechanisms (generation–recombination (GR), tunneling, or diffusion dark current) as a function of temperature and bias. The bias evolution of the power spectral density (PSD) is measured in dark conditions for several temperatures. At the operating bias of the detectors, the arrays show a white noise–dominated spectrum up to 100 K with a minor 1/f contribution (corner frequency around 10 Hz), while for higher temperatures the spectra are 1/f dominated. The 1/f noise component is compared to the dominating dark current mechanism in the same temperature and bias regimes. A strong correlation between the 1/f noise component and the dominating dark current (I) is found, with the PSD proportional to I for tunneling currents and I2 for GR and diffusion currents. Very low noise coefficients of αGR = 4.8 × 10−9 Hz−1, αdiff = 1.9 × 10−10 Hz−1, and αtun = 2.1 × 10−16 A Hz−1 are observed for these detectors. 

In 2019, IRnova launched a full-scale production of a reduced size, weight and power integrated detector dewar cooler assemblies (Oden MW; VGA format with 15 μm pixel pitch) covering the full mid-wavelength infrared spectral domain (3.7 μm - 5.1 μm). Oden MW exhibits excellent performance with operating temperatures up to 110 K at F/5.5 with typical values of temporal and spatial noise equivalent temperature of 22 mK and 7 mK, respectively, and an operability higher than 99.85%. More recently, IRnova developed a new detector design with a cut-off wavelength of 5.3 μm which can potentially allow an operating temperature of the detector up to 150K with excellent performance demonstrated on single pixels with a quantum efficiency as high as 46% at 4 μm without antireflection coating, a turn on bias lower than -100 mV and a dark current density as low as 8 × 10-6 A/cm2, which is a factor of < 5 higher than Rule07. The dark current was also found independent of the device size ranging from 10 μm to 223 μm indicating that surface leakage currents are not limiting the dark current. The achievable operating temperature of an FPA made of this new detector design has been estimated to be <150 K with F/5.5 optics. These outstanding results demonstrate that this new generation of detector design is an excellent candidate for future high operating temperature and high-definition focal plane array.

In this paper, results from the development of InAs/GaSb superlattice focal plane arrays (FPAs) at IRnova will be presented. A versatile and robust detector design is used that allows for adjustment of the detection cut-off wavelength from 2.5 mu m up to 14.5 mu m with only minor changes in the detector design. Performance of the fabricated detectors has been reviewed in terms of external quantum efficiency (EQE), dark current and noise for three designs with cut-off wavelengths of 4, 5.5 and 11 mu m at 80 K (referred to as DEEP BLUE, RED HOT and VLWIR, respectively). Measurements on the 15 mu m sized photodiodes demonstrated 70 % EQE for the MWIR designs, and almost 40 % for VLWIR. At the same time, the dark current stayed close to the Rule07 benchmark for all studied samples. Noise mechanisms have been discussed and their relation to the passivation was examined. Mature in-house processing and passivation technique resulted in very high spatial uniformity of VGA focal plane arrays (FPAs), i.e. low relative deviations of EQE (< 6 %) and of dark current density (< 12 %), and narrow noise distributions for both RED HOT and DEEP BLUE FPAs. We show also that >99.5 % of these arrays operate close to the fundamental noise limit.