Development of IR detectors: NEDT vs era (after Ref. 5).
History of the development of IR detectors and systems. Three generation systems can be considered for principal military and civilian applications: First generation (scanning systems), second generation (staring systems—electronically scanned), and third generation (multicolor functionality and other on-chip functions).
Hybrid IR FPA with independently optimized signal detection and readout: (a) indium bump technique; (b) loophole technique.
Imaging array formats compared with the complexity of microprocessor technology as indicated by transistor count. The timeline design rule of MOS/CMOS features is shown at the bottom (after Ref. 17 with completions). The number of pixels on an IR array has been growing exponentially, in accordance with Moore’s law for 25 years with a doubling time of approximately 19 months (insert of figure—after Ref. 18).
Sixteen HgCdTe SCAs were assembled for the VISTA telescope. The SCAs are attached to a precision ground plate that ensures that all pixels are within of the desired focus. The detectors are ready to be placed in the telescope camera’s vacuum chamber and cooled to 72 K (after Ref. 17).
Trends for design rule minimum and maximum bias voltage of silicon foundry requirements (after Ref. 1).
The photocomposition of a detector array die using array stitching based on photolithographic stepper.
NEDT as a function of detectivity. The effects of nonuniformity are included for , 0.1%, 0.2%, and 0.5%. Note that for , detectivity is not the relevant figure of merit.
Composition and wavelength diagram of Sb-based III-V material systems.
Target and background contrast reversal in the MWIR spectral range (after Ref. 32).
Comparison of the detection and identification range between current second-generation TDI scanned LWIR imagers and the LWIR and MWIR bands of third-generation imager in a format with pixels (after Ref. 33).
Evolution of HgCdTe crystal growth technology from 1958 to present (after Ref. 57).
A time line of the evolution of HgCdTe IR detectors and key developments in process technology which made them possible (after Ref. 57).
Cross sections of -on- homojunction HgCdTe photodiodes formatted by (a) ion implantation into acceptor-doped (usually Hg vacancies) -type LPE film grown by Te-solution slider (Sofradir), (b) ion beam milling, which forms -type islands in -type Hg-vacancy doped layer grown by Te-solution LPE on CdZnTe, and epoxied onto silicon ROIC wafer (cylindrical lateral collection diodes).
DRS’s high-density vertically integrated photodiode (HDVIP™) HgCdTe photodiode (after Ref. 63).
Cross sections of -on- DLHJ HgCdTe photodiodes: (a) mesa structure; (b) planar structure. The active -type regions are sandwiched between CdZnTe substrates and high-doped, wider-gap regions.
Current-voltage characteristics at various temperatures for a cutoff HgCdTe photodiode.
vs cutoff wavelength for RSC’s -on- HgCdTe photodiode data at various temperatures compared to the theoretical 1D diffusion model (after Ref. 69).
The measured (Teledyne Scientific and Imaging) and predicted detectivity of -on- HgCdTe photodiodes as a functions of wavelength and temperature (after Ref. 70). For comparison, the measured detectivities of QDIPs (Refs. 71–79) at 77 K are shown.
Band diagram of demonstrated QWIP structures: (a) bound to extended (after Ref. 83) and (b) bound to miniband. Three mechanisms creating dark current are also shown in (a): ground-state sequential tunneling (1), intermediate thermally assisted tunneling (2), and thermionic emission (3). The gray indicates extended states through which current flows.
In typical photoresponse curves of bound-to-quasibound and bound-to-continuum QWIPs at a temperature of 77 K the dark current (lower left) decreases significantly when the first excited state is dropped from the continuum to the well top, bound-to-quasibound QWIP, without sacrificing the responsivity (upper right). The first excited state now resonating with barrier top produces sharper absorption and photoresponse (after Ref. 84).
Grating light-coupling mechanisms used in QWIPs: (a) gratings with optical cavity, (b) random scatterer reflector, and (c) corrugated QWs.
Quantum efficiency vs wavelength for a HgCdTe photodiode and GaAs/AlGaAs QWIP detector with similar cutoffs.
Current-voltage characteristics of a QWIP detector having a peak response of at various temperatures, along with the 300 K background window current measured at 30 K with an 180° FOV (after Ref. 87).
Current density vs temperature for a HgCdTe photodiode and a GaAs/AlGaAs QWIP with (after Ref. 88).
Peak responsivity, gain (a), and peak detectivity (b) of a low-noise QWIP vs bias voltage (after Ref. 91).
Generalized frequency response of QWIP detector (after Ref. 94).
InAs/GaInSb SLS: (a) band edge diagram illustrating the confined electron and hole minibands which form the energy band gap; (b) change in cutoff wavelength with change in one SL parameter—InAs layer width (after Ref. 96).
Cross section schematic of InAs/GaInSb SL photodiode.
Experimental data and theoretical prediction of the product as a function of temperature for InAs/GaInSb photodiode with cutoff wavelength. The activated trap density is taken as a constant in the simulation over the whole temperature range (after Ref. 104).
Schematic of modified type-II LWIR photodiodes: (a) band profiles at of enhanced WSL (after Ref. 107), (b) SL (band alignment of standard and M shape SLs are shown) (after Ref. 110).
Dependence of the product of InAs/GaInSb SLS photodiodes on cutoff wavelength compared to theoretical and experimental trendlines for comparable HgCdTe photodiodes at 77 K (after Ref. 111).
The predicted detectivity of type-II and -on- HgCdTe photodiodes as functions of wavelength and temperature (after Ref. 70).
Schematic of conventional QD detector structure.
DWELL IR detector: (a) the operation mechanism, (b) experimentally measured spectral tunability by varying well width from 55 to 100 Å (after Ref. 75).
The predicted thermal detectivity vs temperature for various MWIR (a) and LWIR (b) photodetectors. The assumed quantum efficiencies are indicated.
Calculated performance of Auger generation-recombination limited HgCdTe photodetectors as a function of wavelength and operating temperature. BLIP detectivity has been calculated for FOV, the background temperature is , and the quantum efficiency . The calculations have been performed for a doping level equal to . The experimental data are taken for commercially available uncooled HgCdTe photoconductors (produced by Vigo System) and uncooled type-II detectors at the Center for Quantum Devices, Northwestern University. The experimental data for QDIPs are gathered from the marked literature for detectors operated at 200 and 300 K.
Structure of a three-color detector pixel. IR flux from the first band is absorbed in layer 3, while longer wavelength flux is transmitted through the next layers. The thin barriers separate the absorbing bands.
Cross section views of unit cells for various back-illuminated dual-band HgCdTe detector approaches: (a) bias-selectable structure reported by Raytheon (Ref. 145), (b) simultaneous design reported by Raytheon (Ref. 146), (c) simultaneous reported by BAE Systems (Ref. 150), (d) simultaneous design reported by Leti (Ref. 151), (e) simultaneous structure based on -on- junctions reported by Rockwell (Ref. 157), and simultaneous structure based on -on- junctions reported by Leti (Ref. 31).
Raytheon’s two-color FPAs with a TDMI scheme in which the detector bias polarity is alternated many times within a single frame period (after Ref. 147).
Typical characteristics for a single mesa, single indium bump two-color TLHJ unit-cell detector design: (a) MWIR1/MWIR2 pixel with cutoff wavelength at 3.1 and at 77 K and 30° FOV (after Ref. 160) and (b) MWIR/LWIR pixel with cutoff wavelength at 5.5 and (after Ref. 161).
Spectral response curves for two-color HgCdTe detectors in various dual-band combinations of MWIR and LWIR spectral bands (after Ref. 38).
A still camera image taken at 78 K with FOV and 60 Hz frame rate using two-color unit-cell MWIR/LWIR HgCdTe/CdZnTe TLHJ FPA hybridized to a TDMI ROIC (after Ref. 162).
NEDT for a two-color camera having 50 mm, lens, as a function of the operating temperature (after Ref. 163).
Detectivity of two color pseudoplanar simultaneous MWIR/LWIR HgCdTe FPA (after Ref. 157).
Two-color HDVIP architecture is composed to two layers of thinned HgCdTe epoxied to a silicon readout: (a) side view, (b) top view (after Ref. 156), and (c) small hole etched to form junction and to contact the Si readout.
Three-color concept and associated zero-bias band diagram (after Ref. 167).
Idealized spectral responses of three-color detector. Effect of negative and positive bias voltages on band gap structure is also show (after Ref. 167).
Spectral response of a three-color HgCdTe detector with cutoff wavelengths of 3, 4, and at various biases (after Ref. 167).
Schematic representation of the dual-band QWIP detector structure (a) and typical responsivity spectra at 77 K and a common bias of 1 V, recorded simultaneously for two QWIPs at the same pixel (b) (after Ref. 43).
Two-color MWIR/LWIR QWIP FPA: (a) 48 FPAs processed on a 4 in. GaAs wafer, (b) 3D view of pixel structure, (c) electrical connections to the common contact, and (d) the pixel connections are brought to the top of each pixel using the gold via connections (after Ref. 180).
Conduction band diagram of a LWIR and a VLWIR two-color detector (after Ref. 172).
Structure cross section of the interlace dual-band FPA (after Ref. 172).
Schematic of the conduction band in a bound-to-quasibound QWIP. A couple quantum-well structure has been used to broaden the responsivity spectrum (after Ref. 43).
NEDT-histogram of the MWIR (a) and LWIR (b) response of a dual-band QWIP FPA (after Ref. 179).
Images of the scene taken with a dual band QWIP demonstration camera with a 100 mm oprics under severe weather conditions (clowdy sky, outside temperature below in winter, 2 pm). The church tower is at a distance of 1200 m. The left image shows the scene in the MW; the right image shows in the LW (after Ref. 181).
Normalized spectral response of the four-band QWIP FPA (after Ref. 183).
Layer diagram of the four-band QWIP device structure and the deep groove 2D-periodic grating structure. Each pixel represents a area of the four-band FPA (after Ref. 183).
One frame of video image taken with the cutoff four-band QWIP camera. The image is barely visible in the spectral band due to the poor optical transmission of the AR layer coated germanium lens (after Ref. 183).
Detectivities of each spectral-band of the four-band QWIP FPA as a function of temperature. Detectivities were estimated using the single pixel test detector data taken at and 300 K background with optics (after Ref. 183).
SEM images illustrating the processing of dual-color InAs/GaSb SLS FPAs. At a pixel pitch of , three contact lands per pixel permit simultaneous and spatially coincident detection of both colors (after Ref. 42).
Normalized photocurrent at 77 K and the photoluminescence signal at 10 K vs wavelength (after Ref. 42).
Imagers delivered by the dual-color InAs/GaSb SLS camera (after Ref. 42).
Schematic structure of the multispectral QDIP device (after Ref. 185).
Simplified band diagram of the structure shown in Fig. 64 at different bias levels (after Ref. 185).
Multicolor response from a DWELL detector. The MWIR (LWIR) peak is possibly a transition from a state in the dot to a higher (lower) lying state in the well, whereas the VLWIR response is possibly from two quantum-confined levels within the QD. This response is visible until 80 K (after Ref. 123).
Spectral response from a DWELL detector with response at and . Note that the response in the two MWIR and LWIR bands can be measured using this detector. The relative intensities of the bands can be altered by the applied bias (after Ref. 55).
Peak responsivity for a 15 stack DWELL detector at 78 K obtained using a calibrated blackbody source. Solid squares: MWIR responsivity; solid triangles: LWIR responsivity; open square: MWIR detectivity; open triangles: LWIR detectivity (after Ref. 52).
NEDT in the MWIR and LWIR bands at 77 K. Irradiance levels for MWIR and LWIR are and , respectively (after Ref. 54).
Measured optical transmission of a Fabry–Pérot tunable filter fabricated on an HgCdTe photoconductor. Applied filter drive voltages range from 0 to 7.5 V of a Fabry–Pérot filter formed on a detector (after Ref. 189).
General concept of MEMS-based tunable IR detector. The detector is located totally under the bottom mirror.
Dual band adaptive FPA (after Ref. 188).
Measured room temperature spectral transmission of a MEMS tunable filter over a range of actuation voltages demonstrating tuning in the LWIR with broadband transmission in the MWIR (after Ref. 188).
Cutoff wavelength for variations of 0.1% and the corresponding cutoff wavelength shift for at 77 K.
Summary of the material properties for the ternary alloy, listed for the binary components HgTe and CdTe, and for several technologically important alloy compositions (after Ref. 56). and calculated for -type HgCdTe with . The last four material properties are independent of or relatively insensitive to alloy composition
Some physical properties of narrow gap semiconductors.
Comparison of the various methods used to grow HgCdTe (after Ref. 57).
Essential properties of LWIR HgCdTe and type-II SL photodiodes and QWIPs at 77 K.
Typical measured performance parameters for single- and dual-color HgCdTe MWIR and LWIR detector configurations for unit-cell FPAs (after Ref. 148).
Performance summary of three best MW/LW FPAs fabricated to date (after Ref. 36).
Performance data of two-color MW/LW and MW/MW HgCdTe FPAs: optics, 60 Hz frame rate (after Ref. 61).
Specification of the dual band QWIP FPAs. (a) AIM Infrarot-Module GmbH (after Ref. 42). (b) QmagiQ LLC (after Ref. 181).
Key characteristics of the dual-color SL IR-module (after Ref. 184).
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