Development of small pixel HgCdTe infrared detectors

After approximately half a century of development, HgCdTe infrared detectors have become the first choice for high performance infrared detectors, which are widely used in various industry sectors, including military tracking, military reconnaissance, infrared guidance, infrared warning, weather forecasting, and resource detection. Further development in infrared applications requires future HgCdTe infrared detectors to exhibit features such as larger focal plane array format and thus higher imaging resolution. An effective approach to develop HgCdTe infrared detectors with a larger array format size is to develop the small pixel technology. In this article, we present a review on the developmental history and current status of small pixel technology for HgCdTe infrared detectors, as well as the main challenges and potential solutions in developing this technology. It is predicted that the pixel size of long-wave HgCdTe infrared detectors can be reduced to5 μm, while that of mid-wave HgCdTe infrared detectors can be reduced to 3 μm. Although significant progress has been made in this area, the development of small pixel technology for HgCdTe infrared detectors still faces significant challenges such as flip-chip bonding, interconnection, and charge processing capacity of readout circuits. Various approaches have been proposed to address these challenges, including three-dimensional stacking integration and readout circuits based on microelectromechanical systems.

Improvement of tunnel compensated quantum well infrared detector

To reduce the difficulty of the epitaxy caused by multiple quantum well infrared photodetector(QWIP)with tunnel compensation structure,an improved structure is proposed.In the new structure,the superlattices are located between the tunnel junction and the barrier as the infrared absorption region,eliminating the effect of doping concentration on the well width in the original structure.Theoretical analysis and experimental verification of the new structure are carried out.The experimental sample is a two-cycle device,each cycle contains a tunnel junction,a superlattice infrared absorption region and a thick barrier.The photosurface of the detector is 200×200μm^2 and the light is optically coupled by 45°oblique incidence.The results show that the optimal operating voltage of the sample is-1.1 V,the dark current is 2.99×10^-8A,and the blackbody detectivity is1.352×10^8 cm·Hz^1/2·W^-1at 77 K.Our experiments show that the new structure can work normally.

High quantum efficiency long-/long-wave dual-color type-Ⅱ InAs/GaSb infrared detector

A long-/long-wave dual-color detector with N-M-π-B-π-M-N structure was developed based on a type-Ⅱ InAs/GaSb superlattice. The saturated responsivity was achieved under low bias voltage for both channels. The device could be operated as a single detector for sequential detection and showed high quantum efficiencies. The peak quantum efficiencies of long-wavelength infrared band-1(blue channel) and long-wavelength infrared band-2(red channel) were 44% at 6.3 μm under 20 mV and 57% at 9.1 μm under-60 mV, respectively. The optical performance for each channel was achieved using a 2 μm thickness absorber. Due to the high QE, the specific detectivities of the blue and red channels reached5.0×10^(11) cm·Hz^(1/2)/W at 6.8 μm and 3.1×10^(11) cm·Hz1^(1/2)/W at 9.1 μm, respectively, at 77 K.

Low Crosstalk Three-Color Infrared Detector by Controlling the Minority Carriers Type of InAs/GaSb Superlattices for Middle-Long and Very-Long Wavelength

We report a type-Ⅱ InAs/GaSb superlattice three-color infrared detector for mid-wave （MW）, long-wave （LW）, and very long-wave （VLW） detections. The detector structure consists of three contacts of NIPIN architecture for MW and LW detections, and hetero-junction NIP architecture for VLW detection. It is found that the spectral crosstalks can be significantly reduced by controlling the minority carriers transport via doping beryllium in the two active regions of NIPIN section. The crosstalk detection at MW, LW, and VLW signals are achieved by selecting the bias voltages on the device. At 77K, the cutoff wavelengths of the three-color detection are 5.3μm （at OmV）, 141μm （at 300mV） and 19μm （at -20mV） with the detectivities of 4.6xlO11 cm.Hzl/ZW-1, 2.3×10^10 cm.Hzl/2W-1, and 1.0×10^10cm.Hzl/2W-1 for MW, LW and VLW. The crosstalks of the MW channel, LW channel, and VLW channel are almost 0, 0.25, and 0.6, respectively.

TEM study on Si_(0.65) Ge_(0.35) /p Si HIP infrared detector

Microstructure of P + Si 0.65 Ge 0.35 /p Si HIP infrared detector has been studied by using localization cross section transmission electron microscopy. The photosensitive region of the detector consists of 6 P + Si 0.65 Ge 0.35 layers and 5 UD Si layers, which are flat and have thickness of 6 nm and 32 nm, respectively. A stress field exists on the interface between Si 0.65 Ge 0.35 and UD Si layers, but no any crystal defect has been found in this region, except the edges of this region. Both Si 0.65 Ge 0.35 and UD Si layers on amorphous SiO 2 layer consist of polycrystals and are in wave. There is defect area in the edges of photosensitive region. The area appears in a shape of inverse triangle and the maximum width is less than 120 nm. The crystal defects are stacking faults and microtwins.

High-performance midwavelength infrared detectors based on InAsSb nBn design

we report n Bn photodetectors based on In As0.91 Sb0.09 with a 100% cut-off wavelength of 4.75 μm at 300 K. The band of an n Bn detector is similar to that of a standard pin detector, but there is special wide bandgap Al As0.08 Sb0.92 barrier layer in the n Bn detector, in which the depletion region of n Bn detector exists. The n Bn design has many advantages, such as low dark current and high quantum efficiency, because the n Bn design can suppress the generation–recombination(GR)current that is the main composition of standard pin detector dark current. The constant slope of the Arrhenius plot of J0–1/T indicates the absence of the generation–recombination dark current. We fabricate an n Bn detector with a quantum efficiency(QE) maximum of ~ 60% under-0.2-V bias voltage. The In As Sb n Bn detectors may be a competitive candidate for midwavelength infrared detector.

MODIFICATION OF ABSORPTION SPECTRUM OF GaAs/AlGaAs QUANTUM WELL INFRARED PHOTODETECTOR BY POSTGROWTH ADJUSTMENT

Quantum well intermixing techniques modify the geometric shape of quantum wells to allow postgrowth adjustments.The tuning effect on the optical response property of a GaAs/AlGaAs quantum well infrared photodetector(QWIP) induced by the interdifussion of Al atoms was studied theoretically.By assuming an improvement of the heterointerface quality and an enhanced Al interdiffusion caused by postgrowth intermixings,the photoluminescence spectrum shows a blue-shifted,narrower and enhanced photoluminescence peak.The infrared optical absorption spectrum also shows the expected redshift of the response wavelength.However,the variation in the absorption peak intensity depends on the boundary conditions of the photo generated carriers.For high-quality QWIP samples,the mean free path of photocarriers is long so that the photocarriers are largely coherent when they transport across quantum wells.In this case,the enhanced Al interdiffusion can significantly degrade the infrared absorption property of the QWIP.Special effects are therefore needed to maintain and/or improve the optical properties of the QWIP device during postgrowth treatments.

Development of Low Dark Current SiGe Near-Infrared PIN Photodetectors on 300 mm Silicon Wafers

SiGe offers a low-cost alternative to conventional infrared sensor material systems such as InGaAs, InSb, and HgCdTe for developing near-infrared (NIR) photodetector devices that do not require cooling and can operate with relatively low dark current. As a result of the significant difference in thermal expansion coefficients between germanium (Ge) and silicon (Si), tensile strain incorporated into SiGe detector devices through specialized growth processes can extend their NIR wavelength range of operation. We have utilized high throughput, large-area complementary metal-oxide semiconductor (CMOS) technology to fabricate Ge based p-i-n (PIN) detector devices on 300 mm Si wafers. The two-step device fabrication process, designed to effectively reduce the density of defects and dislocations arising during deposition that form recombination centers which can result in higher dark current, involves low temperature epitaxial deposition of Ge to form a thin p+ seed layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. Phosphorus was then ion-implanted to create devices with n+ regions of various doping concentrations. Secondary ion mass spectroscopy (SIMS) has been utilized to determine the doping profiles and material compositions of the layers. In addition, electrical characterization of the I-V photoresponse of different devices from the same wafer with various n+ region doping concentrations has demonstrated low dark current levels (down to below 1 nA at -1 V bias) and comparatively high photocurrent at reverse biases, with optimal response for doping concentration of 5 × 1019 cm-3.

Development of long-wavelength infrared detector and its space-based application requirements

Infrared detection technology has greatly expanded the ability of mankind to study the earth and the universe. In recent years, the demand for long-wavelength infrared detectors is increasing for their advantages in exploring the earth and the universe. A variety of long-wavelength infrared detectors have been made based on thermal resistive effect, photoelectric effect, etc., in the past few decades. Remarkable achievements have been made in infrared materials, device fabrication,readout circuit, and device package. However, high performance long-wavelength infrared detectors, especially those for large format long-wavelength infrared detector focus plane array, are still unsatisfactory. Low noise, high detectivity, and large format long-wavelength infrared detector is necessary to satisfy space-based application requirements.

Gradient refractive structured NiCr thin film absorber for pyroelectric infrared detectors

A gradient refractive structured NiCr film that has a high extinction coefficient at far infrared range(8-μm–24 μm) is presented as an absorber for pyroelectric infrared detectors. The absorber features high absorption efficiency due to the low reflection off the structured surface and high absorption across the film thickness. The refractive index and extinction coefficient are extracted using spectroscopic ellipsometry. It is found that the single NiCr film exhibits an increasing refractive index as the gas atmosphere pressure increases, hence the three-layer gradient NiCr absorber can be fabricated by adjusting the gas atmosphere pressure during sputtering deposition. Essential Macleod software has been used to generate an efficient film structure design and the calculations show similar absorptance trend compared to the experimental measurement result. The results indicate that the gradient refractive structured metal thin film absorber can provide high absorption for applications in thermal sensing.

MOCVD Ga_xIn_(1-x)As_(1-y)Sb_y Alloys and the Infrared Detector

Ga_xIn_(1-x)As_(1-y)Sb_y alloys have been grown by atmospheric pressure MOCVD on n-GaSb(Te-doped) substrate.The sohd composition was determined by using electron microprobe.The alloys of GalnAsSb with composition in miscibility gap were successfully grown.The optical properties of Ga_xIn_(1-x)As_(1-y)Sb_y lavers were characterized by the photoluminescence and the infrared absorption.The spectral responses of p^+-GaInAsSb/p-Ga_xIn_(1-x)As_(1-y)Sb_y/n-GaSb detectors showed wavelength cut off at 2.4μm and detectivity- D~*=5×10~8 cmHz^(1/2)/W at room temperature.

HREM study on stacking structure of SiGe/Si infrared detector

Stacking structure and defects in SiGe/P Si infrared detector were studied by using localization high resolution electron microscopy (HREM). The photosensitive region in the detector consists of 3 P + Si 0.65 Ge 0.35 layers and 2 UD Si (undoped Si) layers. The interface between Si 0.65 Ge 0.35 and UD Si is not sharp and has a transition zone with non uniform contrast. The misfit stress of interface is distributed gradiently along the normal direction of the interface. Therefore the crystal defects and serious lattice deformations on the interface have not been found. A defect area with a shape of inverted triangle exists in the edge of photosensitive region. The main types of the defects in the area are stacking faults and microtwins. The stacking faults are on (111), and the thickness of the most microtwins is less than 4 interplanar spacing and the twin plane is (111). The Si 0.65 Ge 0.35 and UD Si layers on amorphous SiO 2 layer consist of polycrystals grown by random nucleation, and are in wave.

Modification of ST2L infrared thermo detector and its application in underground coal mines

Infrared thermo detector is a kind of non-contact instrument used to measure the surface temperature of objects. It incorporates high technologies of optics, infrared and electronics, and has been increasingly popularized in China. Firstly, the advantages and shortcomings of ST2L infrared thermo detector were analyzed. Then based on the requirement of detecting buried geological structures in underground coalmines and the features of ST2L, two projects had been studied to modify ST2L: 1) Increasing the resolution of temperature measurements by means of improving the electrical circuit and carrying out field test; 2) Realizing flame protection of ST2L and passing the state-level test and appraisement. In addition, actual application experiments had been carried out for detecting underground buried geological structures (fault, fold, crushing zone, crack, porosity, gas and spontaneous combustion areas, etc.). Some good results have been achieved and valuable conclusions have been drawn.

Wet etching and passivation of GaSb-based very long wavelength infrared detectors

The etching and passivation processes of very long wavelength infrared(VLWIR)detector based on the InAs/GaSb/AlSb type-II superlattice have been studied.By studying the effect of each component in the citric acid solution(citric acid,phosphoric acid,hydrogen peroxide,deionized water),the best solution ratio is obtained.After comparing different passivation materials such as sulfide+SiO_(2),Al_(2)O_(3),Si_(3)N_(4) and SU8,it is found that SU8 passivation can reduce the dark current of the device to a greater degree.Combining this wet etching and SU8 passivation,the of VLWIR detector with a mesa diameter of 500μm is about 3.6Ω·cm^(2) at 77 K.

TEC Colling Shortwave Infrared 320×256 Focal Plane Detector

The short-wave HgCdTe thin film material was grown by liquid phase epitaxy on CdTe substrate,Adopt n on p injection bonding and function and flip-flop mixing process,With a low noise readout circuit,sealed with a high airtightness cellular-metal shell,Using a four-stage Thermo Electric Cooler(TEC),320×256 Short Wave Infrared Focal Plane Cooling Detecto r available to operate at near room temperature(210K).Its main photoelectric performance are signal-to-noise ratio greater than 400,nonuniformity equivalent to 4.69%,operability equivalent to 99.76%,frame rate equivalent to 115Hz,component weight less than 150grams.

A review on MBE-grown HgCdSe infrared materials on GaSb(211)B substrates

We review our recent efforts on developing HgCdSe infrared materials on Ga Sb substrates via molecular beam epitaxy(MBE) for fabricating next generation infrared detectors with features of lower production cost and larger focal plane array format size. In order to achieve high-quality HgCdSe epilayers, ZnTe buffer layers are grown before growing HgCdSe, and the study of misfit strain in ZnTe buffer layers shows that the thickness of ZnTe buffer layer needs to be below 300 nm in order to minimize the generation of misfit dislocations. The cut-off wavelength/alloy composition of HgCdSe materials can be varied in a wide range by varying the ratio of Se/Cd beam equivalent pressure during the HgCdSe growth.Growth temperature presents significant impact on the material quality of HgCdSe, and lower growth temperature leads to higher material quality for HgCdSe. Typically, long-wave infrared HgCdSe(x = 0.18, cut-off wavelength of 10.4 μm at 80 K) presents an electron mobility as high as 1.3×10~5cm^2·V^(-1)·s^(-1), a background electron concentration as low as 1.6×10^(16)cm^(-3), and a minority carrier lifetime as long as 2.2 μs. These values of electron mobility and minority carrier lifetime represent a significant improvement on previous studies of MBE-grown HgCdSe reported in the open literatures,and are comparable to those of counterpart HgCdTe materials grown on lattice-matched CdZnTe substrates. These results indicate that HgCdSe grown at the University of Western Australia, especially long-wave infrared can meet the basic material quality requirements for making high performance infrared detectors although further effort is required to control the background electron concentration to below 10^(15)cm^(-3). More importantly, even higher quality HgCdSe materials on GaSb are expected by further optimizing the growth conditions, using higher purity Se source material, and implementing postgrowth thermal annealing and defect/impurity gettering/filtering. Our results demonstrate the great potential of HgCdSe infrared materials grown on GaSb substrates for fabricating next generation infrared detectors with features of lower cost and larger array format size.

Surface plasmon-enhanced dual-band infrared absorber for VO_x-based microbolometer application

We propose a periodic structure as an extra absorption layer（i.e., absorber） based on surface plasmon resonance effects, enhancing dual-band absorption in both middle wavelength infrared（MWIR） and long wavelength infrared（LWIR）regions. Periodic gold disks are selectively patterned onto the top layer of suspended SiN/VO_2/SiN sandwich-structure.We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak. Simulation results show that the absorber has two absorption peaks at wavelengths λ =4.8 μm and λ = 9 μm with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions, respectively. In addition, the absorber achieves broad spectrum absorption in LWIR region, in the meanwhile, tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk. Thus, this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector, furthermore, the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.

Design of Diode Type Un-Cooled Infrared Focal Plane Array Readout Circuit

The diode infrared focal plane array uses the silicon diodes as a sensitive device for infrared signal measurement. By the infrared radiation, the infrared focal plane can produces small voltage signals. For the traditional readout circuit structures are designed to process current signals, they cannot be applied to it. In this paper, a new readout circuit for the diode un-cooled infrared focal plane array is developed. The principle of detector array signal readout and small signal amplification is given in detail. The readout circuit is designed and simulated by using the Central Semiconductor Manufacturing Corporation （CSMC） 0.5 μm complementary metal-oxide-semiconductor transistor （CMOS） technology library. Cadence Spectre simulation results show that the scheme can be applied to the CMOS readout integrated circuit （ROIC） with a larger array, such as 320×240 size array.

Advantages of QWIP technology in infrared thermal cameras

Standard GaAs/AlGaAs quantum well infrared photodetectors(QWIP)have been seriously considered as atechnological choice for the 3^(rd) generation of thermal imagers in the long wave infrared band(LWIR)for some time.Alternative technology like MCT(HgCdTe)was the technology choice of the 2^(nd) generation because of its high quantum efficiency.In the paper,measurements on the QWIP technology will be presented and a comparison with alternative technology will be done.

Calculate Thermal Infrared Intensity of the Hull’s Military Ship

Stealth technology emphasizes on the reduction in reflection and radiation energies, the surface of target's body in the range of visual, radar, thermal and near IR and so on. Providing solutions to reduce thermal IR intensity radiation is one of the appropriate actions in passive defense for identifying power and targeting enemy. Therefore, questions are brought up: How much is the thermal IR intensity radiation of surface of the hall’s vessel? How much is the effect of each parameter? This thesis tries to provide the software to answer these questions. The provided software measures thermal IR intensity radiation of the surface of the hall’s vessel by the material substance, the temperature of the surface of the hall’s vessel, the situation and characteristic of the thermal detector, noticing the coefficient of environment atmospheric transmittal. This software by changing the effective parameters on thermal IR radiation calculates the thermal radiation on thermal detector in different situations.