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State-of-the-art Hg1−xCdxTe multilayer structures grown by molecular beam epitaxy on (211)-oriented Cd1−yZnyTe substrates have been characterized and their strain and relaxation analyzed. Techniques for measuring lattice mismatch, strain, and crystal quality by measuring symmetric and asymmetric diffraction profiles in different azimuths were adapted and performed in combination with dislocation delineation for full-wafer and multilayer characterization. It was found that the degree of lattice mismatch and in turn the strain state of epitaxial multilayers can be made uniform across full wafers in optimized structures. A strong correlation was revealed between the Zn composition of the Cd1−yZnyTe substrates and the crystal quality of the active layers in the multilayer structures. This method can be generalized to optimize multilayer structures to minimize relaxation by the generation of extended defects.

A major limitation hindering the widespread use of synthetic phages in medical and industrial settings is the lack of an efficient phage-engineering platform. Classical T4 phage engineering and several newly proposed methods are often inefficient and time consuming and consequently, only able to produce an inconsistent range of genomic editing rates between 0.03–3%. Here, we review and present new understandings of the CRISPR/Cas9 assisted genome engineering technique that significantly improves the genomic editing rate of T4 phages. Our results indicate that crRNAs selection is a major rate limiting factor in T4 phage engineering via CRISPR/Cas9. We were able to achieve an editing rate of > 99% for multiple genes that functionalizes the phages for further applications. We envision that this improved phage-engineering platform will accelerate the fields of individualized phage therapy, biocontrol, and rapid diagnostics.

In this work, impurity ‘hot spot’ macro-defects—high impurity level macro-defect contaminates were examined. ‘Hot spots’ have very high localized concentrations of: K, Mg, Ni, Cr, Mn, Ca, Al, Na, Fe, and Cu. For example, these ‘hot spot’ macro-defects can have Cu concentrations > 1 × 1018 cm−3. Focused ion beam scanning transmission electron microscopy analysis of four ‘hot spots’ was performed. The origin of ‘hot spot’ defects is unresolved—however, our analysis has shown ‘hot spots’ can arise due to molecular beam epitaxy spit defects and CdZnTe substrate defects. The estimated ‘hot spot’ density is ∼ 30 cm−2. The presence of impurity ‘hot spot’ macro-defects in HgCdTe/CdZnTe is confirming evidence for the occurrence of L. Bubulac’s impurity ‘pipe’ mechanism.

Mercury cadmium telluride (HgCdTe, or MCT) with low n-type indium doping concentration offers a means for obtaining high performance infrared detectors. Characterizing carrier transport in materials with ultra low doping (ND = 1014 cm−3 and lower), and multi-layer material structures designed for infrared detector devices, is particularly challenging using traditional methods. In this work, Hall effect measurements with a swept B-field were used in conjunction with a multi-carrier fitting procedure and Fourier-domain mobility spectrum analysis to analyze multi-layered MCT samples. Low temperature measurements (77 K) were able to identify multiple carrier species, including an epitaxial layer (x = 0.2195) with n-type carrier concentration of n = 1 × 1014 cm−3 and electron mobility of μ = 280000 cm2/Vs. The extracted electron mobility matches or exceeds prior empirical models for MCT, illustrating the outstanding material quality achievable using current epitaxial growth methods, and motivating further study to revisit previously published material parameters for MCT carrier transport. The high material quality is further demonstrated via observation of the quantum Hall effect at low temperature (5 K and below).

Ultra-low-doped mercury cadmium telluride (HgCdTe, or MCT) is of significant interest for infrared detectors designed to suppress Auger recombination. Measurement of low doping levels in multi-layered structures is difficult with traditional 4-point Hall effect measurements. Multi-layered Hg.79Cd.21Te samples were analyzed using variable magnetic field Hall effect measurements and a multi-carrier fitting procedure. The measurements resolve two distinct carrier species corresponding to surface and/or buffer layer conduction and conduction through the primary low-doped material. High-quality electronic transport is achieved, including the demonstration of an epitaxial layer (x = 0.2195) with n = 1.09 × 1014 cm−3 and μ = 275,000 cm2/Vs at 77 K. This technique shows promise as a way to analyze layers with significantly lower doping, and a starting point to understand and advance the development of HgCdTe epilayers with very low doping concentration.

We review recent advances in the HgCdTe material quality and detector performance achieved at Teledyne using molecular beam epitaxy growth and the double-layer planar hetero-junction (DLPH) detector architecture. By using an un-doped, fully depleted absorber, Teledyne’s DLPH architecture can be extended for use in high operating temperatures and other applications. We assess the potential achievable performance for long wavelength infrared (LWIR) hetero-junction p-lightly-doped n or p-intrinsic-n (p-i-n) detectors based on recently reported results for 10.7 μm cutoff 1 K × 1 K focal plane arrays (FPAs) tested at temperatures down to 30 K. Variable temperature dark current measurements show that any Shockley–Read–Hall currents in the depletion region of these devices have lifetimes that are reproducibly greater than 100 ms. Under the assumption of comparable lifetimes at higher temperatures, it is predicted that fully-depleted background radiation-limited performance can be expected for 10-μm cutoff detectors from room temperature to well below liquid nitrogen temperatures, with room-temperature dark current nearly 400 times lower than predicted by Rule 07. The hetero-junction p-i-n diode is shown to have numerous other significant potential advantages including minimal or no passivation requirements for pBn-like processing, low 1/f noise, compatibility with small pixel pitch while maintaining high modulation transfer function, low crosstalk and good quantum efficiency. By appropriate design of the FPA dewar shielding, analysis shows that dark current can theoretically be further reduced below the thermal equilibrium radiative limit. Modeling shows that background radiation-limited LWIR HgCdTe operating with f/1 optics has the potential to operate within √2 of background-limited performance at 215 K. By reducing the background radiation by 2/3 using novel shielding methods, operation with a single-stage thermo-electric-cooler may be possible. If the background radiation can be reduced by 90%, then room-temperature operation is possible.

Background Grape phylloxera (Daktulosphaira vitifoliae Fitch) is a major insect pest that negatively impacts commercial grapevine performance worldwide. Consequently, the use of phylloxera resistant rootstocks is an essential component of vineyard management. However, the majority of commercially available rootstocks used in viticulture production provide limited levels of grape phylloxera resistance, in part due to the adaptation of phylloxera biotypes to different Vitis species. Therefore, there is pressing need to develop new rootstocks better adapted to specific grape growing regions with complete resistance to grape phylloxera biotypes. Results Grapevine rootstock breeding material, including an accession of Vitis cinerea and V. aestivalis, DRX55 ([M. rotundifolia x V. vinifera] x open pollinated) and MS27-31 (M. rotundifolia specific hybrid), provided complete resistance to grape phylloxera in potted plant assays. To map the genetic factor(s) of grape phylloxera resistance, a F1 V. cinerea x V. vinifera Riesling population was screened for resistance. Heritability analysis indicates that the V. cinerea accession contained a single allele referred as RESISTANCE TO DAKTULOSPHAIRA VITIFOLIAE 2 (RDV2) that confers grape phylloxera resistance. Using genetic maps constructed with pseudo-testcross markers for V. cinerea and Riesling, a single phylloxera resistance locus was identified in V. cinerea. After validating SNPs at the RDV2 locus, interval and linkage mapping showed that grape phylloxera resistance mapped to linkage group 14 at position 16.7 cM. Conclusion The mapping of RDV2 and the validation of markers linked to grape phylloxera resistance provides the basis to breed new rootstocks via marker-assisted selection that improve vineyard performance. Electronic supplementary material The online version of this article (10.1186/s12870-018-1590-0) contains supplementary material, which is available to authorized users.

State-of-the-art as-received (112)B CdZnTe substrates were examined for surface impurity contamination, polishing damage, and tellurium precipitates/inclusions. A maximum surface impurity concentration of Al = 7.5 × 1014, Si = 3.7 × 1013, Cl = 3.12 × 1015, S = 1.7 × 1014, P = 7.1 × 1013, Fe = 1.0 × 1013, Br = 1.9 × 1012, and Cu = 4 × 1012 atoms cm−2 was observed on an as-received 6 × 6 cm wafer. As-received CdZnTe substrates have scratches and residual polishing grit on the (112)B surface. Polishing scratches are 0.3 nm in depth and 0.1 μm wide. The polishing grit density was observed to vary from wafer-to-wafer from ∼5 × 106 to 2 × 108 cm−2. Te precipitate/inclusion size and density was determined by near-infrared automated microscopy. A Te precipitate/inclusion diameter histogram was obtained for the near-surface (top ~140 μm) of a 6 × 6 cm substrate. The average areal Te precipitate/inclusion density was observed to be fairly uniform. However, there was a large density of Te precipitates/inclusions with a diameter significantly greater than the mean. Te precipitate/inclusion density >10 μm diameter = 2.8 × 103 cm−3. The large Te precipitates/inclusions are laterally non-uniformly distributed across the wafer.

State-of-the-art (112)B CdZnTe substrates were examined for near-surface tellurium precipitate-related defects. The Te precipitate density was observed to be fairly uniform throughout the bulk of the wafer, including the near-surface region. After a molecular beam epitaxy (MBE) preparation etch, exposed Te precipitates, small pits, and bumps on the (112)B surface of the CdZnTe wafer were observed. From near-infrared and dark field microscopy, the bumps and small pits on the CdZnTe surface are associated with strings of Te precipitates. Raised bumps are Te precipitates near the surface of the (112)B CdZnTe where the MBE preparation etch has not yet exposed the Te precipitate(s). An exposed Te precipitate sticking above the etched CdZnTe surface plane occurs when the MBE preparation etch rapidly undercuts a Te precipitate. Shallow surface pits are formed when the Te precipitate is completely undercut from the surrounding (112)B surface plane. The Te precipitate that was previously located at the center of the pit is liberated by the MBE preparation etch process.

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternate inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale HgCdTe detector production. Growth of HgCdTe on these alternate substrates has its own difficulty, namely large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In this work, a novel structure was developed that allows for etch pit density of less than 4 × 105/cm2 for HgCdTe-on-Si. This is almost two orders of magnitude less than the as-grown etch pit density of 1.1 × 107/cm2. This value of 3.35 × 105/cm2 is below the

Alternate substrates for molecular beam epitaxy growth of HgCdTe including Si, Ge, and GaAs have been under development for more than a decade. MBE growth of HgCdTe on GaAs substrates was pioneered by Teledyne Imaging Sensors (TIS) in the 1980s. However, recent improvements in the layer crystal quality including improvements in both the CdTe buffer layer and the HgCdTe layer growth have resulted in GaAs emerging as a strong candidate for replacement of bulk CdZnTe substrates for certain infrared imaging applications. In this paper the current state of the art in CdTe and HgCdTe MBE growth on (211)B GaAs and (211) Si at TIS is reviewed. Recent improvements in the CdTe buffer layer quality (double crystal rocking curve full-width at half-maximum ≈ 30 arcsec) with HgCdTe dislocation densities of ≤106 cm−2 are discussed and comparisons are made with historical HgCdTe on bulk CdZnTe and alternate substrate data at TIS. Material properties including the HgCdTe majority carrier mobility and dislocation density are presented as a function of the CdTe buffer layer quality.

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternative inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale production of HgCdTe detectors. Growth of HgCdTe on these alternative substrates has its own difficulty, namely a large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In the work described herein, HgCdTe-on-Si diodes have been produced with R0A0 of over 400 Ω cm2 at 78 K and cutoff of 10.1 μm. Further, these diodes have good uniformity at 78 K at both 9.3 μm and 10.14 μm.

A model is proposed to explain disparities found in the operability values and histograms for long-wavelength infrared HgCdTe focal-plane arrays fabricated on Si substrates compared with those fabricated on CdZnTe. The starting point for the model is the close agreement between the aerial density of discrete species (particles, contamination spots, crystalline defects on Si surface) in various interfaces in the HgCdTe/CdTe/Si structure and the density of failed pixels in the array. The density of discrete species is acquired by applying a newly developed variation of the secondary-ion mass spectrometry (SIMS) depth-profiling technique to samples that have been deuterated to enhance detection. A mechanism of selective activation of threading dislocations in a HgCdTe layer on Si is proposed to link discrete species with failed detector pixels.

Arrays of x-ray microcalorimeters will enable broadband, high-resolution x-ray spectroscopy to study and substantiate black holes, dark matter, and other celestial phenomenon. At EPIR we continue to achieve growth of high-quality, low-doped, single-crystal HgCdTe, and HgTe epilayers on Si and CdZnTe to be employed by NASA in these instruments. Excellent low-temperature heat capacities (with no significant electronic term) have been demonstrated in integrated devices, with both HgTe and HgCdTe showing improvement over the HgTe used previously. Goal resolutions ≤4 eV have been achieved with good yield for both HgTe and HgCdTe.

Single-crystalline CdTe(133) films have been grown by metalorganic chemical vapor deposition on Si(211) substrates. We studied the effect of various growth parameters on the surface morphology and structural quality of CdTe films. Proper oxide removal from the Si substrate is considered to be the principal factor that influences both the morphology and epitaxial quality of the CdTe films. In order to obtain single-crystalline CdTe(133) films, a two-stage growth method was used, i.e., a low-temperature buffer layer step and a high- temperature growth step. Even when the low-temperature buffer layer shows polycrystalline structure, the overgrown layer shows single-crystalline structure. During the subsequent high-temperature growth, two-dimensional crystallites grow faster than other, randomly distributed crystallites in the buffer layer. This is because the capturing of adatoms by steps occurs more easily due to increased adatom mobility. From the viewpoint of crystallographic orientation, it is assumed that the surface structure of Si(211) consists of (111) terrace and (100) step planes with an interplanar angle of 54.8°. This surface structure may provide many preferable nucleation sites for adatoms compared with nominally flat Si(100) or (111) surfaces. The surface morphology of the resulting films shows macroscopic rectangular-shaped terrace—step structures that are considered to be a (111) terrace with two {112} step planes directed toward 〈110〉.

The use of silicon as an alternative substrate to bulk CdZnTe for epitaxial growth of HgCdTe for infrared detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low-defect-density HgCdTe on silicon where the lattice mismatch is ∼19%. This is especially true for long-wavelength infrared (LWIR) HgCdTe detectors where the performance can be limited by the high (∼5 × 106 cm−2) dislocation density typically found in HgCdTe grown on silicon. The current status of LWIR (9 μm to 11 μm at 78 K) HgCdTe on silicon focal-plane arrays (FPAs) is reviewed. Recent progress is covered including improvements in noise equivalent differential temperature (NEDT) and array operability. NEDT of 99% are highlighted for 640 × 480 pixel, 20-μm-pitch FPAs.

Reverse current in diodes can be dominated by generation processes, depending exponentially on temperature according to the rate-limiting step in the generation process. In this report, the current-voltage-temperature (IVT) relationship is analyzed for several midwave infrared and long-wave infrared (MWIR x = 0.295, LWIR x = 0.233) Hg1−x Cd x Te (MCT) diodes. The energy varied from diode to diode. At high reverse biases, the energy tends toward the band gap energy. Close to zero bias, the energy ranged from 0.06 to 0.1 eV. Deep level transient spectroscopy (DLTS) showed a broad peak centered at 55–80 K for the MWIR MCT. Comparison of the DLTS spectrum to a simulation based on the energy and capture cross section from a rate window analysis shows that the peak is a band of traps. The capacitance transient amplitude increased as the filling pulse increased from 1 µs to 0.1 s, consistent with capture at a dislocation. A shift to lower temperatures for the peak was also observed when the diodes are cooled under forward bias. The shift is reversible, indicating that the traps consist at least partially of a bistable defect.

It has been reported that the basic electrical properties of n-type long wave length infrared (LWIR) HgCdTe grown on silicon, including the majority carrier mobility (μ e) and minority carrier lifetime (τ), are qualitatively comparable to those reported for LWIR HgCdTe grown on bulk CdZnTe by molecular beam epitaxy (MBE). Detailed measurements of the majority carrier mobility have revealed important differences between the values measured for HgCdTe grown on bulk CdZnTe and those measured for HgCdTe grown on buffered silicon substrates. The mobility of LWIR HgCdTe grown on buffered silicon by MBE is reported over a large temperature range and is analyzed in terms of standard electron scattering mechanisms. The role of dislocation scattering is addressed for high dislocation density HgCdTe grown on lattice-mismatched silicon. Differences between the low temperature mobility data of HgCdTe grown on bulk CdZnTe and HgCdTe grown on silicon are partially explained in terms of the dislocation scattering contribution to the total mobility.

The as-grown molecular beam epitaxy (MBE) (211)B HgCdTe surface has variable surface topography, which is primarily dependent on substrate temperature and substrate/epilayer mismatch. Nano-ripple formation and cross-hatch patterning are the predominant structural features observed. Nano-ripples preferentially form parallel to the \( [\bar {1}11] \) and are from 0 A to 100 A in height with a wavelength between 0.1 μm and 0.8 μm. Cross-hatch patterns result from slip dislocations in the three {111} planes intersecting the (211) growth surface. The cross-hatch step height is 4 ± 1 A (limited data set). This indicates that only a bi-layer slip (Hg/Cd + Te) in the {111} slip plane occurs. For the deposition of MBE (211)B HgCdTe/CdTe/Si, the reorientation of multiple nano-ripples coalesced into “packets” forms cross-hatch patterns. The as-grown MBE (211)B CdTe/Si surface is highly variable but displays nano-ripples and no cross-hatch pattern. Three types of defects were observed by atomic force microscopy (AFM): needle, void/hillock, and voids.

Preliminary results of a study of the hydrogenation of HgCdTe epilayers grown by molecular beam epitaxy on Si substrates using a glow-discharge plasma are presented. The aim of the program is to employ H to passivate the detrimental opto-electronic effects of threading dislocations present in the HgCdTe epilayers. Secondary ion mass spectroscopy depth profiling has been performed to characterize 1H and 2H incorporation. It has been found that H can be controllably incorporated in HgCdTe epilayers to levels in the 1014 cm−3 to 1018 cm−3 range while maintaining the sample at temperatures lower than 60°C. Profiles indicate that H accumulates in regions of known high defect density or in highly strained regions. Analysis of the H depth profile data indicates that the current density-time product is a good figure of merit to predict the H levels in the HgCdTe epilayer. There are progressive differences in the 1H and 2H uptake efficiencies as a function of depth. Magneto-Hall measurements show consistently higher mobilities at low temperatures for majority carriers in hydrogenated samples.

We have fabricated a series of 256 pixel×256 pixel, 40 µm pitch LWIR focal plane arrays (FPAs) with HgCdTe grown on (211) silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s double layer planar heterostructure (DLPH) diode architecture. The 78 K detector and focal plane array (FPA) performance are discussed in terms of quantum efficiency (QE), diode dark current and dark current operability. The FPA dark current and the tail in the FPA dark current operability histograms are discussed in terms of the HgCdTe epitaxial layer defect density and the dislocation density of the individual diode junctions. Individual diode zero bias impedance and reverse bias current-voltage (I-V) characteristics vs. temperature are discussed in terms of the dislocation density of the epitaxial layer, and the misfit stress in the epitaxial multilayer structure, and the thermal expansion mismatch in the composite substrate. The fundamental FPA performance limitations and possible FPA performance improvements are discussed in terms of basic device physics and material properties.

The use of silicon as a substrate alternative to bulk CdZnTe for epitaxial growth of HgCdTe for infrared (IR) detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low defect density HgCdTe on silicon where the lattice mismatch is ∼19%. This is especially true for LWIR HgCdTe detectors where the performance can be limited by the high (∼5×106 cm−2) dislocation density typically found in HgCdTe grown on silicon. We have fabricated a series of long wavelength infrared (LWIR) HgCdTe diodes and several LWIR focal plane arrays (FPAs) with HgCdTe grown on silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s planar diode architecture. The diode and FPA and results at 78 K will be discussed in terms of the high dislocation density (∼5×106 cm2) typically measured when HgCdTe is grown on silicon substrates.

This paper reports the further development of the model for the analysis of FTIR transmission spectra from the dual-color Hg1−xCdxTe (MCT) structures for the constituent layer thickness and alloy composition. The previously reported model1 was shown to suffer from excessively high uncertainty in the provided individual layer thickness and low convergence rate for some types of structures, attributed primarily to inaccuracies in the model representation of the MCT dielectric function. Since last report, we have substantially improved the FTIR analysis accuracy by developing a better MCT dielectric function approximation, which is based on the interpolation of the measured spectroscopic ellipsometry (SE) experimental spectral dielectric functions at few discrete alloy compositions. Based on this, the optical model for graded layers was also created and calibrated against the traditional FTIR data reduction technique. The new model was shown to produce the most accurate fits to the experimental FTIR transmission spectra from single- and two-color detector structures, and has demonstrated a better convergence rate. The new model was tested to predict both band cutoff wavelengths for the actual two-color MWIR/LWIR SUMIT detectors.15 We have demonstrated that the model prediction from as-grown structures was in good agreement with the actual two-color device data, as measured on performance evaluation chips (PECs), thus validating the modeling technique for routine postgrowth wafer screening.

In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024×1024 focal plane arrays (FPAs) using Rockwell Scientific’s double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, >5E6 cm−2), and these dislocations act as conductive pathways for tunneling currents that reduce the RoA and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.

The reproducible molecular-beam epitaxy (MBE) growth of dual-band Hg1−xCdxTe (MCT) heterostructures requires routine post-growth wafer analysis for constituent layer thickness and alloy composition, therefore, demanding nondestructive characterization techniques that offer quick data feedback. This paper reports a multilayer structure model, which can be least-square fit directly to either Fourier transform infrared (FTIR) transmission or reflection spectra to provide individual layer thickness, alloy composition, and grading information for various complex structures. The model, we developed, is based on an accurate representation of both the real and imaginary parts of the MCT dielectric function across and above Eg as a function of alloy composition. The parametric, MCT optical-dielectric function for compositions varying between x=0.17 to x=0.5 was developed in the range from 400 cm−1 to 4,000 cm−1, based on a semi-empirical model for the absorption coefficient and extrapolation of the refractive index across Eg. The model parameters were refined through simultaneous fits to multiple reflection and transmission data sets from as-grown, double-layer planar heterostructure (DLPH) structures of variable thickness. The multilayer model was tested on a variety of simple DLPH structures with thick absorber layers (>8 µm) and was compared against traditional FTIR analysis and cross-section optical microscopy and showed good agreement in both composition and thickness. Model fits to dual-color MCT data and subsequent analysis of the internal parameter correlation have demonstrated that error bars on absorber layer composition and thickness could be as low as ∼0.0005 and ∼0.02 µm, correspondingly.

Lattice mismatch between the substrate and the absorber layer in single-color HgCdTe infrared (IR) detectors and between band 1 and band 2 in two-color detectors results in the formation of crosshatch lines on the surface and an array of misfit dislocations at the epi-interfaces. Threading dislocations originating in the substrate can also bend into the interface plane and result in misfit dislocations because of the lattice mismatch. The existence of dislocations threading through the junction region of HgCdTe IR-photovoltaic detectors can greatly affect device performance. High-quality CdZnTe substrates and controlled molecular-beam epitaxy (MBE) growth of HgCdTe can result in very low threading-dislocation densities as measured by the etch-pit density (EPD ∼ 104cm−2). However, dislocation gettering to regions of high stress (such as etched holes, voids, and implanted-junction regions) at elevated-processing temperatures can result in a high density of dislocations in the junction region that can greatly reduce detector performance. We have performed experiments to determine if the dislocations that getter to these regions of high stress are misfit dislocations at the substrate/absorber interface that have a threading component extending to the upper surface of the epilayer, or if the dislocations originate at the cap/absorber interface as misfit dislocations. The preceding mechanisms for dislocation motion are discussed in detail, and the possible diode-performance consequences are explored.

Hg1−xCdxTe is an important material for high-performance infrared detection for a wide spectral range, from 1.7 µm to beyond 14 µm. An accurate understanding of the relationship between optical absorption and bandgap energy of this semiconductor alloy is needed for pre-process layer screening, detector design, and interpretation of detector performance. There is currently a disparity among the infrared detector community in relating the optical absorption properties to HgCdTe alloy composition and bandgap energy. This disagreement may stem from a misunderstanding of absorption properties, where existing models were developed decades ago using either bulk material or material with nonuniform composition. In this work, we have initiated an investigation of the optical absorption properties of HgCdTe with uniform composition grown by molecular-beam epitaxy (MBE) with in-situ compositional control via spectroscopic ellipsometry. The absorption properties show unique characteristics in the bandtail region, with insignificant temperature dependence. The absorption properties above the bandgap suggest a hyperbolic bandstructure as opposed to the common assumption of a parabolic bandstructure. The temperature dependence of the bandgap energy shows good agreement to the commonly used expression developed previously by Hansen et al.

We report on Hg1−xCdxTe mid-wavelength infrared (MWIR) detectors grown by molecular-beam epitaxy (MBE) on CdZnTe substrates. Current-voltage (I-V) characteristics of HgCdTe-MWIR devices and temperature dependence of focal-plane array (FPA) dark current have been investigated and compared with the most recent InSb published data. These MWIR p-on-n Hg1−xCdxTe/CdZnTe heterostructure detectors give outstanding performance, and at 68 K, they are limited by diffusion currents. For temperatures lower than 68 K, in the near small-bias region, another current is dominant. This current has lower sensitivity to temperature and most likely is of tunneling origin. High-performance MWIR devices and arrays were fabricated with median RoA values of 3.96 × 1010 Ω-cm2 at 78 K and 1.27 × 1012 Ω-cm2 at 60 K; the quantum efficiency (QE) without an antireflection (AR) coating was 73% for a cutoff wavelength of 5.3 µm at 78 K. The QE measurement was performed with a narrow pass filter centered at 3.5 µm. Many large-format MWIR 1024 × 1024 FPAs were fabricated and tested as a function of temperature to confirm the ultra-low dark currents observed in individual devices. For these MWIR FPAs, dark current as low as 0.01 e−/pixel/sec at 58 K for 18 × 18 µm pixels was measured. The 1024 × 1024 array operability and AR-coated QE at 78 K were 99.48% and 88.3%, respectively. A comparison of these results with the state-of-the-art InSb-detector data suggests MWIR-HgCdTe devices have significantly higher performance in the 30–120 K temperature range. The InSb detectors are dominated by generation-recombination (G-R) currents in the 60–120 K temperature range because of a defect center in the energy gap, whereas MWIR-HgCdTe detectors do not exhibit G-R-type currents in this temperature range and are limited by diffusion currents.

The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45° oriented growth to the 0° oriented growth.

The importance of certain positive crossmatches (CM+) in kidney transplantation remains controversial. Fifty consecutive kidney transplants were performed across a CM+ between Jan. 1990 – April 1994. In 19 cases there was an isolated B-cell CM+ (Group I), in 24 an historic T-cell IgM CM+ (Group II) and in 7 an historic T-cell IgG CM+ (Group III). Comparing groups I:II:III: early acute rejection affected 32%, 42%, 57% of grafts; mean serum creatinine at 3 months was 166, 150, 229 umol/l (p

The number of renal transplants has been increasing steadily over the last twenty years. This increase has been associated with a significant improvement in the one year graft and patient survival. However, as survival improves, long term complications are becoming more clinically important. We, therefore, retrospectively reviewed our experience of renal transplantation in 165 patients between January 1970 and December 1980, and describe in detail the complications experienced by those whose grafts functioned for 10 years or longer. The 10 year patient survival rate was 47% and graft survival rate was 30%. The graft survival rate for living related grafts was superior to that of cadaveric grafts. The major cause of mortality in the first year following renal transplantation was infection and in subsequent years, cardiovascular disease predominated. Patients whose grafts functioned for 10 years or more developed a variety of complications including infection, skin cancer and hepatic dysfunction. Clinicians involved in the long term care of the patients need to be aware of these problems and skilled in their management.

It is well recognised that haemodialysis and renal transplant patients are at increased risk of developing non-A, non-B hepatitis. Recently the genome of hepatitis C virus (HCV), the major causative agent for non-A, non-B hepatitis, has been isolated. Anti-HCV seroprevalence was assessed in all haemodialysis patients (266) in Ireland who in March 1990 had been dialysed for at least 6 months. For comparative purposes, 272 patients who had functioning renal transplants for greater than 6 months were also studied. Potential risk factors such as age, number of blood transfusions and time on dialysis were evaluated. The prevalence of HCV infection as evidenced by antibody detection was only 1.1% for transplant and 1.7% for haemodialysis patients. This compares to a reported incidence of between 10% and 50% found elsewhere. Two of the 5 anti-HCV positive haemodialysis patients and 2 of the 3 transplant patients had biochemical evidence of liver disease. From stored sera it was possible to ascertain when patients acquired HCV. Whether the very low prevalence of anti-HCV in Irish patients is due to the low prevalence of the virus in the general population, the policy of non reimbursement of blood donors, genetic or other factors, remains to be determined.

We compared the incidence of clinical CMV illness in 25 renal transplant recipients treated with OKT3 for steroid resistant cellular rejection with 88 renal transplant patients treated only with conventional immunosuppression (cyclosporin A and steroids). Nine (36%) patients in the OKT3 group developed CMV illness compared to (2.3%) amongst those treated conventionally (p < 0.0005). Patients who received OKT3 were divided into four groups according to the CMV antibody status of the donor and recipient. Six of the 9 episodes of CMV infection occurred in patients not previously exposed to CMV, who received a kidney from a CMV positive donor. Three (12%) of the patients treated with OKT3 died of CMV disease. A further 2 patients died of other causes giving an overall mortality in the OKT3 treated group of 20%. We concluded that when OKT3 therapy is used in association with donor/recipient CMV mismatch it is associated with a high CMV morbidity and mortality.

Between 1980 and 1990, 862 renal transplants were performed at our unit. Forty-six of these were given to 38 children. The mean age of the children was 8.6 years. Reflux nephropathy accounted for 39% of the primary renal diseases, followed by congenital disorders (30%), and glomerulonephritis (16%). Seventy percent of the grafts were from cadaveric donors. The one year patient survival was 90%, and the one year graft survival 61%. Seven children received a second graft with a one year graft survival of 71%.

Severe hypothermia is associated with serious patient morbidity and mortality. The groups most frequently affected are the elderly, the very young and substance abusers. We describe three such cases which were successfully treated using warmed peritoneal dialysis. Two patients recovered completely and were left with no long term deficits. The third patient recovered from the acute event, but succumbed later to an underlying medical condition. Warmed peritoneal lavage is an efficient, cost effective approach which is easily performed without specialist equipment, and involves minimal risk to the patient.