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This work investigates the structural properties of HgCdTe thin films grown on InSb (211)B substrates using molecular beam epitaxy (MBE). The Cd composition of thin films is accurately determined using non-destructive approaches based on x-ray diffraction (XRD) and reflectance infrared spectroscopy. The as-grown HgCdTe thin films exhibit characteristic surface defects with a size of 7–10 μm and density of ∼105 cm−2, resulting in an additional spread in XRD full width at half maximum. Cross-sectional transmission electron microscopy results indicate that these defects are caused by surface In droplet formation during the oxide removal process of InSb substrate, which subsequently results in the formation of In4Te3 inclusions and extended defects in MBE-grown HgCdTe. Our findings provide additional confirmation that suppressing thermally induced damage of the InSb substrate is necessary for fabricating high-performance infrared detectors using HgCdTe grown on InSb substrates. [ABSTRACT FROM AUTHOR]

The ever-present demand for high-performance HgCdTe infrared detectors with larger array size and lower cost than currently available technologies based on lattice-matched CdZnTe (211)B substrates has fuelled research into heteroepitaxial growth of HgCdTe and CdTe buffer layers on lattice-mismatched alternative substrates with a (211)B orientation. Driven by the large lattice mismatch, the heteroepitaxial growth of (Hg)CdTe can result in (133)B-orientated material, which, however, has been less explored in comparison to (211)B-oriented growth. Herein, we report on the structural properties of heteroepitaxially grown single-crystal II–VI CdTe (133)B-oriented buffer layers on III–V GaAs (211)B substrates. Azimuthal-dependent x-ray double-crystal rocking curve measurements for the CdTe buffer layers show that the full-width at half-maximum value obtained along the GaAs [ 1 ¯ 11 ] direction is narrower than that obtained along the GaAs [ 01 1 ¯ ] direction, which is presumably related to the in-plane anisotropic structural characteristics of the grown CdTe layers. By incorporating strained CdZnTe/CdTe superlattice-based dislocation filtering layers (DFLs), a significant improvement in material quality has been achieved in (133)B-orientated CdTe buffer layers, including a reduced etch pit density in the low-105 cm−2 range and improved surface roughness. These results indicate that the CdTe (133)B DFL buffer layer process is a feasible approach for growing high-quality CdTe and HgCdTe materials on large-area, low-cost alternative substrates. [ABSTRACT FROM AUTHOR]

In this paper, we present a study on the direct growth of H g 0.7 C d 0.3 T e thin films on layered transparent van der Waals mica (001) substrates through weak interface interaction through molecular beam epitaxy. The preferred orientation for growing H g 0.7 C d 0.3 T e on mica (001) substrates is found to be the (111) orientation due to a better lattice match between the H g 0.7 C d 0.3 T e layer and the underlying mica substrate. The influence of growth parameters (mainly temperature and Hg flux) on the material quality of epitaxial H g 0.7 C d 0.3 T e thin films is studied, and the optimal growth temperature and Hg flux are found to be approximately 190 °C and 4.5 × 10 − 4 Torr as evidenced by higher crystalline quality and better surface morphology. H g 0.7 C d 0.3 T e thin films (3.5 µm thick) grown under these optimal growth conditions present a full width at half maximum of 345.6 arc sec for the X-ray diffraction rocking curve and a root-mean-square surface roughness of 6 nm. However, a significant number of microtwin defects are observed using cross-sectional transmission electron microscopy, which leads to a relatively high etch pit density (mid- 10 7   c m − 2 ) in the H g 0.7 C d 0.3 T e thin films. These findings not only facilitate the growth of HgCdTe on mica substrates for fabricating curved IR sensors but also contribute to a better understanding of growth of traditional zinc-blende semiconductors on layered substrates. [ABSTRACT FROM AUTHOR]

We report on the structural and optical properties of heteroepitaxial II–VI CdTe (211)B buffer layers with strained CdZnTe/CdTe superlattice layers, investigated by employing non-destructive methods including high-resolution x-ray diffraction, cathodoluminescence, and photoluminescence spectroscopy. X-ray diffraction reciprocal space mapping measurements revealed that the superlattice layers are coherently strained, leading to a spread in x-ray double-crystal rocking curve full-width at half-maximum values but better in-plane lattice-matching with HgCdTe. Both cross-sectional cathodoluminescence and photoluminescence measurements confirm the coherent growth of superlattice layers and their dislocation filtering effects. Both these techniques in CdTe layers are found to be well correlated with the dislocation density as determined by etch pit density measurements. The results indicate the potential of these non-destructive methods to be further developed into general-purpose techniques capable of characterizing the defect evolution in semiconductor heteroepitaxy. [ABSTRACT FROM AUTHOR]

Van der Waals epitaxial (vdW) growth of semiconductor thin films on 2D layered substrates has recently attracted considerable attention since it provides a potential pathway for realizing monolithically integrated devices and flexible devices. In this work, direct growth of epitaxial HgCdTe (111) thin films on 2D layered transparent mica substrates is achieved via molecular beam epitaxy. The full width at half maximum of the ω‐mode X‐ray diffraction peak is measured to be around 306 arc sec. Mid‐wave infrared photoconductors based on the as‐grown HgCdTe thin films have been demonstrated and the self‐heating effect has been evaluated. A peak responsivity at the wavelength of around 3500 nm is measured to be about 110 V W−1 at 80 K and 8 V W−1 at room temperature under a bias of 25 V cm−1. Twinning defects are observed, limiting the crystallinity and mobility‐lifetime product in HgCdTe/mica. Benefiting from the vdW epitaxial growth, an etch‐free layer transfer process for lifting off the HgCdTe from the mica substrate has been demonstrated, leading to large area free‐standing HgCdTe thin films. [ABSTRACT FROM AUTHOR]

Microbial sulfur‐containing secondary metabolites show various biological activities, but the C−S bond‐forming in their biosynthetic metabolism has not been thoroughly understood. Here, we present genetic, biochemical and structural characterization of a cytochrome P450 monooxygenase CxnD exhibiting C−S bond forming activity in S‐heterocyclization of chuangxinmycin biosynthesis. In vivo and in vitro analyses demonstrated that CxnD generated an indole‐fused dihydrothiopyran skeleton from a L‐Trp‐derived thiol intermediate. Furthermore, X‐ray crystal structure of CxnD in complex with a substrate analogue and structure‐based mutagenesis revealed intimate details of the substrate binding mode. A radical mechanism initiated by abstraction of the imino hydrogen atom or an electron from indole group of the substrate was proposed for CxnD, which provided valuable insights into the molecular basis for the intra‐molecular C(sp2)−H thiolation by the P450 in chuangxinmycin biosynthesis. [ABSTRACT FROM AUTHOR]

Unipolar nBn photodetector structures have recently emerged as a viable alternative to the traditional p-n junction infrared photodiode approach. However, realization of a unipolar nBn detector technology using the mercury--cadmium--telluride (HgCdTe) alloy system is a challenging task because of the lack of a barrier material with a favorable valenceband offset. In this paper, advanced quantum mechanical calculations, based on the nonequilibrium Green's function (NEGF) formalism, are used to demonstrate that it is possible to achieve diffusion-limited dark current performanceinHgCdTenBn detectorsby incorporating a type-III HgTe/CdTe superlattice (SL) barrier layer. Optimal design parameters for CdTe layer thickness, HgTe layer thickness, and total number of periods are presented in order to achieve maximum hole current transmission through the barrier layer, and therefore diffusion-limited dark current performance. The NEGF simulation framework herein presented allows greater insight into effects associatedwith electronand holewave function propagation in the SL barrier layer aswell as the calculation of individual carrier current components. The presented results form a good basis for the fabrication of high-performance SL barrier HgCdTe nBn detectors. [ABSTRACT FROM AUTHOR]