Growth of Hg0.7Cd0.3Te on Van Der Waals Mica Substrates via Molecular Beam Epitaxy.

In this paper, we present a study on the direct growth of Hg0.7Cd0.3Te thin films on layered transparent van der Waals mica (001) substrates through weak interface interaction through molecular beam epitaxy. The preferred orientation for growing Hg0.7Cd0.3Te on mica (001) substrates is found to be the (111) orientation due to a better lattice match between the Hg0.7Cd0.3Te layer and the underlying mica substrate. The influence of growth parameters (mainly temperature and Hg flux) on the material quality of epitaxial Hg0.7Cd0.3Te 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. Hg0.7Cd0.3Te 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-107 cm-2) in the Hg0.7Cd0.3Te 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.

Broadband GaAsSb Nanowire Array Photodetectors for Filter-Free Multispectral Imaging.

Highly compact, filter-free multispectral photodetectors have important applications in biological imaging, face recognition, and remote sensing. In this work, we demonstrate room-temperature wavelength-selective multipixel photodetectors based on GaAs0.94Sb0.06 nanowire arrays grown by metalorganic vapor phase epitaxy, providing more than 10 light detection channels covering both visible and near-infrared ranges without using any optical filters. The nanowire array geometry-related tunable spectral photoresponse has been demonstrated both theoretically and experimentally and shown to be originated from the strong and tunable resonance modes that are supported in the GaAsSb array nanowires. High responsivity and detectivity (up to 44.9 A/W and 1.2 × 1012 cm √Hz/W at 1 V, respectively) were obtained from the array photodetectors, enabling high-resolution RGB color imaging by applying such a nanowire array based single pixel imager. The results indicate that our filter-free wavelength-selective GaAsSb nanowire array photodetectors are promising candidates for the development of future high-quality multispectral imagers.

Optically Tunable Electrical Oscillations in Oxide-Based Memristors for Neuromorphic Computing.

The application of hardware-based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V3O5. The devices exhibit electroforming-free operation with switching parameters that can be tuned by optical illumination. Using temperature-dependent electrical measurements, conductive atomic force microscopy (C-AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V3O5, which eventually affects the oscillation dynamics. Furthermore, V3O5 is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as -4.6% K-1 at 423 K. The utility of these devices is illustrated by demonstrating in-sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

Nanoscale distribution of Bi atoms in InP1-xBix.

The nanoscale distribution of Bi in InPBi is determined by atom probe tomography and transmission electron microscopy. The distribution of Bi atoms is not uniform both along the growth direction and within the film plane. A statistically high Bi-content region is observed at the bottom of the InPBi layer close to the InPBi/InP interface. Bi-rich V-shaped walls on the (-111) and (1-11) planes close to the InPBi/InP interface and quasi-periodic Bi-rich nanowalls in the (1-10) plane with a periodicity of about 100 nm are observed. A growth model is proposed to explain the formation of these unique Bi-related nanoscale features. These features can significantly affect the deep levels of the InPBi epilayer. The regions in the InPBi layer with or without these Bi-related nanostructures exhibit different optical properties.

Influence of GaAsBi Matrix on Optical and Structural Properties of InAs Quantum Dots.

InAs/GaAsBi dot-in-well structures were fabricated using gas-source molecular beam epitaxy and investigated for its optical and structural properties. GaAsBi-strained buffer layer and strain reduction layer are both effective to extend the photoluminescence (PL) emission wavelength of InAs quantum dot (QD). In addition, a remarkable PL intensity enhancement is also obtained compared with low-temperature-grown GaAs-capped InAs QD sample. The GaAsBi matrix also preserves the shape of InAs QDs and leads to increase the activation energy for nonradiative recombination process at low temperature. Lower density and larger size of InAs QDs are obtained on the GaAsBi surface compared with the QDs grown on GaAs surface.

Anomalous photoluminescence in InP1-xBix.

Low temperature photoluminescence (PL) from InP1-xBix thin films with Bi concentrations in the 0-2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 µm in optical coherent tomography (OCT).

Existence of Multiple Solutions for a Quasilinear Biharmonic Equation.

Using three critical points theorems, we prove the existence of at least three solutions for a quasilinear biharmonic equation.