Anisotropic Photoresponse Research Articles

Quantum well thickness control of a hybrid perovskite to achieve a tunable anisotropic photoresponse

The thickness of the quantum well determines the photosensitivity to linearly polarized light in metal-halide perovskite single-crystal devices.

A direction-sensitive photodetector based on the two-dimensional WSe2/MoSe2 lateral heterostructure with enhanced photoresponse

Photodetectors based on anisotropic materials are attracting lots of attention. This research systematically investigates the anisotropic photoresponse of photodetectors based on the two-dimensional WSe2/MoSe2 lateral heterostructure through quantum transport simulations. The transport direction is crucial for photocurrent. In the armchair direction, the photocurrent is sensitive to ultraviolet light, while in the zigzag direction, cyan light is significant. The photocurrent magnitude in the zigzag direction is 79 times larger than that in the armchair direction. The extinction ratio (ER) also exhibits strong anisotropy between the two directions. Infrared and visible light have more influence on the ER in the armchair direction, and ultraviolet light is crucial in the zigzag direction. The research provides a promising candidate for directional sensitivity photodetectors.

Inducing Strong Light-Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire.

Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high-performance photonic and optoelectronic devices. Here, we report a new strategy to engineer the light–matter interaction and symmetry of monolayer MoS2 by integrating it with one-dimensional (1D) AlGaAs nanowire (NW). Our results show that the photoluminescence (PL) intensity of MoS2 increases strongly in the mixed-dimensional structure because of electromagnetic field confinement in the 1D high refractive index semiconducting NW. Interestingly, the 1D NW breaks the 3-fold rotational symmetry of MoS2, which leads to a strong optical anisotropy of up to ∼60%. Our mixed-dimensional heterostructure-based phototransistors benefit from this and exhibit an improved optoelectronic device performance with marked anisotropic photoresponse behavior. Compared with bare MoS2 devices, our MoS2/NW devices show ∼5 times enhanced detectivity and ∼3 times higher photoresponsivity. Our results of engineering light–matter interaction and symmetry breaking provide a simple route to induce enhanced and anisotropic functionalities in 2D materials.

Textured Bi4Ti3O12 Ceramics: One‐Step Spark Plasma Sintering and Their Single‐Crystal‐Like Polar Anisotropy

Texturing is the most effective way to engineer the performance of bismuth layer–structured ferroelectric (BLSF) ceramics by utilizing the strong anisotropy of grains, but the existing processing approaches are still complex. Herein, a one‐step spark plasma sintering (SPS) approach is demonstrated to prepare textured Bi4Ti3O12 (BiT) ceramics with high performance. The degree of orientation can be controlled from 57% to 95% by only adjusting the sintering temperature from 840 to 1000 °C. The largest spontaneous polarization (Ps) of ≈32.2 μC cm−2 is obtained in 95% <001> textured ceramics along the direction perpendicular to the SPS pressure, accompanied with the maximum electro‐strain of ≈0.14% and piezoelectric coefficient of 14.3 pC N−1. Moreover, under the same conditions of poling and illumination, the textured ceramics exhibit unique anisotropic photoresponse in which the photocurrent polarity is dependent on the testing orientations. In particular, a short‐circuit photocurrent density of 8.76 nA cm−2 is achieved along the direction of SPS pressure after positive poling, while the value goes to −79.4 nA cm−2 along direction perpendicular to the SPS pressure. These results are expected to provide a paradigm to achieve highly textured BLSF ceramics for electric and photoelectric applications.

Centimeter-sized single crystals of 2D hybrid perovskites toward ultraviolet photodetection with anisotropic photoresponse

Centimeter-sized high-quality single crystals made into photodetectors exhibited considerable anisotropic properties and sensitive photodetection capabilities under ultraviolet illumination.

Anisotropic photoresponse behavior of a LaAlO3 single-crystal-based vacuum-ultraviolet photodetector.

Nowadays, vacuum-ultraviolet (VUV) photodetectors (PDs) have attracted extensive attention owing to their potential applications in space exploration, radiation monitoring, and the semiconductor industry. Benefiting from its intrinsic ultra-wide band-gap, chemical robustness, and low-cost features, LaAlO3 shows great promise in developing next-generation compact, cheap, and easy-to-fabricate VUV PDs. In this work, we report the unique anisotropic photoresponse behavior of LaAlO3 single crystals for VUV photodetection applications. First of all, with the guidance of density functional theory (DFT) calculations along with the comprehensive material characterization, the anisotropic carrier transport behavior of LaAlO3 single crystals was confirmed. Thereafter, after exploring the metal-semiconductor-metal (MSM) device configuration along different substrate orientations, including (100), (110), and (111)-LaAlO3 single crystals, we found that the (110)-LaAlO3 VUV PD exhibits the best device performance under VUV illumination, with a responsivity of 2.23 mA W-1, a high detectivity of 3.72 × 1011 Jones, and a photo-to-dark-current ratio of 5.48 × 103. This work not only provides a feasible avenue to explore the anisotropic optoelectronic behavior of ultra-wide band-gap semiconductors but also expands the application of the low-cost oxide perovskite family in the field of VUV photodetection.

Nonmonotonic wavelength dependence of the polarization-sensitive infrared photoresponse of an anisotropic semimetal.

Layered semimetals with in-plane anisotropy are promising for advanced polarization-sensitive infrared detection. The investigation of the polarization-dependent photoresponse of semimetals over the whole visible-to-long-wave-infrared range and revealing the physical connection between their optoelectronic properties, optical properties, and electronic band structures is required, but there have been very few studies of this kind. In this work, we conducted a thorough investigation on the polarization-dependent infrared photoresponse of WTe2 over the visible-to-long-wave-infrared range and discovered a textbook-like perfect consistency between the wavelength-dependent polarization-sensitive photoresponse and the anisotropic dielectric constant mainly affected by interband transitions near the Weyl point. It is revealed that the polarization sensitivity and the responsivity both vary non-monotonically with the wavelength. This phenomenon is attributed to the polarization selective excitation of interband transitions associated with asymmetrically distributed electron orbitals around the Weyl points. Concerning the infrared detection properties of WTe2, a maximum responsivity of 0.68 mA W-1 is obtained under self-powered operation. The power dependence of the photoresponse is linear, and the response time is around 14 μs. This work would provoke further studies about the anisotropic photoresponse associated with the transitions even closer to the Dirac or Weyl points, and it provides an approach to select the right semimetal for the right wavelength range of infrared polarization detection.

Anisotropic Properties of Quasi‐1D In4Se3: Mechanical Exfoliation, Electronic Transport, and Polarization‐Dependent Photoresponse

AbstractTheoretical and experimental investigations of various exfoliated samples taken from layered In4Se3 crystals are performed. In spite of the ionic character of interlayer interactions in In4Se3 and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few‐nanometer‐thick flakes of In4Se3 by mechanical exfoliation of its bulk crystals. The In4Se3 flakes exfoliated on Si/SiO2 have anisotropic electronic properties and exhibit field‐effect electron mobilities of about 50 cm2 V−1 s−1 at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS2 and TiS3. In4Se3 devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry‐dependent band structure calculations for the most expected ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In4Se3 crystals is possible, while the fast anisotropic photoresponse makes In4Se3 a competitive electronic material, in the TMC family, for emerging optoelectronic device applications.

Low temperature anisotropic photoresponse study of bulk ZrS3 single crystal

The present work shows zirconium trisulphide (ZrS3) single crystals-based photodetector functionality synthesized through the Direct Vapor Transport (DVT) technique. The elemental-chemical, surface morphology, structural phase, crystallinity and vibrational modes of the crystals were analyzed using Energy Dispersive Analysis of X-rays (EDAX), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy respectively. These characterizations revealed the pure and layered crystals grown having a monoclinic phase with good crystallinity. Time-dependent photo-response of the detector fabricated from ZrS3 single crystals possessing smooth surface was recorded under the illumination of white light for different incident illumination levels (20 mW/cm2 to 120 mW/cm2) at room temperature. Further, a low-temperature photo-response upto 100 K for the incident light intensity of 120 mW/cm2 was carried out to validate the stability and durability of the detector. Typical detector parameters like responsivity, detectivity, sensitivity and response times were calculated and their variations are studied thoroughly concerning incident intensity and low-temperature. Furthermore, owing to the layered structure of the material, the photo-response of the device was recorded in both parallel (⊥to c-axis) and perpendicular (║to c-axis) direction of the crystallographic b-axis and device parameters were calculated at the room as well as low temperatures. The device exhibited strong anisotropy that originated from the layered structure of the grown crystals and involved an anisotropic charge conduction mechanism at the room as well as low temperatures.

Mid-Infrared Photodetection of Type-II Dirac Semimetal 1T-PtTe2 Grown by Molecular Beam Epitaxy.

Mid-infrared (MIR) photodetection is of significance in civil and military applications because it shows superiority in absorbing the vibration of various molecules and covering atmospheric transmission windows. Recently, the PtTe2, a typical type-II Dirac semimetal, has come under the spotlight due to its unique photodetection sensibility in the MIR region and robust stability in the atmosphere. Here, the high-quality and large-scale 1T-PtTe2 thin films with air stability were grown by molecular beam epitaxy. Broadband photoresponse of the photodetectors of PtTe2 from 420 nm to 10.7 μm shows high responsivity and detectivity of 0.2 mA W-1 and 2.6 × 107 Jones at 10.7 μm and 1.6 mA W-1 and 2.2 × 108 Jones at 4.7 μm under the atmosphere, respectively. Moreover, the photodetectors exhibit high sensitivity in visible and near-infrared regions (8.2 mA W-1 at 650 nm and 15.6 mA W-1 at 960 nm). The power- and polarization-dependent photoresponse measurements reveal the linear relationship of power photoresponse and obvious anisotropic photoresponse (the ratio of anisotropy ellipse is 8.3 at 10.7 μm), respectively. These results suggest that the PtTe2 could be expected to be an advanced photodetection material for polarization angle-sensitive detection, infrared imaging, and photodetection from the visible to MIR range.

Anisotropic photoresponse of layered rhenium disulfide synaptic transistors

Layered ReS2 with direct bandgap and strong in-plane anisotropy shows great potential to develop high-performance angle-resolved photodetectors and optoelectronic devices. However, systematic characterizations of the angle-dependent photoresponse of ReS2 are still very limited. Here, we studied the anisotropic photoresponse of layered ReS2 phototransistors in depth. Angel-resolved Raman spectrum and field-effect mobility are tested to confirm the inconsistency between its electrical and optical anisotropies, which are along 120° and 90°, respectively. We further measured the angle-resolved photoresponse of a ReS2 transistor with 6 diagonally paired electrodes. The maximum photoresponsivity exceeds 0.515 A⋅W−1 along b-axis, which is around 3.8 times larger than that along the direction perpendicular to b axis, which is consistent with the optical anisotropic directions. The incident wavelength- and power-dependent photoresponse measurement along two anisotropic axes further demonstrates that b axis has stronger light–ReS2 interaction, which explains the anisotropic photoresponse. We also observed angle-dependent photoresistive switching behavior of the ReS2 transistor, which leads to the formation of angle-resolved phototransistor memory. It has simplified structure to create dynamic optoelectronic resistive random access memory controlled spatially through polarized light. This capability has great potential for real-time pattern recognition and photoconfiguration of artificial neural networks (ANN) in a wide spectral range of sensitivity provided by polarized light.

Low‐Symmetry and Nontoxic 2D SiP with Strong Polarization‐Sensitivity and Fast Photodetection

AbstractThe in‐plane anisotropic feature of 2D layered materials has captured enormous research interest due to their application in polarization‐sensitive photodetection. Here, silicon phosphide (SiP), as a novel member of group IV–V 2D materials, is first introduced to the anisotropic 2D materials family with a high in‐plane anisotropy. The low‐symmetry structure, optical and optoelectronic properties are investigated systematically. Impressively, the photodetectors based on 2D SiP demonstrate high performance with low dark current, a fast response speed of 30 µs, and a strong anisotropic photoresponse with an anisotropic factor of 2.9. Furthermore, a strong polarization‐sensitive photodetector with a dichroic ratio up to 2.3 is realized based on the intrinsic linear dichroism of 2D SiP. This work not only provides an insight into the in‐plane anisotropic properties of 2D SiP, but also sheds light on its great potentials in anisotropic optoelectronic applications.

Directly written DPP-DTT/SrTiO3organic/inorganic heterojunctions for anisotropic self-powered photodetectors

Direct writing technique was developed to fabricate DPP-DTT/SrTiO3 photodetectors with parallel and perpendicular configurations, showing identical self-powered but anisotropic photoresponse, which exhibits great potential for broad applications.

Terahertz Emission Spectroscopy and Microscopy on Ultrawide Bandgap Semiconductor β-Ga2O3

Although gallium oxide Ga2O3 is attracting much attention as a next-generation ultrawide bandgap semiconductor for various applications, it needs further optical characterization to support its use in higher-performance devices. In the present study, terahertz (THz) emission spectroscopy (TES) and laser THz emission microscopy (LTEM) are applied to Sn-doped, unintentionally doped, and Fe-doped β-Ga2O3 wafers. Femtosecond (fs) laser illumination generated THz waves based on the time derivative of the photocurrent. TES probes the motion of ultrafast photocarriers that are excited into a conduction band, and LTEM visualizes their local spatiotemporal movement at a spatial and temporal resolution of laser beam diameter and a few hundred fs. In contrast, one observes neither photoluminescence nor distinguishable optical absorption for a band-to-band transition for Ga2O3. TES/LTEM thus provides complementary information on, for example, the local mobility, surface potential, defects, band bending, and anisotropic photo-response in a noncontact, nondestructive manner. The results indicated that the band bends downward at the surface of an Fe-doped wafer, unlike with an n-type wafer, and the THz emission intensity is qualitatively proportional to the product of local electron mobility and diffusion potential, and is inversely proportional to penetration depth, all of which have a strong correlation with the quality of the materials and defects/impurities in them.

Anisotropic study of photo-bolometric effect in Sb0.15Ge0.85Se ternary alloy at low temperature

To foster high-performance optoelectronic devices, alloy engineering has shown great potential for synthesis of the materials. Here, we demonstrate the effect of Sb doping on structural and optoelectronic properties in GeSe multi-layered single crystals synthesized by DVT. The stoichiometric proportion of elements was determined by EDAX. The orthorhombic structure of the compounds was confirmed by XRD, the increase in lattice volume inveterate successful substitution of Sb+3 on Ge+2 lattice sites. The substitution was reassured by the blue shift in the vibrational mode peaks of Raman spectra. Successively, the dynamic I-t characteristics of the ternary alloys based photodetectors were studied. Among all, Sb0.15Ge0.85Se ternary alloy showed negative photo-response under the illumination of different monochromatic lights, due to amplified carrier-phonon interactions as a result of high lattice strain. Owing to the layered structure of transition metal chalcogenides, the anisotropy in the dynamic I-t characteristics was studied. The compound showed higher photo-response for the contacts taken parallel to c-axis than connections made perpendicular to c-axis because of higher effective mass in the later configuration. Anisotropic photo-response was also studied at low temperatures in the range 300 K–100 K. The investigation presents a novel photo-response for application in the field of photodetection.

Investigation of anisotropic photoresponse in Re0.2Sn0.8Se2 ternary alloy at low temperature conditions

Photodetectors which can operate at low temperature with multiple configurations are building blocks for the future technology in the field of Photonics. In this work, we have investigated the low temperature anisotropic photoresponse of Re0.2Sn0.8Se2 ternary alloy grown by direct vapor transport (DVT) technique. The time-dependent photoresponse of the Re0.2Sn0.8Se2 ternary alloy is recorded at different temperatures ranging from 300 to 60 K. At 300 K, Re0.2Sn0.8Se2 ternary alloy shows excellent photoresponse in both parallel and perpendicular configurations. We have observed that the Re0.2Sn0.8Se2 ternary alloy retains its outstanding photoresponse ability even at a low temperature of 60 K, in both the parallel and perpendicular configurations. Moreover, the critical parameters related to photodetection properties such as photoresponsivity (Rλ), spectral detectivity (D*), and rise time are evaluated. Our work demonstrates the potential of Re-doped SnSe2 ternary alloys for optoelectronic devices function at low temperatures.

High-speed femtosecond laser plasmonic lithography and reduction of graphene oxide for anisotropic photoresponse

Micro/nanoprocessing of graphene surfaces has attracted significant interest for both science and applications due to its effective modulation of material properties, which, however, is usually restricted by the disadvantages of the current fabrication methods. Here, by exploiting cylindrical focusing of a femtosecond laser on graphene oxide (GO) films, we successfully produce uniform subwavelength grating structures at high speed along with a simultaneous in situ photoreduction process. Strikingly, the well-defined structures feature orientations parallel to the laser polarization and significant robustness against distinct perturbations. The proposed model and simulations reveal that the structure formation is based on the transverse electric (TE) surface plasmons triggered by the gradient reduction of the GO film from its surface to the interior, which eventually results in interference intensity fringes and spatially periodic interactions. Further experiments prove that such a regular structured surface can cause enhanced optical absorption (>20%) and an anisotropic photoresponse (~0.46 ratio) for the reduced GO film. Our work not only provides new insights into understanding the laser-GO interaction but also lays a solid foundation for practical usage of femtosecond laser plasmonic lithography, with the prospect of expansion to other two-dimensional materials for novel device applications.

Tunable and anisotropic photoresponse of layered Re0.2Sn0.8Se2 ternary alloy

In order to produce high-performance optoelectronic devices, alloy engineering has been exploited in ternary transition metal dichalcogenides. In the present study, we demonstrated the effect of rhenium incorporation on the structural and electrical response in SnSe2 layered crystals grown by direct vapour transport technique. Elemental conformation was characterized by EDAX. The powder X-ray diffraction shows the hexagonal phase and high crystallinity of grown compounds, which is also confirmed by the TEM SAED pattern. Perfectly hexagonal shaped microcrystals are shown in SEM surface micrograph. Raman spectra indicate the redshift in the vibrational mode peaks of SnSe2 with the rhenium doping. Current-time characteristic was measured to study to the effect of alloy engineering on the photoresponse ability of the grown compound. Among all, Re0.2Sn0.8Se2 ternary alloy shows the enhanced photoresponse under polychromatic illumination, showing the suppression of deep-level defect states after incorporation of Re in SnSe2 lattice structure. These materials have a layered structure and exhibit the anisotropic conductivity. Hence the anisotropic photodetection characteristics of Re0.2Sn0.8Se2 ternary alloy based photodetectors are further studied in detail. Photocurrent and photo responsivity are higher along the symmetric contacts, whereas along the asymmetric contacts both the quantities are lower in magnitude because the photogenerated carriers have to cross the perpendicular resistance of is layers stacked together by the weak Vander Waal's forces. Increasing the bias voltage enhances the photoresponsivity from 5.141 mAW−1 to 67.231 mAW−1 and photodetectivity 0.971 to 3.452 × 109 Jones. Anisotropic photoresponse was also studied under the monochromatic light. Results provide the significant understanding of tunable and layered structure dependent anisotropic photoresponse ability of TMDC materials.

Nonlinear, anisotropic, and giant photoconductivity in intrinsic and doped graphene

We present a framework to calculate the anisotropic and non-linear photoconductivity for two band systems with application to graphene. In contrast to the usual perturbative (second order in the optical field strength) techniques, we calculate photoconductivity to all orders in the optical field strength. In particular, for graphene, we find the photoresponse to be giant (at large optical field strengths) and anisotropic. The anisotropic photoresponse in graphene is correlated with polarization of the incident field, with the response being similar to that of a half-wave plate. We predict that the anisotropy in the simultaneous measurement of longitudinal ($\sigma_{xx}$) and transverse $(\sigma_{yx})$ photoconductivity, with four probes, offers a unique experimental signature of the photo-voltaic response, distinguishing it from the thermal-Seebeck and bolometric effects in photoresponse.

Highly sensitive detection of polarized light using a new group IV–V 2D orthorhombic SiP

Seeded flux growth of bulk o-SiP single crystals with layered structure and in-plane anisotropic photoresponse.