A Simple-Structured Perovskite Wavelength Sensor for Full-Color Imaging Application.

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI3/Au photodetectors on an MAPbI3 single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI3 single crystals. The high-performance MAPbI3 wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.

Non-Ultrawide Bandgap Semiconductor GaSe Nanobelts for Sensitive Deep Ultraviolet Light Photodetector Application.

In this paper, the authors report the fabrication of a sensitive deep ultraviolet (DUV) photodetector by using an individual GaSe nanobelt with a thickness of 52.1 nm, which presents the highest photoresponse at 265 nm illumination with a responsivity and photoconductive gain of about 663 A W-1 and 3103 at a 3 V bias, respectively, comparable to or even better than other reported devices based on conventional wide bandgap semiconductors. According to the simulation, this photoelectric property is associated with the wavelength-dependent absorption coefficient of the GaSe crystal, for which incident light with shorter wavelengths will be absorbed near the surface, while light with longer wavelengths will have a larger penetration depth, leading to a blueshift of the absorption edge with decreasing thickness. Further finite element method (FEM) simulation reveals that the relatively thin GaSe nanobelt exhibits an enhanced transversal standing wave pattern compared to its thicker counterpart at a wavelength of 265 nm, leading to an enhanced light-matter interaction and thereby more efficient photocurrent generation. The device can also function as an effective image sensor with acceptable spatial resolution. This work will shed light on the facile fabrication of a high-performance DUV photodetector from non-ultrawide bandgap semiconductors.

Highly Sensitive Ultraviolet and Visible Wavelength Sensor Composed of Two Identical Perovskite Nanofilm Photodetectors.

This work reports the design of a wavelength sensor composed of two identical perovskite (FA0.85 Cs0.15 PbI3 ) photodetectors (PDs) that are capable of discriminating incident wavelength in a quantitative way. Due to strong wavelength-dependent absorption coefficient, the penetration depth of the photons in the FA0.85 Cs0.15 PbI3 nanofilms increases with the increasing wavelength, leading to a gradual decrease of photo-generated current for PD1, but an increase of photocurrent in PD2, according to the theoretical simulation of Technology Computer Aided Design. This special evolution of photo-generated current as a function of wavelength facilitates the quantitative determination of the wavelength since the current ratio of both PDs monotonously decreases with the increase of wavelength from 265 to 810 nm. The average absolute error and the average relative error are estimated to be 7.6 nm and 1.68%, respectively, which are much better than other semiconductors materials-based wavelength sensors previously reported. It is believed that the present perovskite film-based wavelength sensor will have potential application in the future color/spectrum optoelectronic devices.

Ultrathin Polymer Nanofibrils for Solar-Blind Deep Ultraviolet Light Photodetectors Application.

Solar-blind deep ultraviolet photodetectors (DUVPDs) based on conventional inorganic ultrawide bandgap semiconductors (UWBS) have shown promising application in various civil and military fields and yet they can hardly be used in wearable optoelectronic devices and systems for lack of mechanical flexibility. In this study, we report a non-UWBS solar-blind DUVPD by designing ultrathin polymer nanofibrils with a virtual ultrawide bandgap, which was obtained by grafting P3HT with PHA via a polymerization process. Optoelectronic analysis reveals that the P3HT-b-PHA nanofibrils are sensitive to DUV light with a wavelength of 254 nm but are virtually blind to both 365 nm and other visible light illuminations. The responsivity is 120 A/W with an external quantum efficiency of up to 49700%, implying a large photoconductive gain in the photoresponse process. The observed solar-blind DUV photoresponse is associated with the resonant mode due to the leakage mode of the ultrathin polymer nanofibrils. Moreover, a flexible image sensor composed of 10 × 10 pixels can also be fabricated to illustrate their capability for image sensing application. These results signify that the present ultrathin P3HT-b-PHA nanofibrils are promising building blocks for assembly of low-cost, flexible, and high-performance solar-blind DUVPDs.

Graphene-Assisted Growth of Patterned Perovskite Films for Sensitive Light Detector and Optical Image Sensor Application.

Controlled growth of high-quality patterned perovskite films on a large scale is essentially required for the application of this class of materials in functional integrated devices and systems. Herein, graphene-assisted hydrophilic-hydrophobic surface-induced growth of Cs-doped FAPbI3 perovskite films with well-patterned shapes by a one-step spin-coating process is developed. Such a facile fabrication technique is compatible with a range of spin-coated perovskite materials, perovskite manufacturing processes, and substrates. By employing this growing method, controllable perovskite photodetector arrays are realized, which have not only prominent photoresponse properties with a responsivity and specific detectivity of 4.8 AW-1 and 4.2 × 1012 Jones, respectively, but also relatively small pixel-to-pixel variation. Moreover, the photodetectors array can function as an effective visible light image sensor with a decent spatial resolution. Holding the above merits, the proposed technique provides a convenient and effective pathway for large-scale preparation of patterned perovskite films for multifunctional application purposes.

Light Confinement Effect Induced Highly Sensitive, Self-Driven Near-Infrared Photodetector and Image Sensor Based on Multilayer PdSe2 /Pyramid Si Heterojunction.

In this study, a highly sensitive and self-driven near-infrared (NIR) light photodetector based on PdSe2 /pyramid Si heterojunction arrays, which are fabricated through simple selenization of predeposited Pd nanofilm on black Si, is demonstrated. The as-fabricated hybrid device exhibits excellent photoresponse performance in terms of a large on/off ratio of 1.6 × 105 , a responsivity of 456 mA W-1 , and a high specific detectivity of up to 9.97 × 1013 Jones under 980 nm illumination at zero bias. Such a relatively high sensitivity can be ascribed to the light trapping effect of the pyramid microstructure, which is confirmed by numerical modeling based on finite-difference time domain. On the other hand, thanks to the broad optical absorption properties of PdSe2 , the as-fabricated device also exhibits obvious sensitivity to other NIR illuminations with wavelengths of 1300, 1550, and 1650 nm, which is beyond the photoresponse range of Si-based devices. It is also found that the PdSe2 /pyramid Si heterojunction device can also function as an NIR light sensor, which can readily record both "tree" and "house" images produced by 980 and 1300 nm illumination, respectively.

Dual-plasmonic Au/graphene/Au-enhanced ultrafast, broadband, self-driven silicon Schottky photodetector.

High-performance photodetectors are desirable for various applications, including multi-wavelength image sensing, communication, and safety monitoring. In this study, we report the construction of a dual-surface plasmon-enhanced silicon Schottky photodetector using Au nanoparticles (NPs)/graphene/Au NPs hybrid structure as the electrode. It was found that the as-assembled device exhibited broad sensitivity, ranging from ultraviolet to near-infrared light (360-1330 nm) at room temperature, with a high response speed of 360 ns and a 3 dB bandwidth of 780 kHz at zero bias. Further theoretical simulation based on the finite-element method revealed that good device performance is associated with the contribution of the Au NPs/graphene/Au NPs electrode: intense dual-plasmonic resonance coupling is induced in a hybrid structure of two layers of metallic NPs separated by a uniform monolayer graphene. It not only can enhance light trapping and the localized electric field at the resonant and off-resonant wavelength regions, but is also beneficial for the tunneling of hot electrons. This work demonstrated the great potential of dual-plasmonic resonance coupling in optoelectronic devices and will lead to the development of advanced plasmonic devices.

Highly sensitive UVA and violet photodetector based on single-layer graphene-TiO2 heterojunction.

A highly sensitive ultraviolet A (UVA) and violet photodetector based on p-type single-layer graphene (SLG)-TiO2 heterostructure was fabricated by transferring chemical vapor deposition derived SLG on the surface of commercial single-crystal TiO2 wafer. Optoelectronic analysis reveals the as-fabricated Schottky junction PD was highly sensitive to light illumination in UVA and violet range, with peak sensitivity at 410 nm and excellent stability and reproducibility, but virtually blind to illumination with wavelength less than 350 nm or more than 460 nm. The on/off ratio of the device was calculated to be 6.8 × 104, which is better than the majority of previously reported TiO2 based PDs. What is more, the rise/fall time were estimated to be 0.74/1.18 ms, much faster than other TiO2 based counterparts. The totality of the above result signifies that the present SLG-TiO2 Schottky junction photodetector may have promising application in future high-speed, high-sensitivity optoelectronic nanodevices and systems.

Plasmonic silver nanosphere enhanced ZnSe nanoribbon/Si heterojunction optoelectronic devices.

In this study, we report a localized surface plasmon resonance (LSPR) enhanced optoelectronic device based on a ZnSe:Sb nanoribbon (NR)/Si nano-heterojunction. We experimentally demonstrated that the LSPR peaks of plasmonic Ag nanoparticles (Ag NPs) can be readily tuned by changing their size distribution. Optical analysis reveals that the absorption of ZnSe:Sb NRs was increased after the decoration of the Ag NPs with strong LSPR. Further analysis of the optoelectronic device confirmed the device performance can be promoted: for example, the short-circuit photocurrent density of the ZnSe/Si heterojunction solar cell was improved by 57.6% from 11.75 to 18.52 mA cm(-2) compared to that without Ag NPs. Meanwhile, the responsivity and detectivity of the ZnSe:Sb NRs/Si heterojunction device increased from 117.2 to 184.8 mA W(-1), and from 5.86 × 10(11) to 9.20 × 10(11) cm Hz(1/2) W(-1), respectively.

Surface plasmon propelled high-performance CdSe nanoribbons photodetector.

In this work, we present a plasmonic photodetector (PPD) with high sensitivity to red light illumination. The ultrasensitive PPD was composed of high-crystalline CdSe nanoribbons (NRs) decorated with plasmonic hollow gold nanoparticles (HGNs) on the surface, which were capable of coupling the incident light due to localized surface plasmon resonance (LSPR). Device analysis reveals that after modification of HGNs, both responsivity and detectivity were considerably improved. Further device performance analysis and theoretical simulation based on finite element method (FEM) find that the optimized performance is due to HGNs induced localized field enhancement and direct electron transfer.

The effect of plasmonic nanoparticles on the optoelectronic characteristics of CdTe nanowires.

In this work, a simple strategy is proposed to improve the device performance of photodetector by modifying plasmonic nanoparticles onto the surface of semiconductors nanostructure. Both experimental analysis and theoretical simulation show that the plasmonic metal nanoparticles (AuNPs) exhibits obvious localized surface plasmon resonance (LSPR) which can trap incident light efficiently, leading to enhanced photocurrents and improved performance of photoelectronic devices. It is also observed that the AuNPs modified CdTeNW photodetector exhibit apparent sensitivity to 510 nm light, to which pure CdTeNWs is virtually blind. What is more, after AuNPs decoration, the response speed of the photodetector is increased substantially from 6.12 to 1.92 s. It is believed that this result will open up new doors for manipulating light and further improving the efficiency of semiconductor nanostructures based optoelectronic devices.

Monolayer graphene film on ZnO nanorod array for high-performance Schottky junction ultraviolet photodetectors.

A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free-standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) film. The single-crystalline [0001]-oriented ZnONR array has a length of about 8-11 µm, and a diameter of 100∼600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I-V characteristics in the temperature range of 80-300 K, the barrier heights of the MLG film/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG film/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices.

High-performance nonvolatile Al/AlO(x)/CdTe:Sb nanowire memory device.

Here we demonstrate a room temperature processed nonvolatile memory device based on an Al/AlO(x)/CdTe:Sb nanowire (NW) heterojunction. Electrical analysis shows an echelon hysteresis composed of a high-resistance state (HRS) and a low-resistance state (LRS), which can allow it to write and erase data from the device. The conductance ratio is as high as 106, with a retention time of 3 × 104 s. Moreover, the SET voltages ranged from +6 to +8 V, whilst the RESET voltage ∼0 V. In addition, flexible memory nano-devices on PET substrate with comparable switching performance at bending condition were fabricated. XPS analysis of the Al/AlO(x)/CdTe:Sb NW heterojunction after controlled Ar⁺ bombardment reveals that this memory behavior is associated with the presence of ultra-thin AlO(x) film. This Al/AlO(x)/CdTe:Sb NW heterojunction will open up opportunities for new memory devices with different configurations.

Fabrication of p-type ZnSe:Sb nanowires for high-performance ultraviolet light photodetector application.

p-type ZnSe nanowires (NWs) with tunable electrical conductivity were fabricated on a large scale by evaporating a mixed powder composed of ZnSe and Sb in different ratios. According to the structural characterization, the Sb-doped ZnSe NWs are of single crystalline form and grow along the [001] direction. The presence of Sb in the ZnSe NWs was confirmed by XPS spectra. Electrical measurement of a single ZnSe:Sb NW based back-gate metal-oxide field-effect-transistor reveals that all the doped NWs exhibit typical p-type conduction characteristics, and the conductivity can be tuned over eight orders of magnitude, from 6.36 × 10(-7) S cm(-1) for the undoped sample to ∼37.33 S cm(-1) for the heavily doped sample. A crossed p-n nano-heterojunction photodetector made from the as-doped nanostructures displays pronounced rectification behavior, with a rectification ratio as high as 10(3) at ±5 V. Remarkably, it exhibits high sensitivity to ultraviolet light illumination with good reproducibility and quick photoresponse. Finally, the work mechanism of such a p-n junction based photodetector was elucidated. The generality of the above result suggests that the as-doped p-type ZnSe NWs will find wide application in future optoelectronics devices.

Sensitive Silicon Nanowire Ultraviolet B Photodetector Induced by Leakage Mode Resonances.

Ultraviolet photodetectors (UVPDs) have played an important role both in civil and military applications. While various studies have shown that traditional UVPDs based on wide-band-gap semiconductors (WBSs) have excellent device performances, it is, however, undeniable that the practical application of WBS-based UVPDs is largely limited by the relatively high fabrication cost. In this work, we propose a new silicon nanowire (Si NW) UVPD that is very sensitive to UVB light illumination. The Si NWs with a diameter of about 36 nm are fabricated by a metal-assisted chemical etching method. Performance analysis revealed that the Si NW device was only sensitive to UVB light and almost blind to illumination in the visible and near-infrared regions. Such abnormal spectral selectivity was associated with the leakage mode resonances (LMRs) of the small diameter, according to our theoretical simulation. Under 300 nm illumination, the responsivity, external quantum efficiency, and specific detectivity were estimated to be 10.2 AW-1, 4.22 × 103%, and 2.14 × 1010 Jones, respectively, which were comparable to or even higher than those of some WBS-based UVPDs. These results illustrate that the small dimension Si NWs are potential building blocks for low-cost and high-performance UVPDs in the future.

Spectral Engineering of InSe Nanobelts for Full-Color Imaging by Tailoring the Thickness.

In this work, we report on the synthesis of InSe nanobelts through a catalyst-free chemical vapor deposition (CVD) growth approach. A remarkable blue shift of the peak photoresponse was observed when the thickness of the InSe nanobelt decreases from 562 to 165 nm. Silvaco Technology Computer Aided Design (TCAD) simulation reveals that such a shift in spectral response should be ascribed to the wavelength-dependent absorption coefficient of InSe, for which incident light with shorter wavelengths will be absorbed near the surface, while light with longer wavelengths will have a greater penetration depth, leading to a red shift of the absorption edge for thicker nanobelt devices. Considering the above theory, three kinds of photodetectors sensitive to blue (450 nm), green (530 nm), and red (660 nm) incident light were achieved by tailoring the thickness of the nanobelts, which can enable the spectral reconstruction of a purple "H" pattern, suggesting the potential application of 2D layered semiconductors in full-color imaging.

UV-light-assisted gas sensor based on PdSe2/InSe heterojunction for ppb-level NO2 sensing at room temperature.

The fabrication of van der Waals (vdWs) heterostructures mainly extends to two-dimensional (2D) materials. Nevertheless, the current processes for obtaining high-quality 2D films are mainly exfoliated from their bulk counterparts or by high-temperature chemical vapor deposition (CVD), which limits industrial production and is often accompanied by defects. Herein, we first fabricated the type-II p-PdSe2/n-InSe vdWs heterostructure using the ultra-high vacuum laser molecular beam epitaxy (LMBE) technique combined with the vertical 2D stacking strategy, which is reproducible and suitable for high-volume manufacturing. This work found that the introduction of 365 nm UV light illumination can significantly improve the electrical transport properties and NO2 sensing performance of the PdSe2/InSe heterojunction-based device at room temperature (RT). The detailed studies confirm that the sensor based on the PdSe2/InSe heterojunction delivers the comparable sensitivity (Ra/Rg = ∼2.6 at 10 ppm), a low limit of detection of 52 ppb, and excellent selectivity for NO2 gas under UV light illumination, indicating great potential for NO2 detection. Notably, the sensor possesses fast response and full recovery properties (275/1078 s) compared to the results in the dark. Furthermore, the mechanism of enhanced gas sensitivity was proposed based on the energy band alignment of the PdSe2/InSe heterojunction with the assistance of investigating the surface potential variations. This work may pave the way for the development of high-performance, room-temperature gas sensors based on 2D vdWs heterostructures through the LMBE technique.

Sn-catalyzed synthesis of SnO2 nanowires and their optoelectronic characteristics.

We report the rational synthesis of one-dimensional SnO(2) nanowires (SnO(2)NWs) via a Sn-catalyzed vapor-liquid-solid (VLS) growth mechanism, in which Sn nanoparticles can direct the oriented growth of SnO(2)NWs at high temperature. I-V measurement of a field effect transistor made of individual SnO(2)NWs exhibits typical n-type semiconducting characteristics with an electron mobility and concentration of 14.36 cm(2) V( - 1) s( - 1) and 1.145 × 10(17) cm( - 3), respectively. The SnO(2)NW-based photodetector shows a high sensitivity to UV light radiation, and a fast light response speed of millisecond rise time/fall time with excellent stability and reproducibility, whereas it is nearly blind to illumination with wavelengths in the visible range. Detailed reasons to account for the detection selectivity and rapid response speed are proposed. The generality of the above results suggests that our SnO(2)NW photodetectors have potential application in nanoscaled optoelectronic devices.

Low-temperature architecture of a cubic-phase CsPbBr3 single crystal for ultrasensitive weak-light photodetectors.

We present the first report of a water-regulated method for obtaining a cubic-phase CsPbBr3 single crystal that could be frozen at low temperature with a CsBr/PbBr2 ratio of 1 : 1. The cubic CsPbBr3 single-crystal photodetector exhibits a superior responsivity of 278 A W-1, an EQE of 6.63 × 104%, and an ultrahigh detectivity of 4.36 × 1013 Jones under low-power 520 nm irradiation at 3 V.

Correction: Construction of PtSe2/Ge heterostructure-based short-wavelength infrared photodetector array for image sensing and optical communication applications.

Correction for 'Construction of PtSe2/Ge heterostructure-based short-wavelength infrared photodetector array for image sensing and optical communication applications' by Yu Lu et al., Nanoscale, 2021, 13, 7606-7612, DOI: 10.1039/D1NR00333J.