Broadband Photosensitivity Research Articles

Plasmon assisted high ultraviolet to visible broad band photosensitivity in lateral Ag NPs-TiO2 nanocomposite film

Noble metal-TiO2 composite films attract great attention because of the extension of its spectral absorption in the visible range due to surface plasmon resonance. Among them, Ag-TiO2 composite is considered to be an ideal candidate for the visible light photosensitivity because of narrow energy distribution of plasmonic hot electrons in Ag and the high density of states in the TiO2 conduction band. Here, we report high broad band photosensitivity from ultraviolet (UV) to visible wavelength of sol-gel grown TiO2 film decorated with Ag nanoparticles (NPs) in a simple planar photoconductive geometry. In addition to UV light, Ag NPs-TiO2 composite film (for 1 nm Ag) shows very high photosensitivity values of ∼105 and ∼104 and responsivity values of 0.1 A/W and 7×10−3 A/W at 10 V bias for 680 nm and 550 nm illuminations respectively while pristine TiO2 show photosensitivity values of 6×102 and 3.3×102 and responsivity values of 2.4×10−4 A/W and 6.6×10−5 A/W for both the visible illuminations. A highly enhanced broad band photosensitivity due to transfer of plasmonically generated hot electrons from Ag to TiO2 is quite interesting without having any device fabricated. The photosensitivity values for Ag NPs for 3 nm and 6 nm layer thicknesses on TiO2 decrease because of coalescence of metal NPs on surface which acts as scattering center and/or light shielding.

High and broadband sensitivity front-side illuminated InGaAs photo field-effect transistors (photoFETs) with SWIR transparent conductive oxide (TCO) gate

By using a transparent conductive oxide (TCO) gate for the short-wave infrared (SWIR) region, the high optical responsivity of 180 A/W at 1550 nm and the broadband photosensitivity up to 1800 nm are demonstrated in InGaAs photo field-effect transistors (photoFETs) with front-side illumination (FSI). The photoresponse of the InGaAs photoFETs through the TCO gate can be reasonably explained by the photovoltaic effect in the photoFET operation. It was found that the spectral responsivity characteristics of TCO gate InGaAs photoFETs exhibit higher and broader responsivity compared with those of the InGaAs photodiode. The TCO gate InGaAs photoFETs are the most promising architecture for a high responsivity and broadband SWIR FSI photodetector for monolithic integration with optical communication devices and Si-LSI.

Ultrasensitive broadband photodetector using electrostatically conjugated MoS2-upconversion nanoparticle nanocomposite

Hybrid or composite nanomaterials have emerged that demonstrates superior optoelectronic performance over pure nanomaterials that lacks broadband usage, or responsivity, or both, mainly because of the limitation of the collection of photogenerated carriers. We have addressed this problem by using a composite of MoS2 and a multi-photon absorbing lanthanide doped upconversion nanoparticles (UCNPs), that emits in the visible, to make a photodetector (PD) device with ultrahigh broadband responsivity. Single flake MoS2 electrostatically conjugated with UCNPs were used to fabricate the PD device with platinum, and gold contacts. The device was irradiated with UV-to-NIR illumination, at different power density, to study its broadband photosensitivity. Photoresponsivities in excess of 100 A W-1 is easily obtained; a highest responsivity of 1254 A W-1 is reported for 980 nm at 1.0 V bias. An unprecedented normalized gain of 7.12 × 10−4 cm2 V−1, and Detectivity of 1.05 × 1015 Jones (@980 nm, 1 V) was obtained which is, to the best of our knowledge, the highest reported till date for this device class. Under vacuum conditions even higher values of these device parameters were obtained, while losing on the response speeds. The photoresponsivity in the nanocomposite followed the trend of the convoluted optical absorption of the individual components. Real application of the PD device was demonstrated using non-laser domestic appliances such as sodium vapour lamp, mobile phone flash light, and air-condition remote controller.

Highly Polarization-Sensitive, Broadband, Self-Powered Photodetector Based on Graphene/PdSe2/Germanium Heterojunction.

Polarization-sensitive photodetection in a broad spectrum range is highly desired due to the great significance in military and civilian applications. Palladium diselenide (PdSe2), a newly explored air-stable, group 10 two-dimensional (2D) noble metal dichalcogenide with a puckered pentagonal structure, holds promise for polarization-sensitive photodetection. Herein, we report a highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction. Owing to the enhanced light absorption of the mixed-dimensional van der Waals heterojunction and the effective carrier collection with graphene transparent electrode, the photodetector exhibits superior device performance in terms of a large photoresponsivity, a high specific detectivity, a fast response speed to follow nanosecond pulsed light signal, and a broadband photosensitivity ranging from deep ultraviolet (DUV) to mid-infrared (MIR). Significantly, highly polarization-sensitive broadband photodetection with an ultrahigh polarization sensitivity of 112.2 is achieved, which represents the best result for 2D layered material-based photodetectors. Further, we demonstrated the high-resolution polarization imaging based on the heterojunction device. This work reveals the great potential of 2D PdSe2 for high-performance, air-stable, and polarization-sensitive broadband photodetectors.

Defect-Assisted Broad-Band Photosensitivity with High Responsivity in Au/Self-Seeded TiO2 NR/Au-Based Back-to-Back Schottky Junctions.

TiO2 nanorods (NRs) have generated much interest for both fundamental understanding of defect formation and technological applications in energy harvesting, optoelectronics, and catalysis. Herein, we have grown TiO2 NR films on glass substrates using a self-seeded approach and annealed them in H2 ambient to modify their surface defects. It has been shown that broad-band photosensing properties of Au/self-seeded TiO2 NR/Au-based two back-to-back Schottky junctions (SJs) for a broad wavelength of light are much superior as compared to those of the pristine and the control samples. Photoresponsivity values for the H2-annealed sample are 0.42, 0.71, 0.07, and 0.08 A/W for detecting, respectively, 350, 400, 470, and 570 nm lights. Very low dark current and high photocurrent lead to a gain value as high as 1.85 × 104 for 400 nm light. Unprecedentedly modified NR-based SJs show excellent photoresponsivity for detecting as low as 25, 36, 48, and 28 μW/cm2 power densities of 350, 400, 470, and 570 nm lights, respectively. It is found that Ti3+ defects play a key role in an efficient photoelectron transfer from TiO2 to Au. Our work, for the first time, highlights the simplicity and reveals the rationale behind the excellent properties of Au/self-seeded TiO2 NR film/Au back-to-back SJs.

Low cost and facile fabrication of broadband laser power meter based on reduced graphene oxide film

Here, we have demonstrated a new type of broadband reduced graphene oxide-based laser power meter in simple and low cost method. The broadband photosensitivity of the device is confirmed by photocurrent measurements at different incident laser wavelengths of 405, 532, 635 and 808nm. It is shown that its photocurrent increases linearly with increasing the power of the laser beam. Also, it is observed that the photocurrent behavior of the device does not depend upon the size of the laser spot. It should be noted that the reduced graphene oxide power meter is the thermal detection device. Therefore, the response of the sample in the vacuum is greatly enhanced in compared to the environmental air. Cooling system can also decrease the time required for the establishment of thermal equilibrium and thus reduce the response time of the power meter. These results open up exciting opportunities for developing broadband photodetectors.

Photosensitive structures based on CuIn5Te8 single crystals: Development and properties

A new ternary compound is synthesized for the first time, and bulk CuIn5Te8 single crystals are grown by directed crystallization of near-stoichiometric melt. It is established from X-ray diffraction patterns of grown crystals that they exhibit the structure of imperfect chalcopyrite with parameters of the unit cell of CuIn5Te8, which were close to those known for the CuInTe2 ternary compound with the composition index n = 0. First, photosensitive structures are fabricated based on CuIn5Te8 crystals, and photosensitivity spectra are obtained for them; it is shown that it is possible to achieve broadband photosensitivity under illumination of the barrier side of these crystals. From the analysis of photosensitivity spectra, the character of band-to-band transitions and corresponding energies of these transitions in CuIn5Te8 are determined. This opens up prospects to use this new semiconductor in photoconverters of solar radiation.

Surface-barrier structures on single crystals of CdMgMnTe quaternary solid solutions: Creation and properties

Planar melt crystallization is used to grow single crystals of Cd-Mg-Mn-Te quaternary alloys along the pseudobinary sections Cd0.75 − x Mg x Mn0.25Te, Cd0.75 − x Mg0.25Mn x Te, and Cd1 − 2x Mg x Mn x Te. The first photosensitive structures, i.e., In/CdMgMnTe Schottky barriers, are fabricated within each indicated single-crystal section. The spectral dependences of the relative quantum efficiency of photoconversion are measured, and the broadband photosensitivity of the new structures is detected. Based on the spectral dependences of the photosensitivity, the nature of the meson transitions is discussed and the corresponding band gaps are determined. The applicability of grown single crystals of CdMgMnTe quaternary alloys to broadband photoconverters of optical radiations is ascertained.

Growth of tetragonal CdP2 single crystals and the properties of barriers on their basis

Large (50 mm long, 20 mm in diameter) CdP2 single crystals with tetragonal symmetry are grown by vapor-phase crystallization for the first time. The unit cell parameters of the single crystals are determined, and it is shown that they have the stoichiometric composition of cadmium diphosphide. Photosensitive In(Cu)/CdP2 structures are fabricated, and their photosensitivity spectra are investigated. It is found that these structures exhibit broadband photosensitivity. The mechanism of photoelectric conversion and the type of interband transitions are discussed. From indirect and direct interband transitions, the bandgap values that are responsible for edge absorption are determined. It is concluded that CdP2 single crystals are feasible for broadband optical converters.

Cd‐free Cu(In,Ga)Se2/In2S3 thin‐film heterostructures

AbstractThe technology of heat treatment of initial Cu‐In‐Ga layers in an inert N2 atmosphere in the presence of Se and S vapors was used in self‐organized growth of homogeneous films of Cu(In,Ga)(S,Se)2 alloys onto which the CdS or In2S3 films were deposited and, on the basis of these structures, thin‐film glass/Mo/p‐Cu(In,Ga)(S,Se)2/(In2S3, CdS)/n‐ZnO/Ni‐Al heterostructures were created. The mechanism of charge transport and the processes of photosensitivity in the obtained structures subjected to irradiation with natural and linearly polarized light are discussed. The broadband photosensitivity of thin‐film heterostructures and induced photopleochroism were detected. These findings indicate that there is an interference antireflection of the structures obtained. It is established that higher solar‐cell efficiency in these heterostructures occurs if In2S3 thin films are used as heterobarriers. This technology can be used in the creation ecologically safe Cd‐free next generation thin‐film solar cells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cadmium-free thin-film Cu(In,Ga)Se2/(In2S3) heterophotoelements: Fabrication and properties

The method of heat treatment of metallic Cu-In-Ga layers in the N2 inert atmosphere in the presence of selenium and sulfur vapors was used to grow homogeneous films of Cu(In,Ga)(S,Se)2 alloys onto which the CdS or In2S3 films were deposited and, on the basis of these structures, the thin-film glass/Mo/p-Cu(In,Ga) (S,Se)2/n-(In2S3,CdS)/n-ZnO/Ni-Al photoelements were fabricated. The mechanisms of charge transport and the processes of photosensitivity in the obtained structures subjected to irradiation with natural and linearly polarized light are discussed. The broadband photosensitivity of thin-film heterophotoelements and the induced photopleochroism were detected; these findings indicate that there is an interference-related blooming of the structures obtained. It is concluded that it is possible to use ecologically safe cadmium-free thin-film heterostructures as high-efficiency photoconverters of solar radiation.

Electro-optic study of acrylate based holographic polymer dispersed liquid crystals with broad band photosensitivity

We describe the electro-optic (EO) modulation of diffraction in holographic polymer dispersed liquid crystals, recently developed for broad band photosensitivity, ranging from visible to near infrared. More than 90% EO modulation achieved for relatively low electric fields confirms the phase separation and formation of liquid crystal sub-micrometer sized droplets in the polymer matrix. Molecular reorientation induced by the applied voltage and a residual electrical current induced heating are at the origin of the EO modulation.

Photosensitivity of heterojunctions obtained using thermal oxidation of indium phosphide

Heterojunctions of the n-Ox/p-InP type have been obtained for the first time by means of thermal oxidation. Stationary current-voltage characteristics of the heterojunctions were measured and the photovoltaic effect in these structures have been studied under exposure to natural and linearly polarized radiation. Specific features of the current transfer and the broadband photosensitivity are discussed. The proposed method of thermal oxidation can be used for the fabrication of effective InP-based heterophotocells.

Long-wavelength photodiodes based on n-GaSb/n-GaInAsSb/p-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.

Photoelectric cells based on n-Ox/n-InSe heterojunctions: fabrication and properties

Rectifying photosensitive n-Ox/n-InSe heterojunctions, where n-Ox is native oxide of InSe, are obtained by the thermal treatment of the n-InSe crystals in air. The spectra of the relative quantum efficiency of the originally obtained heterojunctions are investigated in natural and linearly polarized radiation. It is shown that the heterojunctions obtained manifest broad-band photosensitivity, and photopleochroism emerges under oblique incidence of the linearly polarized radiation. The nature of the photopleochroism revealed is discussed. It is concluded that the isotype Ox/InSe structures can be used as photoconverters of natural and linearly polarized radiation.

Chronic actinic dermatitis

Chronic actinic dermatitis is a photosensitive skin disease that most commonly affects elderly Caucasian males, but can also affect younger patients, particularly those with an atopic background. The clinical presentation is that of a recurrent dermatitis of the photo-exposed sites that can progress to a more lichenified and generalized appearance in the chronic phase. Investigation is best performed at specialist phototesting centers using monochromator phototesting and reveals broadband photosensitivity. Positive patch and/or photopatch testing to allergens is seen in approximately 75% of patients. The etiology of chronic actinic dermatitis has not yet been fully elucidated but a probable basis is that of delayed T-cell-mediated cellular hypersensitivity to an as yet unknown photo-induced antigen. The clinical treatment of chronic actinic dermatitis can be problematic and is focused around physical measures to prevent recurrent exacerbations and suppressive methods to limit the severity of such episodes...

Photosensitivity of GaAs: NGaP: N/GaAs (GaP) heterojunctions in linearly polarized radiation

Results are presented of investigations of the photoelectric properties of nitrided layer/GaAs (GaP) heterojunctions prepared by plasma treatment of GaAs and GaP crystals in the presence of nitrogen ions. The heterojunctions exhibited broad-band photosensitivity relative to the intensity of the natural radiation. It was established that when linearly polarized radiation is obliquely incident on the surface of nitrided layers, polarization photosensitivity occurs which is controlled by the angle of incidence Θ and increases proportionately as Θ2. The spectral dependences of the induced photopleochroism are attributed to the antireflecting properties of the wide-gap layers. Nitrided-layer heterojunctions can be used as broad-band photoanalyzers for linearly polarized radiation.