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Numerical simulations are performed for SiGeC/Si electrooptic modulators and photodetectors operating at near-IR wavelengths. The addition of carbon provides the ability to lattice match layers with high germanium composition to silicon, which is shown to allow structures with a substantial increase in the optical confinement factor. In addition, SiGeC/Si heterostructures provide strong confinement of large electron and hole concentrations. The large optical confinement factor and strong carrier confinement enable broadband electrooptic modulators with sub-100 μm lengths and switching times below 0.5 ns with 25 mA current as well as photodetectors with quantum efficiencies as high as 90% for 300 μm length.

A photovoltaic photodetector harnessing near infrared band gap absorption by thin films of post-synthetically sorted semiconducting single walled carbon nanotubes (s-SWCNTs) is described. Peak specific detectivity of 6×10¹¹ Jones at -0.1 V bias at 1210 nm is achieved using a heterojunction device architecture: indium tin oxide/ ca. 5 nm s-SWCNT / 120 nm C₆₀ / 10 nm 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) / Ag. The photodiodes are characterized by a series resistance of 2.9 Ω cm² and a rectification ratio of 10⁴ at ±1V. These results are expected to guide the exploration of new classes of solution-processable, mechanically flexible, integrable, thin film photovoltaic photodetectors with tunable sensitivity in the visible and infrared spectra based on semiconducting carbon nanotubes.

Modern integrated circuits have active components on the order of nanometers. However, optical devices are often limited by diffraction effects with dimensions measured in wavelengths. Nanoscale photodetectors capable of converting light into electrical signals are necessary for the miniaturization of optoelectronic applications. Strong coupling of light and free electrons in plasmonic nanostructures overcomes these limitations by confining light into sub-wavelength volumes with intense local electric fields. Localized electric fields are intensified at nanorod ends and in nanogap regions between nanostructures. Hot carriers generated within these high-field regions from nonradiative decay of surface plasmons can be injected into the conduction band of adjacent semiconductors, enabling sub-bandgap photodetection. The optical properties of these plasmonic photodetectors can be tuned by modifying antenna materials and geometric parameters like size, thickness, and shape. Electrical interconnects provide connectivity to convert light into electrical signals. In this work, interconnected nanogap antennas fabricated with 35 nm gaps are encapsulated with ALD-deposited ${\mathrm{\text{TiO}}}_2$, enabling photodetection via Schottky barrier junctions. Photodetectors with high responsivity (12$\mu$A/mW) are presented for wavelengths below the bandgap of ${\mathrm{\text{TiO}}}_2$ (3.2eV). These plasmonic nanogap antennas are sub-wavelength, tunable photodetectors with sub-bandgap responsivity for a broad spectral range.

Doping of the lead telluride and related alloys with the group III impurities results in the appearance of unique physical features of the material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review physical principles of operation of the photodetecting devices based on the group III doped IV–VI including possibilities of fast quenching of the persistent photoresponse, construction of a focal-plane array, new readout technique, and others. Comparison of performance of the state of the art Ge(Ga) and Si(Sb) photodetectors with their lead telluride based analogs shows that the responsivity of PbSnTe(In) photodetectors is by several orders of magnitude higher. High photoresponse is detected at the wavelength of 241 μm in PbSnTe(In), and it is possible that the photoconductivity spectrum covers all the submillimeter wavelength range.

The effect of grain boundary on the characteristics of poly-Si metal–insulator–semiconductor photodetector is investigated utilizing two-dimensional device simulator. In the investigation, the trap states in grain boundary are composed of two types: tail states and deep-level states, both of which consist of acceptor-like trap and donor-like trap. The simulation results show that the photocurrent of photodetector decreases considerably in the case of tail states above 5 ×19 cm^-3, but less susceptible to deep-level states. Furthermore, it is found that the spectral responsivities of the photodetector decrease when the energy level of acceptor-like traps shifts towards the midgap, but keep unchanged for the case of donor-like traps.

We report on fabrication and characterization of SnO₂–Sin–n made by deposition of SnO₂ film onto monocrystalline silicon substrate by rapid photothermal oxidation (RPO) of Sn with condition 500°C/120 s. The film has been characterized by techniques such as XRD, optical transmission, and Hall effect. The XRD spectrum showed that the grown SnO₂ was polycrystalline in nature with tetragonal crystal structure. From optical transmittance data the band gap of SnO₂ film was calculated and found to be 3.9 eV. The electrical measurement revealed that the SnO₂ film was n-type. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics of SnO₂–Si heterojunction were investigated. The ideality factor of junction estimated from I–V characteristics was 1.8 at 300 K. The spectral responsivity of heterojunction having two peaks of response located at 650 nm and 850 nm.

In this study, we report, for the first time, on synthesis of lanthanum oxide ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ nanoparticles NPs by laser ablation in water without using surfactant. The effect of laser wavelength on the optical and structural properties of ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ NPs was investigated. X-ray diffraction studies show formation of polycrystalline lanthanum oxide with pure cubic phase and the crystallinity of the nanoparticles synthesized with $\lambda =532$ nm was better than that prepared with $\lambda =1064$ nm. The optical absorption investigations reveal that a strong absorption peak at 234 nm was observed for ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ NPs prepared at 532 nm laser wavelength. The optical energy gap of ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ NPs synthesized with 532 and 1064 nm laser wavelengths were 5 and 4.5 eV, respectively. Scanning electron microscope (SEM) investigation indicated the formation of nanoparticles with average particle size of 35 nm for ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ prepared with 532 nm and was 75 nm for ${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$ prepared with 1064 nm laser wavelength. The effect of laser wavelength on the optoelectronic properties of hybrid In/p-${\mathrm{\text{La}}}_2{\mathrm{\text{O}}}_3$/n-Si photodetector was studied. The responsivity studies of the photodetectors show the presence of two response peaks at 250 and 750 nm.

Two-dimensional material-based photodetectors (PDs) show great potential owing to unique optoelectronic characteristics and attract much attention in research. However, poor absorption of two-dimensional material remains a vital restriction. Responsivity improvement by applying Au nanoparticles (NPs) through surface plasmon (SP) is studied both in theory and simulation. The effect of size and NPs distribution density is analyzed concerning absorption promotion and fabrication feasibility. Both absorption spectrum and inner electric field are studied. A novel face-to-face PD is proposed that performs better in visible range. The results can be helpful in two-dimensional material PD design and fabrication where high responsivity is required.

To form a tungsten disulfide film, a tungsten trioxide film is deposited first and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high-temperature environment. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment and the bias voltage during each process was monitored. In this experiment, a sapphire substrate and a silicon substrate with 200nm silicon dioxide are used. Then use optical instruments such as Raman optics, ellipsometers and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Moreover, two-dimensional tungsten disulfide thin film has a response to light, gas and pH and related devices have been successfully fabricated in experiments. Among them, comparing the single-layer film and the double-layer film, the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.

A GaAs/AlGaAs multi-quantum well (MQW) structure has been grown by solid source molecular beam epitaxy (MBE) and fabricated to detectors. A spectral response curve of the detector with full width at half maximum (FWHM) = 3.78 μm and peak wavelength = 9.73 μm has been obtained at a bias of E = 3 × 10³Vcm^-1 at T = 77 K. We study the bandwidth of the GaAs/AlGaAs quantum well infrared photodetector (QWIP) by using effective mass approximation. It is found that the transmissivity of the electron through the potential barrier reaches its maximum value (T = 1) on the condition of resonance transmission in a multi-quantum well structure, if the energy state is defined as a conduction state when the transmissivity of electron through the potential barrier on which is bigger than 1/2, then, a series of separated conduction microbands were formed above the barriers which consist of conduction states. Under the influence of an external electric field, the conduction microbands stagger periodically among the quantum wells to form a Wannier–Stark ladder. When optical excitation occurs, electrons not only vertically transit from Fermi level EF in a quantum well to conduction microbands above the well, but also obliquely transit to the conduction microbands above the neighboring well, and the formed photocurrent peaks overlap together; consequently, the bandwidth of the photoresponsive spectrum is improved. The calculated bandwidth of the photocurrent spectrum agrees well with the measured one in our experiment.

A surface acoustic wave ultraviolet photodetector was fabricated on a ZnO thin film with pure and Ni-doped ZnO nanorods deposited on a Si substrate. Piezoelectric ZnO thin films were grown on Si through radio-frequency magnetron sputtering, and ZnO nanorods were synthesized on ZnO thin films by using the hydrothermal method. The crystalline structure, surface morphology, and luminescent characteristics of ZnO films and nanorods were examined using X-ray diffraction and photoluminescence spectrometers and scanning electron microscope. The performance of the surface acoustic wave photodetector was evaluated using the variations in surface capacitance, insertion loss, and phase shift. ZnO nanorods became shorter and thicker with an increase in the concentration of Ni doping; however, the variations in surface capacitance of Ni-doped ZnO nanorods were greater than those of pure ZnO nanorods obtained under ultraviolet irradiation. Devices with Ni-doped ZnO nanorods exhibited larger shifts in insertion loss and phase than those with pure ZnO nanorods did.

To obtain high performance optoelectronic devices, ferroelectric materials have received a lot of attention due to the various emerging effects on channel materials induced by the ferroelectric polarization. In this work, a special photodetector with the channel material of a triple-layer MoS₂ on a polarized LiNbO₃ substrate was fabricated. The device has a high responsivity of 113.1A/W and a high specific detectivity of up to $7.286\times 10^{12}$ Jones under red illumination, while maintaining the rise and fall time of 32 and 22ms, respectively. Meanwhile, the dark current of this device can be as low as $2.66\times 10^{-11}$A with a bias of 5.0V because the channel material MoS₂ is almost depleted under the internal electrical field induced by the polarized LiNbO₃. This work promises a feasible way for the future development of integrated high-sensitivity photodetectors.

In this work, the La-doped ZnO thin films were fabricated with different La concentrations by the use of sol–gel technique to synthesize the photodevice. The transparent metal oxide La-doped ZnO thin films were grown on glass and $p$-Si substrates using spin coating technique. Optical, surface morphology and electrical characterization of the fabricated Al/$p$-Si/La:ZnO/Al devices have been performed using $I$–$V$ and $C$/$G$–$V$ characteristics under dark and different illumination conditions. Herein, from $I$–$V$ characteristics, the crucial electronic parameters such as barrier height, ideality factor and series resistance were investigated. The photodevice transient photocurrent increases with the increase of illumination intensity. The current ratios of $I_{\mathrm{\text{on}}}$/$I_{\mathrm{\text{off}}}$ were calculated for the fabricated devices. Among the devices, the highest photoresponse was found to be about 2186 for the Al/$p$-Si/La(0.5 wt.%):ZnO/Al structure. The $R_s$–$V$ behavior of fabricated device confirms the presence of interface states. The obtained results and photoresponse behaviors suggested that Al/$p$-Si/La:ZnO/Al devices can enhance the applications in optoelectronic devices such as photodetectors.

Reduced graphene oxide (rGO) has attracted interest in its potential application in large area photodetectors owing to its ease of manufacture and wideband optical absorbance. Here, we report that thin rGO films produced via vacuum filtration of GO followed by reduction by immersion in L-ascorbic acid are capable of sensing light through a bolometric mechanism. The photoresponse of these rGO thin films can be further enhanced by dropcasting graphene quantum dots (GQDs) on the rGO surface. These GQDs were observed to increase the opacity of the rGO film and hence its absorptivity of light, thereby enabling a significant increase in the photoresponse of the device.

Nonlinear processes in quantum well infrared photodetectors (QWIP) are reviewed. Being an intersubband dipole transition based photoconductor, the nonlinear behaviors in QWIPs are caused by both the (extrinsic) photoconductive transport mechanism and (intrinsic) nonlinear optical processes. Extrinsic nonlinearity leads to a degradation of QWIP performance at high incident power or low operating temperatures. Some intrinsic nonlinear QWIP properties are useful in applications, such as in autocorrelation of short pulses by two-photon absorption. The general area of QWIP nonlinear properties has not been extensively investigated. We point out some directions for further studies and hope to stimulate more research activities.

Zinc oxide (ZnO) is a wide bandgap semiconductor with excellent photoresponse in ultra-violet (UV) regime. Tuning the bandgap of ZnO by alloying with cadmium can shift its absorption cutoff wavelength from UV to visible (Vis) region. Our work aims at synthesis of Zn${}_{1-x}$Cd_xO nanoparticles by co-precipitation method for the fabrication of photodetector. The properties of nanoparticles were analyzed using X-ray diffractometer, UV–Vis spectrometer, scanning electron microscope and energy dispersive spectrometer. The incorporation of cadmium without altering the wurtzite structure resulted in the red shift in the absorption edge of ZnO. Further, the photoresponse characteristics of Zn${}_{1-x}$Cd_xO nanopowders were investigated by fabricating photodetectors. It has been found that with Cd alloying the photosensitivity was increased in the UVA-violet as well in the blue region.

ZnS nanostructures are synthesized by a wet chemical route using starch as green capping agent under nitrogen environment. The as-prepared nanostructures are characterized structurally, optically and electrically. X-ray diffraction (XRD) spectra confirm that the zinc sulfide (ZnS) nanoparticles have cubic phase (zinc blende). UV–Vis spectrum of the sample clearly shows that the absorption peak exhibits blue shift compared to their bulk counterpart, which confirms the quantum confinement effect of the nanostructures. Its photoluminescence (PL) spectrum shows near band gap emission at 392nm and extrinsic emission at 467nm. The particle sizes calculated from XRD and UV studies are in fair agreement with high resolution transmission electron microscopy (HRTEM) results. Starch is found to be a noble capping agent in bringing quantum confinement. The synthesis under nitrogen environment has been observed to produce quality products by reducing the oxide traces. Moreover, the I–V characteristics under dark and illumination show that ZnS can be more suitable as photodetector.

Photodetectors (PDs) based on single-walled carbon nanotube film/silicon and graphene/silicon heterojunctions have been realized for fast applications. We investigated the response of the PDs to femtosecond pulsed laser using a three-electrode configuration for photoconductive operations. Both junction PDs exhibit rise times of some nanoseconds, detecting light from ultraviolet (275nm) to infrared (1150nm). Applying a gate voltage $V_G$, the rise time decreases down to about 1ns, making our devices comparable to most commercial PDs.

In this paper, photoelectrochemical etching of the n-type silicon (n-Si) wafers is used to prepare porous silicon (PSi) with current density of 10 mA.cm${}^{-2}$ for 10 min. Moreover, the structural and morphological properties of the n-PSi were analyzed by using XRD and AFM, FTIR and PL. XRD patterns of PSi show that the films are single-crystalline, with cubic structure. The major peak characteristics are allocated to plane (004). The atomic force microscope image and the distribution chart of the grains of the n-PSi displayed that the grain sizes were −8.98. FTIR is a powerful and easy-to-use technique to obtain the surface chemical state of PSi. The convenience results from the transparency of silicon for IR light and the high surface area. The basic features begin from the knowledge of the bondings to hydrogen, [Si–H], and to oxygen [Si–O]. The model calculations sometimes provide useful information in the assignment. By examining FTIR, the active bonds showed the formation of PSi. PL spectra were measured in the range of (600–900) nm, the emission peak for the fixed excitation wavelength at 500 nm, and spectral 1.78 eV and 1.24 eV. PSi is recognized as an attractive building block for photonic devices because of its novel properties including high ratio of surface to volume and high light absorption. We first report NIR and VIS (PDs) fabricated by PSi as a carrier collector and a photoexcitation layer.

Zinc oxide and dye are utilized to absorb and convert incident photons to electric energy using a sandwich construction with an active area of 1.5 × 1.5 cm², which improves the photodetector’s performance as a light sensor. A variable variation of solution concentration according to the ratio of mass and volume was used to extract natural dye from Barago officinalis. The Barago officinalis absorbance was investigated by spectrophotometer at a wavelength of 200–1000 nm. This indicates that UV absorption has occurred, and note that when an increase in the spectral response at concentration of 1, there appears an improvement in the infrared region with a wave length of 950 nm and the enhanced sensitivity in the long wavelength region could be attributed to formation of dye aggregates within the devices which led to the highest value of qualitative detection up to 1.3 × 10${}^{13}$ W${}^{-1}$ cm Hz${}^{1/2}$ thus increasing quantum efficiency to (119)% at the wavelength (950 nm).