Lead sulfide colloidal quantum dots (PbS CQDs) exhibit tunable infrared bandgaps via quantum confinement but suffer from trap states predominantly localized on {100} facets, which severely degrade device performance in large CQDs due to increased facet exposure. To address the persistent challenge of fabricating high-quality large CQD films (>1.7 mu m exciton peak), we developed a solution-phase exchange method to synthesize defect-controlled PbS CQDs. Furthermore, a self-powered p-i-n photodetector integrating a WOx interfacial modification layer was engineered. The WOx layer enhances contact quality at the metal electrode/PbS CQD film interface, which achieves an ultra-low dark current density of 4.54 nA cm(-2) at -0.5V. Then, the device demonstrates excellent responsivity and detectivity across a broad range of illumination wavelengths, from 0.36 mu m to 1.7 mu m. Notably, the device achieves an exceptional detectivity for infrared light at 1.7 mu m, exceeding 10(10) Jones. These findings pave the way for designing and developing novel device structures for high-performance infrared photovoltaic detectors with extended wavelength capabilities.

Electrochemical etching is a scalable route to engineer nanoporous architectures in doped GaN, but cross-comparative investigations spanning the full electrolyte chemical window are still very limited. Here, we explore the electrochemical etching of Si-doped n-GaN in acidic, alkaline, and neutral electrolytes and correlate morphology, optical properties, and surface chemistry by using various characterization and simulation methodologies. Our findings reveal that the electrolyte with different pH values not only affects the pore size and density but also alters the dominant etching mode, which leads to morphologies ranging from interconnected "sponge-like" three-dimensional pore networks to intact surfaces with slightly and anisotropically etched pores beneath. We have established semiquantitative models to elaborate the changes in near-band edge absorption due to disorders of the pores and to describe the surface oxidation/hydroxylation, through respective optical and x-ray photoelectron spectroscopy measurements. The models are further corroborated with the Raman observations, supporting a unified picture in which porosification increases disorder/local strain fluctuations. We envisage that this work offers important information on the electrochemical etching of III-nitrides using electrolytes in full pH ranges and proposes new analytical methods, which are valuable in developing power-efficient GaN optoelectronic devices.

Mid-wave infrared photodetectors offer significant potential for a wide range of important applications. Due to their unique sub-wavelength localization properties, infrared photodetectors based on surface plasmon polaritons (SPPs) have garnered considerable research interest. Many of these applications require bandwidth response from the infrared photodetectors. In this paper, Dammann gratings (DGs) with a one-dimensional (1D) metal/dielectric layer structure were designed to achieve a diffraction field distribution modulated by a non-sinc function, which in turn was used to excite SPPs resonance. These gratings are capable of supporting multi-order SPPs resonance, facilitating enhanced bandwidth absorption across multiple resonant orders. By varying the combinations of diffraction slit spacings within a single period, the DGs could achieve distinct phase difference distributions. Specifically, DGs with a lattice constant of d = 27.3 μm demonstrated the ability to generate two to four orders of strong diffraction intensity distribution within 4-5 μm range, thereby enabling multi-order resonance-enhanced absorption of SPPs. Furthermore, the SPPs response of the DGs exhibited improved tolerance to variations in polarization angles across a broadband spectrum. This multi-order SPPs resonance-enhanced structure presents significant potential for applications in infrared detection, including the development of large-scale infrared photodetector units.

Broadband photodetector (PD) that can response to a broad spectrum from ultraviolet (UV) to near infrared (NIR) has attracted much research activities due to its many potential applications in a variety of fields, such as image sensing, optical communications, environmental monitoring, and day and night surveillance. In this work, a high -performance broadband PD based on NiO/TiO 2 /n-Si heterojunction is reported. The device consisted of a 2 nm TiO 2 tunnelling layer, which was deposited by magnetron sputtering technique, between NiO and n -Si. The heterojunction photodetector (HPD) exhibits high sensitivity toward a broad spectrum from 341 to 1050 nm. It yields maximal responsivity of 1.47, 0.58, 0.82, 0.97, 1.62 and 1.21 A/W under 341, 365, 660, 850, 940 and 1050 nm illumination, respectively, at a bias voltage of -1 V. The corresponding detectivities are between 2.6 x 10 11 and 7.3 x 10 11 Jones. The external quantum efficiency ( EQE ) as high as 553 % indicates a remarkable gain of the HPD. Notably, the HPD shows self-powered characteristics with an ultrahigh responsivity of 1.15 A/W and detectivity of 6.38 x 10 12 Jones. In addition, the fast response speed of less than 0.1 s is obtained under zero bias. The results demonstrate the development of low-cost, self-powered and high -performance silicon based broadband HPD.

Lead sulfide nanocrystals, also known as lead sulfide colloidal quantum dots (PbS CQDs), have a tunable bandgap, a large exciton Bohr radius and a wide size distribution. The high-quality PbS CQDs have shown excellent photoelectric properties in the field of infrared photodetectors. Monodisperse PbS CQDs can be successfully synthesized by hot injection method in solution, using elemental sulfur and lead oxide as reaction precursors. The synthesized CQDs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis- NIR spectrophotometer. It is concluded that the PbS CQDs synthesized under the condition of 120°C and 90 min are truncated octahedrons. I- can further passivate the exposed (200) crystal plane when tetrabutylammonium iodide (TBAI) was used for ligand exchange. The prepared CQDs films can be applied to infrared photodetectors and solar cells. Finally, the particle size of CQDs was analyzed by Scherrer formula and the probability statistical model was proposed. The correction coefficient of the particle size of PbS CQDs related to the shape factor was summarized.

Ultraviolet (UV) photodetectors have found wide-ranging applications, ranging from optical communications to chemical detection. High performance UV photodetectors that can be self-powered are highly desirable in many applications as they can minimize energy consumption during operation. Herein, a self-powered UV photodetector, which consisted of poly(9-vinylcarbazole) (PVK)/amorphous-WO3 organic-inorganic heterojunction with PEDOT:PSS as a hole transport layer, was fabricated using a two-step method at low temperature. The effect of WO3, PVK and PEDOT:PSS films on the performances of the photodetector was also investigated. Under optimized parameters, the PEDOT:PSS/PVK/WO3 photodetector exhibited a maximum responsivity of 12.41 AW-1, specific detectivity of 1.80 x 1013 Jones, photo-dark current ratio of 103 at reverse bias and typical rectification characteristic when exposed to 365 nm light irradiation. The photoelectric conversion mechanism of this novel PVK/WO3 heterojunction is discussed using energy band diagrams. This work presents a method to produce a high performance WO3-based heterostructure at low temperature, which has the potential for UV imaging.

In this work, two-dimensional graphene oxide (GO) (e.g., oxygenated graphene sheets with epoxy, hydroxyl, and carboxyl groups) was reduced to zero-dimensional Br-doped GO quantum dots (Br-GODs) using a one-step method. The GO, which exhibits poor electrical conductivity, was reduced to Br-GODs using hydrobromic acid as a bromine source and reducing agent during hydrothermal reaction. The morphology, structural and photoelectric properties of GO and Br- GODs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible near infrared (UV-Vis-NIR) absorption spectroscopy, photoluminescence (PL), photoluminescence emission (PLE), Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). A photodetector based on Br-GODs material, consisting of interdigitated electrodes, was prepared. The responsivity (R) and detectivity (D*) of the photodetector can reach a maximum of 0.54 A/W and 4.33 × 1013 Jones, respectively, under 850 nm illumination.

Zero-dimensional graphene quantum dots (GQDs) exhibit many different properties, such as strong fluorescence, nonzero bandgap and solubility in solvents, compared to two-dimensional graphene. GQDs are biocompatible and have low toxicity; hence, they are widely used in the biomedical field. The edge effect of GQDs is of particular interest because edge modification can regulate the performance of nanomaterials. In this review, various preparation methods for GQDs, which can be divided into three main categories, namely top-down, bottom-up and chemical methods, are discussed. The unique optical, electrical, thermal and magnetic properties of GQDs are reviewed. The functionalization of GQDs by doping with heteroatoms and forming composites with other materials is studied, and the characteristics of these GQDs are also discussed. The applications of these GQDs in the fields of optics, electricity, optoelectronics, biomedicine, energy, agriculture and other emerging interdisciplinary fields are reviewed to highlight the enormous potential of nanomaterials. This review reports on the recent advancement in GQD research and suggests future directions for the development of GQDs.

Cobalt sulfide (CoS) is a zero bandgap transition metal chalcogenides (TMCs). However, the bandgap of CoS can be altered when it exists as low-dimensional material, such as quantum dots (QDs), via different preparation methods. In this work, CoS QDs were successfully prepared by liquid-phase ultrasonic exfoliation method and CoS QDs film was obtained by spin coating CoS QDs solution onto a substrate. The morphology, structural, chemical properties, thickness, vibration peaks and chemical bonds of CoS QDs were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), atomic force microscopy (AFM), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The absorption and fluorescence characteristics of the CoS QDs were studied using ultraviolet-visible-near infrared (UV-Vis-NIR) and fluorescence spectroscopies. Results show that the average size of CoS QDs was 9.1 nm and average thickness was 8.4 nm and CoS QDs solution and film exhibited absorption in the infrared band. With an increase of excitation and emission wavelength, both the photoluminescence (PL) peak and photoluminescence excitation (PLE) peak of CoS QDs solution and film showed red-shift, which demonstrates Stokes shift effect and dependency on wavelength and have near-infrared luminescence characteristics. The infrared absorption and near-infrared luminescence properties of CoS QDs solution and film imply that they can be found important application in the field of infrared detection. Such novel material is expected to play a crucial role in low-cost, high performance infrared photodetector.

Transition metal chalcogenides (TMCs) have wide-ranging applications in nanoelectronics and optoelectronics due to their unique energy band structure and excellent properties. Iron(Ⅱ) sulfide quantum dots (FeS QDs) are environmentally friendly semiconductor material and exhibit excellent near-infrared properties because of their narrow bandgap, which is essential for infrared detectors. In this paper, FeS QDs were prepared by liquid phase ultrasonic exfoliation and the solution of FeS QDs was spin-coated on a quartz substrate to form a film. The morphology, structural and optical properties of FeS QDs solutions and films were studied. FeS QDs demonstrated good dispersion with average particle size and height of approximately 11.7 and 10.4 nm, respectively. The calculated average particle size of FeS QDs was 12.7 nm using the Debye-Scherrer formula, which is in good agreement with the TEM characterization. The ultraviolet-visible-near infrared (UV-Vis-NIR) characterization of the FeS QDs solutions and films exhibited obvious absorption in the ultraviolet to near-infrared wavelength band, and the absorption was stable in the near-infrared wavelength band. The photoluminescence (PL) characterization of the FeS QDs solutions and films revealed luminescence properties in the near-infrared wavelength band, and the peak position appeared to be red-shifted with an increase in excitation wavelength, which suggests excitation wavelength-dependent luminescence properties. The FeS QDs exhibit good infrared characteristics and can potentially be used in infrared photovoltaic and photodetector.

Quantum dots infrared photodetector (QDIP) has found important applications due to its many advantages, such as long effective carrier life, low dark current, high operating temperature, facile preparation and low cost. In recent years, infrared photodetectors consisting of PbS and HgTe colloidal quantum dots (CQDs) have reported breakthroughs in the detection of short-wave infrared (SWIR) and mid-wave infrared (MWIR) demonstrating detectivity of 1×1013 Jones and 1×1011 Jones, respectively. However, these materials contain Pb and Hg elements, which are harmful to human and the environment. Therefore, the development of non-toxic quantum dot materials is highly desirable for QDIP. In this work, Ag2Se CQDs were studied for use in infrared photodetector. The novel CQDs have the advantages of low toxicity, good infrared optical properties, which can obtain adjustable infrared absorption due to its small bulk band gap of 0.15 eV, and biocompatibility etc. The Ag2Se CQDs were prepared by hot injection method and were characterized by Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), Fourier Transform Infrared spectrum (FTIR), Atomic Force Microscope (AFM) and X-ray Photoelectron Spectroscopy (XPS). These Ag2Se CQDs demonstrated good monodispersion, size uniformity and crystallization. Interestingly, the exciton peak appeared in the infrared band of 3-4 μm. Subsequently, Ag2Se CQDs photodetector was produced by spin coating the CQDs onto a 5 μm interdigital electrode. The device exhibited a low dark current of 1.3×10-6 mA with responsivity of 5 A/W and detectivity of 1.5×1013 Jones. The results of this work show that Ag2Se CQDs are expected to have potential applications in QDIP.

AbstractUltraviolet (UV) photodetectors have gained much attention due to their numerous important applications ranging from environmental monitoring to space communication. To date, most p‐NiO/n‐Si heterojunction photodetectors (HPDs) exhibit poor UV responsivity and slow response. This is mainly due to a small valence band offset (ΔEV) at the NiO/Si interface and a high density of dangling bonds at the silicon surface. Herein, an UV HPD consisting of NiO/Al2O3/n‐Si is fabricated using magnetron sputtering technique. The HPD has a large rectification ratio of 2.4 × 105. It also exhibits excellent UV responsivity (R) of 15.8 A/W at −5 V and and detectivity (D*) of 1.14 × 1013 Jones at −4 V, respectively. The excellent performance of the HPD can be attributed to the defect passivation at the interfaces of the heterojunction and the efficient separation of photogenerated carriers by the Al2O3 nanolayer. The external quantum efficiency (EQE) of the HPD as high as 5.4 × 103%, hence implying a large optical gain due to carrier proliferation resulting from impact ionization. Furthermore, the ultrafast response speed with a rise time of 80 µs and a decay time of 184 µs are obtained.

The tunable band gap of PbS colloidal quantum dots (CQDs) from ultraviolet (UV) to short-wave infrared (SWIR) bands provides many potential applications in optoelectronics. However, synthesis of large-sized CQDs that exhibit good stability and sensitivity for extended wavelength still remains a technological challenge. In this paper, a novel broadband photodetector based on small size PbS CQDs (with exciton absorption peak at 927 nm) and Bi2Te3 (with wide spectral sensitivity and high absorption) was devel-oped and studied. The device, which comprised of ITO/AZO/PbS CQDs/Bi2Te3/Al, provided an excellent band alignment that facilitated charge dissociation and transmission hence improving the device sensi-tivity. Furthermore, wavelength extension was also realized through the synergistic effect of these mate-rials, thus demonstrating broadband photodetection with high sensitivity. The heterostructure photodetector demonstrated good performance in the visible and near infrared ranges, especially at a wavelength of 1050 nm exhibiting a high responsivity (R) and detectivity (D*) of 161 A/W and 3.2 x 1013 Jones, respectively. In addition, the device exhibited excellent stability and reversibility after one month of storage without any encapsulation. This work lays a good foundation for the construction of the next generation of highly sensitive broadband CQDs photodetectors.& COPY; 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The ultraviolet (UV) photodetector has found many applications, ranging from optical communication to environmental monitoring. There has been much research interest in the development of metal oxide-based UV photodetectors. In this work, a nano-interlayer was introduced in a metal oxide-based heterojunction UV photodetector to enhance the rectification characteristics and therefore the device performance. The device, which consists of nickel oxide (NiO) and zinc oxide (ZnO) sandwiching an ultrathin dielectric layer of titanium dioxide (TiO2), was prepared by radio frequency magnetron sputtering (RFMS). After annealing, the NiO/TiO2/ZnO UV photodetector exhibited a rectification ratio of 104 under UV irradiation of 365 nm at zero bias. The device also demonstrated a high responsivity of 291 A/W and a detectivity of 6.9 × 1011 Jones at +2 V bias. Such a device structure provides a promising future for metal oxide-based heterojunction UV photodetectors in a wide range of applications.

SnTe is a new two-dimensional (2D) material, which has many merits, such as the bandgap of SnTe film can be adjusted by changing the film thickness hence its photoelectric properties can be regulated. SnTe belongs to topological crystal insulator (TCI) and has gapless topological surface states as well as exhibiting high carrier mobility at room temperature. SnTe has a narrow band gap and has potential for wavelength extension in the development of novel infrared photodetectors. Si is a traditional semiconductor material and has been widely used in the preparation of various semiconductor devices due to its numerous merits, such as low-cost and well-established preparation methodology. However, the detection wavelength of Si photoelectric detector is limited by its relatively large bandgap (1.12 eV). Recently, some progress has been made in fabricating photovoltaic detectors consisting of new 2D materials and Si. In this study, an efficient and low-cost magnetron sputtering method was used to prepare SnTe nanofilm on Si substrate. A photovoltaic detector based on the vertical heterostructure of SnTe/Si was fabricated using Al as electrode material. J-V characterization of the SnTe/Si heterostructure showed that the device exhibited good diode and photovoltaic characteristics under the illumination of various LED light sources with wavelength between 400 and 1450 nm, and its photocurrent was larger than the dark current. Moreover, under 850 nm illumination, the SnTe/Si device has a high responsivity (R) of 260 mA/W and detectivity (D*) of 3.36×1010 cmHz1/2W-1. Therefore, the device demonstrated potential application in the field of broadband photoelectric detection.

Lead sulfide colloidal quantum dots (PbS CQDs) are promising optoelectronic materials due to their unique properties, such as tunable band gap and strong absorption, which are of immense interest for application in photodetectors and solar cells. However, the tunable band gap of PbS CQDs would only cover visible short-wave infrared; the ability to detect longer wavelengths, such as mid- and long-wave infrared, is limited because they are restricted by the band gap of the bulk material. In this paper, a novel photodetector based on the synergistic effect of PbS CQDs and bismuth telluride (Bi2Te3) was developed for the detection of a mid-wave infrared band at room temperature. The device demonstrated good performance in the visible-near infrared band (i.e., between 660 and 850 nm) with detectivity of 1.6 × 1010 Jones at room temperature. It also exhibited photoelectric response in the mid-wave infrared band (i.e., between 4.6 and 5.1 μm). The facile fabrication process and excellent performance (with a response of up to 5.1 μm) of the hybrid Bi2Te3/PbS CQDS photodetector are highly attractive for many important applications that require high sensitivity and broadband light detection.

Ultraviolet (UV) photodetector has found extensive applications, ranging from optical communication to ozone sensing. Wide bandgap metal oxide heterostructures have gained significant interest in the development of UV photodetectors due to their excellent electronic and optical properties, as well as ease of fabrication. However, there are surface and interface issues at these heterostructures that have detrimental effects on device perfor-mance. In this work, UV photodetector consisting of p-NiO/SiO2/n-ZnO heterostructure was prepared by RF magnetron sputtering method. The device exhibited remarkable performances, such as having a rectification ratio of 57, responsivity (R) of 5.77 AW-1, external quantum efficiency (EQE) of 1.96 x 103% and rise time of 0.048 s at a low power consumption of-0.1 V under 365 nm UV irradiation. This work demonstrated a method for low-cost fabrication of photodetectors with rectification behavior and at low power consumption.

Photodetectors convert optical signals into electrical signals and have found many important applications ranging from environmental monitoring to communication systems. At present, most photodetectors are based on either bulk materials or epitaxially grown materials (such as InSb and HgCdTe), which limit its widespread applications due to relatively high fabrication cost. However, photodetector based on organic polymer/colloidal quantum dots (CQDs) can provide a low-cost alternative. In this paper, a broadband photodetector consisting of organic polymer phenyl-c61-butyric acid methyl ester (PCBM) and PbS CQDs was fabricated. Combining the advantages of PbS CQDs and organic polymer PCBM, the device demonstrated good spectral response ranging from the UV to the NIR with a maximum responsivity and detectivity of 0.3 A/W and 6.6 × 1011 Jones, respectively, under illumination of 850 nm incident light. The device can be fabricated on almost any substrate due to the solution-processibility of CQDs. Furthermore, the use of organic polymer substrate can significantly reduce the cost of device and broaden its applications (such as in flexible electronics). This work provides a simple and efficient strategy to fabricate photodetector that exhibits multi-band response at relatively low-cost.