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.
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.
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.
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.
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.
As one of the cornerstones of photoelectric detection system, ultraviolet (UV) detector has the ability to convert UV signal into electrical signal, which is widely used in optical communication, biomedicine, and other fields. NiO has a strong absorption of UV light due to its wide band gap of 3.4 to 4.1eV. In addition, NiO exhibits a p-type conduction at room temperature. Thus, it is often used to form a pn junction in combination with a n-type semiconductor for photodetection. Si has the unique advantages of being integrated and compatible with CMOS processes. By constructing the NiO/n-Si heterojunction, the advantages of Si and NiO can be combined to prepare high performance and low-cost UV detectors. However, most of the reported NiO/n-Si UV detectors showed large dark current and low UV responsivity. Besides the defects in the silicon and NiO, the thickness of NiO film is an important factor that affects the performance. Herein, the NiO/n-Si UV photovoltaic detectors with different NiO film thicknesses were fabricated. The effect of NiO film thicknesses, such as 32, 74, 113, 147, 198 and 270 nm, on the performance of NiO/n-Si UV detector was investigated. A NiO/n-Si UV detector with a NiO thickness of 198 nm showed the excellent performance with a low dark current of 0.6 μA at -1 V and a high rectification ratio of 1.8×104 at ±1 V. The maximum responsivity (R) and detectivity (D*) of the device were 1.3 A/W and 5.7×1011 Jones, respectively, under 365 nm UV illumination. This work demonstrated that controlling NiO thickness has an essential influence on the performance optimization of NiO/n-Si UV photovoltaic detector.
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.
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.
Silicon (Si) based photodetectors have been widely used in numerous applications due to their low-cost, high efficiency and good process compatibility. In this paper, a photodetector based on Si mesa heterojunction is reported. Si was doped by ion implantation and used to fabricate a photodetector. The conditions of ion implantation were simulated using a software to obtain the required process parameters before the commencement of the implantation process. The process involved deposition of 100 nm SiO2 film on to the Si substrate, and B ions were injected with 160 keV energy, 6×1014 cm-2 injection dose and at 7° dip angle. After ion implantation, the material was annealed at 900 ℃ for 30 min to repair crystal damages and activate the impurity level. Subsequently, a Si-based mesa heterojunction photodetector was fabricated using a series of standard processes. The photosensitive area of each device unit was 2.04 × 10-2 mm2 . The responsivity of the photodetector in the near ultraviolet and visible bands was more than 0.14 A/W under the bias of -2V. The responsivity of the device was measured using a 1073 K blackbody source, and the voltage responsivity of the blackbody was 1.35×102 V/W. Results from the C-V measurements revealed that the Si has a carrier concentration in the order of 1019 cm-3, which is in good agreement with the simulated results. The experimental results showed that ion implantation has an important effect on the electronic properties of the material and can greatly improve the photoelectric properties of devices.
Ultraviolet (UV) photodetector has been widely used in astronomical observation, missile warning, optical communication, flame and environmental detections and so on. Herein, recent research progress on UV focal plane detectors is summarized, including commonly used materials in this field. Furthermore, commercially available UV focal plane detectors, and its structure and performance are also discussed. Finally, the practical problems limiting the further development and application of UV focal plane detectors are summarized and discussed in this paper.
In this article, the band structures of InAs/InAsSb superlattices are calculated by sp3s* model, which is based on empirical tight-bonding method (ETBM). First, the band structures of InAs/InAsSb superlattice with varies period are calculated, the calculated bandgap results are consistent with experiment values. The conduction band edge (Ec level) for the two sets of InAs/InAsSb T2SLs are approximately independent of the cutoff wavelength (or band gap), and they are significantly lower than the conduction band edges of InAs/GaSb. The relationship between periodic structure and cutoff wavelength is obtained under the condition of strain balance. Then the holes effective mass at Γ point of mini-band along the growth direction for different structure InAs/InAsSb superlattice are derived. Finally, the composition segregation function is included in our model in order to study the impact of Sb segregation on InAs/InAsSb superlattice. These material parameters obtained from our calculated results can be used in the design of T2SL-based IR detectors.
As a topological crystal insulator, tin telluride (SnTe) has unique properties that are different from those of traditional topological insulators. Due to its helical multi-surface states, strong topological protection characteristics, gapless topological surface states, narrow bulk band gap, high mobility at room temperature and other excellent properties, SnTe has a great application potential in photodetectors with minimal energy consumption, broad spectrum and ultra-fast response. However, the preparation of large area high quality SnTe nanofilms is still a big challenge. Here, we report a facile and efficient preparation method for large area SnTe nanofilm (2 cm ×2 cm) by RF magnetron sputtering method. The nanofilm having a thickness of 5.8 nm and surface roughness of 0.51 nm was obtained. Moreover, the prepared nanofilm was crystallized without annealing treatment and exhibited uniform surface. The photoconductive prototype device based on the SnTe nanofilm demonstrated a significant photoelectric response under an illumination of 365, 555 and 850 nm light source at room temperature. Furthermore, the ultraviolet, visible and near infrared photoelectric performance of the device remained stable even after six months in the atmosphere of the drying cabinet. These results indicate that the SnTe nanofilm has potential applications in broad spectrum photodetectors.
Herein, SnSe2 QDs have successfully been prepared by liquid-phase ultrasonic exfoliation of the group IV metal-sulfide compounds. The morphology and structure of the SnSe2 QDs were characterized by transmission electron microscopy (TEM) and high-resolution transmission microscopy (HR-TEM), and the composition of the materials was analyzed by X-ray diffraction (XRD) and Raman spectroscopy (Raman). The absorbance of the samples with different wavelengths was analyzed by UV-Vis spectrophotometer, and the fluorescence intensity at different excitation wavelengths was studied by fluorescence spectrometer (PL), and the effect of different centrifugal speeds on the particle size of QDs and the spectral red-shift caused by the size effect was investigated. The average lateral sizes of SnSe2 QDs samples obtained at centrifugal speeds of 3500, 1500 and 500 rpm were 1.86 nm, 2.73 nm, and 3.3 nm, respectively. The SnSe2 QDs exhibited significant absorption in the infrared band and red-shift with increasing QDs size, The results demonstrated the potential use of this new material in infrared detection.
Silicon has been widely used in the field of low-cost photodetectors. However, the use of traditional silicon material for high performance infrared detectors is hindered by its indirect band gap. Recently, black silicon has attracted the attention of researchers working on optoelectronics as it can be considered a new type of material with high absorption, and expansion of the response band can be achieved by supersaturated doping. Importantly the material is compatible with the silicon process. With the development of science and technology, the application of photodetectors can have a great impact on our lives, so the research on black silicon photodetectors is also becoming popular. Up to now, significant progress has been made in the development of black silicon photodetectors. This paper summarizes the preparation of black silicon materials and the application prospect of black silicon photodetectors.
Colloidal quantum dots (CQDs) have been widely applied in the design and development of optoelectronic devices due to their controllable size, tunable band gap and inexpensive low temperature solution processing etc. However, the preparation method of quantum dots film is a critical part of the preparation process of optoelectronic devices, which can restrict the application of CQDs in optoelectronic devices. In this paper, different preparation technologies of CQDs film are summarized. The advantages and disadvantages of different preparation technologies of CQDs film are discussed to suggest suitable options for different CQDs film based optoelectronic devices.
HgCdTe films with low defect density grown by molecular beam epitaxy(MBE) has been proved to be irreplaceable materials for fabricating high performance infrared focal plane arrays(IRFPAs) such as dual band detector, high operating temperature(HOT) detector and avalanche photodiode(APD) detector. CdZnTe is the best choice of substrates for epitaxy of HgCdTe owning to the perfectly matched lattice. However, the Cd-rich or Te-rich precipitates in CdZnTe substrates are hard to completely eliminate. These precipitates in the CdZnTe substrates induced the formation of precipitate-related defects at the HgCdTe layer, resulting in detrimental device performance, especially for detectors with small pixel size and high operability. To understand the origin of the precipitate-related defects at the HgCdTe layer, we investigated the influences of Cd-rich and Te-rich precipitates in CdZnTe substrates on dislocations and macro-defects in HgCdTe gown by MBE. Gridlines were produced by photolithographic and wet etching process to locate small defects in SEM according to the location in dark field microscopy. Results indicated that Cd-rich precipitate leads to formation of a dislocation cluster in HgCdTe film. Etch pit density(EPD) in dislocation cluster area is in the range of 2×106 to 6×106 cm-2, about one to two orders of magnitude larger than EPD in a normal region. EPD in the cluster varies with depth of Cd-rich precipitates, and the relationship between them accords well with 1/h dislocation fall-off law, suggesting a minimum EPD of 5×105 cm-2 in dislocation cluster. In contrast, no dislocation cluster was found in HgCdTe film on CdZnTe with Te-rich precipitates, but Te-rich precipitates can lead to macro-defects, even under the optimum growth conditions. The typical macro-defect density resulted from Te-rich precipitates of state-of-the-art HgCdTe/CdZnTe is range from 100 to 500 cm-2, which is considered limited by Te-rich precipitates with size of 100 to 1000 nm if the high-density macro-defects caused by particles or pollution residues on CdZnTe substrates are excluded.
Graphene has received intensive attention in recent years because of the special physical and chemical properties. However, up to now graphene has not been widely used in optoelectronic fields yet, which is mainly caused by its semimetal properties. Therefore, changing its properties from semimetal to semiconductor is becoming a focal point. Recently, aiming at tuning the energy band of graphene, we have carried out systematic studies on the preparations of graphene based materials and devices, the CVD growth techniques of monolayer and double layer graphenes have been developed, the large-area doped graphene films have been fabricated to tune the structure-related optical and electrical properties. A novel graphene oxide (GO) preparation method namely “Tang-Lau method” has been invented, the graphene quantum dots growths by microwave assisted hydrothermal method and “Soft-Template method” have been developed, the Cl, S and K doped graphene quantum dots preparations by hydrothermal methods have also been invented. Systematic investigations have been carried out for the effect of preparation parameters on the properties of graphene based materials, the effects of size, doping elements on the energy level of graphene based materials have been explored and discussed. Based on the semiconducting graphene based materials, some novel room temperature photodetectors covering detection wavebands from UV, Vis and NIR have been designed and fabricated.
The study of FT-IR spectrum, Raman spectrum, UV-Vis absorption spectrum as well as photoluminescence spectrum on
organic ultraviolet semiconductor KIP-OUVS-1 has been investigated. The main vibrational peaks of organic ultraviolet
semiconductor KIP-OUVS-1 in FT-IR spectrum and Raman spectrum have been assigned. The study of UV-Vis solution
absorption spectrum on the organic ultraviolet semiconductor KIP-OUVS-1 shows that there is an obvious ultraviolet
absorption peak in 210~280nm range, there are several ultraviolet absorption peaks in 290~390nm range too. The
photoluminescence spectra of organic ultraviolet semiconductor KIP-OUVS-1 at different excitation wavelengths have
also been investigated, the result shows that in the excitation wavelength of 220~360nm range, the shapes for different
photoluminescence peaks are similar under different excitation wavelengths, the sole difference among them is strength
of the peaks. At 280nm and 300nm excitation wavelengths, the relatively strong peaks have been gotten, at 220nm and
250nm excitation wavelengths, however, the photoluminescence peaks are relatively weak. Furthermore, for organic
ultraviolet semiconductor KIP-OUVS-1, the photoluminescence peaks have a stokes' red shift compared with those
absorption peaks for the solution samples, and an enantiomorphous symmetry, which is the powerful experimental proof
of Franck-Condon theory, between the absorption spectrum and photoluminescence spectrum has been observed too. For
the reason that the organic ultraviolet semiconductor KIP-OUVS-1 may be used to prepare large-area thin film and
flexible device on low-price, flexible substrates by means of thermal evaporation and solution method, thus, the authors
deduce that the organic ultraviolet semiconductor KIP-OUVS-1 may have an important application potential in
ultraviolet optoelectronic detecting or lighting field.
In order to increase the species of organic infrared semiconductor, we synthesized organic infrared semiconductor
phthalocyanine gadolinium by using o-phthalodinitrile and GdCl3 as reactants, ammonium molybdate as catalyzer.
Under light and dark field modes of microscope, the translucency emerald-like powder of phthalocyanine gadolinium
has been observed, the size of the small grain for the sample is around 5μm in diameter, the size of larger grain may
reach to several tens of microns. The main vibrational peaks in FT-IR spectrum and Raman spectrum have been
assigned. Elementary analysis shows that the experimental data of phthalocyanine gadolinium in the main agree with
those of calculated data. The UV-Vis absorption spectrum of the sample indicates the sandwich-like structure of
phthalocyanine gadolinium. The organic infrared semiconductor phthalocyanine gadolinium thin film on quartz
substrate has been prepared with our synthesized powdered sample by using solution method. The characterizations of
XRD and UV-Vis-NIR absorption have been carried out for the phthalocyanine gadolinium thin film on quartz substrate,
XRD shows that phthalocyanine gadolinium diffractions occur at 2θ=6.851,8.290 and 8.820 degrees, the corresponding
plane spacings (d) for the diffraction peaks are 12.8921, 10.6570, and 10.0176Å.The diffraction peaks locate at low
diffraction angle, suggesting that the molecular size of the phthalocyanine gadolinium is big that causes the large
spacing of crystal planes. The UV-Vis-NIR absorption of phthalocyanine gadolinium thin film on quartz substrate
implies that within near infrared band there is a absorption in the 1.3~2.0μm wavelength range peaked at ca. 1.75μm,
indicating the important potential application value of phthalocyanine gadolinium in the field of organic infrared
optoelectronics.
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