Ultraviolet light detector based on cadmium sulfide nanosheets

Abstract

This invention is an ultraviolet light detector and it is related to the field of optical-electrical properties of semiconductor materials with the ability to receive ultraviolet rays and convert them into electrical signals, which is based on cadmium sulfide nanosheets and especially has high light sensitivity and a very favorable response time compared to ultraviolet light. Cadmium sulfide nanostructures are prepared with a high area-to-volume ratio to escalate the light absorption factor to function in ultraviolet optical sensors with a high reacting haste. By operating the deposited zinc oxide nucleate layer on the glass substrate and refining cadmium sulfide semiconductor deposition parameters, the cadmium sulfide nanosheets could grow on the layer of zinc oxide nucleate by chemical bath technique. Attaining this morphology from cadmium sulfide led to developments in the detecting abilities of the designed sensor.

Description

Ultraviolet Light Detector Based on Cadmium Sulfide Nanosheets

[0001] Among the articles and inventions, various methods have been used to make ultraviolet detectors, which are not economically viable and time-consuming, and working with the chemicals used is very dangerous and harmful to the environment.

[0002] In this invention, we recorded a very high current by nanostructuring the cadmium sulfide material. On the other hand, cadmium sulfide is cheap and affordable compared to other materials. Also, the chemical bath coating method is considered low-risk and industrial.

[0003] C03C 25 / 6226

[0004] United States Patent 7132668

[0005] MgZnO based UV detectors

[0006] Photoconductive devices (1,2) comprising MgxZn1−xO, that is preferably epitaxially deposited on a substrate (21), optionally also including a buffer layer (22), wherein x has a value such that the layer is sensitive to UV light. The a MgZnO device (2) having predetermined electrical and optical properties and first and second electrodes (3) deposited on a surface of the device, the second electrode being spaced from the first electrode. A voltage source (4) is connected across the first and second electrodes to create an electric field within the device. In operation, when the surface of the device upon which the electrodes are deposited is subjected to a photon emission, electron-hole pairs are created within the device and flow within the device because of the electric field.

[0007] In this registered patent, the construction of a suitable three-element semiconductor alloy for producing an ultraviolet detector showed a shallow current under light. In our claimed patent, we recorded a much higher current by nanostructuring the cadmium sulfide material. On the other hand, cadmium sulfide is cheap and affordable compared to other materials. Also, the chemical bath coating method is considered a low-risk and industrial method.

[0008] GB2071415

[0009] SCHOTTKY BARRIER PHOTOVOLTAIC DETECTOR AND PROCESS

[0010] A platinum-cadmium sulfide Schottky barrier photovoltaic UV / IR detector is fabricated with both the ohmic and barrier contacts 70, 72 located on the same side of the cadmium sulfide substrate 30 to facilitate wire attachment by high- speed bonding techniques. A titanium-gold-titanium infrared shield structure 32 is deposited directly on the substrate and is utilized to provide a connection between the ohmic contact and the substrate. An insulating layer 34 of silicon dioxide covers the shield structure. A thin layer 36 of platinum is deposited directly on the substrate in a small central optically active area surrounded by the insulated shield structure. A metal boundary layer 42A overlies the periphery of the platinum layer and prevents the barrier contact metalization from affecting the properties of the Schottky barrier. Both the ohmic and barrier contacts 70, 72 may be formed of a titanium adhesion layer and a layer of gold.

[0011] The mentioned patent uses some methods alike ours but in the deposition process, we used the chemical bath method and we also did not include titanium and gold in our experiment. In addition, comprising silicon is not an economical choice so we refused it while the mentioned invention operated it for covering.

[0012] US20180090525

[0013] Dual band ultraviolet (UV) and infrared radiation detector

[0014] A dual band infrared and ultraviolet radiation detector having an ultraviolet radiation detector embedded within a pair of IR anti-reflection layers wherein a first one of the infrared anti-reflection layer reflects ultraviolet energy passing through from the semiconductor, ultraviolet radiation detector back to the semiconductor, ultraviolet radiation detector.

[0015] The mentioned patent does not refer to nanosheet and any glass substrate deposition process in its method, so it has a different method than our claimed design.

[0016] IN201811044538

[0017] LOW-COST ELECTROCHEMICAL SENSOR

[0018] The invention is directed to electrochemical sensor. The sensor comprising: a substrate forming electrode of the sensor. A conducting layer deposited over the substrate with an optional adhesive layer between metal layer and substrate and chemical bath deposited chalcogenide sensing layer for detection of heavy metals in water samples below 1ppm level. The layer deposited by this method is uniform, free from pinholes and has good adhesion with the underlying conductive layer. The use of this layer for the sensing application help in reducing the complexity and time taken for the fabrication of chalcogenide sensors. Electrochemical sensors so developed have a stable response. This invention provides a cost-efficient, low temperature and easy to use method for the deposition of the sensing layer for the detection of cadmium in water samples using electrochemical techniques.

[0019] This patent’s method is similar to ours but the biggest difference between them is their main goal because the mentioned patent ends up a sensor while we designed a detector device for ultraviolet light.

[0020] Single CdS Nanorod for Hight Responsivity UV-Visible Photodetector

[0021] 22 May 2017

[0022] 1D nanoscale photodetectors have been extensively investigated for the unique geometry structure and novel physical and chemical properties. The 1D CdS materials have received much attention in the field due to its high photosensitivity and fast response, while how to achieve high responsivity is still in development, despite it is the crucial target to the excellent photodetector. Single crystal CdS nanorods (NRs) are synthesized on SiO2 / Si substrate over large scale via the chemical vapor deposition method. The individual single CdS nanorod photodetector have been fabricated by using photolithography process and the responsivity of the photodetector is investigated systematically. At a very low percentage of illumination intensity (2%, 0.5 mW cm−2) under 450 nm, the photodetector exhibited a high responsivity and reached at 1.23 × 104 A W−1 with the bias voltages of 2 V. The good crystallinity and large surface of CdS nanorod are the reasons of this excellent performance of CdS based photodetector. The strategy proposed herein appears to hold great potential for a high responsivity with low illumination intensity.

[0023] The mentioned article proposes a method to make a detector like ours but their components are different.

[0024] Effect of ZnO seed layer on the growth of CdS nanostructures for optoelectronic applications

[0025] September 2018

[0026] In this study, the influence of the ZnO seed layer on the growth of CdS nanostructures using chemical bath deposition method was studied. Applied ZnO seed layer led to change the surface morphology of deposited CdS on glass substrate from particle shape to nanosheet. The results indicated an improvement in the homogeneity and uniformity of the grown CdS nanostructures on ZnO seed layer, which can be due to the low lattice mismatch between ZnO and CdS structures. This change led to variation in crystal structure from cubic to hexagonal. The UV-Vis spectroscopy illustrated the higher absorption coefficient for CdS nanosheet related to CdS particle shape due to the high specific surface area. The calculated band gap of this sample by Tuac plot showed the value of 2.62 eV, which was increased compared to the cadmium sulfide with the bulk structure, which is due to the improved crystal quality of nanosheets. The results showed improved optoelectrical properties of optical detectors based on cadmium sulfide nanoparticles compared to the other samples.

[0027] This article shows an aspect of our experiments for the claimed device but we did not use some of the mentined components like ZnO.

[0028] Nanoparticulate CdS 2D array by chemical bath deposition: Characterization and optoelectronic study

[0029] 15 March 2019

[0030] CdS nanoflake arrays (NFAs) have been synthesized through a simple one-step chemical bath deposition method. Morphology and structural characterizations revealed good crystal quality and growth uniformity of this structure. A visible-light photodetector based on the NFAs has been fabricated as well. Under the illumination with 440 nm light and 1.1 mW / cm2, its responsivity can reach as high as 629 A / W and the specific detectivity runs up to 1.4 × 1013 Jones. We attribute this high performance to the synergy effect of the enhanced light absorption and optimized carrier transport, which is resulted from this special nanoflake array structure and the vertical device design. Our study indicates that CdS NFAs have great potential in large-scale production and wide application in the field of high performance photodetector.

[0031] This article proposes an approach to the usage of CdS NFAs in photodetectors and helps us to understand our claimed method more clearly but it does not cover the whole process of ours.

[0032]

[0033] Nowadays, the necessity of designing and creating ultraviolet sensors to detect and trace its producing source, and quick tracking of fire sources in a fire extinguishing system is felt more than before. The detecting speed is one of the current challenges in business detectors. Also, the availability of a detector that can detect the low amount of radiation and notify it is one of the demands of this electronic industry. The purpose of this invention is to design and create an ultraviolet detector with a high responding speed based on the cadmium sulfide nanostructures with the high suface-area-to-valume ratio due to the most possible ultraviolet light attraction to use in the flame detectors in fire extinguishing systems industrial and domestic (home) consumption. Since, a considerable amount of ultraviolet light diffuses before the things ablaze, having an ultraviolet detector based on a semiconductor nanomaterials structure with a high responding speed can be helpful to distinguish the fire right in time. On the other hand, the economic expenses of producing these sensors according to global standards can increase non-oil exports.Solution of Problem

[0034] Cadmium sulfide deposition on the glass substrates with nanostructural surface morphology to increase the input light absorption coefficient in optic-electric consumption is considered one of the huge challenges in nanoscience that caused the researchers to study synthesis and deposition of semiconductor materials with decent surface morphology. According to the present theories, using a thin layer of nucleate with near lattice constant to the cadmium sulfide structure can ease the nucleation and thin layers of cadmium sulfide growth with nanostructure morphology. Designing cadmium sulfide nanostructures with a high area-to-volume ratio to increase the light absorption coefficient to be used in ultraviolet optical sensors with a high responding speed is the technical challenge of this patent. To solve this challenge, by using the deposited zinc oxide nucleate layer on the glass substrate and improving cadmium sulfide semiconductor deposition parameters, we could grow the cadmium sulfide nanosheets on the layer of zinc oxide nucleate by chemical bath method. Also, achieving this decent morphology from cadmium sulfide led to improvements in the detecting capacities of the designed sensor. This nucleate layer increased the adhesiveness of the cadmium sulfide’s layer to the substrate which raises the sensor’s lifetime. Presenting this solution related to using a zinc oxide nucleate layer and the improvements of cadmium sulfide deposition to achieve nanosheets morphology is considered an innovation. According to the analysis, deposited nanostructures show the light absorption improvements to be used in ultraviolet areas as an optical sensor. The whole methods of this patent such as providing the substrate, washing it, zinc oxide deposition, cadmium sulfide nanostructures growth, and metal joints are explained in the following:

[0035] 1- the method of providing a substrate and washing it:

[0036] It has three steps; first, the substrates were cut in 2×1 cm size. Then the glass substrates using hydrochloric acid (HSI) and di-ionized water with a volume ratio of 2:5 were put in the electronic bath for 10 minutes so the contamination on its surface was removed, then the substrates were washed with the di-ionized water for 1o minutes in the electronic bath. Hence, the drops of hydraulic acid got out of their surface and the substrate became purified.

[0037] 2- Zinc oxide deposition:

[0038] Using a zinc oxide target with 99 / 99% purity with 3-inch diameter the target was fixated to a 4 cm substrate and the deposition on the glass substrates was pre-processed parallel with the target. First, the vacuum chamber reached 10-5×6 mbar by rotary and turbomolecular pumps. Hence, the gas particles in the chamber and the penetrated oxygen on the surface of the substrates exit. We entered the argon gas with a 10-3×6.9 bar extrusion press to the chamber and with the input variable frequencies, the ionized particles of argon gas encountered the target. The sputtering inserted power was fixed at 13b watt and it took 44 minutes for a thin layer with 200 nanometer thickness to be created on the surface of substrates.

[0039] 3- Synthesis and deposition of cadmium sulfide:

[0040] The deposition was used as the primary source of cadmium chloride as a cadmium source, thiourea as a sulfur source, ammonia as a metal complexion in addition to a pH reaction regulator, and di-ionized water for dilution.

[0041] In this research, first, we provided cadmium chloride solutions and thiourea with various molarities at room tempreture and transferred the prepared substrates to the reactionary plate. to perceive the reaction, first, we transferred the 100 ml of cadmium chloride solution with a decent molarity to the reaction plate. After 20 minutes had passed, under stirring conditions with the appropriate speed to completely dissolve the cadmium salt in the deionized water, we added ammonia drop by drop to the cadmium chloride solution until the pH of the reaction reached 10. After finishing the ammonia, we observed that the color of the solution changed from colorless to milky white. Finally, we transferred 100 ml of the thiourea solution with decent molarity to the plate (a combination of cadmium salt and ammonia) and the plate tempreture slowly went to 80 degrees from 27 degrees. By adding the thiourea to the solution, we observed that the milky solution turned into a light blow, and then by continuing the process and tempreture increasing to 80 degrees Celsius, the solution turns into bright yellow. After the synthesis and deposition, we brought the substrates out of the reactionary plate and washed them with di-ionized water to eliminate the weak particles composed on them. It was seen that the composed layers on the substrate were bright yellow which shows the successful deposition of the cadmium sulfide on the substrates, however, to make sure about the purity of the layers out of any illumination, we analyzed them with X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) tests. [Table. 1]

[0042] 4- Making the ultraviolet detector and examining its electric properties:

[0043] To do the metal joints by sputtering, we deposited 200 nanometers of platinum under the vacuum condition on the thin cadmium sulfide layers deposited on the zinc oxide nucleate layer. [Schematic. 2]

[0044] The pattern used in these connections was an interdigitated arrangement, and platinum was deposited with the same pattern on thin layers of cadmium sulfide, finally, the manufactured parts were used to check electrical-optical tests.

[0045] To make an ultraviolet detector and to better collect charge carriers on the surface of cadmium sulfide nanostructures, platinum as an electrode in the form of an interdigitated Schottky contact with a interdigitated arrangement comprising four lines for each electrode was placed on the said samples under vacuum using the sputtering method. The Schottky contact has a 200 nm thickness (approximately) and 3030 × 5050 micrometer size and the distance between each line is around 433 micrometer. [Schematic. 1]

[0046] Eventually, the manufactured sensors were ready for detection and electric-optic tests. A simple and functional device was used to perform detection tests and check optical detectors as accurately as possible. In this device, light-emitting diodes in the range of different wavelengths are installed in a black box made of plexiglass, which has an approximate power of 1.1 mW at a distance of 6.5 cm from the sample surface. Among the advantages of this device, we can mention the wide range of wavelengths, different light intensities in each wavelength, the possibility of precise and remote control, the possibility of pulsating radiations in different ways, and its repeatability. As a result, according to the mentioned cases, it is possible to easily obtain the parameters of response time and speed, sensitivity, efficiency, and finally the performance of optical detectors under different radiations of electromagnetic rays. The important point is that due to the location of the mentioned electromagnetic rays in a completely dark and controllable chamber, the device has high safety for use as a laboratory tool. Investigating the electrical properties, current transfer, as well as performance of metal-semiconductor-metal optical detectors is done by direct current measurements, which include dark current, determining the response of the detector under light irradiation with different intensities at a fixed wavelength, and studying the behavior of the response spectrum of the optical detector under radiations with different wavelengths. The amount of current obtained under light irradiation as well as investigating its behavior under different irradiations can determine the performance of an optical detector including responsiveness, sensitivity, and efficiency. To investigate the electro-optical behavior of the detectors, the Keithly 2400 device has been used to apply the bias voltage and determine the current passing through the optical detector in the dark and under light. [Diagram. 4]

[0047] The microcontroller (electrical module) displays the resistance (explained in by [Formula. 1] and [Formula. 2] in the Examples section) in the detector section as the intensity of ultraviolet radiation.Advantage Effects of the Invention

[0048] 1- Low power consumption of the device with a working voltage of 5 volts

[0049] 2- High selectivity to input wavelengths in the ultraviolet range

[0050] 3- Economical cost of construction and production

[0051] 4- Fast response to received light (less than 300 milliseconds)

[0052] 5- High sensitivity of the device to ultraviolet light, which we reported as 94.

Claims

According to claim 1, An ultraviolet light detector by using the deposited zinc oxide nucleate layer on the glass substrate and improving cadmium sulfide semiconductor deposition parameters, which grew the cadmium sulfide nanosheets on the layer of zinc oxide nucleate with chemical bath method, and has 4 main steps.According to claim 1, the substrates were prepared by cutting in 2×1 cm size.According to claim 2, the glass substrates using hydrochloric acid (HSI) and di-ionized water with a volume ratio of 2:5 were put in the electronic bath for 10 minutes so the contamination on its surface was removed.According to claim 3, the substrates were washed with the di-ionized water for 1o minutes in the electronic bath so the drops of hydraulic acid got out of their surface and the substrate became cleansed.According to claim 1, a zinc oxide target with 99 / 99% purity with a 3-inch diameter was fixated to a 4 cm substrate and the deposition on the glass substrates was pre-processed parallel with the target.According to claim 5, the vacuum chamber reached 10-5×6 mbar by rotary and turbomolecular pumps so the gas particles in the chamber and the penetrated oxygen on the surface of the substrates exit.According to claim 6, the argon gas was entered into the chamber with a 10-3×6.9 bar extrusion press to the chamber and with the input variable frequencies and the ionized particles of argon gas encountered the target.According to claim 7, the sputtering inserted power was fixed at 13b watt, and after 44 minutes a thin layer with 200 nanometer thickness was created on the surface of substrates.According to claim 1, for the synthesis and deposition of cadmium sulfide, 100 ml of cadmium chloride solution with a decent molarity was moved to the reaction plate.According to claim 9, after 20 minutes under stirring conditions and suitable speed, the cadmium salt was dissolved in the deionized water.According to claim 10, the ammonia was added drop by drop to the cadmium chloride solution until the pH of the reaction reached 10 and the solution changed from colorless to milky white.According to claim 11, 100 ml of the thiourea solution with decent molarity was added to the plate and the tempreture from 27 went to 80 degrees, hence the milky solution turned into a light yellow.According to claim 12, by remaining the process, the tempreture went to 80 degrees Celsius, and the solution became bright yellow.According to claim 13, the substrates were taken out of the reactionary plate and washed with di-ionized water until the weak yellow particles composed on them were seen which shows the deposition of the cadmium sulfide on the substrates.According to claim 1, for performing the metal joints sputtering, 200 nanometers of platinum under the vacuum condition were deposited on the thin cadmium sulfide layers deposited on the zinc oxide nucleate layer.According to claim 15, platinum was deposited with the interdigitated pattern on thin layers of cadmium sulfide.According to claim 16, to collect charge carriers on the surface of cadmium sulfide nanostructures, platinum as an electrode in the form of an interdigitated Schottky contact with the interdigitated method comprising four lines for each electrode was placed on the samples under vacuum using the sputtering method and the sensors were made.According to claim 17, light-emitting diodes in the range of different wavelengths were installed in a black box made of plexiglass with an approximate power of 1.1 mW at a distance of 6.5 cm from the sample surface.

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