阅读说明：本技术 一种二维材料光探测器及其制备方法 (Two-dimensional material photodetector and preparation method thereof ) 是由 陈雪霞 杨珣 董林 单崇新 于 2020-11-28 设计创作，主要内容包括：本发明提出了一种二维材料光探测器及其制备方法,针对单原子层二维材料存在的吸收效率低的问题,二维材料光探测器,包括衬底,衬底的上端设有图案化的光学涂层,光学涂层上设有单原子层二维的过渡族金属硫化物MX_2薄膜,MX_2薄膜一端置于光学涂层上,另一端置于衬底上,光学涂层和MX_2薄膜上均设置有电极。本发明由二维材料-介质层-金属(2D-I-M)构成的光学干涉涂层以提升原子层厚度MX2的光探测性能。(The invention provides a two-dimensional material photodetector and a preparation method thereof, aiming at the problem of low absorption efficiency of a monoatomic layer two-dimensional material, the two-dimensional material photodetector comprises a substrate, wherein the upper end of the substrate is provided with a patterned optical coating, and the optical coating is provided with a monoatomic layer two-dimensional transition group metal sulfide MX 2 Film, MX 2 One end of the film is arranged on the optical coating, the other end is arranged on the substrate, the optical coating and MX 2 The thin films are all provided with electrodes. The optical interference coating formed by the two-dimensional material, the dielectric layer and the metal (2D-I-M) improves the optical detection performance of the atomic layer thickness MX 2.)

1. A two-dimensional material photodetector comprising a substrate (1), characterized in that: the upper end of the substrate (1) is provided with a patterned optical coating (2), and the optical coating (2) is provided with a monoatomic layer two-dimensional transition group metal sulfide MX₂Film (3), MX₂One end of the film (3) is arranged on the optical coating (2), the other end is arranged on the substrate (1), and the optical coating (2) and MX₂The thin films (3) are all provided with electrodes.

2. A two-dimensional material photodetector as defined in claim 1, wherein: the optical coating (2) is a dielectric layer/reflective layer film.

3. A two-dimensional material photodetector as claimed in claim 1 or 2, wherein: MX₂In the formula, M is a transition metal element from group IV to group VI, and X is a chalcogen element.

4. A two-dimensional material photodetector as defined in claim 3, wherein: MX₂Is MoS₂、MoSe₂、MoTe₂、WS₂Or WSe₂。

5. A two-dimensional material photodetector as defined in claim 1, wherein: the substrate is a sapphire substrate.

6. A two-dimensional material photodetector as defined in claim 1, wherein: the electrode is a Ti/Au electrode.

7. A two-dimensional material photodetector as defined in claim 2, wherein: the reflecting layer is an Ag layer, an Al layer or an Au layer, and the dielectric layer is a non-light-absorbing semiconductor or insulator.

8. A two-dimensional material photodetector as claimed in claim 2 or 7, wherein: the dielectric layer/light reflecting layer film is a NiO/Au film, the NiO/Au film comprises an Au layer and a NiO layer positioned on the upper side of the Au layer, and the thickness of the NiO layer is 25nm-125 nm.

9. A two-dimensional material photodetector as defined in claim 8, wherein: the thickness of the NiO layer was 75 nm.

10. A method for manufacturing a two-dimensional material photodetector according to any one of claims 1 to 9, comprising the steps of:

(1) preparation of monolayer of transition group metal sulfide MX by chemical vapor deposition₂A film;

(2) cleaning a substrate, preparing a pattern on the sapphire substrate by adopting an ultraviolet lithography technology, then sequentially depositing a metal layer and a dielectric layer on the substrate with photoresist by using a magnetron sputtering method, and removing the photoresist by using acetone after deposition to obtain a patterned optical coating;

(3) MX is transferred by wet method₂Transferring the thin film onto a patterned optical coating, and selectively attaching MX onto the substrate and the dielectric layer₂A thin film respectively in the dielectric layer and MX₂Electrodes were prepared by photolithography and thermal evaporation.

Technical Field

The invention relates to the technical field of optical detectors, in particular to a two-dimensional material optical detector and a preparation method thereof.

Background

The rapid development of the information modern semiconductor industry technology and the gradually increasing integration density of electronic components are approaching toThe limits of moore's law; meanwhile, the second law of moore indicates that the smaller the chip size, the corresponding processing cost increases exponentially, and the development of the conventional semiconductor technology has reached a bottleneck stage, for which ultra-thin materials are required to break the bottleneck. In recent years, two-dimensional layered materials are more and more concerned by people and become hot materials for competitive research of researchers in various countries. Two-dimensional materials represented by graphene are greatly concerned due to excellent physicochemical properties, and the carrier mobility of field effect transistors is up to 200000cm²V^-1s^-1Is far higher than a silicon-based device, and simultaneously has good mechanical flexibility and higher thermal conductivity. However, the graphene has no band gap, so that the current switching ratio of the transistor is very low, and the development of the graphene in the field of optoelectronic devices is limited to a certain extent. Inspired by single-layer graphene, other two-dimensional layered materials with atomic layer thicknesses are continuously researched and discovered. With continuous scientific research, transition group Metal Sulfides (TMDs) with a graphene-like structure are discovered, and the molecular structure general formula of the material is as follows: MX₂Wherein M represents Ti, Zr, Hf, V, Nb, Ta, Mo, W, etc. of groups IV to VI of the transition group metal elements in the periodic Table of the elements, and X represents S, Se, Te, etc. of chalcogens in the periodic Table of the elements. At MX₂In the structure, two X atomic layers sandwich a middle layer of metal M atoms. The binary material has the further characteristic that in the process of changing from a bulk material to a single layer, the band gap of the binary material slightly increases along with the reduction of the number of layers, and a sudden change from an indirect band gap to a direct band gap exists, wherein the change is caused by a quantum local effect.

In MoS₂For example, as the number of layers of molybdenum disulfide is reduced, at the K point of the brillouin zone, the change of the transition energy of indirect excitons can be ignored, but the energy of direct band gap is monotonically increased; when reduced to monolayer thickness, the direct bandgap transition will reach a maximum of 1.9 eV.

Two-dimensional materials of atomic layer thickness that have been found to date have hexagonal boron nitride, black phosphorus, and some Transition Metal Sulfides (TMDs) such as MoS in addition to graphene₂,MoSe₂,MoTe₂,WS₂,WSe₂And the like. Sulfurization of these transition metalsThe material not only has the characteristics of good mechanical flexibility, high carrier mobility, strong interaction with photons and the like, but also has a natural optical band gap which graphene does not have, so that the transition metal sulfide material becomes a two-dimensional material which is researched more at present. The two-dimensional layered ultrathin materials with the atomic thickness can be combined with a planar semiconductor process by virtue of excellent performance and van der Waals force to design a novel photoelectronic device with excellent performance, and a new way is opened for the development of the semiconductor technology.

Molybdenum disulfide (MoS)₂) Which is a typical representation of TMDs, is combined with interlayer spacing of about 0.65nm, hexagonal structure by van der waals forces. The single-layer molybdenum disulfide consists of three S-Mo-S atoms, and the molybdenum atoms in the middle of the two S atoms are separated to form a sandwich structure. MoS₂There are three crystal structures of (a): 1T type, 2H type and 3R type, wherein the MoS2 structure of the 3R type and the 1T type belongs to metastable state, and the 2H type has good stability at normal temperature and is MoS₂Common crystal structure. For MoS₂The energy of the direct band gap is much larger than that of the indirect band gap in the bulk, the single-layer molybdenum disulfide is the direct band gap with the band gap of 1.8eV, and the bulk is the indirect band gap with the band gap of 1.2 eV. Current single layer MoS₂The growth preparation technology of (2) is mature, can grow to the size of inches by using a chemical vapor deposition technology, and can change the photoelectric property of the material by doping. Due to the unique atomic structure, adjustable band gap performance and mature growth technology, the molybdenum disulfide has great application value in the research of micro-nano optoelectronic devices.

In view of the unique structure of TMDs, the material is widely applied to the fields of detectors, memories, LEDs, field effect transistors, flexible wearable devices and the like. However, the quantum efficiency of the single-layer TMDs is low, which is about 0.1% -10%. The ultra-thin thickness results in very low light absorption rate, which severely limits the application of the optical detection device in the field of optical detection. In order to optimize the performance of the TMDs material, people combine the TMDs material with optical systems such as microcavities, nanostructured surfaces, metal nanostructures, etc., to customize a specific external optical environment for the TMDs, and to achieve the regulation and control of the TMDs optical performance. Typical examples include lasers that combine TMDs with photonic crystal microcavities to achieve monoatomic layer gain materials, combinations of TMDs with FPs to achieve exciton polaritons, bonding to a nanostructured surface to form functionalized surfaces, and the like. However, these methods all require the introduction of complex fabrication processes, adding sub-wavelength nanopatterns inside or outside the two-dimensional material, which severely increase the fabrication costs and disturb and destroy the electro-optical properties of the two-dimensional material.

Disclosure of Invention

Aiming at the problem of low absorption efficiency of a monoatomic layer two-dimensional material, the invention provides a two-dimensional material optical detector and a preparation method thereof, wherein an optical interference coating formed by a two-dimensional material, a dielectric layer and a metal (2D-I-M) is used for increasing the thickness MX of an atomic layer₂The light detection performance of (1).

The technical scheme of the invention is realized as follows: a two-dimensional material photodetector comprises a substrate, a patterned optical coating is arranged at the upper end of the substrate, and a monoatomic layer two-dimensional transition group metal sulfide MX is arranged on the optical coating₂Film, MX₂One end of the film is arranged on the optical coating, the other end is arranged on the substrate, the optical coating and MX₂The thin films are all provided with electrodes.

Further, the optical coating is a dielectric layer/reflective layer film.

Further, MX₂In the formula, M is a transition metal element from group IV to group VI, and X is a chalcogen element.

Further, MX₂Is MoS₂、MoSe₂、MoTe₂、WS₂Or WSe₂。

Further, the substrate is a sapphire substrate.

Further, the electrodes are Ti/Au electrodes.

Furthermore, the reflecting layer is an Ag layer, an Al layer or an Au layer, and the dielectric layer is a non-light-absorbing semiconductor or insulator.

Further, the dielectric layer/light reflecting layer film is a NiO/Au film, the NiO/Au film comprises an Au layer and a NiO layer positioned on the upper side of the Au layer, and the thickness of the NiO layer is 25nm-125 nm.

Further, the thickness of the NiO layer was 75 nm.

A method for preparing a two-dimensional material photodetector comprises the following steps:

(1) preparation of monolayer of transition group metal sulfide MX by chemical vapor deposition₂A film;

(2) cleaning a substrate, preparing a pattern on the sapphire substrate by adopting an ultraviolet lithography technology, then sequentially depositing a metal layer and a dielectric layer on the substrate with photoresist by using a magnetron sputtering method, and removing the photoresist by using acetone after deposition to obtain a patterned optical coating;

(3) MX is transferred by wet method₂Transferring the thin film onto a patterned optical coating, and selectively attaching MX onto the substrate and the dielectric layer₂A thin film respectively in the dielectric layer and MX₂Electrodes were prepared by photolithography and thermal evaporation.

The invention has the beneficial effects that:

the two-dimensional material optical detector provided by the invention has the advantage that the thickness MX of an atomic layer is increased by the optical interference coating formed by the two-dimensional material, the dielectric layer and the metal (2D-I-M)₂The optical detection performance and the preparation method are low in cost, interference and damage to the photoelectric property of the two-dimensional material cannot be caused, and the responsivity of the two-dimensional material optical detector is exponentially increased along with the increase of voltage and can be as high as 780A/W to the maximum.

Light has high reflectivity at the interface of the dielectric layer and gold and is accompanied by phase shift, and reflected light interference is cancelled when the phase shift phi 1 generated by the reflection of the metal surface and the propagation phase shift phi 1 in the dielectric layer are accumulated to be pi. This structure is similar to a Fabry-Perot cavity, as shown in fig. 4, and utilizes the principle of multi-beam interference. Light cannot be transmitted out of the metal in the structure and is reflected by the metal into the air, and when the light is destructively interfered with the light in the air, the light is limited to be resonantly absorbed in the structure. The conditions for destructive interference of reflected light are: phi 1+ phi 2 is pi. In the 2D-I-M structure of the invention, as shown in FIG. 5, light is limited in a very small space (< lambda/4 n) between the two-dimensional material and the metal, and is absorbed by the superposition of single-layer two-dimensional materials so as to realize high light absorption efficiency, and the resonance absorption peak can be regulated and controlled by the thickness of the dielectric layer, the metal and the type of the dielectric layer. According to the working principle, the 2D-I-M structure has universal applicability to improving the light absorption performance of two-dimensional materials, and only appropriate metal and dielectric layers need to be selected according to corresponding absorption wave bands. For near ultraviolet bands, Ag or Al metal can be used as a reflecting layer; and Au thin films can be used in the visible and near-infrared wave bands; but sapphire is required in the mid-infrared band because sapphire has a refractive index similar to that of metal in the mid-infrared band. The dielectric layer is made of semiconductor or insulator material which does not absorb the light of the wave band.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a MoS transferred on a patterned NiO/Au film₂An optical photograph of (a);

FIG. 2 is a schematic diagram of a two-dimensional material photodetector according to the present invention;

FIG. 3 is a response curve of the photodetector corresponding to different NiO thicknesses;

FIG. 4 is a graph of the peak responsivity of a photodetector with 75nm thick NiO at different voltages;

FIG. 5 is a schematic view of the optical effect of the optical coating at the dielectric layer-gold interface;

FIG. 6 is a schematic diagram of the optical effect of the optical coating of the 2D-I-M structure of the present invention.

In FIG. 2, substrate 1, optical coating 2, MX₂A membrane 3, an electrode 4.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

A two-dimensional material photodetector comprises a substrate 1, a patterned optical coating 2 is arranged at the upper end of the substrate 1, and a monoatomic layer two-dimensional transition group metal sulfide MX is arranged on the optical coating 2₂Film 3, MX₂One end of the film 3 is arranged on the optical coating 2, the other end is arranged on the substrate 1, the optical coating 2 and MX₂The thin films 3 are each provided with an electrode 4. The optical coating is a dielectric layer/reflective layer film. The reflecting layer is an Ag layer, an Al layer or an Au layer, and the dielectric layer is a non-light-absorbing semiconductor or insulator.

MX₂In the formula, M is a transition metal element from group IV to group VI, and X is a chalcogen element. MX₂Is MoS₂、MoSe₂、MoTe₂、WS₂Or WSe₂And the like.

For near ultraviolet bands, Ag or Al metal can be used as a reflecting layer; and Au thin films can be used in the visible and near-infrared wave bands; but sapphire is required in the mid-infrared band because sapphire has a refractive index similar to that of metal in the mid-infrared band. The dielectric layer is made of semiconductor or insulator material which does not absorb the light of the wave band.

By MX₂Is MoS₂The substrate is a sapphire substrate, the optical coating is a NiO/Au thin film, the electrode is a Ti/Au electrode, and the specific preparation method of the two-dimensional material optical detector is as follows.

The preparation method of the two-dimensional material photodetector comprises the following steps:

(1) preparation of a monolayer of a transition group metal sulfide MoS by chemical vapor deposition₂A film.

The specific method comprises the following steps:

(a) using Si/SiO₂For growing a substrate, cleaning the surface of the substrate by using ethanol, acetone and deionized water in sequence;

(b) 100mg of sulfur powder, 5mg of Mo powder were weighed in a tube furnace, S powder was placed on the upper edge of the air flow, Mo powder was placed on the lower edge of the air flow, and cleaned Si/SiO was added₂The substrate is reversely buckled above the corundum boat containing Mo powder;

(c) argon is used as protective gas, the gas flow is set to be 20-100sccm, the temperature is increased to 100 ℃ at the speed of 20 ℃/min and is kept for 30min, water absorbed in S powder is removed, the temperature is increased to 750 ℃ at the speed of 30 ℃/min and is kept for 10-30min, and the reaction is naturally cooled to the normal temperature after the reaction is finished.

After the reaction in the tube furnace, a molybdenum disulfide film with the size of up to 40 mu m can be obtained on the substrate.

In the step (c), when the growth is carried out for 15min under the three conditions of gas flow of 20sccm, 50sccm and 100sccm, the sizes of MoS2 which grows respectively are 20 microns, 35 microns and 10 microns; setting the temperature at 750 ℃ as 10min, 15min, 20min and 30min, controlling the flow of protective gas as 50sccm, and MoS as the growth time is prolonged₂Gradually increased in size, but after increasing to 20min, the sample size did not increase significantly and at triangular MoS₂Restarting to grow a layer of MoS on the sample₂Sample, MoS obtained₂The samples are mostly of a mixed structure of single and multiple layers. In this example, the gas flow rate is 50sccm, and the temperature is kept at 750 ℃ for 15 min.

(2) Cleaning a substrate, preparing a pattern on the sapphire substrate by adopting an ultraviolet lithography technology, then depositing an Au layer and a NiO layer on the substrate with photoresist in sequence by using a magnetron sputtering method, and removing the photoresist by using acetone after deposition to obtain the patterned NiO/Au film. The patterned NiO/Au thin film exposes the substrate in the patterned portion.

The specific method of the ultraviolet lithography technology is as follows:

1. firstly, ultrasonically cleaning a single-polished sapphire substrate in deionized water, alcohol and acetone solutions for 15min respectively, then, uniformly coating photoresist on the sapphire substrate, wherein the conditions of spin-coating photoresist are firstly 20s,600 r/s, then 50s and 5000 r/s;

2. pre-baking: heating the sapphire substrate with the photoresist being coated in a spinning mode at 115 ℃ for 1.5 min;

3. photoetching: carrying out exposure treatment by using an ultraviolet lithography machine and a prepared mask plate, wherein the exposure time is 15 s;

4. and (3) developing: developing the exposed sample in a developing solution for 50s, washing the sample with deionized water after a pattern appears, removing the residual developing solution, and finally drying with nitrogen;

5. post-baking: the developed sample was heated at 115 ℃ for 30 s.

The specific method for sequentially depositing the Au layer and the NiO layer on the substrate with the photoresist by using the magnetron sputtering method comprises the following steps:

1. gold plating conditions: vacuum degree of 4.1X 10^-4The gas flow rate: ar (10sccm), DC sputtering power: 50W, sputtering time: and 8 min.

2. NiO deposition conditions: degree of vacuum of 3.5X 10^-4And the flow rate of the mixed gas is as follows: ar (10sccm), O2(10sccm), RF sputtering power: 60W, sputtering time: 50-250 min.

And after the magnetron sputtering process is finished, placing the sample in an acetone solution for soaking for 30min, and removing the photoresist to obtain the patterned NiO/Au structure.

The sputtering time of NiO with different thicknesses is different, and the growth rate of NiO is 0.5nm/min according to the test result of a film thickness meter. Therefore, 50min is required at 25nm, 100min is required at 50nm, 150min is required at 75nm, 200min is required at 100nm, and 250min is required at 125 nm.

(3) MoS is transferred by wet method₂The film was transferred to a patterned NiO/Au film, selected as MX bridging the substrate and NiO together₂Thin films in NiO and MoS, respectively₂Electrodes were prepared by photolithography and thermal evaporation.

The specific method of wet transfer is as follows:

1. MoS is grown by a spin coater at the speed of 4000r/min₂SiO of (2)₂Spin-coating polymethyl methacrylate (PMMA) on Si for 1min, and then heating the spin-coated sample on a heating table at 120 ℃ for 60 min;

2. the dried sample was then suspended with the adhesive side facing up in a 2mol/L NaOH solution, and after 30min it was seen that the PMMA film was suspended in the NaOH solution and separated from the SiO2/Si substrate. The PMMA was transferred into the ionized water with tweezers and the process was repeated three times to ensure that the film was clean.

3. With prepared patterningThe NiO/Au substrate is used for connecting the PMMA film, then the PMMA film is baked on a heating table at 60 ℃ for 30min and then at 110 ℃ for 30min so as to promote the adsorption of the PMMA film and the substrate and remove excessive water, finally the sample is subjected to PMMA removal in acetone to obtain the structure shown in figure 1, and the NiO and Al are simultaneously lapped on the NiO and Al as shown in figure 1₂O₃MoS on (sapphire substrate)₂And preparing a device.

The preparation method of the electrode comprises the following steps:

mixing MoS₂After transfer to a patterned NiO/Au film, a triangular MoS was selected that was lapped on both sapphire and NiO₂In NiO and MoS respectively₂The Ti/Au electrode was prepared by photolithography and thermal evaporation, with the Ti electrode below and the Au electrode above. The device structure shown in fig. 2 is finally obtained.

1. Glue homogenizing: first, the transferred MoS was determined under a microscope₂The sample had been lapped on the edge portion of the NiO/Au pattern. Then spin coating a layer of photoresist on the substrate, and the procedure of spin coating the photoresist has two steps, firstly 20s,600r, and then 50s, 5000 r.

2. Pre-baking: heating the sample coated with the photoresist at 115 ℃ for 1.5min

3. Photoetching: after the sample position is determined by the laser direct writing microscope window, MoS is firstly carried out₂The exposed part of the sapphire substrate can be patterned into an electrode pattern, and then electrodes are etched on the NiO/Au.

4. And (3) developing: developing the laser direct-writing etched sample in a developing solution for 50s, washing the sample with deionized water after an obvious electrode pattern appears, removing the residual developing solution, and finally drying with nitrogen.

5. Post-baking: the developed sample was heated at 115 ℃ for 30 s.

6. And placing the prepared sample on a vacuum thermal evaporation table to prepare a Ti/Au electrode. After the thermal evaporation process is completed, the sample is placed in an acetone solution to be soaked for 30min, the photoresist is removed, and finally the device is prepared as shown in fig. 2.

And (3) carrying out performance test on the prepared two-dimensional material photodetector:

for NiO with different thickness, the optical coating formed by the NiO and the Au thin film selectively absorbs light with different wavelengths. By testing the reflection spectra of the NiO/Au structures with the NiO thicknesses of 25nm, 50nm, 75nm, 100nm and 125nm, it can be known that the NiO/Au optical coating corresponding to the NiO with the thickness of 75nm has the lowest reflectivity at the position of 600-680nm of red light, and the Au thin film is completely opaque, which indicates that the absorption of the red light is strongest under the condition, so the thickness of 75nm is selected as the thickness condition for preparing the device.

Tests have also shown that the absorption of red light increases with increasing thickness from 25nm, and that after a thickness of 75nm, the absorption decreases sharply with increasing thickness. FIG. 3 shows the response curves of the devices corresponding to different NiO thicknesses under 9V reverse bias, and it can be seen from FIG. 3 that the two-dimensional material photodetector has a response range to light from 250nm to 690nm, and the device with a thickness of 75nm has the highest responsivity, the responsivity is 265A/W at 430nm, and the responsivity is 100A/W at 620 nm. For a device thickness of 50nm, the responsivity is much smaller than that of 75nm, 22.6A/W and 6.7A/W at 430nm and 620nm, respectively, and 2.3A/W and 0.66A/W at 100 nm.

FIG. 4 shows the variation of peak responsivity of a device with a thickness of 75nm under different reverse bias voltages, and it can be known that the responsivity of a two-dimensional material photodetector increases exponentially with the increase of voltage, and can reach as high as 780A/W.

In the preparation method, the reflecting layer Au layer can be directly replaced by an Ag layer or an Al layer, and the dielectric layer can also select a semiconductor or insulator material which does not absorb light of the wave band according to the light of different wave bands.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.