CN113594240A - BJT (bipolar junction transistor) based on two-dimensional transition metal chalcogenide and preparation method thereof - Google Patents
BJT (bipolar junction transistor) based on two-dimensional transition metal chalcogenide and preparation method thereof Download PDFInfo
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- -1 transition metal chalcogenide Chemical class 0.000 title claims abstract description 79
- 238000002360 preparation method Methods 0.000 title abstract description 43
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- 229910052751 metal Inorganic materials 0.000 claims abstract description 76
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- 238000000034 method Methods 0.000 claims description 26
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- 238000011065 in-situ storage Methods 0.000 claims description 9
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- 238000001755 magnetron sputter deposition Methods 0.000 description 2
- TVWWSIKTCILRBF-UHFFFAOYSA-N molybdenum trisulfide Chemical compound S=[Mo](=S)=S TVWWSIKTCILRBF-UHFFFAOYSA-N 0.000 description 2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66969—Multistep manufacturing processes of devices having semiconductor bodies not comprising group 14 or group 13/15 materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/24—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only semiconductor materials not provided for in groups H01L29/16, H01L29/18, H01L29/20, H01L29/22
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
- H01L29/73—Bipolar junction transistors
- H01L29/7317—Bipolar thin film transistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
- H01L29/73—Bipolar junction transistors
- H01L29/735—Lateral transistors
Abstract
The invention discloses a BJT based on two-dimensional transition metal chalcogenide and a preparation method thereof, belonging to the field of semiconductor micro devices and comprising the following steps: a monocrystalline silicon substrate with a dielectric layer, a P-type film, an N-type film, a P-type film and electrodes positioned on the upper surfaces of the films, wherein the two-dimensional transition metal chalcogenide compound on the surface of the dielectric layer is sequentially and transversely connected with the monocrystalline silicon substrate; the preparation method comprises the following steps: preparing a shielding layer on the upper surface of a monocrystalline silicon substrate with a dielectric layer, and spin-coating a first precursor solution containing a sulfur element and a transition metal element; spin-coating a photoresist on the upper surface of the obtained sample, removing the shielding layer, spin-coating a second precursor solution formed by dissolving a metal salt in the first precursor solution on the upper surface of the sample, and removing the photoresist; carrying out laser irradiation on the obtained sample in vacuum; and preparing a metal electrode on the upper surface of the sample to obtain the BJT. The invention completes the film preparation and doping in one step, and solves the problem that the film is easy to be damaged and the device performance is influenced in the existing preparation process of the two-dimensional material BJT.
Description
Technical Field
The invention belongs to the field of semiconductor micro devices, and particularly relates to a BJT (bipolar junction transistor) based on a two-dimensional transition metal chalcogenide and a preparation method thereof.
Background
Two-dimensional Transition Metal chalcogenides (TMDCs) have extremely high electron mobility and excellent properties in terms of light, electricity, chemistry, mechanics, and the like, and thus have attracted much attention in recent years, in which the Transition Metal chalcogenides have similar crystal structures and atomic structures and similar properties in terms of semiconductors, for example, the band gap of a layered Transition Metal chalcogenide changes with the number of layers, and MoS is used as a material for the Transition Metal chalcogenide2For example, the band gap (1.25eV to 1.8eV) varies with the number of layers. MoS2Has higher carrier mobility, and currently has single-layer MoS2The carrier mobility of the film can reach 400cm2V-1s-1The multilayer film can reach 500cm2V-1s-1。
At present, because the surface state density of the horizontal junction is low, the recombination of carriers can be effectively reduced, and the BJT based on the horizontal junction has a good amplification effect on low current. In the conventional BJT prepared by using a two-dimensional material, the P region and the N region are usually made of different semiconductor materials, and the formed PN junction is a heterogeneous PN junction. For example, in patent document CN 104617135 a entitled "two-dimensional material element and semiconductor device", a two-dimensional material element is disclosed in which a first two-dimensional material and a second two-dimensional material are contained, the first two-dimensional material is an n-type semiconductor, the second two-dimensional material is a p-type semiconductor, the first metal chalcogenide-based material includes a first metal atom, the second metal chalcogenide-based material includes a second metal atom, and the first and second metal atoms are different from each other; or the first metal chalcogenide based material includes a first chalcogen atom, the second metal chalcogenide based material includes a second chalcogen atom, and the first and second chalcogen atoms are different from each other. The PN junction in the prepared BJT is a heterogeneous PN junction, a directional transfer process is inevitably needed in the preparation process, and the two-dimensional film is extremely small in thickness and extremely easy to damage in the transfer process, so that the performance of the final BJT device is influenced.
In order to solve the problem, in the patent document with the application publication number of CN 108666375A and the invention name of 'a nano-layered transverse homogeneous PN diode and the preparation method and application thereof', a homogeneous PN junction is provided, wherein the thin film layer includes a p-type transition metal chalcogenide film and an n-type transition metal chalcogenide film which are prepared from the same transition metal chalcogenide and are laterally connected, in the preparation process, firstly preparing an n-type transition metal chalcogenide film on a dielectric layer in situ, then carrying out low-power magnetron sputtering doping and annealing on the appointed part in the n-type transition metal chalcogenide film to form a p-type transition metal chalcogenide region, because the traditional directional transfer process is omitted and the used doping gas is oxygen, the preparation cost is lower, and the damage to the transition metal chalcogenide film in the doping process is small. However, in the magnetron sputtering doping process, the surface of the film needs to be bombarded by the glow starting gas, so that the film still has certain damage, and the doping is only performed on the surface of the film, so that the doping concentration is not easy to be accurately controlled. In addition, since the n-type transition metal chalcogenide film is prepared by Chemical Vapor Deposition (CVD), the area of the film is often only in the order of μm, which greatly limits the practical application of the prepared device.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a BJT based on a two-dimensional transition metal chalcogenide and a preparation method thereof, aiming at reducing the damage degree of a thin film in a nano layered transition metal chalcogenide transverse homogeneous BJT in the preparation process, improving the performance and stability of a device and realizing controllable doping concentration.
To achieve the above objects, according to one aspect of the present invention, there is provided a BJT based on a two-dimensional transition metal chalcogenide, including: a monocrystalline silicon substrate with a dielectric layer;
the thin film layer is positioned on the upper surface of the dielectric layer; the thin film layer comprises three transition metal chalcogenide thin films which are transversely connected, namely a first P-type doped thin film, an N-type doped thin film and a second P-type doped thin film which sequentially form an emitter region, a base region and a collector region; three transition metal chalcogenide films in the thin film layer are prepared by laser irradiation of a precursor solution which is spin-coated on the upper surface of the dielectric layer, and the precursor solution for preparing the P-type doped thin film is prepared by in-situ doping metal salt of the precursor solution for preparing the N-type doped thin film;
and electrodes respectively positioned on the upper surfaces of the emitter region, the base region and the collector region to respectively form an emitter, a base and a collector.
The invention provides a BJT based on two-dimensional transition metal chalcogenide, wherein a thin film layer of the BJT comprises a first P type doped transition metal chalcogenide thin film, an N type doped transition metal chalcogenide thin film and a second P type doped transition metal chalcogenide thin film which are sequentially and transversely connected and respectively form an emitter region, a base region and a collector region, the P type doped thin film and the N type doped thin film in the thin film layer are simultaneously prepared by laser irradiation of a precursor solution spin-coated on the upper surface of a dielectric layer, the precursor solution for preparing the P type doped thin film is prepared by in-situ doped metal salt of the precursor solution for preparing the N type doped thin film, the finally prepared thin films of three regions are composed of the same two-dimensional transition metal chalcogenide, the formed BJT is a PNP type BJT, and PN junctions in the BJT are homogeneous PN junctions, the BJT has a simple structure, the preparation process needs no directional transfer, and the damage to the film caused by the directional transfer is avoided.
Because the doping object is a precursor solution, the doping process is carried out before the film is formed, so that the damage to the film after the film is formed is avoided, and the damage degree of the prepared film is reduced to the maximum extent; because the concentration of the metal salt and the doping concentration of the precursor solution obtained after doping have a fixed relation, the precise control of the doping concentration can be realized by controlling the concentration of the metal salt, so that the doping concentration in the device can be controlled; because the doping of the solution is not limited to the doping of the surface of the film, the doping effect is more stable, and the performance of the finally prepared device is more stable.
The film is prepared by performing laser irradiation on the precursor solution, so that the prepared device can have a film with a larger area, and is convenient for connecting pins in practical application.
Further, the two-dimensional transition metal chalcogenide in the thin film layer is MoS2。
MoS2The band gap of the silicon-based semiconductor material is changed along with the change of the layer number, and the silicon-based semiconductor material has higher carrier mobility; in the BJT based on the two-dimensional transition metal chalcogenide provided by the invention, the thin films of the emitter region, the base region and the collector region are all MoS2And the thin film and the whole BJT have better amplification performance.
Further, the thickness of the thin film layer is 0.5nm-2 nm.
The BJT of the two-dimensional transition metal chalcogenide provided by the invention, whereinMoS2The film has a thickness of 0.5nm-2nm and has good optical and electrical properties.
Furthermore, the electrode is of a double-layer structure and comprises a Ti metal layer directly contacted with the thin film layer and a protective layer positioned on the Ti metal layer; the protective layer serves to conduct electricity and prevent the Ti metal layer from being oxidized.
The BJT based on the two-dimensional transition metal chalcogenide provided by the invention has the advantages that the electrode has a double-layer structure; directly with MoS2One layer of the film contact is a Ti metal layer, and better ohmic contact can be realized because the work function of titanium is similar to that of molybdenum disulfide (MoS 2); one layer on the Ti metal layer is a protective layer which is used for preventing the Ti metal layer from being oxidized while conducting electricity; the electrode structure ensures good conductivity and stable performance.
Further, the thickness of the Ti metal layer is 5nm to 30nm, whereby good ohmic contact can be achieved.
Further, the protective layer is an Au metal layer.
The Au metal layer is used as a protective layer in the double-layer electrode structure, so that the Ti metal layer at the bottom layer can be effectively protected from being oxidized while the conductivity is provided.
Furthermore, the thickness of the Au metal layer is 50nm-200nm, so that better conductivity can be ensured, and the Ti metal layer can be effectively prevented from being oxidized.
According to another aspect of the present invention, there is provided a method for preparing the above-mentioned BJT based on a two-dimensional transition metal chalcogenide, comprising the steps of:
(S1) preparing a shielding layer on the upper surface of the dielectric layer in the monocrystalline silicon substrate with the dielectric layer, and only exposing the middle area of the dielectric layer;
(S2) spin-coating a first precursor solution on the dielectric layer with the shielding layer, and drying after soaking to obtain a sample A; the first precursor solution comprises sulfur elements and two-dimensional transition metal elements;
(S3) after the photoresist is coated on the upper surface of the sample A in a spinning mode, removing the shielding layer to obtain a sample B;
(S4) spin-coating a second precursor solution on the upper surface of the sample B, drying after soaking, and removing the photoresist to obtain a sample C; the second precursor solution is formed by fully dissolving metal salt in the first precursor solution;
(S5) placing the sample C in a vacuum environment for laser irradiation to form a first P-type doped transition metal chalcogenide film, an N-type doped transition metal chalcogenide film and a second P-type doped transition metal chalcogenide film which are sequentially and transversely connected on the upper surface of the dielectric layer and respectively serve as an emitter region, a base region and a collector region to obtain a sample D;
(S6) spin-coating photoresist in the sample D to respectively prepare required electrode patterns on an emitter region, a base region and a collector region in the sample D, and then respectively depositing electrodes on the upper surfaces of the emitter region, the base region and the collector region to be used as an emitter, a base and a collector to obtain a sample E;
(S7) removing the photoresist in the sample E, resulting in the BJT based on the two-dimensional transition metal chalcogenide.
According to the preparation method provided by the invention, the precursor solution of the P-type thin film is prepared by doping the solution of the metal salt in the precursor solution of the N-type thin film, the required N-type and P-type two-dimensional transition metal chalcogenide thin films can be synthesized in one step by spin coating the corresponding precursor solutions according to the distribution of the emitter region, the base region and the collector region in the dielectric layer, directional transfer is not needed, the preparation process is controllable and easy to operate, the damage to the thin film is small, and the prepared BJT has good and stable performance. In addition, because the concentration of the metal salt in the second precursor solution is directly related to the doping concentration of the P-type thin film, the doping concentration of the P-type thin film in the BJT can be controlled by controlling the concentration of the metal salt in the second precursor solution in the preparation process.
Further, the first precursor solution is a mixed solution of molybdenum pentachloride and thiourea dissolved in an alcohol solvent.
According to the invention, the mixed solution obtained by dissolving molybdenum pentachloride and thiourea in an alcohol solvent is used as a first precursor solution for preparing the N-type film, so that the MoS-based film can be prepared2The BJT is thin-film, in addition, in the process of preparing the first precursor solution, reaction products except molybdenum disulfide are gaseous, impurities are not easily generated in the generated molybdenum sulfide crystal, and after the reaction is finished, unreacted thiourea in the first precursor solution can be decomposed without impurity residues.
Further, in the first precursor solution, the molar ratio of sulfur atoms to molybdenum atoms is 30: 1-4: 1.
the invention sets the mol ratio of sulfur atoms to molybdenum atoms in the first precursor solution to be 30: 1-4: 1, can avoid leading to the molybdenum pentachloride reaction incompletely because of the thiourea concentration is too low, also can avoid leading to molybdenum disulfide further reaction to form molybdenum trisulfide because of the thiourea concentration is too high.
Further, in the second precursor solution, the molar ratio of the sulfur atoms to the molybdenum atoms is 30: 1-4: 1, the concentration of the metal salt is 1-20 mmol/L.
The molar ratio of the sulfur element to the molybdenum element in the first precursor solution is set to be 30: 1-4: 1, incomplete reaction of molybdenum pentachloride caused by too low concentration of thiourea and further reaction of molybdenum disulfide caused by too high concentration of thiourea to form molybdenum trisulfide can be avoided; the doping concentration of the prepared P-type film can meet the basic application requirement by setting the concentration of the metal salt in the second precursor solution to be 1-20 mmol/L.
Further, the metal salt is one or more of gold chloride, silver nitrate and copper nitrate.
The properties of copper, silver or gold are stable, the elements are used as doping elements, the damage to the transition metal chalcogenide film in the doping process is small, and the prepared BJT has stable performance.
Further, in the step (S5), the laser power of the laser irradiation is 100-400mJ, the irradiation frequency is 2-10Hz, the pulse number is 1000-3000 times, and the spot size is 9cm2The size of the square is 2-4mm/s, and the laser moving speed is higher than that of the square.
The laser irradiation process is controlled according to the parameters, and the damage to the film can be reduced.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the BJT based on the two-dimensional transition metal chalcogenide is a PNP type BJT, a P type doped thin film and an N type doped thin film in a thin film layer are prepared by laser irradiation of a precursor solution which is spin-coated on the upper surface of a dielectric layer at the same time, the precursor solution for preparing the P type doped thin film is prepared by in-situ doping metal salt of the precursor solution for preparing the N type doped thin film, the thin films of an emitting region, a base region and a collecting region are prepared by the same two-dimensional semiconductor material, formed PN junctions are homogeneous PN junctions, the BJT has a simple structure, the preparation of the P type doped thin film and the N type doped thin film can be simultaneously completed by doping without directional transfer, and because a doping object is the precursor solution, the doping process is carried out before the thin film is formed, the thin film is prevented from being damaged after the thin film is formed, and the damage degree of the prepared thin film is reduced to the greatest extent, the device performance is improved.
(2) According to the BJT of the two-dimensional transition metal chalcogenide, the precursor solution for preparing the P-type doped film is prepared by in-situ doping of the precursor solution for preparing the N-type doped film with the metal salt, and the doping concentration can be controlled by controlling the concentration of the metal salt because the concentration of the metal salt and the doping concentration of the precursor solution obtained after doping have a fixed relation, so that the doping concentration in the device can be controlled.
(3) According to the BJT of the two-dimensional transition metal chalcogenide, the precursor solution for preparing the P-type doped thin film is prepared by in-situ doping of the precursor solution for preparing the N-type doped thin film with metal salt, and the doping of the solution is not limited to the doping of the surface of the thin film, so that the doping effect is more stable, and the performance of the finally prepared device is more stable.
(4) The BJT based on the two-dimensional transition metal chalcogenide provided by the invention has the film of MoS2The film has high carrier mobility, and the BJT has good amplification performance; in the preferred scheme, the electrode is of a double-layer structure and is directly connected with MoS2One layer in contact with the film is a Ti metal layer due to the work function of titanium and molybdenum disulfide (MoS)2) Similarly, better ohmic contact can be achieved; one layer on the Ti metal layer is a protective layer which is used for preventing the Ti metal layer from being oxidized while conducting electricity; the electrode structure ensures good conductivity and stable performance.
(5) According to the preparation method provided by the invention, the precursor solution of the P-type thin film is prepared by doping the solution of the metal salt in the precursor solution of the N-type thin film, the required N-type and P-type two-dimensional transition metal chalcogenide thin films can be synthesized in one step by spin coating the corresponding precursor solutions according to the distribution of the emitter region, the base region and the collector region in the dielectric layer, directional transfer is not needed, the preparation process is controllable and easy to operate, the damage to the thin film is small, and the prepared BJT has good and stable performance.
(6) According to the preparation method provided by the invention, the precursor solution of the P-type thin film is prepared in a doping mode, and in the preparation process, the doping concentration of the P-type thin film in the BJT can be controlled by controlling the concentration of the metal salt in the second precursor solution.
(7) The preparation method provided by the invention can realize the control of the doping concentration of the P-type film by controlling the concentration of the metal salt in the second precursor solution, so that the preparation method can be applied to a plurality of fields such as photoelectric detection, micro integrated sensors, wearable equipment and the like.
(8) According to the preparation method provided by the invention, the damage to the film in the preparation process is small, the larger film is easy to prepare, and the pin is convenient to connect in practical application; experiments show that in the BJT prepared by the invention, the change range of the film area can be from mum magnitude to cm magnitude.
(9) According to the preparation method provided by the invention, the damage to the film in the preparation process is small, and the larger base region width is easy to prepare, so that the process precision requirement is effectively reduced under the condition of ensuring the amplification efficiency, and the preparation difficulty is reduced; experiments show that the maximum base region width of the BJT prepared by the invention can reach 10-30 μm.
Drawings
Fig. 1 is a schematic structural diagram of a BJT based on a two-dimensional transition metal chalcogenide according to an embodiment of the present invention;
FIG. 2 is a top view of an electrode angle for a two-dimensional transition metal chalcogenide based BJT according to an embodiment of the present invention;
fig. 3 is a flowchart of a process for preparing a two-dimensional transition metal chalcogenide-based BJT according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
In order to reduce the damage degree of a thin film in a nano layered transition metal chalcogenide transverse homogeneous BJT in the preparation process, improve the performance and stability of a device and realize controllable doping concentration, the invention provides a BJT based on a two-dimensional transition metal chalcogenide and a preparation method thereof, and the overall thought is as follows: the BJT is characterized in that a P-type doped thin film and an N-type doped thin film in a thin film layer are simultaneously prepared by laser irradiation of a precursor solution spin-coated on the upper surface of a dielectric layer, the precursor solution for preparing the P-type doped thin film is prepared by in-situ doping of metal salt in the precursor solution for preparing the N-type doped thin film, doping is completed before the thin film is formed, the damage degree of the prepared thin film is reduced to the maximum extent, and the doping concentration can be controlled by controlling the concentration of the metal salt, so that the doping concentration of the device can be controlled; correspondingly, in the preparation method, the precursor solution of the P-type thin film is prepared by doping metal salt in the precursor solution of the N-type thin film, after the corresponding precursor solution is spin-coated according to the distribution of the emitter region, the base region and the collector region in the dielectric layer, the needed N-type and P-type two-dimensional transition metal chalcogenide thin films can be synthesized in one step by laser irradiation, directional transfer is not needed, the preparation process is controllable and easy to operate, the damage to the thin film is small, and the prepared BJT has good and stable performance.
The BJT based on two-dimensional transition metal chalcogenide provided by the present invention, as shown in fig. 1 and 2, comprises: a monocrystalline silicon substrate with a dielectric layer;
the thin film layer is positioned on the upper surface of the dielectric layer; the thin film layer comprises three transition metal chalcogenide thin films which are transversely connected, namely a first P-type doped thin film, an N-type doped thin film and a second P-type doped thin film which sequentially form an emitter region, a base region and a collector region; three transition metal chalcogenide films in the thin film layer are prepared by laser irradiation of a precursor solution which is spin-coated on the upper surface of the dielectric layer, and the precursor solution for preparing the P-type doped thin film is prepared by in-situ doping metal salt of the precursor solution for preparing the N-type doped thin film;
and electrodes respectively positioned on the upper surfaces of the emitter region, the base region and the collector region to respectively form an emitter, a base and a collector.
The silicon dioxide dielectric layer is compact relative to other types of dielectric layers, has few dangling bonds and is easy to obtain, and the device has good preparation performance and cannot be influenced by the dielectric layers; in a preferred embodiment of the invention, the monocrystalline silicon substrate is in particular P-doped monocrystalline silicon and the dielectric layer is silicon dioxide (SiO)2) A dielectric layer.
Due to MoS2The band gap of the silicon-based semiconductor material is changed along with the change of the layer number, and the silicon-based semiconductor material has higher carrier mobility; in some preferred embodiments of the present invention, the two-dimensional transition metal chalcogenide in the thin film layer is MoS2(ii) a In the BJT prepared by the method, the thin films of the emitter region, the base region and the collector region are all MoS2The whole BJT has better amplification performance; in order to ensure that the thin film layer has better optical property and electrical propertyIn a further preferred embodiment of the invention, the MoS can be2The thickness of the thin film layer is 0.5nm-2 nm.
In order to further improve the performance of the BJT device, in some further preferred embodiments of the present invention, the electrode is a double-layer structure including a Ti metal layer directly contacting the thin film layer, and a protective layer on the Ti metal layer; the protective layer is used for conducting electricity and preventing the Ti metal layer from being oxidized; due to the work function of titanium and molybdenum disulfide (MoS)2) Similarly, the Ti metal layer is used as a direct contact with MoS in the double-layer electrode structure2One layer of the film contact is a Ti metal layer, so that better ohmic contact can be realized; one layer on the Ti metal layer is a protective layer which is used for preventing the Ti metal layer from being oxidized while conducting electricity; the electrode structure ensures good conductivity and stable performance.
In order to further improve the performance of the BJT device, in some further preferred embodiments of the present invention, the Ti metal layer has a thickness of 5nm to 30nm, thereby enabling a good ohmic contact; the protective layer is an Au metal layer, the conductivity and stability of Au are good, and the Ti metal layer on the bottom layer can be effectively protected from being oxidized while the conductivity is provided; the preferred thickness of the Au metal layer is 50nm to 200 nm.
The BJT based on the two-dimensional transition metal chalcogenide prepared by the invention is a lateral homogenous BJT, because the doping is carried out before the thin film is formed, and the doping object is a precursor solution used for preparing the thin film, the damage to the thin film is reduced to the greatest extent, the doping concentration is controllable, the doping effect is stable, and finally the performance and the stability of the device are improved.
The present invention also provides a method for preparing the BJT based on the two-dimensional transition metal chalcogenide, as shown in fig. 3, comprising the following steps:
(S1) preparing a shielding layer on the upper surface of the dielectric layer in the monocrystalline silicon substrate with the dielectric layer, and only exposing the middle area of the dielectric layer;
in some optional embodiments, two adhesive tapes can be directly pasted on two sides of the dielectric layer to serve as shielding layers, and the strip-shaped area in the middle is exposed;
(S2) spin-coating a first precursor solution on the dielectric layer with the shielding layer, and drying after soaking to obtain a sample A;
the first precursor solution comprises sulfur elements and two-dimensional transition metal elements;
(S3) after the photoresist is coated on the upper surface of the sample A in a spinning mode, removing the shielding layer to obtain a sample B;
as shown in fig. 3, in sample B, two sides of the dielectric layer are exposed, the middle region is spin-coated with the first precursor solution, and a photoresist is disposed above the first precursor solution, and the photoresist plays a role of shielding in the subsequent steps;
(S4) spin-coating a second precursor solution on the upper surface of the sample B, drying after soaking, and removing the photoresist to obtain a sample C;
the second precursor solution is formed by fully dissolving metal salt in the first precursor solution;
when the second precursor solution is prepared, any metal salt which does not react with the reactant and the product under the laser condition can be selected to avoid generating new impurities in the second precursor solution;
in the sample B, the photoresist in the middle area of the dielectric layer can play a role of shielding, so that the spin-coated first precursor solution is prevented from being polluted when the spin-coated second precursor solution is adopted;
in the finally obtained sample C, a first precursor solution is spin-coated in the middle area of the dielectric layer, and second precursor solutions are spin-coated on the two sides of the dielectric layer;
(S5) placing the sample C in a vacuum environment for laser irradiation to form a first P-type doped transition metal chalcogenide film, an N-type doped transition metal chalcogenide film and a second P-type doped transition metal chalcogenide film which are sequentially and transversely connected on the upper surface of the dielectric layer and respectively serve as an emitter region, a base region and a collector region to obtain a sample D;
(S6) spin-coating photoresist in the sample D to respectively prepare required electrode patterns on an emitter region, a base region and a collector region in the sample D, and then respectively depositing electrodes on the upper surfaces of the emitter region, the base region and the collector region to be used as an emitter, a base and a collector to obtain a sample E;
(S7) the photoresist in sample E is removed, resulting in a BJT based on a two-dimensional transition metal chalcogenide, i.e., sample F in fig. 3.
In order to obtain a clean P-type silicon substrate, in some preferred embodiments of the present invention, before the step (S1), the method further comprises:
and ultrasonically cleaning a p-type silicon substrate with a silicon dioxide dielectric layer on the upper surface by using acetone to remove organic dirt on the substrate and the dielectric layer, then cleaning the substrate by using alcohol to remove the acetone on the surface, finally washing by using deionized water, and blow-drying by using a nitrogen gun.
In some alternative embodiments of the invention, the MoS-based material is obtained for preparation2The first precursor solution of the thin-film BJT is a mixed solution obtained by dissolving molybdenum pentachloride and thiourea in an alcohol solvent; therefore, in the process of preparing the first precursor solution, reaction products except molybdenum disulfide are in a gaseous state, impurities are not easily generated in the generated molybdenum sulfide crystal, and after the reaction is finished, unreacted thiourea in the first precursor solution can be decomposed without impurity residues;
the alcohol solvent can be methanol, ethanol or isopropanol; the preferable dissolving and stirring speed is 1500-2000rpm, the stirring time is 0.8h-1.5h, the thiourea and the molybdenum pentachloride are caused, the sulfur concentration of the precursor solution is 15-25g/L, and the molybdenum concentration is 4-15 g/L; finally, the molar ratio of the sulfur element to the molybdenum element in the first precursor solution is 30: 1-4: 1.
in some optional embodiments of the present invention, in the step (S2), the spin coating process of the first precursor solution specifically includes: soaking for 30-60s, and then spin-coating for 20-60s at a rotation speed of 1000-4000 rpm. And then drying the sample at the temperature of 80-100 ℃ for 1-3 min to obtain a sample A.
In some optional embodiments of the present invention, the metal salt used for preparing the second precursor solution is one or more of gold chloride, silver nitrate and copper nitrate, the properties of copper, silver or gold are relatively stable, these elements are used as doping elements, the damage to the transition metal chalcogenide film in the doping process is small, and the prepared BJT has stable performance; the concentration of the metal salt determines the doping concentration of the metal in the molybdenum disulfide film, and the concentration can be 1-20 mmol/L.
In some preferred embodiments of the present invention, in the step (S5), the laser power of the laser irradiation is 100-2The size of the square is 2-4mm/s, and the laser moving speed is 2-4 mm/s; thereby further reducing damage to the film during film preparation.
In some preferred embodiments of the present invention, a photolithography process and electron beam evaporation of metal are used, a photoresist is first used to prepare a desired electrode pattern on the upper surface of a sample on which a transition metal chalcogenide is grown, and then an electrode is directly prepared by electron beam evaporation, so that the electrode can be in close contact with the surface of the transition metal chalcogenide, and the contact resistance is low.
In general, according to the preparation method provided by the invention, the precursor solution of the P-type thin film is prepared by doping the solution of the metal salt in the precursor solution of the N-type thin film, after the corresponding precursor solution is spin-coated according to the distribution of the emitter region, the base region and the collector region in the dielectric layer, the required N-type and P-type two-dimensional transition metal chalcogenide thin films can be synthesized in one step by laser irradiation, directional transfer is not required, the preparation process is controllable and easy to operate, the damage to the thin film is small, and the prepared BJT has good and stable performance. In addition, because the concentration of the metal salt in the second precursor solution is directly related to the doping concentration of the P-type thin film, the doping concentration of the P-type thin film in the BJT can be controlled by controlling the concentration of the metal salt in the second precursor solution in the preparation process.
MoS2Is a typical two-dimensional transition metal chalcogenide, and in the following examples, unless otherwise specified, all two-dimensional transition metal chalcogenides refer to MoS2。
The following are examples.
Example 1:
200mg of thiourea and 80mg of molybdenum pentachloride are dissolved in 3.75mL of isopropanol, the magnetic stirring speed is 1500rpm, the stirring time is 1h, and the dissolving temperature is 70 ℃, so that a precursor solution A is obtained. Using acetone to reactCarrying out ultrasonic cleaning on p-type silicon with the thickness of 300 mu m and a silicon dioxide dielectric layer with the thickness of 100nm on the surface to remove organic dirt on the substrate and the dielectric layer, then cleaning the substrate by using alcohol to remove acetone on the surface, finally washing by using deionized water and drying by using a nitrogen gun. Two adhesive tapes are pasted on the surface of the substrate to be used as shielding layers, and the strip-shaped area is exposed. Taking 0.1mL of precursor solution A, spin-coating on the upper surface of the substrate dielectric layer, soaking for 60s, and then spin-coating for 30s at 3000 rpm. Followed by drying at 90 ℃ for 1 min. And then spin-coating AZ5214 photoresist on the surface of the sample, and photoetching and developing the area A of the precursor solution by adopting a proper mask to prepare a photoresist shielding layer. And removing the adhesive tape, adding 0.1mL of silver nitrate with the concentration of 5mmol/L into 0.1mL of precursor solution A, and fully dissolving to obtain precursor solution B. And spin-coating the precursor solution B on the upper surface of the substrate and drying. Removing the photoresist on the surface of the sample, placing the sample in a vacuum chamber, irradiating with laser power of 400mJ and radiation frequency of 2Hz, the number of pulses is 1500 times, the laser movement rate is 2mm/s, and the spot size is 9cm2A square of size. And then, spin-coating photoresist on the sample, preparing an electrode pattern by using a proper mask, evaporating a Ti film with the thickness of 15nm by adopting an electron beam, evaporating an Au film with the thickness of 150nm on the Ti, and finally removing the photoresist from the sample to obtain the sample to be detected with the electrode on the surface.
Example 2:
200mg of thiourea and 50mg of molybdenum pentachloride are dissolved in 3.75mL of isopropanol, the magnetic stirring speed is 1500rpm, the stirring time is 1h, and the dissolving temperature is 70 ℃, so that a precursor solution A is obtained. Ultrasonic cleaning of 300 μm thick p-type silicon with a 100nm thick silicon dioxide dielectric layer on the top surface with acetone to remove organic dirt on the substrate and dielectric layer, followed by cleaning of the substrate with alcohol to remove acetone on the surface, finally rinsing with deionized water and blow-drying with a nitrogen gun. Two adhesive tapes are pasted on the surface of the substrate to be used as shielding layers, and the strip-shaped area is exposed. Taking 0.1mL of precursor solution A, spin-coating on the upper surface of the substrate dielectric layer, soaking for 30s, and then spin-coating for 60s at 1500 rpm. Followed by drying at 90 ℃ for 2 min. And then spin-coating AZ5214 photoresist on the surface of the sample, and photoetching and developing the area A of the precursor solution by adopting a proper mask to prepare a photoresist shielding layer. And removing the adhesive tape, adding 0.1mL of 10mmol/L copper nitrate solution into 0.1mL of precursor solution A, and fully dissolving to obtain precursor solution B. And spin-coating the precursor solution B on the upper surface of the substrate and drying. After removing the photoresist on the surface of the sample, placing the sample in a vacuum chamber, irradiating by using laser with the laser power of 100mJ and the radiation frequency of 8Hz, wherein the pulse number is 1000 times, the laser moving speed is 4mm/s, and the spot size is a square with the size of 9cm 2. And then, spin-coating photoresist on the sample, preparing an electrode pattern by using a proper mask, evaporating a Ti film with the thickness of 10nm by adopting an electron beam, evaporating an Au film with the thickness of 50nm on the Ti, and finally removing the photoresist from the sample to obtain the sample to be detected with the electrode on the surface.
Example 3:
200mg of thiourea and 80mg of molybdenum pentachloride are dissolved in 3.75mL of isopropanol, the magnetic stirring speed is 2000rpm, the stirring time is 1.5h, and the dissolving temperature is 70 ℃, so that a precursor solution A is obtained. Ultrasonic cleaning of 300 μm thick p-type silicon with a 100nm thick silicon dioxide dielectric layer on the top surface with acetone to remove organic dirt on the substrate and dielectric layer, followed by cleaning of the substrate with alcohol to remove acetone on the surface, finally rinsing with deionized water and blow-drying with a nitrogen gun. Two adhesive tapes are pasted on the surface of the substrate to be used as shielding layers, and the strip-shaped area is exposed. Taking 0.1mL of the precursor solution A, spin-coating on the upper surface of the substrate dielectric layer, soaking for 60s, and then spin-coating for 60s at the rotating speed of 2500 rpm. Followed by drying at 90 ℃ for 1 min. And then spin-coating AZ5214 photoresist on the surface of the sample, and photoetching and developing the area A of the precursor solution by adopting a proper mask to prepare a photoresist shielding layer. And removing the adhesive tape, adding 0.1mL of 1mmol/L gold chloride solution into 0.1mL of precursor solution A, and fully dissolving to obtain precursor solution B. And spin-coating the precursor solution B on the upper surface of the substrate and drying. After removing the photoresist on the surface of the sample, placing the sample in a vacuum chamber, irradiating by using laser with the laser power of 200mJ and the radiation frequency of 8Hz, wherein the pulse number is 1500 times, the laser moving speed is 4mm/s, and the spot size is a square with the size of 9cm 2. And then, spin-coating photoresist on the sample, preparing an electrode pattern by using a proper mask, evaporating a Ti film with the thickness of 20nm by adopting an electron beam, evaporating an Au film with the thickness of 70nm on the Ti, and finally removing the photoresist from the sample to obtain the sample to be detected with the electrode on the surface.
Example 4:
300mg of thiourea and 80mg of molybdenum pentachloride are dissolved in 3.75mL of isopropanol, the magnetic stirring speed is 3000rpm, the stirring time is 0.5h, and the dissolving temperature is 70 ℃, so that a precursor solution A is obtained. Ultrasonic cleaning of 300 μm thick p-type silicon with a 100nm thick silicon dioxide dielectric layer on the top surface with acetone to remove organic dirt on the substrate and dielectric layer, followed by cleaning of the substrate with alcohol to remove acetone on the surface, finally rinsing with deionized water and blow-drying with a nitrogen gun. Two adhesive tapes are pasted on the surface of the substrate to be used as shielding layers, and the strip-shaped area is exposed. Taking 0.1mL of precursor solution A, spin-coating on the upper surface of the substrate dielectric layer, soaking for 30s, and then spin-coating for 60s at 2000 rpm. Followed by drying at 90 ℃ for 1 min. And then spin-coating AZ5214 photoresist on the surface of the sample, and photoetching and developing the area A of the precursor solution by adopting a proper mask to prepare a photoresist shielding layer. Removing the adhesive tape, adding 0.1mL of gold chloride solution with the concentration of 1mmol/L into 0.1mL of precursor solution A, and fully dissolving to obtain precursor solution B. And spin-coating the precursor solution B on the upper surface of the substrate and drying. Removing the photoresist on the surface of the sample, placing the sample in a vacuum chamber, irradiating with laser power of 200mJ and radiation frequency of 8Hz, the number of pulses is 1500 times, the laser movement rate is 4mm/s, and the spot size is 9cm2A square of size. And then, spin-coating photoresist on the sample, preparing an electrode pattern by using a proper mask, evaporating a Ti film with the thickness of 20nm by adopting an electron beam, evaporating an Au film with the thickness of 100nm on the Ti, and finally removing the photoresist from the sample to obtain the sample to be detected with the electrode on the surface.
Due to the preparation of said MoS-based2The steps of the homojunction BJTs are the same, and the differences between the embodiments are only the differences between the parameters, and the above examples only show the parameters in the individual embodiments.
The invention discloses a method based on MoS2BJT with N-type MoS2As theThe base region of the BJT device can realize heavy doping of an emitting region and improve the emitting performance of the BJT; the film preparation and doping technology adopting laser irradiation can simplify the film preparation process, complete the film preparation and doping in one step, and selectively and quantitatively dope MoS2A film; and a homogeneous structure is adopted, transfer is not needed, and interface states are few. The prepared homojunction BJT has wide application prospect in the fields of integrated circuits, photodetectors and the like.
It should be noted that, when other two-dimensional transition metal chalcogenides are used to prepare the BJT, the corresponding reactants are used to prepare the first precursor solution; further examples, which will not be enumerated here.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A BJT based on a two-dimensional transition metal chalcogenide, comprising: a monocrystalline silicon substrate with a dielectric layer;
the thin film layer is positioned on the upper surface of the dielectric layer; the thin film layer comprises three two-dimensional transition metal chalcogenide thin films which are transversely connected, namely a first P-type doped thin film, an N-type doped thin film and a second P-type doped thin film which sequentially form an emitter region, a base region and a collector region; three transition metal chalcogenide films in the thin film layers are prepared by laser irradiation of a precursor solution spin-coated on the upper surface of the dielectric layer, and the precursor solution for preparing the P-type doped thin film is prepared by in-situ doping of metal salt in the precursor solution for preparing the N-type doped thin film;
and electrodes respectively positioned on the upper surfaces of the emitter region, the base region and the collector region respectively form an emitter, a base and a collector.
2. The method of claim 1 based on a two-dimensional transition metal chalcogenideBJT, wherein the two-dimensional transition metal chalcogenide in the thin film layer is MoS2；
Preferably, the thin film layer has a thickness of 0.5nm to 2 nm.
3. The two-dimensional transition metal chalcogenide-based BJT of claim 2, wherein said electrode is a bilayer structure comprising a Ti metal layer directly in contact with said thin film layer, and a protective layer over said Ti metal layer; the protective layer is used for conducting electricity and preventing the Ti metal layer from being oxidized.
4. The two-dimensional transition metal chalcogenide-based BJT of claim 3, wherein said Ti metal layer has a thickness in the range of 5nm to 30 nm.
5. The two-dimensional transition metal chalcogenide-based BJT of claim 3, wherein said protective layer is a Au metal layer;
preferably, the thickness of the Au metal layer is 50nm-200 nm.
6. The method for preparing a BJT based on a two-dimensional transition metal chalcogenide as claimed in any one of claims 1 to 5, comprising the following steps:
(S1) preparing a shielding layer on the upper surface of the dielectric layer in the single crystal silicon substrate with the dielectric layer, exposing only the middle region of the dielectric layer;
(S2) spin-coating a first precursor solution on the dielectric layer on which the shielding layer is prepared, and drying after soaking to obtain a sample A; the first precursor solution comprises sulfur elements and two-dimensional transition metal elements;
(S3) after spin-coating a photoresist on the upper surface of the sample A, removing the shielding layer to obtain a sample B;
(S4) spin-coating a second precursor solution on the upper surface of the sample B, drying after soaking, and removing the photoresist to obtain a sample C; the second precursor solution is formed by fully dissolving metal salt in the first precursor solution;
(S5) placing the sample C in a vacuum environment for laser irradiation, so as to form a first P-type doped transition metal chalcogenide film, an N-type doped transition metal chalcogenide film and a second P-type doped transition metal chalcogenide film which are sequentially and transversely connected on the upper surface of the dielectric layer, wherein the first P-type doped transition metal chalcogenide film, the N-type doped transition metal chalcogenide film and the second P-type doped transition metal chalcogenide film are respectively used as an emitter region, a base region and a collector region, and a sample D is obtained;
(S6) spin-coating photoresist in the sample D to respectively prepare required electrode patterns on an emitter region, a base region and a collector region in the sample D, and then respectively depositing electrodes on the upper surfaces of the emitter region, the base region and the collector region to serve as an emitter, a base and a collector to obtain a sample E;
(S7) removing the photoresist in the sample E, resulting in the two-dimensional transition metal chalcogenide-based BJT.
7. The method according to claim 6, wherein the first precursor solution is a mixed solution of molybdenum pentachloride and thiourea dissolved in an alcohol solvent.
8. The method according to claim 7, wherein the molar ratio of the sulfur atoms to the molybdenum atoms in the first precursor solution is 30: 1-4: 1.
9. the method according to any one of claims 6 to 8, wherein in the step (S5), the metal salt is one or more of gold chloride, silver nitrate and copper nitrate.
10. The method according to any one of claims 6 to 8, wherein in the step (S5), the laser power of the laser irradiation is 100-400mJ, the irradiation frequency is 2-10Hz, the pulse number is 1000-3000 times, and the spot size is 9cm2The size of the square is 2-4mm/s, and the laser moving speed is higher than that of the square.
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| CN107523811A (en) * | 2017-08-10 | 2017-12-29 | 华中科技大学 | A kind of two-dimentional Transition-metal dichalcogenide film and preparation method thereof |
| CN108666375A (en) * | 2018-04-20 | 2018-10-16 | 华中科技大学 | A kind of nano lamellar transverse direction homogeneity PN diodes and the preparation method and application thereof |
| CN108899267A (en) * | 2018-06-22 | 2018-11-27 | 华中科技大学 | A kind of preparation method of metal-doped molybdenum disulfide film |
| CN109616541A (en) * | 2018-10-29 | 2019-04-12 | 华中科技大学 | Transition-metal dichalcogenide transverse direction homogeneity joint solar cell and preparation method thereof |
| CN109920852A (en) * | 2019-02-28 | 2019-06-21 | 华中科技大学 | Device preparation method, two-dimensional material device and MoS2Field effect transistor |
| CN112687737A (en) * | 2020-12-24 | 2021-04-20 | 华中科技大学 | Horizontal homojunction bipolar transistor and preparation method thereof |
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