Molybdenum disulfide-based asymmetric structure Schottky diode

Abstract

The invention belongs to the technical field of diode structure design and preparation, particularly provides an asymmetric structure Schottky diode based on molybdenum disulfide, and aims to solve the problems that an existing molybdenum disulfide Schottky diode is poor in unidirectional conductivity under the same metal electrode structure and complex in preparation process under different metal electrode structures. The molybdenum disulfide thin film of the continuous layered stepped structure is creatively provided in the Schottky diode design, different thickness areas of the molybdenum disulfide thin film have different work functions, the maximum thickness position of the molybdenum disulfide thin film is in ohmic contact with the metal thin film, and the minimum thickness position of the molybdenum disulfide thin film is in Schottky contact with the metal thin film. Therefore, the Schottky contact and the ohmic contact are simultaneously constructed by only one metal and one semiconductor material, the aim of simplifying the structure and the preparation process of the diode device is fulfilled, and the unilateral conductivity of the diode device is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of diode structure design and preparation, relates to a Schottky diode, and specifically provides an asymmetric Schottky diode based on molybdenum disulfide. Background Art

[0002] With the rapid development of semiconductor technology, Schottky diodes based on metal-semiconductor structures are becoming increasingly important in the fields of renewable energy, electronic components, and detection and sensing. For common semiconductor materials such as metal oxide materials and silicon-based materials, based on their own work function characteristics, energy level matching conditions with metals, and semiconductor process technology characteristics, commonly used Schottky diodes basically use two metals with different work functions as electrodes to contact the semiconductor materials, forming Schottky contacts and ohmic contacts respectively, which imposes certain restrictions on the structure and process of Schottky diodes.

[0003] Molybdenum disulfide has been widely used in the semiconductor field due to its own two-dimensional structure, which brings advantages such as high carrier mobility and ideal band structure. Among them, Schottky diodes constructed by molybdenum disulfide and metal materials have been widely studied. For example, the Chinese patent with application number CN 202310176490.X discloses a heterojunction diode based on molybdenum disulfide. Its diode structure adopts a symmetrical semiconductor-metal heterojunction structure, and uses the same metal film as the two electrodes of the diode, which are respectively in Schottky contact with the molybdenum disulfide film. However, the working state of the device is poor due to the mutual breakdown of the Schottky junction, resulting in poor unidirectional conductivity. Another example is the Chinese patent with application number CN 202310797064.8, which uses different metal materials as metal electrodes to form different types of contacts with molybdenum disulfide thin films, and uses a coating process to reduce surface impurity adsorption and defects, constructs a device with excellent performance, and achieves good rectification characteristics. However, because it uses different metals as electrodes, its device structure and preparation process are relatively complex. At the same time, the morphology of the molybdenum disulfide film under the deposition process is poor and has an unstable working current. It can be seen that the currently common molybdenum disulfide diodes are divided into the same metal electrode structure and the different metal electrode structure. The molybdenum disulfide Schottky diodes under the two structures each face many problems. Therefore, it is extremely necessary to design a Schottky heterojunction diode with a simpler structure and a more streamlined preparation process. Summary of the invention

[0004] The purpose of the present invention is to provide an asymmetric structure Schottky diode based on molybdenum disulfide, so as to solve the problems of poor unidirectional conductivity of the existing molybdenum disulfide Schottky diode under the same metal electrode structure and complicated preparation process under different metal electrode structures; utilizing the characteristic that the work function of the two-dimensional molybdenum disulfide material is affected by its thickness, the present invention proposes a Schottky diode based on a continuous layered step structure molybdenum disulfide film, utilizing the relationship between the work function of the molybdenum disulfide film and the metal work function, based on a metal and a semiconductor material, Schottky contact and ohmic contact are simultaneously formed, so as to achieve the goal of simplifying the diode device structure and preparation process.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A Schottky diode based on an asymmetric structure of molybdenum disulfide comprises: a silicon wafer substrate 1, a molybdenum disulfide film 2, a first metal film electrode 3-1 and a second metal film electrode 3-2; characterized in that the molybdenum disulfide film adopts a continuous layered step structure, and its thickness decreases in a step-like manner from one side to the other side; the molybdenum disulfide film is arranged on the silicon wafer substrate, the first metal film electrode and the second metal film electrode are arranged on the silicon wafer substrate and are located on both sides of the molybdenum disulfide film, the first metal film electrode covers the side with the largest thickness of the molybdenum disulfide film and forms an ohmic contact on the contact surface, and the second metal film electrode covers the side with the smallest thickness of the molybdenum disulfide film and forms a Schottky contact on the contact surface.

[0007] Furthermore, the maximum thickness of the molybdenum disulfide film is 15-30 nm, and the minimum thickness is 0.5-10 nm. Different thickness regions of the molybdenum disulfide film have different work functions, so as to realize an asymmetric heterojunction.

[0008] Furthermore, the thickness of the first metal film electrode and the second metal film electrode is 30-50 nm.

[0009] Furthermore, the first metal film electrode and the second metal film electrode are made of the same material, and the work function range is 4.85 to 5.25 eV.

[0010] Furthermore, the molybdenum disulfide film is prepared by a mechanical stripping process and is disposed on the surface of a silicon wafer substrate by a transfer process.

[0011] Furthermore, the metal film is deposited on the surface of the molybdenum disulfide film and the silicon wafer substrate by a magnetron sputtering process.

[0012] In terms of working principle:

[0013] The continuous layered stepped structure molybdenum disulfide film proposed in the present invention has a non-uniform thickness, and the continuous layered stepped structure molybdenum disulfide film material has different work functions in different thickness regions thereof. The work function of the continuous layered stepped structure molybdenum disulfide film at the maximum thickness is greater than the work function of the metal film, and the molybdenum disulfide film forms an ohmic contact with the metal film here; the work function of the continuous layered stepped structure molybdenum disulfide film at the minimum thickness is less than the work function of the metal film, and the molybdenum disulfide film forms a Schottky contact with the metal film here; therefore, the present invention uses only one metal and one semiconductor material to simultaneously construct a Schottky contact and an ohmic contact, thereby achieving the goal of simplifying the diode device structure and the preparation process.

[0014] In summary, the beneficial effects of the present invention are:

[0015] The present invention provides an asymmetric Schottky diode based on molybdenum disulfide, wherein a continuous layered stepped-structured molybdenum disulfide film is obtained by combining a mechanical stripping and a transfer process; based on the continuous layered stepped-structured molybdenum disulfide film, an ohmic contact is formed with a metal film at its maximum thickness, and a Schottky contact is formed with the metal film at its minimum thickness, and different types of contacts are constructed with metals by utilizing different thickness regions of the molybdenum disulfide film, and the Schottky diode is prepared by using only one metal and one semiconductor material, thereby achieving the goal of simplifying the diode device structure and preparation process, and effectively improving the unidirectional conductivity of the diode device, and the Schottky diode can be widely used in the preparation field of Schottky diodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of the Schottky diode in an embodiment of the present invention, wherein 1 is a silicon wafer substrate, 2 is a molybdenum disulfide film, 3-1 is a first metal film electrode, and 3-2 is a second metal film electrode.

[0017] Figure 2 It is a schematic diagram of the structure of a Schottky diode in a comparative example of the present invention.

[0018] Figure 3 The AFM scans of the heterojunction of the Schottky diode in the embodiment and the comparative example of the present invention, wherein (a) is the embodiment and (b) is the comparative example.

[0019] Figure 4 The AFM thickness scans of the heterojunction of the Schottky diode in the embodiment of the present invention and the comparative example.

[0020] Figure 5 1 is a current-voltage characteristic curve diagram of the Schottky diode in the embodiment of the present invention and the comparative example.

[0021] Figure 6 The graph is a logarithmic curve of the current-voltage characteristics of the Schottky diode in the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further explained in detail below in conjunction with the accompanying drawings, embodiments and comparative examples.

[0023] This embodiment provides an asymmetric Schottky diode based on molybdenum disulfide, whose structure is as follows: Figure 1 As shown, it includes: a silicon wafer substrate 1, a molybdenum disulfide film 2, a first metal film electrode 3-1 and a second metal film electrode 3-2; wherein the molybdenum disulfide film 2 adopts a continuous layered step structure, and its thickness decreases in a step-like manner from one side to the other side, that is, the molybdenum disulfide film 2 has a non-uniform thickness; the molybdenum disulfide film 2 is arranged on the silicon wafer substrate 1, the first metal film electrode 3-1 and the second metal film electrode 3-2 are arranged on the silicon wafer substrate 1 and are located on both sides of the molybdenum disulfide film 2, the first metal film electrode 3-1 covers the side with the largest thickness of the molybdenum disulfide film 2 and forms an ohmic contact on the contact surface, and the second metal film electrode 3-2 covers the thickness of the molybdenum disulfide film 2 The thickness of the molybdenum disulfide film is the smallest on the side, and a Schottky contact is formed on the contact surface; in the asymmetric structure Schottky diode, the contact type constructed by the contact between the molybdenum disulfide film and the metal film is regulated by the thickness-work function relationship of the continuous layered step structure molybdenum disulfide. The thickest part of the molybdenum disulfide film forms an ohmic contact with the metal film, that is, a heterojunction constructed by the metal film electrode 3-1 and the molybdenum disulfide film 2, and the thinnest part of the molybdenum disulfide film forms a Schottky contact with the metal film, that is, a heterojunction constructed by the metal film electrode 3-2 and the molybdenum disulfide film 2. The Schottky diode is realized by only one metal and one semiconductor material, which simplifies the diode device structure and preparation process, and improves the unidirectional conductivity of the diode device.

[0024] Furthermore, in this embodiment, a 1cm×1cm silicon wafer with an insulating oxide layer is first used as a substrate, which is soaked in chemicals such as acetone, ethanol, and deionized water in sequence and then blown dry for use; secondly, a continuous layered stepped structure molybdenum disulfide film is configured on the surface of the silicon wafer substrate based on a peeling transfer process, wherein the thickest part of the molybdenum disulfide film is about 15 to 30nm, and the thinnest part of the molybdenum disulfide film is about 0.5 to 10nm; finally, a palladium metal film with a thickness of 50nm is deposited on the surface of the molybdenum disulfide film and part of the surface of the silicon wafer substrate through a magnetron sputtering process to form an asymmetric Schottky diode.

[0025] Furthermore, in this embodiment, the molybdenum disulfide film is prepared by a mechanical stripping process and is configured on the surface of a silicon wafer substrate by a transfer process; the mechanical stripping process is specifically as follows: a block of molybdenum disulfide material is placed on the surface of a tape colloid and fixed, and the material is repeatedly pasted with tape, and the process is repeated 4 to 5 times to obtain a molybdenum disulfide film material; PDMS is used to lightly adhere the molybdenum disulfide film material, and the PDMS is placed on the surface of a glass slide, and the color of the molybdenum disulfide material adhered to the PDMS surface is observed using an optical microscope, and a complete molybdenum disulfide material that is partially blue and partially yellow is selected to obtain a continuous layered stepped structure molybdenum disulfide film; The transfer process is specifically as follows: invert the glass slide with PDMS on it in the previous step on the transfer table fixture and fix it, place the silicon wafer substrate on the silicon wafer stage and fix it by adsorption, gently turn the knob to make the glass slide slowly approach the silicon wafer substrate until the PDMS is completely in contact with the silicon wafer substrate, use an observation device to confirm that the molybdenum disulfide film is attached to the surface of the silicon wafer substrate, start the heating device to heat the silicon wafer substrate to 110°C and keep it for 15 to 20 minutes, release the molybdenum disulfide film on the PDMS surface to the surface of the silicon wafer substrate, and finally gently turn the knob to separate the PDMS and the silicon wafer substrate to obtain a silicon wafer substrate with a continuous layered step structure molybdenum disulfide film adhered to it.

[0026] The beneficial effects of the present invention are described in detail below in combination with tests. In order to more intuitively illustrate the beneficial effects of the present invention, the present invention provides a comparative example. In the comparative example, a molybdenum disulfide Schottky diode such as Figure 2 As shown, the difference between it and the present embodiment is that a symmetrical structure is adopted, that is, the MoS2 film adopts a structure with uniform thickness, and the metal films on both sides form Schottky contacts with the MoS2 film.

[0027] The embodiments and comparative examples were characterized by AFM atomic force microscope scanning. Figure 3 As shown, both the embodiment and the comparative example achieve effective coverage of the molybdenum disulfide film by the metal film, thereby constructing a heterojunction.

[0028] The overlap of the molybdenum disulfide film and the metal film in the embodiment and the comparative example (such as Figure 3 AFM atomic force microscope scanning is performed to obtain the thickness of the MoS2 film in each heterojunction region, as shown in FIG. Figure 4 As shown, the thinnest part (about 8.5 nm) and thickest part (about 17 nm) of the continuous layered stepped structure MoS2 film of the embodiment participate in the construction of Schottky heterojunction and Ohmic heterojunction respectively, and the MoS2 film of uniform thickness (about 8 nm) of the comparative example participates in the construction of Schottky heterojunction.

[0029] The current-voltage test was carried out on the embodiment and the comparative example, and the results are as follows Figure 5As shown, the IV curve of the embodiment shows obvious unidirectional conductivity, and the turn-on voltage is about -2V, indicating that the device in the embodiment has only one Schottky contact and the other end is an ohmic contact; the IV curve of the comparative example shows a symmetrical structure within the positive and negative voltage range, and the turn-on voltage is about ±10V, indicating that its structure is a double Schottky heterojunction, and the current is turned on by mutual breakdown.

[0030] The current-voltage test was performed on the embodiment and the comparative example, and a current-voltage logarithmic curve was obtained. Figure 6 As shown, the current level of the embodiment in the negative voltage range is much higher than the current level in the positive voltage range, and the current level of the comparative example presents an approximately symmetrical structure. The results show that the metal-molybdenum disulfide contact on one side of the embodiment is a Schottky contact, and the metal-molybdenum disulfide contact on the other side is an ohmic contact, with obvious unidirectional conductivity, indicating that the embodiment is a Schottky diode.

[0031] In summary, the present invention provides an asymmetric Schottky diode based on molybdenum disulfide, which effectively simplifies the device structure and preparation process, and optimizes the unidirectional conductivity of the device by modulating the thickness-work function of the molybdenum disulfide film and utilizing different thickness regions of the molybdenum disulfide film to construct ohmic contact and Schottky contact with metal.

[0032] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. An asymmetric Schottky diode based on molybdenum disulfide, comprising: A silicon wafer substrate 1, a molybdenum disulfide film 2, a first metal film electrode 3-1 and a second metal film electrode 3-2; characterized in that the molybdenum disulfide film adopts a continuous layered step structure, and its thickness decreases in a step-like manner from one side to the other side; the molybdenum disulfide film is arranged on the silicon wafer substrate, the first metal film electrode and the second metal film electrode are arranged on the silicon wafer substrate and are located on both sides of the molybdenum disulfide film, the first metal film electrode covers the side of the molybdenum disulfide film with the largest thickness and forms an ohmic contact on the contact surface, and the second metal film electrode covers the side of the molybdenum disulfide film with the smallest thickness and forms a Schottky contact on the contact surface.

2. The asymmetric Schottky diode based on molybdenum disulfide according to claim 1, characterized in that: The maximum thickness of the molybdenum disulfide film is 15nm-30nm, and the minimum thickness is 0.5nm-10nm.

3. The asymmetric Schottky diode based on molybdenum disulfide according to claim 1, characterized in that: The thickness of the first metal film electrode and the second metal film electrode is 30-50 nm.

4. The asymmetric Schottky diode based on molybdenum disulfide according to claim 1, characterized in that: The first metal film electrode and the second metal film electrode are made of the same material, and the work function range is 4.85-5.25 eV.

5. The asymmetric Schottky diode based on molybdenum disulfide according to claim 1, characterized in that: The molybdenum disulfide film is prepared by a mechanical stripping process and is arranged on the surface of a silicon wafer substrate by a transfer process.

6. The asymmetric Schottky diode based on molybdenum disulfide according to claim 1, characterized in that: The metal film is deposited on the surface of the molybdenum disulfide film and the silicon wafer substrate by using a magnetron sputtering process.

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