Two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons

Abstract

The invention discloses a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, and relates to the technical field of photoelectric detection. The device structurally comprises a substrate, a two-dimensional heterojunction formed on the substrate comprises an upper two-dimensional material layer and a lower two-dimensional material layer which are provided with anisotropic lattice structures, and a source electrode and a drain electrode formed on the two-dimensional heterojunction are in contact with the two two-dimensional material layers correspondingly. The two kinds of anisotropic materials form a second-class energy band heterojunction with an interlayer exciton state, interlayer excitons can break through intrinsic band gap limitation of a photosensitive material to achieve infrared light response, transition of the interlayer exciton state is changed into direct transition through momentum matching of the interlayer excitons, the light absorption efficiency of a heterojunction device is enhanced, and the photoelectric conversion efficiency of the heterojunction device is improved. And the light responsivity is improved. Meanwhile, the anisotropy of interlayer excitons is sensitive to infrared polarized light, and finally the heterojunction device achieves infrared polarization response breaking through the band gap limitation of the photosensitive material.

Description

Technical Field

[0001] A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons. Through the momentum matching and anisotropy of interlayer excitons, the band gap limitation of photosensitive materials is broken, the light absorption efficiency of heterojunction interlayer exciton states is improved, and the responsiveness of the device is improved, and the device responds to infrared polarized light, which relates to the field of photoelectric detection technology. Background Art

[0002] Traditional infrared photodetectors that are only sensitive to light intensity are increasingly unable to meet the needs of target detection in specific scenarios, which makes broadband polarization infrared detection crucial in modern navigation, medical diagnosis, military reconnaissance, and remote sensing. At present, two-dimensional materials have significant advantages in the development of such photodetectors due to their advantages such as atomic-level thickness, no dangling bonds, and natural in-plane anisotropy. These advantages help to circumvent the challenges faced by traditional compound semiconductors in lattice matching and the high cost of producing high-quality materials. Therefore, there is great potential for realizing low-cost, high-performance infrared polarization detection technology. In addition, although some high-performance polarization infrared photodetectors have been reported, the broadband photoresponse with polarization sensitivity is mainly limited by the band gap of existing materials.

[0003] In recent years, the emergence of a promising infrared detection technology based on interlayer excitons in two-dimensional van der Waals heterojunctions has provided the potential to overcome the limitation of spectral band gaps. This approach is to stack two-dimensional materials to form heterojunctions with two types of energy band arrangements, in which the conduction band minimum and valence band maximum are staggered on different materials. The interlayer exciton states generated by interlayer coupling in these heterojunctions are smaller than the band gap of the parent material, and the corresponding transition energy can be flexibly determined by selecting the required materials. Therefore, interlayer excitons can effectively extend the photoresponse to the infrared band without the need to use relatively rare narrow-band materials.

[0004] Despite these advantages, the photoresponsivity of heterojunctions based on interlayer excitons is still low, such as WSe2 / MoSe2 and WSe2 / MoS2. This is mainly due to the obvious spatial separation between electrons and holes in interlayer excitons, which reduces the overlap of electron-hole wave functions. As a result, the vibration intensity, oscillator strength and light absorption in interlayer excitons are 3 to 4 orders of magnitude lower than those in intralayer excitons. At the same time, unless the interlayer twist angle can be carefully controlled, interlayer excitons usually exhibit indirect band gap transitions, which often lead to momentum mismatch and low light absorption efficiency. Summary of the invention

[0005] The present invention provides a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, so that the two-dimensional heterojunction detector can break through the intrinsic band gap of the photosensitive material and realize infrared polarized light response based on the interlayer excitons, and the momentum matching of the interlayer excitons improves the light absorption efficiency of the interlayer excited state.

[0006] The technical solution of the present invention is as follows:

[0007] A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, the device structure comprising: a substrate (1), a two-dimensional heterojunction formed on the substrate (1), the two-dimensional heterojunction comprising two upper and lower layers, namely, a two-dimensional material layer A (2) with an anisotropic lattice structure and a two-dimensional material layer B (3) with an anisotropic lattice structure, the source and drain electrodes formed on the two-dimensional heterojunction respectively contacting the two layers of two-dimensional materials; wherein the source electrode (4) is prepared on the surface of the material layer A (2); and the drain electrode is prepared on the surface of the material layer B (3).

[0008] Furthermore, the two-dimensional material A layer (2) and the two-dimensional material B layer (3) forming the two-dimensional heterojunction both have anisotropic lattice structures. The two-dimensional material A layer (2) and the two-dimensional material B layer (3) form a stepped structure.

[0009] Furthermore, the anisotropic two-dimensional material layer A (2) and the two-dimensional material layer B (3) form a second type of energy band heterojunction, and the transition energy level E of the interlayer exciton state between the two-dimensional material layer A (2) and the two-dimensional material layer B (3) is g The transition from the valence band maximum of the two-dimensional material B layer (3) to the conduction band minimum of the two-dimensional material A layer (2) is the Γ point in the reciprocal space, E g is a direct band gap; the transition energy level E g The band gap width is smaller than that of any two-dimensional material constituting the heterojunction, and photoelectric conversion that breaks through the band gap limitation of the photosensitive material itself can be achieved.

[0010] It is further preferred that the materials corresponding to the two-dimensional material layer A (2) and the two-dimensional material layer B (3) are one ReS2 and the other CrPS4.

[0011] Furthermore, when the incident photon energy is less than the band gap energy of each photosensitive material and greater than the interlayer exciton state transition energy E g When the polarization direction of the incident polarized light rotates from the a-axis to the b-axis of CrPS4, due to the anisotropy of the interlayer excitons, the current output by the device gradually changes from a maximum value to a minimum value.

[0012] The present invention provides a method for preparing a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, comprising the following steps:

[0013] First, the two-dimensional material A layer (2) is transferred to the substrate through PDMS; then the two-dimensional material B layer (3) is transferred to the two-dimensional material A layer (2) through PDMS; the source and drain electrodes (4) and (5) are prepared by ultraviolet exposure lithography technology, electron beam evaporation coating technology, lift-off technology, etc.; and vacuum high-temperature annealing is performed for several hours (preferably annealing at 250°C for 2 hours).

[0014] The beneficial effects of the present invention are:

[0015] The present invention uses a stack of two-dimensional materials with anisotropic lattice structures to form a second type of heterojunction energy band. The resulting interlayer transition energy level difference allows the light response to break through the limitation of the photosensitive material band gap. At the same time, the valence band maximum and conduction band minimum of the interlayer band gap are located at the Γ point in the K space, so the direct band gap transition formed can enhance the light absorption efficiency and improve the light response of the device, and the anisotropy of the interlayer excitons is used to achieve infrared polarized light response. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the heterojunction device of the present invention;

[0017] Figure 2 (a) is a schematic diagram of the energy band structure of a heterojunction device;

[0018] Figure 2 (b) is a schematic diagram of the energy band structure of a heterojunction device in k-space;

[0019] Figure 3 (a) and (b) are the theoretical and experimental light absorption spectra of heterojunction devices, respectively;

[0020] Figure 4 (a) is a schematic diagram of the photocurrent scanning of the heterojunction device under infrared wavelength irradiation;

[0021] Figure 4 (b) is a schematic diagram of the polar coordinates of the photocurrent of the heterojunction device at different polarization angles. DETAILED DESCRIPTION

[0022] The present invention provides a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0023] The embodiment of the present invention provides a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, the device structure is as follows Figure 1As shown, the structure of the device is, from bottom to top: substrate (1), a first anisotropic two-dimensional material (2), a second anisotropic two-dimensional material (3), and source-drain metal electrodes (4) and (5).

[0024] Among them, the first and second two-dimensional materials are ReS2 and CrPS4 respectively; the corresponding thickness of the ReS2 layer is 10nm, and the corresponding thickness of the CrPS4 layer is 18nm.

[0025] The two two-dimensional materials are sequentially transferred to the substrate by mechanical exfoliation and PDMS dry transfer;

[0026] The source and drain electrodes (4) and (5) are connected to the materials (2) and (3) respectively by using ultraviolet lithography technology and electron beam evaporation coating technology. The metal electrodes are Ti / Au with thicknesses of 10 / 70 nm respectively.

[0027] like Figure 2 As shown, the design of momentum matching and anisotropic interlayer excitons in the ReS2 / CrPS4 heterojunction device is shown. Figure 2 (a) shows the interlayer transition energy level E g is the energy difference between the valence band of CrPS4 and the conduction band of ReS2, E g Smaller than the intrinsic band gap of the two materials that make up the heterojunction. Figure 2 (b) shows E g In k-space, it is a direct bandgap transition, E g The direct band gap is about 0.81 eV, and the dispersion asymmetry in the valence band from the Γ point to the M point and the K point respectively indicates that the interlayer excitons are anisotropic.

[0028] like Figure 3 The figure shows the absorption spectrum of the ReS2 / CrPS4 heterojunction device. Figure 3 (a) is a schematic diagram of the absorption spectrum obtained by theoretical calculation of the heterojunction device. The light absorption efficiency in the short-wave infrared band is maximum and minimum along the a-axis and b-axis of CrPS4. Figure 3 (b) is a schematic diagram of the absorption spectrum of the heterojunction device experimentally measured. As the polarization angle changes, the light absorption efficiency also varies, and the directions of maximum and minimum light absorption efficiency are consistent with theoretical calculations.

[0029] like Figure 4 As shown, it is the photocurrent scanning diagram and the polar coordinate diagram of the photocurrent of the ReS2 / CrPS4 heterojunction device. Figure 4 (a) The wavelength of light is 1550nm and the power density is 0.318mW / cm 2Under light irradiation, the photocurrent scanning diagram of the device can determine that the light excitation comes entirely from the overlapping area of ​​the two materials, that is, the photoelectric response phenomenon caused by interlayer transition, and the light response is 0.3A / W. Figure 4 (b) is the polar coordinate diagram of the photocurrent of the device at different polarization angles under 1550nm light irradiation. The photoresponse is maximum when the polarization direction of the incident light is along the a-axis of CrPS4 and minimum along the b-axis, and the polarization ratio reaches 1.3.

[0030] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons, characterized in that: The device structure comprises: a substrate (1), a two-dimensional heterojunction formed on the substrate (1), the two-dimensional heterojunction comprising two layers, namely, a two-dimensional material layer A (2) having an anisotropic lattice structure and a two-dimensional material layer B (3) having an anisotropic lattice structure, and source and drain electrodes formed on the two-dimensional heterojunction respectively contact the two layers of two-dimensional materials; wherein the source electrode (4) is prepared on the surface of the material layer A (2); and the drain electrode is prepared on the surface of the material layer B (3).

2. A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons according to claim 1, characterized in that: The two-dimensional material A layer (2) and the two-dimensional material B layer (3) forming the two-dimensional heterojunction both have anisotropic lattice structures. The two-dimensional material A layer (2) and the two-dimensional material B layer (3) form a stepped structure.

3. A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons according to claim 1, characterized in that: The anisotropic two-dimensional material A layer (2) and the two-dimensional material B layer (3) form a second type of energy band heterojunction. The transition energy level E of the interlayer exciton state between the two-dimensional material A layer (2) and the two-dimensional material B layer (3) is g The transition from the valence band maximum of the two-dimensional material B layer (3) to the conduction band minimum of the two-dimensional material A layer (2) is the Γ point in the reciprocal space, E g is a direct band gap; the transition energy level E g The band gap width is smaller than that of any two-dimensional material constituting the heterojunction, and photoelectric conversion that breaks through the band gap limitation of the photosensitive material itself can be achieved.

4. A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons according to claim 1, characterized in that: The materials corresponding to the two-dimensional material A layer (2) and the two-dimensional material B layer (3) are ReS2 and CrPS4 respectively.

5. A two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons according to claim 4, characterized in that: When the incident photon energy is less than the band gap energy of each photosensitive material and greater than the interlayer exciton state transition energy E g When the polarization direction of the incident polarized light rotates from the a-axis to the b-axis of CrPS4, due to the anisotropy of the interlayer excitons, the current output by the device gradually changes from a maximum value to a minimum value.

6. A method for preparing a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons according to any one of claims 1 to 5, characterized in that: The following steps are involved: First, the two-dimensional material A layer (2) is transferred onto the substrate through PDMS; then the two-dimensional material B layer (3) is transferred onto the two-dimensional material A layer (2) through PDMS; the source and drain electrodes are prepared by ultraviolet exposure lithography technology, electron beam evaporation coating technology, lift-off technology, etc.; and vacuum high-temperature annealing is performed for several hours.

7. Application of a two-dimensional heterojunction device with momentum matching and anisotropic interlayer excitons as described in any one of claims 1 to 5 for responding to and detecting infrared polarized light.

8. According to the method of claim 7, the anisotropy of the interlayer excitons is sensitive to infrared polarized light, and finally the heterojunction device realizes an infrared polarization response that breaks through the band gap limitation of the photosensitive material.

Images