Compound thin film heterojunction and preparation method and application thereof

Abstract

The invention discloses a compound thin film heterojunction and a preparation method and application thereof, and belongs to the technical field of semiconductor manufacturing and nano materials. The preparation method comprises the steps that a substrate with an AxBy thin film is provided, A is a metal element, B is a chalcogenide element, ion irradiation is conducted on the AxBy thin film through an ion beam, the specific element B is selectively and preferentially removed through the intrinsic sputtering yield difference of the ion beam on different elements in the thin film, and therefore the controllable component gradient is actively constructed in the depth direction of the thin film; when local components reach a phase change critical point, in-situ induction phase change is carried out in the thin film, and a vertical heterojunction with an atomic-scale diffusion interface is formed. The method is completed in one step, the process is simple, the position of the heterojunction can be accurately regulated and controlled through irradiation parameters, and the obtained heterojunction can be used for preparing semiconductor devices such as high-speed transistors, laser diodes, photoelectric detectors and solar cells.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing and nanomaterials technology, specifically relating to a compound thin film heterojunction, its preparation method and application. Background Technology

[0002] Heterojunctions, as the core building blocks of modern semiconductor devices (such as high-speed transistors, laser diodes, photodetectors, and solar cells), directly determine the performance limits of these devices due to their interface quality. Traditional heterojunction fabrication techniques mainly follow two paths, but both have inherent limitations that are difficult to overcome. Layer-by-layer epitaxial growth techniques (such as molecular beam epitaxy (MBE) and chemical vapor deposition (CVD): These methods form heterojunctions by sequentially epitaxially growing different material layers on different substrates. While they can obtain high-quality single-crystal interfaces, their drawbacks are extremely prominent. First, the process requirements are extremely stringent, typically requiring ultra-high vacuum environments, precise lattice matching, and complex in-situ monitoring systems, resulting in exceptionally high equipment investment and manufacturing costs. Second, the growth process is limited by the thermodynamic compatibility between materials; many high-performance material combinations with large lattice mismatches are difficult to epitaxially achieve high quality, limiting the range of material choices. Furthermore, layer-by-layer growth is a serial process with low production efficiency, making it difficult to meet the demands of large-scale integrated applications. Physical stacking and transfer techniques: To overcome the limitations of lattice matching, mechanical exfoliation and precise stacking techniques have been developed to manually stack pre-prepared two-dimensional materials or thin films into heterojunctions. While this method relaxes the restrictions on material selection, it introduces new problems: interface contamination. Polymer residues, adsorbed gases, and dust introduced during the transfer process severely degrade interface properties, increasing carrier scattering and recombination centers; interface stress and wrinkles, due to interlayer van der Waals forces and alignment errors, can lead to uncontrollable strain and structural defects at the interface; poor process repeatability and scalability make it difficult to achieve high-precision, high-consistency mass production. Meanwhile, ion irradiation technology, as a mature material modification method, is widely used in the semiconductor industry for doping, defect engineering, surface etching, and modification. However, existing ion irradiation applications are mostly for homogenization or patterning. This either uniformly changes the overall properties of the material throughout the irradiated area (e.g., introducing uniform defects, achieving amorphization) or selectively removes (etches) the material using a mask. To date, no technology has reported utilizing the intrinsic differences in the interaction between ions and different elements in a material (such as sputtering yield and scattering cross section) to use ion irradiation as a precise tool for reconstructing composition space. By selectively and gradient-wise removing elements in the depth direction of a single homogeneous film, a continuously changing composition distribution can be actively sculpted. This composition gradient can then be used as a driving force to induce local phase transitions in situ within the film, ultimately achieving a one-step transformation from a single homogeneous film to an embedded heterojunction.

[0003] Therefore, developing a new method that can construct high-quality heterojunctions in situ within a single material with simple processing, strong controllability, and compatibility with existing technologies has become a technological bottleneck that urgently needs to be overcome in the field of semiconductor materials and devices. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention discloses a compound thin film heterojunction, its preparation method, and its application, in order to solve the technical problems of complex traditional heterojunction preparation processes and easy interface contamination.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide an in-situ preparation method for compound thin film heterojunctions, comprising the following steps: S1: Provides A x B y The substrate of the thin film has element A as a metallic element and element B as a chalcogenide element; A x B y The initial phase of the thin film is the first phase; the numerical ratio of x to y is 0.1 to 10:1; S2: Using an ion beam to treat A x B y The thin film is irradiated, and the sputtering yield of elements A and B differs depending on the energy of the ion beam. This results in the selective and preferential removal of element B, creating a continuous composition gradient from the surface of the thin film to its interior, where the concentration of element A increases and the concentration of element B decreases. When the local composition reaches the critical point of phase transition, a phase transition is induced in that region, forming a second phase near the surface of the thin film. The first phase and the second phase are connected by the continuous composition gradient to form a vertical heterojunction.

[0006] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, A x B y The thickness of the thin film is 5~500nm.

[0007] Furthermore, the metallic element is selected from Cu, Ag, or Au; the chalcogen elements are selected from S, Se, or Te.

[0008] Furthermore, in step S2, the ion beam is Ga + Ion beam, energy 10~50 keV, irradiation dose 1×10²²~1×10² 5 ions / cm², incident angle is 0~80°.

[0009] The compound thin film heterojunction prepared by the above preparation method includes a binary compound thin film; the binary compound thin film contains a second phase located on the surface and a first phase located at the bottom; the second phase is formed by the first phase through a composition gradient phase transition induced by ion irradiation, and the two phases are atomically connected through a continuous composition gradient.

[0010] The present invention also discloses the application of the above-mentioned compound thin film heterojunction in the fabrication of semiconductor devices.

[0011] Furthermore, semiconductor devices include high-speed transistors, laser diodes, photodetectors, or solar cells.

[0012] The beneficial effects of this invention are: 1. In-situ integrated preparation: a heterojunction is formed directly in a single thin film by single-step irradiation, without the need for material growth, transfer or stacking.

[0013] 2. High intrinsic quality of the interface: The composition of the heterojunction interface is continuously and gradually changed, forming an atomic-level diffusion interface, free from defects or contamination introduced by external forces.

[0014] 3. Nanoscale precise control: By adjusting the irradiation time or dose, the thickness of the new phase layer can be precisely controlled to the nanoscale, thereby defining the electrical active region of the heterojunction. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of an in-situ preparation method for compound thin film heterostructures. Figure 2 For CuTe thin films in Ga + STEM-HAADF atomic resolution image before ion irradiation; Figure 3 For CuTe thin films in Ga + Fourier transform pattern before ion irradiation; Figure 4 CuTe thin film with Ga + STEM-HAADF atomic resolution image after 30 s of ion irradiation; Figure 5 CuTe thin film with Ga + Fourier transform pattern after 30 seconds of ion irradiation; Figure 6 CuTe thin film with Ga + STEM-HAADF atomic resolution image after 100 s of ion irradiation; Figure 7 CuTe thin film with Ga + Fourier transform pattern after 100s of ion irradiation. Detailed Implementation

[0016] A schematic diagram of the in-situ preparation method of the compound thin film heterojunction in this invention is shown below. Figure 1 As shown, for a specific binary compound thin film A x B yWhen irradiated with an ion beam, the intrinsic difference in sputtering yield between elements A (light atoms) and B (heavy atoms) leads to the preferential removal of element B from the surface. This removal process disrupts the original compositional homogeneity of the film, creating a continuous compositional gradient from the surface, enriched in element A and depleted in element B. This gradient is distributed along the depth direction of the film. When the composition of a certain depth region in the film reaches another thermodynamically stable phase region of the material's phase diagram due to the continuous removal of element B, a phase transition in the crystal structure occurs in that region. As irradiation continues, this phase transition region advances from the surface into the interior of the film. At a certain irradiation dose, the film will exhibit a structure where the surface layer is the new phase and the bottom layer is the original phase, naturally connected by a transition region with continuously varying composition, thus forming a vertical heterojunction with a diffusion interface in situ inside the film.

[0017] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0018] Example 1 The in-situ preparation method of Cu1.4Te / CuTe heterostructure in CuTe thin film includes the following steps: S1: A thin layer with a thickness of 80 nm was obtained from a bulk CuTe single crystal using a mechanical exfoliation method, and then transferred to a 400-mesh copper mesh micro-grating substrate to obtain a substrate with a CuTe thin film; the STEM-HAADF atomic resolution image of the CuTe thin film and its Fourier transform (FFT) pattern are shown below. Figures 2-3 As shown, the STEM image reveals a perfect, uniform atomic lattice. The lattice constants (a=3.1Å, b=4.0Å) measured by FFT analysis are completely consistent with the projection of the standard CuTe crystal structure under the

[001] band axis; this indicates that the CuTe film is a pure, well-crystallized CuTe single crystal (first phase).

[0019] S2: Select two adjacent regions on the same thin film and irradiate the CuTe thin film with an ion beam using a focused ion beam (FIB) system. Ion source: Ga + Accelerating voltage: 30keV (energy parameter); Beam current: 50pA; Incident angle: 0° (vertical incidence); Ambient temperature: 300K (room temperature); Irradiation was performed on two adjacent regions for 30s and 100s respectively.

[0020] Aberration-corrected scanning transmission electron microscopy (STEM) was used to image samples obtained at three different irradiation times using high-angle annular dark field (HAADF) imaging in the

[001] direction to obtain atomic resolution information, and Fourier transform (FFT) analysis was performed.

[0021] STEM-HAADF atomic resolution image of the thin film after 30 s irradiation and its Fourier transform (FFT) pattern are shown below. Figures 4-5 As shown, clear and regular vertical moiré fringes appear in the STEM image. Moiré fringes are interference patterns generated by the superposition of two sets of lattices with similar periods. Their appearance directly and irrefutably proves that there is a region with differences between the upper and lower crystal structures in the direction of electron beam penetration (i.e., the direction of film thickness). The FFT pattern was precisely calibrated. Points A and B, marked by yellow circles, correspond to interplanar spacings of 1.55 Å and 2.0 Å, respectively, originating from the (020) and (200) crystal planes of the bottom CuTe phase. Point C, marked by blue circles, corresponds to an interplanar spacing of ~2.0 Å, originating from the (200) crystal plane of the surface Cu1.4Te phase. The satellite spots marked by red circles are moiré superlattice diffractions caused by the lattice mismatch (ratio 5:4) between the upper Cu1.4Te (a=4.0 Å) and the lower CuTe (a=3.2 Å). The above characterization shows that the CuTe film has differentiated into two layers (Cu1.4Te and CuTe) with different chemical compositions and crystal structures, and the two layers are coherent or semi-coherently connected (as evidenced by the moiré fringes), thus forming a high-quality vertical heterojunction in situ.

[0022] STEM-HAADF atomic resolution image of the thin film after 100 s irradiation and its Fourier transform (FFT) pattern are shown below. Figures 6-7 As shown, the STEM image reveals an overall change in atomic arrangement. FFT analysis shows a new diffraction pattern with a lattice constant a=b=4.0Å, which matches the crystal structure of the Cu1.4Te phase, indicating that the entire film has completely transformed into the second phase (Cu1.4Te).

[0023] In Example 1, 30keV Ga was used. + The sputtering efficiency of ions on Te atoms is much higher than that on Cu atoms, leading to the preferential removal of Te from the surface. At an intermediate dose of 30 s, the loss of surface Te results in relative Cu enrichment, forming a gradient from the surface (Cu enrichment) to the interior (normal composition). When the surface Cu / Te atomic ratio increases to approximately 1.4:1 due to Te removal, the thermodynamically stable phase in this region transforms from CuTe to Cu1.4Te. Therefore, at the intermediate dose of 30 s, the phase transition is not yet complete, forming a heterojunction structure of surface Cu1.4Te / bottom CuTe. After 100 s of irradiation, the entire film completely transforms into the second phase (Cu1.4Te). The irradiation dose (time) determines the position of the phase transition front (i.e., the heterojunction interface). Therefore, by precisely controlling the irradiation parameters, precise engraving of nanoscale heterojunction geometries can be achieved.

[0024] This invention utilizes CuTe / Ga +This specific system fully demonstrates and confirms a novel paradigm for heterojunction fabrication. Although the embodiments focus on a single system, this invention protects the general method based on "using ion beam selective sputtering to generate a compositional gradient, thereby inducing an in-situ phase transition to form a heterojunction".

[0025] Anyone skilled in the art, upon learning of the contents of this invention, will be motivated to attempt to apply this method to other material systems. For example, considering Ag... + Au + Ions typically exhibit high sputtering yields for chalcogenide elements (S, Se, Te), and systems such as Ag-Te and Au-Se also possess abundant composition-dependent phases (e.g., Ag₂Te, AgTe, etc.), making these systems obvious candidates for applying the method of this invention. Furthermore, changing the ion species (e.g., using Ar) + Xe + Adjusting energy and incident angle to optimize selectivity are both conventional technical methods.

[0026] Therefore, based on the core principles revealed in this invention, extending them to other binary or multi-component compound systems that meet the conditions of "elemental sputtering yield difference" and "composition-dependent phase transition" is direct and requires no inventive effort. All variations, modifications, or applications that do not depart from the spirit and scope of this invention should be included within the protection scope of this invention.

Claims

1. A method for in-situ preparation of a compound thin-film heterostructure, characterized in that, Includes the following steps: S1: Provides A x B y The substrate of the thin film has element A as a metallic element and element B as a chalcogenide element; wherein A x B y The initial phase of the thin film is the first phase; the numerical ratio of x to y is 0.1 to 10:1; S2: Using an ion beam to treat the A x B y The thin film is irradiated, and the sputtering yield of elements A and B differs depending on the energy of the ion beam. This results in the selective and preferential removal of element B, creating a continuous composition gradient from the surface of the thin film to its interior, where the concentration of element A increases and the concentration of element B decreases. When the local composition reaches the critical point of phase transition, a phase transition is induced in that region, forming a second phase near the surface of the thin film. The first phase and the second phase are connected by the continuous composition gradient to form a vertical heterojunction.

2. The in-situ preparation method of the compound thin film heterojunction according to claim 1, characterized in that: A x B y The thickness of the thin film is 5~500nm.

3. The in-situ preparation method of the compound thin film heterojunction according to claim 1, characterized in that: The metallic element is selected from Cu, Ag, or Au; the chalcogen elements are selected from S, Se, or Te.

4. The in-situ preparation method of the compound thin film heterojunction according to claim 1, characterized in that: In step S2, the ion beam is Ga + Ion beam, energy 10~50 keV, irradiation dose 1×10²²~1×10² 5 ions / cm², incident angle is 0~80°.

5. A compound thin-film heterojunction prepared by the method according to any one of claims 1 to 4, characterized in that: The invention includes a binary compound thin film; the binary compound thin film comprises a second phase located on the surface and a first phase located at the bottom; the second phase is formed by the first phase through a composition gradient phase transition induced by ion irradiation, and the two phases are atomically connected through a continuous composition gradient.

6. The application of the compound thin film heterojunction according to claim 5 in the fabrication of semiconductor devices.

7. The application according to claim 6, characterized in that: The semiconductor device includes a high-speed transistor, a laser diode, a photodetector, or a solar cell.

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