Light emitting thin film structure on non-single crystal substrate

Abstract

The application discloses a light-emitting thin film structure on a non-single crystal substrate, and belongs to the technical field of light-emitting semiconductor thin films and light-emitting devices.The structure comprises, from bottom to top, a non-single crystal substrate, a superlattice structure composed of n periodic alternately stacked two-dimensional material interface layers and III group nitride buffer layers, which are used for gradually reducing crystal defects and releasing stress, and an N type layer, a light-emitting layer, a P type layer and a P+ type layer which are stacked on the superlattice structure.By adopting the periodic combination of the two-dimensional material interface layers and the nitride buffer layers, a periodic superlattice structure of an "interface layer-buffer layer" is provided in the application, wherein the number of periods n is greater than or equal to 2.By optimizing material selection and stacking mode, the structure can significantly reduce the lattice defects of the outermost buffer layer, and when depositing the thin film used for the PN junction of a light-emitting diode, the lattice defects in the thin film can be greatly reduced, and the crystalline quality can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of light-emitting semiconductor thin films and light-emitting devices, and particularly relates to light-emitting thin film structures on non-single-crystal substrates. Background Technology

[0002] The principle of lighting sources is to convert electrical energy into light energy. They are mainly divided into three categories: thermal radiation sources, gas discharge sources, and semiconductor sources. Thermal radiation sources, such as light bulbs, emit light through the heating of a tungsten filament. They are characterized by excellent color rendering and fast start-up. Early lighting was dominated by incandescent lamps. Gas discharge sources, including fluorescent lamps and high-pressure mercury lamps, utilize gas ionization to emit light. They have good energy efficiency and lifespan and are widely used in industrial and commercial fields. Semiconductor sources are based on semiconductor PN junction recombination light emission, namely light-emitting diodes (LEDs). The PN junctions used emit blue light with a wavelength of 380-450nm. To obtain other colors of light, generally... Adding phosphor in front of the PN junction that emits blue light is sufficient. Currently, LEDs have become the mainstream of lighting due to their energy-saving characteristics, but the conversion efficiency of phosphors still limits the improvement of white LED performance. The wavelength of 380-450nm is short-wavelength, high-energy light. Different wavelengths of blue light have different harmful effects on the human eye. Among them, high-energy blue light in the range of 400nm to 460nm can damage the human eye and may even cause visual fatigue, myopia, cataracts, macular degeneration, glaucoma and other damages. In particular, blue light between 435nm and 440nm has the greatest harmful effect on the eyes. This effect gradually decreases as the wavelength increases or decreases.

[0003] A common method is to encapsulate several PN junctions coated with different phosphors onto a substrate to obtain LED chips. By adjusting the light intensity ratio of red, green, and blue LEDs, different colors of light can be obtained. The substrate can be any material, such as plastic or ceramic. The structure of LEDs is the same: an N+ layer, an N-type layer, a light-emitting layer, a P-type layer, a P+ layer, an N-type metal contact, and a P-type metal contact electrode on a single-crystal substrate. The only difference is the top phosphor (blue, yellow / green, red). The short-wavelength light emitted by the recombination of the LED bands excites the phosphor to achieve a secondary light conversion, transforming it into blue light (warm blue light), 530nm green light, and 620nm red light suitable for the human eye. These are called blue LEDs, green LEDs, and red LEDs, but their actual luminous efficacy is generally low. For example, the actual luminous efficacy of white LEDs is less than 60 lumens per watt.

[0004] According to current technology, PN junctions used for lighting or displays are made from epitaxial wafers deposited on a single-crystal sapphire substrate. The sapphire used is a single crystal, and the diameter is generally 2 inches, 4 inches, or 6 inches. Some light-emitting semiconductor PN junctions are also deposited on non-single-crystal substrates. The resulting devices can also emit light, but the luminous efficiency is not as good as that of thin-film LEDs deposited on a single-crystal sapphire substrate.

[0005] In existing technologies, the fabrication of light-emitting thin film structures faces two major challenges: Firstly, when fabricating on traditional single-crystal substrates (such as sapphire), it is difficult to achieve large-area, high-efficiency mass production due to limitations in substrate size and cost. Secondly, in order to overcome the size limitations and switch to non-single-crystal substrates, the contradiction of reduced epitaxial quality leading to significant deterioration of luminescent performance is faced.

[0006] Current mainstream white LEDs rely on narrow-spectrum blue PN junctions fabricated on monocrystalline sapphire substrates, which offer high luminous efficiency. However, the small substrate size and high cost limit the expansion of device area and production capacity. Furthermore, due to the narrow spectrum emitted, phosphor conversion is required to achieve white light, which involves energy loss. Excessive blue light content may also pose a risk of blue light hazard. To address the size bottleneck, the industry has attempted to deposit luminescent films on non-monocrystalline substrates (such as glass, polycrystalline, or flexible substrates). While this significantly increases the deposition area and reduces production costs, lattice mismatch and surface defects between the substrate and the film result in poor epitaxial crystal quality. This directly manifests as reduced luminous efficiency and an increase in defect states. Insufficient synergistic optimization between the substrate and device structure further amplifies the loss of photoelectric performance, ultimately limiting the overall improvement of white LEDs in luminous efficiency, reliability, and spectral quality.

[0007] Based on this, the present invention designs a light-emitting thin film structure on a non-single-crystal substrate to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to solve the dilemma of existing technologies where "single-crystal substrates have excellent performance but limited area" and "non-single-crystal substrates have large area but poor performance". The fundamental problem lies in how to balance epitaxial quality and large-scale production, while optimizing spectral design and substrate-device synergy to achieve efficient, safe and low-cost white light illumination. Therefore, this invention proposes a light-emitting thin film structure on a non-single-crystal substrate.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A light-emitting thin film structure on a non-single-crystal substrate, comprising, from bottom to top: Non-single-crystal substrates: such as silicon, sapphire, glass, metal, or flexible polymer substrates; Defect filtering superlattice structure: composed of n periodically stacked "two-dimensional material interface layer / semiconductor buffer layer" units (n≥1); The i-th interface layer (i=1,2,...,n) is directly grown on the underlying layer. The material is selected from one or more of graphene, molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and boron nitride (BN), and its thickness is [missing information]. The atomic arrangement is mostly a two-dimensional lattice, but there are a small number of amorphous or defective regions, especially in the first interface layer; The i-th buffer layer (i=1,2,...,n) is grown on the corresponding i-th interface layer. The material is selected from one or more of aluminum nitride (AlN) and aluminum gallium nitride (AlGaN), and its thickness is... This buffer layer inherits and partially filters the defects of the underlying interface layer, but its own defect density decreases significantly with the increase of the number of cycles i. In this embodiment, a first interface layer forms a preliminary ordered two-dimensional template on an amorphous substrate, and a first buffer layer is epitaxially grown on it, where some defects are restricted or terminated. Subsequently, a second interface layer is formed on the first buffer layer with improved quality, and its own defects are much fewer than those of the first interface layer. This process is repeated cycle by cycle, and the crystal quality of each buffer layer is better than that of the previous layer, thereby achieving an exponential decrease in defect density and a gradual relaxation of stress. LED functional layer structure: grown on the nth buffer layer; Including an N-type semiconductor layer (such as Si-doped GaN), with a thickness of ; The light-emitting layer (such as an InGaN multi-quantum-well or uniform layer) has a thickness of ; The thickness of the P-type semiconductor layer (such as Mg / Zn-doped GaN) is... ; Optional highly doped P+ type contact layer; Electrodes: N-type metal electrode and P-type metal electrode, which form ohmic contacts with the N-type layer and P-type layer (or P+ type layer), respectively.

[0010] As a further description of the above technical solution: The growth method of the two-dimensional material interface layer is low-pressure chemical vapor deposition (LPCVD), in which graphene is grown on a metal catalytic substrate by introducing a methane (CH4) precursor at around 1000°C, or by using a chalcogenide precursor to grow a transition metal dichalcogenide compound.

[0011] As a further description of the above technical solution: The semiconductor buffer layer is grown by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0012] As a further description of the above technical solution: The light-emitting layer is designed as needed as follows: Monochromatic emission is achieved by using a single-component InGaN layer and controlling the bandgap by adjusting the In composition to achieve blue and green monochromatic light emission (spectral width of about 100nm), or by doping with specific rare earth impurities to emit light through impurity energy levels. Multicolor / broad spectrum luminescence involves introducing luminescent media (such as regions with different In compositions or multiple dopants) that can emit different center wavelengths (such as λ1, λ2, λ3) into the luminescent layer. After spectral synthesis, broad spectrum white light suitable for illumination is produced.

[0013] As a further description of the above technical solution: To improve luminous efficiency, an electron blocking layer (such as AlGaN) can be inserted between the P-type layer and the luminescent layer, or a transparent substrate and optimized electrode pattern can be used to reduce light absorption and loss.

[0014] This invention also provides a method for preparing the above-mentioned light-emitting thin film structure, the key steps of which include: S1: A first two-dimensional material interface layer is deposited on a non-single-crystal substrate by LPCVD. S2: Deposit a first semiconductor buffer layer (such as AlN) on the first interface layer using the MOCVD / MBE method. S3: Repeat the alternating deposition process of S1-S2 for n cycles to form a superlattice structure; S4: On the superlattice structure, an N-type layer, a light-emitting layer, a P-type layer and a P+ type layer are epitaxially grown sequentially. S5: Using a mask process, N-type electrodes and P-type electrodes are directly deposited sequentially without photolithography etching to remove some functional layers, thus completing the fabrication of LED devices or arrays.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. In this invention, a periodic superlattice structure of “interface layer-buffer layer” is proposed, wherein the number of periods n≥2. By optimizing the material selection and stacking method, this structure can significantly reduce the lattice defects of the outermost buffer layer. When depositing a thin film for the PN junction of a light-emitting diode on this basis, the lattice defects in the thin film can be greatly reduced, and the crystal quality can be effectively improved.

[0016] 2. In this invention, the traditional phosphor light emission method is abandoned, and instead a light-emitting thin film layer is introduced to construct a double-injection PN junction light-emitting device. This method can improve the photoelectric performance of the device and increase the luminous efficiency.

[0017] 3. In this invention, by embedding a multilayer thin film structure with a light-emitting layer in a PN junction, multiple center wavelengths of light can be emitted in a single light-emitting layer through controllable doping. Based on the principle of spectral synthesis, these different wavelengths of light can be fused to form broadband white light, thus obtaining a broadband output suitable for lighting devices without relying on phosphors.

[0018] 4. In this invention, after growing the N⁺ layer, the N-type contact electrode is directly fabricated using a mask process, avoiding complex photolithography steps and significantly reducing process costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an existing light-emitting diode fabricated using a single-crystal sapphire substrate. Figure 2 This is a schematic diagram of a phosphorless light-emitting diode structure based on the light-emitting thin film structure on a non-single-crystal substrate proposed in this invention. Figure 3 This is a schematic diagram of a monochromatic light thin film structure deposited on a non-single-crystal substrate, as proposed in this invention. Figure 4 This is a schematic diagram of a multicolor light thin film structure deposited on a non-single-crystal substrate, which is a light-emitting thin film structure proposed in this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: Fabrication of Blue LEDs on Silicon Substrates Provides a surface-clean (100) silicon substrate; On a silicon substrate, a monolayer of graphene was grown at 1000°C using LPCVD with methane as the carbon source as the first interface layer. -0.34nm); An AlN buffer layer was grown on graphene using the MOCVD method, with a thickness of [missing information]. =50nm; Repeat the above steps to grow a total of 5 cycles (n=5) of “graphene / AlN” superlattice. The thickness of the interface layer and buffer layer in each cycle can remain unchanged or be finely adjusted. On the AlN buffer layer of the 5th period, the growth continues with a Si-doped n-type GaN layer (=2μm) and an In0.2Ga0.8N multi-quantum-well light-emitting layer. =100nm), Mg-doped p-type GaN layer (=200nm) and highly doped p+ type GaN contact layer; Using a mask, Ti / Al / Ni / Au was deposited as an N-type electrode and Ni / Au was deposited as a P-type electrode, respectively. Tests show that, compared to the traditional structure of growing AlN buffer layers directly on silicon, the dislocation density of the LEDs prepared by this invention is reduced by more than two orders of magnitude, and the luminous intensity is increased by about 5 times.

[0022] Example 2: Fabrication of a broadband white LED The structure is similar to that of Example 1, except that: The light-emitting layer is designed as a composite active region containing In0.15Ga0.85N (emission peak -450nm blue light) and In0.3Ga0.7N (emission peak -550nm yellow-green light), or doped with impurities that can emit red light. Under current drive, multispectral recombination produces white light without the need for phosphors.

[0023] Working principle and usage: Deposition of interface layer and buffer layer: A first interface layer is deposited on the surface of a non-single-crystal substrate. The material of the first interface layer is selected from two-dimensional materials, including graphene, molybdenum disulfide (MoS2), transition metal dichalcogenides (such as WS2, MoSe2), and boron nitride (BN). The first interface layer is directly deposited on the non-single-crystal substrate, mostly forming a two-dimensional lattice, with some amorphous defects, and a thickness of ; A first buffer layer with a thickness of is deposited on the first interface layer. The buffer layer material is selected from aluminum nitride or aluminum gallium nitride. At this time, the first buffer layer contains some defects. Deposited thickness on the first buffer layer The second interface layer is also made of two-dimensional materials, such as graphene and molybdenum disulfide. The defects in the second interface layer are far fewer than those in the first interface layer. The thickness of the deposition on the second interface layer is The second buffer layer, after deposition, has far fewer defects than the first buffer layer; Repeat the above steps to continue depositing more interface layers and buffer layers until the nth interface layer and the nth buffer layer are completed, forming a superlattice structure with n alternating periods of interface layer-buffer layer combination. This superlattice is composed of alternating growth of different semiconductor materials, and its band structure is significantly different from that of conventional semiconductors. It continuously reduces the stress between the amorphous substrate and the light-emitting layer, improves the crystal structure of the thin film, and gradually reduces the defects in the film layer and continuously improves the crystal structure.

[0024] Fabrication of light-emitting devices: The deposition thickness after the superlattice is The N-type semiconductor layer is made of silicon-doped GaN (Si:GaN). Deposition thickness is The light-emitting layer is made of InGaN. Deposition thickness is The P-type semiconductor layer is made of magnesium / zinc doped GaN (Mg / Zn:GaN). Deposition thickness is p+ type semiconductor layer; A mask with an LED array pattern for different purposes, such as lighting or small display screens, is placed on the sample surface. After deposition, there is no need to remove part of the thin film layer using photolithography and etching methods. A second electrode mask is placed to deposit N-type metal contacts, and a third electrode mask is placed to deposit P-type metal contacts, thus completing the fabrication of the light-emitting device and its array device on a non-single-crystal substrate.

[0025] Two-dimensional crystals are grown on an amorphous substrate, i.e., the first interface layer: Two-dimensional crystal properties: Graphene and MoS2 are two-dimensional crystals with atomic-level thickness, consisting of planar crystal materials composed of a single atomic layer or several atomic layers. Graphene is composed of a single layer of carbon atoms, which are bonded by sp² hybridization to form a single-layer hexagonal honeycomb lattice. It has multiple properties such as high strength (tensile strength is 200 times that of steel), almost complete transparency, high electrical conductivity (electron mobility 200,000 cm² / (V·s), one of the materials with the lowest electrical resistance), and high thermal conductivity (5300 W / (m·K), exceeding that of carbon nanotubes and diamond). It is used in flexible displays and high-speed transistors. Single-layer MoS2 has a typical hexagonal symmetrical layered structure, with a molybdenum atom layer sandwiched between two sulfur atom layers to form an S-Mo-S triatomic layer structure. The Mo atom is located at the center of the hexagon, and the surrounding S atoms form a flat triangular prism, so that the Mo atom is equidistantly surrounded. It has a direct band gap (about 1.8 eV) and is used in flexible transistors and photodetectors. Two-dimensional crystal growth is the phenomenon of depositing an ordered (1×1) two-dimensional crystal structure capping layer on a substrate surface with low coverage. The substrate guides the epitaxial film growth through its two-dimensional crystal structure, orientation, and lattice parameters. This process is also known as quasi-isomorphic growth. Low-pressure CVD deposition is used. Under low-pressure conditions, argon gas is introduced into a quartz tube, and the surface of a 300 nm thick Ni film (or copper foil) is heated to 1000 °C. A CH4 precursor is then introduced, and the CH4 decomposes on the Ni surface. After a period of growth, a large-area few-layer graphene film is deposited on the metal surface. This film grows layer by layer, including monolayer graphene (a type of graphene composed of a single layer with a benzene ring structure (i.e., hexagonal)). Graphene is a two-dimensional carbon material composed of periodically and tightly packed carbon atoms (honeycomb structure), bilayer graphene, and few-layer graphene (a two-dimensional carbon material composed of 3-10 layers of periodically and tightly packed carbon atoms in benzene ring structure stacked in different stacking methods (including ABC stacking and ABA stacking)). The electronic structure of graphene changes accordingly through the induction of gas molecule adsorption, changing its carrier concentration, or forming multilayer AB stacked graphene seeds on the surface of copper foil, and laterally epitaxially growing multilayer graphene, finally obtaining a large-area AB stacked graphene film with controllable layer thickness. Compared with atmospheric pressure CVD, the low-pressure environment reduces gas phase side reactions and improves film uniformity.

[0026] Growth of a buffer layer on a two-dimensional crystal: The structural characteristics of aluminum nitride (AlN) are used as a buffer layer when growing semiconductors such as GaN using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). This significantly improves the epitaxial quality of semiconductors such as GaN. The AlN buffer layer has two main functions: first, it provides nucleation centers with the same orientation as the substrate (two-dimensional crystal), reducing the interface free energy and accelerating horizontal growth; second, the top surface of AlN's crystal structure is a regular hexagon, similar to the benzene ring of graphene, which makes it easy to nucleate and crystallize on two-dimensional crystals. Gallium nitride (GaN) has a distinctive structural feature, employing GaN as a buffer layer. GaN exists in a hexagonal wurtzite 2H structure, which consists of a lattice formed by gallium and nitrogen atoms. Each gallium atom is surrounded by four nitrogen atoms, and each nitrogen atom is also surrounded by four gallium atoms. This structure is called the zincblende structure or helical alkene structure. In the structure of gallium nitride, nitrogen atoms form covalent bonds with the surrounding gallium atoms, giving the crystal a stable structure. At the same time, nitrogen atoms accept electrons from gallium atoms, forming positive and negative ions in the gallium nitride crystal. This combination of covalent and ionic bonds gives gallium nitride excellent electron mobility and optical properties.

[0027] Periodic growth of the interface layer-buffer layer: Lattice matching technology is a key technology for the epitaxial growth of heterostructures in the field of electronics. Its core lies in the control of the uniformity of the periodic arrangement of atoms at the interface of heterostructure materials. When the difference between the lattice constants of the substrate and the epitaxial layer is less than 0.1%, dislocation-free epitaxial growth can be achieved. By controlling the uniformity of the lattice constants of different material layers, interface defects can be reduced and device performance can be improved. The function and fabrication of the buffer layer: The AlN buffer layer is a key structural layer used to alleviate interfacial stress or optimize performance. This layer achieves its function by reducing lattice mismatch, regulating band structure, and suppressing atomic diffusion. It reduces heterogeneous lattice mismatch and prevents damage to the absorption layer. The buffer layer fabrication technology adopts physical vapor deposition. A typical process, such as the AlGaN buffer layer, increases the lateral breakdown voltage to 10kV. The design adopts the periodic growth of the interface layer-buffer layer, namely the AlN / GaN / AlN composite interface insertion layer to shield the disordered scattering of the alloy substrate. The stress control technology, including the periodic growth of the interface layer-buffer layer, namely the AlN / AlGaN / GaN superlattice and multi-step buffer layer, is used to alleviate the internal stress and strain of semiconductors such as GaN substrates. This provides high-quality GaN substrate materials for the fabrication of white LEDs for high-brightness, high-power, and long-life semiconductor lighting, and provides a growth method and array chip fabrication basis for the fabrication of nitride homoepitaxial LEDs.

[0028] The fabrication process of light-emitting devices includes: The design of the light-emitting layer is similar to that of phosphorless blue, single-color, and multi-color LEDs, except that the material of the light-emitting layer is different. The light-emitting layer has a thickness of [missing information]. A single semiconductor layer with a perfect crystal structure, few defects, and a single composition emits light close to monochromatic light when biased, with a spectral width of approximately 100 nm. Blue LEDs are fabricated by adjusting the bandgap of the semiconductor material in the emitting layer. Monochromatic light is obtained by doping the emitting layer with luminescent impurities. To obtain a broad-spectrum light-emitting device, the central frequency of the multicolor emitting layer includes a dual spectrum of wavelengths λ1 and λ2. By synthesizing these two λ1 and λ2 spectra, a broader spectrum of light can be obtained. Furthermore, a luminescent medium that can emit a central wavelength of λ3 can be added to the emitting layer to further obtain a broader spectrum, suitable for lighting applications. Carrier injection design was employed, and N+ and N-type semiconductor layers were fabricated to provide a large number of electrons for the light-emitting layer. Their thicknesses were respectively... , And TLM; a P-type semiconductor layer and a P+ type semiconductor layer are prepared to improve the injection of a large number of holes into the light-emitting layer. In addition, in order to ensure smooth carrier injection, two types of carrier injection ohmic connections, P-type metal contacts and N-type metal contacts, are prepared. To improve luminous efficiency, it is essential to select appropriate semiconductor materials. Wide-bandgap semiconductors such as gallium nitride (GaN) or indium gallium nitride (InGaN) can emit short-wavelength light with high photon energy and relatively high luminous efficiency. The luminous efficiency can be optimized by adjusting the In ratio. x Ga1₋ x The N-band structure and electron mobility allow for adjustment of the emission wavelength. Doping with luminescent rare-earth impurities induces impurity energy levels to emit the desired monochromatic light. Optimizing the impurity doping ratio increases carrier density and improves electron-hole recombination rate, thereby enhancing luminescence efficiency. In terms of structural design, an electron blocking layer can be inserted between the P-type layer and the luminescent layer to improve electron recombination efficiency, or a transparent substrate can be used to remove the absorption region of the traditional substrate, thus improving quantum efficiency. Optimizing the metal electrode structure increases side emission to reduce losses.

[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A light-emitting thin film structure on a non-single-crystal substrate, characterized in that, include: Non-single-crystal substrate; A superlattice structure is formed on the surface of the non-single crystal substrate, the superlattice structure being composed of n periodically stacked interface layers and buffer layers; Where n is an integer greater than or equal to 2; Each cycle consists of an interface layer and a buffer layer stacked sequentially. The interface layer is a two-dimensional material layer, and the buffer layer is a group III nitride layer; An N-type semiconductor layer, a light-emitting layer, a P-type semiconductor layer, and a P+ type semiconductor layer are sequentially stacked on the superlattice structure.

2. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The two-dimensional material of the two-dimensional material layer is selected from at least one of graphene, molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), or boron nitride (BN).

3. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The material of the group III nitride layer is aluminum nitride (AlN) or aluminum gallium nitride (AlGaN).

4. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The crystal defect density of the (i+1)th interface layer in the superlattice structure is lower than that of the ith interface layer, and the crystal defect density of the (i+1)th buffer layer is lower than that of the ith buffer layer, where i is an integer from 1 to n-1.

5. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The N-type semiconductor layer is a silicon-doped gallium nitride (Si:GaN) layer, and the P-type semiconductor layer is a magnesium-doped or zinc-doped gallium nitride (Mg / Zn:GaN) layer.

6. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The material of the light-emitting layer is indium gallium nitride (InGaN), and its composition and thickness are configured to emit a spectrum with a center wavelength in the blue light band when energized, with a full width at half maximum (FWHM) of approximately 100 nanometers.

7. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The light-emitting layer is doped with rare earth impurities, which are configured to form impurity energy levels in the light-emitting layer so that the light-emitting thin film structure emits monochromatic light.

8. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The light-emitting layer includes a light-emitting medium capable of emitting at least two different center wavelengths, so that the light-emitting thin film structure emits broadband composite light.

9. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, An electron blocking layer is also disposed between the P-type semiconductor layer and the light-emitting layer.

10. The light-emitting thin film structure on a non-single-crystal substrate according to claim 1, characterized in that, The structure further includes an N-type metal ohmic contact electrode disposed on the N-type semiconductor layer and a P-type metal ohmic contact electrode disposed on the P+ type semiconductor layer.

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