A deep ultraviolet LED with improved light extraction efficiency

Abstract

This patent discloses a deep ultraviolet LED (DUV) with improved light extraction efficiency. The patent comprises a sequentially stacked anti-reflection layer, a sapphire substrate, an N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer. A nucleation pattern is etched on the surface of the sapphire substrate away from the N-type semiconductor layer, and an anti-reflection layer is deposited. A laser annealing process is then used to melt the anti-reflection layer, which then self-assembles based on the nucleation pattern to form a number of hemispherical or hemi-ellipsoidal aggregates. This invention significantly improves the back-light extraction efficiency of deep ultraviolet LEDs by self-assembling hemispherical shapes from thin film materials, eliminating the need for complex graphical processes such as nanoimprinting, photolithography, and plasma etching.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and in particular to a deep ultraviolet LED with improved light extraction efficiency. Background Art

[0002] Currently, high-power, high-brightness blue LEDs have become a key development focus in the LED industry, with widespread use in indoor and outdoor lighting. Blue LEDs utilize a GaN system, which allows for substrate lift-off. However, UV LEDs, due to their AlN structure, are not suitable for substrate lift-off. Consequently, most products on the market utilize a flip-chip structure. In this approach, light emitted from the active area is extracted through a transparent sapphire substrate.

[0003] Semiconductor deep ultraviolet (DUV) light sources have significant application value in lighting, sterilization, medical treatment, printing, biochemical testing, high-density information storage, and secure communications. Deep UV LEDs using AlGaN as their luminescent material have an emission wavelength covering the 230-365nm UV band, making them ideal for developing DUV LED devices in this wavelength range and offering unmatched advantages over other traditional UV light sources. Currently, the biggest bottleneck in the development of DUV LEDs is photoelectric conversion efficiency. Commercial blue LEDs have a photoelectric conversion efficiency of approximately 70%, while commercial UV LEDs have an efficiency of less than 4%. Regarding internal quantum efficiency, blue LEDs achieve over 95%, while UV LEDs can reach 70%. Therefore, the most crucial factor determining the performance of UV LEDs is light extraction efficiency—that is, how to extract light from the material—which has become a key research focus in the industry.

[0004] For sapphire, the refractive index is 2.5 in the ultraviolet band. According to the refractive index formula, when light passes from a material with a refractive index of n1 to a material with a refractive index of n2, the light is refracted, and the refracted light satisfies n1Sin(θ1)=n2Sin(θ2). When n1>n2, that is, from a denser medium to a less dense medium, and when θ1 is greater than the following angle, Sin(θ1)=n2 / n1, the light is totally reflected, and this angle is called the total reflection angle. For ultraviolet light, when light passes from sapphire to air, the total reflection angle is 24°, that is, when the angle of incidence is greater than 24°, the light will be totally reflected. Assuming that the light emitted from the active area is isotropic, theoretically only 8.6% of the light falls within this angle of incidence. As the chip size increases, the proportion of light that can escape decreases. For a 20 mil x 20 mil chip, only 44.6% of the light incident on the front surface escapes. When the chip area is increased to 45 mil x 45 mil, only 20% of the light incident on the front surface escapes. As the chip area increases, the proportion of light energy escaping from the front surface decreases. Therefore, larger chips are more urgently in need of increased light extraction, which necessitates the development of a new deep ultraviolet LED design approach to address the shortcomings of existing technologies. Summary of the Invention

[0005] The object of the present invention is to provide a deep ultraviolet LED with improved light extraction efficiency, so as to solve the problem of poor light extraction effect of deep ultraviolet LEDs in the prior art.

[0006] In order to solve the above technical problems, the present invention provides a deep ultraviolet LED with improved light extraction efficiency, comprising an anti-reflection layer, a sapphire substrate, an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer stacked in sequence; a nucleation area pattern is provided on the surface of the sapphire substrate away from the N-type semiconductor layer, the nucleation area pattern is composed of an array of several cross-shaped grooves, and the anti-reflection layer is composed of an array of several hemispherical or semi-ellipsoidal condensates, and each condensate is filled in a corresponding cross-shaped groove.

[0007] In this process, a nucleation area pattern is etched on the surface of the sapphire substrate away from the N-type semiconductor layer, an anti-reflection layer is deposited, and then a laser annealing process is used to melt the anti-reflection layer. The layer then self-assembles to form a number of agglomerates based on the nucleation area pattern. The ratio of the sum of the projected areas of the agglomerates in the anti-reflection layer to the area of the sapphire substrate is greater than 20%.

[0008] Preferably, the aggregate is any one of gallium oxide, silicon oxide, and boron oxide.

[0009] Preferably, the plurality of cross-shaped grooves in the nucleation region pattern are arranged in a triangular periodic array, and the center spacing between adjacent cross-shaped grooves is 200-500 μm.

[0010] Preferably, each cross-shaped groove in the nucleation area pattern consists of a first groove portion and a second groove portion, and the first groove portion and the second groove portion intersect vertically; the length of the first groove portion and the second groove portion is 200-500 μm.

[0011] Specifically, when the length of the first groove portion is equal to the length of the second groove portion, the aggregate is a hemispherical structure.

[0012] Specifically, when the length of the first groove portion is greater than the length of the second groove portion, the aggregate is a semi-ellipsoidal structure.

[0013] Preferably, the band gap energy of the anti-reflection layer is greater than the photon energy emitted by the diode; the refractive index of the anti-reflection layer is n1, and the refractive index of the sapphire substrate is n2, satisfying n1≥0.8*n2.

[0014] In addition, the deep ultraviolet LED with improved light extraction efficiency also includes a first reflective layer, a second reflective layer, an N electrode and a P electrode; the first reflective layer and the N electrode are stacked in sequence on the step structure of the N-type semiconductor layer, and the second reflective layer and the P electrode are stacked in sequence on the P-type semiconductor layer.

[0015] Preferably, the N-type semiconductor layer is N-type Al xGa 1-x N, the light-emitting layer is a single-layer or multi-layer quantum well structure, and the quantum well is Al z Ga 1-z N, and satisfy x ≥ z.

[0016] The beneficial effects of the present invention are as follows: different from the existing technical features, the present invention provides a deep ultraviolet LED with improved light extraction efficiency, by etching a nucleation area pattern on the surface of the sapphire substrate away from the N-type semiconductor layer, self-assembling to form an anti-reflection layer with a plurality of condensates, and utilizing the refraction of hemispherical or hemispherical condensates to allow light falling into the condensates to escape from the light-transmitting layer to the air, thereby significantly improving the light extraction efficiency of the deep ultraviolet LED and making the preparation process more simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 2 is a schematic structural diagram of an embodiment of a deep ultraviolet LED for improving light extraction efficiency according to the present invention;

[0018] Figure 2 is a schematic diagram of the graphical structure of the sapphire substrate in Example 1 of the present invention;

[0019] Figure 3 is a schematic diagram of the graphical structure of the sapphire substrate in Example 2 of the present invention;

[0020] In the figure: 1-anti-reflection layer, 11-condensate, 2-sapphire substrate, 3-N-type semiconductor layer, 4-light-emitting layer, 5-P-type semiconductor layer, 6-first reflection layer, 7-second reflection layer, 8-N electrode, 9-P electrode. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] See also Figure 1 The present invention provides a deep ultraviolet LED with improved light extraction efficiency, comprising an anti-reflection layer 1, a sapphire substrate 2, an N-type semiconductor layer 3, a light-emitting layer 4, and a P-type semiconductor layer 5 stacked in sequence; a nucleation area pattern 21 is provided on the surface of the sapphire substrate 2 away from the N-type semiconductor layer 3, and the nucleation area pattern 21 is composed of a plurality of cross-shaped groove arrays; the anti-reflection layer is composed of a plurality of hemispherical or hemispherical condensates 11 arranged in an array, and each condensate 11 is filled in a corresponding cross-shaped groove.

[0023] In this embodiment, a nucleation area pattern is etched on the surface of the sapphire substrate away from the N-type semiconductor layer, and an anti-reflection layer is deposited. The anti-reflection layer film can be deposited by evaporation or sputtering. Then, a laser annealing process is used to melt the anti-reflection layer, and self-assemble to form a number of agglomerates based on the nucleation area pattern. That is, the nucleation area pattern on the sapphire substrate can, on the one hand, play an anti-reflection role, and on the other hand, facilitate the self-assembly formation of agglomerates, thereby eliminating the need for complex graphical process flows such as nanoimprinting, photolithography, and plasma etching, making the preparation process simpler.

[0024] Specifically, the ratio of the sum of the projected areas of the aggregates in the antireflection layer to the area of the sapphire substrate is greater than 20%. This is because if the aggregate coverage is too low, it is difficult to achieve a good antireflection effect. The size of the first and second grooves determines the size of the aggregates, while the distance between the groove centers determines the density of the aggregates. Specifically, the aggregates are any high-transmittance thin film material, including gallium oxide, silicon oxide, or boron oxide.

[0025] Specifically, the nucleation zone pattern comprises a plurality of cross-shaped grooves arranged in a triangular periodic array, with the center spacing between adjacent cross-shaped grooves being 200 to 500 μm. Each cross-shaped groove in the nucleation zone pattern comprises a first groove portion and a second groove portion, and the first groove portion and the second groove portion intersect perpendicularly. The length of the first groove portion and the second groove portion is 200 to 500 μm. The length relationship between the first groove portion and the second groove portion has the following two cases:

[0026] A) When the length of the first groove portion is equal to the length of the second groove portion, the aggregate is a hemispherical structure.

[0027] B) When the length of the first groove portion is greater than the length of the second groove portion, the aggregate is a semi-ellipsoidal structure.

[0028] Specifically, the band gap energy of the antireflection layer is greater than the photon energy emitted by the diode. The refractive index of the antireflection layer is n1, and the refractive index of the sapphire substrate is n2, satisfying n1≥0.8*n2.

[0029] In addition, the deep ultraviolet LED with improved light extraction efficiency also includes a first reflective layer 6, a second reflective layer 7, an N electrode 8 and a P electrode 9; the first reflective layer 6 and the N electrode 8 are sequentially stacked on the step structure of the N-type semiconductor layer 3, and the second reflective layer 7 and the P electrode 9 are sequentially stacked on the P-type semiconductor layer 5; the first reflective layer and the second reflective layer are used to reflect ultraviolet light so that more ultraviolet light can be emitted from the side of the anti-reflection layer. The N-type semiconductor layer is an N-type Al x Ga 1-x N, the light-emitting layer is a single-layer or multi-layer quantum well structure, and the quantum well is Al z Ga 1-z N, and satisfy x ≥ z.

[0030] The preparation effect of the AlN thin film with the function of improving luminous efficiency in the present invention is characterized and analyzed through specific examples and comparative examples.

[0031] Example 1

[0032] The specific preparation steps in this embodiment are as follows:

[0033] (1) An N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer are grown sequentially on a sapphire substrate using the MOCVD method.

[0034] (2) Etching a nucleation pattern on the surface of the sapphire substrate away from the N-type semiconductor layer, such as Figure 2 As shown, each cross-shaped groove 210 in the nucleation area pattern consists of a first groove portion 211 and a second groove portion 212 . The lengths of the first groove portion 211 and the second groove portion 212 are both 250 μm, and the center distance between adjacent cross-shaped grooves is 300 μm.

[0035] (3) Etching a nucleation pattern on the surface of the sapphire substrate away from the N-type semiconductor layer and depositing an anti-reflection layer; then using a laser annealing process to melt the anti-reflection layer, and self-assemble based on the nucleation pattern to form a number of hemispherical agglomerates.

[0036] (4) Etching the P-type semiconductor layer and the light-emitting layer until reaching the N-type semiconductor layer, depositing the first reflective layer and the N-electrode in sequence at the step structure of the N-type semiconductor layer, and depositing the second reflective layer and the P-electrode in sequence on the P-type semiconductor layer to obtain a deep ultraviolet LED sample.

[0037] Example 2

[0038] The specific preparation steps in this embodiment are as follows:

[0039] (1) An N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer are grown sequentially on a sapphire substrate using the MOCVD method.

[0040] (2) Etching a nucleation pattern on the surface of the sapphire substrate away from the N-type semiconductor layer, such as Figure 3 As shown, each cross-shaped groove 220 in the nucleation zone pattern consists of a first groove portion 221 and a second groove portion 222, the length of the first groove portion 221 is 150 μm, the length of the second groove portion 222 is 300 μm, and the center distance between adjacent cross-shaped grooves is 500 μm.

[0041] (3) Etching a nucleation pattern on the surface of the sapphire substrate away from the N-type semiconductor layer and depositing an anti-reflection layer; then using a laser annealing process to melt the anti-reflection layer, and self-assemble based on the nucleation pattern to form a number of semi-ellipsoidal aggregates.

[0042] (4) Etching the P-type semiconductor layer and the light-emitting layer until reaching the N-type semiconductor layer, depositing the first reflective layer and the N-electrode in sequence at the step structure of the N-type semiconductor layer, and depositing the second reflective layer and the P-electrode in sequence on the P-type semiconductor layer to obtain a deep ultraviolet LED sample.

[0043] Comparative Example 1

[0044] This comparative example is based on the preparation steps of Example 1, except for step (3) of Example 1, that is, only the nucleation area pattern is etched on the surface of the sapphire substrate away from the N-type semiconductor layer, and no anti-reflection layer structure is provided. The other steps are consistent with Example 1.

[0045] Comparative Example 2

[0046] This comparative example is based on the preparation steps of Example 1, except for steps (2) and (3) of Example 1, that is, the surface of the sapphire substrate away from the N-type semiconductor layer is not etched, and the anti-reflection layer structure is not provided. The other steps are consistent with Example 1.

[0047] The light output power of the samples prepared in Examples 1 to 2 and Comparative Examples 1 to 2 was tested, and the results are shown in Table 1. As can be seen from the data in Table 1, compared with Comparative Examples 1 and 2, Examples 1 to 2 have a significant effect on improving the light output power, proving that the design method of using a nucleation area pattern combined with a coacervate structure of a transmittance-enhancing layer can achieve a better light output effect than the existing LED design method. In Example 1, due to the high density of the coacervate, the light output is more significantly improved. Comparative Example 1 only etches the groove array, which has an impact on light scattering and has little light output effect.

[0048] Table 1

[0049] Nucleation zone pattern Agglomerates Optical power / mW Example 1 Equal length cross groove array Hemispherical 36 Example 2 Non-uniform length cross groove array semi-ellipsoidal 30.5 Comparative Example 1 Equal length cross groove array none 21.8 Comparative Example 2 none none 21

[0050] Different from the existing technical features, the present invention provides a deep ultraviolet LED with improved light extraction efficiency. By etching a nucleation area pattern on the surface of the sapphire substrate away from the N-type semiconductor layer, a transmittance-enhancing layer with several condensates is self-assembled. The refraction of hemispherical or hemispherical condensates is utilized to allow light falling into the condensates to escape from the light-transmitting layer into the air, thereby significantly improving the light extraction efficiency of the deep ultraviolet LED and making the preparation process more simple.

[0051] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0052] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A deep ultraviolet LED with improved light extraction efficiency, characterized in that: It includes an anti-reflection layer, a sapphire substrate, an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer stacked in sequence; The sapphire substrate is provided with a nucleation area pattern on a side away from the N-type semiconductor layer. The nucleation area pattern is formed by an array of a plurality of cross-shaped grooves. The anti-reflection layer is formed by an array of a plurality of hemispherical or hemispherical condensates. Each condensate is filled in a corresponding cross-shaped groove. A nucleation pattern is etched on the surface of the sapphire substrate away from the N-type semiconductor layer, an anti-reflection layer is deposited, and then a laser annealing process is used to melt the anti-reflection layer. The layer is self-assembled based on the nucleation pattern to form a plurality of aggregates; the ratio of the sum of the projected areas of the plurality of aggregates in the anti-reflection layer to the area of the sapphire substrate is greater than 20%; The cross-shaped grooves in the nucleation area pattern are arranged in a triangular periodic array, and the center spacing between adjacent cross-shaped grooves is 200-500 μm; Each cross-shaped groove in the nucleation area pattern consists of a first groove portion and a second groove portion, and the first groove portion and the second groove portion intersect vertically; the length of the first groove portion and the second groove portion is 200-500 μm.

2. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: The condensate is made of any one of gallium oxide, silicon oxide and boron oxide.

3. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: When the length of the first groove portion is equal to the length of the second groove portion, the aggregate is a hemispherical structure.

4. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: When the length of the first groove portion is greater than the length of the second groove portion, the aggregate is a semi-ellipsoidal structure.

5. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: The band gap energy of the antireflection layer is greater than the photon energy of the diode; The refractive index of the anti-reflection layer is n1, and the refractive index of the sapphire substrate is n2, satisfying n1≥0.8*n2.

6. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: The deep ultraviolet LED with improved light extraction efficiency further includes a first reflective layer, a second reflective layer, an N electrode and a P electrode; The first reflective layer and the N-electrode are sequentially stacked on the stepped structure of the N-type semiconductor layer, and the second reflective layer and the P-electrode are sequentially stacked on the P-type semiconductor layer.

7. The deep ultraviolet LED with improved light extraction efficiency according to claim 1, characterized in that: The N-type semiconductor layer is N-type Al x Ga 1-x N, the light-emitting layer is a single-layer or multi-layer quantum well structure, the quantum well is Al z Ga 1-z N, and satisfy x ≥ z.

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