Semiconductor light emitting epitaxial structure with enhanced light extraction efficiency and method of fabricating the same

Abstract

A semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency and its fabrication method are disclosed. The structure includes a substrate, and a buffer layer, an N-type semiconductor layer, a refractive index gradient layer, an active layer, and a P-type semiconductor layer sequentially stacked on the substrate. The refractive index gradient layer comprises an In composition, which gradually increases from the N-type semiconductor layer towards the active layer, resulting in a monotonically increasing refractive index. This invention aims to solve the problem of low light extraction efficiency caused by the inability of the refractive index gradient layer to actively guide light in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and particularly relates to a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency and its preparation method. Background Technology

[0002] Semiconductor light-emitting devices are widely used in lighting, displays, and other fields, but low light extraction efficiency remains a core technological bottleneck. This is because there is a large refractive index difference between the semiconductor material and the external medium, causing most of the light generated in the active region to undergo total internal reflection at the emission interface, becoming trapped inside the device and unable to be effectively emitted. To improve light extraction efficiency, the industry typically employs patterned substrate technology, forming micron-scale patterned structures on the substrate surface to scatter the light that would otherwise be totally internally reflected, thus altering its propagation path. However, the direction of the scattered light is random, and some light still cannot be effectively extracted from the emission surface.

[0003] In existing technologies, to further mitigate the abrupt change in refractive index at the light-emitting interface, a scheme has emerged in which a refractive index gradient layer is placed on the light-emitting surface of the chip, the back side of the substrate, or the passivation layer. The refractive index of this type of gradient layer decreases layer by layer from the inside of the chip to the outside, thereby reducing total internal reflection loss. However, these gradient layers are all placed in the region after the light has undergone total internal reflection, passively compensating for the loss, and cannot actively guide or correct the direction of light propagation at the source. Their ability to control the light propagation mode near the active layer is limited. In fact, the refractive index of the active layer is usually higher than that of the N-type semiconductor layer; therefore, if a gradient layer with a monotonically increasing refractive index could be placed between the two, it would be possible to actively guide the light. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a semiconductor light-emitting epitaxial structure and preparation method that enhances light extraction efficiency, thereby solving the problem that in existing technologies, the refractive index gradient layer cannot actively guide light and has low light extraction efficiency.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: A semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency includes a substrate and a buffer layer, an N-type semiconductor layer, a refractive index gradient layer, an active layer, and a P-type semiconductor layer sequentially stacked on the substrate. The refractive index gradient layer includes an In component, and the content of the In component gradually increases from the N-type semiconductor layer toward the active layer, so that the refractive index of the refractive index gradient layer monotonically increases.

[0006] Furthermore, the refractive index gradient layer is a first InGaN sublayer, and the In composition in the first InGaN sublayer gradually increases from the N-type semiconductor layer toward the active layer.

[0007] Furthermore, the In composition ratio of the first InGaN sublayer near the N-type semiconductor layer is 0, and the In composition ratio of the first InGaN sublayer near the active layer is 0.15 to 0.30.

[0008] Furthermore, the refractive index gradient layer includes a GaN sublayer and a plurality of second InGaN sublayers sequentially disposed from the N-type semiconductor layer toward the active layer. The number of second InGaN sublayers is at least two, and the In composition in each second InGaN sublayer is different from that in the others. The In composition between two adjacent second InGaN sublayers gradually increases from the N-type semiconductor layer toward the active layer.

[0009] Furthermore, among the plurality of second InGaN sublayers, the In composition ratio of the first second InGaN sublayer closest to the GaN sublayer is ≤0.10, and the In composition ratio of the second InGaN sublayer closest to the end of the active layer is 0.15 to 0.30.

[0010] Furthermore, the total thickness of the refractive index gradient layer is 50 nm to 200 nm.

[0011] A method for fabricating a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency, used to fabricate the aforementioned semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency, includes the following steps: S1, a substrate is provided, and a buffer layer is grown on the substrate; S2, An N-type semiconductor layer is grown on the buffer layer; S3, a refractive index gradient layer is grown on the N-type semiconductor layer. The refractive index gradient layer includes an In component. The content of the In component gradually increases from the N-type semiconductor layer toward the active layer, so that the refractive index of the refractive index gradient layer increases monotonically. S4, an active layer is grown on the refractive index graded layer; S5, a P-type semiconductor layer is grown on the active layer.

[0012] Furthermore, the refractive index gradient layer is grown using MOCVD technology, and trimethylgallium, ammonia, and trimethylindium are introduced. The growth temperature of the refractive index gradient layer is 700℃~850℃, and the growth pressure of the refractive index gradient layer is 100Torr~500Torr.

[0013] Furthermore, during the growth of the refractive index gradient layer, the flow rate of trimethylindium increases linearly from 0 μmol / min to 10 μmol / min to 200 μmol / min, so that the content of the In component gradually increases from the N-type semiconductor layer toward the active layer.

[0014] Furthermore, during the growth of the refractive index gradient layer, the flow rate of trimethylindium is increased in the range of 10 μmol / min to 200 μmol / min, and a growth interruption is set after each increase in flow rate. The growth interruption time is 2 to 5 seconds, so that the content of the In component gradually increases from the N-type semiconductor layer to the active layer.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: by setting a refractive index gradient layer containing In component between the N-type semiconductor layer and the active layer, and making the In component gradually increase from the N-type semiconductor layer to the active layer, the refractive index of the refractive index gradient layer increases monotonically, thereby deflecting the light propagation direction towards the normal direction of the light-emitting surface, actively correcting the direction of the light, and enabling more light to reach the light-emitting interface at an angle less than the critical angle of total internal reflection, effectively improving the light extraction efficiency of the semiconductor light-emitting epitaxial structure. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the refractive index gradient layer composed of a first InGaN sublayer in the semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to an embodiment of the present invention, in which a GaN sublayer and a second InGaN sublayer form a refractive index gradient layer.

[0017] Explanation of key component symbols: 10. Substrate; 20. Buffer layer; 30. N-type semiconductor layer; 40. Refractive index gradient layer; 401. First InGaN sublayer; 402. GaN sublayer; 403. Second InGaN sublayer; 50. Active layer; 60. P-type semiconductor layer.

[0018] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0019] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be thorough and complete.

[0020] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "up," "down," and similar expressions used herein are for illustrative purposes only and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0021] In this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The term "and / or" as used herein includes any and all combinations of one or more of the related listed items.

[0022] Example 1: Please see Figure 1 A semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency includes a substrate 10, and a buffer layer 20, an N-type semiconductor layer 30, a refractive index gradient layer 40, an active layer 50 and a P-type semiconductor layer 60 sequentially stacked on the substrate 10. The refractive index gradient layer 40 is composed of a first InGaN sublayer 401. The In content of the first InGaN sublayer 401 gradually increases from the N-type semiconductor layer 30 towards the active layer 50. The In content of the first InGaN sublayer 401 near the N-type semiconductor layer 30 is 0, and the In content of the first InGaN sublayer 401 near the active layer 50 is 0.25, so that the refractive index of the refractive index gradient layer 40 continuously increases. The total thickness of the refractive index gradient layer 40 is 150 nm. The active layer 50 is an InGaN / GaN multi-quantum-well structure, comprising several alternately stacked InGaN quantum well layers and GaN quantum barrier layers.

[0023] Wherein: the substrate 10 is a patterned sapphire substrate; the buffer layer 20 is an AlN layer with a thickness of 30 nm; the N-type semiconductor layer 30 is an n-GaN layer with a thickness of 2 μm; in the active layer 50, the InGaN quantum well layer has a thickness of 3 nm and an In composition ratio of 0.15; the GaN quantum barrier layer has a thickness of 10 nm; and the P-type semiconductor layer 60 is a p-GaN layer with a thickness of 150 nm.

[0024] The present invention also provides a method for preparing a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency, which is used to prepare the above-mentioned semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency, and includes the following steps: S1 provides a substrate 10; S2, a buffer layer 20 is grown on the substrate 10; S3, An N-type semiconductor layer 30 is grown on the buffer layer 20; S4, a refractive index gradient layer 40 is grown on the N-type semiconductor layer 30. The refractive index gradient layer 40 includes an In component. The content of the In component gradually increases from the N-type semiconductor layer 30 toward the active layer 50, so that the refractive index of the refractive index gradient layer 40 increases monotonically. S5, an active layer 50 is grown on the refractive index graded layer 40; S6, a P-type semiconductor layer 60 is grown on the active layer 50.

[0025] The refractive index gradient layer 40 is grown using MOCVD technology, with trimethylgallium, ammonia, and trimethylindium introduced. Within the first InGaN sublayer 401, the growth temperature is 750°C, the growth pressure is 200 Torr, the trimethylgallium flow rate is 100 μmol / min, the ammonia flow rate is 5000 sccm, and the trimethylindium flow rate is 0 μmol / min at the initial stage of growth and 100 μmol / min at the end of growth, increasing linearly with growth time. This ensures that the In content within the first InGaN sublayer 401 gradually increases from the N-type semiconductor layer 30 towards the active layer 50. The active layer 50 is grown at 750°C with a growth pressure of 200 Torr. The P-type semiconductor layer 60 is grown at 950°C with a growth pressure of 200 Torr, with trimethylgallium, ammonia, and magnesia introduced.

[0026] Example 2 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the proportion of In composition on the side of the first InGaN sublayer 401 closest to the active layer 50 is 0.15.

[0027] Example 3 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the In composition ratio of the first InGaN sublayer 401 near the active layer 50 is 0.30.

[0028] Example 4 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the total thickness of the refractive index gradient layer 40 is 50nm.

[0029] Example 5 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the total thickness of the refractive index gradient layer 40 is 200nm.

[0030] Comparative Example 1 The difference between this comparative example and Example 1 is that the semiconductor light-emitting epitaxial structure does not include the refractive index gradient layer 40, and the N-type semiconductor layer 30 is directly connected to the active layer 50. The fabrication method does not include the step of growing the refractive index gradient layer 40 on the N-type semiconductor layer 30.

[0031] Comparative Example 2 This comparative example is basically the same as Example 1, except that in this example, the In content of the first InGaN sublayer 401 gradually decreases from the N-type semiconductor layer 30 towards the active layer 50. The In content of the first InGaN sublayer 401 near the N-type semiconductor layer 30 is 0.25, and the In content of the first InGaN sublayer 401 near the active layer 50 is 0. In the preparation method, the trimethylindium flow rate decreases linearly with the growth time. The trimethylindium flow rate is 100 μmol / min in the initial stage of growth and 0 μmol / min in the final stage of growth.

[0032] Comparative Example 3 This comparative example is basically the same as Example 1, except that in this example, the proportion of In composition in the first InGaN sublayer 401 near the active layer 50 is 0.08.

[0033] Comparative Example 4 This comparative example is basically the same as Example 1, except that in this example, the proportion of In composition on the side of the first InGaN sublayer 401 closest to the active layer 50 is 0.40.

[0034] Comparative Example 5 This comparative example is basically the same as Example 1, except that in this example, the total thickness of the refractive index gradient layer 40 is 20 nm.

[0035] Comparative Example 6 This comparative example is basically the same as Example 1, except that in this example, the total thickness of the refractive index gradient layer 40 is 300 nm.

[0036] Example 6 Please see Figure 2 The difference between this embodiment and Embodiment 1 is that the refractive index gradient layer 40 is composed of a GaN sublayer 402 and several second InGaN sublayers 403.

[0037] The GaN sublayer 402 and several second InGaN sublayers 403 are sequentially arranged from the N-type semiconductor layer 30 toward the active layer 50. In this embodiment, there are 5 second InGaN sublayers 403, the total thickness of the refractive index gradient layer 40 is 100 nm, wherein the GaN sublayer 402 has a thickness of 20 nm, and each second InGaN sublayer 403 has a thickness of 16 nm. The In composition ratio of the first second InGaN sublayer 403 near the GaN sublayer 402 is 0.05, and the In composition ratio of the last second InGaN sublayer 403 near the active layer 50 is 0.25. The In composition in each second InGaN sublayer 403 is different from each other. The In composition content between two adjacent second InGaN sublayers 403 gradually increases from the N-type semiconductor layer 30 to the active layer 50. The In composition of each layer is 0.05, 0.10, 0.15, 0.20, and 0.25 respectively, so that the refractive index of the refractive index gradient layer 40 increases in a stepwise manner.

[0038] In the preparation method, the refractive index graded layer 40 is grown using MOCVD technology, and trimethylgallium, ammonia, and trimethylindium are introduced. First, a GaN sublayer 402 is grown. Then, on the GaN sublayer 402, the growth temperature is 750°C, the growth pressure is 200 Torr, the trimethylgallium flow rate is 100 μmol / min, the ammonia flow rate is 5000 sccm, and the trimethylindium flow rate increases layer by layer in the range of 10 μmol / min to 200 μmol / min, to sequentially grow each of the second InGaN sublayers 403 with gradually increasing In content from the N-type semiconductor layer 30 towards the active layer 50. A growth interruption is set between the switching of the trimethylindium flow rate, and the growth interruption time is 3 seconds.

[0039] Example 7 This embodiment is basically the same as Embodiment 6, except that in this embodiment, the second InGaN sublayer 403 has two layers, the total thickness of the refractive index gradient layer 40 is 100nm, the GaN sublayer 402 has a thickness of 20nm, and the thickness of each second InGaN sublayer 403 is 40nm. The In composition ratio of the first second InGaN sublayer 403 closest to the GaN sublayer 402 is 0.10, and the In composition ratio of the last second InGaN sublayer 403 closest to the active layer 50 is 0.25. The In composition of each layer is 0.10 and 0.25 respectively.

[0040] Example 8 This embodiment is basically the same as Embodiment 6, except that in this embodiment, the second InGaN sublayer 403 has 9 layers, the total thickness of the refractive index gradient layer 40 is 100nm, the GaN sublayer 402 has a thickness of 10nm, and the thickness of each second InGaN sublayer 403 is 10nm. The In composition ratio of the first second InGaN sublayer 403 closest to the GaN sublayer 402 is 0.03, and the In composition ratio of the last second InGaN sublayer 403 closest to the active layer 50 is 0.27. The In compositions of each layer are 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24, and 0.27, respectively.

[0041] Example 9 This embodiment is basically the same as embodiment 6, except that in this embodiment, the total thickness of the refractive index gradient layer 40 is 50nm, the GaN sublayer 402 is 10nm thick, and each second InGaN sublayer 403 is 8nm thick.

[0042] Example 10 This embodiment is basically the same as embodiment 6, except that in this embodiment, the total thickness of the refractive index gradient layer 40 is 200nm, the GaN sublayer 402 has a thickness of 35nm, and each second InGaN sublayer 403 has a thickness of 33nm.

[0043] Example 11 This embodiment is basically the same as embodiment 6, except that in this embodiment, the In composition ratio of the first second InGaN sublayer 403 closest to the GaN sublayer 402 is 0.01, and the In composition of each layer is 0.01, 0.07, 0.13, 0.19, and 0.25 respectively.

[0044] Example 12 This embodiment is basically the same as embodiment 6, except that in this embodiment, the In composition ratio of the last second InGaN sublayer 403 near the active layer 50 is 0.30, and the In composition of each layer is 0.05, 0.11, 0.17, 0.23, and 0.30 respectively.

[0045] Comparative Example 7 This comparative example is basically the same as Example 6, except that in this example, the In content between two adjacent second InGaN sub-layers 403 gradually decreases from the N-type semiconductor layer 30 toward the active layer 50. The In content of the first second InGaN sub-layer 403 near the GaN sub-layer 402 is 0.25, and the In content of the last second InGaN sub-layer 403 near the active layer 50 is 0.05. The In content of each layer is 0.25, 0.20, 0.15, 0.10, and 0.05, respectively.

[0046] Comparative Example 8 This comparative example is basically the same as Example 6, except that in this example, the refractive index gradient layer 40 does not contain a GaN sublayer 402, but is composed of six layers of second InGaN sublayers 403 stacked sequentially. The total thickness of the refractive index gradient layer 40 is 100 nm, and the thickness of each second InGaN sublayer 403 is 16 nm. The In composition ratio of the first second InGaN sublayer 403 near the N-type semiconductor layer 30 is 0, and the In composition ratio of the last second InGaN sublayer 403 near the active layer 50 is 0.25. The In compositions of each layer are 0, 0.05, 0.10, 0.15, 0.20, and 0.25, respectively.

[0047] Comparative Example 9 This comparative example is basically the same as Example 6, except that in this example, the second InGaN sublayer 403 has 12 layers, the total thickness of the refractive index gradient layer 40 is 100nm, and the In composition of each layer is 0.02, 0.04, 0.07, 0.09, 0.12, 0.14, 0.17, 0.19, 0.22, 0.24, 0.27, and 0.30, respectively.

[0048] Comparative Example 10 This comparative example is basically the same as Example 6, except that in this example, the total thickness of the refractive index gradient layer 40 is 30nm, wherein the GaN sublayer 402 has a thickness of 5nm, and each second InGaN sublayer 403 has a thickness of 5nm.

[0049] Comparative Example 11 This comparative example is basically the same as Example 6, except that in this example, the total thickness of the refractive index gradient layer 40 is 250 nm, the GaN sublayer 402 has a thickness of 50 nm, and each second InGaN sublayer 403 has a thickness of 40 nm.

[0050] Comparative Example 12 This comparative example is basically the same as Example 6, except that in this example, the In composition in each of the second InGaN sublayers 403 is the same, and the In composition of each layer is 0.15, 0.15, 0.15, 0.15, 0.15, 0.15 in sequence.

[0051] Comparative Example 13 This comparative example is basically the same as Example 6, except that in this example, the In composition ratio of the last second InGaN sublayer 403 near the active layer 50 is 0.10, and the In composition of each layer is 0.05, 0.06, 0.07, 0.08, and 0.10 respectively.

[0052] Comparative Example 14 This comparative example is basically the same as Example 6, except that in this example, the In composition ratio of the first second InGaN sublayer 403 closest to the GaN sublayer 402 is 0.005, and the In composition of each layer is 0.005, 0.07, 0.13, 0.19, and 0.25 respectively.

[0053] Comparative Example 15 This comparative example is basically the same as Example 6, except that in this example, the In composition ratio of the last second InGaN sublayer 403 near the active layer 50 is 0.40, and the In composition of each layer is 0.05, 0.11, 0.17, 0.23, and 0.40 respectively.

[0054] Furthermore, the light extraction efficiency of the semiconductor light-emitting epitaxial structures with enhanced light extraction efficiency prepared in the above embodiments and comparative examples was tested. The testing method included the following steps: Referring to SJ / T11394-2009 "Test Methods for Semiconductor Light Emitting Diodes" and IEC60747-5-8:2019 "Semiconductor Devices - Part 5-8: Photoelectric Efficiency Test Methods for Light Emitting Diodes" - the external quantum efficiency of the semiconductor light-emitting epitaxial structures with enhanced light emission efficiency prepared in the above embodiments and comparative examples was tested.

[0055] The testing equipment includes an integrating sphere, a spectrometer, a DC power supply, and an optical power meter. During testing, an epitaxial structure is fabricated into a chip sample and placed at the center of the integrating sphere. A set current is injected by the DC power supply at room temperature, causing the active layer to emit light. The integrating sphere collects all the light emitted by the chip sample, the spectrometer measures its spectral power distribution, and the optical power meter records the total optical output power P_out.

[0056] The external quantum efficiency η_EQE of the chip sample is calculated using the following formula: η_EQE=P_out / (I×V)×100% In the formula, P_out is the optical output power, I is the injection current, and V is the forward voltage across the chip sample.

[0057] The percentage improvement in light extraction efficiency Δη of each embodiment and comparative example relative to the baseline is calculated using the following formula: Δη=(η_EQE_i η_EQE_0) / η_EQE_0×100% In the formula, η_EQE_i is the power efficiency of the sample under test, and η_EQE_0 is the power efficiency of the chip sample without the refractive index gradient layer 40 prepared in Comparative Example 1.

[0058] The specific parameters used in Examples 1 to 9 and Comparative Examples 1 to 10 of the manufacturing process according to the present invention, and the corresponding test results obtained therefrom, are shown in Table 1.

[0059] Table 1:

[0060] A comparison of Examples 1 to 3 with Comparative Examples 2 to 4 shows that when the refractive index gradient layer 40 is composed of a first InGaN sublayer 401, the endpoints of the In composition variation in the first InGaN sublayer 401 of Examples 1, 2, and 3 are 0.25, 0.15, and 0.30, respectively, resulting in light extraction efficiency improvements of 13%, 6%, and 18%, respectively. As the In composition endpoint increases, the improvement in light extraction efficiency also increases, with each example showing an improvement of at least 5%. In Comparative Example 2, the In composition variation direction is decreasing, yet the light extraction efficiency decreases, indicating that a gradual increase in In composition from the N-type semiconductor layer 30 towards the active layer 50 is beneficial for improving light extraction efficiency. In Comparative Example 3, the In composition endpoint is only 0.08, resulting in a light extraction efficiency improvement of only 3%, lower than the other examples, indicating that the refractive index variation is insufficient when the In composition endpoint is too low. In Comparative Example 4, the In composition endpoint is 0.40, resulting in a light extraction efficiency improvement of 4%, lower than the other examples, indicating that the effect tends to saturate when the In composition endpoint is too high. This indicates that an In composition endpoint of 0.15 to 0.30 in the first InGaN sublayer 401 is beneficial for balancing the improvement in light extraction efficiency with structural rationality.

[0061] A comparison of Examples 4 to 5 with Comparative Examples 5 to 6 shows that the total thicknesses of the refractive index gradient layer 40 in Examples 4, 1, and 5 are 50 nm, 150 nm, and 200 nm, respectively, with light extraction efficiency improvements of 8%, 13%, and 16%. As the total thickness increases, the improvement in light extraction efficiency increases accordingly, with each example showing an improvement of at least 5%. Comparative Example 5 has a total thickness of 20 nm, but its light extraction efficiency improvement is only 3%, indicating insufficient light deflection when the thickness is too small. Comparative Example 6 has a total thickness of 300 nm, with a light extraction efficiency improvement of 4%, lower than the other examples, indicating that the light extraction efficiency improvement tends to saturate when the thickness is too large. This demonstrates that a total thickness of the refractive index gradient layer 40 within the range of 50 nm to 200 nm is advantageous in balancing light extraction efficiency improvement with epitaxial costs.

[0062] A comparison of Examples 6 to 8 with Comparative Example 9 shows that when the refractive index gradient layer 40 consists of one GaN sublayer 402 and several second InGaN sublayers 403, the number of second InGaN sublayers 403 in Examples 7, 6, and 8 are 2, 5, and 9, respectively, resulting in light extraction efficiency improvements of 6%, 12%, and 17%. As the number of layers increases, the fineness of the refractive index gradient increases, and the improvement in light extraction efficiency increases accordingly. Comparative Example 9 has 12 layers, with a light extraction efficiency improvement of 4%, lower than the examples, indicating that excessive layers increase process complexity and lead to saturation. This suggests that having 2 to 9 layers of the second InGaN sublayer 403 is advantageous for balancing light extraction efficiency improvement and process controllability.

[0063] A comparison of Examples 9 to 10 with Comparative Examples 10 to 11 shows that the total thicknesses of the refractive index gradient layer 40 in Examples 9, 6, and 10 are 50 nm, 100 nm, and 200 nm, respectively, with light extraction efficiency improvements of 7%, 12%, and 15%, respectively. This trend is consistent with the case when the refractive index gradient layer 40 consists of a single first InGaN sublayer 401. Comparative Example 10 has a total thickness of 30 nm, with a light extraction efficiency improvement of only 3%; Comparative Example 11 has a total thickness of 250 nm, with a light extraction efficiency improvement of 4%, both lower than the examples. This further verifies the rationality of the total thickness of the refractive index gradient layer 40 being in the range of 50 nm to 200 nm.

[0064] A comparison of Examples 11 to 12 with Comparative Examples 13 to 15 shows that in the second InGaN sublayer 403 of Examples 11, 6, and 12, the first layer In composition is 0.01, 0.05, and 0.05, respectively, and the last layer In composition is 0.25, 0.25, and 0.30, respectively, resulting in light extraction efficiency improvements of 9%, 12%, and 16%, respectively. In Comparative Example 13, the last layer In composition is only 0.10, resulting in a light extraction efficiency improvement of only 4%, indicating that the total refractive index change is insufficient when the last layer In composition is too low. In Comparative Example 14, the first layer In composition is 0.005, resulting in a light extraction efficiency improvement of only 4%, indicating that the initial deflection effect is weak when the first layer In composition is too low. In Comparative Example 15, the last layer In composition is 0.40, resulting in a light extraction efficiency improvement of only 4%, indicating that the effect tends to saturate when the last layer In composition is too high. This indicates that in each of the second InGaN sublayers 403, an In composition greater than 0 and not exceeding 0.10 in the first layer and an In composition in the last layer within the range of 0.15 to 0.30 is beneficial for balancing improved light extraction efficiency with structural rationality.

[0065] A comparison between Comparative Example 7 and Example 6 shows that the light extraction efficiency decreases when the In content decreases, further verifying the effect of gradually increasing the In content on improving light extraction efficiency. A comparison between Comparative Example 8 and Example 6 shows that the light extraction efficiency is only improved by 3% when the refractive index gradient layer 40 does not contain a GaN sublayer 402, indicating that incorporating a GaN sublayer 402 in a multilayer structure is beneficial for improving light extraction efficiency. A comparison between Comparative Example 12 and Example 6 shows that the light extraction efficiency is only improved by 2% when the In content of each second InGaN sublayer 403 is the same, indicating that a gradual increase in the In content between layers is beneficial for achieving a step-like change in refractive index.

[0066] In summary, this invention, by setting a refractive index gradient layer 40 between the N-type semiconductor layer 30 and the active layer 50, and gradually increasing the In composition from the N-type semiconductor layer 30 towards the active layer 50, can actively correct the direction of light and improve the light extraction efficiency. When the refractive index gradient layer 40 is composed of a first InGaN sublayer 401, it is more suitable to control the In composition endpoint of the first InGaN sublayer 401 within the range of 0.15 to 0.30. When the refractive index gradient layer 40 is composed of a GaN sublayer 402 and several second InGaN sublayers 403, it is more suitable to control the In composition of the first layer of the second InGaN sublayer 403 to be greater than 0 and not more than 0.10, the In composition of the last layer to be controlled within the range of 0.15 to 0.30, and the number of layers to be controlled within the range of 2 to 9. The total thickness of the refractive index gradient layer 40 is more suitable to be controlled within the range of 50 nm to 200 nm. Within the aforementioned range, the light extraction efficiency of each embodiment is improved by no less than 5%. Compared with the passive remedial scheme in the prior art that sets the refractive index gradient layer in the light-emitting surface, the back of the substrate, or the passivation layer and the refractive index decreases from the inside to the outside, the present invention actively guides and corrects the direction of light propagation at the source by incorporating a refractive index gradient layer 40 with increasing refractive index, resulting in a significant improvement in light extraction efficiency.

[0067] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency, characterized in that, The material includes a substrate, and a buffer layer, an N-type semiconductor layer, a refractive index gradient layer, an active layer, and a P-type semiconductor layer sequentially stacked on the substrate. The refractive index gradient layer includes an In component, and the content of the In component gradually increases from the N-type semiconductor layer toward the active layer, so that the refractive index of the refractive index gradient layer increases monotonically.

2. The semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to claim 1, characterized in that, The refractive index gradient layer is a first InGaN sublayer, and the In composition in the first InGaN sublayer gradually increases from the N-type semiconductor layer toward the active layer.

3. The semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to claim 2, characterized in that, The In composition percentage of the first InGaN sublayer near the N-type semiconductor layer is 0, and the In composition percentage of the first InGaN sublayer near the active layer is 0.15 to 0.

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4. The semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to claim 1, characterized in that, The refractive index gradient layer includes a GaN sublayer and a plurality of second InGaN sublayers sequentially disposed from the N-type semiconductor layer toward the active layer. The number of second InGaN sublayers is at least two, and the In composition in each second InGaN sublayer is different from that in the others. The In composition between two adjacent second InGaN sublayers gradually increases from the N-type semiconductor layer toward the active layer.

5. The semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to claim 4, characterized in that, In a plurality of second InGaN sublayers, the In composition ratio of the first second InGaN sublayer closest to the GaN sublayer is ≤0.10, and the In composition ratio of the second InGaN sublayer closest to the end of the active layer is 0.15 to 0.

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6. The semiconductor light-emitting epitaxial structure for enhancing light extraction efficiency according to claim 1, characterized in that, The total thickness of the refractive index gradient layer is 50 nm to 200 nm.

7. A method for preparing a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency, used to prepare the semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1, a substrate is provided, and a buffer layer is grown on the substrate; S2, An N-type semiconductor layer is grown on the buffer layer; S3, a refractive index gradient layer is grown on the N-type semiconductor layer. The refractive index gradient layer includes an In component. The content of the In component gradually increases from the N-type semiconductor layer toward the active layer, so that the refractive index of the refractive index gradient layer increases monotonically. S4, an active layer is grown on the refractive index graded layer; S5, a P-type semiconductor layer is grown on the active layer.

8. The method for preparing a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency according to claim 7, characterized in that, The refractive index graded layer is grown using MOCVD technology, with trimethylgallium, ammonia, and trimethylindium introduced. The growth temperature of the refractive index graded layer is 700℃~850℃, and the growth pressure is 100Torr~500Torr.

9. The method for preparing a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency according to claim 7, characterized in that, During the growth of the refractive index gradient layer, the flow rate of trimethylindium increases linearly from 0 μmol / min to 10 μmol / min to 200 μmol / min, so that the content of the In component gradually increases from the N-type semiconductor layer toward the active layer.

10. The method for preparing a semiconductor light-emitting epitaxial structure with enhanced light extraction efficiency according to claim 7, characterized in that, During the growth of the refractive index gradient layer, the flow rate of trimethylindium is increased in the range of 10 μmol / min to 200 μmol / min, and a growth interruption is set after each increase in flow rate. The growth interruption time is 2 to 5 seconds, so that the content of the In component gradually increases from the N-type semiconductor layer to the active layer.

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