Reversed polarity LED epitaxial wafer for improving light extraction efficiency and preparation method thereof

Abstract

The invention relates to the technical field of LEDs, in particular to a reversed-polarity LED epitaxial wafer capable of improving light extraction efficiency and a preparation method of the reversed-polarity LED epitaxial wafer. The reversed-polarity LED epitaxial wafer sequentially comprises a GaAs substrate, a buffer layer, a corrosion cut-off layer, an N-type ohmic contact layer, an electrode protection layer, a coarsening layer, a first refractive index gradual change layer, an N-type limiting layer, a second refractive index gradual change layer, an N-side waveguide layer, a multi-quantum well light-emitting layer, a P-side waveguide layer, a third refractive index gradual change layer, a P-type limiting layer, a transition layer and a high-smoothness GaP mirror surface layer from bottom to top. Through the design of the refractive index gradual change layer and the high-smoothness GaP mirror surface layer, not only can internal reflection loss caused by refractive index mutation caused by a pre-reaction compound be reduced, but also a GaP material with a low-roughness surface can be prepared, so that the light extraction efficiency of a reverse polarity LED is bidirectionally improved.

Description

Technical Field

[0001] This invention relates to the field of LED technology, specifically to a reverse polarity LED epitaxial wafer with improved light extraction efficiency and its preparation method. Background Technology

[0002] The quaternary AlGaInP system is the most important material system for preparing high-brightness reverse polarity red LED epitaxial wafers. In recent decades, with the rapid development of high-brightness AlGaInP reverse polarity red LEDs, corresponding products have been widely used in stage lighting, automotive lighting, outdoor lighting, high-end displays and other fields.

[0003] By optimizing the growth and structure of epitaxial materials, the internal quantum efficiency of epitaxial wafers for reverse polarity red LEDs has reached over 90%, but the light extraction efficiency remains below 50%. For example, the epitaxial structure of conventional reverse polarity LEDs in the industry is as follows: Figure 1 As shown, from bottom to top, the structure includes a GaAs substrate 100, a buffer layer 101, an etching stop layer 102, an N-type ohmic contact layer 103, an electrode protection layer 104, a roughening layer 105, an N-type confinement layer 106, an N-side waveguide layer 107, a multi-quantum-well light-emitting layer 108, a P-side waveguide layer 109, a P-type confinement layer 110, a transition layer 111, and a window layer 112. However, to optimize the energy barrier design, the Al composition varies significantly between the AlGaInP epitaxial functional layers. At the interfaces of these functional layers, abrupt changes in composition generate numerous pre-reacting compounds. These compounds cause abrupt changes in refractive index, leading to internal optical reflection and resulting in internal reflection losses between epitaxial layers, thus reducing light extraction efficiency. Simultaneously, the growth window layer is typically made of GaP. Due to the lattice mismatch between GaP and the GaAs substrate, increasing growth thickness leads to increased surface roughness. This rough surface results in lower reflectivity during subsequent P-plane mirror fabrication, affecting the final P-plane mirror performance and hindering high light extraction efficiency. Therefore, while existing reverse-polarity red LEDs have high internal luminous efficiency, the internal reflection caused by abrupt changes in refractive index between epitaxial layers and the high roughness of the luminous window layer material limit the light source's emission from the LED epitaxial layers, resulting in very low light extraction efficiency.

[0004] Therefore, developing a reverse polarity LED epitaxial wafer that can improve light extraction efficiency is of great significance for enhancing the overall luminous brightness of red LEDs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an anti-polarity LED epitaxial wafer with improved light extraction efficiency and its preparation method. This anti-polarity LED epitaxial wafer not only has good specular reflection effect but also eliminates internal reflection caused by abrupt changes in refractive index at the interface, thereby improving the light extraction efficiency of the anti-polarity LED and increasing the LED brightness.

[0006] The first objective of this invention is to provide a reverse polarity LED epitaxial wafer with improved light extraction efficiency. The reverse polarity LED epitaxial wafer comprises, from bottom to top, a GaAs substrate, a buffer layer, an etching stop layer, an N-type ohmic contact layer, an electrode protection layer, a roughening layer, a first refractive index gradient layer, an N-type confinement layer, a second refractive index gradient layer, an N-side waveguide layer, a multi-quantum-well light-emitting layer, a P-side waveguide layer, a third refractive index gradient layer, a P-type confinement layer, a transition layer, and a high-smoothness GaP mirror layer. The high-smoothness GaP mirror layer consists of a low forward rotation speed ratio GaP nucleation layer, a high forward rotation speed ratio GaP annealing layer, and a high reverse rotation speed ratio GaP window layer from bottom to top.

[0007] This invention is based on the conventional anti-polarity LED epitaxial structure. By designing the GaP window layer as a three-layer high-smoothness GaP mirror layer and controlling the rotation process of both the graphite small disk and the graphite large disk, the invention aims to reduce the risk of lattice distortion during the initial nucleation of GaP material, improve the temperature field uniformity of the GaP layer during high-temperature annealing, and enhance the lattice size flatness. The final product is a high-smoothness GaP mirror layer with low surface roughness, which not only has good mirror reflection effect but also improves current spread, effectively enhancing the light extraction efficiency of anti-polarity LEDs. Simultaneously, by inserting a first refractive index gradually changing layer between the roughening layer and the N-type confinement layer, a second refractive index gradually changing layer between the N-type confinement layer and the N-side waveguide layer, and a third refractive index gradually changing layer between the P-side waveguide layer and the P-type confinement layer, the invention effectively avoids the generation of excess pre-reacted compounds in the AlGaInP material with a sudden change in Al composition, thereby eliminating the internal reflection problem caused by the sudden change in refractive index at the interface and further improving the light extraction efficiency of the LED.

[0008] Furthermore, the material of the first refractive index gradual layer is (Al) z1 Ga 1-z1 ) 0.5 In 0.5 P, with a thickness of 50nm–100nm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The value of z1 ranges from 0.75 to 0.85.

[0009] Furthermore, the material of the second refractive index gradient layer is (Al) z2Ga 1-z2 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 17 cm -3 The value of z2 ranges from 0.85 to 0.95.

[0010] Furthermore, the material of the third refractive index gradual-varying layer is (Al). z3 Ga 1-z3 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~2×10 17 cm -3 The value of z3 ranges from 0.85 to 0.95.

[0011] Furthermore, the thickness of the GaP nucleation layer with low forward rotation speed ratio is 30 nm to 50 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The thickness of the GaP annealed layer with high forward rotation speed ratio is 200nm–300nm, and the doping concentration is 2×10⁻⁶. 18 cm -3 ~4×10 18 cm -3 The thickness of the GaP window layer with high reverse rotation speed ratio is 1000nm–2000nm, and the doping concentration is 3×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0012] The second objective of this invention is to provide a method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency. This method utilizes MOCVD (metal-organic chemical vapor deposition) equipment to grow, from bottom to top, a buffer layer, an etching stop layer, an N-type ohmic contact layer, an electrode protection layer, a roughening layer, a first refractive index gradient layer, an N-type confinement layer, a second refractive index gradient layer, an N-side waveguide layer, a multiple quantum well light-emitting layer, a P-side waveguide layer, a third refractive index gradient layer, a P-type confinement layer, a transition layer, a low forward rotation speed ratio GaP nucleation layer, a high forward rotation speed ratio GaP annealing layer, and a high reverse rotation speed ratio GaP window layer. The materials of the first, second, and third refractive index gradual layer were all epitaxially grown using a method of blowing H2 / N2 mixed gas onto the back of the bottom graphite disk.

[0013] The low forward rotation speed ratio GaP nucleation layer, high forward rotation speed ratio GaP annealing layer, and high reverse rotation speed ratio GaP window layer are grown using graphite small disks and large disks at specific rotation modes and speed ratios. Specifically, the reverse polarity LED is grown in a planetary reaction chamber MOCVD system, and the forward rotation speed ratio is defined as the simultaneous counterclockwise rotation of both the large and small graphite disks, while the reverse rotation speed ratio is defined as the small graphite disk rotating counterclockwise but the large graphite disk rotating clockwise.

[0014] This invention proposes a high-smoothness GaP mirror layer structure and a special growth process design, which can improve the mirror reflection effect of the P-side reflector process. The combination of the two can effectively improve the light extraction efficiency of reverse polarity LEDs. At the same time, by introducing H2 / N2 mixed gas to back-purge the graphite disk, three layers of gradually changing refractive index are grown. Refractive index elimination is achieved in the barrier abrupt region where the Al composition gradually changes. The principle is to balance the surface temperature of the epitaxial wafer by adjusting the ratio of H2 / N2 mixed gas flow on the back of the graphite disk, avoiding the generation of excess pre-reacted compounds in the AlGaInP material with abrupt Al composition changes. This eliminates the internal reflection problem caused by the abrupt change in refractive index at the interface, thereby further improving the light extraction efficiency of the LED.

[0015] Furthermore, the growth steps of the first refractive index gradient layer are as follows: setting the reaction chamber temperature to 720℃±10℃, introducing TMAl, TMGa, TMIn, and PH3 onto the roughened layer, and growing (Al) z1 Ga 1-z1 ) 0.5 In 0.5 The P material uses SiH4 as the N-type dopant, and the back of the graphite disk is purged with a mixture of H2 / N2 gas during the growth of the first refractive index gradient layer. The set flow rate of H2 is 3000 sccm to 4000 sccm, and the set flow rate of N2 is 1000 sccm to 2000 sccm.

[0016] Furthermore, the growth steps of the second refractive index gradual-varying layer are as follows: The reaction chamber temperature is set to 700℃±10℃, and TMAl, TMGa, TMIn, and PH3 are introduced onto the N-type confinement layer to grow (Al... z2 Ga 1-z2 ) 0.5 In 0.5The P material uses SiH4 as the N-type dopant, and the back of the graphite disk is purged with a mixture of H2 and N2 gas during the growth of the second refractive index gradient layer. The set flow rate of H2 is 1500 sccm to 2000 sccm, and the set flow rate of N2 is 500 sccm to 1000 sccm.

[0017] Furthermore, the growth steps of the third refractive index gradually varying layer are as follows: The reaction chamber temperature is set to 720℃±10℃, and TMAl, TMGa, TMIn, and PH3 are introduced into the P-side waveguide layer to grow (Al... z3 Ga 1-z3 ) 0.5 In 0.5 The P-material uses Cp2Mg as the P-type dopant, and the back of the graphite disk is purged with a H2 / N2 mixed gas during the growth of the third refractive index gradient layer. The set flow rate of H2 is 1500 sccm to 2000 sccm, and the set flow rate of N2 is 500 sccm to 1000 sccm.

[0018] The proposed refractive index gradient layer structure design with mixed gas purging in this invention uniformly regulates the surface temperature of the epitaxial wafer by controlling the ratio of H2 / N2 mixed gas flow on the back of the graphite disk. This reduces the generation of excess pre-reacted compounds at the AlGaInP barrier change layer interface caused by abrupt changes in Al composition, effectively preventing internal reflection loss caused by abrupt changes in refractive index due to pre-reacted compounds. This increases the probability of photon escape and improves light extraction efficiency.

[0019] Furthermore, the growth steps of the low forward rotation speed ratio GaP nucleation layer are as follows: the reaction chamber temperature is set to 760℃±10℃, TMGa and PH3 are introduced into the transition layer to grow GaP material, Cp2Mg is used as the P-type dopant, and both the graphite small disk and the graphite large disk rotate counterclockwise during the growth of the low forward rotation speed ratio GaP nucleation layer, with the ratio of the rotation speed of the graphite small disk to that of the graphite large disk being 3:1. In this technical solution, by setting a low forward rotation speed ratio, the surface gas eddies of the GaP nucleation layer can be kept stable, preventing eddy current stratification, thereby reducing the risk of lattice distortion during the initial nucleation of GaP material, thus ensuring the uniform arrangement and growth of nucleated atomic layers, resulting in a smooth and flat GaP nucleation layer.

[0020] Furthermore, the growth step of the high forward rotation speed ratio GaP annealing layer is as follows: the reaction chamber temperature is set to 790℃±10℃, TMGa and PH3 are introduced into the low forward rotation speed ratio GaP nucleation layer to grow GaP material, Cp2Mg is used as the P-type dopant, and both the graphite small disk and the graphite large disk are set to rotate counterclockwise during the growth of the high forward rotation speed ratio GaP annealing layer, with the ratio of the rotation speed of the graphite small disk to that of the graphite large disk being 10:1. In this technical solution, by setting a high forward rotation speed ratio, the temperature field uniformity of the epitaxial wafer surface during high-temperature annealing of the GaP layer can be improved, avoiding problems such as uneven lattice stress release caused by over-annealing or under-annealing of the GaP high-temperature layer, thereby improving the GaP lattice relaxation while releasing stress.

[0021] Furthermore, the growth step of the high reverse rotation speed ratio GaP window layer is as follows: the reaction chamber temperature is set to 690℃±10℃, TMGa and PH3 are introduced into the high forward rotation speed ratio GaP annealed layer to grow GaP material. Cp2Mg is used as the P-type dopant, and the graphite small disk rotates counterclockwise while the graphite large disk rotates clockwise during the growth of the high reverse rotation speed ratio GaP window layer, with the ratio of the rotation speed of the graphite small disk to that of the graphite large disk being 10:1. In this technical solution, by setting a high reverse rotation speed ratio, the uneven flow field on the epitaxial wafer surface can be improved when growing thicker GaP material. By controlling the graphite small disk and the graphite large disk to rotate in opposite directions, the flow fields of the graphite small disk and the graphite large disk cancel each other out, thereby improving the uniformity of the growth rate in the GaP window layer, improving the lattice size flatness, and finally obtaining a GaP mirror epitaxial layer with extremely small surface roughness.

[0022] Compared with the prior art, the present invention has the following advantages: 1. This invention is based on the conventional anti-polarity LED epitaxial structure and replaces the GaP window layer with a high-smoothness GaP mirror layer. This structure consists of a GaP nucleation layer with a low forward rotation speed ratio, a GaP annealing layer with a high forward rotation speed ratio, and a GaP window layer with a high reverse rotation speed ratio. By setting the rotation speed ratio characteristics of graphite disks and graphite disks at different stages, the invention aims to reduce the risk of lattice distortion during the initial nucleation of GaP material, improve the uniformity of the temperature field during high-temperature annealing of the GaP layer, and enhance the flatness of the lattice size. Finally, a high-smoothness GaP mirror layer with low surface roughness is prepared, which not only has a good mirror reflection effect but also improves current spread, ultimately improving the light extraction efficiency of anti-polarity LEDs.

[0023] 2. This invention proposes a refractive index gradually varying layer structure design with mixed gas purging. A first refractive index gradually varying layer is inserted between the roughening layer and the N-type confinement layer, a second refractive index gradually varying layer is inserted between the N-type confinement layer and the N-side waveguide layer, and a third refractive index gradually varying layer is inserted between the P-side waveguide layer and the P-type confinement layer. The surface temperature of the epitaxial wafer is uniformly controlled by the ratio of H2 / N2 mixed gas flow on the back of the graphite disk, reducing the generation of excess pre-reacted compounds at the AlGaInP barrier change layer interface where Al composition changes abruptly. This effectively prevents internal reflection loss caused by refractive index abrupt changes due to pre-reacted compounds, improves light extraction efficiency, and results in high brightness of the reverse polarity LED. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a conventional reverse polarity LED epitaxial wafer; Figure 2 This is a schematic diagram of the structure of the reverse polarity LED epitaxial wafer of the present invention; Figure 3 This is a schematic diagram of the structure of the high-smoothness GaP mirror layer of the present invention; Figure 4 This is a surface morphology diagram of the high-smoothness GaP layer of the reverse polarity LED epitaxial wafer of the present invention; Figure 5 This is a surface morphology diagram of the GaP window layer of a conventional reverse polarity LED epitaxial wafer; Figure 6 This is a comparison chart of the brightness of the epitaxial wafers of the reverse polarity LED of this invention and conventional reverse polarity LEDs under different currents.

[0025] Explanation of the labels in the diagram: 100. GaAs substrate; 101. Buffer layer; 102. Etching stop layer; 103. N-type ohmic contact layer; 104. Electrode protection layer; 105. Roughening layer; 106. N-type confinement layer; 107. N-side waveguide layer; 108. Multi-quantum well light-emitting layer; 109. P-side waveguide layer; 110. P-type confinement layer; 111. Transition layer; 112. Window layer; 113. First refractive index gradient layer; 114. Second refractive index gradient layer; 115. Third refractive index gradient layer; 116. High-smoothness GaP mirror layer; 1161. Low forward rotation ratio GaP nucleation layer; 1162. High forward rotation ratio GaP annealing layer; 1163. High reverse rotation ratio GaP window layer. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] In the description of this application, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0028] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0029] Please see Figures 1 to 6 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0030] One embodiment of the present invention provides an inverse polarity LED epitaxial wafer for improving light extraction efficiency, the schematic diagram of which is shown below. Figure 2 As shown, in accordance with the epitaxial growth sequence, from bottom to top, the layers include GaAs substrate 100, buffer layer 101, etching stop layer 102, N-type ohmic contact layer 103, electrode protection layer 104, roughening layer 105, first refractive index gradient layer 113, N-type confinement layer 106, second refractive index gradient layer 114, N-side waveguide layer 107, multi-quantum-well light-emitting layer 108, P-side waveguide layer 109, third refractive index gradient layer 115, P-type confinement layer 110, transition layer 111, and high-smoothness GaP mirror layer 116.

[0031] In some specific embodiments, the high-smoothness GaP mirror layer is composed of a low forward rotation speed ratio GaP nucleation layer 1161, a high forward rotation speed ratio GaP annealing layer 1162, and a high reverse rotation speed ratio GaP window layer 1163, as shown in the schematic diagram below. Figure 3 As shown.

[0032] In some specific embodiments, the first refractive index gradual layer is inserted between the roughening layer and the N-type confinement layer, and the material of the first refractive index gradual layer is (Al). z1 Ga 1-z1 ) 0.5 In 0.5 P, with a thickness of 50nm–100nm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The value of component z1 ranges from 0.75 to 0.85.

[0033] In some specific embodiments, a second refractive index gradually varying layer is inserted between the N-type confinement layer and the N-side waveguide layer, wherein the material of the second refractive index gradually varying layer is (Al). z2 Ga 1-z2 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 17 cm -3 The value of z2 ranges from 0.85 to 0.95.

[0034] In some specific embodiments, the third refractive index gradually changing layer is inserted between the P-side waveguide layer and the P-type confinement layer, and the material of the third refractive index gradually changing layer is (Al). z3 Ga 1-z3 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~2×10 17 cm -3 The value of z3 ranges from 0.85 to 0.95.

[0035] In some specific embodiments, the thickness of the low forward rotation speed ratio GaP nucleation layer is 30 nm to 50 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 ~2×10 18 cm -3The thickness of the GaP annealed layer with high forward rotation speed ratio is 200nm–300nm, and the doping concentration is 2×10⁻⁶. 18 cm -3 ~4×10 18 cm -3 The thickness of the GaP window layer with high reverse rotation speed ratio is 1000nm–2000nm, and the doping concentration is 3×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0036] In another embodiment, the present invention also provides an inverse polarity LED epitaxial wafer with improved light extraction efficiency. The epitaxial layer material is grown in a planetary MOCVD system. On a GaAs substrate, from bottom to top, the following layers are grown sequentially: a buffer layer, an etching stop layer, an N-type ohmic contact layer, an electrode protection layer, a roughening layer, a first refractive index gradient layer, an N-type confinement layer, a second refractive index gradient layer, an N-side waveguide layer, a multiple quantum well light-emitting layer, a P-side waveguide layer, a third refractive index gradient layer, a P-type confinement layer, a transition layer, a low forward rotation speed ratio GaP nucleation layer, a high forward rotation speed ratio GaP annealing layer, and a high reverse rotation speed ratio GaP window layer. Specifically, the following steps are included: (1) MOCVD is pumped to a low pressure of 50 mbar in pure H2 atmosphere, and the reaction chamber is set to 400℃. Then, the GaAs substrate is transferred to the reaction chamber through a robotic hand transfer chamber, and then the temperature is rapidly increased to 780℃ and held at 780℃ for 4 min to 8 min.

[0037] (2) Growth of buffer layer: The reaction chamber temperature was set to 720℃±10℃. TMGa and AsH3 were introduced into the GaAs substrate to grow a GaAs buffer layer material with a thickness of 100nm~200nm. SiH4 was used as the N-type dopant with a doping concentration of 2×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0038] (3) Growth of the corrosion stop layer: The reaction chamber temperature is set to 720℃±10℃. TMGa, TMIn, and PH3 are introduced into the buffer layer to grow GaInP material with a thickness of 50nm~150nm. SiH4 is used as the N-type dopant with a doping concentration of 2×10⁻⁶. 18 cm -3 ~3×10 18 cm -3 .

[0039] (4) Growth of N-type ohmic contact layer: The reaction chamber temperature is set to 720℃±10℃. TMGa and AsH3 are introduced into the corrosion stop layer to grow GaAs material with a thickness of 50nm~70nm. SiH4 is used as the N-type dopant with a doping concentration of 3×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0040] (5) Growth of electrode protective layer: The reaction chamber temperature is set to 720℃±10℃. TMGa, TMIn, and PH3 are introduced into the N-type ohmic contact layer to grow GaInP material with a thickness of 10nm~50nm. SiH4 is used as the N-type dopant with a doping concentration of 2×10⁻⁶. 18 cm -3 ~3×10 18 cm -3 .

[0041] (6) Growth of roughened layer: The reaction chamber temperature is set to 720℃±10℃. TMAl, TMGa, TMIn, and PH3 are introduced onto the electrode protective layer to grow a (Al) layer with a thickness of 3000nm~3500nm. y1 Ga 1-y1 ) 0.5 In 0.5 P material, where y1 ranges from 0.35 to 0.65, uses SiH4 as the N-type dopant with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 .

[0042] (7) Growth of the first refractive index gradient layer: The reaction chamber temperature is set to 720℃±10℃. TMAl, TMGa, TMIn, and PH3 are introduced into the roughened layer to grow a (Al) layer with a thickness of 50nm~100nm. z1 Ga 1-z1 ) 0.5 In 0.5 The P material has a z1 value ranging from 0.75 to 0.85, and uses SiH4 as the N-type dopant with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the first refractive index gradient layer. The set flow rate of H2 was 3000 sccm to 4000 sccm, and the set flow rate of N2 was 1000 sccm to 2000 sccm.

[0043] (8) Growth of N-type confinement layer: Set the reaction chamber temperature to 720℃±10℃, and introduce TMAl, TMIn, and PH3 onto the first refractive index gradient layer to grow an Al layer with a thickness of 300nm~500nm. 0.5 In 0.5 P-material, using SiH4 as the N-type dopant, with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 .

[0044] (9) Growth of a second refractive index gradient layer: The reaction chamber temperature is set to 700℃±10℃. TMAl, TMGa, TMIn, and PH3 are introduced onto the N-type confinement layer to grow a (Al) layer with a thickness of 20nm~50nm. z2 Ga 1-z2 ) 0.5 In 0.5 For the P material, the z2 value ranges from 0.85 to 0.95, and SiH4 is used as the N-type dopant with a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 17 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the second refractive index gradient layer, with the H2 flow rate set to 1500 sccm to 2000 sccm and the N2 flow rate set to 500 sccm to 1000 sccm.

[0045] (10) Growth of N-side waveguide layer: Set the reaction chamber temperature to 700℃±10℃, and introduce TMAl, TMGa, TMIn, and PH3 onto the second refractive index gradient layer to grow a (Al) waveguide layer with a thickness of 10nm~50nm. y2 Ga 1-y2 ) 0.5 In 0.5 The material is P, where the value of y2 ranges from 0.6 to 0.8, and the N-side waveguide layer is undoped.

[0046] (11) Growth of a multi-quantum-well light-emitting layer: The reaction chamber temperature was set to 700℃±10℃. TMAl, TMGa, TMIn, and PH3 were introduced into the N-side waveguide layer to grow the wells and barriers, which were respectively (Al... x1 Ga 1-x1 ) 0.5 In 0.5 P / (Al x2 Ga 1-x2 ) 0.5 In 0.5The P-type quantum well material has a single-layer well thickness of 3.5 nm to 6.5 nm, where x1 ranges from 0.06 to 0.12, a single-layer barrier thickness of 10 nm to 12 nm, where x2 ranges from 0.6 to 0.8, and a number of period pairs of 8 to 15. The quantum well light-emitting layer is undoped.

[0047] (12) Growth of P-side waveguide layer: The reaction chamber temperature was set to 700℃±10℃. TMAl, TMGa, TMIn, and PH3 were introduced into the multi-quantum-well light-emitting layer to grow a (Al) waveguide layer with a thickness of 80nm~200nm. y3 Ga 1-y3 ) 0.5 In 0.5 P-material, where y3 ranges from 0.6 to 0.8, and the P-side waveguide layer is undoped; (13) Growth of a third refractive index gradient layer: The reaction chamber temperature was set to 720℃±10℃. TMAl, TMGa, TMIn, and PH3 were introduced into the P-side waveguide layer to grow a (Al) layer with a thickness of 20nm~50nm. z3 Ga 1-z3 ) 0.5 In 0.5 For the P-type material, the z3 value ranges from 0.85 to 0.95, and Cp2Mg is used as the P-type dopant with a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 17 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the third refractive index gradient layer. The set flow rate of H2 was 1500 sccm to 2000 sccm, and the set flow rate of N2 was 500 sccm to 1000 sccm.

[0048] (14) Growth of P-type confinement layer: The reaction chamber temperature is set to 720℃±20℃. TMAl, TMIn, and PH3 are introduced into the third refractive index gradient layer to grow Al with a thickness of 450nm~800nm. 0.5 In 0.5 The P-material uses Cp₂Mg as the P-type dopant with a doping concentration of 0.7 × 10⁻⁶. 18 cm -3 ~1×10 18 cm -3 .

[0049] (15) Growth transition layer: Set the reaction chamber temperature to 720℃±10℃, and introduce TMGa, TMAl, TMIn, and PH3 onto the P-type confinement layer to grow a (Al) layer with a thickness of 10nm~20nm. y4 Ga 1-y4 )0.5 In 0.5 P material, using Cp₂Mg as the dopant, with a doping concentration of 2 × 10⁻⁶. 18 cm -3 ~4×10 18 cm -3 The value of y4 ranges from 0.16 to 0.40.

[0050] (16) Growth of GaP nucleation layer with low forward rotation speed ratio: The reaction room temperature was set to 760℃±10℃. TMGa and PH3 were introduced into the transition layer to grow GaP material with a thickness of 30nm~50nm. Cp2Mg was used as the P-type dopant with a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 Meanwhile, during the growth of GaP nucleation layers with a low forward rotation speed ratio, both the graphite disk and the graphite disk are set to rotate counterclockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 3:1.

[0051] (17) Growth of GaP annealing layer with high forward rotation speed ratio: The reaction chamber temperature was set to 790℃±10℃. TMGa and PH3 were introduced into the low forward rotation speed ratio GaP nucleation layer to grow GaP material with a thickness of 200nm~300nm. Cp2Mg was used as the P-type dopant with a doping concentration of 2×10⁻⁶. 18 cm -3 ~4×10 18 cm -3 Meanwhile, during the growth of the GaP annealed layer, both the graphite disk and the graphite disk are set to rotate counterclockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 10:1.

[0052] (18) Growth of a GaP window layer with a high reverse rotation speed ratio: The reaction chamber temperature was set to 690℃±10℃. TMGa and PH3 were introduced into the GaP annealed layer with a high forward rotation speed ratio to grow GaP material with a thickness of 1000nm~2000nm. Cp2Mg was used as the P-type dopant with a doping concentration of 3×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 Meanwhile, during the growth of the GaP window layer with a high reverse rotation speed ratio, the graphite disk is set to rotate counterclockwise while the graphite disk rotates clockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 10:1.

[0053] (19) Take out the wafer: After the growth is completed, reduce the temperature of the MOCVD reaction chamber to less than 110°C, then adjust the pressure to 1000 mbar, open the reaction chamber and take out the epitaxial wafer.

[0054] To further illustrate the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0055] Example 1 An epitaxial wafer for an inverse polarity LED with improved light extraction efficiency is grown in a planetary MOCVD system, specifically including the following steps: (1) MOCVD was pumped to a low pressure of 50 mbar in a pure H2 atmosphere, and the reaction chamber was set to a temperature of 400 °C. Then, the GaAs substrate was transferred to the reaction chamber by a robotic hand transfer chamber, and then the temperature was rapidly increased to 780 °C and held at 780 °C for 6 min.

[0056] (2) Growth of buffer layer: The reaction chamber temperature was set to 720℃. TMGa and AsH3 were introduced into the GaAs substrate to grow a GaAs buffer layer material with a thickness of 200nm. SiH4 was used as the N-type dopant with a doping concentration of 5×10⁻⁶. 18 cm -3 .

[0057] (3) Growth of the corrosion stop layer: The reaction chamber temperature is set to 720℃. TMGa, TMIn, and PH3 are introduced into the buffer layer to grow a GaInP material with a thickness of 150nm. SiH4 is used as the N-type dopant with a doping concentration of 3×10⁻⁶. 18 cm -3 .

[0058] (4) Growth of N-type ohmic contact layer: The reaction chamber temperature was set to 720℃. TMGa and AsH3 were introduced into the corrosion stop layer to grow a GaAs material with a thickness of 70nm. SiH4 was used as the N-type dopant with a doping concentration of 5×10⁻⁶. 18 cm -3 .

[0059] (5) Growth of electrode protective layer: The reaction chamber temperature was set to 720℃. TMGa, TMIn, and PH3 were introduced into the N-type ohmic contact layer to grow a GaInP material with a thickness of 50nm. SiH4 was used as the N-type dopant with a doping concentration of 3×10⁻⁶. 18 cm -3 .

[0060] (6) Growth of roughened layer: The reaction chamber temperature is set to 720℃. TMAl, TMGa, TMIn, and PH3 are introduced onto the electrode protective layer to grow a 3500nm thick (Al) layer. 0.45 Ga 0.55 ) 0.5 In 0.5P-material, using SiH4 as the N-type dopant, with a doping concentration of 1×10⁻⁶. 18 cm -3 .

[0061] (7) Growth of the first refractive index gradient layer: The reaction chamber temperature is set to 720℃. TMAl, TMGa, TMIn, and PH3 are introduced into the roughened layer to grow a 100nm thick (Al) layer. 0.8 Ga 0.2 ) 0.5 In 0.5 P-material, using SiH4 as the N-type dopant, with a doping concentration of 1×10⁻⁶. 18 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the first refractive index gradient layer, with the H2 flow rate set at 3000 sccm and the N2 flow rate set at 1000 sccm.

[0062] (8) Growth of N-type confinement layer: The reaction chamber temperature is set to 720℃. TMAl, TMIn, and PH3 are introduced into the first refractive index gradient layer to grow an Al layer with a thickness of 500 nm. 0.5 In 0.5 P-material, using SiH4 as the N-type dopant, with a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0063] (9) Growth of a second refractive index gradient layer: The reaction chamber temperature is set to 700℃. TMAl, TMGa, TMIn, and PH3 are introduced onto the N-type confinement layer to grow a 20nm thick (Al) layer. 0.9 Ga 0.1 ) 0.5 In 0.5 P-material, using SiH4 as the N-type dopant, with a doping concentration of 2 × 10⁻⁶. 17 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the second refractive index gradient layer, with the H2 flow rate set at 1500 sccm and the N2 flow rate set at 500 sccm.

[0064] (10) Growth of the N-side waveguide layer: The reaction chamber temperature was set to 700℃. TMAl, TMGa, TMIn, and PH3 were introduced into the second refractive index gradient layer to grow a 50nm thick (Al) waveguide layer. 0.7 Ga 0.3 ) 0.5 In 0.5 P material, with the N-side waveguide layer being undoped.

[0065] (11) Growth of a multi-quantum-well light-emitting layer: The reaction chamber temperature is set to 700℃. TMAl, TMGa, TMIn, and PH3 are introduced into the N-side waveguide layer to grow the wells and barriers, which are respectively (Al... 0.09 Ga 0.91 ) 0.5 In 0.5 P / (Al 0.75 Ga 0.25 ) 0.5 In 0.5 The P-type quantum well material has a single-layer well thickness of 3.5 nm to 6.5 nm, a single-layer barrier thickness of 10 nm to 12 nm, 10 pairs of periods, and an undoped quantum well light-emitting layer.

[0066] (12) Growth of P-side waveguide layer: The reaction chamber temperature was set to 700℃. TMAl, TMGa, TMIn, and PH3 were introduced into the multi-quantum-well light-emitting layer to grow a 160nm thick (Al) waveguide layer. 0.7 Ga 0.3 ) 0.5 In 0.5 P-material, with the P-side waveguide layer being undoped; (13) Growth of a third refractive index gradient layer: The reaction chamber temperature was set to 720℃. TMAl, TMGa, TMIn, and PH3 were introduced into the P-side waveguide layer to grow a 50nm thick (Al) layer. 0.9 Ga 0.1 ) 0.5 In 0.5 The P-material uses Cp₂Mg as the P-type dopant with a doping concentration of 2 × 10⁻⁶. 17 cm -3 The back of the graphite disk was purged with a mixture of H2 and N2 gas during the growth of the third refractive index gradient layer, with the H2 flow rate set at 1500 sccm and the N2 flow rate set at 500 sccm.

[0067] (14) Growth of P-type confinement layer: The reaction chamber temperature was set to 720℃, and TMAl, TMIn, and PH3 were introduced into the third refractive index gradient layer to grow an Al layer with a thickness of 600 nm. 0.5 In 0.5 The P-material uses Cp₂Mg as the P-type dopant with a doping concentration of 1×10⁻⁶. 18 cm -3 .

[0068] (15) Growth transition layer: Set the reaction chamber temperature to 720℃, and introduce TMGa, TMAl, TMIn, and PH3 into the P-type confinement layer to grow a 12nm thick Al-Al transition layer. 0.3 Ga 0.7 ) 0.5In 0.5 The P material uses Cp₂Mg as the dopant with a doping concentration of 2.2 × 10⁻⁶. 18 cm -3 .

[0069] (16) Growth of GaP nucleation layer with low forward rotation speed ratio: The reaction room temperature was set to 760℃. TMGa and PH3 were introduced into the transition layer to grow a GaP material with a thickness of 33nm. Cp2Mg was used as the P-type dopant with a doping concentration of 2×10⁻⁶. 18 cm -3 Meanwhile, during the growth of GaP nucleation layers with a low forward rotation speed ratio, both the graphite disk and the graphite disk are set to rotate counterclockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 3:1.

[0070] (17) Growth of GaP annealing layer with high forward rotation speed ratio: The reaction chamber temperature was set to 790℃. TMGa and PH3 were introduced into the GaP nucleation layer with low forward rotation speed ratio to grow a GaP material with a thickness of 300nm. Cp2Mg was used as the P-type dopant with a doping concentration of 3×10⁻⁶. 18 cm -3 Meanwhile, during the growth of the GaP annealed layer, both the graphite disk and the graphite disk are set to rotate counterclockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 10:1.

[0071] (18) Growth of a GaP window layer with a high reverse rotation speed ratio: The reaction chamber temperature was set to 690℃. TMGa and PH3 were introduced into the GaP annealed layer with a high forward rotation speed ratio to grow a GaP material with a thickness of 1200nm. Cp2Mg was used as the P-type dopant with a doping concentration of 5×10⁻⁶. 18 cm -3 Meanwhile, during the growth of the GaP window layer with a high reverse rotation speed ratio, the graphite disk is set to rotate counterclockwise while the graphite disk rotates clockwise, and the ratio of the rotation speed of the graphite disk to that of the graphite disk is 10:1.

[0072] (19) Take out the wafer: After the growth is completed, reduce the temperature of the MOCVD reaction chamber to less than 110°C, then adjust the pressure to 1000 mbar, open the reaction chamber and take out the epitaxial wafer.

[0073] Comparative Example 1 A conventional reverse polarity LED epitaxial wafer, fabricated using conventional methods, is shown in the schematic diagram below. Figure 1 As shown.

[0074] Test case 1. The surfaces of the reverse polarity LED epitaxial wafers obtained in Example 1 and Comparative Example 1 were tested using AFM (Atomic Force Microscopy). The results are as follows: Figure 4 and Figure 5 As shown in the figure. By comparison, it can be seen that the surface roughness (vertical height 0.4nm~14.6nm) of the reverse polarity LED epitaxial wafer obtained in Example 1 of the present invention is significantly smaller than that of the conventional reverse polarity LED epitaxial wafer (vertical height -0.4nm~25.2nm), with higher density and smoother surface, resulting in better specular reflection and effectively improving the light extraction efficiency of the reverse polarity LED.

[0075] 2. The brightness of the reverse polarity LED obtained in Example 1 and the reverse polarity LED obtained in Comparative Example 1 was tested and compared after being powered on at different currents. The results are as follows: Figure 6 As shown, the luminous brightness of the reverse polarity LED obtained in Embodiment 1 of the present invention is significantly improved compared with that of conventional reverse polarity LEDs, and the luminous efficiency is significantly improved.

[0076] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A reverse polarity LED epitaxial wafer with improved light extraction efficiency, characterized in that, The reverse polarity LED epitaxial wafer comprises, from bottom to top, a GaAs substrate, a buffer layer, an etching stop layer, an N-type ohmic contact layer, an electrode protection layer, a roughening layer, a first refractive index gradient layer, an N-type confinement layer, a second refractive index gradient layer, an N-side waveguide layer, a multi-quantum-well light-emitting layer, a P-side waveguide layer, a third refractive index gradient layer, a P-type confinement layer, a transition layer, and a high-smoothness GaP mirror layer. The high-smoothness GaP mirror layer consists of a low forward rotation speed ratio GaP nucleation layer, a high forward rotation speed ratio GaP annealing layer, and a high reverse rotation speed ratio GaP window layer from bottom to top.

2. The reverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 1, characterized in that, The material of the first refractive index gradual layer is (Al) z1 Ga 1-z1 ) 0.5 In 0.5 P, with a thickness of 50nm–100nm and a doping concentration of 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The value of z1 ranges from 0.75 to 0.85; the material of the second refractive index gradient layer is (Al). z2 Ga 1-z2 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 17 cm -3 The value of z2 ranges from 0.85 to 0.95; the material of the third refractive index gradient layer is (Al). z3 Ga 1-z3 ) 0.5 In 0.5 P, with a thickness of 20nm–50nm and a doping concentration of 1×10⁻⁶. 17 cm -3 ~2×10 17 cm -3 The value of z3 ranges from 0.85 to 0.

95.

3. The reverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 1, characterized in that, The thickness of the low forward rotation speed ratio GaP nucleation layer is 30nm–50nm, and the doping concentration is 1×10⁻⁶. 18 cm -3 ~2×10 18 cm -3 The thickness of the GaP annealed layer with high forward rotation speed ratio is 200nm–300nm, and the doping concentration is 2×10⁻⁶. 18 cm -3 ~4×10 18 cm -3 The thickness of the GaP window layer with high reverse rotation speed ratio is 1000nm–2000nm, and the doping concentration is 3×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

4. A method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to any one of claims 1 to 3, characterized in that, Using an MOCVD apparatus, the following layers are grown sequentially from bottom to top on a GaAs substrate: buffer layer, etching stop layer, N-type ohmic contact layer, electrode protection layer, roughening layer, first refractive index gradient layer, N-type confinement layer, second refractive index gradient layer, N-side waveguide layer, multi-quantum well light-emitting layer, P-side waveguide layer, third refractive index gradient layer, P-type confinement layer, transition layer, low forward rotation speed ratio GaP nucleation layer, high forward rotation speed ratio GaP annealing layer, and high reverse rotation speed ratio GaP window layer. The materials of the first, second, and third refractive index gradual layer were all epitaxially grown using a method of blowing H2 / N2 mixed gas onto the back of the bottom graphite disk.

5. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the first refractive index gradual-varying layer are as follows: The reaction chamber temperature is set to 720℃±10℃. TMAl, TMGa, TMIn, and PH3 are introduced into the roughened layer to grow (Al... z1 Ga 1-z1 ) 0.5 In 0.5 The P material uses SiH4 as the N-type dopant, and the back of the graphite disk is purged with a mixture of H2 and N2 gas during the growth of the first refractive index gradient layer. The set flow rate of H2 is 3000 sccm to 4000 sccm, and the set flow rate of N2 is 1000 sccm to 2000 sccm.

6. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the second refractive index gradual-varying layer are as follows: The reaction chamber temperature is set to 700℃±10℃. TMAl, TMGa, TMIn, and PH3 are introduced onto the N-type confinement layer to grow (Al... z2 Ga 1-z2 ) 0.5 In 0.5 The P material uses SiH4 as the N-type dopant, and the back of the graphite disk is purged with a mixture of H2 and N2 gas during the growth of the second refractive index gradient layer. The set flow rate of H2 is 1500 sccm to 2000 sccm, and the set flow rate of N2 is 500 sccm to 1000 sccm.

7. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the third refractive index gradient layer are as follows: The reaction chamber temperature is set to 720℃±10℃. On the P-side waveguide layer, TMAl, TMGa, TMIn, and PH3 are introduced to grow (Al... z3 Ga 1-z3 ) 0.5 In 0.5 The P-material uses Cp2Mg as the P-type dopant, and the back of the graphite disk is purged with a H2 / N2 mixed gas during the growth of the third refractive index gradient layer. The set flow rate of H2 is 1500 sccm to 2000 sccm, and the set flow rate of N2 is 500 sccm to 1000 sccm.

8. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the low forward rotation speed ratio GaP nucleation layer are as follows: the reaction chamber temperature is set to 760℃±10℃, TMGa and PH3 are introduced into the transition layer to grow GaP material, Cp2Mg is used as the P-type dopant, and the graphite disks and graphite large disks are set to rotate counterclockwise during the growth of the low forward rotation speed ratio GaP nucleation layer, and the ratio of the rotation speed of the graphite disk to the rotation speed of the graphite large disk is 3:

1.

9. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the high forward rotation speed ratio GaP annealing layer are as follows: the reaction chamber temperature is set to 790℃±10℃, TMGa and PH3 are introduced into the low forward rotation speed ratio GaP nucleation layer to grow GaP material, Cp2Mg is used as the P-type dopant, and the graphite small disk and the graphite large disk are set to rotate counterclockwise during the growth of the high forward rotation speed ratio GaP annealing layer, and the ratio of the rotation speed of the graphite small disk to the rotation speed of the graphite large disk is 10:

1.

10. The method for preparing an inverse polarity LED epitaxial wafer with improved light extraction efficiency according to claim 4, characterized in that, The growth steps of the high reverse rotation speed ratio GaP window layer are as follows: the reaction chamber temperature is set to 690℃±10℃, TMGa and PH3 are introduced into the high forward rotation speed ratio GaP annealed layer to grow GaP material, Cp2Mg is used as the P-type dopant, and the graphite small disk rotates counterclockwise while the graphite large disk rotates clockwise during the growth of the high reverse rotation speed ratio GaP window layer, and the ratio of the rotation speed of the graphite small disk to the rotation speed of the graphite large disk is 10:1.

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