A quaternary yellow-green LED epitaxial wafer and a preparation method thereof

Abstract

The present invention relates to the field of LED technology, and specifically to a quaternary yellow-green LED epitaxial wafer and a preparation method thereof. The quaternary yellow-green LED epitaxial wafer includes, from bottom to top, a GaAs substrate, a GaAs buffer layer, an N-type gradient doped waveguide layer, a single quantum well active layer, a P-type gradient doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer. The present invention adopts the design of an N / P-type gradient doped waveguide layer combined with a single quantum well active layer, a P-type self-absorption layer, and a P-type GaP / GaAsP periodic current expansion layer, and adopts MOCVD technology for growth. The obtained low-brightness, high-reliability quaternary yellow-green LED epitaxial wafer structure has the characteristics of high antistatic performance, excellent aging performance, good surface flatness and uniformity, and low production cost and raw material cost, etc. It is used to replace the binary and ternary LEDs grown by LPE technology, and has better reliability and application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of LEDs, and in particular to a quaternary yellow-green LED epitaxial wafer and a preparation method thereof. Background Art

[0002] LED has the advantages of wide adjustable wavelength range, high luminous efficiency, low energy consumption, long life, small size and strong designability. It is widely used in digital product display, indoor high-resolution display, mobile phone backlight, household lamps and other scenes. At present, the low-brightness yellow-green LED chips on the market use binary and ternary growth materials. Their brightness is much lower than that of quaternary chips, and their reliability is extremely high. The application range of low-brightness LED is very wide, and there is a large market demand in optoelectronic communication device indicator lights, mobile phone / tablet breathing lights, small household appliance display lights, etc. However, the raw materials and material costs of producing binary and ternary yellow-green LED chips are relatively high. The production process generally uses liquid phase epitaxy (LPE), the process is relatively complicated, and the epitaxy uniformity and flatness are poor. The labor cost and production time are higher than those of quaternary chips. Therefore, it is of great significance to develop quaternary low-brightness, high-reliability yellow-green LED epitaxial wafers to replace binary and ternary LEDs.

[0003] At present, the conventional binary and ternary yellow-green LED epitaxial wafer structures are as follows Figure 1 As shown, the LPE epitaxial technology is used to grow the N-type GaP electron layer 101 and the P-type GaP hole layer 102 from bottom to top on the N-type GaP substrate 100. However, the conventional two- and three-element yellow-green LED epitaxial wafers adopt the liquid phase epitaxy LPE growth technology. The uniformity of the grown epitaxial material is poor, and the thickness control is uneven, which easily leads to poor crystal flatness of the grown epitaxial wafer, seriously affecting the reliability and stability of the LED chip during use. At the same time, its overall production cost is high, the product yield is low, and it is not suitable for large-scale production. The structure of the conventional four-element yellow-green LED epitaxial wafer is as follows Figure 2 As shown, the GaAs buffer layer 201, the N-type confinement layer 202, the multi-quantum well active layer 203, the P-type confinement layer 204, the P-type transition layer 205, and the P-type window layer 206 are grown sequentially from bottom to top on the N-type GaAs substrate 200 using MOCVD technology. Although the existing quaternary yellow-green LED epitaxial wafer is grown using metal organic vapor phase epitaxy (MOCVD), the corresponding PN junction is a heterojunction device, and the quantum well structure is generally used for light emission, but it is constrained by the influence of the material system, and the lowest luminous efficiency is much higher than that of the two- and three-series LEDs, and the antistatic ability is also much weaker than that of the two- and three-series LED chips with homojunctions. Therefore, if the quaternary system is to replace the two- and three-series LEDs, how to reduce the brightness and improve the antistatic performance is a key difficulty that needs to be overcome. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a quaternary yellow-green LED epitaxial wafer and a preparation method thereof. The quaternary yellow-green LED epitaxial wafer is grown using MOCVD technology, has low brightness and high reliability, and can be used to replace binary and ternary LEDs grown using the original LPE technology. The epitaxial wafer structure has good surface flatness and uniformity, and has low production and raw material costs, and has better reliability and application prospects.

[0005] The first object of the present invention is to provide a quaternary yellow-green LED epitaxial wafer, which comprises, from bottom to top, a GaAs substrate, a GaAs buffer layer, an N-type gradient doped waveguide layer, a single quantum well active layer, a P-type gradient doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer;

[0006] The materials of the N-type gradually doped waveguide layer and the P-type gradually doped waveguide layer are (Al x1 Ga 1-x1 ) 0.5 In 0.5 P, and all of them are graded doping structures, where the value of x1 ranges from 0.7 to 0.8;

[0007] The material of the single quantum well active layer is (Al y1 Ga 1-y1 ) 0.5 In 0.5 P, where the value range of y1 is 0.2~0.3.

[0008] The present invention proposes a single heterojunction wide-well luminous region design, selects AlGaInP material as a single junction luminous layer, and grows a high-bandgap gradient doped waveguide layer on both sides of the luminous region. By means of the principle of impurity element diffusion, the non-radiative recombination in the impurity energy level is enhanced by intentional doping, thereby reducing the radiative recombination luminous efficiency and achieving the purpose of reducing brightness; at the same time, in conjunction with the single heterojunction wide-well luminous layer, the space charge region width of the PN junction can be reduced to the maximum extent, greatly improving the antistatic ability of the LED chip. In addition, in addition to adopting the N / P type gradient doped waveguide layer combined with the single quantum well active layer in the quaternary LED epitaxial wafer structure, the present invention also adopts the design of a P type self-absorption layer and a P type periodic current expansion layer, which can obtain a high-reliability quaternary yellow-green light LED with low brightness and adjustable brightness, and its photoelectric performance can completely replace the original two- and three-element LEDs, improve the crystal quality and flatness of the epitaxial wafer, and greatly reduce the production cost, increase the production capacity, and have better reliability and application prospects.

[0009] Furthermore, the thickness of the N-type gradient doped waveguide layer is 200nm-400nm, the N-type dopant is SiH4, and the gradient of the gradient doping structure is as follows: the initial growth doping concentration is 5×1017 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 , and the rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

[0010] Furthermore, the thickness of the P-type gradient doped waveguide layer is 200nm-400nm, the P-type dopant is Cp2Mg (cyclopentadienyl magnesium), and the gradient of the gradient doping structure is as follows: the initial growth doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then the layer growth begins in a gradual manner until the end, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and the rate of gradual increase of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s. The present invention designs a waveguide layer structure with gradual doping on both sides of the light-emitting region, which can not only enhance the non-radiative recombination in the impurity energy level by intentional doping based on the principle of impurity element diffusion, thereby reducing the radiative recombination luminescence efficiency and achieving the purpose of reducing brightness, but also avoid the decrease in crystal quality caused by excessive bulk material doping, thereby improving the crystal quality.

[0011] Furthermore, the single quantum well active layer has a thickness of 60 nm to 80 nm and is non-doped.

[0012] Furthermore, the material of the P-type self-absorption layer is GaAs, the thickness is 5nm to 10nm, and the doping concentration is 0.5×10 18 cm -3 ~1×10 18 cm -3The P-type dopant used is Cp2Mg. Since GaAs has a narrow bandgap, it has an absorption effect in the visible light band. In this technical solution, by inserting a thin GaAs self-absorption layer into the P-type layer that emits light from the front, most of the light sources facing upward can be absorbed, and only the local large-angle and side-emitting photons are emitted to the outside. The purpose of adjusting the filter intensity can also be achieved by controlling the thickness of the GaAs self-absorption layer.

[0013] Furthermore, the P-type periodic current spreading layer is a periodic structure of 15 to 20 pairs of GaP / GaAsP alternating growth cycles, wherein the thickness of GaP in each pair of periodic structures is 400 nm to 600 nm, and the doping concentration is 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg; the thickness of GaAsP in each pair of periodic structures is 50nm~100nm, and the doping concentration is 1×10 18 cm -3 ~3×10 18 cm -3 , and the P-type dopant used is Cp2Mg. In this technical solution, a small amount of As is incorporated into GaP to form a GaAsP wide lattice material, which not only increases the lattice appropriately but also has a higher mobility, which can effectively improve the antistatic and anti-aging properties of the chip; periodic growth can ensure that in a current expansion layer material of sufficient thickness, the lattice size will not deviate too much from the substrate, the mismatch at the lattice interface is smaller, and it is not easy to introduce more deep energy level recombination, so that it is not easy to have problems such as brightness attenuation during long-term lighting, and the reliability is good.

[0014] The second purpose of the present invention is to provide a method for preparing a quaternary yellow-green LED epitaxial wafer, using MOCVD equipment to sequentially grow a GaAs buffer layer, an N-type gradient doped waveguide layer, a single quantum well active layer, a P-type gradient doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer on a GaAs substrate; the P-type periodic current expansion layer is a periodic structure with a cycle number of 15 to 20 pairs of GaP / GaAsP alternately grown. The present invention adopts MOCVD equipment and growth technology to grow a low-brightness, high-reliability quaternary yellow-green LED epitaxial wafer on a GaAs substrate, which is used to replace the existing binary and ternary LEDs, which can greatly reduce production costs and raw material costs, and improve production capacity. The epitaxial material grown by MOCVD technology has high crystal quality, good uniformity and crystal flatness, and has higher reliability and stability than binary and ternary LEDs.

[0015] Furthermore, the growth step of the N-type gradient doped waveguide layer is as follows: setting the temperature of the reaction chamber to 700°C ± 20°C, introducing TMAl, TMGa, TMIn, and PH3 on the GaAs buffer layer, and growing (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the N-type dopant is SiH4, and the initial doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 The rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s; the P-type gradient doped waveguide layer growth step is: set the reaction chamber temperature to 730 ℃ ± 20 ℃, introduce TMAl, TMGa, TMIn, PH3 into the single quantum well active layer, and grow (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the P-type dopant is Cp2Mg, and the initial doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then, the doping concentration gradually increases from the initial doping concentration until the end of the layer growth, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 The doping concentration gradually increases at a rate of 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

[0016] Furthermore, the growth step of the P-type self-absorption layer is as follows: setting the temperature of the reaction chamber to 730°C ± 20°C, introducing TMGa and AsH3 into the P-type graded doped waveguide layer, and growing GaAs material, wherein the doping concentration is 0.5×10 18 cm-3 ~1×10 18 cm -3 , the P-type dopant is Cp2Mg.

[0017] Furthermore, the growth step of the P-type periodic current spreading layer is as follows: setting the temperature of the reaction chamber to 800°C ± 20°C, introducing TMGa and PH3 into the P-type graded doped waveguide layer, and first growing a layer of GaP material, wherein the doping concentration of GaP is 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg, and then AsH3 is introduced to grow a layer of GaAsP material. The set flow rate of AsH3 is 20sccm~50sccm, and the doping concentration of GaAsP is 1×10 18 cm -3 ~3×10 18 cm -3 The P-type dopant used is Cp2Mg, and GaP / GaAsP is grown in a repeated cycle.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention adopts a single heterojunction wide-well light-emitting area design, and designs a gradient doped waveguide layer structure on both sides of the light-emitting area. By means of the principle of impurity element diffusion, the non-radiative recombination in the impurity energy level can be enhanced by intentional doping, thereby reducing the radiative recombination luminescence efficiency and achieving the purpose of reducing brightness. At the same time, in conjunction with the single heterojunction wide-well light-emitting layer, the space charge region width of the PN junction can be reduced to the maximum extent, greatly improving the antistatic ability of the LED chip.

[0020] 2. The present invention grows a P-type GaAs self-absorption layer on one side of the P-type light-emitting region of the conventional quaternary yellow-green light LED epitaxial structure. By controlling the thickness of the GaAs self-absorption layer, the purpose of adjusting the filter intensity can be achieved, thereby realizing the low-brightness quaternary LED epitaxial structure design.

[0021] 3. The present invention adjusts the P-type GaP window layer material to a periodic current spreading layer structure of alternating growth of GaP / GaAsP, and forms a GaAsP wide lattice material by incorporating a small amount of As into GaP. Not only is the lattice appropriately enlarged but also has a higher mobility, the antistatic performance of the chip is further effectively improved; at the same time, the periodic growth of the material can ensure that the lattice size in the current spreading layer material of sufficient thickness does not deviate too much from the substrate, the mismatch at the lattice interface is smaller, and it is not easy to introduce more deep energy level recombination, so that problems such as brightness attenuation are not likely to occur during long-term lighting, and the reliability is good.

[0022] 4. The present invention adopts MOCVD technology to grow low-brightness, high-reliability four-element yellow-green LED to replace the binary and ternary LEDs grown by the original LPE technology. The scheme adopts the design of N / P type gradient doped waveguide layer combined with single quantum well active layer, P type self-absorption layer, and P type GaP / GaAsP periodic current expansion layer. The obtained epitaxial wafer structure has high antistatic performance, excellent aging performance, good surface flatness and uniformity, and low production cost and raw material cost, and has better reliability and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of conventional binary and ternary yellow-green LED epitaxial wafers;

[0024] Figure 2 This is a schematic diagram of the structure of a conventional four-element yellow-green LED epitaxial wafer;

[0025] Figure 3 This is a schematic diagram of the structure of a quaternary yellow-green LED epitaxial wafer of the present invention;

[0026] Figure 4 The surface morphology of the quaternary yellow-green LED epitaxial wafer of the present invention is photographed; (a) is a high-magnification optical microscopic observation of the LED, and (b) is a SEM image of the LED;

[0027] Figure 5 These are photos of the surface morphology of conventional binary and ternary LED epitaxial wafers; (a) is a high-magnification optical microscopic observation of the LED, and (b) is a SEM image of the LED.

[0028] Explanation of the numbers in the schematic diagram:

[0029] 100, GaP substrate; 101, N-type GaP electron layer; 102, P-type GaP hole layer; 200, GaAs substrate; 201, GaAs buffer layer; 202, N-type confinement layer; 203, multi-quantum well active layer; 204, P-type confinement layer; 205, P-type transition layer; 206, P-type window layer; 207, N-type gradient doped waveguide layer; 208, single quantum well active layer; 209, P-type gradient doped waveguide layer; 210, P-type self-absorption layer; 211, P-type periodic current spreading layer. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] In the description of the present application, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present application.

[0032] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0033] See also Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the form, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0034] A four-element yellow-green LED epitaxial wafer is provided in one embodiment of the present invention, and its structural schematic diagram is shown as follows: Figure 3 As shown, from bottom to top, it includes a GaAs substrate 200, a GaAs buffer layer 201, an N-type gradient doped waveguide layer 207, a single quantum well active layer 208, a P-type gradient doped waveguide layer 209, a P-type self-absorption layer 210, a P-type transition layer 205, and a P-type periodic current expansion layer 211.

[0035] In some embodiments, the N-type graded doped waveguide layer material is (Al x1 Ga 1-x1 ) 0.5 In 0.5The value range of P,x1 is 0.7~0.8, the thickness is 200nm~400nm, and the N-type dopant is SiH4. x1 Ga 1-x1 ) 0.5 In 0.5 The initial growth doping concentration of P is 5×10 17 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 , and the rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

[0036] In some embodiments, the material of the single quantum well active layer is (Al y1 Ga 1-y1 ) 0.5 In 0.5 P, where y1 ranges from 0.2 to 0.3, the thickness is 60nm to 80nm, and it is non-doped.

[0037] In some embodiments, the P-type graded doped waveguide layer material is (Al x1 Ga 1-x1 ) 0.5 In 0.5 The value range of P,x1 is 0.7~0.8, the thickness is 200nm~400nm, and the P-type dopant is Cp2Mg. x1 Ga 1-x1 ) 0.5 In 0.5 The initial growth doping concentration of P is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then the layer growth begins in a gradual manner until the end, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and the rate of gradual increase of doping concentration is 0.01×10 17 cm -3 / s~0.02×1017 cm -3 / s. The above structure uses a single-junction light-emitting layer of AlGaInP material, and grows a high-bandgap gradient doped waveguide layer on both sides, which can reduce the radiation recombination luminescence efficiency and achieve the purpose of reducing brightness; at the same time, with a single heterojunction wide-well light-emitting layer, the width of the space charge region of the PN junction can be reduced to the maximum extent, greatly improving the antistatic ability of the LED chip. The gradient waveguide layer design can avoid the degradation of crystal quality caused by excessive bulk material doping.

[0038] In some embodiments, the material of the P-type self-absorption layer is GaAs, the thickness is 5nm to 10nm, and the doping concentration is 0.5×10 18 cm -3 ~1×10 18 cm -3 The P-type dopant used is Cp2Mg. A P-type GaAs self-absorption layer is grown on one side of the P-type light-emitting region. By controlling the thickness of the GaAs self-absorption layer, the filter intensity can be adjusted, thereby realizing the low-brightness quaternary LED epitaxial structure design.

[0039] In some embodiments, the P-type periodic current spreading layer is a periodic structure of 15 to 20 pairs of GaP / GaAsP alternately grown cycles, wherein the thickness of GaP in each pair of periodic structures is 400 nm to 600 nm, and the doping concentration is 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg; the thickness of GaAsP in each pair of periodic structures is 50nm~100nm, and the doping concentration is 1×10 18 cm -3 ~3×10 18 cm -3 , and the P-type dopant used is Cp2Mg. Using a periodic current expansion layer grown alternately with GaP / GaAsP to replace the P-type GaP window layer can increase the lattice and have a higher mobility, effectively improving the anti-static and anti-aging properties of the chip; the material is grown periodically to ensure that in a current expansion layer material of sufficient thickness, the lattice size will not deviate too much from the substrate, the mismatch at the lattice interface is smaller, and it is not easy to introduce more deep energy level recombination, so that it is not easy to have problems such as brightness attenuation during long-term lighting, and the reliability is good.

[0040] In another embodiment, the present invention also provides a method for preparing a quaternary yellow-green LED epitaxial wafer, using MOCVD equipment to sequentially grow a GaAs buffer layer, an N-type gradient doped waveguide layer, a single quantum well active layer, a P-type gradient doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer on a GaAs substrate. Specifically, the method comprises the following steps:

[0041] (1) The MOCVD was evacuated to 50 mbar in a pure H2 atmosphere, and the reaction chamber temperature was set to 400°C. The GaAs substrate was then transferred to the reaction chamber through a robot transfer bin, and then the temperature was rapidly raised to 750°C and maintained at 750°C for 10 min.

[0042] (2) Growth of GaAs buffer layer: The reaction chamber temperature was set to 700±20℃, TMGa and AsH3 were introduced, and GaAs buffer layer material with a thickness of 200nm to 300nm was grown. SiH4 was used as the N-type dopant with a doping concentration of 3×10 18 cm -3 ~5×10 18 cm -3 .

[0043] (3) Growth of N-type graded doped waveguide layer: Set the reaction chamber temperature to 700℃±20℃, introduce TMAl, TMGa, TMIn, and PH3 onto the GaAs buffer layer, and grow (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the N-type dopant is SiH4, and the initial doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 The rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

[0044] (4) Growth of single quantum well active layer: Set the temperature of the reaction chamber to 700℃±20℃, introduce TMAl, TMGa, TMIn, and PH3 into the N-type graded doped waveguide layer, and grow (Al) with a thickness of 60nm to 80nm.y1 Ga 1-y1 ) 0.5 In 0.5 P material, the value range of y1 is 0.2~0.3, and this layer is undoped.

[0045] (5) Growth of P-type graded doped waveguide layer: Set the temperature of the reaction chamber to 730℃±20℃, introduce TMAl, TMGa, TMIn, and PH3 into the single quantum well active layer, and grow (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the P-type dopant is Cp2Mg, and the initial doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then, the doping concentration gradually increases from the initial doping concentration until the end of the layer growth, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 The doping concentration gradually increases at a rate of 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

[0046] (6) Growth of P-type self-absorption layer: Set the temperature of the reaction chamber to 730℃±20℃, introduce TMGa and AsH3 into the P-type graded doped waveguide layer, and grow GaAs material with a thickness of 5nm to 10nm. The doping concentration is 0.5×10 18 cm -3 ~1×10 18 cm -3 The P-type dopant used in this layer is Cp2Mg.

[0047] (7) Growth of P-type transition layer: Set the temperature of the reaction chamber to 730℃±20℃, introduce TMGa, TMAl, TMIn, and PH3 into the P-type self-absorption layer, and grow (Al) with a thickness of 10nm to 20nm. x2 Ga 1-x2 ) 0.5 In 0.5 P material, dopant is Cp2Mg, doping concentration is 1×10 18 cm -3 ~2×10 18 cm -3 , the value range of x2 is 0.3~0.4.

[0048] (8) Growth of P-type periodic current spreading layer: The reaction chamber temperature was set to 800±20℃, TMGa and PH3 were introduced into the P-type graded doped waveguide layer, and GaP material with a thickness of 400nm to 600nm was grown. The doping concentration of GaP was 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg, and then AsH3 is introduced to grow GaAsP material with a thickness of 50nm to 100nm. The set flow rate of AsH3 is 20sccm to 50sccm, and the doping concentration of GaAsP is 1×10 18 cm -3 ~3×10 18 cm -3 The P-type dopant used is Cp2Mg. The above-mentioned GaP and GaAsP growth combination forms the first pair of P-type current spreading layers, and then repeats the cycle to grow 14 to 19 pairs of GaP / GaAsP structures.

[0049] (9) Taking out the wafer: After the growth is completed, the temperature of the MOCVD reaction chamber is lowered to 110°C, and then the pressure is adjusted to 1000 mbar, the reaction chamber is opened, and the epitaxial wafer is taken out.

[0050] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with specific embodiments.

[0051] Example 1

[0052] A method for preparing a quaternary yellow-green LED epitaxial wafer specifically comprises the following steps:

[0053] (1) The MOCVD was evacuated to 50 mbar in a pure H2 atmosphere, and the reaction chamber temperature was set to 400°C. The GaAs substrate was then transferred to the reaction chamber through a robot transfer bin, and then the temperature was rapidly raised to 750°C and maintained at 750°C for 10 min.

[0054] (2) Growth of GaAs buffer layer: The reaction chamber temperature was set to 720°C, TMGa and AsH3 were introduced, and a GaAs buffer layer material with a thickness of 300 nm was grown. SiH4 was used as an N-type dopant with a doping concentration of 5×10 18 cm -3 .

[0055] (3) Growth of N-type graded doped waveguide layer: Set the temperature of the reaction chamber to 720°C, introduce TMAl, TMGa, TMIn, and PH3 onto the GaAs buffer layer, and grow (Al 0.7 Ga 0.3 ) 0.5 In0.5 P material, N-type dopant is SiH4, and the initial doping concentration is 10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.5×10 17 cm -3 The rate of gradual decrease of doping concentration is 0.02×10 17 cm -3 / s.

[0056] (4) Growth of single quantum well active layer: Set the temperature of the reaction chamber to 700°C, introduce TMAl, TMGa, TMIn, and PH3 into the N-type graded doped waveguide layer, and grow a 60nm thick (Al 0.3 Ga 0.7 ) 0.5 In 0.5 P material, this layer is undoped.

[0057] (5) Growth of P-type graded doped waveguide layer: Set the temperature of the reaction chamber to 750°C, introduce TMAl, TMGa, TMIn, and PH3 into the single quantum well active layer, and grow (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P material, P-type dopant is Cp2Mg, and the initial doping concentration is 0.25×10 17 cm -3 Then, the doping concentration gradually increases from the initial doping concentration until the end of the layer growth, and the final doping concentration is 10×10 17 cm -3 The doping concentration gradually increases at a rate of 0.02×10 17 cm -3 / s.

[0058] (6) Growth of P-type self-absorption layer: The reaction chamber temperature is set to 750°C, TMGa and AsH3 are introduced into the P-type graded doped waveguide layer to grow GaAs material with a thickness of 5 nm. The doping concentration is 1×10 18 cm -3 The P-type dopant used in this layer is Cp2Mg.

[0059] (7) Growth of P-type transition layer: Set the temperature of the reaction chamber to 750°C, introduce TMGa, TMAl, TMIn, and PH3 into the P-type self-absorption layer, and grow (Al) with a thickness of 10 nm. 0.35 Ga 0.65 ) 0.5 In 0.5P material, dopant is Cp2Mg, doping concentration is 2×10 18 cm -3 .

[0060] (8) Growth of P-type periodic current spreading layer: The reaction chamber temperature was set to 810°C, TMGa and PH3 were introduced into the P-type graded doped waveguide layer, and GaP material with a thickness of 500 nm was grown. The doping concentration of GaP was 3×10 18 cm -3 The P-type dopant used was Cp2Mg, and then AsH3 was introduced to grow GaAsP material with a thickness of 50nm. The set flow rate of AsH3 was 30sccm, and the doping concentration of GaAsP was 3×10 18 cm -3 The P-type dopant used is Cp2Mg. The above-mentioned GaP and GaAsP growth combination forms a first pair of P-type current spreading layers, and then the cycle growth 15 is repeated to form the GaP / GaAsP structure.

[0061] (9) Taking out the wafer: After the growth is completed, the temperature of the MOCVD reaction chamber is lowered to 110°C, and then the pressure is adjusted to 1000 mbar, the reaction chamber is opened, and the epitaxial wafer is taken out.

[0062] Comparative Example 1

[0063] A conventional two-element or three-element LED epitaxial wafer is prepared by conventional methods, and its structural schematic diagram is shown as follows: Figure 1 shown.

[0064] Test example

[0065] The quaternary yellow-green LED epitaxial wafer obtained in Example 1 and the conventional binary and ternary LED epitaxial wafers obtained in Comparative Example 1 were observed using a high-power optical microscope and a scanning electron microscope (SEM), respectively. The results are as follows: Figures 4 to 5 As shown, (a) is a high-magnification optical microscopic observation of LED (magnified 50 times), and (b) is a SEM image of LED (magnified 10,000 times). Figure 4 and Figure 5 It can be seen that the LED epitaxial wafer prepared by the present invention has a smooth and clear appearance and a complete crystal growth quality; while the conventional binary and ternary structure LED epitaxial wafers have poor crystal flatness and obvious lattice defects.

[0066] In summary, the present invention adopts the design of N / P type gradient doped waveguide layer combined with single quantum well active layer, P type self-absorption layer, P type GaP / GaAsP periodic current expansion layer, and uses MOCVD technology for growth. The obtained low brightness, high reliability quaternary yellow-green LED epitaxial wafer structure has the characteristics of high antistatic performance, excellent aging performance, good surface flatness and uniformity, and low production cost and raw material cost. It is used to replace the binary and ternary LEDs grown by the original LPE technology, and has better reliability and application prospects.

[0067] Finally, it should be emphasized that the above 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 may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A quaternary yellow-green LED epitaxial wafer, characterized in that: The quaternary yellow-green LED epitaxial wafer includes, from bottom to top, a GaAs substrate, a GaAs buffer layer, an N-type gradient doped waveguide layer, a single quantum well active layer, a P-type gradient doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer; The materials of the N-type gradually doped waveguide layer and the P-type gradually doped waveguide layer are (Al x1 Ga 1-x1 ) 0.5 In 0.5 P, and all of them are graded doping structures, where the value of x1 ranges from 0.7 to 0.8; The material of the single quantum well active layer is (Al y1 Ga 1-y1 ) 0.5 In 0.5 P, where the value range of y1 is 0.2 to 0.3; The thickness of the N-type gradient doped waveguide layer is 200nm-400nm, the N-type dopant is SiH4, and the gradient of the gradient doping structure is as follows: the initial growth doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 , and the rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s; The thickness of the P-type gradient doped waveguide layer is 200nm-400nm, the P-type dopant is Cp2Mg, and the gradient of the gradient doping structure is as follows: the initial growth doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then the layer growth begins in a gradual manner until the end, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and the rate of gradual increase of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

2. A quaternary yellow-green LED epitaxial wafer according to claim 1, characterized in that: The thickness of the single quantum well active layer is 60nm-80nm and is non-doped.

3. The quaternary yellow-green LED epitaxial wafer according to claim 1, characterized in that: The material of the P-type self-absorption layer is GaAs, with a thickness of 5nm to 10nm and a doping concentration of 0.5×10 18 cm -3 ~1×10 18 cm -3 , the P-type dopant used is Cp2Mg.

4. The quaternary yellow-green LED epitaxial wafer according to claim 1, characterized in that: The P-type periodic current spreading layer is a periodic structure with 15 to 20 pairs of GaP / GaAsP alternately grown cycles, wherein the thickness of GaP in each pair of periodic structures is 400 nm to 600 nm, and the doping concentration is 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg; the thickness of GaAsP in each pair of periodic structures is 50nm~100nm, and the doping concentration is 1×10 18 cm -3 ~3×10 18 cm -3 , the P-type dopant used is Cp2Mg.

5. A method for preparing a quaternary yellow-green LED epitaxial wafer according to any one of claims 1 to 4, characterized in that: A GaAs buffer layer, an N-type gradually doped waveguide layer, a single quantum well active layer, a P-type gradually doped waveguide layer, a P-type self-absorption layer, a P-type transition layer, and a P-type periodic current expansion layer are sequentially grown on a GaAs substrate by using MOCVD equipment; the P-type periodic current expansion layer is a periodic structure with 15 to 20 pairs of cycle pairs of alternately grown GaP / GaAsP.

6. The method for preparing a quaternary yellow-green LED epitaxial wafer according to claim 5, characterized in that: The growth steps of the N-type gradient doped waveguide layer are as follows: setting the temperature of the reaction chamber to 700°C ± 20°C, introducing TMAl, TMGa, TMIn, and PH3 on the GaAs buffer layer, and growing (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the N-type dopant is SiH4, and the initial doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 , and keep this doping concentration to grow for 100nm, and then start to gradually decrease until the growth of this layer ends, and the final doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 The rate of gradual decrease of doping concentration is 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s; the P-type gradient doped waveguide layer growth step is: set the reaction chamber temperature to 730 ℃ ± 20 ℃, introduce TMAl, TMGa, TMIn, PH3 into the single quantum well active layer, and grow (Al x1 Ga 1-x1 ) 0.5 In 0.5 P material, where the value of x1 ranges from 0.7 to 0.8, the P-type dopant is Cp2Mg, and the initial doping concentration is 0.25×10 17 cm -3 ~0.5×10 17 cm -3 Then, the doping concentration gradually increases from the initial doping concentration until the end of the layer growth, and the final doping concentration is 5×10 17 cm -3 ~10×10 17 cm -3 The doping concentration gradually increases at a rate of 0.01×10 17 cm -3 / s~0.02×10 17 cm -3 / s.

7. The method for preparing a quaternary yellow-green LED epitaxial wafer according to claim 5, characterized in that: The growth steps of the P-type self-absorption layer are as follows: setting the temperature of the reaction chamber to 730°C ± 20°C, introducing TMGa and AsH3 into the P-type gradient doped waveguide layer, and growing GaAs material, wherein the doping concentration is 0.5×10 18 cm -3 ~1×10 18 cm -3 , the P-type dopant is Cp2Mg.

8. The method for preparing a quaternary yellow-green LED epitaxial wafer according to claim 5, characterized in that: The growth steps of the P-type periodic current spreading layer are as follows: setting the temperature of the reaction chamber to 800°C ± 20°C, introducing TMGa and PH3 into the P-type graded doped waveguide layer, and first growing a layer of GaP material, wherein the doping concentration of GaP is 2×10 18 cm -3 ~5×10 18 cm -3 The P-type dopant used is Cp2Mg, and then AsH3 is introduced to grow a layer of GaAsP material. The set flow rate of AsH3 is 20sccm~50sccm, and the doping concentration of GaAsP is 1×10 18 cm -3 ~3×10 18 cm -3 The P-type dopant used is Cp2Mg, and GaP / GaAsP is grown in a repeated cycle.

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