A novel red light LED epitaxial structure and a preparation method thereof

Abstract

The application provides a novel red light LED epitaxial structure and a preparation method thereof. The novel red light LED epitaxial structure comprises an epitaxial layer, and the epitaxial layer comprises an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are stacked in sequence. The P-type semiconductor layer comprises a P-type AlInP limiting layer, a P-type DBR layer and a P-type GaP window layer in sequence in a direction away from the active layer. The P-type DBR layer is a distributed Bragg reflector. The preparation method comprises the following steps: S1, generating the epitaxial layer, and forming a temporary substrate on a side of the P-type GaP window layer away from the P-type DBR layer; and S2, laser scanning the temporary substrate to remove the temporary substrate, and the P-type DBR layer is used for reflecting laser when the laser is scanned. The damage to the active layer can be reduced, and the light emitting efficiency and reliability of the device are ensured.

Description

Technical Field

[0001] This invention relates to the field of semiconductor fabrication technology, and in particular to a novel red LED epitaxial structure and its fabrication method. Background Technology

[0002] AlGaInP-based red light-emitting diodes have wide applications in solid-state lighting, automotive lighting, displays, and optoelectronic sensing. Traditional AlGaInP red LED epitaxial structures are usually grown on GaAs substrates, but GaAs substrates have strong absorption of visible light, resulting in low luminous efficiency. To solve this problem, a flip-chip AlGaInP-based red LED structure is adopted. After removing the GaAs substrate, the epitaxial layer GaP is bonded to a sapphire substrate. Then, laser lift-off technology is used to lift the sapphire substrate and complete the transfer of the core, so as to effectively avoid the light absorption loss of the GaAs substrate. Deep ultraviolet lasers are widely used in laser lift-off technology due to their high photon energy and good processing efficiency. However, in actual processes, it has been found that the photon energy of a 266nm laser is approximately 4.66eV. When it penetrates the epitaxial layer, some of the laser energy reaches the multiple quantum well layer. Since the bandgap of AlGaInP material is only about 2.0eV, which is much lower than the photon energy of a 266nm laser, this portion of the laser energy is strongly absorbed by the quantum well, generating photogenerated carriers and local thermal effects. This leads to an increase in non-radiative recombination centers in the quantum well, causing lattice damage in the active region, and consequently, a significant decrease in the luminous efficiency of the device. How to effectively reduce or avoid the optical and thermal damage to the quantum well caused by high-energy lasers is a key problem that urgently needs to be solved in the manufacturing process of AlGaInP-based red LEDs. Summary of the Invention

[0003] The purpose of this invention is to provide a novel red LED epitaxial structure and its fabrication method. The technical problem to be solved is to provide an LED epitaxial structure that reduces damage to the active layer during laser lift-off of a sapphire substrate.

[0004] To achieve the above objectives, the solution of the present invention is: a novel red LED epitaxial structure, comprising an epitaxial layer, wherein the epitaxial layer comprises an N-type semiconductor layer, an active layer and a P-type semiconductor layer stacked sequentially, characterized in that: the P-type semiconductor layer comprises a P-type AlInP confinement layer, a P-type DBR layer and a P-type GaP window layer sequentially along the direction away from the active layer, wherein the P-type DBR layer is a distributed Bragg reflector layer.

[0005] Furthermore, the N-type semiconductor layer sequentially includes an N-type GaAs buffer layer, an N-type GaInP etch stop layer, an N-type GaAs ohmic contact layer, an N-type current spreading layer, and an N-type AlInP confinement layer along the direction close to the active layer.

[0006] Furthermore, the P-type DBR layer is formed by the periodic alternation of a first DBR sublayer and a second DBR sublayer along the direction away from the active layer, with a growth cycle of... 10. Each cycle begins with the first DBR sublayer and ends with the second DBR sublayer; The first DBR sublayer material is (Al) X Ga 1-X ) 0.5 In 0.5 P, the material of the second DBR sublayer is AlInP; The refractive index of the first DBR sublayer is The refractive index of the second DBR sublayer is The refractive index of the P-type GaP window layer is , , .

[0007] Furthermore, the Al component of the first DBR sublayer is 0.5, and the Al component is maintained at a constant level during growth.

[0008] Furthermore, the P-type GaP window layer is used for wafer bonding with the temporary substrate, and the P-type DBR layer is used to reflect the laser light incident from the temporary substrate side and passing through the P-type GaP window layer, so as to reduce the energy of the laser light reaching the active layer. The optical thickness of the first DBR sublayer and the second DBR sublayer is 1 / 4 of the incident laser wavelength.

[0009] Furthermore, the temporary substrate is a sapphire substrate.

[0010] Furthermore, the P-type DBR layer is used to reflect laser light with a wavelength of 266nm, and the growth thickness of the first DBR sublayer is... The growth thickness of the second DBR sublayer is .

[0011] Furthermore, during the growth of the P-type DBR layer, the temperature was maintained at 700-720℃, and Cp2Mg was continuously introduced for P-type doping.

[0012] Furthermore, the P-type AlInP confinement layer includes a first AlInP confinement layer and a second AlInP confinement layer stacked sequentially in the direction away from the active layer; the first AlInP confinement layer is not doped, and the second AlInP confinement layer is P-type doped. The growth thickness of the first AlInP confinement layer is: nm, where The value is a positive integer, ranging from 1 to 3, and the growth thickness of the second AlInP confinement layer is... nm, where It is a positive integer, and its value ranges from 10 to 12.

[0013] This invention also provides a method for fabricating a novel red LED epitaxial structure, which includes the following steps: S1, the epitaxial layer is generated, and a temporary substrate is formed on the side of the P-type GaP window layer away from the P-type DBR layer; S2, laser scans the temporary substrate to remove it; the P-type DBR layer is used to reflect the laser during scanning.

[0014] Furthermore, the following steps are also included: Step S11: Provide an N-type GaAs substrate, and sequentially grow an N-type semiconductor layer, an active layer, and a P-type semiconductor layer on the N-type GaAs substrate in a direction away from the N-type GaAs substrate to obtain an epitaxial layer; Step S12: After the epitaxial layer growth is completed, the epitaxial layer with the N-type GaAs substrate is wafer-bonded to the temporary substrate through the P-type GaP window on the side away from the active layer, so that the epitaxial layer is transferred onto the temporary substrate; the temporary substrate is a sapphire substrate. Step S13: Remove the N-type GaAs substrate to expose the N-type semiconductor layer. The epitaxial layer is fixed to the temporary substrate on one side of the P-type GaP window layer. The temporary substrate is located on the side of the P-type GaP window away from the P-type DBR layer. Step S14: The temporary substrate is scanned and peeled off using a laser with a wavelength of 266nm to obtain the epitaxial layer.

[0015] After adopting the above solution, the beneficial effects of the present invention are as follows: (1) A P-type DBR layer is set between the P-type confinement layer and the P-type window layer to reduce the damage of laser to the active layer. The P-type DBR layer is a distributed Bragg reflection layer, which can reflect laser during the preparation of the epitaxial layer. When the laser enters, it is efficiently reflected when it reaches the P-type DBR layer after passing through the P-type window layer, reducing the laser from continuing to propagate towards the active layer, suppressing the formation of photogenerated carriers and local thermal effects at the quantum well, reducing non-radiative recombination centers, achieving the purpose of protecting the quantum well, and improving the internal quantum efficiency and stability of the device. (2) The P-type DBR layer is obtained by periodically alternating growth of the first DBR sublayer and the second DBR sublayer with different refractive indices. A refractive index ladder structure with obvious alternating high and low refractive indices is formed in the P-type window layer, the second DBR sublayer, the first DBR sublayer and the P-type confinement layer, forming an effective optical reflection interface.

[0016] (3) In the preparation process of this invention, the sapphire substrate is used as a temporary transfer carrier for the epitaxial layer. After the substrate transfer is completed, it is removed, and finally an independent epitaxial structure without substrate is obtained. The P-type DBR layer in the epitaxial layer can reflect the laser efficiently when the sapphire substrate is lifted by laser, so that the quantum well is effectively protected and the lossless transfer of the epitaxial layer is realized. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the extensional structure according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the epitaxial structure grown on a GaAs substrate according to an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the bonding structure between the epitaxial structure and the sapphire substrate in an embodiment of the present invention.

[0020] Label Explanation: 1-N-type semiconductor layer, 2-N-type GaAs buffer layer, 3-N-type GaInP etch stop layer, 4-N-type GaAs ohmic contact layer, 5-N-type current spreading layer, 6-N-type AlInP confinement layer, 7-active layer, 8-P-type AlInP confinement layer, 9-P-type DBR layer, 10-P-type GaP window layer, 11-temporary substrate, 12-P-type semiconductor layer, 13-GaAs substrate, 81-first AlInP confinement layer, 82-second AlInP confinement layer, 91-first DBR sublayer, 92-second DBR sublayer. Detailed Implementation

[0021] 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. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Key points combined Figure 1 As shown, the present invention provides a novel red LED epitaxial structure, including an epitaxial layer comprising an N-type semiconductor layer 1, an active layer 7, and a P-type semiconductor layer 12 stacked sequentially. In this specific embodiment, the N-type semiconductor layer 1 includes, in sequence along the direction close to the active layer 7, an N-type GaAs buffer layer 2, an N-type GaInP etching stop layer 3, an N-type GaAs ohmic contact layer 4, an N-type current spreading layer 5, and an N-type AlInP confinement layer 6. The active layer 7 (i.e., the MQW layer) is the core layer in the LED that undertakes the function of radiative recombination light emission, allowing electrons and holes to recombine and emit light in this region.

[0023] In this specific embodiment, the active layer 7 adopts a multi-quantum well structure, which is composed of multiple quantum well layers and quantum barrier layers stacked alternately. A quantum confinement effect is formed between the quantum well layers and the quantum barrier layers, which confines the charge carriers within the quantum well layers for recombination and luminescence.

[0024] The P-type semiconductor layer 12 includes, in sequence, a P-type AlInP confinement layer 8, a P-type DBR layer 9, and a P-type GaP window layer 10 along the direction away from the active layer 7. The P-type DBR layer 9 is disposed between the P-type AlInP confinement layer 8 and the P-type GaP window layer 10. The P-type DBR layer 9 is a distributed Bragg reflector layer used to reflect laser light during the fabrication of the epitaxial layer, thereby reducing damage to the multi-quantum-well structure. Specifically, during the fabrication of the epitaxial layer, a temporary substrate 11 serves as a temporary transfer carrier for the epitaxial layer. The temporary substrate 11 is preferably a sapphire substrate. The P-type GaP window layer 10 is used for wafer bonding with the temporary substrate 11. The P-type DBR layer 9 is used to reflect laser light incident from one side of the temporary substrate 11 and passing through the P-type GaP window layer 10, thereby reducing the energy of the laser light reaching the active layer 7.

[0025] The P-type DBR layer 9 is formed by the alternating growth of a first DBR sublayer 91 and a second DBR sublayer 92 along a direction away from the active layer 7, with a growth cycle of... 10. Each cycle begins with the first DBR sublayer 91 and ends with the second DBR sublayer 92; the refractive index of the first DBR sublayer 91 is... The refractive index of the second DBR sublayer 92 is The refractive index of the p-type GaP window layer 10 is , , This allows the P-type semiconductor layer 12 to form a distinct, periodically alternating refractive index step from low to high on the side away from the active layer 7, creating an effective optical reflection interface. Furthermore, the P-type GaP window layer 10 is grown on the surface of the second DBR sublayer 92 in the last period of the P-type DBR layer 9, which also forms a refractive index step from low to high between the P-type DBR layer 9 and the P-type GaP window layer 10, ensuring the integrity of the period of the P-type DBR layer 9. The optical thickness of the first DBR sublayer 91 and the second DBR sublayer 92 is 1 / 4 of the incident laser wavelength to obtain a high reflectivity for the laser.

[0026] To ensure conductivity, Cp2Mg was introduced throughout the growth of the P-type DBR layer 9 for P-type doping.

[0027] In this specific embodiment, the material of the first DBR sublayer 91 is (Al). X Ga 1-X ) 0.5 In0.5 P, the material of the second DBR sublayer 92 is AlInP, and the growth thickness of the first DBR sublayer 91 is P. The growth thickness of the second DBR sublayer 92 is ;in, The wavelength of the laser. Specifically (Al) X Ga 1-X ) 0.5 In 0.5 The refractive index of P material Specifically, regarding the refractive index of AlInP material, this invention targets the reflection of laser light with a wavelength of 266 nm. At a wavelength of 266 nm, , The growth thickness of the first DBR sublayer 91 is approximately The growth thickness of the second DBR sublayer 92 is approximately This allows for an optical thickness of approximately 66.5 nm per layer, achieving high reflectivity. Furthermore, the reflectivity is enhanced by alternating growth of the first DBR sublayer 91 and the second DBR sublayer 92 at least 10 times. Additionally, slight variations in composition lead to changes in refractive index. , The growth thickness of the first DBR sublayer 91 is The growth thickness of the second DBR sublayer 92 is Preferably, the Al composition of the first DBR sublayer 91 is 0.5, and the Al composition is maintained at a constant level during growth.

[0028] In this specific embodiment, the p-type AlInP confinement layer 8 includes a first AlInP confinement layer 81 and a second AlInP confinement layer 82 stacked sequentially in the direction away from the active layer 7. The first AlInP confinement layer 81 is close to the active layer 7 and grows on the surface of the active layer 7. The second AlInP confinement layer 82 grows on the first AlInP confinement layer 81. The first AlInP confinement layer 81 is undoped. During the growth process, the second AlInP confinement layer 82 is p-type doped by introducing Cp2Mg, thus becoming a doped AlInP layer. The growth thickness of the first AlInP confinement layer 81 is smaller than the growth thickness of the second AlInP confinement layer 82.

[0029] The first AlInP confinement layer 81 of the P-type AlInP confinement layer 8 can prevent Mg from diffusing to the active layer 7 and causing nonradiative recombination, thus reducing luminescence efficiency. The second AlInP confinement layer 82 is the core of the confinement layer, and its main function is to provide holes. Since the mobility of holes is usually low, this layer is highly doped. At the same time, in order to avoid carrier aggregation, increasing the thickness can enhance the current spreading effect and improve the light extraction efficiency.

[0030] The growth thickness of the first AlInP confinement layer 81 is nm, where The value is a positive integer, ranging from 1 to 3, and the growth thickness of the second AlInP confinement layer 82 is... nm, where The integer is a positive integer, ranging from 10 to 12, so that the thickness of the P-type AlInP confinement layer 8 is... Integer multiples of the same thickness can further enhance reflectivity, and the periodic thickness design can reduce stress accumulation during growth and reduce lattice defects.

[0031] This invention provides a method for fabricating a novel red LED epitaxial structure, comprising the following steps: S1, the epitaxial layer is generated, and a temporary substrate 11 is formed on the side of the P-type GaP window layer 10 away from the P-type DBR layer 9; S2, laser scans temporary substrate 11 to remove temporary substrate 11, P-type DBR layer 9 is used to reflect laser during scanning.

[0032] Key points combined Figures 2-3 As shown, the epitaxial layer is grown on an N-type GaAs substrate 13 and then transferred to a temporary substrate 11. The N-type GaAs substrate 13 is first removed, which can be achieved using conventional processes in the art. Then, the temporary substrate 11 is removed by laser to obtain a substrate-free epitaxial layer. The specific steps include: Step S11: Provide an N-type GaAs substrate 13, and sequentially grow an N-type semiconductor layer 1, an active layer 7, and a P-type semiconductor layer 12 on the N-type GaAs substrate 13 in a direction away from the N-type GaAs substrate 13 to obtain an epitaxial layer; Step S12: After the epitaxial layer growth is completed, the epitaxial layer with the N-type GaAs substrate 13 is wafer-bonded to the temporary substrate 11 through the P-type GaP window layer 10 on the side opposite to the active layer 7, so that the epitaxial layer is transferred to the temporary substrate 11; the temporary substrate 11 is a sapphire substrate.

[0033] Step S13: Remove the N-type GaAs substrate 13 to expose the N-type semiconductor layer 1. The epitaxial layer is fixed on the temporary substrate 11 with the P-type GaP window layer 10 on one side. The temporary substrate 11 is located on the side of the P-type GaP window layer 10 away from the P-type DBR layer 9. Step S14: The temporary substrate 11 is scanned and peeled off using a laser with a wavelength of 266nm to obtain the epitaxial layer.

[0034] In this specific embodiment, in order to better match the N-type GaAs substrate 13 lattice, the Al composition of the first DBR sublayer 91 is 0.5, and the Al composition is kept constant during growth.

[0035] Furthermore, the epitaxial layer growth in step S11 includes the following: S111, an N-type GaAs buffer layer 2, an N-type GaInP etch stop layer 3, an N-type GaAs ohmic contact layer 4, an N-type current spread layer 5, an N-type AlInP confinement layer 6, and an active layer 7 are sequentially grown on the surface of an N-type GaAs substrate 13. S112, first grow an undoped first AlInP confinement layer 81 on the surface of the active layer 7, and then grow a doped second AlInP confinement layer 82 on the surface of the first AlInP confinement layer 81. S113, a P-type DBR layer 9 is grown on the surface of the second AlInP confinement layer 82. The P-type DBR layer 9 is formed by periodically alternating first DBR sublayer 91 and second DBR sublayer 92 in a direction away from the active layer 7 for at least 10 cycles. Each cycle begins with the first DBR sublayer 91 and ends with the second DBR sublayer 92. The material of the first DBR sublayer 91 is (Al... 0.5 Ga 0.5 ) 0.5 In 0.5 P, the material of the second DBR sublayer 92 is AlInP; S114, in step S113, a P-type window layer 10 with GaP material is grown on the surface of the last second DBR sublayer 92. In step S111, metal-organic chemical vapor deposition (MOCVD) is used to grow sequentially on GaAs substrate 13; N-type GaAs buffer layer 2: The temperature is maintained at 700-720℃, and TMGa, AsH3 and SiH4 are introduced; N-type GaInP corrosion stop layer 3: The temperature is maintained at 700-720℃, and TMGa, TMIn, PH3 and SiH4 are introduced; N-type GaAs ohmic contact layer 4: Temperature maintained at 700-720℃, TMGa, AsH3 and SiH4 are introduced; N-type current extension layer 5: The temperature is maintained at 700-720℃, and TMAl, TMGa, TMIn, PH3 and SiH4 are introduced; N-type AlInP confinement layer 6: The temperature is maintained at 700-720℃, and TMAl, TMIn, PH3 and SiH4 are introduced; Active layer 7: The temperature is maintained at 680-720℃, and TMAl, TMGa, TMIn and PH3 are introduced; In step S112, the P-type AlInP confinement layer 8 is grown in two stages, with the temperature maintained at 700-720℃. First, TMAl, TMIn, and PH3 are introduced to a predetermined thickness D1 to grow an undoped first AlInP confinement layer 81 on the surface of the MQW layer. Then, TMAl, TMIn, and PH3 are continuously introduced, as well as Cp2Mg, to a predetermined thickness D2 to grow a doped second AlInP confinement layer 82 on the surface of the first AlInP confinement layer 81. In step S113, at the end of the growth of the second AlInP confinement layer 82, the temperature is maintained at 700-720℃. During the growth of the P-type DBR layer 9, Cp2Mg is continuously introduced for P-type doping, with a doping concentration of 1×10⁻⁶. 18 cm -3 The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A novel red LED epitaxial structure, characterized in that: The device includes an epitaxial layer comprising an N-type semiconductor layer, an active layer, and a P-type semiconductor layer stacked sequentially. The P-type semiconductor layer, along a direction away from the active layer, comprises a P-type AlInP confinement layer, a P-type DBR layer, and a P-type GaP window layer, wherein the P-type DBR layer is a distributed Bragg reflector layer.

2. The novel red LED epitaxial structure as described in claim 1, characterized in that: The N-type semiconductor layer, along the direction close to the active layer, sequentially includes an N-type GaAs buffer layer, an N-type GaInP etch stop layer, an N-type GaAs ohmic contact layer, an N-type current spreading layer, and an N-type AlInP confinement layer.

3. The novel red LED epitaxial structure as described in claim 1, characterized in that: The P-type DBR layer is formed by the periodic alternation of a first DBR sublayer and a second DBR sublayer along the direction away from the active layer, with a growth cycle of...

10. Each cycle begins with the first DBR sublayer and ends with the second DBR sublayer; The first DBR sublayer material is (Al) X Ga 1-X ) 0.5 In 0.5 P, the material of the second DBR sublayer is AlInP; The refractive index of the first DBR sublayer is The refractive index of the second DBR sublayer is The refractive index of the P-type GaP window layer is , , .

4. The novel red LED epitaxial structure as described in claim 3, characterized in that: The Al composition of the first DBR sublayer is 0.5, and the Al composition is maintained at a constant level during growth.

5. The novel red LED epitaxial structure as described in claim 3, characterized in that: The P-type GaP window layer is used for wafer bonding with the temporary substrate, and the P-type DBR layer is used to reflect the laser light incident from the temporary substrate side and passing through the P-type GaP window layer to reduce the energy of the laser light reaching the active layer. The optical thickness of the first DBR sublayer and the second DBR sublayer is 1 / 4 of the incident laser wavelength.

6. The novel red LED epitaxial structure as described in claim 5, characterized in that: The temporary substrate is a sapphire substrate.

7. The novel red LED epitaxial structure as described in claim 5, characterized in that: The P-type DBR layer is used to reflect laser light with a wavelength of 266nm, and the growth thickness of the first DBR sublayer is [missing information]. The growth thickness of the second DBR sublayer is .

8. The novel red LED epitaxial structure as described in claim 1, characterized in that: During the growth of the P-type DBR layer, the temperature is maintained at 700-720℃, and Cp2Mg is continuously introduced for P-type doping.

9. The novel red LED epitaxial structure as described in claim 1, characterized in that: The P-type AlInP confinement layer includes a first AlInP confinement layer and a second AlInP confinement layer stacked sequentially in the direction away from the active layer; the first AlInP confinement layer is not doped, and the second AlInP confinement layer is P-type doped. The growth thickness of the first AlInP confinement layer is: nm, where The value is a positive integer, ranging from 1 to 3, and the growth thickness of the second AlInP confinement layer is... nm, where It is a positive integer, and its value ranges from 10 to 12.

10. A method for fabricating a novel red LED epitaxial structure, characterized in that: To fabricate the novel red LED epitaxial structure as described in any one of claims 1-9, the following steps are included: S1, the epitaxial layer is generated, and a temporary substrate is formed on the side of the P-type GaP window layer away from the P-type DBR layer; S2, laser scans the temporary substrate to remove it; the P-type DBR layer is used to reflect the laser during scanning.

11. The method for preparing the novel red LED epitaxial structure as described in claim 10, characterized in that: It also includes the following steps: Step S11: Provide an N-type GaAs substrate, and sequentially grow an N-type semiconductor layer, an active layer, and a P-type semiconductor layer on the N-type GaAs substrate in a direction away from the N-type GaAs substrate to obtain an epitaxial layer; Step S12: After the epitaxial layer growth is completed, the epitaxial layer with the N-type GaAs substrate is wafer-bonded to the temporary substrate through the P-type GaP window on the side away from the active layer, so that the epitaxial layer is transferred onto the temporary substrate; the temporary substrate is a sapphire substrate. Step S13: Remove the N-type GaAs substrate to expose the N-type semiconductor layer. The epitaxial layer is fixed to the temporary substrate on one side of the P-type GaP window layer. The temporary substrate is located on the side of the P-type GaP window away from the P-type DBR layer. Step S14: The temporary substrate is scanned and peeled off using a laser with a wavelength of 266nm to obtain the epitaxial layer.

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