Epitaxial wafer of red light Micro LED and preparation method thereof

Abstract

The invention discloses a red light micro light emitting diode epitaxial wafer and a preparation method thereof, and the epitaxial wafer is characterized in that an n-side electron buffer layer and an n-side AlInP transition layer are sequentially arranged between an N-type AlInP limiting layer and a multi-quantum well layer. And the n-side electron buffer layer is a periodic Al < x > In < 1-x > As < y > P < 1-y > / Al < 0.4 > In < 0.6 > P composite combination layer. According to the invention, electrons are decelerated through the superlattice structure of the n-side electron buffer layer, and stress is buffered through the n-side AlInP transition layer to improve the crystal quality of the multi-quantum well, so that electron leakage is significantly reduced, and the internal quantum efficiency of the device is improved while the working voltage is not increased.

Description

Technical Field

[0001] This invention relates to the field of light-emitting diode semiconductors, and more specifically, to an epitaxial wafer of a red Micro LED and its fabrication method. Background Technology

[0002] Micro LEDs (micro-light-emitting diodes) are widely recognized as the next-generation display technology due to their advantages such as high brightness, wide color gamut, high reliability, high resolution, fast response, low power consumption, and long lifespan. Their applications are extensive, ranging from micro-displays and consumer electronics such as virtual reality (VR), augmented reality (AR), and smartwatches, to large-screen displays, and extending to emerging fields such as biosensors, optogenetics, and visible light communication.

[0003] Although Micro LED technology has developed rapidly, it still faces many challenges, among which luminous efficiency has always been a focus of attention. For red Micro LEDs, a core issue lies in the severe asymmetry of carrier mobility. The electron mobility (approximately 500 cm² / V·s) is much higher than the hole mobility (approximately 50 cm² / V·s).

[0004] This imbalance means that, under electrical injection, a large number of high-energy electrons do not undergo radiative recombination with holes in the multiple quantum well (MQW) active region. Instead, under strong electric fields or thermal excitation, they easily overcome the potential barrier of the MQW and leak directly into the P-type region of the LED structure. These leaked electrons are captured by the non-radiative recombination centers in the P-type region, causing severe optical power loss and ultimately leading to a significant decrease in the luminous efficiency of Micro LEDs.

[0005] To solve the problem of electron leakage, such as Figure 1 In the conventional red-light Micro LED epitaxial structure shown, a common improvement method is to add a P-type electron blocking layer (EBL) between the P-type AlGaInP waveguide layer and the P-type AlInP confinement layer. This layer is usually made of AlInP material, with an Al composition of 60% to 70% and a thickness controlled between 150 Å and 300 Å.

[0006] However, this P-EBL scheme has serious inherent drawbacks. First, to achieve a sufficient barrier height to block electrons, the Al content in the EBL must be very high (60% ~ 70%). The significant difference in lattice constant between the AlInP layer with such a high Al content and the GaAs substrate leads to severe lattice mismatch. Second, the thicker the EBL layer, the better the blocking effect, but the greater the stress accumulated from the lattice mismatch. These two factors combined cause quality deterioration of the epitaxial layer during growth, resulting in a large number of dislocations and deep-level defects between layers. Ironically, these defects introduced by the EBL themselves become new nonradiative recombination centers, further trapping carriers and reducing the internal quantum efficiency of the device, significantly diminishing the effectiveness of the P-EBL scheme.

[0007] Therefore, how to effectively suppress electron leakage while avoiding the introduction of additional lattice defects and non-radiative recombination centers to improve the luminous efficiency of red Micro LEDs has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the problems of low luminous efficiency in existing red Micro LEDs due to severe electron leakage, and the further deterioration of efficiency caused by lattice mismatch when attempting to block electrons using the traditional P-EBL scheme, this invention provides a novel epitaxial wafer structure for red Micro LEDs and its fabrication method. This invention aims to effectively suppress electron leakage and improve carrier injection balance by optimizing the N-side epitaxial structure without introducing additional crystal defects, thereby enhancing the internal quantum efficiency of the device.

[0009] To achieve the above objectives, the present invention provides a red-light micro-LED epitaxial wafer, comprising a substrate and an N-type AlInP confinement layer (202), a multi-quantum well layer, and a P-type layer sequentially grown on the substrate. The core of the present invention lies in the sequential addition of an n-side electron buffer layer and an n-type AlInP transition layer between the N-type AlInP confinement layer and the multi-quantum well layer.

[0010] Preferably, the n-side electron buffer layer is a periodic Al x In 1-x As y P 1-y / Al 0.4 In 0.6 A composite layer of P, i.e., a superlattice structure.

[0011] More preferably, the Al x In 1-x As y P 1-yThe Al component x is 0.7 ~ 0.8, and the As component y is 0.3 ~ 0.4. This component range is precisely designed. If the Al component is below 0.7, the barrier height is insufficient and cannot effectively reduce the electron mobility; if it is above 0.8, although the barrier can be increased, it will introduce deep-level defects and become a nonradiative recombination center, which will reduce the internal quantum efficiency.

[0012] More preferably, the number of pairs of the composite combination layers is 3 to 6. The Al x In 1-x As y P 1-y The material has a thickness of 20 ~ 50 Å, and the Al 0.4 In 0.6 The thickness of the P material is 20 to 50 Å. This thickness is designed to "decelerate" rather than "completely block" the voltage; if the thickness is too thick, the barrier will be difficult to tunnel through, leading to an increase in voltage, while if it is too thin, the effect will be insignificant.

[0013] A particularly preferred technical feature is that the Al x In 1-x As y P 1-y Materials and the Al 0.4 In 0.6 The thickness of the P material is designed to gradually increase in the direction approaching the multi-quantum-well layer. This gradient periodic design aims to achieve a gradual reduction in the kinetic energy of high-speed electrons.

[0014] Preferably, the material of the n-type AlInP transition layer is Al. 0.5 In 0.5 P, with a thickness of 100 ~ 200 Å.

[0015] Preferably, both the n-side electron buffer layer and the n-type AlInP transition layer are undoped layers. This is a deliberate design choice because doping introduces impurity atoms, which can become point defects or nonradiative recombination centers. Maintaining these critical layers near the active region in their intrinsic state minimizes the defect density near the active region, thereby increasing the radiative recombination probability.

[0016] The present invention also provides a corresponding preparation method, which employs metal-organic chemical vapor deposition (MOCVD). The core step is to sequentially grow an n-side electron buffer layer and an n-type AlInP transition layer after growing an N-type AlInP confinement layer and before growing a multi-quantum-well layer.

[0017] Preferably, in the step of growing the n-side electron buffer layer (i.e., the superlattice layer), the growth rate is controlled to be 2 Å / s to 3 Å / s. This slower growth rate is crucial for obtaining a steep, clear superlattice interface and is a prerequisite for achieving the "speed bump" effect described later.

[0018] Compared with the prior art, the present invention has the following significant advantages by innovatively introducing an n-side electron buffer layer and an n-type AlInP transition layer on the N-side: 1. “Slowing down” and “current limiting” effects on electrons: This invention transfers the electronic control function from the P side to the N side, fundamentally avoiding the defects of P-EBL.

[0019] "Speed ​​bump" mechanism: The superlattice structure of the n-side electron buffer layer is composed of two different semiconductor materials (Al... x In 1- x As y P 1-y And Al 0.4 In 0.6 The P-EBL is constructed by alternating layers of extremely thin material. This artificially creates numerous abrupt heterojunction interfaces. Electrons traversing this superlattice must repeatedly experience a "conduction band bottom rise-fall" process, much like "continuous speed bumps" on a highway. Although the height of a single barrier is lower than that of a conventional P-EBL, this design breaks down the "one-time, difficult task" of electrons crossing a large barrier into "repetitive tasks" of crossing multiple small barriers. This significantly reduces the average migration speed and kinetic energy of electrons through frequent tunneling and interface interactions.

[0020] Scattering mechanism: Al x In 1-x As y P 1-y As a quaternary alloy, its atomic-level compositional fluctuations generate random potential field fluctuations, resulting in strong "alloy disorder scattering" of electrons. Simultaneously, the interface phonon modes introduced by the superlattice structure enhance "electron-phonon interactions." Both mechanisms further slow down electron motion and reduce mobility.

[0021] 2. Improved crystal quality and defect suppression: This is another major advantage of the present invention compared to the prior art.

[0022] Stress buffer: 100 ~ 200 Å n-side Al inserted between the superlattice and multiple quantum wells 0.5 In 0.5 The P-transition layer provides a crucial "stress and lattice constant gradient buffer".

[0023] Effects: This transition layer significantly reduces crystal defects such as mismatch dislocations that may occur during subsequent MQW growth, substantially improving the crystal quality of the MQW and reducing the density of nonradiative recombination centers in the active region. Furthermore, both this layer and the superlattice layer are designed to be undoped, preventing the introduction of impurity defects at the source and further increasing the radiative recombination probability.

[0024] 3. Improve carrier injection balance and maintain low operating voltage: Through the above mechanism, electrons are effectively "slowed down" and confined within the active region, resulting in a longer residence time and a better balance with the injected holes, thus significantly improving the radiative recombination probability (i.e., internal quantum efficiency, IQE).

[0025] The key point is that the superlattice structure of this invention "decelerates" rather than "completely blocks" electrons, allowing them to pass through via tunneling and other means. Therefore, the increase in the device's series resistance and operating voltage is relatively mild. This contrasts sharply with the voltage rise caused by the high barrier in the P-EBL scheme.

[0026] The technical solution provided by this invention successfully achieves effective “deceleration” and “current limiting” of electrons on the N side. At the same time, it optimizes the growth quality of MQW through the transition layer, significantly improves the carrier injection balance, and ultimately greatly improves the internal quantum efficiency of red Micro LED without increasing the operating voltage. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the epitaxial structure of a conventional red Micro LED in the prior art.

[0028] Figure 2 This is a schematic diagram of the epitaxial structure of a red Micro LED according to an embodiment of the present invention.

[0029] Marked in the image: 600: GaAs substrate 601: GaAs Buffer Layer 200: n-AlGaInP current-spreading layer 201: n-AlGaInP Ohmic Contact Layer 202: n-AlInP confinement layer 203: n-side electron buffer layer 204: n-side AlInP transition layer 205: Multiple quantum wells 206: p-AlInP electron blocking layer 207:p-AlInP confinement layer 208: p-AlGaInP transition layer 209: p-GaP current-spreading layer 210: p-GaP ohmic contact layer Detailed Implementation

[0030] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will be described in conjunction with the accompanying drawings. Figure 2 A preferred embodiment of the present invention will be described in detail below.

[0031] This embodiment provides a method for fabricating a high-efficiency red-light Micro LED epitaxial wafer using Metal-Organic Vapor Chemical Deposition (MOCVD). The growth temperature of each layer in the reaction chamber is controlled between 710 and 750 °C. Depending on the different epitaxial layers being grown, TMGa (trimethylgallium), TMAl (trimethylaluminum), TMIn (trimethylindium), PH3 (phosphine), and AsH3 (arsine) are selected as source gases.

[0032] like Figure 2 As shown, the growth steps of the epitaxial wafer are as follows: 1. Provide a GaAs substrate (600).

[0033] 2. A GaAs buffer layer (601) with a thickness of 1500 ~ 3000 Å is grown on a GaAs substrate (600). An N-type doping source (Si2H6 or SiH4) is introduced, with a doping concentration of 1 × 10⁻⁶. 18 ~ 3×10 18 carriers / cm 3 .

[0034] 3. Grow an n-AlGaInP current-spreading layer (200) with a thickness of 5000 ~ 10000 Å. Introduce an N-type doped source (Si₂H₆ or SiH₄) with a doping concentration of 1 × 10⁻⁶. 18 ~ 3×10 18 carriers / cm 3 .

[0035] 4. Grow an n-AlGaInP ohmic contact layer (201) with an Al composition of 0.3 ~ 0.4 and a thickness of 5000 ~ 15000 Å. Introduce an N-type doping source (Si₂H₆ or SiH₄) with a doping concentration greater than 5 × 10⁻⁶. 18 carriers / cm 3 .

[0036] 5. Grow an n-AlInP confinement layer (202) with a thickness of 2000 ~ 4000 Å. Introduce an N-type doped source (Si2H6) with a doping concentration of 1 × 10⁻⁶. 18 ~ 2×10 18 carriers / cm 3 .

[0037] 6. Grow an n-side electron buffer layer (203). This layer is a periodic Al. x In 1-x As y P 1-y / Al 0.4 In 0.6 A composite layer of P. Among them, Al x In 1-x As y P 1-y The Al component x is 0.7 ~ 0.8, and the As component y is 0.3 ~ 0.4. Al x In 1-x As y P 1-y The material thickness is 20 ~ 50 Å, Al 0.4 In 0.6 The thickness of the P material is 20–50 Å. The number of superlattice combination layers is 3–6 pairs. Preferably, the thickness of the two materials is designed to gradually increase near the subsequent multi-quantum well layer (205), for example, 20 Å for the first pair, with each subsequent layer increasing by 5 Å. This layer is undoped. In particular, the growth rate of this layer is controlled at 2 Å / s–3 Å / s to ensure a steep and clear superlattice interface.

[0038] 7. Growth of n-side Al 0.5 In 0.5 A P-transition layer (204) with a thickness of 100 ~ 200 Å is formed. This layer is undoped.

[0039] 8. A multi-quantum-well layer (205) is grown as the active region. The quantum well material is AlGaInP with a thickness of 30–50 Å; the quantum well barrier material is AlGaInP with a thickness of 50–100 Å. The number of pairs of potential wells and barriers is 3–8. This layer is undoped.

[0040] 9. Growth of a p-AlInP electron blocking layer (206), this layer is Al 0.65 In 0.35 P material, with a thickness controlled between 100 and 200 Å. This layer is undoped.

[0041] 10. Grow a p-AlInP confinement layer (207) with a thickness of 2000 ~ 3000 Å. Introduce a p-type doped source (Cp₂Mg) with a doping concentration of 0.6 × 10⁻⁶ Å. 18 ~ 1.5×10 18 carriers / cm 3 .

[0042] 11. Growth of a p-type AlGaInP transition layer (208). A p-type dopant source (Cp₂Mg) is introduced, with a doping concentration of 2 × 10⁻⁶. 18 ~3×10 18 carriers / cm 3 .

[0043] 12. Grow a p-GaP current-extending layer (209) with a thickness of 3000 ~ 8000 Å. Introduce a p-type doped source (Cp₂Mg) with a doping concentration of 2 × 10⁻⁶. 18 ~ 3×10 18 carriers / cm 3 .

[0044] 13. Grow a p-GaP ohmic contact layer (210) with a thickness of 300 ~ 1000 Å. Introduce a p-type doped source (CBr4) with a doping concentration greater than 5 × 10⁻⁶ Å. 19 carriers / cm 3 .

[0045] In summary, the epitaxial growth process completes the fabrication of a high-efficiency red Micro LED epitaxial wafer according to this embodiment.

[0046] Comparison of experimental data: To verify the beneficial effects of the present invention, an epitaxial wafer using the optimized structure (example) of the present invention was compared with a conventional epitaxial structure (…). Figure 1 A comparative test was conducted (as shown in the figure). Compared with the conventional structure, the optimized structure of this invention: (1) Electron leakage current from 3.2 mA / cm 2 Significantly reduced to 2.2 mA / cm 2 The decrease was about 31%, which proves that the "deceleration" effect of the n-side electron buffer layer (203) is very significant;

[0047] (2) The internal quantum efficiency increased from 42% to 49%, achieving an absolute improvement of 7%, which is a direct result of suppressing electron leakage and improving crystal quality.

[0048] (3) The operating voltage is maintained at 2.22V, which is basically the same as the conventional structure of 2.23V, proving that the N-side optimized structure of the present invention does not introduce additional electrical losses.

[0049] The structure of this embodiment can effectively prevent the problem of electrons jumping to the P-type region due to their high mobility, significantly reduce electron leakage, improve the internal quantum efficiency by 7% (absolute value), and maintain a stable operating voltage, thus proving the effectiveness and advancement of the technical solution of this invention.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A red micro light emitting diode epitaxial wafer, comprising a substrate (600) and sequentially grown on the substrate (600) an N-type AlInP confinement layer (202), a multiple quantum well layer (205) and a P-type layer; characterized in that, between the N-type AlInP confinement layer (202) and the multiple quantum well layer (205), sequentially arranged are an n-side electron buffer layer (203) and an n-type AlInP transition layer (204). Both the n-side electron buffer layer (203) and the n-side AlInP transition layer (204) are undoped layers.

2. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The n-side electron buffer layer (203) is a periodic Al x In 1-x As y P 1-y / Al 0.4 In 0.6 P's composite combination layer.

3. The red micro light emitting diode epitaxial wafer of claim 2, wherein, The Al x In 1- x As y P 1-y The Al component x is 0.7 ~ 0.8, and the As component y is 0.3 ~ 0.

4.

4. The red micro light emitting diode epitaxial wafer of claim 2, wherein, The number of the composite combination layers is 3-6 pairs; the Al x In 1-x As y P 1-y The thickness of the material and the Al 0.4 In 0.6 The thickness of the P material is 20-50 Å.

5. The red micro light emitting diode epitaxial wafer of claim 2, wherein, The Al x In 1- x As y P 1-y The material and the Al 0.4 In 0.6 The thickness of the P material is designed to gradually increase in the direction close to the multiple quantum well layer (205).

6. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The material of the n-type AlInP transition layer (204) is Al 0.5 In 0.5 P, with a thickness of 100 ~ 200 Å.

7. The red micro light emitting diode epitaxial wafer of claim 1, wherein, 8.A method for preparing a red micro light emitting diode epitaxial wafer, using metal organic chemical vapor deposition to sequentially grow on a substrate (600) an N-type AlInP confinement layer (202), a multiple quantum well layer (205) and a P-type layer; characterized in that, the method comprises, after growing the N-type AlInP confinement layer (202) and before growing the multiple quantum well layer (205), sequentially growing an n-side electron buffer layer (203) and an n-type AlInP transition layer (204). ​ ​ 9. The production method according to claim 8, characterized by, The n-side electron buffer layer (203) is a periodic Al x In 1-x As y P 1-y / Al 0.4 In 0.6 P composite combination layer; and, in the step of growing the n-side electron buffer layer (203), the growth rate is controlled to be 2 Å / s ~ 3 Å / s.

10. The method of claim 9, wherein, The Al x In 1-x As y P 1-y The Al component x is 0.7~ 0.8, the As component y is 0.3 ~ 0.4; the logarithm of the composite combination layer is 3 ~ 6 pairs; the Al x In 1-x As y P 1-y The thickness of the material and the Al 0.4 In 0.6 The thickness of the P material is each 20 ~ 50 Å.

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