Dual-wavelength light emitting diode epitaxial structure with three active regions

Abstract

The invention discloses a dual-wavelength light emitting diode epitaxial structure with three active regions and a growth method thereof. The structure sequentially comprises a substrate, a buffer layer, a first n-type layer, a first stress release layer, a first quantum well layer for photoluminescence of green light, a second n-type layer serving as a middle contact layer, a second stress release layer, a second quantum well layer for electroluminescence of blue light, a third quantum well layer for mixed luminescence, an electron blocking layer and a p-type layer from bottom to top. The first quantum well layer is arranged outside a current path for photon recovery, and the third quantum well layer is arranged on the topmost layer to enhance hole injection and optical pumping, so that the green light peak intensity ratio is remarkably improved, and meanwhile, the problems of electric leakage luminescence and wavelength drift under small current are solved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronics technology, specifically relating to an epitaxial structure of a dual-wavelength light-emitting diode with three active regions. Background Technology

[0002] Light-emitting diodes (LEDs), as the fourth generation of lighting sources, have been widely used in general lighting, backlight displays, and automotive lighting due to their advantages such as high efficiency, energy saving, and environmental friendliness. GaN-based LEDs typically achieve light emission by growing InGaN / GaN multiple quantum wells on sapphire or silicon substrates. By adjusting the indium content in the InGaN quantum wells, the bandgap can be changed, thereby controlling the emission wavelength.

[0003] However, monochromatic LEDs are insufficient for achieving full-spectrum lighting or micro-LED applications. Traditional white LEDs employ a "blue chip + yellow phosphor" scheme, which suffers from high Stokes energy loss, color temperature drift due to phosphor aging, and limited color rendering index. Therefore, phosphor-free LEDs capable of simultaneously emitting multiple wavelengths (such as blue and green light) have become a research hotspot by directly growing them on a monolithic epitaxial layer.

[0004] Existing monolithic dual-wavelength LED technology mainly employs the sequential growth of quantum wells with different In compositions within the same active region, such as first growing a green light well and then growing a blue light well. This traditional architecture suffers from the following significant physical limitations and technical challenges: "Green light gap" and insufficient peak-to-intensity ratio: InGaN materials suffer from a severe efficiency degradation problem in the long-wavelength (green and red) bands, known as the "green light gap." This is due to the high dislocation density caused by the large lattice mismatch resulting from high In content (>20%), and the reduced radiative recombination efficiency caused by the strong piezoelectric polarization field. In traditional two-color stacked structures, limited by carrier injection efficiency and distribution characteristics, the final spectrum usually results in blue light intensity dominating and green light component being extremely weak, making it difficult to achieve the desired spectral modulation effect.

[0005] Thermal degradation problem: Green quantum wells require high In content and are typically grown at lower temperatures. Blue quantum wells, on the other hand, require higher growth temperatures, with even higher temperatures for the p-type layer. If green quantum wells are grown first, the subsequent high-temperature process will cause segregation and degradation of In atoms within the green quantum well, severely impairing green light efficiency.

[0006] Light emission instability and leakage under low current: V-pits are a common defect in GaN-based LEDs. While these defects are used in some designs to improve light extraction or shield dislocations, they also create leakage paths. At low current densities, charge carriers can easily leak through the V-pits or recombine nonradiatively at the defects. For dual-wavelength structures, if the green light trap is located deep within the V-pits or in a region of high defect density, weak parasitic luminescence or color shift may occur at low currents, affecting the display's contrast and the purity of the cutoff state.

[0007] Wavelength drift: When the current density of a purely electroluminescent green LED changes, its wavelength will undergo a significant blue shift due to factors such as the shielding effect of the polarization electric field, resulting in unstable color temperature of the device when operating at high current.

[0008] In summary, the industry urgently needs a new epitaxial structure design that can significantly enhance the luminescence intensity of green light, balance the dual-color spectrum, and solve the instability problem under low current while ensuring crystal quality. Summary of the Invention

[0009] The main objective of this invention is to provide an epitaxial structure of a dual-wavelength light-emitting diode with three active regions and its growth method, which enhances the luminescence intensity of green light relative to blue light by introducing a photoluminescence mechanism and optimizing the spatial layout of the quantum well.

[0010] Another objective of this invention is to avoid unintended luminescence of the green layer under low current through a special layer structure design, and to improve the wavelength drift phenomenon that varies with current.

[0011] The technical solution of the present invention is as follows: An epitaxial structure of a dual-wavelength light-emitting diode with three active regions includes: a substrate, and a buffer layer and an undoped gallium nitride layer, a first n-type gallium nitride layer, a first stress relief layer, a first multiple quantum well layer, a second n-type gallium nitride layer, a second stress relief layer, a second multiple quantum well layer, a third multiple quantum well layer, an electron blocking layer, and a p-type gallium nitride layer sequentially stacked on the substrate; wherein, the first multiple quantum well layer is configured as a photoluminescent layer that generates light of a first wavelength; the second multiple quantum well layer is configured as an electroluminescent layer that generates light of a second wavelength; the third multiple quantum well layer is configured as a hybrid electroluminescent and photoluminescent layer that generates light of the first wavelength; the second n-type gallium nitride layer is configured as an N-type electrode contact layer for forming an N-type electrode contact region after exposure; the first multiple quantum well layer is located on the side of the second n-type gallium nitride layer away from the p-type gallium nitride layer, such that the first multiple quantum well layer is located outside the main current injection path when the device is operating.

[0012] The first quantum well layer has a smaller band width than the second quantum well layer and is configured to absorb photons emitted from the second quantum well layer toward the substrate and convert them into photons of a first wavelength.

[0013] The third quantum well layer is disposed adjacent to the electron blocking layer to preferentially obtain hole injection; and the band width of the third quantum well layer is smaller than that of the second quantum well layer, and is configured to absorb photons emitted by the second quantum well layer.

[0014] Both the first stress relief layer and the second stress relief layer are InGaN / GaN superlattice structures.

[0015] The indium composition of the first and third quantum well layers is higher than that of the second quantum well layer; wherein the first wavelength ranges from 510 nm to 540 nm, and the second wavelength ranges from 440 nm to 460 nm.

[0016] The technical solution of the present invention has the following beneficial effects: Significantly improves the green light peak intensity ratio: By introducing a first quantum well layer and a third quantum well layer, this invention converts the blue light energy that was originally transmitted towards the substrate into green light, and by utilizing the efficient injection position of the third quantum well layer, it effectively improves the spectral imbalance problem of "strong blue and weak green" in traditional dual-wavelength LEDs.

[0017] Avoiding thermal degradation: By placing a portion of the green light trap at the bottom layer, although facing challenges in terms of thermal budget for subsequent growth, this invention effectively maintains the quality of the first multi-quantum well layer through the protection of the intermediate layer and an optimized growth process. The third multi-quantum well layer at the top layer grows after the blue light trap, effectively avoiding thermal damage to the green light trap caused by high-temperature blue light growth.

[0018] Improved low-current performance: The third multi-quantum-well layer is located on top of the epitaxial layer, far from the depths of the V-shaped pit that usually originates at the bottom interface. This reduces the impact of leakage current channels on the green light-emitting region, making it less prone to parasitic emission of green light due to leakage current at extremely low currents (below the turn-on voltage), thus improving the signal-to-noise ratio of the device in the off state.

[0019] Wavelength stability: The photoluminescence mechanism is less dependent on current density and is not affected by the increased band tilt caused by QCSE. Introducing photoluminescent components helps neutralize the blue shift caused by electroluminescence components with increasing current, thereby improving the overall color stability of the spectrum. Attached Figure Description

[0020] Figure 1 : A schematic cross-sectional view of the dual-wavelength LED epitaxial structure described in this embodiment of the invention.

[0021] Explanation of markings in the diagram: 10 - Substrate; 20 - Buffer layer and undoped gallium nitride layer; 30 - First N-type gallium nitride layer; 40 - First stress relief layer; 50 - First multi-quantum well layer; 60 - Second N-type gallium nitride layer; 70 - Second stress relief layer; 80 - Second multiple quantum well layer; 90 - Third multi-quantum well layer; 100 - Electron blocking layer; 110 - P-type gallium nitride layer; 120 - N electrode; 130 - P electrode.

[0022] Figure 2 : A schematic diagram of the working principle and photon / carrier transport mechanism of this invention.

[0023] Figure 3 Comparison of EL (electroluminescence) spectra of the present invention and existing technologies under standard operating current.

[0024] Figure 4 : EL spectrum variation of existing technology (traditional dual-wavelength LED structure) under different current densities (5mA, 80mA, 150mA).

[0025] Figure 5 : EL spectrum variation diagram of the present invention under different current densities (5mA, 80mA, 150mA). Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Example:

[0028] like Figure 1 As shown, this embodiment provides an epitaxial structure for achieving dual-wavelength emission. Based on a sapphire PSS substrate 10, this structure utilizes epitaxial growth techniques such as metal-organic chemical vapor deposition (MOCVD) to achieve dual-wavelength emission of blue and green light through specific layer stacking, and significantly enhances the peak intensity ratio of the green light.

[0029] The specific composition and formation process of this epitaxial structure are as follows: First, a buffer layer and an undoped gallium nitride layer 20 are grown on the PSS substrate 10. This layer serves as the basis for epitaxial growth, improving crystal quality and providing a good interface for the subsequent growth of functional layers.

[0030] Next, an underlying structure is sequentially grown on the buffer layer and the undoped gallium nitride layer 20, including a first N-type gallium nitride layer 30, a first stress relief layer 40, and a first multi-quantum well layer 50. The first stress relief layer 40 is used to alleviate stress caused by lattice mismatch; the first multi-quantum well layer 50 is configured as a photoluminescent (PL) layer in the green light band. Notably, this multi-quantum well layer 50 is located outside the subsequently formed current path and is mainly used to absorb short-wavelength photons and convert them into green light.

[0031] Subsequently, an intermediate layer and an upper active region are grown on the multi-quantum well layer 50. First, a second N-type gallium nitride layer 60 is grown and configured as the N-electrode contact layer of the device. Then, a second stress relief layer 70, a second multi-quantum well layer 80, and a third multi-quantum well layer 90 are sequentially grown on the second N-type gallium nitride layer 60.

[0032] The second quantum well layer 80 is configured as a blue-light-band electroluminescent (EL) layer and serves as the primary excitation source for the device. The third quantum well layer 90, a newly added core layer of this invention, is grown directly on top of the second quantum well layer 80 and is located closest to the p-type layer. The third quantum well layer 90 is configured as a green-light-band hybrid light-emitting layer, capable of both electroluminescence (EL) and photoluminescence (PL) when excited by blue light.

[0033] Finally, an electron blocking layer 100 and a p-type gallium nitride layer 110 are sequentially grown on the third quantum well layer 90 to complete the epitaxial growth.

[0034] After epitaxial growth is completed, the structure is processed using photolithography and etching. Part of the upper structure (from the P-type gallium nitride layer 110 to the second stress-relieving layer 70) is etched away until a portion of the surface of the second N-type gallium nitride layer 60 is exposed. Subsequently, an N-electrode 120 is fabricated on the exposed surface of the second N-type gallium nitride layer 60, and a P-electrode 130 is fabricated on the surface of the P-layer 110.

[0035] like Figure 2 As shown, the working principle of this embodiment is as follows: When current is injected between the P electrode 130 and the N electrode 120, the current mainly flows through the P-type gallium nitride layer 110, the electron blocking layer 100, the third multiple quantum well layer 90, the second multiple quantum well layer 80, the second stress relief layer 70, and merges into the second N-type gallium nitride layer 60.

[0036] During this process: The second quantum well layer 80 (blue light layer) receives current injection and generates high-intensity blue light through the electroluminescence (EL) mechanism.

[0037] The third multiple quantum well layer 90 (green light layer) is located on top and immediately adjacent to the p-type gallium nitride layer 110. On the one hand, it receives hole injection for electroluminescence (EL); on the other hand, it absorbs blue light generated by the adjacent second multiple quantum well layer 80 for photoluminescence (PL). This hybrid excitation mode (EL+PL) significantly enhances the luminescence intensity of the green light.

[0038] Although the first quantum well layer 50 (bottom green light layer) is located outside the current path (i.e. below the N electrode 120), it can absorb the blue light radiated downwards by the second quantum well layer 80 and convert it into green light through photoluminescence (PL), thus realizing photon recovery.

[0039] By adding a third quantum well layer 90 closest to the P side and setting a first quantum well layer 50 at the bottom layer, this invention effectively improves the peak intensity ratio of green light in the dual-wavelength spectrum using a dual mechanism of "electrical excitation + optical excitation". At the same time, since the third quantum well layer 90 is located far from the depth of the V-shaped pit that usually originates from the bottom interface, leakage luminescence under small current is effectively reduced, and the problem of wavelength drift with current is improved.

[0040] To further verify the technical effect of the present invention, the spectral characteristics of the LED device prepared in the embodiments of the present invention were compared with those of existing technology devices using a traditional structure (i.e., the green quantum well is located at the bottom layer and relies solely on electroluminescence).

[0041] like Figure 3 As shown, the EL spectra of the present invention and the prior art are compared. Under the same test conditions, the green light peak intensity of the prior art is lower, with a green light peak intensity ratio (green light peak intensity / blue light peak intensity) of only 13.67%. The present invention, by introducing a bottom photoluminescent first multi-quantum-well layer 50 and a top hybrid-emission third multi-quantum-well layer 90, significantly enhances the radiative recombination efficiency in the green light band. Test results show that the present invention increases the green light peak intensity ratio to 22.42%, significantly improving the spectral imbalance of "strong blue and weak green" in traditional dual-wavelength LEDs and achieving more balanced dual-color emission.

[0042] like Figure 4 and Figure 5 As shown, the spectral stability and leakage characteristics of the two structures under different driving currents (5mA, 80mA, 150mA) were further compared.

[0043] refer to Figure 4For the existing epitaxial structure, under low current (5mA) driving, the spectrum exhibits abnormal characteristics: almost no emission signal in the blue light band, while a significant emission peak appears in the green light band. This indicates that at low current density, carriers experience severe leakage through defect channels such as V-shaped pits, causing the current to skip the upper blue quantum well and leak directly to the lower green quantum well for recombination and emission. This "green light leakage" phenomenon not only reduces the device's low current efficiency but also leads to parasitic emission problems in the cutoff state. Furthermore, as the current increases from 5mA to 150mA, the green peak intensity ratio of the existing technology changes drastically, indicating that its emission color drifts significantly with current and has poor color stability.

[0044] refer to Figure 5 In this embodiment of the invention, even under low current (5mA) driving, a clear blue emission peak can still be observed in the spectrum, and no abnormal exclusive emission phenomenon of green light is observed. This indicates that by optimizing the quantum well position (placing the green light layer on the top layer of the current injection path and the bottom layer outside the path), the present invention effectively suppresses the leakage channel for carriers to directly penetrate into the deep defect region, thus avoiding parasitic emission under low current. Furthermore, as the current increases from 5mA to 150mA, the change in the green light peak intensity ratio of the present invention is relatively small (e.g., the increase from 13.35% to 24.43% is relatively smooth). Compared with the prior art, the present invention exhibits superior spectral stability and color consistency over a wide current density range.

Claims

1. An epitaxial structure of a dual-wavelength light-emitting diode with three active regions, characterized in that, include: Substrate (10), and a buffer layer and an undoped gallium nitride layer (20), a first n-type gallium nitride layer (30), a first stress relief layer (40), a first multi-quantum well layer (50), a second n-type gallium nitride layer (60), a second stress relief layer (70), a second multi-quantum well layer (80), a third multi-quantum well layer (90), an electron blocking layer (100), and a p-type gallium nitride layer (110) sequentially stacked on the substrate; wherein the first multi-quantum well layer (50) is configured as a photoluminescent layer that generates light of a first wavelength; the second multi-quantum well layer (6 ... The quantum well layer (80) is configured as an electroluminescent layer that generates light of a second wavelength; the third quantum well layer (90) is configured as a hybrid electroluminescent and photoluminescent layer that generates light of a first wavelength; the second n-type gallium nitride layer (60) serves as an N-type electrode contact layer, and a portion of its surface is used to form an N-electrode (120); the first quantum well layer (50) is located on the side of the second n-type gallium nitride layer (60) away from the p-type gallium nitride layer (110), such that when the device is in operation, the first quantum well layer (50) is located outside the main current injection path.

2. The epitaxial structure of a dual-wavelength light-emitting diode with three active regions according to claim 1, characterized in that, The first quantum well layer (50) has a smaller band width than the second quantum well layer (80) and is configured to absorb photons emitted from the second quantum well layer (80) toward the substrate and convert them into photons of a first wavelength.

3. The epitaxial structure of a dual-wavelength light-emitting diode with three active regions according to claim 1, characterized in that, The third quantum well layer (90) is disposed adjacent to the electron blocking layer (100) to preferentially obtain hole injection; and the band width of the third quantum well layer (90) is smaller than the band width of the second quantum well layer (80), and is configured to absorb photons emitted by the second quantum well layer (80).

4. The epitaxial structure of a dual-wavelength light-emitting diode with three active regions according to claim 1, characterized in that, Both the first stress relief layer (40) and the second stress relief layer (70) are InGaN / GaN superlattice structures.

5. The epitaxial structure of a dual-wavelength light-emitting diode with three active regions according to claim 1, characterized in that, The indium composition of the first quantum well layer (50) and the third quantum well layer (90) is higher than that of the second quantum well layer (80); wherein the first wavelength ranges from 510nm to 540nm and the second wavelength ranges from 440nm to 460nm.

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