Miniature light emitting diode epitaxial structure suitable for low working current density

Abstract

The invention relates to the field of semiconductor devices, in particular to a miniature light-emitting diode epitaxial structure suitable for low working current density, which comprises a substrate, and a buffer layer, an N-type semiconductor layer, a stress release layer, a multi-quantum well light-emitting layer and a P-type semiconductor layer which are sequentially stacked on the substrate, the number of alternating cycles of well layers and barrier layers of the multi-quantum well light-emitting layer ranges from 1 to 5, the main component of each well layer is In < x > Ga < 1-x > N, x ranges from 0.13 to 0.18, the thickness ranges from 2 nm to 3.5 nm, the main component of each barrier layer is In < y > Ga < 1-y > N, y ranges from 0.01 to 0.05, and the thickness ranges from 4 nm to 8 nm. The multi-quantum well light-emitting layer is alternately formed by adopting InGaN with different In contents, the band gap of the barrier layer is relatively small, the number of cycles is reduced, the thickness of the barrier layer is reduced, and a hole is easy to penetrate through the plurality of barrier layers, so that the quantum efficiency of the Micro-LED under the condition of relatively low working current density is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, and in particular to a micro light-emitting diode epitaxial structure suitable for low operating current density. Background Technology

[0002] Micro-LEDs are miniaturized LEDs, with individual LEDs measuring only 1-50 μm in size. For microdisplays, the size requirements for Micro-LEDs are even more stringent, with dimensions below 10 μm. In practical applications, multiple Micro-LEDs need to be transferred in batches onto a circuit board containing a lower electrode and transistors. After fabricating a protective layer and upper electrode, and then encapsulating them, a display with high brightness, long lifespan, and high efficiency is formed.

[0003] Due to the significant reduction in size compared to traditional LEDs, the peak external quantum efficiency (EQE) of Micro-LEDs is considerably lower than that of LEDs with the same epitaxial structure due to multiple factors such as dislocation density, sidewall defects, and electron leakage. Furthermore, the current density (J / L) corresponding to the peak EQE is also significantly lower. Peak EQE The current density will shift towards higher current densities, meaning that Micro-LEDs require higher current densities to achieve their peak EQE. However, Micro-LEDs used in microdisplays typically operate at low current densities, i.e., less than 20 A / cm². 2 Operating at current densities below a certain threshold means that Micro-LEDs struggle to achieve optimal EQE at display operating current densities. On the other hand, research indicates that when the current density exceeds 20 A / cm²... 2 At this time, the lifespan of Micro-LEDs is significantly shortened. Therefore, in the actual application environment of Micro-LEDs, the operating current density is low. Micro-LEDs, which are miniaturized directly using the epitaxial structure of traditional LEDs, cannot achieve high quantum efficiency at this operating current density, which is not conducive to image display. Summary of the Invention

[0004] The purpose of this invention is to provide a micro LED epitaxial structure suitable for low operating current density.

[0005] To achieve the above objectives, the present invention provides the following technical solution: An epitaxial structure for a micro LED suitable for low operating current density includes a substrate and a buffer layer, an N-type semiconductor layer, a stress relief layer, a multi-quantum-well light-emitting layer, and a P-type semiconductor layer sequentially stacked on the substrate. The multi-quantum-well light-emitting layer includes periodically alternating well layers and barrier layers with a period number of any value from 1 to 5. The main component of the well layers is In.x Ga 1-x N and x are any values ​​from 0.13 to 0.18, and the thickness is any value from 2 nm to 3.5 nm. The main component of the barrier layer is In. y Ga 1-y N and y are any values ​​from 0.01 to 0.05, and the thickness is any value from 4 nm to 8 nm.

[0006] Optionally, the multi-quantum-well light-emitting layer further includes an AlN layer with a thickness of any value between 0.3 nm and 1 nm, a growth temperature of any value between 750°C and 850°C, and a growth pressure of any value between 200 torr and 300 torr. The AlN layer is formed on the side of the multi-quantum-well light-emitting layer close to the P-type semiconductor layer.

[0007] Optionally, the system further includes an electron blocking layer disposed between the multi-quantum-well light-emitting layer and the p-type semiconductor layer. The electron blocking layer includes a first blocking layer composed of magnesium-doped aluminum gallium nitride, wherein the aluminum content in the aluminum gallium nitride is any value between 15% and 20%, and the magnesium doping concentration is 8 × 10⁻⁶. 18 cm -3 ~1×10 20 cm -3 The growth temperature of the first barrier layer is any value between 900℃ and 1000℃, and the thickness of the electron barrier layer is any value between 15nm and 30nm.

[0008] Optionally, the electron blocking layer further includes a second blocking layer, wherein the first blocking layer and the second blocking layer are grown alternately periodically, with the number of periods being any value from 5 to 10, and the thickness of the first blocking layer and the second blocking layer being any value from 1 nm to 3 nm, and the composition of the second blocking layer is gallium nitride.

[0009] Optionally, the N-type semiconductor layer is formed of gallium nitride-doped silicon, and the silicon doping concentration in the N-type semiconductor layer is 3 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 The thickness is any value in the range of 2μm to 3μm, wherein the P-type semiconductor layer is formed of gallium nitride-doped magnesium, and the magnesium doping concentration in the P-type semiconductor layer is 1×10⁻⁶. 19 cm -3 ~1×10 20 cm -3 Any value in the range, with a thickness of any value between 100nm and 300nm.

[0010] Optionally, the growth temperature of the well layer of the multi-quantum-well light-emitting layer is any value between 700°C and 800°C, the growth temperature of the barrier layer of the multi-quantum-well light-emitting layer is any value between 800°C and 900°C, the growth pressure is any value between 200 torr and 500 torr, the growth temperature of the N-type semiconductor layer is any value between 1000°C and 1050°C, and the growth pressure is any value between 200 torr and 400 torr.

[0011] Optionally, the micro LED epitaxial structure suitable for low operating current density further includes a P-type transition layer, which is formed of gallium nitride-doped magnesium, with a thickness of any value between 5 nm and 20 nm, and the magnesium doping concentration in the P-type transition layer is 1 × 10⁻⁶. 20 cm -3 ~5×10 20 cm -3 Any value in the range.

[0012] Optionally, the stress relief layer includes a first stress layer and a second stress layer that grow alternately in a periodic manner, with the number of periods being any value from 5 to 20, and the thickness of both the first stress layer and the second stress layer being any value from 3 nm to 10 nm, wherein the main component of the first stress layer is In. z Ga 1-z N and z are any values ​​from 0.01 to 0.05, the growth temperature is any value from 800℃ to 900℃, the main component of the second stress layer is GaN, the growth temperature is any value from 1000℃ to 1050℃, and it is attached to the N-type semiconductor layer.

[0013] Optionally, the buffer layer includes a first buffer layer formed on the surface of the substrate and a second buffer layer formed on the surface of the first buffer layer. The first buffer layer is composed of low-temperature gallium nitride, with a thickness of any value between 10 nm and 90 nm, a growth temperature of any value between 450 °C and 550 °C, and a growth pressure of any value between 400 torr and 550 torr. The second buffer layer is composed of undoped gallium nitride, with a thickness of any value between 1 μm and 2 μm, a growth temperature of any value between 1000 °C and 1080 °C, and a growth pressure of any value between 300 torr and 600 torr. The flow rate ratio of nitrogen source gas to metal source gas is greater than or equal to 1000.

[0014] Optionally, the substrate is any one of sapphire, gallium nitride single crystal, silicon carbide, and silicon.

[0015] The beneficial effects of this invention are as follows: A multi-quantum-well light-emitting layer is formed by periodically alternating InGaN layers with varying In content. The bandgap is varied within the layer solely by adjusting the In content, and the barrier layer bandgap is relatively small, allowing for more uniform hole injection into multiple quantum wells. Reducing the number of cycles and the thickness of the barrier layer helps improve the uniformity of carrier distribution, thereby facilitating the effective filling of all well layers. This reduces the difficulty for holes to penetrate multiple barrier layers and reach quantum wells far from the P-type semiconductor layer, improving carrier concentration matching and thus enhancing the injection efficiency of carriers at low injection depths. It also increases the radiative recombination rate and reduces non-radiative recombination, thereby improving the quantum efficiency of Micro-LEDs at lower operating current densities.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 These are the internal quantum efficiency detection graphs for each Micro-LED in Embodiments 1, 2, 3, and 4 of the present invention; Figure 2 The current density-voltage curves of each Micro-LED in Embodiments 1, 2, and 4 of this invention are shown. Figure 3 The energy band diagrams of each Micro-LED in Embodiments 1 and 2 of the present invention are shown below. Figure 4 These are the internal quantum efficiency detection graphs for each Micro-LED in Embodiments 1 and 5 of the present invention; Figure 5 The current density-voltage curves of each Micro-LED in Embodiments 1 and 5 of the present invention are shown. Figure 6 The graphs show the internal quantum efficiency of each Micro-LED in Embodiment 1 and Comparative Example 1 of the present invention. Figure 7 This is a diagram showing the in-mesa quantum efficiency distribution of some Micro-LEDs in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] This invention application protects a micro-LED epitaxial structure suitable for low operating current density, comprising a substrate and a buffer layer, an N-type semiconductor layer, a stress relief layer, a multi-quantum-well emitting layer, and a P-type semiconductor layer sequentially stacked on the substrate. The multi-quantum-well emitting layer includes periodically alternating well layers and barrier layers, with a period number of any value from 1 to 5, for example, any value from 1, 2, 3, 4, and 5. The main component of the well layers is In. x Ga 1-x N and x are any values ​​from 0.13 to 0.18, for example, any values ​​from 0.13, 0.14, 0.15, 0.16, 0.17, and 0.18; the thickness is any value from 2 nm to 3.5 nm, for example, any values ​​from 2 nm, 2.5 nm, 3 nm, and 3.5 nm; and the main component of the barrier layer is In. y Ga 1-y N and y are any values ​​from 0.01 to 0.05, for example, any value from 0.01, 0.02, 0.03, 0.04 and 0.05, and the thickness is any value from 4nm to 8nm, for example, any value from 4nm, 5nm, 6nm, 7nm and 8nm.

[0023] A multi-quantum-well light-emitting layer is formed by periodically alternating InGaN with varying In content. The bandgap within the layer is varied only by adjusting the In content, and the relatively small barrier bandgap allows for more uniform hole injection into multiple quantum wells. Reducing the number of cycles and the barrier thickness helps improve the uniformity of carrier distribution, thus facilitating efficient filling of all well layers. This reduces the difficulty for holes to penetrate multiple barriers to reach quantum wells far from the P-type semiconductor layer, improves carrier concentration matching, and consequently enhances the injection efficiency of carriers at low injection rates. It also increases the radiative recombination rate and reduces non-radiative recombination, thereby improving the quantum efficiency of Micro-LEDs at lower operating current densities.

[0024] In some embodiments, the multi-quantum-well light-emitting layer further includes an AlN layer with a thickness of any value from 0.3 nm to 1 nm, a growth temperature of any value from 750 °C to 850 °C (e.g., any value from 750 °C, 800 °C, and 850 °C), and a growth pressure of any value from 200 torr to 300 torr (e.g., any value from 200 torr, 250 torr, and 300 torr). The AlN layer is formed on the side of the multi-quantum-well light-emitting layer near the P-type semiconductor layer, and its thickness can be, for example, any value from 0.3 nm, 0.5 nm, 0.7 nm, 0.9 nm, and 1 nm. The extremely thin AlN layer passivates the surface of the InGaN layer and suppresses In volatilization and diffusion, thereby improving color point uniformity and long-term stability.

[0025] In some embodiments, an electron blocking layer is further included between the multi-quantum-well light-emitting layer and the P-type semiconductor layer. The electron blocking layer includes a first blocking layer composed of magnesium-doped aluminum gallium nitride. The aluminum content in the aluminum gallium nitride is any value from 15% to 20%, for example, any value from 15%, 16%, 17%, 18%, 19%, and 20%. The magnesium doping concentration is 8 × 10⁻⁶. 18 cm -3 ~1×10 20 cm -3 Any value in, for example, can be 8×10 18 cm -3 1×10 19 cm -3 3×10 19 cm -3 5×10 19 cm -3 8×10 19 cm -3 and 1×10 20 cm -3The growth temperature of the first barrier layer is any value in the range of 900℃ to 1000℃, for example, any value in the range of 900℃, 920℃, 940℃, 960℃, 980℃ and 1000℃, and the thickness of the electron barrier layer is any value in the range of 15nm to 30nm, for example, any value in the range of 15nm, 20nm, 25nm and 30nm.

[0026] The electron blocking layer, a standard structure in traditional LEDs, is designed to improve efficiency at high current densities by significantly reducing electron leakage and thus increasing radiative recombination. However, the presence of the electron blocking layer significantly increases the device's turn-on and operating voltages, reducing electro-optical conversion efficiency. In Micro-LED applications, where the operating current density is lower, traditional electron blocking layers cannot meet the efficiency improvement requirements and may even have negative effects. Therefore, the electron blocking layer needs to be redesigned and optimized.

[0027] Compared to traditional electron blocking layers, magnesium-doped aluminum gallium nitride (AlGaN) layers effectively improve electron blocking capability, prevent electron leakage, and enhance carrier injection efficiency, thereby improving internal quantum efficiency (IQE) and electro-optical conversion efficiency. Simultaneously, due to the high bandgap and suitable p-type conductivity of magnesium-doped AlGaN layers, recombination efficiency losses between electrons and holes can be reduced at low current densities without significantly increasing the device's turn-on voltage. Therefore, moderately magnesium-doped AlGaN layers can maintain high electro-optical conversion efficiency while adapting to low current density environments, avoiding the negative impacts of traditional electron blocking layers and achieving high internal quantum efficiency (IQE).

[0028] In some embodiments, the electron blocking layer further includes a second blocking layer, wherein the first blocking layer and the second blocking layer are grown alternately periodically, and the number of periods is any value from 5 to 10, for example, any value from 5, 6, 7, 8, 9 and 10. The thickness of the first blocking layer and the second blocking layer is any value from 1 nm to 3 nm, for example, any value from 1 nm, 1.5 nm, 2 nm, 2.5 nm and 3 nm. The composition of the second blocking layer is gallium nitride.

[0029] Under low current density conditions, the electron blocking layer of the superlattice structure not only enhances the recombination efficiency of electrons and holes but also reduces the problems of increased turn-on voltage and decreased electro-optical conversion efficiency caused by traditional blocking layers. Furthermore, the superlattice structure can alleviate stress mismatch between materials, improve crystal quality, and reduce defects caused by high doping while maintaining high blocking performance, ultimately contributing to improved IQE and electro-optical conversion efficiency of Micro-LED devices.

[0030] The electron blocking layer can be selected based on specific requirements. Choosing a low-doped electron blocking layer can reduce the effective hole barrier height and increase the effective electron barrier height, thereby enhancing hole injection efficiency while effectively blocking electrons and achieving better carrier concentration matching. Eliminating the electron blocking layer removes the hole barrier between the electron blocking layer and the P-type semiconductor layer, significantly reducing the turn-on voltage and lowering epitaxial costs and process complexity, which is highly effective for energy saving in large-scale display applications. Using a periodic structure of a first and second electron blocking layer as the electron blocking layer can effectively reduce the forward voltage, optimize the effective electron / hole barrier height, and thus improve the performance of extremely small sizes at low current densities.

[0031] In some embodiments, the N-type semiconductor layer is formed of gallium nitride-doped silicon, and the silicon doping concentration in the N-type semiconductor layer is 3 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 Any value in, for example, can be 3 × 10 18 cm -3 5×10 18 cm -3 7×10 18 cm -3 9×10 18 cm -3 1×10 19 cm -3 3×10 19 cm -3 and 5×10 19 cm -3 The thickness is any value in the range of 2μm to 3μm, for example, any value among 2.4μm, 2.6μm, 2.8μm, and 3μm. The P-type semiconductor layer is formed by gallium nitride doped with magnesium, and the magnesium doping concentration in the P-type semiconductor layer is 1×10⁻⁶. 19 cm -3 ~1×10 20 cm -3 Any value in, for example, can be 1×10 19 cm -3 3×10 19 cm -3 5×10 19 cm -3 7×10 19 cm -3 9×10 19 cm -3 and 1×10 20 cm -3The thickness can be any value in the range of 100nm to 300nm, for example, any value among 100nm, 150nm, 200nm, 250nm, and 300nm. By constraining the doping amount and thickness within the N-type and P-type semiconductor layers, the injection amount of carriers into the multi-quantum-well light-emitting layer under low current can be optimized, thereby controlling the quantum efficiency of Micro-LEDs at lower operating current densities.

[0032] In some embodiments, the growth temperature of the well layer of the multi-quantum-well light-emitting layer is any value between 700°C and 800°C, for example, any value among 700°C, 720°C, 740°C, 760°C, 780°C, and 800°C; the growth temperature of the barrier layer of the multi-quantum-well light-emitting layer is any value between 800°C and 900°C, for example, any value among 800°C, 820°C, 840°C, 860°C, 880°C, and 900°C; and the growth pressure is any value between 200 torr and 500 torr, for example, 200 torr. The growth temperature of the N-type semiconductor layer is any value among torr, 300 torr, 400 torr, and 500 torr, for example, any value among 1000℃ to 1050℃, such as 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, and 1050℃, and the growth pressure is any value among 200 torr to 400 torr, for example, any value among 200 torr, 250 torr, 300 torr, 350 torr, and 400 torr.

[0033] In some embodiments, the epitaxial structure suitable for low operating current density micro-LEDs further includes a P-type transition layer, which is formed of gallium nitride-doped magnesium and has a thickness of any value from 5 nm to 20 nm, for example, any value from 5 nm, 10 nm, 15 nm, and 20 nm, and the magnesium doping concentration in the P-type transition layer is 1 × 10⁻⁶. 20 cm -3 ~5×10 20 cm -3 Any value in, for example, can be 1×10 20 cm -3 2×10 20 cm -3 3×10 20 cm -3 4×10 20 cm -3 and 5×10 20 cm -3 Any value in the range. Increasing the magnesium doping level helps to achieve better ohmic contact, facilitates electrical connection between the P-type semiconductor layer and the electrode, and reduces losses in current transmission.

[0034] In some embodiments, the stress relief layer includes a first stress layer and a second stress layer that are periodically alternately grown, with the number of periods being any value from 5 to 20, for example, any value from 5, 10, 15, and 20. The thickness of both the first and second stress layers is any value from 3 nm to 10 nm, for example, any value from 3 nm, 5 nm, 7 nm, 9 nm, and 10 nm. The main component of the first stress layer is In. z Ga 1-z N and z are any values ​​from 0.01 to 0.05, for example, any values ​​from 0.01, 0.02, 0.03, 0.04, and 0.05. The growth temperature is any value from 800℃ to 900℃, for example, any value from 800℃, 820℃, 840℃, 860℃, 880℃, and 900℃. The main component of the second stress layer is GaN, and the growth temperature is any value from 1000℃ to 1050℃, for example, any value from 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, and 1050℃, and it is attached to the N-type semiconductor layer. The superlattice structure suppresses dislocation propagation during the growth of the quantum well light-emitting layer, alleviating the stress mismatch between the N-type semiconductor layer and the quantum well light-emitting layer.

[0035] In some embodiments, the buffer layer includes a first buffer layer formed on the surface of the substrate and a second buffer layer formed on the surface of the first buffer layer. The first buffer layer is composed of low-temperature gallium nitride, and its thickness is any value from 10 nm to 90 nm, for example, any value from 10 nm, 30 nm, 50 nm, 70 nm, and 90 nm. The growth temperature is any value from 450°C to 550°C, for example, any value from 450°C, 470°C, 490°C, 510°C, 530°C, and 550°C. The growth pressure is any value from 400 torr to 550 torr, for example, any value from 400 torr, 430 torr, 460 torr, 490 torr, 520 torr, and 550 torr. The buffer layer is composed of undoped gallium nitride, with a thickness of any value between 1 μm and 2 μm, for example, any value between 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, and 2 μm; a growth temperature of any value between 1000℃ and 1080℃, for example, any value between 1000℃, 1020℃, 1040℃, 1040℃, and 1080℃; a growth pressure of any value between 300 torr and 600 torr, for example, any value between 300 torr, 400 torr, 500 torr, and 600 torr; and a flow rate ratio of nitrogen source gas to metal source gas greater than or equal to 1000, for example, any value between 1000, 1300, 1500, and 2000.

[0036] In some embodiments, the substrate is any one of sapphire, gallium nitride single crystal, silicon carbide, and silicon.

[0037] Please refer to the following examples for details.

[0038] Example 1: Please see Figure 1 The preferred embodiment of this application shows a micro LED epitaxial structure suitable for low operating current density, including a substrate and a buffer layer, an N-type semiconductor layer, a stress relief layer, a multi-quantum well light-emitting layer, an electron blocking layer, a P-type semiconductor layer and a P-type transition layer sequentially stacked on the substrate.

[0039] The substrate is sapphire with a size of 10μm.

[0040] The buffer layer comprises a first buffer layer and a second buffer layer. The first buffer layer is composed of low-temperature gallium nitride and has a thickness of 50 nm. The second buffer layer is composed of undoped gallium nitride and has a thickness of 1 μm. The buffer layers are grown on the substrate surface. Initially, the growth temperature is set to 550 °C, the pressure is set to 500 torr, and the nitrogen source gas to metal source gas flow ratio (V / III) is set to 1300 during growth to obtain the first buffer layer at low temperature. The growth temperature is then adjusted to 1050 °C, and the growth pressure is adjusted to 600 torr to obtain the second buffer layer.

[0041] The N-type semiconductor layer is an electron injection layer, made of silicon-doped gallium nitride. The silicon doping concentration in the N-type semiconductor layer is 1 × 10⁻⁶. 19 cm -3 The thickness is approximately 2.5 μm. The N-type semiconductor layer is grown on the surface of the completed buffer layer, with the growth temperature set to 1050 °C and the growth pressure set to 150 torr.

[0042] The stress relief layer comprises a first stress layer and a second stress layer that are periodically grown alternately, with a period number of 20, and both the first and second stress layers have a thickness of 2.5 nm. The material of the first stress layer is In. 0.03 Ga 0.97 The second stress layer is made of GaN. The stress relief layer is grown on the surface of the completed N-type semiconductor layer. The second stress layer grown in the first layer is attached to the N-type semiconductor layer. The growth temperature needs to be adjusted to 850℃, and the growth temperature needs to be adjusted to 1050℃ when growing the first stress layer.

[0043] The multi-quantum-well light-emitting layer comprises periodically alternating well layers and barrier layers, with a period number of 3. The first barrier layer is attached to the stress-relieving layer, and the barrier layer is composed of In. 0.02 Ga 0.98 The N layer has a thickness of 5.5 nm. The well layer is composed of In.0.16 Ga 0.84 N, with a thickness of 2.3 nm. The multi-quantum-well light-emitting layer is grown on the surface of the stress-relief layer after growth, with the well layer grown at a temperature of 750 °C. The barrier layer is grown at a temperature of 850 °C, and the growth pressure needs to be adjusted to 350 torr.

[0044] The multi-quantum-well light-emitting layer also includes an AlN layer with a thickness of 0.6 nm. The AlN layer is prepared after the well layer and barrier layer are grown, at a growth temperature of 830 °C and a growth pressure of 240 torr.

[0045] The electron blocking layer is a monolayer thin film formed of magnesium-doped aluminum gallium nitride (p-AlGaN), with aluminum comprising 15% and magnesium doping concentration of 2 × 10⁻⁶. 19 cm -3 Its growth temperature is 950℃ and its thickness is 22nm.

[0046] The p-type semiconductor hole injection layer is formed of gallium nitride-doped magnesium, with a thickness of 170 nm and a magnesium doping concentration of 5 × 10⁻⁶. 19 cm -3 .

[0047] The P-type transition layer is also formed by gallium nitride-doped magnesium, with a thickness of 12 nm and a magnesium doping concentration of 3 × 10⁻⁶. 20 cm -3 .

[0048] Example 2: The only difference between this embodiment and Embodiment 1 is that the magnesium doping concentration in the electron blocking layer is adjusted to 4 × 10⁻⁶ in this embodiment. 18 cm -3 .

[0049] Example 3: The only difference between this embodiment and Embodiment 1 is that the magnesium doping concentration in the electron blocking layer is adjusted to 4 × 10⁻⁶. 15 cm -3 4×10 17 cm -3 4×10 19 cm -3 4×10 20 cm -3 and 4×10 21 cm -3 .

[0050] Example 4: The only difference between this embodiment and Embodiment 1 is that no electron blocking layer is provided in this embodiment.

[0051] The IQE of the Micro-LEDs in Examples 1, 2, 3, and 4 were measured at different current densities. The test results can be found in [link to relevant documentation]. Figure 1 It can be seen that Micro-LEDs have strict requirements on the doping concentration of the electron blocking layer, and when the doping concentration of the electron blocking layer is 2×10⁻⁶... 19 cm -3 At that time, Micro-LED had the highest IQE.

[0052] The operating voltages of the Micro-LEDs in Examples 1, 2, and 4 were measured at different current densities. The test results are available in [link to relevant documentation]. Figure 2 It can be seen that, under the same current density, the Micro-LED structure without an electron blocking layer has the lowest turn-on voltage. This is because the structure with an electron blocking layer has a hole barrier, which increases the turn-on voltage. Therefore, when the requirements for turn-on voltage, process cost and difficulty are high, the Micro-LED structure without an electron blocking layer can be selected.

[0053] The Micro-LEDs in Examples 1 and 2 were tested at a current density of 10 A / cm². 2 For the electron energy at that time, please refer to the detection results. Figure 3 As can be seen, the Micro-LED epitaxial structure in Example 1 has a higher effective electron barrier height and a lower effective hole barrier height, which means that it can effectively block electrons while reducing the obstruction to holes.

[0054] Example 5: The only difference between this embodiment and Embodiment 1 is that the electron blocking layer in this embodiment includes a first blocking layer and a second blocking layer. The material of the first blocking layer is the same as that of the electron blocking layer in Embodiment 1, and the second blocking layer is made of gallium nitride. The thickness of both the first blocking layer and the second blocking layer is 1.5 nm. They are periodically arranged to form a superlattice structure, and the first blocking layer is attached to the multi-quantum well light-emitting layer.

[0055] The internal quantum efficiency and operating voltage of the Micro-LEDs in Examples 1 and 5 were measured at different current densities. The results can be found in [link to relevant documentation]. Figure 4 and Figure 5 It can be seen that at lower current densities, the electron blocking layer of the superlattice structure can increase the internal quantum efficiency and reduce the forward voltage, thereby increasing the electro-optic conversion efficiency. Therefore, when high requirements are placed on the turn-on voltage and electro-optic conversion efficiency, the electron blocking layer of the superlattice structure can be selected.

[0056] Comparative Example 1: The only difference between this comparative example and Example 1 is that the number of cycles of the well layer and the barrier layer of the multi-quantum well light-emitting layer in this comparative example is adjusted to 1, 5, 6, 8 and 10, respectively.

[0057] The internal quantum efficiency of the Micro-LEDs in Example 1 and Comparative Example 1 was measured at different current densities. The results can be found in [link to relevant documentation]. Figure 6 It can be seen that at low current densities, epitaxial structures with a period number less than or equal to 5 have higher internal quantum efficiency.

[0058] The Micro-LEDs in Example 1 and a portion of the Micro-LEDs in Comparative Example 1 were tested at a current density of 10 A / cm². 2 For the quantum efficiency distribution within the time frame, please refer to the test results. Figure 7 It can be seen that the 3-period structure of Micro-LED has a lower sidewall efficiency degradation and a smaller area affected by the sidewalls. Therefore, the preferred quantum well period number for the epitaxial structure is 3.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A micro-light-emitting diode epitaxial structure suitable for low operating current density, characterized in that, The system includes a substrate and a buffer layer, an N-type semiconductor layer, a stress relief layer, a multi-quantum-well light-emitting layer, and a P-type semiconductor layer sequentially stacked on the substrate. The multi-quantum-well light-emitting layer includes periodically alternating well layers and barrier layers, with a period number of any value from 1 to 5. The main component of the well layers is In. x Ga 1-x N and x are any values ​​from 0.13 to 0.18, and the thickness is any value from 2 nm to 3.5 nm. The main component of the barrier layer is In. y Ga 1-y N and y are any values ​​from 0.01 to 0.05, and the thickness is any value from 4 nm to 8 nm.

2. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The multi-quantum-well light-emitting layer further includes an AlN layer with a thickness of any value between 0.3 nm and 1 nm, a growth temperature of any value between 750°C and 850°C, and a growth pressure of any value between 200 torr and 300 torr. The AlN layer is formed on the side of the multi-quantum-well light-emitting layer close to the P-type semiconductor layer.

3. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, It also includes an electron blocking layer disposed between the multi-quantum-well light-emitting layer and the P-type semiconductor layer. The electron blocking layer includes a first blocking layer, which is composed of magnesium-doped aluminum gallium nitride. The aluminum content in the aluminum gallium nitride is any value between 15% and 20%, and the magnesium doping concentration is 8 × 10⁻⁶. 18 cm -3 ~1×10 20 cm -3 The growth temperature of the first barrier layer is any value between 900℃ and 1000℃, and the thickness of the electron barrier layer is any value between 15nm and 30nm.

4. The micro LED epitaxial structure suitable for low operating current density as described in claim 3, characterized in that, The electron blocking layer further includes a second blocking layer. The first blocking layer and the second blocking layer are grown alternately periodically, with the number of periods being any value between 5 and 10. The thickness of the first blocking layer and the second blocking layer is any value between 1 nm and 3 nm. The composition of the second blocking layer is gallium nitride.

5. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The N-type semiconductor layer is formed of gallium nitride-doped silicon, and the silicon doping concentration in the N-type semiconductor layer is 3 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 The thickness is any value in the range of 2μm to 3μm, wherein the P-type semiconductor layer is formed of gallium nitride-doped magnesium, and the magnesium doping concentration in the P-type semiconductor layer is 1×10⁻⁶. 19 cm -3 ~1×10 20 cm -3 Any value in the range, with a thickness of any value between 100nm and 300nm.

6. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The growth temperature of the well layer of the multi-quantum-well light-emitting layer is any value between 700°C and 800°C, the growth temperature of the barrier layer of the multi-quantum-well light-emitting layer is any value between 800°C and 900°C, and the growth pressure is any value between 200 torr and 500 torr. The growth temperature of the N-type semiconductor layer is any value between 1000°C and 1050°C, and the growth pressure is any value between 200 torr and 400 torr.

7. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, It also includes a P-type transition layer, which is formed of gallium nitride-doped magnesium, with a thickness of any value between 5 nm and 20 nm, and the magnesium doping concentration in the P-type transition layer is 1 × 10⁻⁶. 20 cm -3 ~5×10 20 cm -3 Any value in the range.

8. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The stress relief layer comprises a first stress layer and a second stress layer that grow alternately in a periodic manner, with the number of periods ranging from 5 to 20. The thicknesses of both the first and second stress layers are ranging from 3 nm to 10 nm. The main component of the first stress layer is In. z Ga 1-z N and z are any values ​​from 0.01 to 0.05, the growth temperature is any value from 800℃ to 900℃, the main component of the second stress layer is GaN, the growth temperature is any value from 1000℃ to 1050℃, and it is attached to the N-type semiconductor layer.

9. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The buffer layer includes a first buffer layer formed on the surface of the substrate and a second buffer layer formed on the surface of the first buffer layer. The first buffer layer is composed of low-temperature gallium nitride, with a thickness of any value between 10 nm and 90 nm, a growth temperature of any value between 450 °C and 550 °C, and a growth pressure of any value between 400 torr and 550 torr. The second buffer layer is composed of undoped gallium nitride, with a thickness of any value between 1 μm and 2 μm, a growth temperature of any value between 1000 °C and 1080 °C, and a growth pressure of any value between 300 torr and 600 torr. The flow rate ratio of nitrogen source gas to metal source gas is greater than or equal to 1000.

10. The micro LED epitaxial structure suitable for low operating current density as described in claim 1, characterized in that, The substrate is any one of sapphire, gallium nitride single crystal, silicon carbide, and silicon.

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