A GaN-based nanoporous structure Micro-LED device

Abstract

The present invention relates to the field of GaN-based optoelectronic devices, and specifically discloses a GaN-based nanoporous structure Micro-LED device, including an n-GaN layer, a quantum well InGaN layer, a p-GaN layer, a Si substrate, a nanoporous GaN and a dipole source; the p-GaN layer, the quantum well InGaN layer, the n-GaN layer and the nanoporous GaN are sequentially arranged on the Si substrate from bottom to top; the dipole source is arranged in the quantum well InGaN layer; the nanoporous GaN contains a periodic nanoporous structure array. The device of the present invention works under the dipole source of the TE mode. Due to the GaN nanoporous structure array, the total interface reflection can be broken, the radiation of photons from the escape cone can be promoted, and the spontaneous radiation effect of carriers can be more easily stimulated, so as to achieve the purpose of improving the Purcell factor and light extraction efficiency.

Description

Technical Field

[0001] The present invention relates to the field of GaN-based optoelectronic devices, and in particular to a GaN-based nanoporous structure Micro-LED device. Background Art

[0002] In recent years, SiC and GaN materials, as third-generation wide bandgap semiconductors, are very suitable for optoelectronic devices. Among them, GaN materials have attracted widespread attention in GaN Micro-LED devices due to their wide bandgap, good stability, strong radiation resistance and high temperature resistance. GaN-based Micro-LED crystals have the advantages of small size, longer life, environmental protection and low power consumption, and are widely used in related fields such as optical interconnection, visible light communication, liquid crystal display and emerging virtual / augmented reality, but their low luminous efficiency has become the main factor restricting their development. Since the luminous efficiency of Micro-LED is equal to the product of its external quantum efficiency and voltage efficiency, and the external quantum efficiency is equal to the product of the internal quantum efficiency and light extraction efficiency, and the internal quantum efficiency has been able to reach a relatively high value, the key to improving the luminous efficiency of Micro-LED lies in how to improve the light extraction efficiency.

[0003] The Purcell factor refers to the ratio of the radiation power of the dipole in the optical microcavity to the emission power of the dipole in the semiconductor material. Its value is also the ratio of the lifetimes of spontaneously radiated carriers in the microcavity and the semiconductor material. In addition, the Purcell factor is also closely related to the local state density in optics, and the spontaneous radiation enhancement effect formed by the Purcell factor is a local effect. The lifetime of radiative and non-radiative composite carriers plays a decisive role in the carrier lifetime of Micro-LED devices. The size of the Purcell factor in the optical microcavity is inversely proportional to the ratio of the lifetime of radiative composite carriers. The spontaneous radiation rate will increase with the increase of the Purcell factor, and the lower the lifetime of radiative composite carriers. Summary of the invention

[0004] The purpose of the present invention is to provide a GaN-based nanoporous structure Micro-LED device, which introduces a periodic nanoporous structure array, can break the interface total reflection, promote the radiation of photons from the escape cone, and thus improve the Purcell factor and light extraction efficiency.

[0005] The present invention is achieved through the following technical solutions:

[0006] A GaN-based nanoporous structure Micro-LED device, comprising an n-GaN layer, a quantum well InGaN layer, a p-GaN layer, a Si substrate, nanoporous GaN and a dipole source;

[0007] The p-GaN layer, the quantum well InGaN layer, the n-GaN layer and the nanoporous GaN are sequentially arranged on the Si substrate from bottom to top;

[0008] The dipole source is arranged in the quantum well InGaN layer;

[0009] The nanoporous GaN contains a periodic nanoporous structure array.

[0010] The present invention utilizes a novel GaN nanoporous structure, and the exciton binding energy of the GaN-based heterostructure can be significantly enhanced, and the probability of the recombination of electrons and holes (exciton recombination) to generate photons is increased; nanoporous GaN is a periodic lattice arrangement structure, which belongs to a grating structure, and can not only produce a photon band gap, but also has a related diffraction effect. Therefore, this effect can be used to break the total reflection in the Micro-LED chip and improve the Purcell factor and light extraction efficiency.

[0011] Furthermore, the nanopore radius of the nanoporous GaN is less than or equal to 100 nm.

[0012] Furthermore, the nanopore radius of the nanoporous GaN is less than or equal to 25 nm.

[0013] Furthermore, the period of the nanoporous GaN is less than or equal to 160 nm; and the depth of the nanoporous GaN is less than or equal to 1000 nm.

[0014] Furthermore, the period of the nanoporous GaN is less than or equal to 140 nm; and the depth of the nanoporous GaN is less than or equal to 1000 nm.

[0015] Furthermore, the radius of the nanopores of the nanoporous GaN is equal to 25 nm, the period of the nanoporous GaN is equal to 140 nm; and the depth of the nanoporous GaN is equal to 600 nm.

[0016] The above-mentioned nanohole radius, as well as the corresponding period and depth, can not only break the total reflection at the interface and promote the radiation of photons from the escape cone, thereby improving the Purcell factor and light extraction efficiency; but also enable the device to have better light output directionality and light field intensity.

[0017] Furthermore, the thicknesses of the n-GaN layer, the quantum well InGaN layer, the p-GaN layer and the Si substrate (4) are 2280 nm, 240 nm, 157 nm and 120 μm respectively.

[0018] Further, PML boundaries and monitors are included;

[0019] The n-GaN layer, quantum well InGaN layer, p-GaN layer, Si substrate, monitor and nanoporous GaN are placed within the PML boundary;

[0020] The PML boundary contains air in the upper part of the n-GaN layer and in the internal gap of the nanoporous GaN;

[0021] The monitor is located above the n-GaN layer (1) and outside or inside the quantum well InGaN layer (2), the p-GaN layer and the Si substrate (4).

[0022] Furthermore, the refractive indices of the n-GaN layer, the quantum well InGaN layer, the p-GaN layer, the Si substrate and the air are 2.47, 2.7, 2.47, 4.58 and 1, respectively.

[0023] Further, the monitors include six power monitors, three field distribution monitors, one refractive index monitor and four time monitors.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. The device of the present invention works under the dipole source of TE mode. Due to the GaN nanoporous structure array, the total interface reflection can be broken, the radiation of photons from the escape cone can be promoted, and the spontaneous radiation effect of carriers can be more easily stimulated, thereby achieving the purpose of improving the Purcell factor and light extraction efficiency.

[0026] 2. The present invention obtains a better device structure model by changing the period and radius of the n-GaN nanoholes in the Micro-LED device; by comparing the light field intensity distribution under different nanohole radii, after the complex light path superposition and coupling effect inside the nanohole structure, a device structure with better light output directionality and light field intensity is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0028] Figure 1 Schematic diagram of the GaN-based nanoporous structure Micro-LED device of the present invention;

[0029] Figure 2 The effect of different radii, periods and nanopore etching depths on the Purcell factor of the GaN-based nanoporous structure Micro-LED device of the present invention;

[0030] Figure 3 The effect of different radii, periods and nanopore etching depths on the light extraction efficiency of the improved GaN-based nanoporous structure Micro-LED device provided by the present invention;

[0031] Figure 4 for Figure 2 and Figure 3 Schematic diagram of the distribution of the light field intensity in the XY plane corresponding to the structure with the better result varying with the nanopore depth;

[0032] Figure 5 for Figure 2 and Figure 3 Schematic diagram of the distribution of the light field intensity in the XZ plane corresponding to the structure with the better result varying with the nanohole depth;

[0033] in, Figures 2 to 5 In the figure, (a), (b), (c) and (d) indicate that the nanopore radii are 25 nm, 50 nm, 75 nm and 100 nm, respectively.

[0034] Marks and corresponding parts names in the attached drawings:

[0035] 1-n-GaN layer; 2-quantum well InGaN layer; 3-p-GaN layer; 4-Si substrate; 5-air; 6-monitor; 7-nanoporous GaN; 8-dipole source; 9-PML boundary. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0037] Embodiment 1:

[0038] A GaN-based nanoporous structure Micro-LED device adopts an advanced nanoporous structure design; this structure can break the total reflection of the interface, promote the radiation of photons from the escape cone, and is beneficial to improve the light extraction efficiency and Purcell factor; at the same time, it has the characteristics of low power consumption, high brightness and fast response rate. The specific structure of the device is as follows Figure 1 As shown:

[0039] It includes an n-GaN layer 1, a quantum well InGaN layer 2, a p-GaN layer 3, a Si substrate 4, a nanoporous GaN 7 and a dipole source 8;

[0040] The p-GaN layer 3, the quantum well InGaN layer 2, the n-GaN layer 1 and the nanoporous GaN 7 are sequentially arranged on the Si substrate 4 from bottom to top;

[0041] The dipole source 8 is arranged in the quantum well InGaN layer 2;

[0042] Nanoporous GaN7 contains a periodic array of nanoporous structures.

[0043] The basic structure of the Micro-LED of this embodiment is a double heterojunction structure, which is mainly composed of p-GaN, InGaN and n-GaN. Inserting the quantum well structure layer into the pn junction depletion region can significantly improve the radiative recombination efficiency. The quantum well layer (InGaN layer) structure places a semiconductor material with a larger bandgap width than the middle layer at both ends of the double heterojunction, thereby forming a well shape on the energy band. When the external environment changes, the carriers are bound in the quantum well, and at the same time, the electron and hole wave functions in the same vertical direction overlap, and the recombination of the carriers generates photons and emits light. The quantum well layer structure can effectively increase the probability of radiative recombination and improve the luminous efficiency of Micro-LED devices.

[0044] This embodiment utilizes a periodic nanoporous structure array, which can significantly enhance the exciton binding energy and increase the probability of generating photons by the recombination of electrons and holes. Not only can a photon band gap be generated, but there is also a related diffraction effect. Therefore, this effect can be used to break the total reflection in the Micro-LED chip and improve the Purcell factor and light extraction efficiency.

[0045] The nanopore radius of the nanoporous GaN 7 is preferably less than or equal to 100 nm, and more preferably less than or equal to 25 nm.

[0046] In a preferred embodiment, the period of the nanoporous GaN 7 is less than or equal to 160 nm; and the depth of the nanoporous GaN 7 is less than or equal to 1000 nm.

[0047] In a preferred embodiment, the nanopore radius of the nanoporous GaN 7 is equal to 25 nm, the period of the nanoporous GaN 7 is equal to 140 nm; and the depth of the nanoporous GaN 7 is equal to 600 nm.

[0048] For example:

[0049] A GaN-based nanoporous structure Micro-LED device includes an n-GaN layer 1, a quantum well InGaN layer 2, a p-GaN layer 3, a Si substrate 4, a nanoporous GaN 7 and a dipole source 8; it also includes a PML boundary 9 and a monitor 6.

[0050] The n-GaN layer 1 is located on the upper surface of the quantum well InGaN layer 2, and its left and right sides are in contact with the PML boundary 9. The thickness of the n-GaN layer 1 is 2280 nm, and the refractive index is 2.47.

[0051] The quantum well InGaN layer 2 is located between the n-GaN layer 1 and the p-GaN layer 3, and its left and right sides are in contact with the PML boundary 9. The quantum well InGaN layer 2 has a thickness of 240 nm and a refractive index of 2.7.

[0052] The p-GaN layer 3 is located on the upper surface of the Si substrate 4, and its left and right sides are in contact with the PML boundary 9. The p-GaN layer 3 has a thickness of 157 nm and a refractive index of 2.47.

[0053] The Si substrate 4 is located on the lower surface of the p-GaN layer 3, and its left and right sides and the lower surface are in contact with the PML boundary 9. The Si substrate 4 has a thickness of 120 μm and a refractive index of 4.58.

[0054] The dipole source 8 is inserted deep into the middle of the quantum well InGaN layer 2. The wavelength of the dipole source 8 is 460 nm.

[0055] The monitors 6 are located above the n-GaN layer 1 and outside or inside the quantum well InGaN layer 2, the p-GaN layer 3 and the Si substrate 4. Because the monitors 6 are numerous and distributed around, the attached Figure 1 Only one monitor 6 is marked; specifically, monitor 6 includes six power monitors, three field distribution monitors, one refractive index monitor and four time monitors, wherein the power monitor and the field distribution monitor are placed at the periphery of the device, and the refractive index monitor and the time monitor are placed inside each material layer of the device.

[0056] The inside of the PML boundary 9 is filled with air 5 on the top of the n-GaN layer 1 and in the internal gap of the nanoporous GaN 7, and the refractive index of the air 5 is 1.

[0057] In this embodiment, left and right are relative to the attached Figure 1 In terms of.

[0058] Comparative experiment:

[0059] The performance of the improved GaN-based nanoporous structure Micro-LED device of the present invention was compared and analyzed under device structures with different nanopore radii, periods and depths.

[0060] like Figure 2 As shown in Figure 2, the simulation results of the Purcell factor changing with etching depth at different nanopore radius and period are shown in Figure 2. Figure 2 As shown in the figure, from the Purcell factor results of different nanopore radii, it can be seen that the Purcell factors of the four groups of different nanopore radii show an oscillating trend and a small fluctuation before the nanopore depth reaches 2000nm. In the range of 2000nm to 2280nm, the Purcell factor has an obvious downward trend. The four groups of simulation results show similar trends. The results show that when the nanopore radius is 25nm, the period and depth are 140nm and 2000nm respectively, Micro-LED reaches the maximum Purcell factor value, as shown in Figure 1. Figure 2In a; when the nanopore radius is 50nm, the period and depth are 120nm and 2200nm respectively, the Micro-LED reaches the maximum Purcell factor value, such as Figure 2 (b) When the nanopore radius is 75 nm, the period and depth are 140 nm and 1600 nm respectively, the Micro-LED reaches the maximum Purcell factor value, such as Figure 2 c; When the nanopore radius increases to 100nm, the period and depth are 160nm and 200nm respectively, the Micro-LED reaches the maximum Purcell factor value, such as Figure 2 It can be found that under different nanopore radii, the maximum peak of the Purcell factor appears in the structure with a smaller nanopore period. The main reason is that under the current simulation conditions, the smaller the nanopore structure period, the easier it is to stimulate the spontaneous radiation effect of carriers.

[0061] Figure 3 The light extraction efficiency varies with etching depth at different nanopore radius and period. Figure 3 As can be seen in Figure a, the light extraction efficiency of the nanopore with a radius of 25 nm rises slowly before the nanopore depth reaches 400 nm, and then shows a pattern of first decreasing and then approaching a flattening state. Figure 3 As shown in Figure b, the structure with a period of 120nm to 180nm shows a downward trend from the beginning, and the structure with a period of 200nm to 300nm shows a similar trend to the structure with a copper nanopore radius of 25nm. When the etching depth increases from 10nm to 1000nm, the light extraction efficiency decreases rapidly, and the light extraction efficiency at each period drops to about 4%. When the nanopore radius is 75nm, as shown in Figure 2 Figure 3 As shown in Figure c, when the etching depth is greater than 1000nm, the change in light extraction efficiency always fluctuates within a small range. This is because when the difference in the dielectric constants of the two materials is large, Bragg scattering will occur at the interface of the two materials, thereby forming a photon band gap, making it impossible for light to transmit within the photon band gap. When the radius of the nanohole increases to 100nm, as shown in Figure c, the light extraction efficiency fluctuates within a small range. Figure 3 As shown in Figure d, the light extraction efficiency decreases rapidly with the change of hole depth, and the decrease is also greater, from about 0.11 at the beginning to about 0.02. Figure 3-5 When the hole depth is 10 nm, the light extraction efficiency of the three groups with different hole radii is maintained at around 0.11. At this time, the influence of different nanopore periods on the light extraction efficiency is negligible.

[0062] From the comparative analysis of the four sets of simulation result graphs, it is easy to see that as the nanopore radius increases, the change in nanopore period has less and less influence on the light extraction efficiency. When the nanopore radius changes, the corresponding peak point position of the light extraction efficiency also changes. When the hole radius is a smaller value of 25nm, the maximum peak point of the light extraction efficiency appears at a nanopore period of 140nm and an etching depth of 600nm; when the hole radius is 50nm, the maximum peak point of the light extraction efficiency appears at a nanopore period of 220nm and an etching depth of 400nm; when the hole radius is 75nm, the maximum peak point of the light extraction efficiency appears at a nanopore period of 220nm and an etching depth of 200nm, as shown in Figure 2. Figure 3 As shown in c; when the hole radius is the larger value of 100nm, the maximum peak point appears at the nanohole period of 260nm and the etching depth of 200nm. The position of the peak point of the light extraction efficiency shows that as the nanohole radius increases, the nanohole period corresponding to the peak point also increases, but its etching depth decreases. When the nanohole radius varies in the range of 25nm to 100nm, the light extraction efficiency shows a trend of gradually decreasing as a whole. And the larger the nanohole radius, the greater the decrease in light extraction efficiency, the faster the rate of decrease, and the smaller the light extraction efficiency value. This is because when the nanohole radius increases, the nanohole's ability to limit dipole radiation becomes weaker, and at the same time, the radiated energy is transmitted more to the left and right sides, so the radiated energy above the structure gradually decreases, resulting in a decrease in light extraction efficiency. And when the nanohole radius gradually increases, the radiation modes inside the Micro-LED increase, and the radiation modes inside the device are mutually coupled, which leads to a fluctuating trend in light extraction efficiency. By comparing and analyzing the simulation results, it was finally concluded that when the nanopore radius is 25nm, the period is 140nm and the etching depth is 600nm, the Purcell factor and light extraction efficiency are both at optimal values. The Purcell factor is 1.02, and the light extraction efficiency reaches 12.97%. At this time, the light extraction efficiency is significantly improved compared with other structures.

[0063] Figure 4 The figure shows the XY plane light field intensity distribution diagram when the wavelength λ is 460nm, under the above-mentioned preferred structure with a nanopore radius of 25nm and a period of 140nm, and the etching depths are 300nm, 900nm, 1500nm, and 2100nm respectively. Figure 4 As can be seen from Figures ad, the light field intensity at different nanopore depths is centrally symmetrically distributed along the XY axis origin. When the etching depth is 300nm, Figure 4 As shown in Figure a, the light energy is mainly radiated from the side edges. As the etching depth increases, the energy of photons radiated from the top of the Micro-LED device gradually increases. Figure 4As shown in Figures ad. When the etching depth reaches 2100nm, the energy of photons radiated from the top is the largest, and the light field intensity distribution uniformity is the best at this time. The energy of photons radiated from the side of the device is relatively small, which effectively avoids excessive loss of light field energy and improves the effective light extraction efficiency. The main reason why the effective light extraction efficiency is better when the depth reaches 2100nm is that the light extraction directionality is better at this depth (most of it is radiated from the top of the device to the outside world), and the photons radiated from the side walls are relatively small.

[0064] Figure 5 for Figure 4 The XZ cross-sectional light field intensity distribution diagram under the structure. Through the comparative analysis of the light field intensity distribution of four groups of different device structures, it can be seen that after the nanoporous structure is introduced into the n-GaN layer, the light energy emitted by the dipole is transmitted along the nanohole, and finally radiates from the top and side wall of the nanohole to the external environment. After the dipole light source radiates, it will pass through multiple nanoholes along the four sides, that is, it needs to penetrate the GaN / air / GaN dielectric material multiple times, resulting in multiple refraction and reflection phenomena. Therefore, compared with the planar structure model, the light path superposition and coupling effect inside the nanohole structure are relatively more complicated. Figure 5 The comparative analysis of the light field intensity of four groups with different nanohole depths once again verified that as the nanohole etching depth increases, the energy of photons radiated from the top of the Micro-LED device increases, while the number of photons escaping from the side decreases. This shows that the exploration and optimization of the structure of the Micro-LED device in the present invention plays an important role in improving its luminous efficiency and light uniformity.

[0065] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0066] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and the like cited in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of the relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

Claims

1. A GaN-based nanoporous structure Micro-LED device, characterized in that: It comprises an n-GaN layer (1), a quantum well InGaN layer (2), a p-GaN layer (3), a Si substrate (4), a nanoporous GaN (7) and a dipole source (8); The p-GaN layer (3), the quantum well InGaN layer (2), the n-GaN layer (1) and the nanoporous GaN (7) are arranged in sequence from bottom to top on the Si substrate (4); The dipole source (8) is arranged in the quantum well InGaN layer (2); The nanoporous GaN (7) contains a periodic nanoporous structure array; The nanopore radius of the nanoporous GaN (7) is less than or equal to 100 nm; the period of the nanoporous GaN (7) is less than or equal to 160 nm; and the depth of the nanoporous GaN (7) is less than or equal to 1000 nm.

2. The GaN-based nanoporous structure Micro-LED device according to claim 1, characterized in that: The nanopore radius of the nanoporous GaN (7) is less than or equal to 25 nm.

3. The GaN-based nanoporous structure Micro-LED device according to claim 1, characterized in that: The period of the nanoporous GaN (7) is less than or equal to 140 nm; the depth of the nanoporous GaN (7) is less than or equal to 1000 nm.

4. The GaN-based nanoporous structure Micro-LED device according to claim 3, characterized in that: The nanopore radius of the nanoporous GaN (7) is equal to 25 nm, the period of the nanoporous GaN (7) is equal to 140 nm; and the depth of the nanoporous GaN (7) is equal to 600 nm.

5. The GaN-based nanoporous structure Micro-LED device according to claim 1, characterized in that: The thicknesses of the n-GaN layer (1), the quantum well InGaN layer (2), the p-GaN layer (3) and the Si substrate (4) are 2280 nm, 240 nm, 157 nm and 120 μm respectively.

6. The GaN-based nanoporous structure Micro-LED device according to claim 1, characterized in that: It also includes PML boundaries (9) and monitors (6); The n-GaN layer (1), the quantum well InGaN layer (2), the p-GaN layer (3), the Si substrate (4), the monitor (6) and the nanoporous GaN (7) are placed within the PML boundary (9); The PML boundary (9) contains air (5) in the upper part of the n-GaN layer (1) and in the internal gap of the nanoporous GaN (7); The monitor (6) is located above the n-GaN layer (1) and outside or inside the quantum well InGaN layer (2), the p-GaN layer (3) and the Si substrate (4).

7. The GaN-based nanoporous structure Micro-LED device according to claim 6, characterized in that: The refractive indices of the n-GaN layer (1), the quantum well InGaN layer (2), the p-GaN layer (3), the Si substrate (4) and the air (5) are 2.47, 2.7, 2.47, 4.58 and 1 respectively.

8. The GaN-based nanoporous structure Micro-LED device according to claim 6, characterized in that: The monitors (6) include six power monitors, three field distribution monitors, one refractive index monitor and four time monitors.

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