Double-color light mixing LED structure and preparation method thereof

Abstract

The invention discloses a double-color light-mixing LED structure and a preparation method thereof, relates to the technical field of semiconductor photoelectronics, and realizes chip-level double-color light mixing by integrating two independent epitaxial light-emitting units on the same epitaxial wafer, thereby not only greatly simplifying the preparation process, but also remarkably improving the light mixing uniformity and the light color stability. The double-color light-mixing LED structure comprises a first epitaxial light-emitting unit in a central area, and the first epitaxial light-emitting unit emits first colored light; the second epitaxial light-emitting unit in the peripheral area emits second colored light, and the peak wavelength of the second colored light is longer than that of the first colored light; the second epitaxial light-emitting unit is arranged around the first epitaxial light-emitting unit, and the first colored light and the second colored light are emitted after being mixed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor optoelectronics, in particular to a dual-color mixed light LED structure and a preparation method thereof. BACKGROUND

[0002] At present, the mainstream implementation scheme of white light LED is to excite yellow phosphor by blue light LED, and yellow light is emitted by the excited yellow phosphor, and white light is generated by mixing blue light and yellow light. However, in specific application scenarios such as automobile headlamps, this scheme has obvious limitations: on the one hand, many phosphor schemes are difficult to stably control the color temperature below 5800K, and with the aging of the phosphor, there is a risk of unqualified annual inspection; on the other hand, from the perspective of light health, the blue light proportion in this technical scheme is relatively high, and the blue light may interfere with the human body's circadian rhythm by inhibiting the secretion of melatonin, which may pose a potential risk of hormone imbalance. Therefore, using two colors of blue light and yellow light, two colors of yellow light and red light, or multi-color mixed light becomes a better alternative.

[0003] With the expansion of application scenarios and the upgrading of user needs, traditional single-color white light has been unable to meet the diversified needs, and multi-color mixed light technology has emerged as the times require. It can not only be used to generate white light, but also can obtain other various colors of light according to different color ratios. However, the preparation process of traditional multi-color mixed light LED is extremely complex: first, different light-emitting wavelength LED chips need to be prepared through semiconductor process, and after strict selection, multi-color chips are integrated through complex packaging process; in addition, optical elements such as microlens array and prism structure are needed to realize uniform mixed light. This multi-process, multi-component preparation method not only greatly increases the production cost, but also increases the difficulty of process control. SUMMARY

[0004] Therefore, the present application provides a dual-color mixed light LED structure and a preparation method thereof, which realizes chip-level dual-color mixed light and significantly improves the mixed light uniformity and light color stability.

[0005] In a first aspect, the present application provides a dual-color mixed light LED structure, comprising: a first epitaxial light-emitting unit in the central region, emitting first color light; a second epitaxial light-emitting unit in the peripheral region, emitting second color light, the peak wavelength of the second color light being longer than that of the first color light; The second epitaxial light-emitting unit is arranged around the first epitaxial light-emitting unit, and the first color light and the second color light are mixed and emitted.

[0006] The double-color mixed light LED structure provided by the application realizes double-color mixed light at the chip level by constructing double light emitting units in the epitaxial layer. The second epitaxial light emitting unit is arranged around the first epitaxial light emitting unit, which significantly shortens the spatial distance of the two colors of light, fundamentally improves the mixed light efficiency, and greatly optimizes the light color uniformity and stability. The design breaks the technical bottleneck of traditional multi-color mixed light LED, and provides a new solution for the high-quality lighting field.

[0007] Based on the optical characteristics, short peak wavelength light is easily scattered by particles or diffusion materials in the air, forming a wide light distribution; and long peak wavelength light is easy to produce a central bright spot due to its strong penetration and low scattering rate. The structure arranges the second color light of long peak wavelength around the first color light of short peak wavelength, effectively utilizes the light propagation characteristics, further strengthens the light mixing effect, and realizes more ideal light color fusion.

[0008] As an optional solution of the double-color mixed light LED structure, the first epitaxial light emitting unit includes a first P-type layer, a first light emitting layer and a first N-type layer in the center region from bottom to top; the second epitaxial light emitting unit includes a second P-type layer, a second light emitting layer and a second N-type layer in the peripheral region from bottom to top; a passivation layer is arranged on the sidewall of the first epitaxial light emitting unit and the second epitaxial light emitting unit, the first epitaxial light emitting unit and the second epitaxial light emitting unit are electrically isolated by the passivation layer; the first epitaxial light emitting unit and the second epitaxial light emitting unit share a P electrode; a first N electrode is arranged on the first N-type layer, and a second N electrode is arranged on the second N-type layer. The vertical structure makes the current pass through the epitaxial layer vertically, and the lateral current is very small, so that the current is more uniformly distributed in the chip. The vertical structure is beneficial to the vertical emission of light, can realize better light beam quality, and improve the light mixing efficiency of the first color light and the second color light.

[0009] As a further improvement of the above-mentioned optional solution, the P electrode is bonded to a permanent substrate, the first N electrode and the permanent substrate are energized to control the light emission of the first epitaxial light emitting unit, and the second N electrode and the permanent substrate are energized to control the light emission of the second epitaxial light emitting unit. The first epitaxial light emitting unit and the second epitaxial light emitting unit are independently controlled, and the parameters of the first color light and the second color light are adjusted, so as to adjust the light mixing quality of the first color light and the second color light.

[0010] As a further improvement of the above-mentioned optional solution, an extension electrode is further arranged on the second N-type layer, the extension electrode is connected with the second N electrode, and the extension electrode is arranged around the first light emitting unit. The extension electrode can increase the contact area with the second N-type layer, and the arrangement around the first light emitting unit can make the current more uniformly distributed on the surface of the second N-type layer, so that the current flows more uniformly through the light emitting layer, and the second epitaxial light emitting unit can emit light uniformly, thereby improving the uniformity of the first color light and the second color light.

[0011] As an optional solution of the dual-color mixed light LED structure, the first color light is blue light, the second color light is yellow light, the white light is emitted after the first color light and the second color light are mixed, and the white light can be used as illumination; or the first color light is yellow light, the second color light is red light, the golden yellow light is emitted after the first color light and the second color light are mixed, and the golden yellow light can be used as a healthy illumination light source or as a car tail lamp.

[0012] In a second aspect, the application further provides a preparation method of the dual-color mixed light LED structure, comprising the following steps: S1, providing a substrate for epitaxial growth; S2, sequentially growing a first N-type layer, a first light-emitting layer, a first P-type layer, a second N-type layer, a second light-emitting layer and a second P-type layer on the substrate; S3, etching the second N-type layer, the second light-emitting layer and the second P-type layer in the central region to expose the first P-type layer in the central region; S4, repairing the electrical properties of the first P-type layer; S5, preparing a P electrode on the exposed surfaces of the first P-type layer and the second P-type layer, bonding the P electrode with a permanent substrate, and removing the substrate; S6, selectively etching the first N-type layer, the first light-emitting layer and the first P-type layer in the peripheral region to expose the second N-type layer in the peripheral region; S7, preparing an N-face passivation layer, preparing a first N electrode on the surface of the first N-type layer in the central region, and preparing a second N electrode on the surface of the second N-type layer, to complete the preparation of the dual-color mixed light LED structure.

[0013] The preparation method of the dual-color mixed light LED structure can prepare two independent epitaxial light-emitting units on the same epitaxial wafer, realize chip-level dual-color mixed light, and greatly simplify the preparation process.

[0014] As an optional solution of the preparation method of the dual-color mixed light LED structure, the electrical property repairing method in step S4 is one or a combination of wet etching, atomic layer etching or high-temperature annealing. When the first P-type layer in the central region is etched, etching damage will be caused to the first P-type layer, and the damage will cause the electrical properties of the material to decrease. The electrical property repairing can reduce or eliminate the etching damage and restore the crystal structure and electrical properties of the material. The three methods can achieve good repairing effect.

[0015] As an optional solution of the preparation method of the dual-color mixed light LED structure, the etching method is one or a combination of inductively coupled plasma dry etching, electron cyclotron resonance plasma etching, and reactive ion etching. The etching methods have good etching selectivity and anisotropy, and can achieve high-precision etching. The etching process has good stability and repeatability, and can achieve consistent etching effects between different batches, which is conducive to process control and quality assurance in large-scale production.

[0016] As a preferred solution of the preparation method of the dual-color mixed light LED structure, the step S5 further includes preparing a P-face passivation layer and activating the first P-type layer and the second P-type layer before the P electrode is prepared. The preparation of the P-face passivation layer can achieve electrical isolation of the sidewalls of the first epitaxial light emitting unit and the second epitaxial light emitting unit, which is conducive to the separate control of the first epitaxial light emitting unit and the second epitaxial light emitting unit, thereby facilitating the adjustment of the mixed light quality. The P-type activation can break the Mg-H bond in the P-type GaN, thereby increasing the hole concentration of the P-type GaN.

[0017] As a preferred solution of the preparation method of the dual-color mixed light LED structure, the step S2 further includes growing a buffer layer before the first N-type layer is grown, and the buffer layer is removed by wet etching and the surface of the first N-type layer is roughened after the substrate is removed in the step S5; and the first N-type layer, the first light emitting layer, and the first P-type layer in the peripheral region are partially etched in the step S6, so that the first N-type layer, the first light emitting layer, and the first P-type layer in the peripheral region are electrically isolated from the first N-type layer, the first light emitting layer, and the first P-type layer in the central region, and part of the second N-type layer in the peripheral region is exposed. The surface of the exposed second N-type layer inherits the roughened morphology after etching, and the light extraction efficiency of the roughened morphology of the first N-type layer surface is lower than that of the first N-type layer surface. Therefore, the etching area of the first N-type layer, the first light emitting layer, and the first P-type layer in the peripheral region is reduced. The first N-type layer, the first light emitting layer, and the first P-type layer in the peripheral region will not emit light and will not block light, while the roughened morphology of the first N-type layer is retained, which can improve the light extraction efficiency. The buffer layer is conducive to improving the crystal quality of the first N-type layer, and when the buffer layer is removed by wet etching and the surface of the first N-type layer is roughened, a better roughening effect can be achieved.

[0018] In summary, the dual-color mixed light LED structure and the preparation method thereof can realize chip-level dual-color mixed light by integrating two independent epitaxial light emitting units on the same epitaxial wafer, which not only greatly simplifies the preparation process, but also significantly improves the mixed light uniformity and light color stability. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The LED epitaxial diagram in the embodiments of the present application.

[0020] Figure 2A schematic diagram after step S3 in the embodiment of the present application.

[0021] Figure 3 A schematic diagram after preparation of the P-face passivation layer in the embodiment of the present application.

[0022] Figure 4 A schematic diagram after preparation of the P electrode in the embodiment of the present application.

[0023] Figure 5 A schematic diagram after bonding in the embodiment of the present application.

[0024] Figure 6 A schematic diagram after removal of the substrate in the embodiment of the present application.

[0025] Figure 7 A schematic diagram after roughening of the first N-type layer in the embodiment of the present application.

[0026] Figure 8 A schematic diagram after step S6 in the embodiment of the present application.

[0027] Figure 9 A schematic diagram after roughening of the second N-type layer in the embodiment of the present application.

[0028] Figure 10 A schematic diagram after preparation of the first N electrode, the second N electrode and the extension electrode in the embodiment of the present application.

[0029] Figure 11 A bird's eye view of the dual-color mixed-light LED structure prepared in the embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following described embodiments are only used to explain the present application, and are not intended to limit the present application.

[0031] Hereinafter, the terms "first", "second", etc. are only used for description convenience, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "second", "first", etc. can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more. Embodiment 1

[0032] The embodiment provides a preparation method of a dual-color mixed-light LED structure, comprising the following steps: Step S1, providing a substrate 1 for epitaxial growth, the substrate 1 is a silicon substrate.

[0033] Step S2, sequentially growing buffer layer 2, first N-type layer 3, first light emitting layer 4, first P-type layer 5, second N-type layer 6, second light emitting layer 7 and second P-type layer 8 on substrate 1, and the epitaxial structure after growth is shown in Figure 1 . Among them, the material of buffer layer 2 is AlN, the materials of first N-type layer 3 and second N-type layer 6 are both N-type GaN, the materials of first P-type layer 5 and second P-type layer 8 are both P-type GaN, first light emitting layer 4 is a blue quantum well, and second light emitting layer 7 is a yellow quantum well. The thickness of buffer layer 2 is 200 nm, the thickness of first N-type layer 3 is 1500 nm, the thickness of first light emitting layer 4 is 100 nm, the thickness of first P-type layer 5 is 300 nm, the thickness of second N-type layer 6 is 500 nm, the thickness of second light emitting layer 7 is 100 nm, and the thickness of second P-type layer 8 is 300 nm.

[0034] Step S3, etching second N-type layer 6, second light emitting layer 7 and second P-type layer 8 in the center region to expose first P-type layer 5 in the center region. Specifically, after a window is made on the surface of second P-type GaN layer 8 using standard photolithography process, mesa etching is performed using inductively coupled plasma dry etching (ICP) to etch second N-type layer 6, second light emitting layer 7 and second P-type layer 8 in the window region to expose first P-type layer 5, and the structure after etching is shown in Figure 2 . Among them, the etching gas of inductively coupled plasma dry etching (ICP) is a mixture of Cl2 and BCl3, the etching rate is 100 nm / min, the low-power etching program with direct current bias of 180V, and the etching time is about 540s.

[0035] In addition, mesa etching can also be completed by using electron cyclotron resonance plasma etching (ECR) or reactive ion etching (RIE).

[0036] Step S4, since the etching in step S3 will inevitably cause damage to first P-type layer 5, it is necessary to repair the electrical performance of first P-type layer 5. Specifically, first P-type GaN layer 5 is treated with 150℃ H3PO4 for one minute and then cleaned. High-temperature annealing is performed on first P-type GaN layer 5 at a temperature of 800℃-1000℃ in NH3 atmosphere to repair, so that first P-type GaN layer 5 restores electrical performance, and the surface after repair is obtained.

[0037] Step S5, preparing P electrode 10 on the exposed surfaces of first P-type layer 5 and second P-type layer 8, bonding P electrode 10 with permanent substrate 12, and removing substrate 1. Specifically, it includes the following steps: Step S51, first, use PECVD to deposit 300nm P-face passivation layer 9 on the exposed surface of the first P-type layer 5 and the second P-type layer 8. After using standard photolithography process to make a window on the surface of the first P-type layer 5 and the second P-type layer 8, use BOE to etch for 50s to expose the surface of the first P-type layer 5 and the second P-type layer 8 at the window position. The completed structure is as shown in Figure 3 .

[0038] Step S52, activate the first P-type layer 5 and the second P-type layer 8 by high-temperature annealing under N2, O2 atmosphere at 500-900℃. Unlike the conventional activation of the P-type GaN layer grown on the outermost layer, the inner P-type GaN layer must be etched to expose the inner P-type GaN layer, so that its surface is exposed to N2, O2 atmosphere for activation.

[0039] Preferably, the present embodiment uses RTA rapid annealing furnace, and the first P-type GaN layer 5 and the second P-type GaN layer 8 are activated by annealing at 550℃ for 3min under N2, O2 atmosphere. The completed structure is as shown in Figure 3 .

[0040] Step S53, use an electron beam evaporation table to prepare the P electrode 10, and alloy the P electrode 10 under N2, O2 atmosphere at 200-400℃. After using standard photolithography process to make a window on the surface of the P electrode 10, use wet etching to prepare the P electrode 10 pattern. The completed structure is as shown in Figure 4 .

[0041] Step S54, specifically, use an electron beam evaporation table to prepare the bonding layer 11 on the surface of the sample completed in step S53 and the permanent substrate 12 respectively, and then bond the P electrode 10 and the permanent substrate 12 through the bonding layer 11. The bonding process is as shown in Figure 5 . The permanent substrate 12 is a metal substrate.

[0042] Step S55, after thinning the substrate 1, remove it completely. The completed structure is as shown in Figure 6 .

[0043] Step S56, use wet etching (KOH) to etch at 60℃ for 5min to remove the buffer layer 2, and roughen the surface of the first N-type layer 3. The completed structure is as shown in Figure 7 .

[0044] Step S6, etch the first N-type layer 3, the first light-emitting layer 4, and the first P-type layer 5 in the surrounding area to expose the second N-type layer 6 in the surrounding area. Specifically, the following steps are included: Step S61: After creating a window on the surface of the first N-type layer 3 using standard photolithography, mesa etching is performed using inductively coupled plasma dry etching (ICP) until the second N-type GaN layer 6 is exposed. The second N-type layer 6 will inherit some of the roughened morphology of the first N-type layer 3. The structure after etching is as follows: Figure 8 As shown. Inductively coupled plasma dry etching (ICP) uses Cl2 and BCl3 as etching gases, with an etching rate of 100 nm / min, a low-power etching program with a DC bias of 180 V, and an etching time of approximately 720 s. The first N-type layer 3, the first light-emitting layer 4, and the first P-type layer 5 are divided into two parts: a central first N-type layer 301, a central first light-emitting layer 401, and a central first P-type layer 501; and surrounding first N-type layers 302, surrounding first light-emitting layers 402, and surrounding first P-type layers 502. The surrounding first N-type layers 302, surrounding first light-emitting layers 402, and surrounding first P-type layers 502 are retained for better light extraction efficiency.

[0045] In addition, dry etching can also use electron cyclotron resonance plasma etching (ECR) or reactive ion etching (RIE) to complete mesa etching.

[0046] Step S62: After creating a window on the surface of the second N-type layer 6 using standard photolithography, etch the P-surface passivation layer 9 with H3PO4 at 150℃ for 5 minutes. The etched structure is as follows. Figure 9 As shown, this etching step completes the isolation between chips.

[0047] At this point, the epitaxial layers are successfully separated through two etching steps. The first N-type layer 301, the first light-emitting layer 401, and the first P-type layer 501 in the middle form the first epitaxial light-emitting unit 101, and the second N-type layer 6, the second light-emitting layer 7, and the second P-type layer 8 form the second epitaxial light-emitting unit 102.

[0048] Step S7: Prepare an N-side passivation layer 13, prepare a first N-electrode 14 on the surface of the first N-type layer 3, and prepare a second N-electrode 15 on the surface of the second N-type layer 6 to complete the preparation of the dual-color mixed-light LED structure.

[0049] Specifically, a 500 nm N-plane passivation layer 13 is deposited and grown on the surfaces of the first epitaxial light-emitting unit 101 and the second epitaxial light-emitting unit 102 using plasma-enhanced chemical deposition (PECVD). After creating a window on the surface of the N-plane passivation layer 13 using standard photolithography, BOE etching is performed for 80 seconds to expose the predetermined electrode positions on the surfaces of the first and second epitaxial light-emitting units 101 and 102. An N-electrode is fabricated using an electron beam evaporation stage, and a first electrode layer 14, a second electrode layer 15, and an extended electrode 16 are fabricated using a lift-off process, completing the fabrication of the dual-color mixed-light LED structure. The completed structure is shown below. Figure 9 ,10 as shown.

[0050] The double-color mixed light LED structure prepared in this embodiment, as shown in Figure 9 , 10 includes a first epitaxial light emitting unit 101 emitting blue light in the central region and a second epitaxial light emitting unit 102 emitting yellow light in the peripheral region, the second epitaxial light emitting unit 102 being arranged around the first epitaxial light emitting unit 101, and the white light being emitted after the mixing of the blue light and the yellow light.

[0051] The first epitaxial light emitting unit 101 includes, from bottom to top, a first P-type layer 5, a first light emitting layer 4 and a first N-type layer 3 in the central region, and the second epitaxial light emitting unit 102 includes, from bottom to top, a second P-type layer 8, a second light emitting layer 7 and a second N-type layer 6 in the peripheral region.

[0052] The sidewalls of the first epitaxial light emitting unit 101 and the second epitaxial light emitting unit 102 are provided with N-face passivation layers 13, and the first epitaxial light emitting unit 101 and the second epitaxial light emitting unit 102 are electrically isolated by the P-face passivation layer 9 and the N-face passivation layer 13.

[0053] The first epitaxial light emitting unit 101 and the second epitaxial light emitting unit 102 share a P electrode 10, the first N-type layer 3 is provided with a first N electrode 14, the second N-type layer 6 is provided with a second N electrode 15 and an extension electrode 16, the extension electrode 16 is connected to the second N-type layer 6, and the extension electrode 16 is arranged around the first light emitting unit 101. The P electrode 10 is bonded to a permanent substrate 12, and the first epitaxial light emitting unit 101 can be controlled to emit light by applying current to the first N electrode 3 and the permanent substrate 12, and the second epitaxial light emitting unit 102 can be controlled to emit light by applying current to the second N electrode 15 and the permanent substrate 12.

[0054] The double-color mixed light LED structure prepared in this embodiment realizes chip-level double-color mixed light by constructing a blue light emitting unit and a yellow light emitting unit in an epitaxial layer. The yellow light emitting unit is arranged around the blue light emitting unit, significantly shortening the spatial distance between the two colors of light, fundamentally improving the mixed light efficiency of the blue light and the yellow light, and greatly optimizing the uniformity and stability of the color of the white light obtained by mixing light. By controlling the sizes of the input blue light and yellow light LED currents respectively, white light output of different color temperatures can be realized.

Claims

1. A dual-color mixed light LED structure, characterized in that, The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure.

2. The dual-color mixed-light LED structure of claim 1, wherein: The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure.

3. The dual-color mixed-light LED structure of claim 2, wherein: The application relates to a double-color light mixing LED structure.

4. The dual-color mixed-light LED structure according to claim 2 or 3, characterized in that: The application relates to a double-color light mixing LED structure.

5. The dual-color mixed-light LED structure of claim 1, wherein: The application relates to a double-color light mixing LED structure.

6. A method for preparing a two-color mixed light LED structure, characterized in that, The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure.

7. The method of claim 6, wherein: The application relates to a double-color light mixing LED structure.

8. The method of claim 6, wherein: The application relates to a double-color light mixing LED structure.

9. The method of claim 6, wherein: The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. 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The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light mixing LED structure. The application relates to a double-color light 10. The method of claim 6, wherein: Before the first N-type layer is grown in step S2, a buffer layer is grown, and after the substrate is removed in step S5, the buffer layer is removed by wet etching and the surface of the first N-type layer is roughened; in step S6, the first N-type layer, the first light-emitting layer and the first P-type layer in the peripheral region are partially etched, so that the first N-type layer, the first light-emitting layer and the first P-type layer in the peripheral region are electrically isolated from the first N-type layer, the first light-emitting layer and the first P-type layer in the central region, and part of the second N-type layer in the peripheral region is exposed, and the surface of the exposed second N-type layer will inherit the roughened topography after etching.

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