Micro-LED epitaxial wafer for laser lift-off, preparation method of Micro-LED epitaxial wafer and Micro-LED

Abstract

The invention discloses a Micro-LED epitaxial wafer for laser lift-off, a preparation method of the Micro-LED epitaxial wafer and a Micro-LED, and relates to the field of semiconductor photoelectric devices. The Micro-LED epitaxial wafer for laser lift-off comprises a substrate, a laser absorption layer, a laser reflection layer and an epitaxial layer, wherein the laser absorption layer, the laser reflection layer and the epitaxial layer are sequentially stacked on the substrate; wherein the laser absorption layer is of a laminated structure composed of one or at least two of a GaN layer, an AlN layer and a Si3N4 layer; the laser reflecting layer comprises a first dielectric layer and a second dielectric layer which are alternately stacked, and the first dielectric layer and the second dielectric layer are different in refractive index and lattice constant. According to the invention, the light-emitting efficiency of the Micro-LED can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic devices, and in particular to a Micro-LED epitaxial wafer for laser lift-off and a preparation method thereof, and a Micro-LED. Background Art

[0002] Micro-LEDs are relatively small in size, usually below 100μm, and can even reach 50μm. However, the vacuum tube limit during the transfer process can only reach 80μm, making it difficult to achieve high-precision and small-size device transfer. Moreover, if the substrate is not peeled off, due to the certain weight and volume of the substrate, the Micro-LED will also be subjected to greater stress and damage during the transfer process, reducing the transfer yield. Therefore, in the existing process, the substrate of the Micro-LED is often peeled off by a laser process before transfer. Specifically, for the currently common GaN-based Micro-LEDs, during the laser peeling process, part of the GaN in the epitaxial layer will absorb the laser energy and undergo thermal decomposition, thereby separating the epitaxial layer from the substrate. During laser peeling, the laser will damage the epitaxial layer, resulting in reduced light efficiency. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a Micro-LED epitaxial wafer for laser peeling and a preparation method thereof, which can reduce laser peeling damage and improve the luminous efficiency of Micro-LED.

[0004] Another technical problem to be solved by the present invention is to provide a Micro-LED.

[0005] In order to solve the above problems, the present invention provides a Micro-LED epitaxial wafer for laser lift-off, which includes a substrate, a laser absorption layer, a laser reflection layer and an epitaxial layer sequentially stacked on the substrate; Wherein, the laser absorption layer is a stacked structure composed of one or at least two of a GaN layer, an AlN layer, and a Si3N4 layer; The laser reflection layer includes a first medium layer and a second medium layer alternately stacked, and the first medium layer and the second medium layer have different refractive indices and lattice constants.

[0006] As an improvement of the above technical solution, the refractive index of the first dielectric layer is smaller than the refractive index of the second dielectric layer, and the lattice constant of the first dielectric layer is larger than the lattice constant of the second dielectric layer.

[0007] As an improvement of the above technical solution, the lattice constant of the first dielectric layer is a, the lattice constant of the second dielectric layer is b, and the lattice constant of the substrate is c; a>c>b, and (ac) / a≤5%.

[0008] As an improvement of the above technical solution, the first dielectric layer is one of a SiO2 layer, a MgF2 layer, a Ta2O5 layer, and an AlGaN layer; The second dielectric layer is one of a TiO2 layer, a LaF3 layer, a SiO2 layer, an AlN layer, and a HfO2 layer.

[0009] As an improvement of the above technical solution, the laser absorption layer is a GaN layer with a thickness of 50nm~500nm.

[0010] As an improvement of the above technical solution, the period number of the laser reflection layer is 4 to 8, the first dielectric layer is a SiO2 layer with a thickness of 35nm to 42nm; the second dielectric layer is a TiO2 layer with a thickness of 15nm to 22nm.

[0011] As an improvement of the above technical solution, the period number of the laser reflection layer is 4-8, the first dielectric layer is a MgF2 layer with a thickness of 40nm-50nm; the second dielectric layer is a LaF3 layer with a thickness of 20nm-30nm.

[0012] As an improvement of the above technical solution, the epitaxial layer includes a buffer layer, an N-type GaN layer, an active layer and a P-type GaN layer stacked in sequence on the laser reflection layer; The buffer layer is an AlN layer, and its thickness is 30nm-80nm; or The buffer layer includes a first sublayer and a second sublayer alternately stacked, with a period number of 5 to 10. The first sublayer is an AlN layer with a thickness of 5 nm to 10 nm, and the second sublayer is an AlGaN layer with a thickness of 2 nm to 8 nm.

[0013] Correspondingly, the present invention also discloses a method for preparing a Micro-LED epitaxial wafer for laser lift-off, which is used to prepare the above-mentioned Micro-LED epitaxial wafer for laser lift-off, and comprises: Providing a substrate, and sequentially growing a laser absorption layer, a laser reflection layer and an epitaxial layer on the substrate; Wherein, the laser absorption layer is a stacked structure composed of one or at least two of a GaN layer, an AlN layer, and a Si3N4 layer; The laser reflection layer includes a first medium layer and a second medium layer which are alternately stacked. The first medium layer and the second medium layer have different refractive indices and lattice constants.

[0014] Correspondingly, the present invention also discloses a Micro-LED, which includes the above-mentioned Micro-LED epitaxial wafer for laser lift-off.

[0015] The implementation of the present invention has the following beneficial effects: The Micro-LED epitaxial wafer for laser stripping in one embodiment of the present invention includes a substrate, a laser absorption layer, a laser reflection layer and an epitaxial layer stacked on the substrate in sequence; wherein the laser absorption layer is a stacked structure composed of one or at least two of a GaN layer, an AlN layer and a Si3N4 layer; the laser reflection layer includes a first dielectric layer and a second dielectric layer stacked alternately, and the first dielectric layer and the second dielectric layer have different refractive indices and lattice constants. Based on the above-mentioned Micro-LED epitaxial wafer, firstly, the laser absorption layer can absorb laser energy, and then decompose or change stress to achieve stripping, and the laser reflection layer can reflect the laser that is not completely absorbed by the laser absorption layer through the matching of refractive index, and emit it from the substrate to avoid laser damage to the epitaxial layer. Secondly, by controlling the different lattice constants of the first dielectric layer and the second dielectric layer, the effect of dislocation kinking and annihilation can be achieved, the dislocation density extending to the epitaxial layer can be reduced, the crystal quality of the epitaxial layer can be improved, and the luminous efficiency of the Micro-LED can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of a Micro-LED epitaxial wafer used for laser lift-off in one embodiment of the present invention; Figure 2 is a schematic structural diagram of a laser reflection layer in one embodiment of the present invention; Figure 3 is a schematic structural diagram of a Micro-LED epitaxial wafer used for laser lift-off in another embodiment of the present invention; Figure 4 Schematic diagram of the structure of a buffer layer in one embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in further detail below.

[0018] See also Figure 1 and Figure 2The present invention discloses a Micro-LED epitaxial wafer for laser stripping, which includes a substrate 100, a laser absorption layer 200, a laser reflection layer 300 and an epitaxial layer 400 stacked on the substrate 100 in sequence; wherein the laser absorption layer 200 is a stacked structure composed of one or at least two of a GaN layer, an AlN layer and a Si3N4 layer; the laser reflection layer 300 includes a first dielectric layer 310 and a second dielectric layer 320 stacked alternately, and the refractive index and lattice constant of the first dielectric layer 310 and the second dielectric layer 320 are different. Based on the Micro-LED epitaxial wafer, on the one hand, the laser absorption layer 200 can absorb laser energy, and then decompose or change stress to achieve stripping, and the laser reflection layer 300 can reflect the laser that is not completely absorbed by the laser absorption layer 200 through the matching of the refractive index, and emit it from the substrate 100, so as to avoid laser damage to the epitaxial layer 400. Secondly, by controlling the different lattice constants of the first dielectric layer 310 and the second dielectric layer 320, dislocation kinking and annihilation can be achieved, thereby reducing the dislocation density extending to the epitaxial layer 400, improving the crystal quality of the epitaxial layer 400, and further improving the luminous efficiency of the Micro-LED.

[0019] Specifically, the substrate 100 may be a sapphire substrate, a silicon substrate, or a silicon carbide substrate, but is not limited thereto. Preferably, in one embodiment, the substrate 100 is a sapphire substrate, which has a high process maturity and is easy to laser lift off. A silicon substrate may have the problem of absorbing laser light, and a silicon carbide substrate has a high cost.

[0020] Specifically, the thickness of the laser absorption layer 200 is 30 nm to 500 nm. If the thickness is too thin, the epitaxial layer 400 is easily damaged; if the thickness is too thick, the peeling cannot be achieved.

[0021] Specifically, the first dielectric layer 310 is one of SiO2 layer, MgF2 layer, Ta2O5 layer, AlGaN layer, AlGaAs layer, TiO2 layer, LaF3 layer, AlN layer, HfO2 layer, and AlAs layer, but not limited thereto. The second dielectric layer 320 is one of SiO2 layer, MgF2 layer, Ta2O5 layer, AlGaN layer, AlGaAs layer, TiO2 layer, LaF3 layer, AlN layer, HfO2 layer, and AlAs layer, but not limited thereto. Based on the above-mentioned first dielectric layer 310 and second dielectric layer 320, the following laser reflection layer 300 can be obtained: AlGaAs / AlAs, SiO2 / TiO2, Ta2O5 / SiO2, AlGaN / AlN, MgF2 / LaF3, SiO2 / HfO2. The above-mentioned laser reflection layer 300 can realize the reflection of laser, and the reflectivity is ≥85%. It should be noted that the laser in this embodiment refers to UV laser, and its wavelength is 180nm~300nm.

[0022] Specifically, the epitaxial layer 400 may be a common GaN epitaxial layer or an AlGaN epitaxial layer in the art, but is not limited thereto. In one embodiment, the epitaxial layer 400 is a GaN epitaxial layer, which includes an N-type GaN layer 410, an active layer 420 (InGaN / GaN multi-quantum well layer) and a P-type GaN layer 430 stacked in sequence, but is not limited thereto.

[0023] Preferably, in one embodiment, the refractive index of the first dielectric layer 310 is less than the refractive index of the second dielectric layer 320, and the lattice constant of the first dielectric layer 310 is greater than the lattice constant of the second dielectric layer 320. Since the lattice constant of the sapphire substrate is relatively large (about 4.76Å) and the lattice constant of the GaN layer is relatively small (3.18Å), the lattice mismatch between the substrate 100 and the epitaxial layer 400 is relatively large. By controlling the lattice constant of the first dielectric layer 310 to be greater than the lattice constant of the second dielectric layer 320, dislocations can be twisted and annihilated, thereby improving the lattice quality of the epitaxial layer 400 and the luminous efficiency of the Micro-LED.

[0024] Further preferably, in one embodiment, the lattice constant of the first dielectric layer 310 is a, the lattice constant of the second dielectric layer 320 is b, and the lattice constant of the substrate 100 is c; a>c>b, and (ac) / a≤5%. Based on the control of the above lattice constant relationship, the luminous efficiency can be further improved.

[0025] Preferably, in one embodiment, the first dielectric layer 310 is one of SiO2 layer, MgF2 layer, Ta2O5 layer, and AlGaN layer; the second dielectric layer 320 is one of TiO2 layer, LaF3 layer, SiO2 layer, AlN layer, and HfO2 layer. The laser reflection layer 300 composed of the first dielectric layer 310 and the second dielectric layer 320 can better reflect the laser and further reduce the damage to the epitaxial layer 400.

[0026] Preferably, in one embodiment, the laser absorption layer 200 is a GaN layer with a thickness of 50nm-500nm. The number of periods of the laser reflection layer 300 is 4-8, the first dielectric layer 310 is a SiO2 layer with a thickness of 35nm-42nm, and the second dielectric layer 320 is a TiO2 layer with a thickness of 15nm-22nm.

[0027] Preferably, in another embodiment, the laser absorption layer 200 is a GaN layer with a thickness of 50nm to 500nm. The number of periods of the laser reflection layer 300 is 4 to 8, the first dielectric layer 310 is a MgF2 layer with a thickness of 40nm to 50nm; the second dielectric layer 320 is a LaF3 layer with a thickness of 20nm to 30nm. This laser reflection layer 300 not only has a high laser reflectivity, but also has a low formation temperature, which avoids the accumulation of excessive thermal stress and further improves the crystal quality of the epitaxial layer 400.

[0028] Preferably, in one embodiment, see Figure 3 The epitaxial layer 400 includes a buffer layer 440, an N-type GaN layer 410, an active layer 420, and a P-type GaN layer 430 sequentially stacked on the laser reflection layer 300. The introduction of the buffer layer 440 can further improve the crystal quality of the epitaxial layer 400. Specifically, the buffer layer 440 can be an AlN layer or a GaN layer, and its thickness is 30nm to 80nm, but is not limited thereto.

[0029] Preferably, in one embodiment, see Figure 4 The buffer layer 440 includes a first sublayer 441 and a second sublayer 442 alternately stacked, and the number of cycles is 5 to 10. The first sublayer 441 is an AlN layer with a thickness of 5 nm to 10 nm, and the second sublayer 442 is an AlGaN layer with a thickness of 2 nm to 8 nm. Based on the buffer layer 440, not only the crystal quality of the epitaxial layer 400 can be improved, but also the residual laser can be reflected, further reducing the damage to the epitaxial layer 400.

[0030] Accordingly, an embodiment of the present invention further discloses a method for preparing the above-mentioned Micro-LED epitaxial wafer for laser lift-off, which comprises: S1. providing a substrate; S2. Growing a laser absorption layer, a laser reflection layer and an epitaxial layer in sequence on the substrate.

[0031] Among them, the laser absorption layer 200 is a stacked structure composed of one or at least two of the GaN layer, the AlN layer, and the Si3N4 layer; the laser reflection layer 300 includes a first dielectric layer 310 and a second dielectric layer 320 alternately stacked, and the refractive index and lattice constant of the first dielectric layer 310 and the second dielectric layer 320 are different. Based on the Micro-LED epitaxial wafer, on the one hand, the laser absorption layer 200 can absorb laser energy, and then decompose or change stress to achieve peeling, and the laser reflection layer 300 can reflect the laser that is not completely absorbed by the laser absorption layer 200 through the matching of refractive index, and emit it from the substrate 100 to avoid laser damage to the epitaxial layer 400. On the other hand, by controlling the different lattice constants of the first dielectric layer 310 and the second dielectric layer 320, the dislocation kinking and annihilation can be played, the dislocation density extending to the epitaxial layer 400 is reduced, the crystal quality of the epitaxial layer 400 is improved, and the luminous efficiency of the Micro-LED is improved.

[0032] Specifically, the laser absorption layer can be grown by MOCVD, CVD, MBE, PVD and other methods, but is not limited thereto. Preferably, in one embodiment, the laser absorption layer is grown by MOCVD, the growth temperature is 800° C. to 900° C., and the growth pressure is 150 torr to 500 torr.

[0033] Specifically, the laser reflection layer can be grown by MOCVD, CVD, PECVD, PVD and other methods, but not limited thereto. Preferably, in one embodiment, SiO2 layers and TiO2 layers can be alternately grown by MOCVD until a laser reflection layer is obtained, wherein when the SiO2 layer is grown, the MO source used includes TEOS, but not limited thereto. The growth temperature of the SiO2 layer is 600°C to 800°C. When the TiO2 layer is grown, the MO source used is titanium tetraisopropoxide, but not limited thereto. The growth temperature of the TiO2 layer is 400°C to 600°C.

[0034] In another embodiment, MgF2 layers and LaF3 layers may be alternately grown by MOCVD until a laser reflection layer is obtained. When the MgF2 layer is grown, the MO source used includes, but is not limited to, magnesium cyclopentadienyl, HF or NF3. The growth temperature of the MgF2 layer is 300°C to 500°C. When the LaF3 layer is grown, the MO source used includes, but is not limited to, trimethyllanthanum, HF or NF3. The growth temperature of the LaF3 layer is 400°C to 600°C.

[0035] Preferably, in one embodiment, when the epitaxial layer includes a buffer layer, it can be grown by MOCVD or PVD, but is not limited thereto. Preferably, in one embodiment, when the buffer layer is an AlN layer, it is grown by MOCVD, and its growth temperature is 900°C to 1000°C. In another embodiment, when the buffer layer is a periodic structure formed by an AlN layer and an AlGaN layer, it is grown by MOCVD, and the growth temperature of the AlN layer is 900°C to 1000°C, and the growth temperature of the AlGaN layer is 800°C to 950°C.

[0036] The present invention will be further described below with specific embodiments: Example 1 This embodiment provides a Micro-LED epitaxial wafer for laser lift-off, which includes a substrate, a laser absorption layer, a laser reflection layer and an epitaxial layer sequentially stacked on the substrate; The substrate is a sapphire substrate, the laser absorption layer is a GaN layer with a thickness of 80 nm, the laser reflection layer includes a first dielectric layer and a second dielectric layer alternately stacked, the period number of which is 5, the first dielectric layer is a TiO2 layer with a thickness of 19 nm, and the second dielectric layer is a SiO2 layer with a thickness of 39.5 nm.

[0037] The epitaxial layer includes an N-type GaN layer, an InGaN / GaN-type multi-quantum well layer and a P-type GaN layer stacked in sequence.

[0038] Example 2 This embodiment provides a Micro-LED epitaxial wafer for laser lift-off, which is different from Embodiment 1 in that: The first dielectric layer is a SiO2 layer, and its thickness is 39.5 nm; the second dielectric layer is a TiO2 layer, and its thickness is 19 nm.

[0039] The rest are the same as in Example 1.

[0040] Example 3 This embodiment provides a Micro-LED epitaxial wafer for laser lift-off, which is different from Embodiment 2 in that: The epitaxial layer also includes a buffer layer, which is an AlN layer, which is arranged on the laser reflection layer and has a thickness of 50 nm.

[0041] The rest is the same as Example 2.

[0042] Example 4 This embodiment provides a Micro-LED epitaxial wafer for laser lift-off, which is different from Embodiment 3 in that: The first dielectric layer is a MgF2 layer, and its thickness is 42.3 nm; the second dielectric layer is a LaF3 layer, and its thickness is 23 nm.

[0043] The rest is the same as Example 3.

[0044] Example 5 This embodiment provides a Micro-LED epitaxial wafer for laser lift-off, which is different from Embodiment 4 in that: The buffer layer includes an AlN layer and an AlGaN layer alternately stacked, the number of periods is 8, the thickness of the AlN layer is 8 nm, and the thickness of the AlGaN layer is 3 nm.

[0045] The rest is the same as Example 4.

[0046] Comparative Example 1 This comparative example provides a Micro-LED epitaxial wafer, which is different from Example 1 in that: The laser absorption layer and the laser reflection layer are not included, and the rest are the same as those in Example 1.

[0047] The Micro-LED epitaxial wafers obtained in Examples 1 to 5 and Comparative Example 1 were prepared into Micro-LEDs with a size of 50 μm×50 μm and a horizontal structure, and 2 The brightness was tested at a current density of , and the brightness improvement rate was calculated based on the data of comparative example 1. The specific results are shown in the following table:

[0048] The above is a preferred embodiment of the invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the invention. These improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A Micro-LED epitaxial wafer for laser lift-off, characterized in that: It includes a substrate, a laser absorption layer, a laser reflection layer and an epitaxial layer sequentially stacked on the substrate; Wherein, the laser absorption layer is a stacked structure composed of one or at least two of a GaN layer, an AlN layer, and a Si3N4 layer; The laser reflection layer includes a first medium layer and a second medium layer which are alternately stacked. The first medium layer and the second medium layer have different refractive indices and lattice constants.

2. The Micro-LED epitaxial wafer for laser lift-off according to claim 1, characterized in that: The refractive index of the first dielectric layer is smaller than the refractive index of the second dielectric layer, and the lattice constant of the first dielectric layer is larger than the lattice constant of the second dielectric layer.

3. The Micro-LED epitaxial wafer for laser lift-off according to claim 1, characterized in that: The lattice constant of the first dielectric layer is a, the lattice constant of the second dielectric layer is b, and the lattice constant of the substrate is c; a>c>b, and (ac) / a≤5%.

4. The Micro-LED epitaxial wafer for laser lift-off according to claim 1, characterized in that: The first dielectric layer is one of a SiO2 layer, a MgF2 layer, a Ta2O5 layer, and an AlGaN layer; The second dielectric layer is one of a TiO2 layer, a LaF3 layer, a SiO2 layer, an AlN layer, and a HfO2 layer.

5. The Micro-LED epitaxial wafer for laser lift-off according to claim 1, characterized in that: The laser absorption layer is a GaN layer, and its thickness is 50nm-500nm.

6. The Micro-LED epitaxial wafer for laser lift-off according to claim 5, characterized in that: The period number of the laser reflection layer is 4-8, the first dielectric layer is a SiO2 layer, and its thickness is 35nm-42nm; the second dielectric layer is a TiO2 layer, and its thickness is 15nm-22nm.

7. The Micro-LED epitaxial wafer for laser lift-off according to claim 5, characterized in that: The number of periods of the laser reflection layer is 4-8, the first dielectric layer is a MgF2 layer, and its thickness is 40nm-50nm; the second dielectric layer is a LaF3 layer, and its thickness is 20nm-30nm.

8. The Micro-LED epitaxial wafer for laser lift-off according to claim 1, wherein: The epitaxial layer includes a buffer layer, an N-type GaN layer, an active layer and a P-type GaN layer sequentially stacked on the laser reflection layer; The buffer layer is an AlN layer, and its thickness is 30nm-80nm; or The buffer layer includes a first sublayer and a second sublayer alternately stacked, with a period number of 5 to 10. The first sublayer is an AlN layer with a thickness of 5 nm to 10 nm, and the second sublayer is an AlGaN layer with a thickness of 2 nm to 8 nm.

9. A method for preparing a Micro-LED epitaxial wafer for laser lift-off, for preparing the Micro-LED epitaxial wafer for laser lift-off as claimed in any one of claims 1 to 8, characterized in that: include: Providing a substrate, and sequentially growing a laser absorption layer, a laser reflection layer and an epitaxial layer on the substrate; Wherein, the laser absorption layer is a stacked structure composed of one or at least two of a GaN layer, an AlN layer, and a Si3N4 layer; The laser reflection layer includes a first medium layer and a second medium layer which are alternately stacked. The first medium layer and the second medium layer have different refractive indices and lattice constants.

10. A Micro-LED, characterized in that: It comprises a Micro-LED epitaxial wafer for laser lift-off as described in any one of claims 1 to 8.

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