Multi-wavelength light emitting diodes and light emitting modules

Abstract

The present invention relates to the field of semiconductor device technology, and in particular to a multi-wavelength light-emitting diode and a light-emitting module. The multi-wavelength light-emitting diode includes a multi-quantum well layer, which includes at least m groups of light-emitting areas that generate light of different wavelengths along a first direction; the first well layer of the first light-emitting area closest to the N-type semiconductor layer in the multi-quantum well layer has the highest In concentration or the smallest bandgap width; the second light-emitting area is arranged on the first light-emitting area, and the bandgap width of the second well layer is greater than or equal to the first well layer; the third light-emitting area is arranged on the second light-emitting area, and the bandgap width of the third well layer is greater than the second well layer; a buffer zone is arranged in the multi-quantum well layer, which is arranged between the first light-emitting area and the second light-emitting area or arranged in the second light-emitting area; the bandgap width of the buffer zone is greater than the second well layer. The light-emitting diode of the present invention can alleviate lattice mismatch, improve the crystal quality of the light-emitting area, and improve the luminous efficiency by setting the buffer zone in conjunction with the parameter settings of the other light-emitting areas.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a multi-wavelength light-emitting diode and light-emitting module. Background Technology

[0002] Light-emitting diodes (LEDs) efficiently convert electrical energy into light energy and are widely used in lighting, displays, and other fields. With technological advancements, the demand for full-spectrum light in white lighting is increasing. Integrating multiple wavelengths on a single chip can effectively reduce the manufacturing cost of full-spectrum devices. Furthermore, in the fabrication of micro LEDs (micro light-emitting diodes), mass transfer technology is one of the main technological bottlenecks. Integrating multiple wavelengths on a single chip can alleviate the technical burden of mass transfer and reduce the manufacturing difficulty of Micro LED products.

[0003] Existing epitaxial technology for multi-wavelength LEDs involves sequentially growing quantum wells of multiple wavelengths in the active region. Because the band gaps of different wavelengths of the emitting region have varying carrier acceptance capabilities, the active region typically grows in a sequence from narrow to wide well band gaps along the N-side to the P-side. Since the emitting region with the narrower band gap grows first, and these narrower band gap regions usually have higher In content or thicker well layers, this leads to a significant lattice mismatch between the emitting region and its preceding and following layers. This, in turn, generates a large piezoelectric polarization field, affecting the crystal quality and luminous efficiency of subsequent emitting regions.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One object of the present invention is to provide a multi-wavelength light-emitting diode that can balance the carrier capture ability of each well layer and buffer the lattice mismatch caused by the bandgap difference of each well layer, so as to improve the luminous efficiency.

[0006] Another object of the present invention is to provide a light-emitting module.

[0007] To achieve the above-mentioned objectives of the present invention, one aspect of the present invention provides a multi-wavelength light-emitting diode, comprising: a multi-quantum well layer disposed between an N-type semiconductor layer and a P-type semiconductor layer;

[0008] The direction from the N-type semiconductor layer to the P-type semiconductor layer is defined as the first direction. The multi-quantum well layer includes m groups of light-emitting regions that generate light of different wavelengths along the first direction. Each light-emitting region includes at least one well layer and one barrier layer, where m ≥ 3.

[0009] The first light-emitting region of the multi-quantum well layer closest to the N-type semiconductor layer has the highest In concentration or the smallest bandgap. The second light-emitting region, which includes a second well layer and a second barrier layer, is disposed on the first light-emitting region, wherein the bandgap of the second well layer is greater than or equal to that of the first well layer. The third light-emitting region, which includes a third well layer and a third barrier layer, is disposed on the second light-emitting region, wherein the bandgap of the third well layer is greater than that of the second well layer.

[0010] The multi-quantum well layer further includes a buffer; the buffer is disposed between the first luminescent region and the second luminescent region, or the buffer is disposed within the second luminescent region; the band gap of the buffer is greater than that of the second well layer.

[0011] In a specific embodiment of the present invention, the buffer includes at least one of an undoped GaN monolayer, a doped GaN monolayer, and a superlattice structure layer; the doping element includes at least one of In, Si, Al, and Mg.

[0012] Furthermore, the buffer comprises an InGaN monolayer and a Si-doped GaN monolayer, wherein the In concentration in the InGaN monolayer is less than or equal to the In concentration in the second well layer; and the In concentration in the InGaN monolayer is greater than or equal to the In concentration in the third well layer.

[0013] In a specific embodiment of the present invention, the superlattice structure layer has a period number of 1 to 50. Further, the superlattice structure layer includes at least one of the following: InGaN / GaN superlattice structure layer, InGaN / AlGaN superlattice structure layer, InAlGaN / GaN superlattice structure layer, and InAlGaN / InGaN superlattice structure layer.

[0014] In a specific embodiment of the present invention, the peak wavelength generated by each light-emitting region of the multi-quantum-well layer gradually decreases in the first direction. Furthermore, the difference in peak wavelength Δλ between adjacent light-emitting regions is ≤25nm.

[0015] In a specific embodiment of the present invention, the bandgap width of the first light-emitting region well layer to the bandgap width of the m-th light-emitting region well layer gradually increases in the first direction.

[0016] In a specific embodiment of the present invention, the In concentration in the first light-emitting region well layer to the In concentration in the m-th light-emitting region well layer gradually decreases in the first direction.

[0017] In a specific embodiment of the present invention, the spectrum of the multiple quantum well layer has at least three peaks between 420 and 480 nm, including a first peak between 435 and 447 nm, a second peak between 445 and 457 nm, and a third peak between 460 and 473 nm.

[0018] Among them, the third peak has the smallest peak intensity, and at least one of the first or second peaks has the largest peak intensity. The ratio of the peak intensity of the third peak to the maximum peak intensity is 0.4 to 0.6; the ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.8 to 1, or the ratio of the peak intensity of the second peak to the peak intensity of the first peak is 0.8 to 1.

[0019] In a specific embodiment of the present invention, one well layer and one barrier layer in each light-emitting region are defined as one cycle, the number of cycles in the first light-emitting region is 1 to 5, the number of cycles in the second light-emitting region is 1 to 5, and the number of cycles in the third light-emitting region is 1 to 15.

[0020] In a specific embodiment of the present invention, the multi-quantum-well layer further includes an (m+1)th light-emitting region close to the P-type semiconductor layer. The light-emitting region adjacent to the (m+1)th light-emitting region and far from the P-type semiconductor layer is the m-th light-emitting region. The (m+1)th light-emitting region satisfies at least one of the following conditions:

[0021] (1) The In concentration of the well layer in the (m+1)th luminescent region is greater than the In concentration of the well layer in the mth luminescent region;

[0022] (2) The bandgap width of the well layer of the (m+1)th luminescent region is smaller than the bandgap width of the well layer of the mth luminescent region.

[0023] In a specific embodiment of the present invention, the multi-quantum well layer includes five groups of light-emitting regions, which are respectively a first light-emitting region, a second light-emitting region, a third light-emitting region, a fourth light-emitting region, and a fifth light-emitting region along the first direction; and satisfy at least one of the following conditions:

[0024] (1) The thicknesses of the individual well layers in the first light-emitting region, the second light-emitting region, the third light-emitting region, the fourth light-emitting region and the fifth light-emitting region are d1, d2, d3, d4 and d5 respectively, and each thickness satisfies: d2≤d3≤d4≤d1, and d4 and d5 satisfy: d4>d5 or d4<d5 or d4=d5;

[0025] (2) The concentrations of In in a single trap layer of the first luminescent region, the second luminescent region, the third luminescent region, the fourth luminescent region and the fifth luminescent region are X1, X2, X3, X4 and X5, respectively. Each concentration satisfies: X1 > X2 > X3 > X4, and X4 and X5 satisfy: X4 > X5 or X4 < X5 or X4 = X5;

[0026] (3) The band gap widths of the individual well layers of the first luminescent region, the second luminescent region, the third luminescent region, the fourth luminescent region and the fifth luminescent region are Eg1, Eg2, Eg3, Eg4 and Eg5, respectively. Each band gap width satisfies: Eg1≤Eg2<Eg3<Eg4, and Eg4 and Eg5 satisfy: Eg4>Eg5 or Eg4<Eg5 or Eg4=Eg5;

[0027] (4) The number of periodic structures of the trap and barrier layers in the first, second, third, fourth and fifth light-emitting regions are Y1, Y2, Y3, Y4 and Y5, respectively, and the number of each periodic structure satisfies: Y1≤Y2≤Y3≤Y4, Y4≥Y5;

[0028] (5) The peak wavelengths generated by the first, second, third, fourth and fifth light-emitting regions are λ1, λ2, λ3, λ4 and λ5, respectively, and each peak wavelength satisfies: λ1>λ2>λ3>λ4, λ5>λ4.

[0029] In another aspect, the present invention provides a light-emitting module, including any of the light-emitting diodes and wavelength conversion units described above; the light generated by the light-emitting diodes is mixed with the wavelength conversion unit to generate white light.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The light-emitting diode of the present invention, by setting a buffer zone between the first light-emitting region and the second light-emitting region or setting a buffer zone in the second light-emitting region, and in conjunction with the parameter settings of the other light-emitting regions, can better balance the difference in carrier capture ability of each well layer caused by the different band gaps of each light-emitting region, and can alleviate the lattice mismatch caused by the band gap difference of each light-emitting region, and improve the crystal quality of the light-emitting region.

[0032] (2) When the light-emitting diode of the present invention is combined with wavelength conversion material, a light-emitting module with high luminous efficiency can be obtained. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the epitaxial structure of a light-emitting diode provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of a multi-quantum well layer provided in an embodiment of the present invention;

[0036] Figure 3 This is another schematic diagram of the structure of the multi-quantum well layer provided in an embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of a light-emitting diode structure provided in an embodiment of the present invention;

[0038] Figure 5 This is a spectral distribution diagram of the light-emitting diode of the present invention;

[0039] Figure 6 This is another spectral distribution diagram of the light-emitting diode of the present invention;

[0040] Figure 7 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 1 of the present invention;

[0041] Figure 8 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 2 of the present invention;

[0042] Figure 9 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 3 of the present invention;

[0043] Figure 10 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 4 of the present invention;

[0044] Figure 11 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 5 of the present invention.

[0045] Figure label:

[0046] 10 - Substrate; 20 - Buffer layer; 30 - N-type semiconductor layer; 40 - Stress relief layer; 50 - Multiple quantum well layer; 60 - P-type semiconductor layer; 51 - First light-emitting region; 52 - Second light-emitting region; 53 - m-th light-emitting region; 500 - Buffer zone; 55 - (m+1)-th light-emitting region; 51a - Well layer of the first light-emitting region; 51b - Barrier layer of the first light-emitting region; 52a - Well layer of the second light-emitting region; 52b - Barrier layer of the second light-emitting region; 53a - Well layer of the m-th light-emitting region; 53b - Barrier layer of the m-th light-emitting region; 55 a - Well layer of the (m+1)th luminescent region; 55b - Barrier layer of the (m+1)th luminescent region; 511 - First well layer; 512 - First barrier layer; 521 - Second well layer; 522 - Second barrier layer; 531 - Third well layer; 532 - Third barrier layer; 541 - Fourth well layer; 542 - Fourth barrier layer; 551 - Fifth well layer; 552 - Fifth barrier layer; P12, P22 - Second peak; P11, P21 - First peak; P13, P23 - Third peak; 501 - InGaN layer; 502 - GaN layer. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0048] 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.

[0049] In existing epitaxial technologies for multi-wavelength LEDs, quantum wells of multiple wavelengths are grown sequentially in the active region. Because the band gaps of the emitting regions at different wavelengths are different, and these band gaps have varying carrier acceptance capabilities, the growth sequence typically shows a narrowing-to-widening band gap from the N-type semiconductor side to the P-type semiconductor layer side. Narrow band gap emitting regions either correspond to high In content or thick well layers, both of which lead to significant lattice mismatch between the emitting region and the layers before and after it, affecting crystal quality and luminous efficiency.

[0050] Based on this, the present invention provides a multi-wavelength light-emitting diode, Figure 1 This is a schematic diagram of the epitaxial structure of a light-emitting diode provided in an embodiment of the present invention. The epitaxial structure of the light-emitting diode includes:

[0051] The substrate 10 includes a buffer layer 20, an N-type semiconductor layer 30, a stress relief layer 40, a multi-quantum well layer 50, and a P-type semiconductor layer 60 sequentially disposed on the substrate 10. The multi-quantum well layer includes m groups of light-emitting regions capable of generating light of different wavelengths, where m ≥ 3. For example, m can be a natural number such as 3, 4, 5, or 6, but is not limited to this.

[0052] Figure 2 This is a schematic diagram of the structure of a multi-quantum-well layer provided in an embodiment of the present invention. The direction from the N-type semiconductor layer 30 to the P-type semiconductor layer 60 is defined as the first direction. The multi-quantum-well layer along the first direction includes m groups of light-emitting regions that generate light of different wavelengths, including a first light-emitting region 51 closest to the N-type semiconductor layer 30, a second light-emitting region 52 adjacent to the first light-emitting region 51, an m-th light-emitting region 53 closest to the P-type semiconductor layer 60, and one or more optional light-emitting regions (not shown, denoted by ...) between the second light-emitting region 52 and the m-th light-emitting region 53.

[0053] Furthermore, each light-emitting region includes at least one periodic structure of alternatingly stacked well layers and barrier layers. For example, the first light-emitting region 51 includes alternatingly stacked well layers 51a and barrier layers 51b of the first light-emitting region, the second light-emitting region 52 includes alternatingly stacked well layers 52a and barrier layers 52b of the second light-emitting region, and the m-th light-emitting region 53 includes alternatingly stacked well layers 53a and barrier layers 53b of the m-th light-emitting region.

[0054] Among them, the well layer 51a of the first luminescent region has the highest In concentration or the smallest bandgap.

[0055] The multi-quantum well layer 50 further includes a buffer 500, which is disposed between the first light-emitting region 51 and the adjacent second light-emitting region 52, or the buffer 500 is disposed within the second light-emitting region 52; it includes at least one of undoped GaN monolayer, doped GaN monolayer and superlattice structure layer, with a thickness > 10 Å.

[0056] When the buffer 500 is located within the second light-emitting area 52, the buffer 500 can be located between two adjacent well layers in the second light-emitting area 52.

[0057] In the multi-quantum well layer 50 of the present invention, the well layer 51a of the first luminescent region that grows first has the highest In concentration or the smallest bandgap width. With the setting of the buffer 500, the difference in carrier capture ability of each well layer caused by the different band gaps of each luminescent region is balanced, and the lattice mismatch caused by the band gap difference of each luminescent region is alleviated, thereby improving the crystal quality of the luminescent region.

[0058] In an embodiment of the present invention, as a preferred embodiment, the thickness of the buffer zone 500 is 100 to 10000 Å, including but not limited to 100 Å, 150 Å, 200 Å, 500 Å, 1000 Å, 2000 Å, 3000 Å, 5000 Å, 6000 Å, 8000 Å, 9000 Å, 10000 Å or any combination thereof.

[0059] In an embodiment of the present invention, as an optional embodiment, the In concentration of the well layer 51a in the first light-emitting region is >3×10⁻⁶. 20 Atoms / cm 3 Or the bandgap of the well layer 51a of the first luminescent region is the minimum, that is, not greater than the bandgap of the well layer of each luminescent region in the entire multi-quantum well layer.

[0060] In an embodiment of the present invention, as an optional embodiment, when the buffer 500 is a doped GaN monolayer, the doping element may include at least one of In, Si, Al and Mg.

[0061] Furthermore, the doped GaN monolayer is an InGaN monolayer, and the In concentration in the InGaN monolayer is less than or equal to the In concentration in the well layer 52a of the second luminescent region; the In concentration in the InGaN monolayer is greater than or equal to the In concentration in the well layer of the third luminescent region adjacent to the second luminescent region. It should be noted that when m=3, the third luminescent region is the m-th luminescent region.

[0062] In an embodiment of the present invention, as an optional embodiment, when the doped GaN monolayer is an InGaN monolayer, the In concentration of the InGaN monolayer can be >3×10⁻⁶. 20 Atoms / cm 3 .

[0063] In an embodiment of the present invention, as an optional embodiment, the buffer 500 comprises an InGaN monolayer and a Si-doped GaN monolayer. Further, the buffer 500 may have the same well-barrier structure as the third luminescent region.

[0064] In an embodiment of the present invention, as an optional embodiment, when the buffer 500 is a superlattice structure layer, the number of periods of the superlattice structure layer is 1 to 50, including but not limited to a range of 1, 2, 5, 8, 10, 20, 30, 40, 50 or any two of them.

[0065] In an embodiment of the present invention, as an optional embodiment, the superlattice structure layer includes at least one of the following: InGaN / GaN superlattice structure layer, InGaN / AlGaN superlattice structure layer, InAlGaN / GaN superlattice structure layer, and InAlGaN / InGaN superlattice structure layer.

[0066] In an embodiment of the present invention, as an optional embodiment, the thickness of a single well layer in the first light-emitting region 51 can be 20 to 60 Å.

[0067] In an embodiment of the present invention, as an optional embodiment, the wavelength peak value generated by each light-emitting region of the multi-quantum-well layer 50 gradually decreases in a first direction. Further, the difference in wavelength peak value Δλ between adjacent light-emitting regions is ≤25 nm.

[0068] In an embodiment of the present invention, as an optional embodiment, the wavelength peak generated by each light-emitting region of the multi-quantum well layer 50 can be 459-473 nm, and the wavelength peak can be 435-447.5 nm.

[0069] In an embodiment of the present invention, as an optional embodiment, the wavelength generated by the first light-emitting region 51 in the multi-quantum well layer 50 can be 459-473 nm.

[0070] In an embodiment of the present invention, as an optional embodiment, the bandgap width of the well layer of each light-emitting region of the multi-quantum well layer 50 gradually increases in the first direction.

[0071] In an embodiment of the present invention, as an optional embodiment, the In concentration in the well layer of each light-emitting region of the multi-quantum well layer 50 gradually decreases in the first direction.

[0072] In an embodiment of the present invention, as an optional embodiment, the thickness of each individual well layer in each light-emitting region of the multi-quantum well layer 50 is substantially consistent in the first direction. "Substantially consistent" means that, in the first direction, the thickness of the individual well layer in each light-emitting region of the multi-quantum well layer 50 satisfies the condition that the thickness of the corresponding individual well layer in adjacent light-emitting regions changes at a rate between -10% and 10% compared to the thickness of the preceding individual well layer.

[0073] In an embodiment of the present invention, as an optional embodiment, the periodic structure of the well layer and barrier layer of the first light-emitting region 51 can be 1 to 5, the periodic structure of the well layer and barrier layer of the second light-emitting region can be 1 to 5, and the periodic structure of the well layer and barrier layer of the third light-emitting region can be 1 to 15.

[0074] In an embodiment of the present invention, as an optional embodiment, the multi-quantum well layer 50 further includes a (m+1)th light-emitting region 55 located near the P-type semiconductor layer 60. Figure 3 This is another schematic diagram of a multi-quantum-well layer provided in an embodiment of the present invention. The direction from the N-type semiconductor layer 30 to the P-type semiconductor layer 60 is defined as a first direction. The multi-quantum-well layer along the first direction includes m+1 groups of light-emitting regions that generate light of different wavelengths. These include a first light-emitting region 51 closest to the N-type semiconductor layer 30, a second light-emitting region 52 adjacent to the first light-emitting region 51, an (m+1)th light-emitting region 55 closest to the P-type semiconductor layer 60, an mth light-emitting region 53 next closest to the P-type semiconductor layer 60, and one or more optional light-emitting regions (not shown, denoted by ...) between the second light-emitting region 52 and the mth light-emitting region 53.

[0075] The (m+1)th luminescent region 55 includes a well layer 55a and a barrier layer 55b of the (m+1)th luminescent region that are stacked alternately.

[0076] In an embodiment of the present invention, as an optional embodiment, the (m+1)th light-emitting region 55 satisfies at least one of the following conditions:

[0077] (1) The In concentration of the well layer 55a in the (m+1)th luminescent region is greater than the In concentration of the well layer 53a in the mth luminescent region;

[0078] (2) The bandgap width of the well layer 55a in the (m+1)th luminescent region is smaller than the bandgap width of the well layer 53a in the mth luminescent region.

[0079] In an embodiment of the present invention, as an optional embodiment, the multi-quantum well layer 50 includes five groups of light-emitting regions, which are respectively a first light-emitting region, a second light-emitting region, a third light-emitting region, a fourth light-emitting region, and a fifth light-emitting region along a first direction; satisfying at least one of the following conditions:

[0080] (1) The thicknesses of the individual well layers in the first light-emitting region, the second light-emitting region, the third light-emitting region, the fourth light-emitting region and the fifth light-emitting region are d1, d2, d3, d4 and d5 respectively, and each thickness satisfies: d2≤d3≤d4≤d1, and d4 and d5 satisfy: d4>d5 or d4<d5 or d4=d5;

[0081] The thickness of a single well layer in each luminescent region includes, but is not limited to, d1, d2, d3, d4, and d5, which can be 20–60 Å, d1, d2, d3, d4, and d5, respectively.

[0082] (2) The concentrations of In in a single trap layer of the first luminescent region, the second luminescent region, the third luminescent region, the fourth luminescent region and the fifth luminescent region are X1, X2, X3, X4 and X5, respectively. Each concentration satisfies: X1 > X2 > X3 > X4, and X4 and X5 satisfy: X4 > X5 or X4 < X5 or X4 = X5;

[0083] The concentration of In in a single well layer of each luminescent region includes, but is not limited to, X1, which can be 8 × 10⁻⁶. 20 Atoms / cm 3 ~5×10 21 Atoms / cm 3 X2 can be 8×10 20 Atoms / cm 3 ~5×10 21 Atoms / cm 3 X3 can be 8×10 19 Atoms / cm 3 ~8×10 20 Atoms / cm 3 X4 can be 5×10 19 Atoms / cm 3 ~7×10 20 Atoms / cm 3 X5 can be 5×10 19 Atoms / cm 3 ~7×10 20 Atoms / cm 3 ;

[0084] (3) The band gap widths of the individual well layers of the first luminescent region, the second luminescent region, the third luminescent region, the fourth luminescent region and the fifth luminescent region are Eg1, Eg2, Eg3, Eg4 and Eg5, respectively. Each band gap width satisfies: Eg1≤Eg2<Eg3<Eg4, and Eg4 and Eg5 satisfy: Eg4>Eg5 or Eg4<Eg5 or Eg4=Eg5;

[0085] (4) The number of periodic structures of the trap and barrier layers in the first, second, third, fourth and fifth light-emitting regions are Y1, Y2, Y3, Y4 and Y5, respectively, and the number of each periodic structure satisfies: Y1≤Y2≤Y3≤Y4, Y4≥Y5;

[0086] The number of periodic structures of the well and barrier layers in each luminescent region includes, but is not limited to, Y1 can be 1 to 5, Y2 can be 1 to 5, Y3 can be 1 to 8, Y4 can be 1 to 15, and Y5 can be 1 to 5.

[0087] (5) The peak wavelengths generated by the first, second, third, fourth and fifth light-emitting regions are λ1, λ2, λ3, λ4 and λ5, respectively, and each peak wavelength satisfies: λ1>λ2>λ3>λ4, λ5>λ4;

[0088] The peak wavelengths generated by each luminescent region include, but are not limited to, λ1, which can be 459nm to 473nm, λ2, which can be 459nm to 473nm, λ3, which can be 445nm to 457nm, λ4, which can be 435nm to 447nm, and λ5, which can be 437nm to 449nm.

[0089] In an embodiment of the present invention, as an optional embodiment, the well layer of the light-emitting region includes InGaN, and the barrier layer of the light-emitting region includes GaN.

[0090] In an embodiment of the present invention, as an optional embodiment, the thickness of the multiple quantum well layer 50 is 100–300 nm. Further, the thickness of the periodic structure of the well layer and barrier layer is 10–19 nm, the thickness of a single well layer can be 1–4 nm, and the thickness of a single barrier layer can be 6–15 nm.

[0091] In an embodiment of the present invention, as an optional embodiment, the stress relief layer 40 comprises an InGaN / GaN superlattice layer. Further, in the stress relief layer 40, the concentration of In is < 3 × 10⁻⁶. 20 Atoms / cm 3 Preferably, the concentration of In is greater than 4 × 10⁻⁶. 19 Atoms / cm 3 .

[0092] In an embodiment of the present invention, as an optional embodiment, the stress relief layer 40 is doped with Si and / or Al.

[0093] In an embodiment of the present invention, as an optional embodiment, the P-type semiconductor layer 60 includes a P-type AlGaN electron blocking layer and a Mg-doped P-type GaN layer. The average doping concentration of Mg in the Mg-doped P-type GaN layer is 1 × 10⁻⁶. 19 ~1×10 21 Atoms / cm 3 .

[0094] In an embodiment of the present invention, as an optional embodiment, the N-type semiconductor layer 30 includes an undoped GaN layer and a Si-doped N-type GaN layer. The thickness of the undoped GaN layer can be 1.5–2.5 μm, and the thickness of the Si-doped N-type GaN layer can be 1.5–2.5 μm; in the Si-doped N-type GaN layer, the Si doping concentration can be 1 × 10⁻⁶. 19 ~1×10 20 Atoms / cm 3 .

[0095] The light-emitting diodes formed from the above epitaxial structures can be fabricated into upright LED chips, flip-chip LED chips, vertical LED chips, Mini LEDs, and Micro LEDs, depending on the specific application requirements; no limitations are imposed here. (For demonstration purposes only.) Figure 4 A schematic diagram of a standard LED chip structure is shown, including any of the above-mentioned multi-wavelength light-emitting diode epitaxial structures.

[0096] Furthermore, a light-emitting diode also includes a current blocking layer, a current spreading layer, an N-electrode, a P-electrode, and an insulating layer;

[0097] A current blocking layer is disposed on the P-type semiconductor layer 60; a current spreading layer is stacked on the P-type semiconductor layer 60 and the current blocking layer; a P electrode is disposed on the current spreading layer and electrically connected to the P-type semiconductor layer 60; an N electrode is disposed in the N-step region and electrically connected to the N-type semiconductor layer 30; an insulating layer covers the P electrode and the N electrode and exposes part of the P electrode and the N electrode, forming an opening.

[0098] The spectral distribution of the light-emitting diode was measured under the action of an applied voltage. The spectrum of the multi-quantum well layer had at least three peaks between 420 and 480 nm, including a first peak between 435 and 447 nm, a second peak between 445 and 457 nm, and a third peak between 460 and 473 nm.

[0099] Among them, the third peak has the smallest peak intensity, and at least one of the first or second peaks has the largest peak intensity. The ratio of the peak intensity of the third peak to the maximum peak intensity is 0.4 to 0.6; the ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.8 to 1, or the ratio of the peak intensity of the second peak to the peak intensity of the first peak is 0.8 to 1.

[0100] like Figure 5The image shows the spectral distribution of a light-emitting diode (LED) chip. Its spectrum exhibits three distinct peaks between 435 and 473 nm. The first peak, P11, has the highest peak intensity, with a relative luminous intensity of 1. The second peak, P12, has a lower peak intensity than the first peak, P11, with a relative luminous intensity of 0.85–0.95. The third peak, P13, has a lower peak intensity than the second peak, P12, with a relative luminous intensity of 0.45–0.55.

[0101] Figure 6 The spectrum of another light-emitting diode chip also has three relatively obvious peaks between 435 and 473 nm. The second peak, P22, has the largest peak intensity and a relative luminous intensity of 1. The first peak, P21, has a relative luminous intensity of 0.85 to 0.9, and the third peak, P23, has the lowest peak intensity and a relative luminous intensity of 0.5 to 0.55.

[0102] In another aspect, the present invention provides a light-emitting module, including any of the above-mentioned light-emitting diodes and a wavelength conversion unit; the light generated by the light-emitting diodes is mixed by the wavelength conversion unit to generate white light.

[0103] Based on this, embodiments of the present invention provide multi-wavelength light-emitting diodes and light-emitting modules, which are described below through embodiments.

[0104] Example 1

[0105] Figure 7 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 1 of the present invention. The multi-quantum well layer 50 of this embodiment includes four groups of light-emitting regions with different bandgap widths: a first light-emitting region, a second light-emitting region, a third light-emitting region, and a fourth light-emitting region, to generate four groups of light with different wavelength peak values ​​λ1, λ2, λ3, and λ4, respectively. The bandgap widths of the well layers of the four light-emitting regions are Eg1, Eg2, Eg3, and Eg4, respectively, where Eg1 ≤ Eg2 < Eg3 < Eg4, and λ1 > λ2 > λ3 > λ4. Among them, λ1 can be 459–473 nm, λ2 can be 459–473 nm, λ3 can be 445 nm–457 nm, and λ4 can be 435 nm–447 nm.

[0106] The first light-emitting region is closest to the N-type semiconductor layer and includes a periodic structure of alternatingly stacked first well layers 511 and first barrier layers 512, with a period number of 1 to 5, such as 1. The second light-emitting region is adjacent to the first light-emitting region and includes a periodic structure of alternatingly stacked second well layers 521 and second barrier layers 522, with a period number of 1 to 5, such as 1. The fourth light-emitting region is closest to the P-type semiconductor layer and includes a periodic structure of alternatingly stacked fourth well layers 541 and fourth barrier layers 542, with a period number of 1 to 15, such as 7. The third light-emitting region is disposed between the second and fourth light-emitting regions and includes a periodic structure of alternatingly stacked third well layers 531 and third barrier layers 532, with a period number of 1 to 8, such as 2.

[0107] Each well layer is an InGaN material layer with a different In concentration, and each barrier layer is a GaN-based material layer. The In concentration in the first well layer 511 is greater than that in the second well layer 521, the In concentration in the second well layer 521 is greater than that in the third well layer 531, and the In concentration in the third well layer 531 is greater than that in the fourth well layer 541. For example, the In concentration in the first well layer 511 can be 8 × 10⁻⁶. 20 Atoms / cm 3 ~5×10 21 Atoms / cm 3 The In concentration in the second well layer 521 can be 8 × 10⁻⁶. 20 Atoms / cm 3 ~5×10 21 Atoms / cm 3 The In concentration in the third well layer 531 can be 8 × 10⁻⁶. 19 Atoms / cm 3 ~8×10 20 Atoms / cm 3 The In concentration in the fourth well layer 541 can be 5 × 10⁻⁶. 19 Atoms / cm 3 ~7×10 20 Atoms / cm 3 .

[0108] The thicknesses of individual well layers in the first, second, third, and fourth luminescent regions are d1, d2, d3, and d4, respectively, and each thickness satisfies the condition: d2 ≤ d3 ≤ d4 ≤ d1. For example, the thickness d1 of the first well layer 511 can be 20–60 Å, specifically 40 Å, but is not limited to this. The thicknesses d2, d3, and d4 of the second, third, and fourth well layers 521, 531, and 541 are basically the same, ranging from 20–60 Å, specifically 30 Å, but are not limited to this. The first barrier layer 512, second barrier layer 522, third barrier layer 532, and fourth barrier layer 542 have basically the same thickness, ranging from 60–150 Å.

[0109] A buffer zone 500 is provided between the first and second light-emitting regions. The buffer zone 500 is a GaN-based monolayer with a thickness d0 > 10 Å. In this embodiment, the buffer zone 500 can also be replaced by either a doped GaN monolayer or a superlattice structure layer.

[0110] In one possible embodiment, the thickness of the buffer 500 is 100–10000 Å, such as 140 Å.

[0111] In a modified embodiment, the buffer 500 is disposed between two adjacent well layers of the second light-emitting region, that is, the buffer 500 is disposed between two adjacent second well layers 521.

[0112] Example 2

[0113] Figure 8 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 2 of the present invention. The multi-quantum well layer 50 in this embodiment refers to Embodiment 1, except that: in the multi-quantum well layer 50, a fifth light-emitting region is also included between the fourth light-emitting region and the P-type semiconductor layer.

[0114] The fifth light-emitting region is closest to the P-type semiconductor layer and includes a periodic structure of alternately stacked fifth well layer 551 and fifth barrier layer 552, with the number of periods ranging from 1 to 5, such as 1.

[0115] The fifth well layer 551 is an InGaN material layer, and the fifth barrier layer 552 is a GaN-based material layer. The thickness of the fifth well layer 551 is greater than that of the fourth well layer; for example, the thickness d5 of the fifth well layer 551 can be 31–38 Å, specifically 35 Å, but is not limited to this. The thickness of the fifth barrier layer 552 is basically the same as that of the fourth barrier layer 542, ranging from 60–150 Å.

[0116] The fifth well layer 551 satisfies one or two of the following conditions:

[0117] (1) The bandgap of the trap layer of the fifth luminescent region is Eg5, and the wavelength generated by the fifth luminescent region is λ5; Eg5 < Eg4, λ5 > λ4; where λ5 can be 437~449nm;

[0118] (2) The In concentration in the fifth well layer 551 is greater than the In concentration in the fourth well layer 541. For example, the In concentration in the fifth well layer 551 can be 5 × 10⁻⁶. 19 Atoms / cm 3 ~7×10 20 Atoms / cm 3 .

[0119] Example 3

[0120] Figure 9 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 3 of the present invention. The multi-quantum well layer 50 in this embodiment refers to Embodiment 2, except that the buffer zone 500 set between the first light-emitting region and the second light-emitting region is different.

[0121] In this embodiment, the buffer zone 500 between the first and second light-emitting regions is an InGaN monolayer. Barrier layers are respectively disposed between the buffer zone 500 containing the InGaN monolayer and the first and second light-emitting regions. Specifically, a first barrier layer 512 is disposed between the buffer zone 500 and the first well layer, and a second barrier layer 522 is disposed between the buffer zone 500 and the second well layer. The thickness of the InGaN monolayer in the buffer zone 500 is 100–10000 Å, such as 132 Å. The In concentration of the buffer zone 500 is greater than or equal to the In concentration of the third well layer 531, and less than or equal to the In concentration of the second well layer 521.

[0122] Example 4

[0123] Figure 10 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 4 of the present invention. The multi-quantum well layer 50 in this embodiment refers to Embodiment 2, except that the buffer zone 500 set between the first light-emitting region and the second light-emitting region is different.

[0124] In this embodiment, the buffer zone 500 between the first luminescent region and the second luminescent region is a superlattice structure layer. The number of periods of the superlattice structure layer can be 1 to 50, such as 1. The thickness of the buffer zone 500 is 125 to 140 Å.

[0125] The superlattice structure layer can be at least one of the following: InGaN / GaN superlattice structure layer, InGaN / AlGaN superlattice structure layer, InAlGaN / GaN superlattice structure layer, and InAlGaN / InGaN superlattice structure layer.

[0126] Example 5

[0127] Figure 11 This is a schematic diagram of the bandgap structure of the multi-quantum well layer provided in Embodiment 5 of the present invention. The multi-quantum well layer 50 of this embodiment includes a first light-emitting region 51 closest to the N-type semiconductor layer, and a second light-emitting region 52, a third light-emitting region, a fourth light-emitting region, and a fifth light-emitting region sequentially disposed on the first light-emitting region 51, and a buffer zone 500 disposed between the first light-emitting region 51 and the second light-emitting region 52. The buffer zone 500 includes an InGaN layer 501 and a GaN layer 502. The InGaN layer 501 is located between the first barrier layer 512 and the GaN layer 502. The InGaN layer 501 has the same bandgap energy level as the third well layer 531, and the GaN layer 502 is the same as the third barrier layer 532. Specifically, the InGaN layer 501 in the buffer zone 500 has the same bandgap energy level as the third well layer 531 and can emit light beams of the same wavelength.

[0128] The first luminescent region 51 contains at least one first well layer 511, and the second luminescent region 52 contains at least one second well layer 521. The band gaps of the first well layer 511 and the second well layer 521 are the same or similar, and the band gap energy level is the smallest in the entire multi-quantum well layer. Specifically, the In concentration and well layer thickness in the first well layer 511 and the second well layer 521 are the same. The InGaN layer 501 in the buffer 500 is identical to at least one third well layer 531 in the third light-emitting region. The number of third well layers 531 in the third light-emitting region is 3 to 5, and the band gap energy level of the third well layer 531 is greater than that of the second well layer 521. The fourth light-emitting region includes several fourth well layers 541, the number of fourth well layers 541 is greater than the number of third well layers 531, and the band gap energy level Eg4 is greater than that of the third well layer 531. The fifth light-emitting region closest to the P-type semiconductor layer includes at least one fifth well layer 551, whose band gap energy level Eg5 is less than that of the fourth well layer 541. The In concentration of the fifth well layer 551 may be the same as that of the fourth well layer 541, but the thickness of the fifth well layer 551 is greater than that of the fourth well layer 541; or the In concentration in the fifth well layer 551 may be greater than that in the fourth well layer 541, but the thickness of the two well layers may be the same. In addition, at least one barrier layer is provided between every two adjacent well layers. This barrier layer can be a GaN layer, an AlGaN layer, or an InAlGaN layer, and its bandgap energy level is higher than that of the well layer.

[0129] Taking Example 2 as an example, the light-emitting diode using Example 2 of the present invention has a luminous efficiency of 1% to 2% higher than that of a conventional light-emitting diode at 60mA.

[0130] As can be seen from the above, the light-emitting diode of the present invention, by setting a buffer zone between the first light-emitting region and the second light-emitting region or setting a buffer zone within the second light-emitting region, and by coordinating the adjustment of the parameters of the remaining light-emitting regions, can better balance the differences in carrier capture capabilities of each well layer caused by the different band gaps in each light-emitting region, and can alleviate the lattice mismatch caused by the band gap differences in each light-emitting region, improve the crystal quality of the light-emitting region, and achieve the effect of improving luminous efficiency.

[0131] An embodiment of the present invention also provides a method for fabricating a multi-wavelength light-emitting diode, comprising the following steps:

[0132] The first half of the growth buffer layer 20 is applied to the substrate 10 for 1 minute to compensate for lattice mismatch and form nucleation islands. The temperature of this layer is controlled at 800°C and the pressure at 150 torr. Then, the second half of the growth buffer layer 20 is applied for 10–25 minutes, during which the temperature is controlled at 1120°C and the pressure at 200 torr. The purpose of this process is to grow GaN with high grain growth quality and low defect density.

[0133] An N-type semiconductor layer 30 is grown on the buffer layer 20 to provide electrons. The N-type semiconductor layer 30 is doped with Si to provide electrons, and the temperature is controlled at 1050°C and the pressure at 200 torr; the silicon doping concentration is 1 × 10⁻⁶. 19 ~2×10 20 Atoms / cm 3 .

[0134] A stress-relieving layer 40 is grown on the N-type semiconductor layer 30 to release the compressive stress caused by lattice mismatch between the subsequently grown InGaN quantum well and the GaN in the N-type semiconductor layer 30. The controlled temperature is 800–900°C, and the pressure is 200 torr. This layer can be a single-layer or multi-layer structure, and can be doped with elements such as Si / Al / In, with a silicon doping concentration of 1 × 10⁻⁶. 17 Atoms / cm 3 ~5×10 18 Atoms / cm 3 The indium doping concentration is 0 to 1 × 10⁻⁶. 20 Atoms / cm 3 .

[0135] A multi-quantum well layer 50 is then grown on the stress-relieving layer 40. This layer generates multi-quantum well convergence luminescence through the convergence of electrons and holes. The temperature of this layer is controlled at 700–800 °C, and the pressure at 200 Tor.

[0136] A p-type semiconductor layer 60 is grown on the multi-quantum-well layer 50. This layer provides holes for the device. The temperature of this layer is controlled at 700–1000 °C, and the pressure is 1000 tor.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-wavelength light emitting diode, characterized in that: include: A multi-quantum well layer disposed between the N-type semiconductor layer and the P-type semiconductor layer; A direction from the N-type semiconductor layer to the P-type semiconductor layer is defined as a first direction, the multi-quantum well layer includes m groups of light-emitting regions that generate light of different wavelengths along the first direction, each light-emitting region includes at least one well layer and one barrier layer, wherein m≥3; The first well layer in the first light-emitting region closest to the N-type semiconductor layer in the multi-quantum well layer has the highest In concentration or the smallest bandgap width; the second light-emitting region including the second well layer and the second barrier layer is arranged on the first light-emitting region, wherein the bandgap width of the second well layer is greater than or equal to the first well layer; the third light-emitting region including the third well layer and the third barrier layer is arranged on the second light-emitting region, wherein the bandgap width of the third well layer is greater than that of the second well layer; The multi-quantum well layer also includes a buffer zone; the buffer zone is arranged between the first light-emitting zone and the second light-emitting zone, or the buffer zone is arranged in the second light-emitting zone; the bandgap width of the buffer zone is greater than that of the second well layer.

2. The multi-wavelength light emitting diode according to claim 1, characterized in that: The buffer zone includes at least one of a non-doped GaN single layer, a doped GaN single layer and a super lattice structure layer, and the doping element is at least one of In, Si, Al and Mg.

3. The multi-wavelength light emitting diode according to claim 2, characterized in that: The buffer zone includes an InGaN single layer and a GaN single layer, wherein the In concentration in the InGaN single layer is less than or equal to the In concentration in the second well layer; and the In concentration in the InGaN single layer is greater than or equal to the In concentration in the third well layer.

4. The multi-wavelength light emitting diode according to claim 2, characterized in that: The superlattice structure layer has a period number of 1 to 50; The superlattice structure layer includes at least one of an InGaN / GaN superlattice structure layer, an InGaN / AlGaN superlattice structure layer, an InAlGaN / GaN superlattice structure layer, and an InAlGaN / InGaN superlattice structure layer.

5. The multi-wavelength light emitting diode according to claim 1, characterized in that: The multi-quantum well layer satisfies at least one of the following conditions: (1) The peak wavelengths generated by each light-emitting region of the multi-quantum well layer gradually decrease in the first direction; the difference Δλ between the peak wavelengths generated by adjacent light-emitting regions is ≤25 nm; (2) the bandgap width of the well layer in the first light-emitting region to the bandgap width of the well layer in the mth light-emitting region gradually increases in the first direction; (3) the In concentration in the well layer of the first light-emitting region to the In concentration in the well layer of the mth light-emitting region gradually decreases in the first direction; (4) The spectrum of the multi-quantum well layer has at least three peaks between 420 and 480 nm, including a first peak between 435 and 447 nm, a second peak between 445 and 457 nm, and a third peak between 460 and 473 nm; Among them, the peak intensity of the third peak is the smallest, at least one of the first peak or the second peak has the maximum peak intensity, and the ratio of the peak intensity of the third peak to the maximum peak intensity is 0.4 to 0.6; the ratio of the peak intensity of the first peak to the peak intensity of the second peak is 0.8 to 1 or the ratio of the peak intensity of the second peak to the peak intensity of the first peak is 0.8 to 1.

6. The multi-wavelength light emitting diode according to claim 3, characterized in that: A well layer and a barrier layer in each light-emitting region are defined as a period. The number of periods in the first light-emitting region is 1 to 5, the number of periods in the second light-emitting region is 1 to 5, and the number of periods in the third light-emitting region is 1 to 15.

7. The multi-wavelength light emitting diode according to any one of claims 1 to 6, characterized in that: The multi-quantum well layer also includes an m+1th light-emitting region close to the P-type semiconductor layer, and a light-emitting region adjacent to the m+1th light-emitting region and away from the P-type semiconductor layer is the mth light-emitting region, and the m+1th light-emitting region satisfies at least one of the following conditions: (1) The In concentration of the well layer of the m+1th light-emitting region is greater than the In concentration of the well layer of the mth light-emitting region; (2) The bandgap width of the well layer of the m+1th light-emitting region is smaller than the bandgap width of the well layer of the mth light-emitting region.

8. The multi-wavelength light emitting diode according to claim 1, characterized in that: The multi-quantum well layer includes five groups of light-emitting regions, which are respectively a first light-emitting region, a second light-emitting region, a third light-emitting region, a fourth light-emitting region and a fifth light-emitting region along the first direction.

9. The multi-wavelength light emitting diode according to claim 8, characterized in that: The thicknesses of the single well layers of the first light-emitting zone, the second light-emitting zone, the third light-emitting zone, the fourth light-emitting zone and the fifth light-emitting zone are d1, d2, d3, d4 and d5 respectively, and each thickness satisfies: d2≤d3≤d4≤d1, and d4 and d5 satisfy: d4>d5 or d4<d5 or d4=d5.

10. The multi-wavelength light emitting diode according to claim 8, characterized in that: The concentrations of In in the single well layers of the first light-emitting zone, the second light-emitting zone, the third light-emitting zone, the fourth light-emitting zone and the fifth light-emitting zone are X1, X2, X3, X4 and X5 respectively, and each concentration satisfies: X1>X2>X3>X4, and X4 and X5 satisfy: X4>X5 or X4<X5 or X4=X5.

11. The multi-wavelength light emitting diode according to claim 8, characterized in that: The bandgap widths of the single well layers of the first light-emitting zone, the second light-emitting zone, the third light-emitting zone, the fourth light-emitting zone and the fifth light-emitting zone are Eg1, Eg2, Eg3, Eg4 and Eg5 respectively, and each bandgap width satisfies: Eg1≤Eg2<Eg3<Eg4, and Eg4 and Eg5 satisfy: Eg4>Eg5 or Eg4<Eg5 or Eg4=Eg5.

12. The multi-wavelength light emitting diode according to claim 8, characterized in that: The number of periodic structures of the well layers and barrier layers of the first light-emitting zone, the second light-emitting zone, the third light-emitting zone, the fourth light-emitting zone and the fifth light-emitting zone are Y1, Y2, Y3, Y4 and Y5 respectively, and the number of each periodic structure satisfies: Y1≤Y2≤Y3≤Y4, Y4≥Y5.

13. The multi-wavelength light emitting diode according to claim 8, characterized in that: The wavelength peaks generated by the first light-emitting area, the second light-emitting area, the third light-emitting area, the fourth light-emitting area and the fifth light-emitting area are λ1, λ2, λ3, λ4 and λ5 respectively, and each wavelength peak satisfies: λ1>λ2>λ3>λ4, λ5>λ4.

14. A light emitting module, characterized in that: It comprises the multi-wavelength light emitting diode according to any one of claims 1 to 13, wherein the light generated by the light emitting diode passes through a wavelength conversion unit and then is mixed to generate white light.

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