Lights and light methods
The Al gradient regrowth layer in the group III nitride semiconductor structure addresses contamination issues by gradually increasing Al composition, enhancing the luminescence efficiency of micro-LED displays by minimizing the effect of impurities at the regrowth interface.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYODA GOSEI CO LTD
- Filing Date
- 2024-11-21
- Publication Date
- 2026-06-02
Smart Images
Figure 2026089833000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a light-emitting element and a method for manufacturing a light-emitting element. [Background technology]
[0002] In recent years, there has been a growing demand for higher resolution displays, and micro-LED displays, which use tiny LEDs on the order of 1 to 100 μm per pixel, have attracted attention. Patent Document 1 describes a monolithic micro-LED display element capable of individually emitting red, green, and blue light from a single element. Patent Document 1 also describes a structure in which three active layers emitting blue, green, and red light are sequentially stacked on the same substrate. [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] Japanese Patent Publication No. 2023-177713 [Overview of the project] [Problems that the invention aims to solve]
[0004] In the light-emitting element described in Patent Document 1, the process requires completing crystal growth, removing the wafer from the growth furnace, forming grooves by dry etching, and then placing the wafer back into the growth furnace to repeat crystal growth. As a result, the wafer is exposed to the atmosphere.
[0005] However, once the wafer is exposed to the atmosphere, the wafer surface will be contaminated by impurities such as O and Si. Such impurities will result in unintentional n-type doping and become non-radiative recombination centers. In addition, an unintentional n-type layer will be formed, changing the band structure. Furthermore, damage will occur on the etching surface due to the formation of grooves. As a result, the internal quantum efficiency and the injection efficiency will decrease. In particular, the active layers for green and blue light emission are close to the regrowth interface contaminated by impurities, and the regrowth interface is located within the pn junction interface. Therefore, the decrease in the light emission efficiency of green and blue light emission is significant.
[0006] The present invention has been made in view of such a background, and aims to provide a light-emitting device with suppressed decrease in light emission efficiency and a method for manufacturing the same.
Means for Solving the Problems
[0007] One aspect of the present invention is In a method for manufacturing a light-emitting device using a group III nitride semiconductor, an n-type layer formation step of forming an n-type layer made of an n-type group III nitride semiconductor on a substrate; a first active layer formation step of forming a first active layer having a predetermined emission wavelength on the n-type layer; an intermediate layer formation step of forming an intermediate layer made of a group III nitride semiconductor containing In on the first active layer; a second active layer formation step of forming a second active layer having an emission wavelength different from that of the first active layer on the intermediate layer; a groove formation step of forming a groove having a depth reaching the intermediate layer from the second active layer side; an Al inclined regrowth layer formation step of forming an Al inclined regrowth layer made of a p-type group III nitride semiconductor on the intermediate layer exposed at the bottom surface of the groove; a p-type layer formation step of forming a p-type layer made of a p-type group III nitride semiconductor on the second active layer and the Al inclined regrowth layer, and the Al composition of the Al inclined regrowth layer gradually increases in the thickness direction toward the p-type layer in the method for manufacturing a light-emitting device.
[0008] Other aspects of the present invention include: In a light-emitting device using a group III nitride semiconductor, circuit board and An n-type layer made of an n-type group III nitride semiconductor is formed on the substrate, A first active layer formed on the n-type layer, having a predetermined emission wavelength, An intermediate layer formed on the first active layer, which is made of a group III nitride semiconductor containing In, A second active layer is formed on the intermediate layer and has an emission wavelength different from that of the first active layer, A groove extending from the second active layer to the intermediate layer, An Al gradient regrowth layer made of a p-type group III nitride semiconductor is formed on the intermediate layer exposed at the bottom surface of the groove, The second active layer and the Al gradient regrowth layer are formed on the p-type layer, which is made of a p-type group III nitride semiconductor, and the p-type layer is formed on the second active layer and the Al gradient regrowth layer, The Al composition of the aforementioned Al gradient regrowth layer gradually increases in the thickness direction as it approaches the p-type layer. The region near the interface between the intermediate layer and the Al gradient regrowth layer is 1 × 10 18 cm -3 A light-emitting element containing the above O or Si. [Effects of the Invention]
[0009] In the above embodiment, an Al gradient regrowth layer is provided on the intermediate layer, and the Al composition of the Al gradient regrowth layer gradually increases in the thickness direction toward the p-type layer. By providing such an Al gradient regrowth layer, it is possible to suppress the decrease in luminescence efficiency due to impurities at the regrowth interface.
[0010] As described above, according to the above embodiment, it is possible to provide a light-emitting element and a method for manufacturing the same in which a decrease in luminous efficiency is suppressed. [Brief explanation of the drawing]
[0011] [Figure 1]A cross-sectional view showing the configuration of a light-emitting element in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 2] This figure shows the Al composition distribution of the Al-graded regrowth layer. [Figure 3] A flowchart illustrating the manufacturing process of a light-emitting element in the first embodiment. [Figure 4] A cross-sectional view showing the element structure at each manufacturing stage of the light-emitting element in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 5] A cross-sectional view showing the element structure at each manufacturing stage of the light-emitting element in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 6] A cross-sectional view showing the element structure at each manufacturing stage of the light-emitting element in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 7] A cross-sectional view showing the element structure at each manufacturing stage of the light-emitting element in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 8] This is a cross-sectional view showing the configuration of the light-emitting element of Example 1, and is a cross-sectional view perpendicular to the main surface of the substrate. [Figure 9] A graph showing the relationship between the thickness of the Al gradient regrowth layer and the luminescence intensity. [Figure 10] This graph shows the relationship between the change in TMAl supply and luminescence intensity during the formation of the Al gradient regrowth layer. [Modes for carrying out the invention]
[0012] The method for manufacturing a light-emitting element is a method for manufacturing a light-emitting element using a group III nitride semiconductor, and comprises an n-type layer formation step of forming an n-type layer made of an n-type group III nitride semiconductor on a substrate; a first active layer formation step of forming a first active layer having a predetermined emission wavelength on the n-type layer; an intermediate layer formation step of forming an intermediate layer made of a group III nitride semiconductor containing In on the first active layer; a second active layer formation step of forming a second active layer having a different emission wavelength from the first active layer on the intermediate layer; a groove formation step of forming a groove with a depth reaching the intermediate layer from the second active layer side; an Al gradient regrowth layer formation step of forming an Al gradient regrowth layer made of a p-type group III nitride semiconductor on the intermediate layer exposed at the bottom surface of the groove; and a p-type layer formation step of forming a p-type layer made of a p-type group III nitride semiconductor on the second active layer and the Al gradient regrowth layer, wherein the Al composition of the Al gradient regrowth layer gradually increases in the thickness direction toward the p-type layer.
[0013] In the method for manufacturing a light-emitting element, the thickness of the Al gradient regrowth layer may be 10 nm or more and 50 nm or less. This can further suppress the decrease in the luminescence efficiency of the first active layer due to impurities at the regrowth interface (the interface between the intermediate layer and the Al gradient regrowth layer).
[0014] In the method for manufacturing a light-emitting element, the minimum value of the Al gradient regrowth layer may be 0% or more and 10% or less. This can further suppress the decrease in the luminescence efficiency of the first active layer due to impurities at the regrowth interface.
[0015] In the method for manufacturing a light-emitting element, the maximum value of the Al gradient regrowth layer may be 10% or more and 30% or less. This can further suppress the decrease in the luminescence efficiency of the first active layer due to impurities at the regrowth interface.
[0016] In the method for manufacturing a light-emitting element, the rate of increase of the Al composition in the thickness direction of the Al gradient regrowth layer may be 0.3 to 1% / nm. This can further suppress the decrease in the luminescence efficiency of the first active layer due to impurities at the regrowth interface.
[0017] In the method for manufacturing a light-emitting element, the Mg concentration of the Al gradient regrowth layer is 1 × 10⁻⁶ 18~1 × 10 22 cm -3 This may also be the case. This can further suppress the decrease in the luminescence efficiency of the first active layer due to impurities at the regrowth interface.
[0018] The light-emitting element uses a group III nitride semiconductor and comprises a substrate, an n-type layer formed on the substrate and made of an n-type group III nitride semiconductor, a first active layer formed on the n-type layer and having a predetermined emission wavelength, an intermediate layer formed on the first active layer and made of a group III nitride semiconductor containing In, a second active layer formed on the intermediate layer and having a different emission wavelength from the first active layer, a groove with a depth extending from the second active layer side to the intermediate layer, an Al gradient regrowth layer formed on the intermediate layer exposed at the bottom of the groove and made of a p-type group III nitride semiconductor, and a p-type layer formed on the second active layer and the Al gradient regrowth layer and made of a p-type group III nitride semiconductor, wherein the Al composition of the Al gradient regrowth layer gradually increases in the thickness direction toward the p-type layer, and the region near the interface between the intermediate layer and the Al gradient regrowth layer is 1 × 10 18 cm -3 Contains the above O or Si.
[0019] (First Embodiment) 1. Configuration of light-emitting elements As shown in Figure 1, the light-emitting element 1 in the first embodiment includes a substrate 10, an n-type layer 11, a first active layer 12, a first intermediate layer 13, a second active layer 14, a second intermediate layer 15, a third active layer 16, electron blocking layers 17, 20A to 20C, p-type layers 18, 21A to 21C, Al gradient regrowth layers 19A to 19C, p-side electrodes 22A to 22C, and an n-side electrode 23. In this specification, the expression "B on A" includes both cases where A and B are in contact and cases where they are not in contact.
[0020] The substrate 10 is a growth substrate for growing a group III nitride semiconductor. Examples include sapphire, Si, GaN, and ScAlMgO4(SAM). A template substrate in which a group III nitride semiconductor such as GaN is formed on a substrate such as sapphire may also be used.
[0021] The n-type layer 11 is an n-type semiconductor provided on the substrate 10 via a low-temperature buffer layer or a high-temperature buffer layer (not shown). However, the buffer layer may be provided as necessary, and it is not necessary to provide a buffer layer when the substrate is GaN. The n-type layer 11 is, for example, n-GaN, n-AlGaN, n-InGaN, etc. The Si concentration is, for example, 1×10 18 ~100×10 18 cm -3 .
[0022] The first active layer 12 is a light-emitting layer having a SQW or MQW structure provided on the n-type layer 11. The emission wavelength of the first active layer 12 is blue and is 430 - 480 nm. The first active layer 12 has a structure in which barrier layers made of AlGaN and well layers made of InGaN are alternately stacked in 1 - 9 pairs. More preferably, it is 1 - 7 pairs, and even more preferably, it is 1 - 5 pairs.
[0023] An underlayer may be provided between the n-type layer 11 and the first active layer 12 as necessary. The underlayer is a semiconductor layer having a superlattice structure provided on the n-type layer 11 and is a layer for relaxing the lattice strain of the semiconductor layer formed on the underlayer. The underlayer is formed by alternately stacking III-nitride semiconductor thin films having different compositions (for example, two of GaN, InGaN, and AlGaN), and the number of pairs is, for example, 3 - 30. It may be undoped or doped with Si at about 1×10 17 ~100×10 17 cm -3 . Also, it is not necessary to have a superlattice structure as long as the strain can be relaxed.
[0024] An ESD layer may also be provided between the n-type layer 11 and the underlayer. The ESD layer is a layer provided for improving the electrostatic breakdown voltage. The ESD layer is, for example, GaN, InGaN, or AlGaN that is undoped or doped with Si at a low concentration.
[0025] The first intermediate layer 13 is a semiconductor layer provided on the first active layer 12. The first intermediate layer 13 is provided to allow for individual control of the light emission from the first active layer 12 and the light emission from the second active layer 14. It also serves to protect the first active layer 12 from etching damage when forming the second groove 31, which will be described later.
[0026] The first intermediate layer 13 has a structure in which a non-doped intermediate layer 13A and an n-type intermediate layer 13B are stacked in order from the first active layer 12 side. The non-doped intermediate layer 12A and the n-type intermediate layer 12B may be made from the same material with impurities removed. The reason for making the first intermediate layer 13 such a two-layer structure will be explained later.
[0027] The material of the first intermediate layer 13 is a group III nitride semiconductor containing In, preferably InGaN. The surfactant effect of In can suppress surface roughness of the first intermediate layer 13 and improve surface flatness. It can also alleviate lattice strain.
[0028] The In composition of the first intermediate layer 13 (the molar ratio of In to the total group III metal of the group III nitride semiconductor) should be set so that it has a band gap that does not absorb light emitted from the first active layer 12 and the second active layer 14. A preferred In composition is 10% or less, more preferably 5% or less, and even more preferably 2% or less. If the In composition is greater than 10%, it will cause the surface of the first intermediate layer 13 to become rough. The In concentration can be any value greater than 0%, and may even be at a doping level (a level that does not form a mixed crystal). For example, an In concentration of 1 × 10⁻⁶ 14 cm -3 The above 1 x 10 22 cm -3 The following are the GaN components.
[0029] The undoped intermediate layer 13A is undoped, while the n-type intermediate layer 13B is Si-doped. The Si concentration of the n-type intermediate layer 13B is 1 × 10⁻⁶. 17 ~1000×10 17 cm -3 It is preferable to do so. Preferably 10 × 10 17 ~100×1017 cm -3 More preferably 20 × 10 17 ~80×10 17 cm -3 The n-type intermediate layer 13B may be modulated with Si, and a portion of the n-type intermediate layer 13B may be undoped.
[0030] The thickness of the first intermediate layer 13 is preferably 20 to 150 nm. If it is thicker than 150 nm, it may cause the surface of the first intermediate layer 13 to become rough. If it is thinner than 20 nm, it may become difficult to control the depth of the second groove 31 to be within the undoped intermediate layer 13A when forming the second groove 31 described later. More preferably it is 30 to 100 nm, and even more preferably 50 to 80 nm.
[0031] Furthermore, the thickness of the undoped intermediate layer 13A is preferably 10 nm or more. This is to control the etching depth and avoid etching damage to the first active layer 12. Also, the thickness of the n-type intermediate layer 13B is preferably 10 nm or more. This is to independently control the luminescence characteristics of each active layer.
[0032] The second active layer 14 is a layer provided on the first intermediate layer 13 and has a quantum well structure of SQW or MQW. The emission wavelength of the second active layer 14 is green, ranging from 510 to 570 nm. The quantum well structure consists of 1 to 7 pairs of alternating barrier layers made of GaN or AlGaN and well layers made of InGaN.
[0033] A strain relaxation layer may be provided between the first intermediate layer 13 and the second active layer 14. By providing a strain relaxation layer, the strain of the second active layer 14 stacked on top of it can be relaxed, thereby improving the crystal quality. The strain relaxation layer is an SQW or MQW structure in which a barrier layer and a well layer are stacked in order, and is a quantum well structure in which the thickness of the well layer is adjusted to be thin so as not to emit light. For example, by making the thickness of the well layer 1 nm or less, it is possible to prevent emission. The barrier layer is AlGaN, and the well layer is InGaN. The wavelength corresponding to the band edge energy of the well layer of the strain relaxation layer only needs to be shorter than the emission wavelength of the second active layer 14; for example, if the emission wavelength is 500 to 560 nm, then it is 400 to 460 nm.
[0034] The second intermediate layer 15 is a semiconductor layer provided on the second active layer 14. The second intermediate layer 15 is provided for the same reasons as the first intermediate layer 13, and is a layer provided to allow for individual control of the light emission from the second active layer 14 and the light emission from the third active layer 16. It also serves to protect the second active layer 14 from etching damage when forming the first groove 30, which will be described later.
[0035] The second intermediate layer 15 has a structure in which a non-doped intermediate layer 15A and an n-type intermediate layer 15B are stacked in order from the second active layer 14 side. The non-doped intermediate layer 15A and the n-type intermediate layer 15B have the same structure as the non-doped intermediate layer 13A and the n-type intermediate layer 13B. In other words, the non-doped intermediate layer 15A and the n-type intermediate layer 15B are made of the same material as the non-doped intermediate layer 13A and the n-type intermediate layer 13B, except for impurities, and the thickness range is also the same as the non-doped intermediate layer 13A and the n-type intermediate layer 13B. The non-doped intermediate layer 15A is non-doped, and the n-type intermediate layer 15B is Si-doped.
[0036] The third active layer 16 is a layer provided on the second intermediate layer 15 and has a quantum well structure of SQW or MQW. The emission wavelength is red, between 590 and 700 nm. The quantum well structure is a structure in which 1 to 7 pairs of barrier layers and well layers made of InGaN are alternately stacked. More preferably 1 to 5 pairs, and even more preferably 1 to 3 pairs.
[0037] A strain-relieving layer may be provided between the second intermediate layer 15 and the third active layer 16. By providing a strain-relieving layer, the strain of the third active layer 16 stacked on top of it can be relieved, thereby improving the crystal quality. The strain-relieving layer may have a structure in which, for example, a first strain-relieving layer and a second strain-relieving layer are stacked in order from the second intermediate layer 15 side.
[0038] The structure of the first strain relaxation layer and the second strain relaxation layer is similar to that of the strain relaxation layer between the first intermediate layer 13 and the second active layer 14 described above. The wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer is, for example, 400 to 460 nm. The wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer is, for example, 510 to 570 nm.
[0039] The electron blocking layer 17 is a semiconductor layer provided on the third active layer 16. The electron blocking layer 17 is a layer that blocks electrons injected from the n-type layer 11 in order to efficiently confine them to the third active layer 16. In addition to its electron blocking function, the electron blocking layer 17 also functions as a protective layer that protects the active layer. The electron blocking layer 17 can be made of any material with a band gap wider than that of the well layer of the third active layer 16, such as AlGaN, GaN, or InGaN. The thickness of the electron blocking layer 17 is preferably 2.0 to 50 nm, and more preferably 2 to 25 nm. The electron blocking layer 17 may be doped with impurities, or it may be doped with Mg. In that case, the Mg concentration is 1 × 10⁻¹⁶. 18 ~1 × 10 21 cm -3 It would be best to do so.
[0040] Furthermore, a strain relaxation layer made of InGaN with a narrower band gap than the electron blocking layer 17 may be provided between the third active layer 16 and the electron blocking layer 17.
[0041] The p-type layer 18 is a semiconductor layer provided on the electron block layer 17. The p-type layer 18 is preferably made of p-GaN or p-InGaN. The thickness of the p-type layer 18 is preferably 10 to 500 nm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm. The Mg concentration of the p-type layer 18 is 1 × 10⁻¹⁶. 19 ~1 × 10 22 cm -3 It would be best to do so.
[0042] A portion of the surface of the p-type layer 18 is etched to form grooves, including a first groove 30 that extends from the p-type layer 18 to the second intermediate layer 15, a second groove 31 that extends to the first intermediate layer 13, and a third groove 32 that extends to the n-type layer 11.
[0043] The first groove 30 is deep enough to reach the undoped intermediate layer 15A of the second intermediate layer 15. In this way, by removing the n-type intermediate layer 15B of the second intermediate layer 15 beneath the p-side electrode 22B, the n-type layer is prevented from being located on the second active layer 14, causing the second active layer 14 to emit light.
[0044] Furthermore, the second groove 31 reaches a depth that extends to the undoped intermediate layer 13A of the first intermediate layer 13. This is for the same reason: by removing the n-type intermediate layer 13B of the first intermediate layer 13 beneath the p-side electrode 22C, the n-type layer is prevented from being located on the first active layer 12, allowing the first active layer 12 to emit light.
[0045] The Al gradient regrowth layers 19A to 19C are semiconductor layers provided on the p-type layer 18, on the undoped intermediate layer 15A exposed at the bottom of the first groove 30, and on the undoped intermediate layer 13A exposed at the bottom of the second groove 31, respectively.
[0046] The Al gradient regrowth layers 19A to 19C are layers designed to suppress the decrease in luminescence efficiency due to the presence of regrowth interfaces. Here, the regrowth interfaces are defined as the interfaces between the undoped intermediate layer 15A and the Al gradient regrowth layer 19B, and the interfaces between the undoped intermediate layer 13A and the Al gradient regrowth layer 19B. As will be described in the manufacturing method below, impurities such as O and Si are present near the regrowth interfaces. For example, 1 × 10⁻¹⁶ particles are present in the region less than 5 nm from the regrowth interface. 18 ~1 × 10 20 cm -3 There is a certain amount of O and Si present.
[0047] Impurities at this regrowth interface can lead to unintended n-type doping, becoming non-luminescent recombination centers, or forming unintended n-type layers that alter the band structure. As a result, the luminescence efficiency decreases. However, by providing Al gradient regrowth layers 19A to 19C, the decrease in luminescence efficiency due to such impurities at the regrowth interface can be suppressed.
[0048] The Al gradient regrowth layers 19A to 19C consist of an Al-containing Mg-doped p-type group III nitride semiconductor. For example, the Al gradient regrowth layers 19A to 19C consist of p-AlGaN. As shown in Figure 2, the Al composition of the Al gradient regrowth layers 19A to 19C increases linearly in the thickness direction towards the electron blocking layers 20A to 20C.
[0049] The minimum Al composition in the Al gradient regrowth layers 19A to 19C, that is, the Al composition at the interface between the Al gradient regrowth layers 19A to 19C and the p-type layer 18, the undoped intermediate layer 15A, and the undoped intermediate layer 13A, is, for example, 0 to 10%. More preferably, the minimum Al composition in the Al gradient regrowth layers 19A to 19C is 1 to 5%.
[0050] The maximum Al composition in the Al gradient regrowth layers 19A to 19C, i.e., the Al composition at the interface between the Al gradient regrowth layers 19A to 19C and the electron block layers 20A to 20C, is, for example, 10 to 30%. More preferably, the maximum Al composition in the Al gradient regrowth layers 19A to 19C is 10 to 20%. Furthermore, it is preferable that the difference in Al composition between the Al gradient regrowth layers 19A to 19C and the electron block layers 20A to 20C be within ±5%. Here, if the electron block layers 20A to 20C have a superlattice structure, this is the difference in Al composition with respect to the barrier layer in the superlattice structure. It is also preferable that the highest Al composition of the electron block layers 20A to 20C is higher than the highest Al composition of the Al gradient regrowth layers 19A to 19C.
[0051] In the first embodiment, the Al composition of the Al gradient regrowth layers 19A to 19C increases linearly, but it may also increase curvilinearly or in steps. In other words, it is sufficient for it to increase monotonically toward the electron blocking layers 20A to 20C. However, in order to enhance the strain relaxation effect of the third active layer 16, it is better to increase the Al composition continuously.
[0052] The thickness of the Al gradient regrowth layers 19A to 19C is preferably 10 to 50 nm. A thickness of 10 nm or more can further suppress the decrease in luminescence efficiency due to impurities at the regrowth interface. However, if the Al gradient regrowth layers 19A to 19C become too thick, the formation of the Al gradient regrowth layers 19A to 19C will cause thermal damage to the first active layer 12, the second active layer 14, and the third active layer 16. For this reason, the thickness of the Al gradient regrowth layers 19A to 19C is preferably 50 nm or less. The thickness of the Al gradient regrowth layers 19A to 19C is more preferably 10 to 40 nm, and even more preferably 15 to 35 nm.
[0053] The rate of increase in Al composition in the thickness direction of the Al gradient regrowth layers 19A to 19C is, for example, 0.3 to 1% / nm. By setting the rate of increase in Al composition within this range, the decrease in luminescence efficiency can be further suppressed. More preferably, the rate of increase in Al composition in the thickness direction of the Al gradient regrowth layers 19A to 19C is 0.4 to 0.8% / nm.
[0054] The Mg concentration in the Al gradient regrowth layer 19A-19C is, for example, 1 × 10⁻⁶ 18 ~1 × 10 22 cm -3 This is preferable. Within this range, co-doping can suppress the n-type transformation of the regrowth interface due to impurities, thereby suppressing a decrease in luminescence efficiency. The Mg concentration of the Al gradient regrowth layers 19A to 19C is preferably 1 × 10⁻⁶. 19 ~1 × 10 21 cm -3 That is the case.
[0055] The reason why the decrease in luminescence efficiency is suppressed by the Al gradient regrowth layers 19A-19C is not well understood, but the following reasons are possible.
[0056] Firstly, the gradual increase in Al composition from the third active layer 16 towards the electron blocking layer 20A-20C may have relieved the strain on the third active layer 16, thereby improving the internal quantum efficiency.
[0057] Secondly, the leakage current due to the impurity layer at the regrowth interface is suppressed, which may have resulted in an improved electron injection efficiency into the third active layer 16. The details of why the injection efficiency improves are as follows: Impurities at the regrowth interface create defects, and these defects form intermediate levels, where electrons are trapped and non-luminescent recombination occurs. If the Al composition increases abruptly, that is, if electron blocking layers 20A to 20C are provided without the Al gradient regrowth layer, the probability of electrons concentrating near the regrowth interface and non-luminescent recombination increases. On the other hand, if the Al composition increases stepwise, that is, if Al gradient regrowth layers 19A to 19C are provided, the electron distribution also broadens, and the number of electrons reflected towards the third active layer 16 without being trapped by defects increases. As a result, the electron injection efficiency into the third active layer 16 improves.
[0058] Thirdly, the improved quality of the impurity layer and the electron blocking layers 20A to 20C may have led to an improvement in the functionality of the electron blocking layers 20A to 20C.
[0059] Furthermore, the Al gradient regrowth layer 19A is not necessarily required. Because the electron blocking layer 17 and the p-type layer 18 are formed, the regrowth interface is far from the third active layer 16, and the regrowth interface is sandwiched between the two p-type layers, the p-type layer 18 and the electron blocking layer 20A. As a result, the influence of impurities at the regrowth interface on the luminescence efficiency of the third active layer 16 is small.
[0060] Furthermore, the Al gradient regrowth layers 19A to 19C may or may not be in contact with the p-type layer 18, the undoped intermediate layer 15A, and the undoped intermediate layer 13A, respectively. In other words, there may be layers such as p-GaN between the Al gradient regrowth layer 19A and the p-type layer 18, between the Al gradient regrowth layer 19B and the undoped intermediate layer 15A, and between the Al gradient regrowth layer 19C and the undoped intermediate layer 13A. However, from the viewpoint of further suppressing the decrease in luminous efficiency, it is preferable that the Al gradient regrowth layers 19A to 19C are in contact with the p-type layer 18, the undoped intermediate layer 15A, and the undoped intermediate layer 13A, respectively. Similarly, it is preferable that the Al gradient regrowth layers 19A to 19C are in contact with the electron blocking layers 20A to 20C.
[0061] The electron blocking layers 20A to 20C are layers provided on top of the Al gradient regrowth layers 19A to 19C, respectively. The electron blocking layers 20A to 20C are layers that block electrons injected from the n-type layer 11 in order to efficiently confine them to the first active layer 12, the second active layer 14, and the third active layer 16.
[0062] The electron blocking layers 20A to 20C may be single layers of GaN or AlGaN, or a structure in which two or more of AlGaN, GaN, and InGaN are stacked, or a structure in which only the composition ratio is changed. A superlattice structure may also be used. A superlattice structure allows for more efficient electron blocking. Examples of superlattice structures include a structure in which p-AlGaN and p-InGaN are stacked alternately, or a structure in which p-AlGaN and p-GaN are stacked alternately.
[0063] The thickness of the electron blocking layers 20A to 20C is preferably 2 to 50 nm, and more preferably 2 to 25 nm.
[0064] Furthermore, the electron blocking layers 20A to 20C are Mg-doped p-type. The p-type configuration allows for efficient injection of holes into the active layer. It also provides a larger barrier to electrons, enhancing the electron blocking function. While the electron blocking layers 20A to 20C may be undoped, it is preferable to dope them with Mg to create a p-type configuration for the reasons mentioned above. The Mg concentration in the electron blocking layers 20A to 20C is 1 × 10⁻¹⁶. 19 ~100×10 20 cm -3 It would be best to do so.
[0065] The p-type layers 21A to 21C are semiconductor layers provided on the electron block layers 20A to 20C, respectively, and are composed of the first layer, second layer, and so on, starting from the electron block layers 20A to 20C side.
[0066] The first layer is preferably made of p-GaN or p-InGaN. The thickness of the first layer is preferably 10 to 500 nm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm. The Mg concentration of the first layer is 1 × 10⁻⁶ 19 ~100×10 20 cm -3 It is preferable to do so. The second layer is preferably p-GaN or p-InGaN. The thickness of the second layer is preferably 2 to 50 nm, more preferably 4 to 20 nm, and even more preferably 6 to 10 nm. The Mg concentration of the second layer is 1 × 10⁻⁶ 20 ~100×10 20 cm -3 It would be best to do so.
[0067] In the first embodiment, the Al gradient regrowth layers 19A to 19C, the electron block layers 20A to 20C, and the p-type layers 21A to 21C are formed separately, but they may also be formed as a continuous film. In that case, layers of the same material as the Al gradient regrowth layers 19A to 19C are formed on the sides of the first groove 30 and the second groove 31, layers of the same material as the electron block layers 20A to 20C are formed, and layers of the same material as the p-type layers 21A to 21C are formed.
[0068] The p-side electrodes 22A to 22C are electrodes provided on the p-type layers 21A to 21C, respectively. The materials for the p-side electrodes 22A to 22C should be materials with high reflectivity of light at the emission wavelength and low contact resistance to the p-type layers 21A to 21C. Examples include Ag, Ni / Au, Co / Au, ITO / Ni / Al, Rh, and Ru. Of the red light emitted from the third active layer 16, the light directed toward the p-type layer 21A is reflected by the p-side electrode 22A and directed toward the substrate 10. Similarly, of the green light emitted from the second active layer 14, the light directed toward the p-type layer 21B is reflected by the p-side electrode 22B and directed toward the substrate 10, and of the blue light emitted from the first active layer 12, the light directed toward the p-type layer 21C is reflected by the p-side electrode 22C and directed toward the substrate 10.
[0069] The n-side electrode 23 is an electrode provided on the n-type layer 11 exposed at the bottom surface of the third groove 32. If the substrate 10 is a conductive material, the n-side electrode 23 may be provided on the back surface of the substrate 10 without providing the third groove 32. The material of the n-side electrode 23 is, for example, Ti / Al or V / Al.
[0070] As described above, in the light-emitting element 1 of the first embodiment, since Al gradient regrowth layers 19A to 19C are provided, the decrease in luminescence efficiency due to the presence of the regrowth interface can be suppressed.
[0071] 2. Operation of light-emitting elements Next, the operation of the light-emitting element 1 in the first embodiment will be described. In the light-emitting element 1 in the first embodiment, red light can be emitted from the third active layer 16 by applying a voltage between the p-side electrode 22A and the n-side electrode 23, green light can be emitted from the second active layer 14 by applying a voltage between the p-side electrode 22B and the n-side electrode 23, and blue light can be emitted from the first active layer 12 by applying a voltage between the p-side electrode 22C and the n-side electrode 23. These light emissions can be controlled individually, and two or more of the blue, green, and red light can be emitted simultaneously.
[0072] Thus, in the first embodiment, the light-emitting element 1 can control the emission of blue, green, and red light by selecting the electrode to which voltage is applied, and can be used as a single pixel on a display.
[0073] 3. Method for manufacturing light-emitting elements Next, the manufacturing process of the light-emitting element 1 in the first embodiment will be described with reference to Figures 3 to 7. Figure 3 is a flowchart showing the manufacturing process of the light-emitting element 1 in the first embodiment. Figures 4 to 7 are cross-sectional views showing the structure at each stage of the manufacturing process, and are cross-sectional views perpendicular to the main surface of the substrate.
[0074] First, prepare the substrate 10 and heat treat the substrate by adding hydrogen, nitrogen, and ammonia as needed.
[0075] Next, a buffer layer is formed on the substrate 10, and then an n-type layer 11, a first active layer 12, a first intermediate layer 13, a second active layer 14, a second intermediate layer 15, a third active layer 16, an electron blocking layer 17, and a p-type layer 18 are formed sequentially on the buffer layer (see Figure 4, step S1 in Figure 3). MOCVD is used to form each layer. The preferred growth temperatures for each layer are as follows.
[0076] The growth temperature of the first active layer 12 is preferably 700 to 950°C. This can improve crystal quality and increase luminescence efficiency. The first active layer 12 consists of a well layer and a barrier layer. The well layer and the barrier layer may be formed at the same temperature, or at different temperatures within the above temperature range. If different temperatures are used, it is preferable that the growth temperature of the well layer be lower than that of the barrier layer.
[0077] The growth temperature of the first intermediate layer 13 is preferably 700 to 1000°C. This is to suppress thermal damage to the first active layer 12. If the temperature is lower than 700°C, pits and point defects caused by threading dislocations are more likely to occur. More preferably, the temperature is 800 to 950°C, and even more preferably 850 to 950°C.
[0078] The growth temperature of the second active layer 14 is preferably 650 to 950°C. This can improve crystal quality and increase luminescence efficiency. The second active layer 14 is composed of a well layer and a barrier layer. The well layer and the barrier layer may be formed at the same temperature, or at different temperatures within the above temperature range. If different temperatures are used, it is preferable to lower the growth temperature of the well layer than the growth temperature of the barrier layer. Furthermore, it is preferable that the growth temperature of the second active layer 14 is lower than the growth temperature of the first active layer 12.
[0079] The growth temperature of the second intermediate layer 15 is preferably within the same range as the growth temperature of the first intermediate layer 13. However, it is preferable that the growth temperature of the second intermediate layer 15 be lower than that of the first intermediate layer 13. This is because the second active layer 14, which emits green light, is more susceptible to thermal damage than the first active layer 12, which emits blue light, and the effect of strain at the interface becomes greater.
[0080] The growth temperature of the third active layer 16 is preferably 500 to 950°C. This can improve crystal quality and increase luminescence efficiency. Each layer of the third active layer 16 may be formed at the same temperature, or at different temperatures within the above temperature range.
[0081] The growth temperature for the electron blocking layer 17 and the p-type layer 18 is preferably 500 to 950°C. This is to suppress thermal damage to the first active layer 12, the second active layer 14, and the third active layer 16. A higher growth temperature is preferable for improving the crystallinity of the electron blocking layer 17 and the p-type layer 18, more preferably 600 to 900°C, and even more preferably 700 to 900°C.
[0082] Next, a portion of the surface of the p-type layer 18 is dry-etched until it reaches the undoped intermediate layer 15A of the second intermediate layer 15 to form the first groove 30, and then dry-etched until it reaches the undoped intermediate layer 13A of the first intermediate layer 13 to form the second groove 31 (see Figure 5, step S2 in Figure 3).
[0083] During the formation of the first groove 30 and the second groove 31, the wafer is removed from the growth furnace and subjected to an etching process. As a result, the wafer is exposed to the atmosphere, and the wafer surface becomes contaminated with impurities such as O and Si.
[0084] Next, Al gradient regrowth layers 19A to 19C are formed on the p-type layer 18, on the undoped intermediate layer 15A of the second intermediate layer 15 exposed by the first groove 30, and on the undoped intermediate layer 13A of the first intermediate layer 13 exposed by the second groove 31, by MOCVD. Next, electron block layers 20A to 20C are formed on the Al gradient regrowth layers 19A to 19C by MOCVD. Next, p-type layers 21A to 21C are formed on the electron block layers 20A to 20C (see Figure 6, step S3 in Figure 3). Note that the p-type layers 21A to 21C are not p-type at this stage, but will become p-type later, so they are referred to as such.
[0085] During the formation of the Al gradient regrowth layers 19A to 19C, the supply amount of Al raw material gas is continuously increased. This ensures that the Al composition of the Al gradient regrowth layers 19A to 19C continuously increases as the layer thickness increases.
[0086] The growth temperature of the Al gradient regrowth layers 19A to 19C is preferably 800 to 1000°C. By setting the growth temperature within this range, it is possible to recover from etching damage caused by the formation of the first groove 30 and the second groove 31 while suppressing thermal damage to the first active layer 12, the second active layer 14, and the third active layer 16. More preferably, the growth temperature of the Al gradient regrowth layers 19A to 19C is 850 to 950°C.
[0087] The growth rate of the Al gradient regrowth layers 19A to 19C is preferably 2 to 10 nm / min. By setting the growth rate within this range, thermal damage to the first active layer 12, the second active layer 14, and the third active layer 16 can be suppressed. More preferably, the growth rate of the Al gradient regrowth layers 19A to 19C is 4 to 8 nm / min.
[0088] By providing the Al gradient regrowth layers 19A to 19C in this manner, it is possible to suppress the decrease in luminescence efficiency due to impurities such as O and Si present at the regrowth interface.
[0089] The growth temperature of the electron blocking layers 20A to 20C is preferably 950°C or lower. This is because the first active layer 12, the second active layer 14, and the third active layer 16 contain InGaN, and this is to suppress thermal damage to the InGaN. The growth temperature of the electron blocking layers 20A to 20C is more preferably 900°C or lower. Furthermore, the growth temperature of the electron blocking layers 20A to 20C is preferably 750°C or higher, and more preferably 800°C or higher.
[0090] The growth temperature for the p-type layers 21A to 21C is preferably 650 to 1000°C, more preferably 700 to 950°C, and even more preferably 800 to 950°C.
[0091] Next, a portion of the surface of the p-type layer 21C is dry-etched until it reaches the n-type layer 11 to form a third groove 32 (see Figure 7, step S4 in Figure 3). Then, the n-side electrode 23 is formed on the n-type layer 11 exposed at the bottom of the third groove 32, and the p-side electrodes 22A to 22C are formed on the p-type layers 21A to 21C. The light-emitting element of the first embodiment is thus manufactured.
[0092] 4. Experimental Results A light-emitting element of Example 1 was fabricated and its luminescence intensity was measured. As shown in Figure 8, the light-emitting element of Example 1 is a structure in which the blue light-emitting structure is extracted from the structure of the light-emitting element 1 in the first embodiment.
[0093] The light-emitting element of Example 1 was fabricated as follows. First, an n-type layer 11, a first active layer 12, and a first intermediate layer 13 were formed on the substrate 10 in this order from the substrate 10 side. Next, the wafer was removed from the growth furnace and dry-etched until the undoped intermediate layer 13A was exposed.
[0094] Next, an Al gradient regrowth layer 19C was formed at a growth rate of approximately 5 nm / min. The growth temperature of the Al gradient regrowth layer 19C was 945°C, and the Mg concentration was 5 × 10⁻⁶. 19 / cm 3 Next, an electron-blocking layer 20C was formed on the Al gradient regrowth layer 19C. The electron-blocking layer 20C had a superlattice structure in which Mg-doped AlGaN and Mg-doped InGaN were alternately stacked. The growth temperature of the electron-blocking layer 20C was set to 890°C. Next, a p-type layer 21C made of Mg-doped GaN was formed.
[0095] Next, a portion of the p-type layer 21C was dry-etched until the n-type layer 11 was exposed, forming the p-side electrode 22C on the p-type layer 21C and the n-side electrode 23 on the n-type layer 11. This completed the fabrication of the light-emitting element of Example 1.
[0096] As a comparative example, a light-emitting element with the same structure as in Example 1 was also fabricated, except that a 35 nm thick Mg-doped GaN layer was provided instead of the Al gradient regrowth layer 19C.
[0097] Figure 9 is a graph showing the relationship between the thickness of the Al gradient regrowth layer 19C and the luminescence intensity. The TMAl supply amount was varied from 5 sccm to 200 sccm during the formation of the Al gradient regrowth layer 19C. The luminescence intensity was measured at a 50 mA drive.
[0098] Figure 9 shows that the emission intensity increases with increasing thickness of the Al gradient regrowth layer 19C. Furthermore, it was found that increasing the thickness of the Al gradient regrowth layer 19C to 10 nm or more resulted in a higher emission intensity compared to the comparative example.
[0099] Figure 10 is a graph showing the relationship between the change in TMAl supply amount and the luminescence intensity during the formation of the Al gradient regrowth layer 19C. The thickness of the Al gradient regrowth layer 19C was set to 16 nm. The luminescence intensity was measured at a 50 mA drive. In Figure 10, the horizontal axis from A to B indicates the change in the TMAl supply amount from A (sccm) to B (sccm) during the formation of the Al gradient regrowth layer 19C. A larger TMAl supply amount results in a higher Al composition. In Figure 10, the horizontal axis at 0 represents the comparative example, i.e., when a GaN layer was formed instead of the Al gradient regrowth layer 19C.
[0100] As shown in Figure 10, when the Al composition was gradually decreased, the luminescence intensity was lower than that of the comparative example. On the other hand, when the Al composition was gradually increased, the luminescence intensity tended to be higher than that of the comparative example, and the luminescence intensity tended to increase as the amount of TMAl supplied increased.
[0101] Figures 9 and 10 show that by providing an Al gradient regrowth layer 19C with a gradually increasing Al composition between the undoped intermediate layer 13A and the electron blocking layer 20C, the decrease in luminescence efficiency due to the presence of the regrowth interface can be suppressed.
[0102] (Other transformation forms) In the first embodiment, three colors of light emission are used: red, green, and blue. However, the present invention is not limited to these three colors, and any two or more colors with different emission wavelengths are acceptable. For example, four colors of light emission, such as red, yellow, green, and blue, can also be used.
[0103] Furthermore, the light-emitting element 1 in the first embodiment can be used not only in display devices such as displays, but also as a light source for optical communication. [Explanation of Symbols]
[0104] 1: Light-emitting element 10: Circuit board 11:n-type layer 12: 1st active layer 13: First Meso-Place 14:Second active layer 15: Second Meso-Marginal Layer 16: 3rd active layer 17, 20A~20C: Electron Block Layer 18, 21A~21C: p-type layer 19A~19C: Al graded regrowth layer 22A~22C:p side electrode 23:n side electrode
Claims
1. In a method for manufacturing a light-emitting element using a group III nitride semiconductor, An n-type layer formation step in which an n-type layer made of an n-type group III nitride semiconductor is formed on a substrate, A first active layer formation step is to form a first active layer having a predetermined emission wavelength on the n-type layer, An intermediate layer formation step is to form an intermediate layer made of a group III nitride semiconductor containing In on the first active layer, A second active layer formation step is performed in which a second active layer having a different emission wavelength from the first active layer is formed on the intermediate layer, A groove forming step in which grooves are formed that extend from the second active layer to the intermediate layer, A step of forming an Al gradient regrowth layer, in which an Al gradient regrowth layer made of a p-type group III nitride semiconductor is formed on the intermediate layer exposed at the bottom surface of the groove, The process includes a p-type layer formation step of forming a p-type layer made of a p-type group III nitride semiconductor on the second active layer and the Al gradient regrowth layer, A method for manufacturing a light-emitting element, wherein the Al composition of the Al gradient regrowth layer gradually increases in the thickness direction toward the p-type layer.
2. The method for manufacturing a light-emitting element according to claim 1, wherein the thickness of the Al gradient regrowth layer is 10 nm or more and 50 nm or less.
3. The method for manufacturing an element-emitting element according to claim 1 or claim 2, wherein the minimum value of the Al gradient regrowth layer is 0% or more and 10% or less.
4. The method for manufacturing an element-emitting element according to claim 1 or claim 2, wherein the maximum value of the Al gradient regrowth layer is 10% or more and 30% or less.
5. The method for manufacturing an light-emitting element according to claim 1 or claim 2, wherein the rate of increase of the Al composition in the thickness direction of the Al gradient regrowth layer is 0.3 to 1% / nm.
6. The Mg concentration in the aforementioned Al gradient regrowth layer is 1 × 10 １８ ~1 x 10 ２２ cm －３ The method for manufacturing a light-emitting element according to claim 1 or claim 2.
7. In a light-emitting device using a group III nitride semiconductor, circuit board and An n-type layer made of an n-type group III nitride semiconductor is formed on the substrate, A first active layer formed on the n-type layer and having a predetermined emission wavelength, An intermediate layer formed on the first active layer and consisting of a group III nitride semiconductor containing In, A second active layer is formed on the intermediate layer and has an emission wavelength different from that of the first active layer, A groove extending from the second active layer to the intermediate layer, An Al gradient regrowth layer made of a p-type group III nitride semiconductor is formed on the intermediate layer exposed at the bottom surface of the groove, The second active layer and the Al gradient regrowth layer are formed on the p-type layer, which is made of a p-type group III nitride semiconductor, and the p-type layer is formed on the second active layer and the Al gradient regrowth layer, The Al composition of the aforementioned Al gradient regrowth layer gradually increases in the thickness direction as it approaches the p-type layer. The region near the interface between the intermediate layer and the Al gradient regrowth layer is 1 × 10 １８ cm －３ A light-emitting element containing the above O or Si.