Lights and light methods

Abstract

To improve the surface flatness of an intermediate layer.SOLUTION: A light emitting element is a group III nitride semiconductor light emitting element, and comprises: an n-layer 11 made of an n-type group III nitride semiconductor; a first active layer 14 provided on the n-layer and having a specified emission wavelength; an intermediate layer 15 provided on the first active layer and made of a group III nitride semiconductor containing In, a second active layer 16 with an emission wavelength different from the first active layer, provided on the intermediate layer, and the intermediate layer has an In composition set to have a band gap that does not absorb light emitted from the first active layer and the second active layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a light-emitting element and a method for manufacturing the same. [Background technology]

[0002] In recent years, there has been a demand for higher resolution displays, and micro-LED displays, which use tiny LEDs on the order of 1 to 100 μm as each pixel, have attracted attention. Various methods for achieving full color are known, but one known method involves sequentially stacking three active layers, each emitting blue, green, and red light, on the same substrate. In this case, an intermediate layer needs to be formed between the active layers in order to drive each active layer individually. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5854419 [Overview of the project] [Problems that the invention aims to solve]

[0004] The intermediate layer must be deposited after the active layer has been laminated. Therefore, the intermediate layer needed to be deposited at a low temperature to avoid thermal damage to the active layer. However, depositing the intermediate layer at a low temperature resulted in a deterioration of the quality and surface flatness of the intermediate layer, which in turn reduced the quality of the active layer formed on top of it.

[0005] Therefore, the objective of the present invention is to improve the surface flatness of the intermediate layer. [Means for solving the problem]

[0006] One aspect of the present invention is, In a light-emitting element made of a group III nitride semiconductor, An n-layer made of an n-type group III nitride semiconductor, A first active layer having a predetermined emission wavelength is provided on the n layer, Provided on the first active layer, and made of a group III nitride semiconductor containing In Furthermore, it has a structure in which a first p-type layer, a second p-type layer, an n-type third layer, and an n-type fourth layer are stacked in order from the first active layer side. The middle class, A second active layer is provided on the intermediate layer and has an emission wavelength different from that of the first active layer, The p layer provided on the second active layer, A groove extending from the p-layer side to the fourth layer, A p electrode provided on the p layer, An electrode provided on the fourth layer exposed on the bottom surface of the groove, It has, The In composition of the intermediate layer is set such that it has a band gap that does not absorb light emitted from the first active layer and the second active layer. hand, The p-type impurity concentration in the second layer is higher than that in the first layer, the n-type impurity concentration in the third layer is higher than that in the fourth layer, and the second and third layers form a tunnel junction structure. The In composition of the second and third layers is higher than that of the In composition of the first and fourth layers. It is located in the light-emitting element.

[0007] Furthermore, in one aspect of the present invention, In a method for manufacturing a light-emitting element made of a group III nitride semiconductor, A process for forming an n-layer made of an n-type group III nitride semiconductor, The steps include forming a first active layer having a predetermined emission wavelength on the n layer, An intermediate layer made of a group III nitride semiconductor containing In is formed on the first active layer at a growth temperature of 700 to 1000°C. The intermediate layer is formed by stacking, in order from the first active layer side, a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer. The process, The process involves forming a second active layer having a different emission wavelength from the first active layer on the intermediate layer, The steps include forming a p layer on the second active layer, The step of forming a groove that extends from the p-layer side to the fourth layer, The step of forming a p electrode on the p layer, A step of forming an electrode on the fourth layer exposed on the bottom surface of the groove, It has, The In composition of the intermediate layer is set such that it has a band gap that does not absorb light emitted from the first active layer and the second active layer. death, The p-type impurity concentration in the second layer is made higher than that of the first layer, and the n-type impurity concentration in the third layer is made higher than that of the fourth layer, so that the second and third layers form a tunnel junction structure. The In composition of the second and third layers is made higher than the In composition of the first and fourth layers. The method for manufacturing light-emitting elements is described. [Effects of the Invention]

[0008] According to the present invention, the surface flatness of the intermediate layer can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] A diagram showing the configuration of a light-emitting element in the first embodiment. [Figure 2] A diagram showing the configuration of a modified light-emitting element. [Figure 3] A diagram showing the configuration of a modified light-emitting element. [Figure 4] A diagram showing the equivalent circuit of the light-emitting element of the first embodiment. [Figure 5] A diagram showing the manufacturing process of a light-emitting element of the first embodiment. [Figure 6] A diagram showing the manufacturing process of a light-emitting element of the first embodiment. [Figure 7] A diagram showing the manufacturing process of a light-emitting element of the first embodiment. [Figure 8] A diagram showing the manufacturing process of a light-emitting element of the first embodiment. [Figure 9] A diagram showing the configuration of a light-emitting element in the second embodiment. [Figure 10] A diagram showing the configuration of the light-emitting element of the third embodiment. [Figure 11] A diagram showing the configuration of the light-emitting element in Experimental Example 1. [Figure 12] AFM image of the surface of the third active layer 18. [Figure 13] A graph showing the relationship between the drive current and the external quantum efficiency. [Figure 14] A graph showing the emission spectrum. [Figure 15] A graph showing the emission spectrum. [Figure 16] A graph showing the emission spectrum. [Figure 17] A graph showing the emission spectrum. [Figure 18] AFM image of the surface of the third active layer 18. [Figure 19] A graph showing the relationship between the drive current and the external quantum efficiency. [Figure 20] A diagram showing the configuration of the light-emitting element in the fourth embodiment. [Figure 21] A diagram showing the equivalent circuit of the light-emitting element in the fourth embodiment. [Figure 22] A diagram showing the configuration of the light-emitting element in the fifth embodiment. [Figure 23] AFM images of the well layer surface of quantum well structure layer 518C when the growth rate is varied. [Figure 24] AFM images of the well layer surface of quantum well structure layer 518C when the In solid phase ratio / In gas phase ratio is changed. [Figure 25] AFM images of the well layer surface of quantum well structure layer 518C when the partial pressure of ammonia is changed. [Modes for carrying out the invention]

[0010] A light-emitting element made of a group III nitride semiconductor comprises an n-layer made of an n-type group III nitride semiconductor, a first active layer provided on the n-layer with a predetermined emission wavelength, an intermediate layer provided on the first active layer and made of a group III nitride semiconductor containing In, and a second active layer provided on the intermediate layer with an emission wavelength different from that of the first active layer. The In composition of the intermediate layer is set to have a band gap that does not absorb light emitted from the first and second active layers.

[0011] The device may also include a groove extending from the second active layer to the intermediate layer, a first p-layer provided on the second active layer and made of a p-type group III nitride semiconductor, a second p-layer provided on the intermediate layer exposed at the bottom of the groove and made of a p-type group III nitride semiconductor, a first p-electrode provided on the first p-layer, and a second p-electrode provided on the second p-layer.

[0012] Furthermore, the intermediate layer has a structure in which a first p-type layer, a second p-type layer, an n-type third layer, and an n-type fourth layer are stacked in order from the first active layer side, the p-type impurity concentration of the second layer is higher than that of the first layer, the n-type impurity concentration of the third layer is higher than that of the fourth layer, the second and third layers form a tunnel junction structure, and the intermediate layer may have a p-layer provided on the second active layer, a groove extending from the p-layer side to the fourth layer, a p-electrode provided on the p-layer, and an electrode provided on the fourth layer exposed at the bottom surface of the groove. This makes it possible to avoid the presence of a regrowth interface and suppress deterioration of device characteristics.

[0013] The In composition of the second and third layers may be higher than that of the first and fourth layers. This can further increase the tunneling probability due to the tunnel junction structure. Also, the In composition of the second layer may be higher than that of the third layer. Furthermore, the thickness of the second layer may be thinner than that of the first layer, and the thickness of the third layer may be thinner than that of the fourth layer.

[0014] The intermediate layer may be InGaN. The In composition of the intermediate layer may be 10% or less. The intermediate layer may be In-doped GaN.

[0015] A method for manufacturing a light-emitting element made of a group III nitride semiconductor comprises the steps of: forming an n layer made of an n-type group III nitride semiconductor; forming a first active layer having a predetermined emission wavelength on the n layer; forming an intermediate layer made of a group III nitride semiconductor containing In on the first active layer at a growth temperature of 700 to 1000°C; and forming a second active layer having a different emission wavelength from the first active layer on the intermediate layer. The In composition of the intermediate layer is set such that it has a band gap that does not absorb light emitted from the first and second active layers.

[0016] The method may also include the steps of: forming a groove extending from the second active layer to the intermediate layer; forming a first p layer and a second p layer made of a p-type group III nitride semiconductor on the second active layer and on the intermediate layer exposed to the bottom surface of the groove, respectively; and forming a first p electrode and a second p electrode on the first p layer and the second p layer, respectively.

[0017] The intermediate layer may be formed by stacking a first p-type layer, a second p-type layer, an n-type third layer, and an n-type fourth layer in order from the first active layer side, wherein the p-type impurity concentration of the second layer is higher than that of the first layer, the n-type impurity concentration of the third layer is higher than that of the fourth layer, and the second and third layers form a tunnel junction structure. The intermediate layer may also include the steps of forming a p-layer on the second active layer, forming a groove extending from the p-layer side to the fourth layer, forming a p-electrode on the p-layer, and forming an electrode on the fourth layer exposed at the bottom of the groove.

[0018] In the method for manufacturing a light-emitting element made of the above-described group III nitride semiconductor, the In composition of the second and third layers may be higher than that of the first and fourth layers. Alternatively, the In composition of the second layer may be higher than that of the third layer. Furthermore, the thickness of the second layer may be made thinner than that of the first layer, and the thickness of the third layer may be made thinner than that of the fourth layer. Additionally, the growth temperature of the second and third layers may be lower than that of the first and fourth layers.

[0019] Furthermore, in the method for manufacturing a light-emitting element made of the above-mentioned group III nitride semiconductor, the In composition of the intermediate layer may be 10% or less. Also, the intermediate layer may be InGaN. Also, the intermediate layer may be In-doped GaN.

[0020] (First Embodiment) Figure 1 shows the configuration of the light-emitting element of the first embodiment. The light-emitting element of the first embodiment is capable of emitting blue, green, and red light. Furthermore, the light-emitting element of the first embodiment is a flip-chip type that extracts light from the back side of the substrate and is mounted face-down on a mounting substrate (not shown). In addition, although the first embodiment has a structure where one pixel is one chip, it may also be a monolithic type. That is, the element structure of the first embodiment may be arranged in a matrix on the same substrate to form a microLED display element.

[0021] As shown in Figure 1, the light-emitting element of the first embodiment includes a substrate 10, an n-layer 11, an ESD layer 12, a base layer 13, a first active layer 14, a first intermediate layer 15, a second active layer 16, a second intermediate layer 17, a third active layer 18, a protective layer 19, regrowth layers 20A to 20C, electron blocking layers 21A to 21C, p-layers 22A to 22C, an n-electrode 23, and p-electrodes 24A to 24C.

[0022] Substrate 10 is a growth substrate for growing Group III nitride semiconductors. Examples include sapphire, Si, and GaN.

[0023] The n-layer 11 is an n-type semiconductor provided on the substrate 10 via a low-temperature buffer layer and a high-temperature buffer layer (not shown). However, the buffer layer may be provided only if necessary, and may not be provided if the substrate is GaN, for example. The n-layer 11 is, for example, n-GaN, n-AlGaN, etc. The Si concentration is, for example, 1 × 10⁻⁶ 18 ~100×10 18 cm -3 That is the case.

[0024] The ESD layer 12 is a semiconductor layer provided on the n layer 11, and is provided to improve electrostatic discharge voltage. The ESD layer 12 may be provided as needed and may be omitted. The ESD layer 12 is, for example, undoped or low-concentration Si-doped GaN, InGaN, or AlGaN.

[0025] The base layer 13 is a superlattice-structured semiconductor layer provided on the ESD layer 12, and is a layer for mitigating lattice strain in the semiconductor layer formed on the base layer 13. The base layer 13 may be provided as needed and may be omitted. The base layer 13 is made by alternately stacking two of the group III nitride semiconductor thin films with different compositions (for example, GaN, InGaN, and AlGaN), with the number of pairs being, for example, 3 to 30. It may be undoped, or Si may be 1 × 10⁻¹⁶ 17 ~100×10 17 cm -3 It may be doped to a certain extent. Also, it does not need to be a superlattice structure as long as the strain can be relieved. Any material that reduces the difference in lattice constants at the heterointerface with the first active layer 14 is acceptable, for example, an InGaN layer, an AlInN layer, or an AlGaIn layer.

[0026] The first active layer 14 is an SQW or MQW structured light-emitting layer provided on the base layer 13. The emission wavelength is blue, between 430 and 480 nm. The first active layer 14 has a structure in which 1 to 7 pairs of barrier layers made of AlGaN and well layers made of InGaN are alternately stacked. More preferably, 1 to 5 pairs, and even more preferably 1 to 3 pairs.

[0027] The first intermediate layer 15 is a semiconductor layer provided on the first active layer 14, and is located between the first active layer 14 and the second active layer 16. The first intermediate layer 15 is provided to allow for individual control of the light emission from the first active layer 14 and the light emission from the second active layer 16. It also serves to protect the first active layer 14 from etching damage when forming the second groove 31, which will be described later.

[0028] The material of the first intermediate layer 15 is a group III nitride semiconductor containing In, and it is preferably InGaN for example. The roughening of the surface of the first intermediate layer 15 can be suppressed by the surfactant effect of In, and the surface flatness can be improved. Also, the lattice strain can be relaxed. The In composition of the first intermediate layer 15 (the molar ratio of In in the total group III metals of the group III nitride semiconductor) may be set to have a band gap that does not absorb the light emitted from the first active layer 14 and the second active layer 16. The preferable 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 15 to be rough. In can be arbitrary as long as it is greater than 0%, and it can also be at the doping level (level that does not form a mixed crystal). For example, the In concentration is 1×10 14 cm -3 or more and 1×10 22 cm -3 or less of GaN.

[0029] Also, the first intermediate layer 15 may be doped with impurities. Preferably, they are n-type impurities. For example, the Si concentration is 1×10 17 ~1000×10 17 cm -3 , preferably 10×10 17 ~100×10 17 cm -3 , and even more preferably 20×10 17 ~80×10 17 cm -3 may be acceptable.

[0030] The thickness of the first intermediate layer 15 is preferably 20~150 nm. If it is thicker than 150 nm, it may cause the surface of the first intermediate layer 15 to be rough. Also, if it is thinner than 20 nm, it may be difficult to control the depth of the second groove 31 to be within the first intermediate layer 15 when forming the second groove 31 described later. More preferably, it is 30~100 nm, and even more preferably 5~80 nm.

[0031] The second active layer 16 is an SQW or MQW structured light-emitting layer provided on the first intermediate layer 15. The emission wavelength is green, between 510 and 570 nm. The second active layer 16 has a structure in which 1 to 7 pairs of barrier layers made of GaN and well layers made of InGaN are alternately stacked. More preferably, there are 1 to 5 pairs, and even more preferably, 1 to 3 pairs. It is also preferable that the number of pairs is equal to or less than the number of pairs in the first active layer 14, and more preferably less.

[0032] The second intermediate layer 17 is a semiconductor layer provided on the second active layer 16, and is located between the second active layer 16 and the third active layer 18. The second intermediate layer 17 is provided for the same reasons as the first intermediate layer 15, and is a layer provided to allow for individual control of the light emission from the second active layer 16 and the light emission from the third active layer 18. It also serves to protect the second active layer 16 from etching damage when forming the third groove 32, which will be described later.

[0033] The material of the second intermediate layer 17 is the same as that of the first intermediate layer 15. The first intermediate layer 15 and the second intermediate layer 17 may be made of the same material. Also, the second intermediate layer 17 may be doped with impurities in the same way as the first intermediate layer 15. Furthermore, the thickness of the second intermediate layer 17 is the same as that of the first intermediate layer 15, and the thicknesses of the first intermediate layer 15 and the second intermediate layer 17 may be the same. However, it is preferable to make the second intermediate layer 17 thinner than the first intermediate layer 15 and to make its In composition higher than that of the first intermediate layer 15. This is because the green-emitting second active layer 16 is more susceptible to thermal damage than the blue-emitting first active layer 14, and the effect of strain at the interface is greater.

[0034] The third active layer 18 is an SQW or MQW structured light-emitting layer provided on the second intermediate layer 17. The emission wavelength is red, between 590 and 700 nm. The third active layer 18 has 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. It is also preferable that the number of pairs is equal to or less than that of the second active layer 16, and more preferably less.

[0035] The protective layer 19 is a semiconductor layer provided on the third active layer 18. The protective layer 19 protects the active layer and also functions as an electron blocking layer. The protective layer 19 can be made of any material with a wider band gap than the well layer of the third active layer 18, such as AlGaN, GaN, or InGaN. The thickness of the protective layer 19 is preferably 2.5 to 50 nm, and more preferably 5 to 25 nm. The protective layer 19 may be doped with impurities, or it may be doped with Mg. In that case, the Mg concentration is 1 × 10⁻¹⁶. 18 ~1000×10 18 cm -3 It would be best to do so.

[0036] A portion of the protective layer 19 is etched to form grooves, including a third groove 32 that reaches the second intermediate layer 17 from the protective layer 19, a second groove 31 that reaches the first intermediate layer 15, and a first groove 30 that reaches the n layer 11.

[0037] The regrowth layers 20A to 20C are provided on the protective layer 19, on the second intermediate layer 17 exposed at the bottom of the third groove 32, and on the first intermediate layer 15 exposed at the bottom of the second groove 31, respectively. The composition of the regrowth layers 20A to 20C is the same as that of the protective layer 19.

[0038] The electron blocking layers 21A to 21C are semiconductor layers provided on the regrowth layers 20A to 20C, respectively, and are layers that block electrons injected from the n layer 11 in order to efficiently confine them to the first active layer 14, the second active layer 16, and the third active layer 18. The electron blocking layers 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 and stacked. A superlattice structure may also be used. The thickness of the electron blocking layers 21A to 21C is preferably 5 to 50 nm, and more preferably 5 to 25 nm. The Mg concentration of the electron blocking layers 21A to 21C is 1 × 10⁻¹⁶ 19 ~100×10 19 cm -3 It would be best to do so.

[0039] The p-layers 22A to 22C are semiconductor layers provided on the electron-blocking layers 21A to 21C, respectively, and are composed of a first layer and a second layer, in that order from the electron-blocking layer 21 side. 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 × 10⁻¹⁶ 19 ~100×10 19 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.

[0040] In the first embodiment, the regrowth layers 20A-20C, electron blocking layers 21A-21C, and p-layers 22A-22C are provided separately, but they may be continuous (see Figure 2). In this case, the regrowth layers, electron blocking layers, and p-layers will also be formed on the sides of the third groove 32 and the second groove 31, but this will have little effect on the operation of the device. The reason is as follows: If the p-electrodes 24A, 24B, and 24C are sufficiently spaced apart, the resistance of the p-layers connecting the p-electrodes 24A, 24B, and 24C is very high, so almost no current flows. In addition, because holes have low mobility, holes do not spread laterally from the region in contact with the electrode, but rather flow predominantly vertically through the pn junction directly beneath the electrode. Therefore, even if the regrowth layers 20A-20C, electron blocking layers 21A-21C, and p-layers 22A-22C are continuous, it will not affect the operation of the device. In other words, when current is passed through p electrode 24A, the current flows directly beneath p electrode 24A, causing the active layer directly beneath p electrode 24A to emit light, while current rarely flows through the active layers directly beneath p electrodes 24B and 24C, resulting in very little light emission.

[0041] Furthermore, as shown in Figure 3, insulating film 27 may be provided on the side surfaces of the third groove 32 and the second groove 31. This insulating film 27 is a mask that remains when selectively growing the regrowth layers 20A to 20C, the electron blocking layers 21A to 21C, and the p layers 22A to 22C.

[0042] The n-electrode 23 is an electrode provided on the n-layer 11 exposed at the bottom surface of the first groove 30. If the substrate 10 is a conductive material, the n-electrode 23 may be provided on the back surface of the substrate 10 without providing the first groove 30. The material of the n-electrode 23 is, for example, Ti / Al.

[0043] The p electrodes 24A to 24C are electrodes provided on the p layers 22A to 22C, respectively. The materials for the p electrodes 24A to 24C include, for example, Ag, Ni / Au, Co / Au, ITO, etc.

[0044] The operation of the light-emitting element of the first embodiment will now be described. In the light-emitting element of the first embodiment, applying a voltage between the p electrode 24A and the n electrode 23 will cause red light to be emitted from the third active layer 18, applying a voltage between the p electrode 24B and the n electrode 23 will cause green light to be emitted from the second active layer 16, and applying a voltage between the p electrode 24C and the n electrode 23 will cause blue light to be emitted from the first active layer 14. Furthermore, it is possible to emit two or more of the blue, green, and red light simultaneously. Thus, in the light-emitting element of the first embodiment, the emission of blue, green, and red light can be controlled by selecting the electrodes to which voltage is applied, and it can be used as a single pixel on a display.

[0045] Figure 4 shows the equivalent circuit of the light-emitting element of the first embodiment. As shown in Figure 4, the light-emitting element of the first embodiment has a structure in which blue, green, and red LEDs are formed within a single element, and full-color light emission can be achieved with a single element. Therefore, it is possible to make the size of a single element much smaller than when blue, green, and red LEDs are prepared individually and arranged on the same substrate to create a full-color light-emitting element for one pixel. Furthermore, with the structure of the first embodiment, the process of preparing and arranging blue, green, and red LEDs individually can be omitted, manufacturing costs can be greatly reduced, and a very low-cost full-color light-emitting element and a light-emitting display using it can be realized.

[0046] In the first embodiment, since the first intermediate layer 15 and the second intermediate layer 17 contain In, the surface flatness of the first intermediate layer 15 and the second intermediate layer 17 can be improved by the surfactant effect of In, and the surface flatness of the second active layer 16 and the third active layer 18 can also be improved. Furthermore, lattice distortion caused by the difference in lattice constants between the base layer 13 and the first active layer 14 can also be mitigated. As a result, the light-emitting element of the first embodiment can improve luminous efficiency.

[0047] Next, the manufacturing process of the light-emitting element of the first embodiment will be described with reference to the figure.

[0048] First, prepare the substrate 10 and heat treat the substrate by adding hydrogen, nitrogen, and ammonia as needed.

[0049] Next, a buffer layer is formed on the substrate 10, and then the n layer 11, ESD layer 12, underlayer 13, first active layer 14, first intermediate layer 15, second active layer 16, second intermediate layer 17, third active layer 18, and protective layer 19 are formed sequentially on the buffer layer (see Figure 5). The preferred growth temperatures for each layer are as follows.

[0050] The growth temperature of the first active layer 14 is preferably 700 to 950°C. This can improve crystal quality and increase luminescence efficiency. The first active layer 14 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.

[0051] The growth temperature of the first intermediate layer 15 is preferably 700 to 1000°C. This is to suppress thermal damage to the first active layer 14. 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.

[0052] The growth temperature of the second active layer 16 is preferably 650 to 950°C. This can improve crystal quality and increase luminescence efficiency. The second active layer 16 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 that the growth temperature of the well layer be lower than that of the barrier layer. Furthermore, it is preferable that the growth temperature of the second active layer 16 is lower than that of the first active layer 14.

[0053] The growth temperature of the second intermediate layer 17 is preferably within the same range as the growth temperature of the first intermediate layer 15. However, it is preferable that the growth temperature of the second intermediate layer 17 be lower than that of the first intermediate layer 15. This is because the second active layer 16, which emits green light, is more susceptible to thermal damage than the first active layer 14, which emits blue light, and the effect of strain at the interface becomes greater.

[0054] The growth temperature of the third active layer 18 is preferably 500 to 950°C. This can improve crystal quality and increase luminescence efficiency. The third active layer 18 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 third active layer 18 is lower than the growth temperature of the second active layer 16.

[0055] The growth temperature of the protective layer 19 is preferably 500 to 950°C. This is to suppress thermal damage to the first active layer 14, the second active layer 16, and the third active layer 18. A higher growth temperature is preferable for improving the crystallinity of the protective layer 19, more preferably 600 to 900°C, and even more preferably 700 to 900°C.

[0056] Next, a portion of the surface of the protective layer 19 is dry-etched until it reaches the second intermediate layer 17 to form the third groove 32, and then dry-etched until it reaches the first intermediate layer 15 to form the second groove 31 (see Figure 6). Preferably, the third groove 32 and the second groove 31 are etched to an intermediate thickness between the second intermediate layer 17 and the first intermediate layer 15.

[0057] Next, regrowth layers 20A to 20C are formed on the protective layer 19, on the second intermediate layer 17 exposed by the third groove 32, and on the first intermediate layer 15 exposed by the second groove 31. The growth temperature is the same as that of the protective layer 19. Here, the regrowth layers 20A to 20C may be formed as a continuous layer as shown in Figure 2. Alternatively, as shown in Figure 3, insulating film 27 may be formed on the sides of the third groove 32 and the second groove 31, and this may be used as a mask to selectively grow the regrowth layers 20A to 20C, so that the regrowth layers 20A to 20C are formed separately.

[0058] Next, electron blocking layers 21A to 21C are formed on the regrowth layers 20A to 20C. The growth temperature of the electron blocking layers 21A to 21C is preferably 750 to 1000°C. This is to suppress thermal damage to the first active layer 14, the second active layer 16, and the third active layer 18. More preferably, it is 750 to 950°C, and even more preferably 800 to 900°C.

[0059] Next, p-layers 22A to 22C are formed on the electron-blocking layers 21A to 21C (see Figure 7). The growth temperature for p-layers 22A to 22C is preferably 650 to 1000°C, more preferably 700 to 950°C, and even more preferably 750 to 900°C.

[0060] Next, a portion of the surface of the p layer 22C is dry-etched until it reaches the n layer 11 to form the first groove 30 (see Figure 8). Then, the n electrode 23 is formed on the n layer 11 exposed at the bottom of the first groove 30, and the p electrodes 24A to 24C are formed on the p layers 22A to 22C. The light-emitting element of the first embodiment is manufactured by the above steps.

[0061] (Second Embodiment) As shown in Figure 9, the light-emitting element of the second embodiment is the same as the light-emitting element of the first embodiment, but with the first intermediate layer 15 and the second intermediate layer 17 replaced by the first intermediate layer 215 and the second intermediate layer 217.

[0062] The first intermediate layer 215 has a structure in which a non-doped layer 215A and an n-type layer 215B are stacked in order from the first active layer 14 side. The non-doped layer 215A and the n-type layer 215B are made of the same material except for impurities, and are GaN or InGaN. The same material as the first intermediate layer 15 of the first embodiment is preferred. The non-doped layer 215A is undoped, and the n-type layer 215B is Si-doped. The Si concentration of the n-type layer 215B is 1 × 10⁻⁶ 17 ~1000×10 17 cm -3 It is preferable that the thickness of the first intermediate layer 215 be the same as that of the first intermediate layer 15, that is, 20 to 150 nm. Furthermore, it is preferable that the thickness of the undoped layer 215A be 10 nm or more. This is to control the etching depth and avoid etching damage to the first active layer 14. Furthermore, it is preferable that the thickness of the n-type layer 215B be 10 nm or more. This is to independently control the luminescence characteristics of each active layer. The n-type layer 215B may be modulated doped with Si, and a non-doped region may be present in a part of the n-type layer 215B.

[0063] The second intermediate layer 217 has a structure in which a non-doped layer 217A and an n-type layer 217B are stacked in order from the second active layer 16 side. The non-doped layer 217A and the n-type layer 217B have the same structure as the non-doped layer 215A and the n-type layer 215B. In other words, the non-doped layer 217A and the n-type layer 217B are made of the same material except for impurities, and are GaN or InGaN. Furthermore, the non-doped layer 217A is undoped, and the n-type layer 217B is Si-doped. However, it is preferable to make it thinner than the first intermediate layer 215 and to have a higher In composition than the first intermediate layer 215. This is for the same reasons as in the case of the second intermediate layer 17. In other words, the second active layer 16, which emits green light, is more susceptible to thermal damage than the first active layer 14, which emits blue light, and the effect of strain at the interface becomes greater.

[0064] The third groove 32 is deep enough to reach the undoped layer 217A of the second intermediate layer 217. In this way, by removing the n-type layer 217B of the second intermediate layer 17 under the p electrode 24B, an n-type layer is prevented from being located on the second active layer 16, causing the second active layer 16 to emit light. Similarly, the second groove 31 is deep enough to reach the undoped layer 215A of the first intermediate layer 215. This is for the same reason; by removing the n-type layer 215B of the first intermediate layer 15 under the p electrode 24C, an n-type layer is prevented from being located on the first active layer 14, causing the first active layer 14 to emit light.

[0065] Here, we will explain the pn junction distance. The pn junction distance corresponds to the depleted film thickness under zero bias. In LEDs, it corresponds to the total film thickness of the undoped or lightly doped active layer sandwiched between a p layer with a high concentration of acceptor impurities and an n layer with a high concentration of donor impurities.

[0066] When the first intermediate layer 215 and the second intermediate layer 217 are undoped, the distance between the pn junctions (thickness of the depletion layer) in the region under the p electrode 24A is the distance from the electron blocking layer 21A, which is highly doped with acceptor impurities, to the n layer 11, which is highly doped with donor impurities, i.e., the thickness of the film including the first active layer 14, the second active layer 16, the third active layer 18, the first intermediate layer 15, and the second intermediate layer 17. Furthermore, under the p electrode 24B, it is the distance from the electron blocking layer 21B, which is highly doped with acceptor impurities, to the n layer 11, i.e., the thickness of the film including the first active layer 14, the second active layer 16, the first intermediate layer 15, and a portion of the second intermediate layer 17. Furthermore, under the p electrode 24C, it is the distance from the electron blocking layer 21C, which is highly doped with acceptor impurities, to the n layer 11, i.e., the thickness of the film including the first active layer 14 and a portion of the first intermediate layer 15.

[0067] Therefore, the distance between the pn junctions differs in each of these three cases, resulting in different driving voltages, current injection efficiency, and reverse currents. Furthermore, when applying a voltage to the p electrode 24A to cause the third active layer 18 to emit light, electron and hole carriers are supplied to all active layers, potentially causing light to be emitted from the second active layer 16 and the first active layer 14 as well. Similarly, when applying a voltage to the p electrode 24B to cause the second active layer 16 to emit light, there is a possibility that light will also be emitted from the first active layer 14.

[0068] In the second embodiment, these problems are solved by the structure of the intermediate layer. Specifically, in the second embodiment, the first intermediate layer 15 consists of two layers: a non-doped layer 215A and an n-type layer 215B highly doped with donor impurities, and the second intermediate layer 17 consists of two layers: a non-doped layer 217A and an n-type layer 217B highly doped with donor impurities, with Si doped into the n-type layers 215B and 217B to make them n-type.

[0069] Therefore, the pn junction distance is the distance from the electron blocking layer 21A to the n-type layer 217B of the second intermediate layer 217 in the region under p electrode 24A, the distance from the electron blocking layer 21B to the n-type layer 215B of the first intermediate layer 215 in the region under p electrode 24B, and the distance from the electron blocking layer 21C to the n-layer 11 in the region under p electrode 24C. In other words, the pn junction distance under all electrodes corresponds to the total film thickness including one active layer and the undoped layer of the intermediate layer, without including multiple active layers. Here, by appropriately controlling the thickness of the undoped layer 215A of the first intermediate layer 215 and the undoped layer 217A of the second intermediate layer 17, the pn junction distance can be made equal in these three cases. As a result, variations in driving voltage, current injection efficiency, and reverse current can be suppressed in these three cases, enabling uniform control. Furthermore, in these three cases, there is only one first active layer 14, one second active layer 16, and one third active layer 18 between the pn junctions, and the n-type layer of the intermediate layer acts as a barrier layer for holes, making it difficult for holes to be injected beyond the n-type layer of the intermediate layer into the lower active layer. As a result, it is possible to suppress the emission of light from active layers other than the one that is to be emitted, which is located between the pn junctions.

[0070] (Third embodiment) As shown in Figure 10, the light-emitting element of the third embodiment is the same as that of the light-emitting element of the first embodiment, but with the second active layer 16 and the third active layer 18 replaced by the second active layer 316 and the third active layer 318.

[0071] The second active layer 316 has a structure in which a strain relaxation layer 316A and a quantum well structure layer (luminescent layer) 316B of SQW or MQW are stacked in sequence. The quantum well structure layer 316B has the same structure as the second active layer 16 of the first embodiment.

[0072] The strain relaxation layer 316A is a SQW structure in which a barrier layer and a well layer are stacked in sequence, 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 light 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 316A only needs to be shorter than the emission wavelength of the quantum well structure layer 316B. For example, if the emission wavelength of the second active layer 16 is 500 to 560 nm, then the well layer should be 400 to 460 nm. Preferably, it should be 40 to 100 nm shorter than the emission wavelength of the quantum well structure layer 316B. In this case, the growth temperature of the strain relaxation layer 316A is 700 to 800°C.

[0073] The wavelength corresponding to the band edge energy of the well layer of the strain relaxation layer 316A may be equal to the emission wavelength of the first active layer 14. In this case, it may be grown at the same growth temperature as the first active layer 14.

[0074] The band edge energy in the well layer of the strain relaxation layer 316A can be controlled by the thickness of the well layer. That is, by making the thickness of the well layer of the strain relaxation layer 316A sufficiently thin, the energy of the subbands in the wells increases, and the band edge energy becomes larger. This allows it to be shorter than the emission wavelength of the quantum well structure layer 316B. The growth temperature is arbitrary, but it may be grown at the same growth temperature as the quantum well structure layer 316B. Furthermore, if the thickness of the well layer of the strain relaxation layer 316A is reduced, the subbands increase even further, and the energy difference with the barrier layer decreases. That is, it approaches the band edge energy of the barrier layer. As a result, carrier confinement in the well layer of the strain relaxation layer 316A becomes more difficult, and emission becomes less likely, so it functions as part of the barrier layer of the quantum well structure layer 316B, while simultaneously obtaining the effect of strain relaxation. In this way, by forming a strain relaxation layer 316A with a well layer that has worse carrier confinement than the well layer of the quantum well structure layer 316B, it is possible to form a strain relaxation layer 316A that does not emit light.

[0075] In short, the material and layer configuration of the strain relaxation layer 316A are set such that the effective lattice constant of the entire strain relaxation layer 316A is between the lattice constant of the first intermediate layer 15 and the lattice constant of the quantum well structure layer 316B, and the thickness of the well layer is set so that the strain relaxation layer 316A does not emit light.

[0076] The strain relaxation layer 316A may be an MQW structure in which two or more pairs of barrier layers and well layers are stacked, but it is preferable to use an SQW structure because the second active layer 316 becomes thicker.

[0077] As described above, by providing the strain relaxation layer 316A, the strain of the quantum well structure layer 316B stacked on top of it can be relaxed, and the crystal quality of the well layer of the quantum well structure layer 316B can be improved.

[0078] It is preferable to set the ratio of the thickness of the first active layer 14 to the thickness of the second active layer 316 to 30% or less. This allows for more efficient relaxation of the strain in the quantum well structure layer 316B, and the distance between pn junctions becomes constant under each p electrode 24A to 24C, resulting in uniform device characteristics under each p electrode 24A to 24C.

[0079] The third active layer 318 has a structure in which the first strain relaxation layer 318A, the second strain relaxation layer 318B, and the SQW or MQW quantum well structure layer 318C are stacked in sequence. The quantum well structure layer 318C has the same structure as the third active layer 18 of the first embodiment.

[0080] The first strain relaxation layer 318A has a structure similar to the strain relaxation layer 316A of the second active layer 316. The wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 318A only needs to be shorter than the emission wavelength of the quantum well structure layer 316B, for example, 400-460 nm.

[0081] The second strain relaxation layer 318B has a wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 318B that is shorter than the emission wavelength of the quantum well structure layer 318C and longer than the wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 318A. For example, it is 510-570 nm. Otherwise, it is the same as the first strain relaxation layer 318A.

[0082] The difference between the wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 318A and the wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 318B, and the difference between the wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 318B and the emission wavelength of the quantum well structure layer 318C, is preferably 40 to 100 nm.

[0083] It is preferable to set the ratio of the thickness of the first active layer 14 to the thickness of the third active layer 318, and the ratio of the thickness of the second active layer 316 to the thickness of the third active layer 318, to 30% or less. This allows for more efficient relaxation of the strain in the quantum well structure layer 318C, and the distance between pn junctions becomes constant under each p electrode 24A to 24C, resulting in uniform device characteristics under each p electrode 24A to 24C.

[0084] By providing the first strain relaxation layer 318A and the second strain relaxation layer 318B in this manner, strain can be relaxed in stages, and the strain of the quantum well structure layer 318C stacked on top of them can be effectively relaxed. As a result, the quality of the well layer of the quantum well structure layer 318C can be improved.

[0085] In the third active layer 318, strain is relieved in two stages by the first strain relief layer 318A and the second strain relief layer 318B, but strain may be relieved in three or more stages by providing three or more strain relief layers. Also, in the second active layer 316, strain may be relieved in stages by providing multiple strain relief layers 316A.

[0086] Furthermore, a strain relaxation layer may also be provided in the first active layer 14 in the same manner. In this case, the growth temperature of the strain relaxation layer is, for example, 800 to 900°C.

[0087] (Other variations) The light-emitting element in this embodiment had three active layers: a first active layer 14, a second active layer 16, and a third active layer 18. However, the present invention can be applied to any structure having two or more active layers with different emission wavelengths. Furthermore, the emission color is not limited to blue, green, and red; any different emission wavelengths are acceptable.

[0088] In this embodiment, it is preferable to control the emission of light by driving the light-emitting element with a PWM circuit using PWM. The light intensity can be easily controlled by the pulse width and pulse period, and wavelength shift due to differences in drive current can also be suppressed.

[0089] (Experimental results) Next, the experimental results related to this embodiment will be described.

[0090] (Experiment 1) A light-emitting element was fabricated by omitting the second intermediate layer 17 and the third active layer 18 from the light-emitting element of the first embodiment, and further omitting the regrowth layer 20B, electron blocking layer 21B, p layer 22B, and p electrode 24B, replacing the first intermediate layer 15 with the first intermediate layer 215 of the second embodiment, and replacing the second active layer 16 with the second active layer 316 of the third embodiment (see Figure 11; hereafter referred to as the light-emitting element of Experimental Example 1). The first intermediate layer 215 was made of InGaN with an In composition of 5%. The wavelength corresponding to the band edge energy of the well layer in the strain relaxation layer 316A of the second active layer 316 was made the same as the emission wavelength of the first active layer 14, and an SQW structure was adopted.

[0091] Figure 12 shows an AFM image of the surface of the second active layer 316 of the light-emitting element in Experimental Example 1. In Figure 12, the upper panel shows a 10 μm square area, and the lower panel shows a 2 μm square area. For comparison, the case where the first intermediate layer 215 is made of GaN and the rest is the same as in Experimental Example 2 is also shown. As shown in Figure 12, the pit density was lower in Experimental Example 1 compared to Experimental Example 2. Also, the surface flatness RMS was 0.88 nm for Experimental Example 1 and 2.6 nm for Experimental Example 2 in the 10 μm square area, and 0.78 nm for Experimental Example 1 and 3.1 nm for Experimental Example 2 in the 2 μm square area. In all cases, Experimental Example 1 was smaller than Experimental Example 2. As a result, it can be seen that the In in the first intermediate layer 215 acted as a surfactant, improving the surface flatness of the first intermediate layer 215, which in turn improved the surface flatness and crystal quality of the second active layer 316 above it.

[0092] Figure 9 is a graph showing the relationship between the drive current and the external quantum efficiency for the light-emitting elements of Experimental Example 1 and Experimental Example 2. The external quantum efficiency is the value when a voltage is applied to the p electrode 24B to cause the second active layer 316 to emit light. As shown in Figure 9, Experimental Example 1 had a higher external quantum efficiency than Experimental Example 2. From this, it can be seen that the external quantum efficiency improved due to an improvement in the crystal quality of the second active layer 316.

[0093] (Experiment 2) For the light-emitting element of the first embodiment (the light-emitting element shown in Figure 1, hereinafter referred to as the light-emitting element of Experimental Example 3), in which the emission wavelength of the first active layer 14 is 430 nm, the emission wavelength of the second active layer 16 is 520 nm, and the emission wavelength of the third active layer 18 is 630 nm, a current was injected into the p electrode 24A and its emission spectrum was measured. The Si concentrations of the n-type layers 215B and 217B were 1 × 10⁻⁶. 18 cm -3 , 2×10 18 cm -3 , 3 x 10 18 cm -3 These were the three patterns. For comparison, the emission spectra were also measured when n-type layer 215B and n-type layer 217B were replaced with undoped layers.

[0094] Figures 14-17 are graphs showing emission spectra, and Figure 14 shows the Si concentration at 3 × 10⁻⁶. 18 cm -3 Figure 15 is 2 × 10 18 cm -3 Figure 16 is 1 × 10 18 cm -3 Figure 17 shows the undoped case. As shown in Figure 17, in the undoped case, not only red emission from the third active layer 18 but also blue emission from the first active layer 14 occurred, and it was found that the red emission was weak and the blue emission was strong. On the other hand, as shown in Figures 14-16, in the case of Si doping, the red emission was as strong as or stronger than the blue emission, and the intensity of the blue emission decreased as the Si concentration increased. Although the intensity of the blue emission from the second active layer 16 decreased, a small amount of green emission also appeared, but as shown in Figure 14, the intensity of the green emission also decreased when the Si concentration became sufficiently high. As a result, it was found that by introducing Si-doped n-type layers 215B and 217B into the first intermediate layer 15 and the second intermediate layer 17, it is possible to suppress emission from active layers other than the third active layer 18, which is the active layer that is to be emitted (first active layer 14, second active layer 16).

[0095] (Experiment 3) Figure 18 shows AFM images of the surface of the quantum well structure layer 316C of the light-emitting element in Experimental Example 2 and Experimental Example 4. Experimental Example 4 is the case in Experimental Example 2 where the strain relaxation layer 316A was not provided on the second active layer 316. In Figure 16, the upper panel shows a 10 μm square area, and the lower panel shows a 2 μm square area. As shown in Figure 18, the surface flatness RMS was 2.6 nm for Experimental Example 2 and 3.8 nm for Experimental Example 4 in the 10 μm square area, and 3.1 nm for Experimental Example 2 and 3.3 nm for Experimental Example 4 in the 2 μm square area. In all cases, Experimental Example 2 was smaller than Experimental Example 4. In other words, the surface flatness was improved. As a result, it can be seen that by introducing the strain relaxation layer 316A on the second active layer 316, the strain on the quantum well structure layer 316B above it was relaxed, improving the surface flatness and crystal quality.

[0096] Figure 19 is a graph showing the relationship between the driving current and the external quantum efficiency for the light-emitting elements of Experimental Example 2 and Experimental Example 4. The external quantum efficiency is the value when a voltage is applied to the p electrode 24A to cause the second active layer 316 to emit light. As shown in Figure 19, Experimental Example 2 had a higher external quantum efficiency than Experimental Example 4. From this, it can be seen that the strain on the second active layer 316 was relaxed, and the surface flatness and crystal quality improved, resulting in an improvement in the external quantum efficiency.

[0097] (Fourth Embodiment) Figure 20 is a diagram showing the configuration of the light-emitting element in the fourth embodiment, and is a cross-sectional view taken from a plane perpendicular to the main surface of the substrate. As shown in Figure 20, the light-emitting element in the fourth embodiment has some of the configuration of the light-emitting element in the first embodiment modified as follows. Components similar to those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0098] As shown in Figure 20, the first intermediate layer 15 and the second intermediate layer 17 are replaced with the first intermediate layer 415 and the second intermediate layer 417. In addition, the protective layer 19, the regrowth layers 20A to 20C, the electron blocking layers 21A to 21C, and the p layers 22A to 22C are omitted, and the electron blocking layer 421A and the p layer 422 are provided on the third active layer 18, with the p electrode 24A provided on the p layer 422. In other words, the light-emitting element of the fourth embodiment does not have a regrowth layer. Furthermore, the first electrode 424B is provided on the first intermediate layer 415 exposed on the bottom surface of the second groove 31, and the second electrode 424C is provided on the second intermediate layer 417 exposed on the bottom surface of the third groove 32. Furthermore, the electron blocking layers 421B and 421C are inserted between the second active layer 16 and the second intermediate layer 17, and between the first active layer 14 and the first intermediate layer 15, respectively.

[0099] The electron block layer 421C is a p-type layer provided on the first active layer 14 and is located between the first active layer 14 and the first intermediate layer 15. The electron block layer 421C is similar to the electron block layers 21A to 21C, except that it is not a regrowth layer and is grown continuously on the first active layer 14.

[0100] The first intermediate layer 415 has a structure in which the first layer 415A, the second layer 415B, the third layer 415C, and the fourth layer 415D are stacked in order from the first active layer 14 side, with the fourth layer 415D exposed at the bottom surface of the second groove 31. The second layer 415B and the third layer 415C form a tunnel junction structure. Thus, the first intermediate layer 415 has the same function as the first intermediate layer 15 of the first embodiment, as well as the function of a tunnel junction.

[0101] The first layer 415A is a semiconductor layer provided on the electron blocking layer 421C. In order to efficiently emit light from the first active layer 14, it is preferable to sandwich the first active layer 14 between a p-type layer and an n-type layer, and the first layer 415A is provided as the p-type contact layer.

[0102] The material of the first layer 415A is the same as that of the first intermediate layer 15 in the first embodiment, except for impurities. That is, it is a group III nitride semiconductor containing In, preferably InGaN. The surfactant effect of In can suppress surface roughness of the first intermediate layer 415 and improve surface flatness. It can also alleviate lattice strain. The In composition of the first intermediate layer 415 should be set to have a band gap that does not absorb light emitted from the first active layer 14, the second active layer 16, and the third active layer 18.

[0103] The preferred In composition of the first layer 415A 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 415 to become rough. The In content can be any amount greater than 0%, and may even be at a doping level (a level that does not form mixed crystals). For example, the In concentration may be 1 × 10⁻⁶. 14 cm -3 The above 1 x 10 22 cm -3 The following are the GaN components.

[0104] The first layer 415A is a p-type semiconductor doped with Mg, a p-type impurity. For example, if the Mg concentration is 1 × 10⁻⁶ 18 ~1 × 10 20 cm -3Preferably 5 × 10 18 ~1 × 10 20 cm -3 More preferably 1 × 10 19 ~1 × 10 20 cm -3 It may also be undoped, but it is preferable that it is doped with Mg as described above. The first layer 415A may use polarization doping that provides a gradient in the In composition in the thickness direction. In this case, it may be undoped. Alternatively, the third layer 415C may be doped with Mg by Mg diffusion from the electron blocking layer 421C which is the layer below the first layer 415A. In this case, the Mg concentration of the electron blocking layer 421C is 1 × 10⁻⁶ 19 ~1 × 10 21 cm -3 The range is good.

[0105] The thickness of the first layer 415A is preferably 10 to 300 nm. If it is thicker than 300 nm, it may cause the surface of the first intermediate layer 415 to become rough. If it is thinner than 10 nm, it may not be possible to sufficiently increase the luminescence efficiency of the first active layer 14. More preferably it is 20 to 200 nm, and even more preferably 30 to 100 nm.

[0106] The second layer 415B is a semiconductor layer provided on the first layer 415A. The stacking of the second layer 415B and the third layer 415C forms a tunnel junction structure.

[0107] The material of the second layer 415B is the same as that of the first layer 415A, except for impurities. The In composition of the second layer 415B may differ from that of the first layer 415A and the fourth layer 415D, in which case it is preferable that it be higher than the In composition of the first layer 415A and the fourth layer 415D. This can further increase the tunneling probability due to the tunnel junction structure. The preferred range of In composition for the second layer 415B is the same as that for the first layer 415A.

[0108] The second layer, 415B, is a p-type semiconductor doped with Mg, a p-type impurity. The Mg concentration is 1 × 10⁻⁶. 20 ~1 × 10 21 cm -3Therefore, the Mg concentration in the second layer 415B is higher than the Mg concentration in the first layer 415A.

[0109] The thickness of the second layer 415B is 5 to 50 nm. Within this range, the tunneling probability of the tunnel junction structure can be sufficiently increased. More preferably, it is 5 to 35 nm, and even more preferably 5 to 20 nm. Furthermore, it is preferable that the thickness of the second layer 415B is thinner than that of the first layer 415A.

[0110] The third layer 415C is a semiconductor layer provided on the second layer 415B. The stacking of the second layer 415B and the third layer 415C forms a tunnel junction structure. This tunnel junction structure allows current to flow from the n-type third layer 415C to the p-type second layer 415B by the tunnel effect, and holes are supplied to the first active layer 14.

[0111] The material of the third layer 415C is the same as that of the first layer 415A, except for impurities. The In composition of the third layer 415C may differ from that of the first layer 415A and the fourth layer 415D, in which case it is preferable that it be higher than the In composition of the first layer 415A and the fourth layer 415D. This can further increase the tunneling probability due to the tunnel junction structure. Also, the In composition of the third layer 415C may differ from that of the second layer 415B. In that case, it is preferable that the In composition of the third layer 415C is lower than the In composition of the second layer 415B. The preferred range of In composition for the third layer 415C is the same as that for the first layer 415A.

[0112] The third layer, 415C, is an n-type semiconductor doped with Si, an n-type impurity. The Si concentration is 1 × 10⁻⁶. 20 ~1 × 10 21 cm -3 That is the case.

[0113] Near the junction interface between the second layer 415B and the third layer 415C, a layer co-doped with Si and Mg may exist, either intentionally or naturally. Since Mg tends to remain in the furnace due to the memory effect, the third layer 415C and the fourth layer 415D may also be doped with Mg. However, the Mg concentration in the third layer 415C and the fourth layer 415D must be lower than their respective Si concentrations.

[0114] The thickness of the third layer 415C is 1 to 30 nm. Within this range, the tunneling probability of the tunnel junction structure can be sufficiently increased. More preferably, it is 2 to 25 nm, and even more preferably 5 to 20 nm. Furthermore, it is preferable that the thickness of the third layer 415C is thinner than that of the fourth layer 415D.

[0115] As described above, the second layer 415B and the third layer 415C, which form the tunnel junction structure, contain In, which reduces the band gap and increases the tunneling probability. In addition, a further layer may be provided between the second layer 415B and the third layer 415C in the area where the tunnel junction occurs. For example, a buffer layer may be provided to suppress the diffusion of Mg from the second layer 415B into the third layer 415C.

[0116] The fourth layer 415D is a semiconductor layer provided on the third layer 415C. In order to efficiently emit light from the second active layer 16, it is preferable to sandwich the second active layer 16 between a p-type layer and an n-type layer, and the fourth layer 415D is provided as the n-type contact layer. It is also a layer that prevents the fourth layer 415C from being exposed when forming the second groove 31.

[0117] The material of the fourth layer 415D is the same as that of the first intermediate layer 15 in the first embodiment, except for impurities. The In composition may be different from that of the first layer 415A.

[0118] The fourth layer, 415D, is an n-type semiconductor doped with Si, an n-type impurity. For example, if the Si concentration is 1 × 10⁻⁶ 17 ~1 × 10 20 cm -3 Preferably 1 × 1018 ~1 × 10 19 cm -3 , more preferably 2 × 10 18 ~8×10 18 cm -3 This is also acceptable. The Si concentration in the third layer 415C is higher than the impurity concentration in the fourth layer 415D.

[0119] The thickness of the fourth layer 415D is preferably 10 to 500 nm. If it is thicker than 500 nm, it may cause the surface of the first intermediate layer 415 to become rough. If it is thinner than 10 nm, it may not be possible to sufficiently increase the luminescence efficiency of the second active layer 16. Also, when forming the second groove 31, it may become difficult to control the depth of the second groove 31 to be within the fourth layer 415D. More preferably, it is 10 to 200 nm, and even more preferably 10 to 100 nm. The thickness of the fourth layer 415D may be different from the thickness of the first layer 415A.

[0120] The electron block layer 421B is a p-type layer provided on the second active layer 16, and is located between the second active layer 16 and the second intermediate layer 17. The electron block layer 421B is the same as the electron block layers 21A to 21C, except that it is not a regrowth layer, but is grown continuously on the second active layer 16.

[0121] The second intermediate layer 417 has a structure in which the first layer 417A, the second layer 417B, the third layer 417C, and the fourth layer 417D are stacked in order from the second active layer 16 side, with the fourth layer 417D exposed at the bottom surface of the third groove 32. The second layer 417B and the third layer 417C form a tunnel junction structure. Thus, the second intermediate layer 417 has the same function as the second intermediate layer 17 of the first embodiment, as well as the function of a tunnel junction.

[0122] The first layer 417A, the second layer 417B, the third layer 417C, and the fourth layer 417D are the same as the first layer 415A, the second layer 415B, the third layer 415C, and the fourth layer 415D of the first intermediate layer 415, respectively. The stacking of the second layer 417B and the third layer 417C forms a tunnel junction structure, allowing current to flow from the n-type third layer 417C to the p-type second layer 417B by tunnel effect, and supplying holes to the second active layer 16.

[0123] Since the first intermediate layer 415 and the second intermediate layer 417 are composed entirely of InGaN, the same effects as the first intermediate layer 15 and the second intermediate layer 17 of Embodiment 1 can be obtained. In other words, surface flatness can be improved and lattice strain can be reduced.

[0124] The average In composition of the first intermediate layer 415 and the average In composition of the second intermediate layer 417 may be different. Preferably, the average In composition of the second intermediate layer 417 is higher than the average In composition of the first intermediate layer 415.

[0125] The electron block layer 421A is a p-type layer provided on the third active layer 18. The electron block layer 421A is the same as the electron block layers 21A to 21C, except that it is grown continuously on the third active layer 18 and is not a regrowth layer.

[0126] The p-layer 422 is a layer provided on the electron block layer 421A. The p-layer 422 is similar to the p-layer 22A, except that it is grown continuously on the electron block layer 421A and is not a regrowth layer.

[0127] Instead of the p layer 422, a tunnel junction structure such as the second layer 415B and the third layer 415C, or the second layer 417B and the third layer 417C, may be used. In this case, the p electrode 24A can be replaced with an electrode made of the n contact material, and the same material as the first electrode 424B and the second electrode 424C can be used. Therefore, all electrodes can be formed in the same process.

[0128] The first electrode 424B is provided on the fourth layer 417D of the second intermediate layer 417, which is exposed on the bottom surface of the third groove 32. The second electrode 424C is provided on the fourth layer 415D of the first intermediate layer 415, which is exposed on the bottom surface of the second groove 31. The first electrode 424B and the second electrode 424C serve as both the anode and cathode electrodes. The first electrode 424B and the second electrode 424C can be made of any material that can make ohmic contact with n-type InGaN, for example, Ti / Al can be used. They may also be made of the same material as the n electrode 23.

[0129] In addition, in the light-emitting element of the fourth embodiment, the second active layer 16 and the third active layer 18 may be replaced with the second active layer 316 and the third active layer 318 of the third embodiment, respectively. In that case, the strain relaxation layer 316A of the second active layer 316 functions as a buffer layer against Mg diffusion from the first intermediate layer 415 to the quantum well structure layer 316B. Furthermore, the first strain relaxation layer 318A and the second strain relaxation layer 318B of the third active layer 318 function as buffer layers against Mg diffusion from the second intermediate layer 417 to the quantum well structure layer 318C. Therefore, a decrease in luminescence efficiency can be suppressed.

[0130] Other modifications described in the first to third embodiments can also be applied to the fourth embodiment. For example, the first and fourth embodiments may be combined as follows. In the fourth embodiment, the second intermediate layer 417 retains its tunnel junction structure, and the first intermediate layer 415 may be configured to have a regrowth layer 20C, an electron block layer 21C, and a p-layer 22C, similar to the first embodiment, instead of the first intermediate layer 15 of the first embodiment.

[0131] This configuration has the following advantages. The first active layer 14 that emits blue light has high luminescence efficiency, so a decrease in luminescence efficiency due to regrowth does not cause significant problems. On the other hand, the second active layer 16 that emits green light has low luminescence efficiency, and a decrease in luminescence efficiency due to regrowth should be avoided as much as possible. Therefore, if the element region that emits blue light is formed by groove formation and regrowth as in the first embodiment, and the element region that emits green light is formed using a tunnel junction structure as in the fourth embodiment, the variation in luminescence efficiency of blue, green, and red can be reduced.

[0132] The operation of the light-emitting element of the fourth embodiment will now be described. In the light-emitting element of the fourth embodiment, red light can be emitted from the third active layer 18 by applying a voltage between the p electrode 24A and the first electrode 424B. Green light can be emitted from the second active layer 16 by applying a voltage between the first electrode 424B and the second electrode 424C. Blue light can be emitted from the first active layer 14 by applying a voltage between the second electrode 424C and the n electrode 23.

[0133] Furthermore, it is possible to emit two or more of the blue, green, and red light simultaneously. Specifically, the voltage is applied as follows: To emit blue, green, and red light, apply the voltage between the p electrode 24A and the n electrode 23. To emit green and red light simultaneously, apply the voltage between the p electrode 24A and the second electrode 424C. To emit blue and green light simultaneously, apply the voltage between the first electrode 424B and the n electrode 23. To emit blue and red light simultaneously, apply the voltage between the p electrode 24A and the first electrode 424B, and between the second electrode 424C and the n electrode 23.

[0134] Thus, in the light-emitting element of the fourth embodiment, the emission of blue, green, and red light can be controlled by selecting the electrode to which voltage is applied, and it can be used as a single pixel on a display.

[0135] Figure 21 shows the equivalent circuit of the light-emitting element of the fourth embodiment. The light-emitting element of the fourth embodiment is equivalent to a configuration in which a red LED, a first tunnel junction (reverse-order tunnel diode), a green LED, a second tunnel junction, and a blue LED are connected in tandem, and electrodes are drawn out from the connection between the red LED and the first tunnel junction, and from the connection between the green LED and the second tunnel junction. The light-emitting element of the fourth embodiment, like the light-emitting element of the first embodiment, also has a structure in which blue, green, and red LEDs are formed within a single element, and full-color light emission can be achieved with a single element.

[0136] Next, the manufacturing process for the fourth embodiment of the light-emitting element will be described.

[0137] First, a substrate 10 is prepared and heat-treated, similar to the first embodiment. Then, a buffer layer, an n-layer 11, an ESD layer 12, a base layer 13, a first active layer 14, an electron blocking layer 421C, a first intermediate layer 415, a second active layer 16, an electron blocking layer 421B, a second intermediate layer 417, a third active layer 18, an electron blocking layer 421A, and a p-layer 422 are sequentially formed on the substrate 10 by the MOCVD method.

[0138] Here, the growth temperatures of the first intermediate layer 415 and the second intermediate layer 417 are within the same range as those of the first intermediate layer 15 and the second intermediate layer 17 in the first embodiment. It is preferable that the growth temperature of the second intermediate layer 417 be lower than that of the first intermediate layer 415. This is because the green-emitting second active layer 16 is more susceptible to thermal damage than the blue-emitting first active layer 14, and the effect of strain at the interface becomes greater.

[0139] Furthermore, in the formation of the first intermediate layer 415, it is preferable to lower the growth temperature of the second layer 415B and the third layer 415C than the growth temperature of the first layer 415A and the fourth layer 415D. This is to increase crystallinity and further enhance the tunnel effect in the tunnel junction. Also, in the formation of the second intermediate layer 417, it is preferable to lower the growth temperature of the second layer 417B and the third layer 417C than the growth temperature of the first layer 417A and the fourth layer 417D.

[0140] Next, a portion of the surface of the p layer 422 is dry-etched until it reaches the fourth layer 417D of the second intermediate layer 417 to form the third groove 32, dry-etched until it reaches the fourth layer 415D of the first intermediate layer 415 to form the second groove 31, and dry-etched until it reaches the n layer 11 to form the first groove 30.

[0141] Next, an n-electrode 23 is formed on the n-layer 11 exposed at the bottom of the first groove 30, a p-electrode 24A is formed on the p-layer 422, a first electrode 424B is formed at the bottom of the third groove 32, and a second electrode 424C is formed at the bottom of the second groove 31. If the first electrode 424B and the second electrode 424C are made of the same material as the n-electrode 23, they can be formed simultaneously in the same process as the n-electrode 23. The light-emitting element of the fourth embodiment is thus manufactured.

[0142] As described above, the light-emitting element in the fourth embodiment eliminates the need for an electron block layer or a regrowth layer for the p-layer by providing a tunnel junction structure in the first intermediate layer 415 and the second intermediate layer 417. Regrowth interfaces are susceptible to etching damage, impurity contamination due to exposure to air, and thermal damage due to regrowth, so the presence of a regrowth interface between p and n layers can degrade device characteristics. However, the light-emitting element in the fourth embodiment does not have a regrowth layer and therefore does not have a regrowth interface between p and n layers, thus avoiding these problems.

[0143] In the first to fourth embodiments, InGaN is used as the well layer in the quantum well structure layer 318C of the third active layer 18 and the third active layer 318, but Eu (europium) doped group III nitride semiconductors, especially GaN, can also be used. In this case as well, red emission can be produced, and the emission wavelength is approximately 620 nm. When Eu-doped GaN is used, strain relaxation of the active layer is not required, so the first strain relaxation layer 318A and the second strain relaxation layer 318B, such as those in the third active layer 318, do not need to be provided. When Eu-doped GaN is used for the well layer, the barrier layer is, for example, AlGaN.

[0144] Similarly, praseodium-doped group III nitride semiconductors, particularly GaN, may be used. They can be used as red light-emitting materials.

[0145] Furthermore, a Tb (terbium)-doped group III nitride semiconductor, particularly GaN, can be used as the well layer in the quantum well structure layer 316B of the second active layer 16 and the second active layer 316. In this case as well, green light emission can be produced.

[0146] Furthermore, a Tm (thulium)-doped group III nitride semiconductor, particularly GaN, can be used as the well layer in the first active layer 14. In this case as well, blue light emission can be produced.

[0147] (Fifth embodiment) Figure 22 is a diagram showing the configuration of the light-emitting element in the fifth embodiment, and is a cross-sectional view taken from a plane perpendicular to the main surface of the substrate. The light-emitting element in the fifth embodiment emits light from yellow to red, and as shown in Figure 22, it has a substrate 510, an n layer 511, a base layer 513, an active layer 518, an electron blocking layer 521, a p layer 522, an n electrode 523, and a p electrode 524.

[0148] The substrate 510, n-layer 511, and underlayer 513 are the same as those in the first embodiment, the substrate 10, n-layer 11, and underlayer 13, respectively. An ESD layer 12 may also be provided between the n-layer 511 and the underlayer 513.

[0149] The base layer 513 is preferably a stack of a superlattice structure layer and a high-concentration n-type GaN layer. The superlattice structure layer is preferably made up of alternating layers of n-type InGaN and n-type GaN, with the number of pairs being, for example, 3 to 30. The Si concentration is, for example, 1 × 10⁻⁶. 17 ~1 × 10 19 cm -3 Therefore, the Si concentration in the high-concentration n-type GaN layer on the superlattice structure layer is 1 × 10⁻⁶. 18 ~1 × 10 19 cm -3 It is preferable to do so. Furthermore, it is preferable that the high-concentration n-type GaN layer be in contact with the active layer 518.

[0150] The active layer 518 is a layer provided on the base layer 513. The active layer 518 has a structure in which a first strain relaxation layer 518A, a second strain relaxation layer 518B, and a quantum well structure layer 518C of SQW or MQW are stacked in order.

[0151] The first strain relaxation layer 518A and the second strain relaxation layer 518B are the same as the first strain relaxation layer 318A and the second strain relaxation layer 318B in the third active layer 318 of the third embodiment. Similar to the third embodiment, by providing the first strain relaxation layer 518A and the second strain relaxation layer 518B, strain can be relaxed in stages, and the strain of the quantum well structure layer 518C laminated thereon can be effectively relaxed. As a result, the quality of the well layer of the quantum well structure layer 518C can be improved. It is preferable that the first strain relaxation layer 518A and the second strain relaxation layer 518B be made of SQW.

[0152] Various modifications of the first strain relaxation layer 318A and the second strain relaxation layer 318B in the third embodiment can also be applied to the first strain relaxation layer 518A and the second strain relaxation layer 518B.

[0153] The quantum well structure layer 518C is an SQW or MQW structured light-emitting layer provided on the second strain relaxation layer 518B. The emission wavelength is yellow to red, ranging from 560 to 700 nm. The third active layer 18 has a structure in which 1 to 7 pairs of well layers made of InGaN and barrier layers made of InGaN with a lower In composition than the well layers are alternately stacked. More preferably, 1 to 5 pairs, and even more preferably 1 to 3 pairs. It is also preferable that the number of pairs is equal to or less than that of the second active layer 16, and more preferably less. The most preferable is SQW. The well layers of the quantum well structure layer 518C are InGaN with an In composition of 35% or more.

[0154] The electron blocking layer 521 is a layer provided on the active layer 518. The electron blocking layer 521 is the same as the electron blocking layer 421A in the fourth embodiment.

[0155] The p-layer 522 is a layer provided on the electronic block layer 521. The p-layer 522 is the same as the p-layer 422 in the fourth embodiment.

[0156] A portion of the p-layer 522 is etched to create a groove that reaches the n-layer 11, and the n-electrode 523 is provided on the n-layer 11 exposed at the bottom of the groove. The material of the n-electrode 523 is the same as that of the n-electrode 23. In addition, the p-electrode 524 is provided on the p-layer 522. The material of the p-electrode 524 is the same as that of the p-electrodes 24A to 24C.

[0157] Next, the manufacturing process for the fifth embodiment of the light-emitting element will be described.

[0158] First, as in the first embodiment, a substrate 10 is prepared and heat-treated. Then, a buffer layer, an n-layer 11, a base layer 13, an active layer 518, an electron blocking layer 521, and a p-layer 522 are sequentially formed on the substrate 10 by the MOCVD method. The method for forming the quantum well structure layer 518C will be described in detail later. The raw material gases used in the MOCVD method are as follows: TMG (trimethylgallium) or TEG (triethylgallium) as the Ga raw material gas, TMI (trimethylindium) as the In raw material gas, TMA (trimethylaluminum) as the Al raw material gas, ammonia as the N raw material gas, silane as the Si dopant gas, bis(cyclopentadienyl)magnesium as the Mg dopant gas, and hydrogen or nitrogen as the carrier gas.

[0159] The growth temperature of the electron blocking layer 521 and the p-layer 522 is preferably 935°C or lower. This is to suppress thermal damage to the active layer 518 and to suppress a decrease in luminescence efficiency. The lower limit of the growth temperature is, for example, 600°C. More preferably, it is 650 to 900°C. Furthermore, the growth temperature of the p-layer 522 is preferably higher than the growth temperature of the electron blocking layer 521.

[0160] Next, a predetermined area of ​​the p layer 522 is dry-etched to form a groove that reaches the n layer 11, and an n electrode 523 is formed on the bottom surface of the groove, and a p electrode 524 is formed on the p layer 522. The light-emitting element according to the fifth embodiment is then manufactured.

[0161] Next, the method for forming the quantum well structure layer 518C will be described in detail. The well layer of the quantum well structure layer 518C is InGaN with an In composition of 35% or more, and it was difficult to obtain high-quality crystals. The inventors diligently conducted research and development to obtain high-quality InGaN with an In composition of 35% or more, and found a method to obtain high-quality InGaN. This method is described below.

[0162] The growth temperature of the quantum well structure layer 518C shall be 700°C or lower. The lower limit of the growth temperature is, for example, 550°C. By setting the growth temperature near the decomposition temperature of InN (630°C), the decomposition and re-evaporation of InN can be suppressed, and InGaN with a high In composition (especially an In composition of 35% or more) can be formed. Preferably, it is 650°C or lower, more preferably 610-650°C, even more preferably 620-640°C, and most preferably 625-635°C.

[0163] The growth rate of the quantum well structure layer 518C shall be 0.8 nm / min or less. This is to suppress surface roughness, abnormal growth, and droplets caused by insufficient migration of raw material atoms at low growth temperatures. Droplets are formed when in aggregates of In are formed on the crystal surface. Preferably, the growth rate is 0.75 nm / min or less, more preferably 0.7 nm / min or less, and even more preferably 0.5 nm / min or less. There is no particular lower limit to the growth rate, but if the growth rate is too slow, it will take a long time to form the quantum well structure layer 518C, so 0.05 nm / min or more is preferred.

[0164] The In solid-state ratio / In gas-state ratio should be 0.75 to 1. Here, the In gas-state ratio is the molar ratio of In to the total Group III metals in the source gas used to form InGaN. The In solid-state ratio is the molar ratio of In to the total Group III metals in the formed InGaN crystal. The In solid-state ratio / In gas-state ratio can be controlled by the growth temperature, In gas-state ratio, Group VIII ratio, etc. By setting the In solid-state ratio / In gas-state ratio within this range, abnormal growth and droplet formation of InGaN can be suppressed. A more preferable In solid-state ratio / In gas-state ratio is 0.85 to 1, and even more preferably 0.9 to 1.

[0165] By setting the growth temperature, growth rate, and In solid-phase ratio / In gas-phase ratio within the above ranges, high-quality crystals can be obtained even in InGaN with an In composition of 35% or more. As mentioned above, setting the growth temperature to below 700°C reduces the efficiency of ammonia decomposition, making it difficult for raw material atoms to migrate and thus difficult to obtain high-quality InGaN. However, by setting the growth rate within the above range, these problems can be resolved, and high-quality InGaN can be obtained.

[0166] The In gas-phase ratio is preferably 40% or higher. This makes it easier to control the In solid-phase ratio / In gas-phase ratio within the above range, thereby suppressing abnormal growth and droplet formation of InGaN. Alternatively, the In gas-phase ratio is preferably 55% or lower.

[0167] The partial pressure of the Ga raw material gas is 1 × 10⁻⁶ -6 ~3×10 -6 atm, the partial pressure of the raw material gas is 1 × 10⁻⁶ -6 ~3×10 -6 It is preferable to use atm. This is to suppress abnormal growth of InGaN and stabilize the growth rate. The Ga source gas is, for example, TMG (trimethylgallium) or TEG (triethylgallium), and the In source gas is, for example, TMI (trimethylindium).

[0168] The growth rate of the barrier layer of the quantum well structure layer 518C should be equal to or faster than the growth rate of the well layer of the quantum well structure layer 518C. Furthermore, the growth temperature of the barrier layer of the quantum well structure layer 518C should be equal to or higher than the growth temperature of the well layer of the quantum well structure layer 518C. If a higher temperature is required, it is preferable to form a first barrier layer of 2-20 nm at the same temperature as the well layer growth temperature, and then increase the temperature to laminate the second barrier layer. This prevents the high-In composition well layer from thermally decomposing during heating. The first and second barrier layers may be made of InGaN, which has a lower In composition than the well layer. Of course, GaN, AlGaN, AlGaInN, or combinations thereof are also acceptable.

[0169] The partial pressure of the nitrogen (N) source gas is preferably 0.15 to 0.2 atm. This suppresses the decomposition and re-evaporation of InN by H2 generated from the decomposition of ammonia, thereby improving the quality of InGaN. Note that the nitrogen used as the carrier gas is not the nitrogen source gas.

[0170] The VIII ratio (molar ratio of ammonia to III metal source gas) is preferably between 30,000 and 80,000. Within this range, the quality of InGaN can be improved.

[0171] The growth temperature of the quantum well structure layer 518C is preferably lower than the growth temperatures of the first strain relaxation layer 518A and the second strain relaxation layer 518B. This is to suppress thermal damage to the first strain relaxation layer 518A and the second strain relaxation layer 518B. Furthermore, the growth temperature of the second strain relaxation layer 518B is preferably lower than the growth temperature of the first strain relaxation layer 518A.

[0172] It is preferable that the growth rate of the quantum well structure layer 518C be slower than the growth rates of the first strain relaxation layer 518A and the second strain relaxation layer 518B. This allows for the formation of a higher quality quantum well structure layer 518C. Furthermore, it is preferable that the growth rate of the second strain relaxation layer 518B be slower than the growth rate of the first strain relaxation layer 518A.

[0173] The In-gas ratio during the formation of the quantum well structure layer 518C is preferably smaller than the In-gas ratio during the formation of the first strain relaxation layer 518A and the second strain relaxation layer 518B. This allows for the formation of the quantum well structure layer 518C with higher quality.

[0174] As described above, according to the fifth embodiment, high-quality crystals can be obtained for InGaN with an In composition of 35% or more, and in particular, it is possible to form InGaN that is a red light-emitting material with an In composition of 40% or more. Therefore, the well layer in the quantum well structure layer 518C can be formed with high quality, and a light-emitting element made of a group III nitride semiconductor with high luminescence efficiency and red light emission can be realized.

[0175] (Variable form of the fifth embodiment) The active layer 518 of the light-emitting element in the fifth embodiment can also be used as the third active layers 18 and 318 of the light-emitting elements in the first to fourth embodiments.

[0176] Furthermore, the InGaN formation method in the fifth embodiment can be used not only for light-emitting devices but also for InGaN in solar cells and photocatalysts.

[0177] Furthermore, according to the fifth embodiment, the quality can be improved not only for InGaN with an In composition of 35% or more, but also for group III nitride semiconductors with an In composition of 35% or more. For example, the quality can also be improved for AlGaInN with an In composition of 35% or more.

[0178] Next, we will describe the experimental results related to the fifth embodiment.

[0179] (Experiment 4) The quantum well structure layer 518C was formed by varying the growth rate. The growth temperature was 637 °C, the In gas phase ratio was 47.5%, the ammonia flow rate was 27 slm. Also, the VIII ratio was 48000, 27000, 20000, and the growth rates were 0.48 nm / min, 0.72 nm / min, 0.96 nm / min, respectively. Also, the In solid phase ratios were 42.0%, 40.0%, 41.0%, respectively, and the In solid phase ratio / In gas phase ratio was 88.4%, 84.2%, 86.3%, respectively.

[0180] Figure 23 is an AFM image of the well layer surface of the quantum well structure layer 518C when the growth rate is varied. It is the surface of an InGaN layer having the same film thickness of 2 - 3 nm as the actual well layer. Figure 23(a) shows the case of a growth rate of 0.48 nm / min, (b) shows the case of 0.72 nm / min, and (c) shows the case of 0.96 nm / min.

[0181] As shown in Figure 23(a), when the growth rate is 0.48 nm / min, there are not many droplets seen on the well layer surface, and the droplet density is 1×10 7 cm -2 , and the diameter of the droplets was approximately 30 nm.

[0182] Also, as shown in Figure 23(b), when the growth rate is 0.72 nm / min, more droplets are seen on the well layer surface than in the case of a growth rate of 0.48 nm / min, and the droplet density is 1×10 8 cm -2 , and the diameter of the droplets was approximately 30 nm.

[0183] Also, as shown in Figure 23(c), when the growth rate is 0.96 nm / min, even more droplets are seen on the well layer surface than in the case of a growth rate of 0.72 nm / min, and their size is also larger. The droplet density is 4×10 8 cm -2 , and the diameter of the droplets was approximately 50 nm.

[0184] From these results, it was found that for reducing droplets, the growth rate of InGaN is preferably 0.75 nm / min or less, and more preferably 0.5 nm / min.

[0185] (Experiment 5) The quantum well structure layer 518C was formed by changing the In solid-phase ratio / In gas-phase ratio. The growth temperature was 637 °C, the growth rate was 0.48 nm / min, and the ammonia flow rate was 27 slm. Also, the VIII ratio was 40000, 40000, 48000, 51000, and the In gas-phase ratio was 57%, 52.5%, 47.5%, 45% respectively. The In solid-phase ratio was 42.0% in all cases, and the In solid-phase ratio / In gas-phase ratio was 73.7%, 80.0%, 88.4%, 93.3% respectively.

[0186] Figure 24 is an AFM image of the well layer surface of the quantum well structure layer 518C when the In solid-phase ratio / In gas-phase ratio is changed. Figure 24(a) shows the case of an In solid-phase ratio / In gas-phase ratio of 73.7%, (b) shows 80.0%, (c) shows 88.4%, and (d) shows 93.3%.

[0187] As shown in Figure 24(a), when the In solid-phase ratio / In gas-phase ratio is 73.7%, many droplets are seen on the well layer surface, and their size is also large. The density of the droplets is 7.5×10 7 cm -2 , and the diameter of the droplets is approximately 130 nm.

[0188] Also, as shown in Figure 24(b), when the In solid-phase ratio / In gas-phase ratio is 80.0%, there are fewer droplets on the well layer surface than in the case of 73.7%, and the size is also smaller. The density of the droplets is 5.0×10 7 cm -2 , and the diameter of the droplets is approximately 80 nm.

[0189] Also, as shown in Figure 24(c), when the In solid-phase ratio / In gas-phase ratio is 88.4%, there are even fewer droplets on the well layer surface than in the case of 80.0%, and the size is also smaller. The density of the droplets is 1.0×10 7 cm-2 The droplet diameter was approximately 30 nm.

[0190] Furthermore, as shown in Figure 24(d), when the In solid phase ratio / In gas phase ratio was 93.3%, no droplets were observed on the well bed surface.

[0191] From these results, it was found that an In solid-phase ratio / In gas-phase ratio of 0.75 or higher is preferable, 0.85 or higher is more preferable, and 0.9 or higher is even preferable.

[0192] (Experiment 6) Quantum well structure layer 518C was formed by varying the partial pressure of ammonia. The growth temperature was set to 637°C. The carrier gas (nitrogen) flow rate was set to three levels: 142 slm, 130 slm, and 110 slm. The ammonia flow rates were set to 15 slm, 27 slm, and 47 slm, respectively, and the partial pressures of ammonia were set to 0.096 atm, 0.172 atm, and 0.299 atm. The VIII ratios were set to 27000, 48000, and 85000 respectively, and the In gas phase ratio was set to 47.5% in all cases. The growth rate was 0.48 nm / min in all cases, the In solid phase ratio was 40%, 42%, and 40%, and the In solid phase ratio / In gas phase ratio was 84.2%, 88.4%, and 84.2%, respectively.

[0193] Figure 25 shows AFM images of the well layer surface of quantum well structure layer 518C when the partial pressure of ammonia is varied. Figure 25(a) shows the case when the partial pressure of ammonia is 0.096 atm, (b) shows the case when it is 0.172 atm, and (c) shows the case when it is 0.299 atm.

[0194] As shown in Figure 25(a), droplets were observed on the well bed surface when the partial pressure of ammonia was 0.096 atm. The density of the droplets was 5.0 × 10⁻⁶. 7 cm -2 The droplet diameter was approximately 50 nm.

[0195] Furthermore, as shown in Figure 25(b), when the partial pressure of ammonia was 0.172 atm, droplets were observed on the well layer surface, but they were fewer in number and smaller in size than when the partial pressure of ammonia was 0.096 atm. The density of the droplets was 1.0 × 10⁻⁶. 7 cm -2 The droplet diameter was approximately 30 nm.

[0196] Furthermore, as shown in Figure 25(c), when the partial pressure of ammonia was 0.299 atm, more droplets were observed on the well layer surface, and they were also larger in size than when the partial pressure of ammonia was 0.172 atm. The density of the droplets was 5.0 × 10⁻⁶. 7 cm -2 The droplet diameter was approximately 50 nm.

[0197] These results indicate that a partial pressure of ammonia is preferably between 0.15 and 0.2 atm. Furthermore, a VIII ratio of 30,000 to 80,000 is preferred. [Industrial applicability]

[0198] The light-emitting element of the present invention can be applied to full-color displays and the like. [Explanation of symbols]

[0199] 10: Circuit board 11:n layer 12:ESD layer 13: Base layer 14: 1st active layer 15, 215, 415: First metropolitan layer 16, 316: 2nd active layer 17, 217, 417: Second meso-mediate layer 18, 318: 3rd active layer 19:Protective layer 20A~20C: Regrowth layer 21A~21C, 421A~C, 521: Electron block layer 22A~22C, 522:p layer 23:n electrode 24A~24C:p electrode 215A, 217A: Undoped layer 215B, 217B: n-type layer 316A: Strain relaxation layer 316B, 318C, 518C: Quantum well structure layer 318A, 518A: First strain relaxation layer 318B, 518B: Second strain relaxation layer 518:Active layer

Claims

1. In a light-emitting element made of a group III nitride semiconductor, An n-layer made of an n-type group III nitride semiconductor, A first active layer having a predetermined emission wavelength is provided on the aforementioned n layer, An intermediate layer is provided on the first active layer and is made of a group III nitride semiconductor containing In, and has a structure in which a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer are stacked in order from the first active layer side. A second active layer is provided on the intermediate layer and has an emission wavelength different from that of the first active layer, The p layer provided on the second active layer, A groove extending from the p-layer side to the fourth layer, A p-electrode provided on the p-layer, An electrode provided on the fourth layer exposed on the bottom surface of the groove, It has, The In composition of the intermediate layer is set such that it has a band gap that does not absorb light emitted from the first active layer and the second active layer. The p-type impurity concentration in the second layer is higher than that in the first layer, the n-type impurity concentration in the third layer is higher than that in the fourth layer, and the second and third layers form a tunnel junction structure. A light-emitting element in which the In composition of the second and third layers is higher than that of the In composition of the first and fourth layers.

2. The light-emitting element according to claim 1, wherein the In composition of the second layer is higher than the In composition of the third layer.

3. The light-emitting element according to claim 1, wherein the thickness of the second layer is thinner than the thickness of the first layer, and the thickness of the third layer is thinner than the thickness of the fourth layer.

4. The light-emitting element according to any one of claims 1 to 3, wherein the intermediate layer is InGaN.

5. The light-emitting element according to any one of claims 1 to 3, wherein the In composition of the intermediate layer is 10% or less.

6. The light-emitting element according to any one of claims 1 to 3, wherein the intermediate layer is In-doped GaN.

7. In a method for manufacturing a light-emitting element made of a group III nitride semiconductor, A process for forming an n-layer made of an n-type group III nitride semiconductor, The steps include forming a first active layer having a predetermined emission wavelength on the n layer, The process involves forming an intermediate layer on the first active layer, made of a group III nitride semiconductor containing In, at a growth temperature of 700 to 1000°C, and stacking the intermediate layer in order from the first active layer side: a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer. The process involves forming a second active layer having a different emission wavelength from the first active layer on the intermediate layer, The steps include forming a p-layer on the second active layer, A step of forming a groove that extends from the p-layer side to the fourth layer, The step of forming a p electrode on the p layer, A step of forming an electrode on the fourth layer exposed on the bottom surface of the groove, It has, The In composition of the intermediate layer is set such that it has a band gap that does not absorb light emitted from the first active layer and the second active layer. The p-type impurity concentration in the second layer is made higher than that of the first layer, and the n-type impurity concentration in the third layer is made higher than that of the fourth layer, so that the second and third layers form a tunnel junction structure. A method for manufacturing a light-emitting element, wherein the In composition of the second and third layers is higher than that of the first and fourth layers.

8. The method for manufacturing a light-emitting element according to claim 7, wherein the In composition of the second layer is higher than the In composition of the third layer.

9. The method for manufacturing a light-emitting element according to claim 7, wherein the thickness of the second layer is made thinner than the thickness of the first layer, and the thickness of the third layer is made thinner than the thickness of the fourth layer.

10. The method for manufacturing a light-emitting element according to any one of claims 7 to 9, characterized in that the In composition of the intermediate layer is 10% or less.

11. The method for manufacturing an light-emitting element according to any one of claims 7 to 9, characterized in that the intermediate layer is InGaN.

12. The method for manufacturing a light-emitting element according to any one of claims 7 to 9, characterized in that the intermediate layer is In-doped GaN.

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