JP2023178174A - Light emitting element and method for manufacturing light emitting element - Google Patents

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

The present invention relates to a light emitting device and a method for manufacturing the same.

In recent years, there has been a demand for higher definition displays, and micro LED displays, in which each pixel is a minute LED on the order of 1 to 100 μm, are attracting attention. Various methods for achieving full color are known; for example, a method is known in which three active layers emitting blue, green, and red light are sequentially laminated on the same substrate. In this case, in order to drive each active layer individually, it is necessary to form an intermediate layer between the active layers.

Patent No. 5854419

The intermediate layer must be deposited after the active layer is deposited. Therefore, it was necessary to form the intermediate layer at a low temperature to avoid thermal damage to the active layer. However, when the intermediate layer is formed at a low temperature, the quality and surface flatness of the intermediate layer deteriorates, and the quality of the active layer formed thereon also deteriorates.

Therefore, an object of the present invention is to improve the surface flatness of the intermediate layer.

One aspect of the present invention is
In a light emitting device made of a group III nitride semiconductor,
an n layer made of an n-type group III nitride semiconductor;
a first active layer provided on the n-layer and having a predetermined emission wavelength;
an intermediate layer provided on the first active layer and made of a group III nitride semiconductor containing In;
a second active layer provided on the intermediate layer and having an emission wavelength different from that of the first active layer;
has
In the light emitting device, the intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer.

Further, one aspect of the present invention is
In a method for manufacturing a light emitting device made of a group III nitride semiconductor,
forming an n layer made of an n-type group III nitride semiconductor;
forming a first active layer with 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;
forming a second active layer having an emission wavelength different from that of the first active layer on the intermediate layer;
has
In the method of manufacturing a light emitting device, the intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer.

According to the present invention, the surface flatness of the intermediate layer can be improved.

FIG. 1 is a diagram showing the configuration of a light emitting element according to a first embodiment. The figure which showed the structure of the light emitting element of a modification. The figure which showed the structure of the light emitting element of a modification. FIG. 3 is a diagram showing an equivalent circuit of the light emitting element of the first embodiment. FIG. 3 is a diagram showing the manufacturing process of the light emitting device of the first embodiment. FIG. 3 is a diagram showing the manufacturing process of the light emitting device of the first embodiment. FIG. 3 is a diagram showing the manufacturing process of the light emitting device of the first embodiment. FIG. 3 is a diagram showing the manufacturing process of the light emitting device of the first embodiment. FIG. 7 is a diagram showing the configuration of a light emitting element according to a second embodiment. FIG. 7 is a diagram showing the configuration of a light emitting element according to a third embodiment. FIG. 3 is a diagram showing the configuration of a light emitting element of Experimental Example 1. An AFM image taken of the surface of the third active layer 18. A graph showing the relationship between drive current and external quantum efficiency. A graph showing the emission spectrum. A graph showing the emission spectrum. A graph showing the emission spectrum. A graph showing the emission spectrum. An AFM image taken of the surface of the third active layer 18. A graph showing the relationship between drive current and external quantum efficiency. FIG. 7 is a diagram showing the configuration of a light emitting element in a fourth embodiment. FIG. 7 is a diagram showing an equivalent circuit of a light emitting element in a fourth embodiment. FIG. 7 is a diagram showing the configuration of a light emitting element in a fifth embodiment. AFM images of the well layer surface of the quantum well structure layer 518C when the growth rate is changed. AFM images of the well layer surface of the quantum well structure layer 518C when the In solid phase ratio/In gas phase ratio is changed. AFM images of the well layer surface of the quantum well structure layer 518C when the partial pressure of ammonia is changed.

A light emitting element made of a group III nitride semiconductor includes an n layer made of an n-type group III nitride semiconductor, a first active layer provided on the n layer and having a predetermined emission wavelength, and a first active layer provided on the n layer and having a predetermined emission wavelength; an intermediate layer made of a Group III nitride semiconductor containing In, and a second active layer provided on the intermediate layer and emitting light at a different wavelength from that of the first active layer. The intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer.

Further, a groove reaching the intermediate layer from the second active layer side, a first p layer provided on the second active layer and made of a p-type group III nitride semiconductor, and a first p layer exposed on the bottom surface of the groove. a second p-layer provided on the intermediate layer and made of a p-type group III nitride semiconductor; a first p-electrode provided on the first p-layer; and a second p-layer provided on the second p-layer. and a second p-electrode provided at.

Further, the intermediate layer includes a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer stacked in order from the first active layer side. The p-type impurity concentration of the second layer is higher than the p-type impurity concentration of the first layer, and the n-type impurity concentration of the third layer is higher than the n-type impurity concentration of the fourth layer. , the second layer and the third layer form a tunnel junction structure, a p-layer provided on the second active layer, a trench reaching the fourth layer from the p-layer side, and a It may have a p-electrode provided on the layer and an electrode provided on the fourth layer exposed at the bottom of the groove. The regrowth interface can be prevented from existing, and deterioration of device characteristics can be suppressed.

The In compositions of the second layer and the third layer may be higher than the In compositions of the first layer and the fourth layer. The tunnel probability due to the tunnel junction structure can be further increased. Moreover, the In composition of the second layer may be higher than the In composition of the third layer. Moreover, the thickness of the second layer may be thinner than the thickness of the first layer, and the thickness of the third layer may be thinner than the thickness of the fourth layer.

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.

A method for manufacturing a light emitting device made of a group III nitride semiconductor includes a step of forming an n layer made of an n-type group III nitride semiconductor, and a step of forming a first active layer having a predetermined emission wavelength on the n layer. a step of 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.; forming a second active layer of wavelength. The intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer.

Further, the step of forming a groove reaching the intermediate layer from the second active layer side, and forming a groove made of a p-type group III nitride semiconductor on the second active layer and on the intermediate layer exposed at the bottom surface of the groove. forming a first p-layer and a second p-layer, respectively, and forming a first p-electrode and a second p-electrode on the first p-layer and the second p-layer, respectively; It may have a step.

The intermediate layer is formed by laminating, 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 p-type impurity concentration of the second layer is higher than the p-type impurity concentration of the first layer, the n-type impurity concentration of the third layer is higher than the n-type impurity concentration of the fourth layer, and the second layer and the third layer form a tunnel junction structure, a step of forming a p layer on the second active layer, and a step of forming a groove reaching the fourth layer from the p layer side, The method may include the steps of forming a p-electrode on the p-layer and forming an electrode on the fourth layer exposed at the bottom of the groove.

In the above method for manufacturing a light emitting device made of a Group III nitride semiconductor, the In compositions of the second layer and the third layer may be higher than the In compositions of the first layer and the fourth layer. Further, the In composition of the second layer may be higher than the In composition of the third layer. Moreover, the thickness of the second layer may be made thinner than the thickness of the first layer, and the thickness of the third layer may be made thinner than the thickness of the fourth layer. Further, the growth temperature of the second layer and the third layer may be lower than the growth temperature of the first layer and the fourth layer.

Furthermore, in the method for manufacturing a light emitting device made of a Group III nitride semiconductor, the In composition of the intermediate layer may be 10% or less. Furthermore, the intermediate layer may be made of InGaN. Furthermore, the intermediate layer may be made of GaN doped with In.

(First embodiment)
FIG. 1 is a diagram showing the configuration of a light emitting element according to the first embodiment. The light emitting element of the first embodiment can emit blue, green, and red light, respectively. Furthermore, the light emitting element of the first embodiment is of a flip-chip type that takes out light from the back side of the substrate, and is mounted face down on a mounting substrate (not shown). Note that in the first embodiment, one pixel has a structure of one chip, but a monolithic type may be used. In other words, it may be a micro LED display element in which the element structure of the first embodiment is arranged in a matrix on the same substrate.

As shown in FIG. 1, the light emitting device 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, and a first intermediate layer 15. 2 active layer 16, second intermediate layer 17, third active layer 18, protective layer 19, regrowth layers 20A to 20C, electron block layers 21A to 21C, p layers 22A to 22C, n electrode 23, and p-electrodes 24A to 24C.

The substrate 10 is a growth substrate on which a group III nitride semiconductor is grown. For example, sapphire, Si, GaN, etc.

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 as necessary, and the buffer layer may not be provided when the substrate is GaN. The n-layer 11 is made of, for example, n-GaN, n-AlGaN, or the like. The Si concentration is, for example, 1×10 ¹⁸ to 100×10 ¹⁸ cm ⁻³ .

The ESD layer 12 is a semiconductor layer provided on the n-layer 11, and is a layer provided to improve electrostatic breakdown voltage. The ESD layer 12 may be provided as necessary and may be omitted. The ESD layer 12 is, for example, undoped or lightly doped with Si, GaN, InGaN, or AlGaN.

The base layer 13 is a semiconductor layer with a superlattice structure provided on the ESD layer 12, and is a layer for relaxing the lattice strain of the semiconductor layer formed on the base layer 13. The base layer 13 may also be provided if necessary, and may be omitted. The base layer 13 is formed by alternately stacking Group III nitride semiconductor thin films having different compositions (for example, two of GaN, InGaN, and AlGaN), and the number of pairs is, for example, 3 to 30. It may be non-doped, or it may be doped with Si at about 1×10 ¹⁷ to 100×10 ¹⁷ cm ⁻³ . Further, it is not necessary to have a superlattice structure as long as strain can be alleviated. Any material may be used as long as it has a small difference in lattice constant at the heterointerface with the first active layer 14, and may be, for example, an InGaN layer, an AlInN layer, or an AlGaIn layer.

The first active layer 14 is a light emitting layer with an SQW or MQW structure provided on the base layer 13. The emission wavelength is blue and ranges from 430 to 480 nm. The first active layer 14 has a structure in which one to seven pairs of barrier layers made of AlGaN and well layers made of InGaN are alternately laminated. More preferably 1 to 5 pairs, still more preferably 1 to 3 pairs.

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 a layer provided so that light emission from the first active layer 14 and light emission from the second active layer 16 can be individually controlled. It also has the role of protecting the first active layer 14 from etching damage when forming a second groove 31, which will be described later.

The material of the first intermediate layer 15 is a group III nitride semiconductor containing In, and is preferably InGaN, for example. The surfactant effect of In can suppress roughness on the surface of the first intermediate layer 15 and improve surface flatness. Furthermore, lattice distortion can be alleviated. The In composition of the first intermediate layer 15 (the molar ratio of In to the entire group III metal of the group III nitride semiconductor) has a band gap that does not absorb light emitted from the first active layer 14 and the second active layer 16. It is sufficient if it is set as follows. A preferable In composition is 10% or less, more preferably 5% or less, and still more preferably 2% or less. If the In composition is greater than 10%, the surface of the first intermediate layer 15 may become rough. In is optional as long as it is greater than 0%, and may be at a doping level (a level that does not form a mixed crystal). For example, GaN has an In concentration of 1×10 ¹⁴ cm ⁻³ or more and 1×10 ²² cm ⁻³ or less.

Further, the first intermediate layer 15 may be doped with an impurity. Preferably it is an n-type impurity. For example, the Si concentration is 1×10 ¹⁷ to 1000×10 ¹⁷ cm ⁻³ , preferably 10×10 ¹⁷ to 100×10 ¹⁷ cm ⁻³ , and more preferably 20×10 ¹⁷ to 80×10 ¹⁷ cm ⁻³ . It's okay.

The thickness of the first intermediate layer 15 is preferably 20 to 150 nm. If it is thicker than 150 nm, the surface of the first intermediate layer 15 may become rough. Moreover, if it is thinner than 20 nm, it may become difficult to control the depth of the second groove 31 within the first intermediate layer 15 when forming the second groove 31, which will be described later. More preferably 30 to 100 nm, still more preferably 50 to 80 nm.

The second active layer 16 is a light emitting layer with an SQW or MQW structure provided on the first intermediate layer 15. The emission wavelength is green and ranges from 510 to 570 nm. The second active layer 16 has a structure in which one to seven pairs of barrier layers made of GaN and well layers made of InGaN are alternately laminated. More preferably 1 to 5 pairs, still more preferably 1 to 3 pairs. Further, it is preferably equal to or less than the number of pairs in the first active layer 14, and more preferably less.

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 reason as the first intermediate layer 15, and is to enable separate control of light emission from the second active layer 16 and light emission from the third active layer 18. This is a layer provided in It also has the role of protecting the second active layer 16 from etching damage when forming a third groove 32, which will be described later.

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. Further, the second intermediate layer 17 may also be doped with an impurity similarly to the first intermediate layer 15. Further, the thickness of the second intermediate layer 17 is also the same as that of the first intermediate layer 15, and the first intermediate layer 15 and the second intermediate layer 17 may have the same thickness. However, it is preferable to make it thinner than the first intermediate layer 15 and to have a larger In composition than 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 influence of distortion at the interface is greater.

The third active layer 18 is a light emitting layer with an SQW or MQW structure provided on the second intermediate layer 17. The emission wavelength is red and ranges from 590 to 700 nm. The third active layer 18 has a structure in which one to seven pairs of barrier layers made of InGaN and well layers made of InGaN are alternately laminated. More preferably 1 to 5 pairs, still more preferably 1 to 3 pairs. Further, it is preferably equal to or less than the number of pairs in the second active layer 16, and more preferably less.

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

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

The regrown layers 20A to 20C are provided on the protective layer 19, on the second intermediate layer 17 exposed on the bottom surface of the third groove 32, and on the first intermediate layer 15 exposed on the bottom surface of the second groove 31, respectively. The structure of the regrown layers 20A to 20C is similar to that of the protective layer 19.

The electron blocking layers 21A to 21C are semiconductor layers provided on the regrowth layers 20A to 20C, respectively, and block electrons injected from the n layer 11 into the first active layer 14, the second active layer 16, and the third active layer. This is a blocking layer to efficiently confine the particles to 18. The electron block layer may be a single layer of GaN or AlGaN, or may have a structure in which two or more of AlGaN, GaN, and InGaN are laminated, or a structure in which they are laminated with only the composition ratio changed. Alternatively, it may have a superlattice structure. The thickness of the electron block layers 21A to 21C is preferably 5 to 50 nm, more preferably 5 to 25 nm. The Mg concentration of the electron block layers 21A to 21C is preferably 1×10 ¹⁹ to 100×10 ¹⁹ cm ⁻³ .

The p layers 22A to 22C are semiconductor layers provided on the electron block layers 21A to 21C, respectively, and are composed of a first layer and a second layer in order from the electron block layer 21 side. The first layer is preferably p-GaN or p-InGaN. The thickness of the first layer is preferably 10 to 500 nm, more preferably 10 to 200 nm, even more preferably 10 to 100 nm. The Mg concentration of the first layer is preferably 1×10 ¹⁹ to 100×10 ¹⁹ cm ⁻³ . 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, even more preferably 6 to 10 nm. The Mg concentration of the second layer is preferably 1×10 ²⁰ to 100×10 ²⁰ cm ⁻³ .

In the first embodiment, the regrowth layers 20A to 20C, the electron block layers 21A to 21C, and the p layers 22A to 22C are provided separately, but they may be provided as one continuous layer (see FIG. 2). In this case, a regrowth layer, an electron block layer, and a p-layer are also formed on the side surfaces of the third groove 32 and the second groove 31, but this hardly affects the operation of the device. The reason is as follows. If the p-electrode 24A, the p-electrode 24B, and the p-electrode 24C are sufficiently separated spatially, the resistance of the p-layer connecting between the p-electrode 24A, the p-electrode 24B, and the p-electrode 24C is very high, so that no current flows. There is almost no flow. In addition, since holes have low mobility, they do not spread laterally from the region in contact with the electrode, but flow predominantly in the vertical direction through the pn junction directly under the electrode. Therefore, even if the regrown layers 20A to 20C, the electron block layers 21A to 21C, and the p layers 22A to 22C are continuous, the operation of the device is not affected. That is, when a current is applied to the p-electrode 24A, the current flows directly under the p-electrode 24A, and as a result, the active layer directly under the p-electrode 24A emits light, and the current flows to the active layer directly under the p-electrodes 24B and 24C, causing light emission. There is very little to do.

Further, as shown in FIG. 3, the insulating film 27 may be provided on the side surfaces of the third groove 32 and the side surfaces of the second groove 31. This insulating film 27 remains as a mask for selectively growing the regrowth layers 20A to 20C, the electron block layers 21A to 21C, and the p layers 22A to 22C.

The n-electrode 23 is an electrode provided on the n-layer 11 exposed at the bottom of the first groove 30. When the substrate 10 is made of 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.

P electrodes 24A to 24C are electrodes provided on p layers 22A to 22C, respectively. The material of the p electrodes 24A to 24C is, for example, Ag, Ni/Au, Co/Au, ITO, or the like.

The operation of the light emitting element of the first embodiment will be explained. In the light emitting device of the first embodiment, red light can be emitted from the third active layer 18 by applying a voltage between the p electrode 24A and the n electrode 23, and the red light can be emitted between the p electrode 24B and the n electrode 23. By applying a voltage to the second active layer 16, green light can be emitted, and by applying a voltage between the p-electrode 24C and the n-electrode 23, the first active layer 14 can emit blue light. can be done. Furthermore, two or more of blue, green, and red can be emitted at the same time. In this manner, the light emitting element of the first embodiment can control blue, green, and red light emission by selecting the electrode to which voltage is applied, and can be used as one pixel of a display.

FIG. 4 shows an equivalent circuit of the light emitting element of the first embodiment. As shown in FIG. 4, the light emitting element of the first embodiment has a structure in which blue, green, and red LEDs are formed in one element, and full-color light emission can be realized with one element. Therefore, it is possible to make the size of one element much smaller than by preparing blue, green, and red LEDs individually and arranging them on the same substrate to create a full-color light-emitting element of 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, and the manufacturing cost can be significantly reduced, resulting in a very low-cost full-color light emitting device. , and a light-emitting display using it can be realized.

Here, 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 due to the surfactant effect of In. The surface flatness of the second active layer 16 and the third active layer 18 can also be improved. Furthermore, lattice strain caused by a difference in lattice constant between the base layer 13 and the first active layer 14 can also be alleviated. As a result, the light emitting element of the first embodiment can improve luminous efficiency.

Next, the manufacturing process of the light emitting device of the first embodiment will be explained with reference to the drawings.

First, the substrate 10 is prepared, and the substrate is heat-treated by adding hydrogen, nitrogen, and, if necessary, ammonia.

Next, a buffer layer is formed on the substrate 10, and the n-layer 11, the ESD layer 12, the base layer 13, the first active layer 14, the first intermediate layer 15, the second active layer 16, and the second intermediate layer are formed on the buffer layer. Layer 17, third active layer 18, and protective layer 19 are formed in this order (see FIG. 5). The preferred growth temperature for each layer is as follows.

The growth temperature of the first active layer 14 is preferably 700 to 950°C. Crystal quality can be improved and luminous efficiency can be increased. The first active layer 14 is composed of a well layer and a barrier layer, but the well layer and the barrier layer may be formed at the same temperature or may be formed at different temperatures within the above temperature range. If the temperatures are different, it is preferable that the growth temperature of the well layer is lower than the growth temperature of the barrier layer.

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. Further, if the temperature is lower than 700°C, pits and point defects due to threading dislocations are likely to occur. The temperature is more preferably 800 to 950°C, even more preferably 850 to 950°C.

The growth temperature of the second active layer 16 is preferably 650 to 950°C. Crystal quality can be improved and luminous efficiency can be increased. The second active layer 16 is composed of a well layer and a barrier layer, but the well layer and the barrier layer may be formed at the same temperature or may be formed at different temperatures within the above temperature range. When the temperatures are different, it is preferable that the growth temperature of the well layer is lower than the growth temperature of the barrier layer. Further, the growth temperature of the second active layer 16 is preferably lower than the growth temperature of the first active layer 14.

The growth temperature of the second intermediate layer 17 is preferably in the same range as the growth temperature of the first intermediate layer 15. However, the growth temperature of the second intermediate layer 17 is preferably lower than the growth temperature 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 influence of distortion at the interface is greater.

The growth temperature of the third active layer 18 is preferably 500 to 950°C. Crystal quality can be improved and luminous efficiency can be increased. The third active layer 18 is composed of a well layer and a barrier layer, but the well layer and the barrier layer may be formed at the same temperature or may be formed at different temperatures within the above temperature range. When the temperatures are different, it is preferable that the growth temperature of the well layer is lower than the growth temperature of the barrier layer. Further, the growth temperature of the third active layer 18 is preferably lower than the growth temperature of the second active layer 16.

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, second active layer 16, and third active layer 18. In order to improve the crystallinity of the protective layer 19, the growth temperature is preferably high, more preferably from 600 to 900°C, still more preferably from 700 to 900°C.

Next, a partial region of the surface of the protective layer 19 is dry-etched until reaching the second intermediate layer 17 to form a third groove 32, and dry-etched until reaching the first intermediate layer 15 to form a second groove 31. (See Figure 6). It is preferable that the third groove 32 and the second groove 31 be etched to a thickness between the second intermediate layer 17 and the first intermediate layer 15.

Next, regrown 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 continuously as shown in FIG. Further, as shown in FIG. 3, an insulating film 27 is formed on the side surfaces of the third groove 32 and the second groove 31, and the regrown layers 20A to 20C are selectively grown using this as a mask. They may be formed separately.

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

Next, p layers 22A to 22C are formed on the electron block layers 21A to 21C (see FIG. 7). The growth temperature of the p layers 22A to 22C is preferably 650 to 1000°C. The temperature is more preferably 700 to 950°C, even more preferably 750 to 900°C.

Next, a first groove 30 is formed by dry etching a part of the surface of the p layer 22C until it reaches the n layer 11 (see FIG. 8). Then, an n-electrode 23 is formed on the n-layer 11 exposed at the bottom of the first groove 30, and p-electrodes 24A-24C are formed on the p-layers 22A-22C. The light emitting device of the first embodiment is manufactured through the above steps.

(Second embodiment)
As shown in FIG. 9, the light emitting element of the second embodiment is different from the light emitting element of the first embodiment in that the first intermediate layer 15 and the second intermediate layer 17 are replaced with the first intermediate layer 215 and the second intermediate layer 217. It has been replaced.

The first intermediate layer 215 has a structure in which a non-doped layer 215A and an n-type layer 215B are laminated 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 preferable. The non-doped layer 215A is non-doped, and the n-type layer 215B is Si-doped. The Si concentration of the n-type layer 215B is preferably 1×10 ¹⁷ to 1000×10 ¹⁷ cm ⁻³ . The thickness of the first intermediate layer 215 is preferably the same as that of the first intermediate layer 15. That is, it is preferably 20 to 150 nm. Further, the thickness of the non-doped layer 215A is preferably 10 nm or more. This is for controlling the etching depth and avoiding etching damage to the first active layer 14. Further, the thickness of the n-type layer 215B is preferably 10 nm or more. This is to independently control the light emitting characteristics of each active layer. The n-type layer 215B may be modulated and doped with Si, or there may be a non-doped region in a part of the n-type layer 215B.

The second intermediate layer 217 has a structure in which a non-doped layer 217A and an n-type layer 217B are laminated 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. That is, 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. Further, the non-doped layer 217A is non-doped, and the n-type layer 217B is doped with Si. However, it is preferable to make it thinner than the first intermediate layer 215 and to have a larger In composition than the first intermediate layer 215. The reason is the same as in the case of the second intermediate layer 17. In other words, 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 distortion at the interface is greater.

The third groove 32 has a depth that reaches the non-doped layer 217A of the second intermediate layer 217. In this way, by removing the n-type layer 217B of the second intermediate layer 17 below the p-electrode 24B, the n-type layer is not located on the second active layer 16, so that the second active layer 16 emits light. ing. Further, the second groove 31 has a depth that reaches the non-doped layer 215A of the first intermediate layer 215. This is also for the same reason, by removing the n-type layer 215B of the first intermediate layer 15 below the p-electrode 24C, the n-type layer is not located on the first active layer 14, and the first active layer 14 is It is made to emit light.

Here, the distance between pn junctions will be explained. The distance between pn junctions corresponds to the thickness of a depleted film at zero bias. In an LED, it corresponds to the total film thickness of a non-doped 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.

When the first intermediate layer 215 and the second intermediate layer 217 are non-doped, the distance between the p-n junctions (thickness of the depletion layer) is such that in the region under the p-electrode 24A, the acceptor impurity is removed from the heavily doped electron blocking layer 21A. The distance to the n-layer 11 heavily doped with donor impurities, that is, the film thickness including the first active layer 14, second active layer 16, third active layer 18, first intermediate layer 15, and second intermediate layer 17 corresponds to Further, below the p-electrode 24B, the distance from the electron blocking layer 21B heavily doped with acceptor impurities to the n-layer 11, that is, the distance between the first active layer 14, the second active layer 16, the first intermediate layer 15, and the This corresponds to the film thickness including a part of the second intermediate layer 17. Further, below the p-electrode 24C, the distance from the electron blocking layer 21C heavily doped with acceptor impurities to the n-layer 11 corresponds to the film thickness including the first active layer 14 and a part of the first intermediate layer 15. do.

Therefore, the distance between the pn junctions is different in these three cases, and the driving voltage, current injection efficiency, and reverse current are different. Furthermore, when applying a voltage to the p-electrode 24A to cause the third active layer 18 to emit light, carriers of electrons and holes are supplied to all the active layers, and the second active layer 16 and the first active layer 14 may also emit light. Similarly, when it is desired to cause the second active layer 16 to emit light by applying a voltage to the p-electrode 24B, there is a possibility that the first active layer 14 will also emit light.

In the second embodiment, such a problem is solved by the structure of the intermediate layer. That is, in the second embodiment, the first intermediate layer 15 is made of two layers, the non-doped layer 215A and the n-type layer 215B doped with a high concentration of donor impurities, and the second intermediate layer 17 is made of the non-doped layer 217A, which is a non-doped layer 217A and an n-type layer 215B doped with a high concentration of donor impurities. There are two layers, a heavily doped n-type layer 217B, and the n-type layers 215B and 217B are doped with Si to make them n-type.

Therefore, the distance between pn junctions is the distance from the electron block layer 21A to the n-type layer 217B of the second intermediate layer 217 in the region under the p electrode 24A, and the distance from the electron block layer 21B to the first The distance from the intermediate layer 215 to the n-type layer 215B is the distance from the electron block layer 21C to the n-layer 11 in the region below the p-electrode 24C. That is, the distance between pn junctions under all electrodes corresponds to the total film thickness including one active layer and the non-doped layer of the intermediate layer, excluding the plurality of active layers. Here, by appropriately controlling the thicknesses of the non-doped layer 215A of the first intermediate layer 215 and the non-doped layer 217A of the second intermediate layer 17, the distance between the pn junctions can be made equal in these three cases. As a result, variations in drive voltage, current injection efficiency, and reverse current can be suppressed in these three cases, and uniform control becomes possible. Furthermore, in these three cases, only one first active layer 14, one second active layer 16, and one third active layer 18 are included between the p-n junctions, and the intermediate n-type layer acts as a barrier layer for holes. Therefore, it becomes difficult for holes to be injected into the lower active layer beyond the n-type intermediate layer. As a result, it is possible to prevent parts of the active layer located between the pn junctions other than the active layer to emit light from being emitted.

(Third embodiment)
As shown in FIG. 10, the light emitting device of the third embodiment is different from the light emitting device of the first embodiment in that the second active layer 16 and the third active layer 18 are replaced with the second active layer 316 and the third active layer 318. It has been replaced.

The second active layer 316 has a structure in which a strain relaxation layer 316A and an SQW or MQW quantum well structure layer (light emitting layer) 316B are laminated in this order. The quantum well structure layer 316B has the same structure as the second active layer 16 of the first embodiment.

The strain relaxation layer 316A has an SQW structure in which a barrier layer and a well layer are sequentially laminated, 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 setting the thickness of the well layer to 1 nm or less, it is possible to prevent the well layer from emitting light. 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 may 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, it is 400 to 460 nm. It is. Preferably, the wavelength is 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.

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.

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 subband within the well increases and the band edge energy increases. Thereby, the emission wavelength may be shorter than the emission wavelength of the quantum well structure layer 316B. Although the growth temperature is arbitrary, 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 made thinner, the subband will further rise, and the energy difference with the barrier layer will become smaller. That is, it becomes close to the band edge energy of the barrier layer. As a result, it becomes difficult for carriers to be confined in the well layer of the strain relaxation layer 316A, making it difficult to emit light, so that it functions as a part of the barrier layer of the quantum well structure layer 316B and also provides a strain relaxation effect at the same time. . In this way, by forming the strain relaxation layer 316A having a well layer with worse carrier confinement than the well layer of the quantum well structure layer 316B, it is possible to form the strain relaxation layer 316A that does not emit light.

In short, the material and layer structure of the strain relaxation layer 316A are set so 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 may be set so that the strain relaxation layer 316A does not emit light.

Although the strain relaxation layer 316A may have an MQW structure in which two or more pairs of barrier layers and well layers are laminated, it is preferable to have an SQW structure because the second active layer 316 becomes thick.

By providing the strain relaxation layer 316A as described above, the strain of the quantum well structure layer 316B stacked thereon can be relaxed, and the crystal quality of the well layer of the quantum well structure layer 316B can be improved. .

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 be 30% or less. Strain in the quantum well structure layer 316B can be more efficiently relaxed, and the distance between p-n junctions becomes constant under each p-electrode 24A to 24C, making device characteristics uniform under each p-electrode 24A to 24C. .

The third active layer 318 has a structure in which a first strain relaxation layer 318A, a second strain relaxation layer 318B, and an SQW or MQW quantum well structure layer 318C are laminated in this order. The quantum well structure layer 318C has the same structure as the third active layer 18 of the first embodiment.

The first strain relief layer 318A has a similar structure to the strain relief 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 may be shorter than the emission wavelength of the quantum well structure layer 316B, for example, 400 to 460 nm.

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 a band edge of the well layer of the first strain relaxation layer 318A. longer than the wavelength corresponding to the energy. For example, it is 510 to 570 nm. Other than that, it is the same as the first strain relaxation layer 318A.

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

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 are set to be 30% or less. It is preferable to do so. Strain in the quantum well structure layer 318C can be more efficiently relaxed, and the distance between p-n junctions becomes constant under each p-electrode 24A to 24C, making device characteristics uniform under each p-electrode 24A to 24C. .

By providing the first strain relaxation layer 318A and the second strain relaxation layer 318B in this way, strain can be relaxed in stages, and the strain of the quantum well structure layer 318C stacked thereon can be effectively relaxed. can be done. As a result, the quality of the well layer of the quantum well structure layer 318C can be improved.

Note that in the third active layer 318, the strain is relaxed in two stages by the first strain relaxation layer 318A and the second strain relaxation layer 318B, but the strain can be relaxed in three or more stages by providing three or more strain relaxation layers. It's okay. Further, in the second active layer 316 as well, a plurality of strain relaxation layers 316A may be provided to relieve strain in stages.

Furthermore, a strain relaxation layer may 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.

(Other variations)
Although the light emitting device of this embodiment has three active layers, the first active layer 14, the second active layer 16, and the third active layer 18, it has two or more active layers with different emission wavelengths. The present invention is applicable to any structure. Furthermore, the color of the emitted light is not limited to blue, green, or red, but may be any color as long as the emitted light has a different wavelength.

It is preferable that the light emitting element of this embodiment is PWM driven by a PWM circuit to control light emission. Light intensity can be easily controlled by the pulse width and pulse period, and wavelength shifts due to differences in drive current can also be suppressed.

(Experimental result)
Next, experimental results regarding this embodiment will be explained.

(Experiment 1)
The second intermediate layer 17 and the third active layer 18 are omitted from the light emitting device of the first embodiment, and the regrowth layer 20B, electron block layer 21B, p layer 22B, and p electrode 24B are omitted and replaced with the first intermediate layer 15. A light-emitting element was fabricated using the first intermediate layer 215 of the second embodiment and the second active layer 316 of the third embodiment instead of the second active layer 16 (see FIG. 11, hereinafter 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 set to be the same as the emission wavelength of the first active layer 14, resulting in an SQW structure.

FIG. 12 is an AFM image taken of the surface of the second active layer 316 of the light emitting element of Experimental Example 1. In FIG. 12, the upper row shows a 10 μm square range, and the lower row shows a 2 μm square range. For comparison, a case (Experimental Example 2) in which the first intermediate layer 215 is made of GaN and the rest is the same as Experimental Example 2 is also shown. As shown in FIG. 12, in Experimental Example 1, the pit density was lower than in Experimental Example 2. Moreover, the surface flatness RMS is 0.88 nm for Experimental Example 1 and 2.6 nm for Experimental Example 2 in a 10 μm square range, and 0.78 nm for Experimental Example 1 and 3.7 nm for Experimental Example 2 in a 2 μm square range. 1 nm, which was smaller in Experimental Example 1 than in Experimental Example 2 in both cases. As a result, the In in the first intermediate layer 215 acts as a surfactant, and the surface flatness of the first intermediate layer 215 is improved, thereby improving the surface flatness and crystal quality of the second active layer 316 thereon. I understand that.

FIG. 9 is a graph showing the relationship between drive current and external quantum efficiency for the light emitting elements of Experimental Example 1 and Experimental Example 2. The external quantum efficiency is when a voltage is applied to the p-electrode 24B to cause the second active layer 316 to emit light. As shown in FIG. 9, Experimental Example 1 had a higher external quantum efficiency than Experimental Example 2. This shows that the external quantum efficiency was improved due to the improved crystal quality of the second active layer 316.

(Experiment 2)
The light-emitting element of the first embodiment (the light-emitting element shown in FIG. 1, hereinafter referred to as the light-emitting element shown in FIG. , the light emitting device of Experimental Example 3), a current was injected into the p-electrode 24A, and its emission spectrum was measured. The Si concentrations of the n-type layer 215B and the n-type layer 217B were set to three patterns: 1×10 ¹⁸ cm ⁻³ , 2×10 ¹⁸ cm ⁻³ , and 3×10 ¹⁸ cm ⁻³ . For comparison, the emission spectrum was also measured when the n-type layer 215B and the n-type layer 217B were replaced with non-doped layers.

14 to 17 are graphs showing emission spectra; FIG. 14 has a Si concentration of 3×10 ¹⁸ cm ⁻³ , FIG. 15 has a Si concentration of 2×10 ¹⁸ cm ⁻³ , and FIG. 16 has a Si concentration of 1×10 ¹⁸ cm ⁻³ , FIG. 17 is non-doped. As shown in FIG. 17, in the case of non-doping, not only red light emission from the third active layer 18 but also blue light emission from the first active layer 14 occurred, and it was found that the red light emission was weak and the blue light emission was strong. On the other hand, as shown in FIGS. 14 to 16, in the case of Si doping, the red emission was as strong as or stronger than the blue emission, and the higher the Si concentration, the lower the intensity of the blue emission. Although the intensity of the blue emission of the second active layer 16 decreased, some green emission also appeared, but as shown in FIG. 14, when the Si concentration became sufficiently high, the intensity of the green emission also decreased. As a result, by introducing the Si-doped n-type layer 215B and n-type layer 217B into the first intermediate layer 15 and the second intermediate layer 17, active layers other than the third active layer 18 which is the active layer desired to emit light ( It was found that light emission from the first active layer 14 and the second active layer 16) can be suppressed.

(Experiment 3)
FIG. 18 is an AFM image taken of the surface of the quantum well structure layer 316C of the light emitting elements of Experimental Examples 2 and 4. Experimental Example 4 is a case where the strain relaxation layer 316A was not provided in the second active layer 316 in Experimental Example 2. In FIG. 16, the upper row shows a 10 μm square range, and the lower row shows a 2 μm square range. As shown in FIG. 18, the surface flatness RMS is 2.6 nm for Experimental Example 2 and 3.8 nm for Experimental Example 4 in a 10 μm square range, and 3.1 nm for Experimental Example 2 and 3.1 nm for Experimental Example 4 in a 2 μm square range. 4 was 3.3 nm, and Experimental Example 2 was smaller than Experimental Example 4 in both cases. That is, the surface flatness was improved. The results show that by introducing the strain relaxation layer 316A into the second active layer 316, the strain of the quantum well structure layer 316B thereon is relaxed, and the surface flatness and crystal quality are improved.

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

(Fourth embodiment)
FIG. 20 is a diagram showing the configuration of a light emitting element in the fourth embodiment, and is a sectional view taken in a plane perpendicular to the main surface of the substrate. As shown in FIG. 20, the light emitting element in the fourth embodiment has a part of the configuration of the light emitting element in the first embodiment modified as follows. Components similar to those in the first embodiment are given the same reference numerals and explanations will be omitted.

As shown in FIG. 20, instead of the first intermediate layer 15 and the second intermediate layer 17, a first intermediate layer 415 and a second intermediate layer 417 are provided. In addition, the protective layer 19, the regrowth layers 20A to 20C, the electron block layers 21A to 21C, and the p layers 22A to 22C are omitted, and an electron block layer 421A and a p layer 422 are provided on the third active layer 18, and on the p layer 422. A p-electrode 24A is provided. In other words, the light emitting device of the fourth embodiment does not have a regrown layer. Further, a first electrode 424B is provided on the first intermediate layer 415 exposed on the bottom surface of the second groove 31, and a second electrode 424C is provided on the second intermediate layer 417 exposed on the bottom surface of the third groove 32. Further, 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.

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 regrown layer but is grown continuously on the first active layer 14.

The first intermediate layer 415 has a structure in which a first layer 415A, a second layer 415B, a third layer 415C, and a fourth layer 415D are laminated in order from the first active layer 14 side, and the bottom surface of the second groove 31 The fourth layer 415D is exposed. The second layer 415B and the third layer 415C form a tunnel junction structure. In this way, the first intermediate layer 415 has a tunnel junction function in addition to the same function as the first intermediate layer 15 of the first embodiment.

The first layer 415A is a semiconductor layer provided on the electron block layer 421C. In order to make the first active layer 14 emit light efficiently, 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. There is.

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, and is preferably InGaN, for example. The surfactant effect of In can suppress the surface roughness of the first intermediate layer 415 and improve the surface flatness. Furthermore, lattice distortion can be alleviated. The In composition of the first intermediate layer 415 may be set so as 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.

The preferable In composition of the first layer 415A is 10% or less, more preferably 5% or less, and still more preferably 2% or less. If the In composition is greater than 10%, the surface of the first intermediate layer 415 may become rough. In is optional as long as it is greater than 0%, and may be at a doping level (a level that does not form a mixed crystal). For example, GaN has an In concentration of 1×10 ¹⁴ cm ⁻³ or more and 1×10 ²² cm ⁻³ or less.

The first layer 415A is a p-type semiconductor doped with Mg, which is a p-type impurity. For example, if the Mg concentration is 1×10 ¹⁸ to 1×10 ²⁰ cm ⁻³ , preferably 5×10 ¹⁸ to 1×10 ²⁰ cm ⁻³ , more preferably 1×10 ¹⁹ to 1×10 ²⁰ cm ^{−3 ,} It's okay. Although it may be non-doped, it is preferably doped with Mg as described above. The first layer 415A may use polarization dope that provides a gradient in the In composition in the thickness direction. In this case, it may be non-doped. Further, the third layer 415C may be doped with Mg by Mg diffusion from the electron block layer 421C, which is the lower layer of the first layer 415A. In this case, the Mg concentration of the electron block layer 421C is preferably in the range of 1×10 ¹⁹ to 1×10 ²¹ cm ⁻³ .

The thickness of the first layer 415A is preferably 10 to 300 nm. If it is thicker than 300 nm, the surface of the first intermediate layer 415 may become rough. Moreover, if it is thinner than 10 nm, there is a possibility that the luminous efficiency of the first active layer 14 cannot be sufficiently increased. More preferably 20 to 200 nm, still more preferably 30 to 100 nm.

The second layer 415B is a semiconductor layer provided on the first layer 415A. A tunnel junction structure is formed by stacking the second layer 415B and the third layer 415C.

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 be different from the In composition of the first layer 415A and the fourth layer 415D, and in that case, it is preferably higher than the In composition of the first layer 415A and the fourth layer 415D. The tunnel probability due to the tunnel junction structure can be further increased. The preferable In composition range of the second layer 415B is the same as that of the first layer 415A.

The second layer 415B is a p-type semiconductor doped with Mg, which is a p-type impurity. The Mg concentration is 1×10 ²⁰ to 1×10 ²¹ cm ⁻³ . The Mg concentration of the second layer 415B is higher than the Mg concentration of the first layer 415A.

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 5 to 35 nm, still more preferably 5 to 20 nm. Further, the thickness of the second layer 415B is preferably thinner than the first layer 415A.

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

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 be different from the In composition of the first layer 415A and the fourth layer 415D, and in that case, it is preferably higher than the In composition of the first layer 415A and the fourth layer 415D. The tunnel probability due to the tunnel junction structure can be further increased. Further, the In composition of the third layer 415C may be different from the In composition of the second layer 415B. In that case, the In composition of the third layer 415C is preferably lower than the In composition of the second layer 415B. The preferable In composition range of the third layer 415C is the same as that of the first layer 415A.

The third layer 415C is an n-type semiconductor doped with Si, which is an n-type impurity. The Si concentration is 1×10 ²⁰ to 1×10 ²¹ cm ⁻³ .

A layer co-doped with Si and Mg may exist intentionally or naturally near the bonding interface between the second layer 415B and the third layer 415C. Since Mg tends to remain in the furnace due to the memory effect, the third layer 415C and the fourth layer 415D may be doped with Mg. However, the Mg concentration of the third layer 415C and the fourth layer 415D needs to be lower than their respective Si concentrations.

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 2 to 25 nm, still more preferably 5 to 20 nm. Further, the thickness of the third layer 415C is preferably thinner than the fourth layer 415D.

As described above, since the second layer 415B and the third layer 415C that form the tunnel junction structure contain In, the band gap becomes small and the tunneling probability becomes high. Note that an additional layer may be provided between the second layer 415B and the third layer 415C within a range where a tunnel junction is formed between the second layer 415B and the third layer 415C. For example, a buffer layer may be provided to suppress Mg in the second layer 415B from diffusing into the third layer 415C.

The fourth layer 415D is a semiconductor layer provided on the third layer 415C. In order to make the second active layer 16 emit light efficiently, 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. There is. This layer also prevents the third layer 415C from reaching and being exposed when forming the second groove 31.

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.

The fourth layer 415D is an n-type semiconductor doped with Si, which is an n-type impurity. For example, if the Si concentration is 1×10 ¹⁷ to 1×10 ²⁰ cm ⁻³ , preferably 1×10 ¹⁸ to 1×10 ¹⁹ cm ⁻³ , more preferably 2×10 ¹⁸ to 8×10 ¹⁸ cm ^{−3 ,} It's okay. The Si concentration of the third layer 415C is higher than the impurity concentration of the fourth layer 415D.

The thickness of the fourth layer 415D is preferably 10 to 500 nm. If it is thicker than 500 nm, the surface of the first intermediate layer 415 may become rough. Moreover, if it is thinner than 10 nm, there is a possibility that the luminous efficiency of the second active layer 16 cannot be sufficiently increased. Furthermore, 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 10 to 200 nm, still more preferably 10 to 100 nm. The thickness of the fourth layer 415D may be different from the thickness of the first layer 415A.

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 similar to the electron block layers 21A to 21C, except that it is not a regrown layer but is grown continuously on the second active layer 16.

The second intermediate layer 417 has a structure in which a first layer 417A, a second layer 417B, a third layer 417C, and a fourth layer 417D are laminated in order from the second active layer 16 side. The fourth layer 417D is exposed. The second layer 417B and the third layer 417C form a tunnel junction structure. In this way, the second intermediate layer 417 has a tunnel junction function in addition to the same function as the second intermediate layer 17 of the first embodiment.

The first layer 417A, second layer 417B, third layer 417C, and fourth layer 417D are the same as the first layer 415A, second layer 415B, third layer 415C, and fourth layer 415D of the first intermediate layer 415, respectively. be. A tunnel junction structure is formed by stacking the second layer 417B and the third layer 417C, and current flows from the n-type third layer 417C to the p-type second layer 417B by the tunnel effect, and holes are transferred to the second active layer. 16.

Since all the layers of the first intermediate layer 415 and the second intermediate layer 417 are made of InGaN, the same effects as the first intermediate layer 15 and the second intermediate layer 17 of the first embodiment can be obtained. In other words, surface flatness can be improved and lattice distortion can be alleviated.

The average In composition of the first intermediate layer 415 and the average In composition of the second intermediate layer 417 may be different. The average In composition of the second intermediate layer 417 is preferably higher than the average In composition of the first intermediate layer 415.

The electron block layer 421A is a p-type layer provided on the third active layer 18. The electron block layer 421A is similar to the electron block layers 21A to 21C, except that it is grown continuously on the third active layer 18 instead of being a regrown layer.

The p layer 422 is a layer provided on the electron block layer 421A. P layer 422 is similar to p layer 22A, except that it is grown continuously on electron block layer 421A rather than on a regrown layer.

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

The first electrode 424B is provided on the fourth layer 417D of the second intermediate layer 417 exposed at the bottom of the third groove 32. Further, the second electrode 424C is provided on the fourth layer 415D of the first intermediate layer 415 exposed on the bottom surface of the second groove 31. The first electrode 424B and the second electrode 424C serve as an anode electrode and a cathode electrode. The first electrode 424B and the second electrode 424C may be made of any material that can make ohmic contact with n-type InGaN; for example, Ti/Al can be used. It may be made of the same material as the n-electrode 23.

Note that in the light emitting device 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. Further, 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 luminous efficiency can be suppressed.

Various other modifications described in the first to third embodiments can also be applied to the fourth embodiment. For example, the first embodiment and the fourth embodiment may be combined as follows. In the fourth embodiment, the second intermediate layer 417 has a tunnel junction structure as it is, and the first intermediate layer 415 is replaced with the first intermediate layer 15 of the first embodiment and is a regrown layer as in the first embodiment. 20C, an electronic block layer 21C, and a p-layer 22C may be provided.

Such a configuration has the following advantages. The blue-emitting first active layer 14 has a high luminous efficiency, so even if the luminous efficiency decreases due to regrowth, there is no problem. On the other hand, the second active layer 16 that emits green light has low luminous efficiency, and it is desired to avoid a decrease in luminous efficiency due to regrowth as much as possible. Therefore, if the blue light emitting element region is formed by trench formation and regrowth as in the first embodiment, and the green light emitting element region is formed using a tunnel junction structure as in the fourth embodiment, the blue, Variations in luminous efficiency for green and red can be reduced.

The operation of the light emitting element of the fourth embodiment will be explained. 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. Further, by applying a voltage between the first electrode 424B and the second electrode 424C, the second active layer 16 can emit green light. Further, by applying a voltage between the second electrode 424C and the n-electrode 23, blue light can be caused to be emitted from the first active layer 14.

Furthermore, two or more of blue, green, and red can be emitted at the same time. Specifically, voltage is applied as follows. When emitting all blue, green, and red light, a voltage is applied between the p-electrode 24A and the n-electrode 23. When emitting green and red light at the same time, a voltage is applied between the p-electrode 24A and the second electrode 424C. When emitting blue and green light at the same time, a voltage is applied between the first electrode 424B and the n-electrode 23. When emitting blue and red light simultaneously, a voltage is applied between the p-electrode 24A and the first electrode 424B and between the second electrode 424C and the n-electrode 23.

In this manner, the light emitting element of the fourth embodiment can control blue, green, and red light emission by selecting the electrode to which voltage is applied, and can be used as one pixel of a display.

FIG. 21 shows an equivalent circuit of the light emitting element of the fourth embodiment. The light emitting element of the fourth embodiment has a red LED, a first tunnel junction (tunnel diode in reverse order), a green LED, a second tunnel junction, and a blue LED connected in cascade, and a connection between the red LED and the first tunnel junction. This is equivalent to a configuration in which the electrode is drawn out from the connecting portion of the green LED and the second tunnel junction. Similarly to the light emitting element of the first embodiment, the light emitting element of the fourth embodiment has a structure in which blue, green, and red LEDs are formed in one element, and full color light emission can be achieved with one element. Can be done.

Next, the manufacturing process of the light emitting device of the fourth embodiment will be explained.

First, similarly to the first embodiment, the substrate 10 is prepared and heat treated. After that, on the substrate 10, a buffer layer, an n-layer 11, an ESD layer 12, a base layer 13, a first active layer 14, an electron block layer 421C, a first intermediate layer 415, a second active layer 16, an electron block layer 421B, The second intermediate layer 417, the third active layer 18, the electron block layer 421A, and the p layer 422 are formed in this order by MOCVD.

Here, the growth temperature of the first intermediate layer 415 and the second intermediate layer 417 is in the same range as that of the first intermediate layer 15 and the second intermediate layer 17 of the first embodiment. The growth temperature of the second intermediate layer 417 is preferably lower than the growth temperature 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 influence of distortion at the interface is greater.

Further, in forming the first intermediate layer 415, the growth temperature of the second layer 415B and the third layer 415C is preferably lower than the growth temperature of the first layer 415A and the fourth layer 415D. This is to improve crystallinity and further enhance the tunnel effect in the tunnel junction. Also, in forming the second intermediate layer 417, it is preferable that the growth temperature of the second layer 417B and the third layer 417C be lower than the growth temperature of the first layer 417A and the fourth layer 417D.

Next, a part 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, and then until it reaches the fourth layer 415D of the first intermediate layer 415. A second groove 31 is formed by dry etching, and a first groove 30 is formed by dry etching until the n layer 11 is reached.

Next, the n-electrode 23 is formed on the n-layer 11 exposed at the bottom of the first groove 30, the p-electrode 24A is formed on the p-layer 422, the first electrode 424B is formed on the bottom of the third groove 32, and the A second electrode 424C is formed on the bottom surface. When 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 device of the fourth embodiment is manufactured through the above steps.

As described above, in the light emitting device according to the fourth embodiment, by providing the tunnel junction structure in the first intermediate layer 415 and the second intermediate layer 417, there is no need to provide an electron block layer or a p-layer regrowth layer. Since etching damage, impurity contamination due to exposure to the atmosphere, and thermal damage due to regrowth occur at the regrowth interface, the presence of the regrowth interface between pn may deteriorate device characteristics. However, since the light emitting device of the fourth embodiment does not have a regrown layer and there is no regrown interface between p and n, such a problem does not occur.

In the first to fourth embodiments, InGaN is used as the well layer in the third active layer 18 and the quantum well structure layer 318C of the third active layer 318. You can also use In this case as well, red light can be emitted, and the emission wavelength is approximately 620 nm. When Eu-doped GaN is used, strain relief of the active layer is not required, so the first strain relief layer 318A and the second strain relief layer 318B, such as the third active layer 318, may not be provided. When Eu-doped GaN is used for the well layer, the barrier layer is, for example, AlGaN.

Similarly, Pr (praseodymium) doped Group III nitride semiconductors, in particular GaN, may be used. It can be used as a red light emitting material.

Further, as well layers in the second active layer 16 and the quantum well structure layer 316B of the second active layer 316, a Tb (terbium)-doped group III nitride semiconductor, particularly GaN, can also be used. In this case as well, green light can be emitted.

Further, as the well layer in the first active layer 14, a Tm (thulium)-doped group III nitride semiconductor, particularly GaN, can also be used. In this case as well, blue light can be emitted.

(Fifth embodiment)
FIG. 22 is a diagram showing the configuration of a light emitting element in the fifth embodiment, and is a sectional view taken in 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 FIG. It has a p layer 522, an n electrode 523, and a p electrode 524.

The substrate 510, the n-layer 511, and the base layer 513 are the same as the substrate 10, the n-layer 11, and the base layer 13 in the first embodiment, respectively. Furthermore, the ESD layer 12 may be provided between the n-layer 511 and the base layer 513.

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 one in which n-type InGaN and n-type GaN are alternately stacked, and the number of pairs is, for example, 3 to 30. The Si concentration is, for example, 1×10 ¹⁷ to 1×10 ¹⁹ cm ⁻³ . The Si concentration of the high concentration n-type GaN layer on the superlattice structure layer is preferably 1×10 ¹⁸ to 1×10 ¹⁹ cm ⁻³ . Further, it is preferable that the high concentration n-type GaN layer be in contact with the active layer 518.

Active layer 518 is a layer provided on 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 an SQW or MQW quantum well structure layer 518C are laminated in this order.

The first strain relief layer 518A and the second strain relief layer 518B are the same as the first strain relief layer 318A and the second strain relief layer 318B in the third active layer 318 of the third embodiment, respectively. Similarly 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 stacked thereon can be reduced in stages. can be effectively alleviated. 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 are made of SQW.

Various modifications of the first strain relief layer 318A and the second strain relief layer 318B in the third embodiment can be similarly applied to the first strain relief layer 518A and the second strain relief layer 518B.

The quantum well structure layer 518C is a light emitting layer with an SQW or MQW structure provided on the second strain relaxation layer 518B. The emission wavelength is yellow to red and 560 to 700 nm. The third active layer 18 has a structure in which one to seven pairs of well layers made of InGaN and barrier layers made of InGaN having an In composition lower than that of the well layers are laminated alternately. More preferably 1 to 5 pairs, still more preferably 1 to 3 pairs. Further, it is preferably equal to or less than the number of pairs in the second active layer 16, and more preferably less. The most preferred is SQW. The well layer of the quantum well structure layer 518C is InGaN with an In composition of 35% or more.

The electron block layer 521 is a layer provided on the active layer 518. The electronic block layer 521 is similar to the electronic block layer 421A of the fourth embodiment.

The p layer 522 is a layer provided on the electron block layer 521. The p layer 522 is similar to the p layer 422 of the fourth embodiment.

A portion of the p layer 522 is etched to provide a groove reaching the n layer 11, and an 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. Furthermore, a p-electrode 524 is provided on the p-layer 522. The material of p-electrode 524 is the same as that of p-electrodes 24A to 24C.

Next, the manufacturing process of the light emitting device of the fifth embodiment will be explained.

First, similarly to the first embodiment, the substrate 10 is prepared and heat treated. Thereafter, a buffer layer, an n-layer 11, a base layer 13, an active layer 518, an electron block layer 521, and a p-layer 522 are sequentially formed on the substrate 10 by MOCVD. A method for forming the quantum well structure layer 518C will be described in detail later. Note that the raw material gases used in the MOCVD method are, for example, as follows. TMG (trimethyl gallium) or TEG (triethyl gallium) for Ga source gas, TMI (trimethyl indium) for In source gas, TMA (trimethyl aluminum) for Al source gas, ammonia for N source gas, and Si dopant gas. is silane, bis(cyclopentadienyl)magnesium is used as the Mg dopant gas, and hydrogen or nitrogen is used as the carrier gas.

The growth temperature of the electron block 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 suppress a decrease in luminous efficiency. The lower limit of the growth temperature is, for example, 600°C. More preferably it is 650 to 900°C. Further, it is preferable that the growth temperature of the p layer 522 is higher than the growth temperature of the electron block layer 521.

Next, a predetermined region of the p layer 522 is dry etched to form a groove reaching the n layer 11, and an n electrode 523 is formed on the bottom of the groove and a p electrode 524 is formed on the p layer 522. The light emitting device according to the fifth embodiment is manufactured through the above steps.

Next, a 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 has been difficult to obtain a high-quality crystal. The inventors conducted intensive research and development to obtain high-quality InGaN with an In composition of 35% or more, and discovered a method for obtaining high-quality InGaN. The method will be explained below.

The growth temperature of the quantum well structure layer 518C is 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.), decomposition and re-evaporation of InN can be suppressed, and InGaN with a high In composition (particularly an In composition of 35% or more) can be formed. The temperature is preferably 650°C or lower, more preferably 610 to 650°C, even more preferably 620 to 640°C, and most preferably 625 to 635°C.

The growth rate of the quantum well structure layer 518C is set to 0.8 nm/min or less. This is to suppress surface roughness, abnormal growth, and droplets due to insufficient migration of raw material atoms at low growth temperatures. A droplet is a lump of In formed on a crystal surface. Preferably it is 0.75 nm/min or less, more preferably 0.7 nm/min or less, still more preferably 0.5 nm/min or less. The lower limit of the growth rate is not particularly limited, but if the growth rate is too slow, it will take time to form the quantum well structure layer 518C, so it is preferably 0.05 nm/min or more.

The In solid phase ratio/In gas phase ratio is set to 0.75 to 1. Here, the In gas phase ratio is the molar ratio of In to the entire group III metal in the raw material gas when forming InGaN. In addition, the In solid phase ratio is the molar ratio of In to the entire group III metal in the formed InGaN crystal. The In solid phase ratio/In gas phase ratio can be controlled by the growth temperature, In gas phase ratio, VIII ratio, and the like. By setting the In solid phase ratio/In gas phase ratio within such a range, abnormal growth and droplets of InGaN can be suppressed. A more preferable In solid phase ratio/In gas phase ratio is 0.85 to 1, and even more preferably 0.9 to 1.

By setting the growth temperature, growth rate, and In solid phase ratio/In gas phase ratio within the above ranges, a high quality crystal can be obtained even if the InGaN has an In composition of 35% or more. As mentioned above, since the growth temperature is low at 700°C or less, the decomposition efficiency of ammonia is low, and migration of raw material atoms is difficult to occur, making it difficult to obtain high-quality InGaN. Such a problem can be solved by setting the value within the range, and high quality InGaN can be obtained.

The In gas phase ratio is preferably 40% or more. It becomes easy to control the In solid phase ratio/In gas phase ratio within the above range, and abnormal growth and droplets of InGaN can be suppressed. Further, the In gas phase ratio is preferably 55% or less.

The partial pressure of the Ga source gas is preferably 1×10 ⁻⁶ to 3×10 ⁻⁶ atm, and the partial pressure of the In source gas is preferably 1×10 ⁻⁶ to 3×10 ⁻⁶ atm. This is to suppress abnormal growth of InGaN and stabilize the growth rate. The Ga source gas is, for example, TMG (trimethyl gallium) or TEG (triethyl gallium), and the In source gas is, for example, TMI (trimethyl indium).

The growth rate of the barrier layer of the quantum well structure layer 518C is preferably equal to or faster than the growth rate of the well layer of the quantum well structure layer 518C. Further, the growth temperature of the barrier layer of the quantum well structure layer 518C is preferably equal to or higher than the growth temperature of the well layer of the quantum well structure layer 518C. When increasing the temperature, it is preferable to form a first barrier layer with a thickness of 2 to 20 nm at the same temperature as the growth temperature of the well layer, and then laminate the second barrier layer at a higher temperature. By doing so, it is possible to prevent the well layer having a high In composition from being thermally decomposed during temperature rise. The first barrier layer and the second barrier layer may be made of InGaN having a lower In composition than the well layer. Of course, it may be GaN, AlGaN, AlGaInN, or a combination thereof.

The partial pressure of the N source gas is preferably 0.15 to 0.2 atm. Decomposition and re-evaporation of InN due to H ₂ generated by decomposition of ammonia can be suppressed, and the quality of InGaN can be improved. Note that the carrier gas nitrogen is not an N source gas.

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

The growth temperature of the quantum well structure layer 518C is preferably lower than the growth temperature 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. Further, the growth temperature of the second strain relaxation layer 518B is preferably lower than the growth temperature of the first strain relaxation layer 518A.

The growth rate of the quantum well structure layer 518C is preferably slower than the growth rate of the first strain relaxation layer 518A and the second strain relaxation layer 518B. The quantum well structure layer 518C can be formed with higher quality. Further, it is preferable that the growth rate of the second strain relief layer 518B is slower than the growth rate of the first strain relief layer 518A.

The In vapor phase ratio when forming the quantum well structure layer 518C is preferably smaller than the In vapor phase ratio when forming the first strain relaxation layer 518A and the second strain relaxation layer 518B. The quantum well structure layer 518C can be formed with higher quality.

As described above, according to the fifth embodiment, a high-quality crystal of InGaN with an In composition of 35% or more can be obtained, and in particular, InGaN that is a red light-emitting material with an In composition of 40% or more can be formed. 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 that emits red light with high luminous efficiency can be realized.

(Variation of the fifth embodiment)
The active layer 518 of the light emitting device in the fifth embodiment can also be used as the third active layer 18, 318 of the light emitting device in the first to fourth embodiments.

Furthermore, the method for forming InGaN in the fifth embodiment can be used not only for light emitting devices but also for InGaN for solar cells, photocatalysts, and the like.

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

Next, experimental results regarding the fifth embodiment will be explained.

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

FIG. 23 is an AFM image of the well layer surface of the quantum well structure layer 518C when the growth rate is changed. This is the surface of an InGaN layer having the same thickness of 2 to 3 nm as the actual well layer. FIG. 23A shows the case where the growth rate is 0.48 nm/min, FIG. 23B shows the case where the growth rate is 0.72 nm/min, and FIG. 23C shows the case where the growth rate is 0.96 nm/min.

As shown in FIG. 23(a), when the growth rate is 0.48 nm/min, few droplets are observed on the well layer surface, the droplet density is 1×10 ⁷ cm ⁻² , and the droplet diameter is approximately It was 30 nm.

Furthermore, as shown in FIG. 23(b), when the growth rate is 0.72 nm/min, more droplets are seen on the well layer surface than when the growth rate is 0.48 nm/min, and the droplet density is 1×10 ⁸ cm ⁻² and the droplet diameter was approximately 30 nm.

Furthermore, as shown in FIG. 23(c), when the growth rate is 0.96 nm/min, more droplets are seen on the well layer surface than when the growth rate is 0.72 nm/min, and their size is also larger. The droplet density was 4×10 ⁸ cm ⁻² and the droplet diameter was approximately 50 nm.

From this result, it was found that in order to reduce droplets, the growth rate of InGaN is preferably 0.75 nm/min or less, and more preferably 0.5 nm/min.

(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. Further, the VIII ratio was set to 40000, 40000, 48000, and 51000, and the In gas phase ratio was set to 57%, 52.5%, 47.5%, and 45%, respectively. The In solid phase ratios were all 42.0%, and the In solid phase ratios/In gas phase ratios were 73.7%, 80.0%, 88.4%, and 93.3%, respectively.

FIG. 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 where the In solid phase ratio/In gas phase ratio is 73.7%, (b) is 80.0%, (c) is 88.4%, and (d) is 93.3%. .

As shown in FIG. 24(a), when the In solid phase ratio/In gas phase ratio is 73.7%, many droplets are seen on the surface of the well layer, their size is large, and the droplet density is 7.7%. 5×10 ⁷ cm ⁻² and the droplet diameter was approximately 130 nm.

Further, as shown in FIG. 24(b), when the In solid phase ratio/In gas phase ratio was 80.0%, there were fewer droplets on the well layer surface than when the droplets were 73.7%, and their sizes were smaller. The droplet density was 5.0×10 ⁷ cm ⁻² and the droplet diameter was approximately 80 nm.

Furthermore, as shown in Fig. 24(c), when the In solid phase ratio/In gas phase ratio was 88.4%, there were fewer droplets on the well layer surface than when the ratio was 80.0%, and the size was smaller. . The droplet density was 1.0×10 ⁷ cm ⁻² and the droplet diameter was approximately 30 nm.

Further, as shown in FIG. 24(d), when the In solid phase ratio/In gas phase ratio was 93.3%, no droplets were observed on the surface of the well layer.

From this result, it was found that the In solid phase ratio/In gas phase ratio is preferably 0.75 or more, more preferably 0.85 or more, and even more preferably 0.9 or more.

(Experiment 6)
A quantum well structure layer 518C was formed by changing the partial pressure of ammonia. The growth temperature was 637°C. In addition, the flow rate of the carrier gas (nitrogen) was set to three levels: 142 slm, 130 slm, and 110 slm, and the flow rate of ammonia was set to 15 slm, 27 slm, and 47 slm, respectively, and the partial pressure of ammonia was set to 0.096 atm, 0.172 atm, and 0.299 atm. And so. Further, the VIII ratios were respectively set to 27,000, 48,000, and 85,000, and the In gas phase ratios were all set to 47.5%. The growth rate was 0.48 nm/min in both cases, the In solid phase ratio was 40%, 42%, and 40%, respectively, and the In solid phase ratio/In gas phase ratio was 84.2%, 88.4%, respectively. It was 84.2%.

FIG. 25 is an AFM image of the well layer surface of the quantum well structure layer 518C when the partial pressure of ammonia is changed. FIG. 25(a) shows the case where the partial pressure of ammonia is 0.096 atm, (b) is 0.172 atm, and (c) is 0.299 atm.

As shown in FIG. 25(a), when the partial pressure of ammonia was 0.096 atm, droplets were observed on the surface of the well layer. The droplet density was 5.0×10 ⁷ cm ⁻² and the droplet diameter was approximately 50 nm.

Furthermore, as shown in Fig. 25(b), when the partial pressure of ammonia was 0.172 atm, droplets were observed on the surface of the well layer, but they were smaller and smaller than when the partial pressure of ammonia was 0.096 atm. It was small. The droplet density was 1.0×10 ⁷ cm ⁻² and the droplet diameter was approximately 30 nm.

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

From this result, it was found that the partial pressure of ammonia is preferably 0.15 to 0.2 atm. Further, it was found that the VIII ratio is preferably 30,000 to 80,000.

The light emitting element of the present invention can be applied to full color displays and the like.

10: Substrate 11: N layer 12: ESD layer 13: Base layer 14: First active layer 15, 215, 415: First intermediate layer 16, 316: Second active layer 17, 217, 417: Second intermediate layer 18 , 318: Third active layer 19: Protective layer 20A to 20C: Regrowth layer 21A to 21C, 421A to C, 521: Electronic block layer 22A to 22C, 522: P layer 23: N electrode 24A to 24C: P electrode 215A , 217A: Non-doped 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 (19)

In a light emitting device made of a group III nitride semiconductor,
an n layer made of an n-type group III nitride semiconductor;
a first active layer provided on the n-layer and having a predetermined emission wavelength;
an intermediate layer provided on the first active layer and made of a group III nitride semiconductor containing In;
a second active layer provided on the intermediate layer and having an emission wavelength different from that of the first active layer;
has
The intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer. a groove reaching the intermediate layer from the second active layer side;
a first p layer provided on the second active layer and made of a p-type group III nitride semiconductor;
a second p layer made of a p-type group III nitride semiconductor, provided on the intermediate layer exposed at the bottom surface of the groove;
a first p-electrode provided on the first p-layer;
a second p-electrode provided on the second p-layer;
The light emitting device according to claim 1, comprising: The intermediate layer 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 laminated in order from the first active layer side. have,
The p-type impurity concentration of the second layer is higher than the p-type impurity concentration of the first layer, and the n-type impurity concentration of the third layer is higher than the n-type impurity concentration of the fourth layer. and the third layer form a tunnel junction structure,
a p layer provided on the second active layer;
a groove reaching the fourth layer from the p-layer side;
a p-electrode provided on the p-layer;
an electrode provided on the fourth layer exposed on the bottom surface of the groove;
The light emitting device according to claim 1, comprising: 4. The light emitting device according to claim 3, wherein the In compositions of the second layer and the third layer are higher than the In compositions of the first layer and the fourth layer. 5. The light emitting device according to claim 3, wherein the second layer has a higher In composition than the third layer. 4. The light emitting device according to claim 3, wherein the second layer has a thickness thinner than the first layer, and the third layer has a thickness thinner than the fourth layer. The light emitting device according to claim 1, wherein the intermediate layer is InGaN. The light emitting device according to claim 1, wherein the intermediate layer has an In composition of 10% or less. The light emitting device according to claim 1, wherein the intermediate layer is In-doped GaN. In a method for manufacturing a light emitting device made of a group III nitride semiconductor,
forming an n layer made of an n-type group III nitride semiconductor;
forming a first active layer with 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;
forming a second active layer having an emission wavelength different from that of the first active layer on the intermediate layer;
has
The intermediate layer has an In composition set so as to have a band gap that does not absorb light emitted from the first active layer and the second active layer.
A method for manufacturing a light emitting element, characterized by: forming a groove reaching the intermediate layer from the second active layer side;
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 at the bottom surface of the trench, respectively;
11. The method for manufacturing a light emitting device according to claim 10, comprising the step of forming a first p electrode and a second p electrode on the first p layer and the second p layer, respectively. The intermediate layer is formed by laminating, 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 p-type impurity concentration of the second layer is higher than the p-type impurity concentration of the first layer, the n-type impurity concentration of the third layer is higher than the n-type impurity concentration of the fourth layer, and layer and the third layer form a tunnel junction structure;
forming a p-layer on the second active layer;
forming a groove reaching the fourth layer from the p-layer side;
forming a p-electrode on the p-layer;
forming an electrode on the fourth layer exposed at the bottom of the groove;
The method for manufacturing a light emitting device according to claim 10. 13. The method for manufacturing a light emitting device according to claim 12, wherein the In composition of the second layer and the third layer is higher than the In composition of the first layer and the fourth layer. The method for manufacturing a light emitting device according to claim 12 or 13, wherein the In composition of the second layer is higher than the In composition of the third layer. 13. The method of manufacturing a light emitting device according to claim 12, wherein the second layer is thinner than the first layer, and the third layer is thinner than the fourth layer. 13. The method for manufacturing a light emitting device according to claim 12, wherein the growth temperature of the second layer and the third layer is lower than the growth temperature of the first layer and the fourth layer. 13. The method for manufacturing a light emitting device according to claim 10, wherein the intermediate layer has an In composition of 10% or less. 13. The method for manufacturing a light emitting device according to claim 10, wherein the intermediate layer is made of InGaN. 13. The method for manufacturing a light emitting device according to claim 10, wherein the intermediate layer is made of GaN doped with In.