Method for controlling the light emission color of a light-emitting element, light-emitting device

Abstract

This invention provides a method for controlling the emission color of a light-emitting element that can expand the color gamut. [Solution] The light-emitting element includes an n-type layer, a first active layer formed on the n-type layer, an intermediate layer formed on the first active layer, a second active layer formed in a part of the intermediate layer, a first p-type layer formed on the second active layer, and a second p-type layer formed in a region of the intermediate layer where the second active layer is not formed. The first active layer emits light at a first wavelength, and the second active layer emits light at a second wavelength longer than the first wavelength when a predetermined first current is injected, and emits light at a third wavelength longer than the first wavelength and shorter than the second wavelength when a second current larger than the first current is injected. By controlling the current injected into the second active layer between the first and second currents, the emission wavelength of the second active layer can be controlled to any wavelength from the second to the third wavelength.

Description

Technical Field

[0001] The present invention relates to a method for controlling the emission color of a light-emitting element and a light-emitting device.

Background Art

[0002] In recent years, higher definition of displays has been demanded, and micro-LED displays in which one pixel is a fine LED on the order of 1 to 100 μm have attracted attention. Patent Document 1 describes a monolithic type micro-LED display element capable of emitting red, green, and blue colors individually with one element. Further, Patent Document 1 describes a structure in which three active layers that emit blue, green, and red colors are sequentially stacked on the same substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, full-color of three primary colors, red, green, and blue, can be realized with one element. However, there has been a desire to further expand the color gamut and improve color reproducibility. For example, there has been a desire to further add yellow emission. In Patent Document 1, it is also conceivable to further increase one yellow light-emitting layer and use four primary colors of red, yellow, green, and blue. However, since the number of crystal growth layers increases and the number of etching times also increases, the yield decreases and the cost increases.

[0005] The present invention has been made in view of such a background, and aims to provide a method for controlling the emission color of a light-emitting element and a light-emitting device capable of expanding the color gamut.

Means for Solving the Problems

[0006] One aspect of the present invention is, A method for controlling the light emission color of a light-emitting element, The light-emitting element is An n-type layer made of an n-type group III nitride semiconductor, A first active layer made of a group III nitride semiconductor formed on the n-type layer, An intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, A second active layer made of a group III nitride semiconductor formed in a part region on the aforementioned intermediate layer, A first p-type layer is formed on the second active layer and is made of a p-type group III nitride semiconductor, A second p-type layer is formed on the intermediate layer in a region where the second active layer is not formed, and is made of a p-type group III nitride semiconductor. The first active layer emits light at a first wavelength, When a predetermined first current is injected into the second active layer, it emits light at a second wavelength longer than the first wavelength, and when a second current greater than the first current is injected, it emits light at a third wavelength longer than the first wavelength and shorter than the second wavelength. The present invention relates to a method for controlling the emission color of a light-emitting element, wherein the emission wavelength of the second active layer is controlled to any wavelength from the second wavelength to the third wavelength by controlling the current injected into the second active layer between the first current amount and the second current amount.

[0007] Other aspects of the present invention include: Light-emitting element and The device includes a control device for controlling the light-emitting color of the light-emitting element, The light-emitting element is An n-type layer made of an n-type group III nitride semiconductor, A first active layer made of a group III nitride semiconductor formed on the n-type layer, An intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, A second active layer made of a group III nitride semiconductor formed in a part region on the aforementioned intermediate layer, A first p-type layer is formed on the second active layer and is made of a p-type group III nitride semiconductor, A second p-type layer is formed on the intermediate layer in a region where the second active layer is not formed, and is made of a p-type group III nitride semiconductor. The first active layer is configured to emit light at a first wavelength. The second active layer is configured to emit light at a second wavelength longer than the first wavelength when a predetermined first current is injected, and to emit light at a third wavelength longer than the first wavelength and shorter than the second wavelength when a second current greater than the first current is injected. The control device is a light-emitting device having a current control unit that controls the emission wavelength of the second active layer to any wavelength from the second wavelength to the third wavelength by controlling the current injected into the second active layer between the first current amount and the second current amount. [Effects of the Invention]

[0008] In the above embodiment, the amount of current injected into the second active layer can be used to selectively emit light at any wavelength from the second to the third wavelength. Therefore, the color gamut of the light-emitting element can be expanded.

[0009] As described above, according to the above embodiment, it is possible to provide a method for controlling emitted color and a light-emitting device that can expand the color gamut. [Brief explanation of the drawing]

[0010] [Figure 1] A block diagram showing the configuration of the light-emitting device in the first embodiment. [Figure 2] A cross-sectional view showing the configuration of the light-emitting element 1 in the first embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Figure 3] A cross-sectional view showing the structure of the third active layer, with the cross-section perpendicular to the main surface of the substrate. [Figure 4] A diagram showing the energy at the lower end of the conduction band and the In composition in the band diagrams of the second strain relaxation layer, well layer, composition gradient layer, and first barrier layer. [Figure 5]A diagram showing the equivalent circuit of a light-emitting element. [Figure 6] A diagram showing how the band structure changes with current value. [Figure 7] A figure showing the change in the emission spectrum with respect to the current value. [Figure 8] A flowchart illustrating the manufacturing process of a light-emitting element. [Figure 9] A cross-sectional view showing the structure at each manufacturing stage of a light-emitting element, with the cross-sectional view being perpendicular to the main surface of the substrate. [Figure 10] A cross-sectional view showing the structure at each manufacturing stage of a light-emitting element, with the cross-sectional view being perpendicular to the main surface of the substrate. [Figure 11] A cross-sectional view showing the structure at each manufacturing stage of a light-emitting element, with the cross-sectional view being perpendicular to the main surface of the substrate. [Figure 12] A cross-sectional view showing the structure at each manufacturing stage of a light-emitting element, with the cross-sectional view being perpendicular to the main surface of the substrate. [Figure 13] A graph showing the emission spectrum of the third active layer of the light-emitting element. [Figure 14] This graph shows the relationship between the current density of the current injected into the third active layer of the light-emitting element and the peak wavelength of the emission from the third active layer. [Figure 15] This graph shows the relationship between the current density of the current injected into the third active layer of the light-emitting element and the full width at half maximum of the emission spectrum of the third active layer. [Figure 16] A cross-sectional view showing the configuration of a light-emitting element in the second embodiment, wherein the cross-sectional view is perpendicular to the main surface of the substrate. [Modes for carrying out the invention]

[0011] The method for controlling the emission color of a light-emitting element is as follows: The light-emitting element comprises an n-type layer made of an n-type group III nitride semiconductor, a first active layer made of a group III nitride semiconductor formed on the n-type layer, an intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, a second active layer made of a group III nitride semiconductor formed in a part of the intermediate layer, a first p-type layer made of a p-type group III nitride semiconductor formed on the second active layer, and a layer formed in a region on the intermediate layer where the second active layer is not formed. The device comprises a second p-type layer made of a p-type group III nitride semiconductor, wherein the first active layer emits light at a first wavelength, the second active layer emits light at a second wavelength longer than the first wavelength when a predetermined first current is injected, and emits light at a third wavelength longer than the first wavelength and shorter than the second wavelength when a second current greater than the first current is injected, and the emission wavelength of the second active layer can be controlled to any wavelength from the second to the third wavelength by controlling the current injected into the second active layer between the first and second currents.

[0012] In a method for controlling the emission color of a light-emitting element, the difference between the second and third wavelengths may be 20 nm or more. This allows for a wider color gamut.

[0013] In a method for controlling the emission color of a light-emitting element, the second wavelength may be red, and the third wavelength may be yellow. This allows for a wider color gamut.

[0014] In a method for controlling the emission color of a light-emitting element, the thickness of the well layer of the second active layer may be between 3.5 nm and 7.0 nm. Within this range, it becomes easy to shift the wavelength from red to yellow.

[0015] In a method for controlling the emission color of a light-emitting element, the emission intensity of the second active layer may be controlled by PWM control of the current injected into the second active layer. Changing the amount of current injected into the second active layer also changes the emission intensity, but the emission intensity can be controlled by PWM control.

[0016] The light-emitting device comprises a light-emitting element and a control device for controlling the light-emitting color of the light-emitting element. The light-emitting element comprises an n-type layer made of an n-type group III nitride semiconductor, a first active layer made of a group III nitride semiconductor formed on the n-type layer, an intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, a second active layer made of a group III nitride semiconductor formed in a part of the intermediate layer, a first p-type layer made of a p-type group III nitride semiconductor formed on the second active layer, and a p-type III The device comprises a second p-type layer made of a pharmaconitride semiconductor, wherein the first active layer is set to emit light at a first wavelength, the second active layer is set to emit light at a second wavelength longer than the first wavelength when a predetermined first current is injected, and to emit light at a third wavelength longer than the first wavelength and shorter than the second wavelength when a second current greater than the first current is injected, and the control device has a current control unit that controls the emission wavelength of the second active layer to any wavelength from the second to the third wavelength by controlling the current injected into the second active layer between the first and second currents.

[0017] In a light-emitting device, the difference between the second and third wavelengths may be 20 nm or more. This allows for a wider color gamut.

[0018] In a light-emitting device, the second wavelength may be red, and the third wavelength may be yellow. This allows for a wider color gamut.

[0019] In the light-emitting device, the thickness of the well layer of the second active layer may be between 3.5 nm and 7.0 nm. Within this range, it becomes easy to shift the wavelength from red to yellow.

[0020] In a light-emitting device, the control device may have a PWM circuit that controls the light emission intensity of the second active layer by controlling the current injected into the second active layer using PWM control. Changing the amount of current injected into the second active layer also changes the light emission intensity, but the light emission intensity can be controlled by PWM control.

[0021] (First Embodiment) 1. Configuration of the light-emitting device Figure 1 is a block diagram showing the configuration of the light-emitting device in the first embodiment. As shown in Figure 1, the light-emitting device in the first embodiment includes a light-emitting element 1 and a control device 2.

[0022] Figure 2 is a cross-sectional view showing the configuration of the light-emitting element 1, and is a cross-sectional view perpendicular to the main surface of the substrate. The light-emitting element 1 is capable of emitting blue, green, and yellow-to-red light. Yellow-to-red means that the emission wavelength can be selected between yellow and red. The light-emitting element 1 is a flip-chip type that extracts light from the back side of the substrate and is mounted face-down on a mounting substrate (not shown).

[0023] Furthermore, the light-emitting element 1 may be a monolithic micro-LED display element. That is, the three subpixels of blue, green, and yellow-to-red in the first embodiment may be considered as one pixel, and the structure of such one pixel may be arranged in a matrix on the same substrate. This structure makes it possible to realize a display on a single chip. In this case, the size of the subpixel is, for example, 1 to 100 μm.

[0024] Furthermore, the light-emitting element 1 may have a structure where each pixel is a single chip.

[0025] The control device 2 is a device that controls the emission color of the light-emitting element 1. Specifically, it is a device that controls the emission of light from each subpixel in one pixel. In particular, the control device 2 can selectively emit light at one wavelength from yellow to red in the yellow to red subpixels. Details of the control will be described later.

[0026] 2. Configuration of light-emitting elements As shown in Figure 1, the light-emitting element 1 in the first embodiment includes a substrate 10, an n-type layer 11, a first active layer 12, a first intermediate layer 13, a second active layer 14, a second intermediate layer 15, a third active layer 16, electron blocking layers 17, 19A to 19C, p-type layers 18, 20A to 20C, an n-side electrode 21, and p-side electrodes 22A to 22C.

[0027] Substrate 10 is a growth substrate for growing Group III nitride semiconductors. Examples include sapphire, Si, GaN, and ScAlMgO4(SAM).

[0028] The n-type layer 11 is an n-type semiconductor provided on the substrate 10 via a low-temperature buffer layer and a high-temperature buffer layer (not shown). However, the buffer layer may be provided only if necessary, and may not be provided if the substrate is GaN, for example. The n-type layer 11 is, for example, n-GaN, n-AlGaN, n-InGaN, etc. The Si concentration is, for example, 1 × 10⁻⁶ 18 ~100×10 18 cm -3 That is the case.

[0029] The first active layer 12 is an SQW or MQW structured light-emitting layer provided on the n-type layer 11. The emission wavelength of the first active layer 12 is blue, ranging from 430 to 480 nm. The first active layer 12 has a structure in which 1 to 9 pairs of barrier layers made of AlGaN and well layers made of InGaN are alternately stacked. More preferably, there are 1 to 7 pairs, and even more preferably, 1 to 5 pairs.

[0030] A base layer may be provided between the n-type layer 11 and the first active layer 12, if necessary. The base layer is a superlattice structure semiconductor layer provided on the n-type layer 11, and is a layer for relaxing the lattice strain of the semiconductor layer formed on the base layer. The base layer is made by alternately stacking two of the group III nitride semiconductor thin films with different compositions (for example, GaN, InGaN, and AlGaN), with the number of pairs being, for example, 3 to 30. It may be undoped, or Si may be 1 × 10⁻¹⁶ 17 ~100×10 17 cm -3 It is acceptable to dope it to a certain extent. Also, it does not need to be a superlattice structure if the strain can be relieved.

[0031] An ESD layer may also be provided between the n-type layer 11 and the underlying layer. The ESD layer is a layer provided for improving the electrostatic breakdown voltage. The ESD layer is, for example, GaN, InGaN, or AlGaN that is undoped or doped with Si at a low concentration.

[0032] The first intermediate layer 13 is a semiconductor layer provided on the first active layer 12. The first intermediate layer 13 is a layer provided to enable individual control of the light emission from the first active layer 12 and the light emission from the second active layer 14. It also has a role of protecting the first active layer 12 from etching damage when forming the second trench 31 described later.

[0033] The first intermediate layer 13 has a structure in which an undoped intermediate layer 13A and an n-type intermediate layer 13B are laminated in order from the side of the first active layer 12. The undoped intermediate layer 12A and the n-type intermediate layer 12B may be made of the same material except for impurities. The reason for forming the first intermediate layer 13 in such a two-layer structure will be described later.

[0034] The material of the first intermediate layer 13 is a group-III nitride semiconductor containing In, and it is preferably InGaN for example. The roughness of the surface of the first intermediate layer 13 can be suppressed by the surfactant effect of In, and the surface flatness can be improved. Also, the lattice strain can be relaxed.

[0035] The In composition of the first intermediate layer 13 (the molar ratio of In in the total group-III metals of the group-III nitride semiconductor) may be set to have a bandgap that does not absorb the light emitted from the first active layer 12 and the second active layer 14. The preferred In composition is 10% or less, more preferably 5% or less, and even more preferably 2% or less. If the In composition is greater than 10%, it will cause the surface of the first intermediate layer 13 to be rough. In is arbitrary as long as it is greater than 0%, and it may be at the doping level (the level at which no mixed crystal is formed). For example, GaN with an In concentration of 1×10 14 cm -3 or more and 1×10 22 cm -3 or less.

[0036] The undoped intermediate layer 13A is undoped, while the n-type intermediate layer 13B is Si-doped. The Si concentration of the n-type intermediate layer 13B is 1 × 10⁻⁶. 17 ~1000×10 17 cm -3 It is preferable to do so. Preferably 10 × 10 17 ~100×10 17 cm -3 More preferably 20 × 10 17 ~80×10 17 cm -3 The n-type intermediate layer 13B may be modulated with Si, and a portion of the n-type intermediate layer 13B may be undoped.

[0037] The thickness of the first intermediate layer 13 is preferably 20 to 150 nm. If it is thicker than 150 nm, it may cause the surface of the first intermediate layer 13 to become rough. If it is thinner than 20 nm, it may become difficult to control the depth of the second groove 31 to be within the undoped intermediate layer 13A when forming the second groove 31 described later. More preferably it is 30 to 100 nm, and even more preferably 50 to 80 nm.

[0038] Furthermore, the thickness of the undoped intermediate layer 13A is preferably 10 nm or more. This is to control the etching depth and avoid etching damage to the first active layer 12. Also, the thickness of the n-type intermediate layer 13B is preferably 10 nm or more. This is to independently control the luminescence characteristics of each active layer.

[0039] The second active layer 14 is a layer provided on the first intermediate layer 13 and has a quantum well structure of SQW or MQW. The emission wavelength of the second active layer 14 is green, ranging from 510 to 570 nm. The quantum well structure consists of 1 to 7 pairs of alternating barrier layers made of GaN or AlGaN and well layers made of InGaN.

[0040] A strain relaxation layer may be provided between the first intermediate layer 13 and the second active layer 14. By providing a strain relaxation layer, the strain of the second active layer 14 stacked on top of it can be relaxed, thereby improving the crystal quality. The strain relaxation layer is an SQW or MQW structure in which a barrier layer and a well layer are stacked in order, and is a quantum well structure in which the thickness of the well layer is adjusted to be thin so as not to emit light. For example, by making the thickness of the well layer 1 nm or less, it is possible to prevent emission. The barrier layer is AlGaN, and the well layer is InGaN. The wavelength corresponding to the band edge energy of the well layer of the strain relaxation layer only needs to be shorter than the emission wavelength of the second active layer 14; for example, if the emission wavelength is 500 to 560 nm, then it is 400 to 460 nm.

[0041] The second intermediate layer 15 is a semiconductor layer provided on the second active layer 14. The second intermediate layer 15 is provided for the same reasons as the first intermediate layer 13, and is a layer provided to allow for individual control of the light emission from the second active layer 14 and the light emission from the third active layer 16. It also serves to protect the second active layer 14 from etching damage when forming the first groove 30, which will be described later.

[0042] The second intermediate layer 15 has a structure in which a non-doped intermediate layer 15A and an n-type intermediate layer 15B are stacked in order from the second active layer 14 side. The non-doped intermediate layer 15A and the n-type intermediate layer 15B have the same structure as the non-doped intermediate layer 13A and the n-type intermediate layer 13B. In other words, the non-doped intermediate layer 15A and the n-type intermediate layer 15B are made of the same material as the non-doped intermediate layer 13A and the n-type intermediate layer 13B, except for impurities, and the thickness range is also the same as the non-doped intermediate layer 13A and the n-type intermediate layer 13B. The non-doped intermediate layer 15A is non-doped, and the n-type intermediate layer 15B is Si-doped.

[0043] The third active layer 16 is a layer provided on the second intermediate layer 15. The emission wavelength of the third active layer 16 can be selected by control by the control device 2, ranging from yellow to red. Yellow is, for example, 570 to 590 nm. Red is, for example, 600 to 750 nm.

[0044] As shown in Figure 3, the third active layer 16 has a structure in which the first strain relaxation layer 16A, the second strain relaxation layer 16B, the well layer 16C, the composition gradient layer 16D, the first barrier layer 16E, the second barrier layer 16F, and the third barrier layer 16G are stacked in order from the second intermediate layer 15 side.

[0045] The first strain relaxation layer 16A is a semiconductor layer provided on the second intermediate layer 15. The first strain relaxation layer 16A is an SQW or MQW structure in which a barrier layer and a well layer are stacked in order, and is a quantum well structure in which the thickness of the well layer is adjusted to be thin so as not to emit light. For example, by making the thickness of the well layer 1 nm or less, it is possible to prevent light emission. The barrier layer is AlGaN, and the well layer is InGaN. The wavelength corresponding to the band edge energy of the well layer of the strain relaxation layer only needs to be shorter than the emission wavelength of the second active layer 14, for example, if the emission wavelength is 500 to 560 nm, then it is 400 to 460 nm. Preferably, it is 40 to 100 nm shorter than the emission wavelength of the second active layer 14.

[0046] The wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 16A may be equal to the emission wavelength of the first active layer 12. In this case, it may be grown at the same growth temperature as the first active layer 12.

[0047] The band edge energy in the well layer of the first strain relaxation layer 16A can be controlled by the thickness of the well layer. That is, by making the thickness of the well layer of the first strain relaxation layer 16A sufficiently thin, the energy of the subbands in the wells increases, and the band edge energy becomes larger. This allows it to be shorter than the emission wavelength of the second active layer 14. The growth temperature of the first strain relaxation layer 16A is arbitrary, but it may be grown at the same growth temperature as the second active layer 14. Furthermore, if the thickness of the well layer of the first strain relaxation layer 16A is reduced, the subbands increase even further, and the energy difference with the barrier layer decreases. That is, it approaches the band edge energy of the barrier layer. As a result, carrier confinement in the well layer of the first strain relaxation layer 16A becomes more difficult, and emission becomes less likely, so it functions as part of the barrier layer of the third active layer 16, while simultaneously obtaining the effect of strain relaxation. In this way, by forming a first strain relaxation layer 16A with a well layer that has worse carrier confinement than the well layer of the third active layer 16, it is possible to form a first strain relaxation layer 16A that does not emit light.

[0048] In short, the material and layer structure of the first strain relaxation layer 16A should be set such that the average lattice constant of the entire first strain relaxation layer 16A is between the lattice constant of the second intermediate layer 15 and the lattice constant of the second strain relaxation layer 16B, and the thickness of the well layer should be set so that the first strain relaxation layer 16A does not emit light.

[0049] The first strain relaxation layer 16A may be either an SQW structure or an MQW structure, but it is preferable to use an SQW structure because the third active layer 16 becomes thicker.

[0050] As described above, by providing the first strain relaxation layer 16A, the strain in the well layer 16C above it can be relaxed, and the crystal quality of the well layer 16C can be improved.

[0051] The second strain relaxation layer 16B is a semiconductor layer provided on the first strain relaxation layer 16A. The wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 16B is shorter than the emission wavelength of the well layer 16C and longer than the wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 16A. For example, it is 510 to 570 nm. Otherwise, it is the same as the first strain relaxation layer 16A.

[0052] The difference between the wavelength corresponding to the band edge energy of the well layer of the first strain relaxation layer 16A and the wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 16B, and the difference between the wavelength corresponding to the band edge energy of the well layer of the second strain relaxation layer 16B and the emission wavelength of the well layer 16C, is preferably 40 to 100 nm.

[0053] By providing the first strain relaxation layer 16A and the second strain relaxation layer 16B in this manner, strain can be gradually relieved, and the strain of the well layer 16C laid on top of them can be effectively relieved. As a result, the quality of the well layer 16C can be improved.

[0054] In the first embodiment, strain is relieved in two stages by the first strain relief layer 16A and the second strain relief layer 16B, but strain may be relieved in three or more stages by providing three or more strain relief layers. Alternatively, only one of the first strain relief layer 16A or the second strain relief layer 16B may be provided. Furthermore, in the second active layer 14, strain may be relieved in stages by providing multiple strain relief layers.

[0055] Furthermore, a superlattice layer may be provided instead of, or in addition to, the first strain relaxation layer 16A and the second strain relaxation layer 16B. The strain in the well layer 16C can be relaxed by the superlattice layer. The superlattice layer is a superlattice structure in which group III nitride semiconductor thin films of different compositions are alternately stacked. For example, GaN and InGaN, or two InGaN with different In compositions. The average In composition in the thickness direction of the superlattice layer is, for example, 2 to 10%. The number of pairs in the superlattice structure is, for example, 1 to 30. The superlattice layer may be undoped, or Si may be 1 × 10⁻⁶ 17 ~100×10 17 cm -3 It's okay to dope it to a certain extent.

[0056] The well layer 16C is a semiconductor layer provided on the second strain relaxation layer 16B. The well layer 16C is made of a non-doped In-containing group III nitride semiconductor, such as InGaN. The emission wavelength of the third active layer 16 is determined by the average In composition of the combined well layer 16C and composition gradient layer 16D. This average In composition is set so that the emission wavelength is red at low current injection and yellow at high current injection. For example, the average In composition of the combined well layer 16C and composition gradient layer 16D is 30-45%. Low current refers to, for example, a current density of 0.1 A / cm². 2 More than 50A / cm 2 High current is defined as a current density of, for example, 50 A / cm². 2 More than 300A / cm 2 The following applies:

[0057] The composition gradient layer 16D is a semiconductor layer provided in contact with the well layer 16C. The composition gradient layer 16D is made of a non-doped In-containing group III nitride semiconductor, such as InGaN. The In composition of the composition gradient layer 16D is set to gradually decrease toward the first barrier layer 16E. Further details will be described later.

[0058] The first barrier layer 16E is a semiconductor layer provided in contact with the composition gradient layer 16D. The first barrier layer 16E functions as a p-side barrier layer for confining carriers in the well layer 16C, and also functions as a protective layer to prevent In from evaporating from the well layer 16C during device formation. The first barrier layer 16E is made of undoped GaN or InGaN. The first barrier layer 16E has a larger bandgap energy than the well layer 16C, for example, with an In composition of 15% or less. Also, the In composition is constant in the thickness direction. The thickness of the first barrier layer 16E is, for example, 0.5 to 10 nm.

[0059] The second barrier layer 16F is a semiconductor layer provided in contact with the first barrier layer 16E. Similar to the first barrier layer 16E, the second barrier layer 16F functions as a p-side barrier layer for confining carriers in the well layer 16C, and also functions as a protective layer to prevent In from evaporating from the well layer 16C during device formation. The second barrier layer 16F is made of undoped AlGaN or AlN. By using a material with a larger bandgap energy than the first barrier layer 16E, its function as a barrier layer is enhanced, allowing for efficient carrier confinement in the well layer 16C and the composition gradient layer 16D. The thickness of the second barrier layer 16F is, for example, 0.5 to 10 nm.

[0060] The third barrier layer 16G is a semiconductor layer provided in contact with the second barrier layer 16F. The third barrier layer 16G functions as a p-side barrier layer for confining carriers in the well layer 16C. The third barrier layer 16G is made of an undoped group III nitride semiconductor with a larger bandgap energy than the well layer 16C, and is such as InGaN, GaN, AlGaN, or AlGaInN. GaN is particularly preferred. The thickness of the third barrier layer 16G is, for example, 2 to 50 nm.

[0061] Next, the In composition of the composition gradient layer 16D will be explained with reference to Figure 4. Figure 4 shows the energy at the lower end of the conduction band and the In composition for the second strain relaxation layer 16B, the well layer 16C, the composition gradient layer 16D, and the first barrier layer 16E in the band diagram.

[0062] As shown in Figure 4, the composition gradient layer 16D is configured such that the In composition in the thickness direction gradually decreases toward the first barrier layer 16E. Conversely, the energy at the lower end of the conduction band of the composition gradient layer 16D is configured to gradually increase toward the first barrier layer 16E.

[0063] The In composition of the composition gradient layer 16D on the well layer 16C side is set to a smaller value than the In composition of the well layer 16C. This reduces the strain caused by the difference between the average lattice constant of the composition gradient layer 16D and the lattice constant of the first barrier layer 16E, compared to when the In composition is the same as that of the well layer 16C, and makes it less likely for defects to occur in the well layer 16C and the composition gradient layer 16D. Preferably, the In composition of the composition gradient layer 16D on the well layer 16C side is 30-70%, more preferably 40-60%, of the In composition of the well layer 16C.

[0064] The In composition of the composition gradient layer 16D on the surface facing the first barrier layer 16E is set to the same value as the In composition of the first barrier layer 16E. This effectively relieves the strain between the composition gradient layer 16D and the first barrier layer 16E. While it is not necessary for the In composition to be exactly the same as that of the first barrier layer 16E, it is preferable for the difference to be as small as possible, preferably 80-110% of the In composition of the first barrier layer 16E. More preferably 90-105%.

[0065] As a result of setting the In composition of the composition gradient layer 16D as described above, the following effects can be obtained. Firstly, the strain between the composition gradient layer 16D and the first barrier layer 16E can be relaxed, and the well layer 16C can be made substantially thicker. As a result, carrier confinement is improved. Secondly, the strain due to the lattice constant difference with the first barrier layer 16E can be reduced, making it less likely for relaxation accompanied by defects to occur in the well layer 16C and the composition gradient layer 16D. Thirdly, the quality of the first barrier layer 16E, the second barrier layer 16F, and the third barrier layer 16G can be improved. Due to these effects, a quantum well structure can be formed without degrading the crystal quality of the well layer 16C.

[0066] For manufacturing purposes, the gas flow is set so that the In composition becomes steeper at the interface between the well layer 16C and the composition gradient layer 16D, and at the interface between the composition gradient layer 16D and the first barrier layer 16E. However, in actual construction, the In composition may be slightly gradient near the interface.

[0067] The combined thickness of the well layer 16C and the composition gradient layer 16D is preferably 3 nm or more. This is because if the combined thickness of the well layer 16C and the composition gradient layer 16D is too thin, subbands will form and the wavelength will shift to the shorter wavelength side. Furthermore, the combined thickness of the well layer 16C and the composition gradient layer 16D is preferably 10 nm or less. This is because if the well layer 16C is too thick, the high In composition will cause strain relaxation, which may lead to defects in the well layer 16C and the composition gradient layer 16D. More preferably, it is 3 to 5 nm. Also, the thickness of the well layer 16C should be below the critical thickness at which defects occur.

[0068] The difference between the maximum and minimum values ​​of the In composition in the composition gradient layer 16D is preferably 10 to 30%. Furthermore, the rate of change of the In composition in the composition gradient layer 16D is preferably 5 to 17% / nm.

[0069] The electron blocking layer 17 is a semiconductor layer provided on the third active layer 16. The electron blocking layer 17 is a layer that blocks electrons injected from the n-type layer 11 in order to efficiently confine them to the third active layer 16. In addition to its electron blocking function, the electron blocking layer 17 also functions as a protective layer that protects the active layer. The electron blocking layer 17 can be made of any material with a band gap wider than that of the well layer of the third active layer 16, such as AlGaN, GaN, or InGaN. The thickness of the electron blocking layer 17 is preferably 2.0 to 50 nm, and more preferably 2 to 25 nm. The electron blocking layer 17 may be doped with impurities, or it may be doped with Mg. In that case, the Mg concentration is 1 × 10⁻¹⁶. 18 ~1000×10 18 cm -3 It would be best to do so.

[0070] Furthermore, a strain relaxation layer made of InGaN with a narrower band gap than the electron blocking layer 17 may be provided between the third active layer 16 and the electron blocking layer 17.

[0071] The p-type layer 18 is a semiconductor layer provided on the electron block layer 17. The p-type layer 18 is preferably made of p-GaN or p-InGaN. The thickness of the p-type layer 18 is preferably 10 to 500 nm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm. The Mg concentration of the p-type layer 18 is 1 × 10⁻¹⁶. 19 ~100×10 19 cm -3 It would be best to do so.

[0072] A portion of the surface of the p-type layer 18 is etched to form grooves, including a first groove 30 that extends from the p-type layer 18 to the second intermediate layer 15, a second groove 31 that extends to the first intermediate layer 13, and a third groove 32 that extends to the n-type layer 11.

[0073] The first groove 30 is deep enough to reach the undoped intermediate layer 15A of the second intermediate layer 15. In this way, by removing the n-type intermediate layer 15B of the second intermediate layer 15 beneath the p-side electrode 22B, the n-type layer is prevented from being located on the second active layer 14, causing the second active layer 14 to emit light.

[0074] Furthermore, the second groove 31 reaches a depth that extends to the undoped intermediate layer 13A of the first intermediate layer 13. This is for the same reason: by removing the n-type intermediate layer 13B of the first intermediate layer 13 beneath the p-side electrode 22C, the n-type layer is prevented from being located on the first active layer 12, allowing the first active layer 12 to emit light.

[0075] The electron blocking layers 19A to 19C are semiconductor layers provided on the p-type layer 18, on the undoped intermediate layer 15A exposed at the bottom of the first groove 30, and on the undoped intermediate layer 13A exposed at the bottom of the second groove 31, respectively. These layers block electrons injected from the n-type layer 11 in order to efficiently confine them to the first active layer 12, the second active layer 14, and the third active layer 16.

[0076] The electron blocking layers 19A to 19C may be single layers of GaN or AlGaN, or they may be a stacked structure of two or more of AlGaN, GaN, and InGaN, or a stacked structure with only the composition ratio changed. They may also be a superlattice structure. A superlattice structure allows for more efficient electron blocking. Examples of superlattice structures include a structure in which p-AlGaN and p-InGaN are stacked alternately, or a structure in which p-AlGaN and p-GaN are stacked alternately.

[0077] The thickness of the electron blocking layers 19A to 19C is preferably 2 to 50 nm, and more preferably 2 to 25 nm.

[0078] Furthermore, the electron blocking layers 19A to 19C are Mg-doped p-type. The p-type configuration allows for efficient injection of holes into the active layer. It also provides a larger barrier to electrons, enhancing the electron blocking function. While the electron blocking layers 19A to 19C may be undoped, it is preferable to dope them with Mg to create the p-type configuration for the reasons mentioned above. The Mg concentration of the electron blocking layers 19A to 19C is 1 × 10⁻⁶. 19 ~100×10 19 cm -3 It would be best to do so.

[0079] The p-type layers 20A to 20C are semiconductor layers provided on the electron block layers 19A to 19C, respectively, and are composed of the first layer, second layer, and so on, starting from the electron block layers 19A to 19C side.

[0080] The first layer is preferably made of p-GaN or p-InGaN. The thickness of the first layer is preferably 10 to 500 nm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm. The Mg concentration of the first layer is 1 × 10⁻⁶ 19 ~100×10 19 cm -3 It is preferable to do so. The second layer is preferably p-GaN or p-InGaN. The thickness of the second layer is preferably 2 to 50 nm, more preferably 4 to 20 nm, and even more preferably 6 to 10 nm. The Mg concentration of the second layer is 1 × 10⁻⁶ 20 ~100×10 20cm -3 It would be best to do so.

[0081] In the first embodiment, the electron blocking layers 19A to 19C are formed separately, and the p-type layers 20A to 20C are formed separately, but they may also be formed as a continuous film. In that case, layers of the same material as the electron blocking layers 19A to 19C are formed on the sides of the first groove 30 and the second groove 31, and layers of the same material as the p-type layers 20A to 20C are formed.

[0082] The n-side electrode 21 is an electrode provided on the n-type layer 11 exposed at the bottom surface of the third groove 32. If the substrate 10 is a conductive material, the n-side electrode 21 may be provided on the back surface of the substrate 10 without providing the third groove 32. The material of the n-side electrode 21 is, for example, Ti / Al or V / Al.

[0083] The p-side electrodes 22A to 22C are electrodes provided on the p-type layers 20A to 20C, respectively. The materials for the p-side electrodes 22A to 22C should be materials with high reflectivity of light at the emission wavelength and low contact resistance to the p-type layers 20A to 20C. Examples include Ag, Ni / Au, Co / Au, ITO / Ni / Al, Rh, Ru, and Mg. Of the red light emitted from the third active layer 16, the light directed toward the p-type layer 20A is reflected by the p-side electrode 22A and directed toward the substrate 10. Similarly, of the green light emitted from the second active layer 14, the light directed toward the p-type layer 20B is reflected by the p-side electrode 22B and directed toward the substrate 10, and of the blue light emitted from the first active layer 12, the light directed toward the p-type layer 20C is reflected by the p-side electrode 22C and directed toward the substrate 10.

[0084] 3. Control of light-emitting elements Next, the control of the light-emitting element 1 in the first embodiment will be described. In the light-emitting device of the first embodiment, the light emission of the light-emitting element 1 is controlled by the control device 2. Figure 5 is a diagram showing the equivalent circuit of the light-emitting element 1. As shown in Figure 5, the light-emitting element 1 is equivalent to a configuration in which three LEDs are independently provided: a yellow-to-red LED, a green LED, and a blue LED. By applying a voltage V1 between the p-side electrode 22A and the n-side electrode 21, yellow-to-red light can be emitted from the third active layer 16. By applying a voltage V2 between the p-side electrode 22B and the n-side electrode 21, green light can be emitted from the second active layer 14. By applying a voltage between the p-side electrode 22C and the n-side electrode 21, blue light can be emitted from the first active layer 12.

[0085] As shown in Figure 5, the control device 2 includes a PWM circuit 2A, a current control unit 2B, and switches SW1 and SW2. The PWM circuit 2A injects the current into the third active layer 16 as periodic pulses. The current control unit 2B controls the amount of current injected into the third active layer 16 (the amount of current injected into the yellow to red LEDs).

[0086] Here, the light emission from the second active layer 14 (green light emission) can be turned on and off by controlling the circuit's conductivity with switch SW1. Similarly, the light emission from the first active layer 12 (blue light emission) can be turned on and off by controlling switch SW2.

[0087] The emission of light (yellow to red light) from the third active layer 16 can be switched on and off by setting the current to 0 using the current control unit 2B, or by setting the duty cycle to 0 using the PWM circuit 2A. When emitting light, it is possible to selectively emit light at any wavelength between yellow and red by changing the amount of current injected into the third active layer 16. As the amount of current injected into the third active layer 16 increases, the wavelength shifts to the shorter wavelength side, and the larger the current, the greater the wavelength shift. Here, the wavelength for yellow is 570-590 nm, and the wavelength for red is 600-750 nm.

[0088] The amount of wavelength shift in response to changes in the amount of current injected into the third active layer 16 depends on the In composition and thickness of the well layer 16C. To easily achieve a wavelength shift from red to yellow, it is preferable to have an In composition of 35-50% and a thickness of 3.5-7.0 nm in the well layer 16C. Furthermore, the current density of the current injected into the third active layer 16 should be 0.5-10 A / cm². 2 Red light, 50-200 A / cm² 2 It is preferable to set it so that it turns yellow.

[0089] As the amount of current injected into the third active layer 16 increases, the emission intensity also increases. Therefore, the current is periodically switched on and off using the PWM circuit 2A to pulse modulate it. This makes it possible to control the emission intensity without changing the amount of current. In other words, wavelength shifting can be achieved without changing the emission intensity. For example, by keeping the duty cycle constant and setting the frequency to an appropriate value between 100 and 10000 Hz, it is possible to make the emission intensity of yellow light equivalent to that of red light. Alternatively, the emission intensity can be controlled by keeping the frequency constant and changing the duty cycle, or by changing both the frequency and the duty cycle.

[0090] The reason why the emission wavelength and emission intensity change with changes in current will be explained with reference to Figure 6. In the light-emitting element 1 of the first embodiment, the substrate 10 side is GaN, and the well layer 16C of the third active layer 16 is InGaN with a high In composition, so strong strain occurs in the well layer 16C and a strong piezoelectric field is generated. That is, a phenomenon called the quantum confined Stark effect (QCSE) occurs. As a result, the energy band structure tilts as shown in the right figure of Figure 6. This tilt reduces the band gap energy. Also, because the distribution of electrons and holes is biased, the probability of carrier recombination decreases.

[0091] When current is injected into the third active layer 16, an electric field is generated in a direction that cancels out the piezoelectric field, weakening the piezoelectric field. Furthermore, the larger the amount of current injected, the greater the weakening of the piezoelectric field. Therefore, as shown in the right, center, and left figures of Figure 6, the larger the amount of current injected, the gentler the slope of the energy band structure becomes, approaching flatter. As the slope approaches flatter, the band gap energy increases. In other words, the wavelength shifts to the shorter wavelength side. Also, as the slope approaches flatter, the bias in the distribution of electrons and holes decreases, so the probability of carrier recombination increases. As a result of the above, as shown in Figure 7, the larger the amount of current injected into the third active layer 16, the more the peak wavelength shifts to the shorter wavelength side, and the greater the optical output.

[0092] Thus, in the light-emitting element of the first embodiment, by selecting the electrode to which voltage is applied and the amount of current injected into the third active layer 16, it is possible to selectively emit light at wavelengths between yellow and red, as well as blue, green, and red light. Therefore, the color gamut can be expanded without increasing the number of active layers of the light-emitting element 1.

[0093] Furthermore, the wavelength shift of the emission wavelength (blue) due to a change in the current injection amount in the first active layer 12 is 10 nm or less, preferably 5 nm or less. Also, the wavelength shift of the emission wavelength (green) due to a change in the current injection amount in the second active layer 14 is 20 nm or less, preferably 10 nm or less. The In composition of the well layer of the second active layer 14 is smaller than that of the well layer of the third active layer 16, and the QCSE effect is smaller, so the wavelength shift is smaller. The In composition of the well layer of the first active layer 12 is even smaller than that of the well layer of the second active layer 14, so the wavelength shift is even smaller. On the other hand, the third active layer 16 has a large In composition in its well layer and a large QCSE effect, so the wavelength shift due to a change in the current injection amount can be larger compared to the first active layer 12 and the second active layer 14, and the emission color can be changed from red to yellow as described above.

[0094] Furthermore, in the first embodiment, the blue and green light emission are simply controlled by switching them on and off using switches SW1 and SW2, but they may also be controlled using PWM, similar to the yellow to red light emission.

[0095] 4. Manufacturing process for light-emitting elements Next, the manufacturing process of the light-emitting element 1 in the first embodiment will be described with reference to Figures 8 to 12. Figure 8 is a flowchart showing the manufacturing process, and Figures 9 to 12 are cross-sectional views showing the configuration of the light-emitting element at each stage of the manufacturing process.

[0096] First, prepare the substrate 10 and heat treat the substrate by adding hydrogen, nitrogen, and ammonia as needed.

[0097] Next, a buffer layer is formed on the substrate 10, and then an n-type layer 11, a first active layer 12, a first intermediate layer 13, a second active layer 14, a second intermediate layer 15, a third active layer 16, an electron blocking layer 17, and a p-type layer 18 are formed sequentially on the buffer layer (see Figure 9, step S1 in Figure 8). MOCVD is used to form each layer. The preferred growth temperatures for each layer are as follows.

[0098] The growth temperature of the first active layer 12 is preferably 700 to 950°C. This can improve crystal quality and increase luminescence efficiency. The first active layer 12 consists of a well layer and a barrier layer. The well layer and the barrier layer may be formed at the same temperature, or at different temperatures within the above temperature range. If different temperatures are used, it is preferable that the growth temperature of the well layer be lower than that of the barrier layer.

[0099] The growth temperature of the first intermediate layer 13 is preferably 700 to 1000°C. This is to suppress thermal damage to the first active layer 12. If the temperature is lower than 700°C, pits and point defects caused by threading dislocations are more likely to occur. More preferably, the temperature is 800 to 950°C, and even more preferably 850 to 950°C.

[0100] The growth temperature of the second active layer 14 is preferably 650 to 950°C. This can improve crystal quality and increase luminescence efficiency. The second active layer 14 is composed of a well layer and a barrier layer. The well layer and the barrier layer may be formed at the same temperature, or at different temperatures within the above temperature range. If different temperatures are used, it is preferable to lower the growth temperature of the well layer than the growth temperature of the barrier layer. Furthermore, it is preferable that the growth temperature of the second active layer 14 is lower than the growth temperature of the first active layer 12.

[0101] The growth temperature of the second intermediate layer 15 is preferably within the same range as the growth temperature of the first intermediate layer 13. However, it is preferable that the growth temperature of the second intermediate layer 15 be lower than that of the first intermediate layer 13. This is because the second active layer 14, which emits green light, is more susceptible to thermal damage than the first active layer 12, which emits blue light, and the effect of strain at the interface becomes greater.

[0102] The growth temperature of the third active layer 16 is preferably 500 to 950°C. This can improve crystal quality and increase luminescence efficiency. Each layer of the third active layer 16 may be formed at the same temperature, or at different temperatures within the above temperature range. If different temperatures are used, it is preferable that the growth temperature of the well layer 16C be lower than that of the composition gradient layer 16D, the first barrier layer 16E, the second barrier layer 16F, and the third barrier layer 16G. Furthermore, it is preferable that the growth temperature of the third active layer 16 be lower than that of the second active layer 14.

[0103] Furthermore, the well layer 16C is preferably formed as follows. The growth temperature of the well layer 16C is preferably 700°C or lower. The lower limit of the growth temperature of the well layer 16C is, for example, 550°C. By setting the growth temperature of the well layer 16C near the decomposition temperature of InN (630°C), the decomposition and re-evaporation of InN can be suppressed, and InGaN with a high In composition (especially an In composition of 35% or more) can be formed. The growth temperature of the well layer 16C is preferably 650°C or lower, more preferably 610-650°C, even more preferably 620-640°C, and most preferably 625-635°C.

[0104] The growth rate of the well layer 16C is preferably 0.8 nm / min or less. This is to suppress surface roughness, abnormal growth, and droplets caused by insufficient migration of raw material atoms at low growth temperatures. Droplets are formed when in aggregates of In are formed on the crystal surface. The growth rate of the well layer 16C is preferably 0.75 nm / min or less, more preferably 0.7 nm / min or less, and even more preferably 0.5 nm / min or less. There is no particular lower limit to the growth rate, but if the growth rate is too slow, it will take a long time to form the well layer 16C, so 0.05 nm / min or more is preferred.

[0105] The In solid-state ratio / In gas-state ratio during well layer 16C formation is preferably 0.75 to 1. Here, the In gas-state ratio is the molar ratio of In to the total Group III metals in the raw material gas used to form InGaN. The In solid-state ratio is the molar ratio of In to the total Group III metals in the formed InGaN crystal. The In solid-state ratio / In gas-state ratio can be controlled by the growth temperature, In gas-state ratio, VIII ratio, etc. By setting the In solid-state ratio / In gas-state ratio during well layer 16C formation within this range, abnormal growth and droplet formation of InGaN can be suppressed. The In solid-state ratio / In gas-state ratio during well layer 16C formation is preferably 0.85 to 1, and more preferably 0.9 to 1.

[0106] By setting the growth temperature, growth rate, and In solid-phase ratio / In gas-phase ratio of well layer 16C within the above range, high-quality crystals can be obtained even for InGaN with an In composition of 35% or more. As mentioned above, setting the growth temperature to below 700°C reduces the efficiency of ammonia decomposition, making it difficult for raw material atoms to migrate and thus difficult to obtain high-quality InGaN. However, by setting the growth rate within the above range, these problems can be resolved, and high-quality InGaN can be obtained.

[0107] It is preferable that the In gas phase ratio during the formation of well layer 16C be 40% or higher. This makes it easier to control the In solid phase ratio / In gas phase ratio within the above range, thereby suppressing abnormal growth and droplet formation of InGaN. Furthermore, it is preferable that the In gas phase ratio be 55% or lower.

[0108] The partial pressure of the Ga raw material gas during the formation of well layer 16C is 1 × 10⁻⁶ -6 ~3×10 -6 atm, the partial pressure of the raw material gas is 1 × 10⁻⁶ -6 ~3×10 -6 It is preferable to use atm. This is to suppress abnormal growth of InGaN and stabilize the growth rate. The Ga source gas is, for example, TMG (trimethylgallium) or TEG (triethylgallium), and the In source gas is, for example, TMI (trimethylindium).

[0109] The growth rates of the composition gradient layer 16D, the first barrier layer 16E, the second barrier layer 16F, and the third barrier layer 16G should be equal to or faster than the growth rate of the well layer 16C. Furthermore, the growth temperatures of the composition gradient layer 16D, the first barrier layer 16E, the second barrier layer 16F, and the third barrier layer 16G should be equal to or higher than the growth temperature of the well layer 16C. If higher temperatures are required, the composition gradient layer 16D, the first barrier layer 16E, and the second barrier layer 16F should be formed at the same temperature as the well layer 16C, and then the third barrier layer 16G should be added at a higher temperature. This prevents the high-In composition well layer 16C from thermally decomposing during the heating process.

[0110] The partial pressure of the nitrogen raw material gas during the formation of well layer 16C is preferably 0.15 to 0.2 atm. This suppresses the decomposition and re-evaporation of InN by H2 generated by the decomposition of ammonia, thereby improving the quality of InGaN. Note that the nitrogen in the carrier gas is not the nitrogen raw material gas.

[0111] The VIII ratio (molar ratio of ammonia to III metal raw material gas) during well layer 16C formation is preferably 30,000 to 80,000. Within this range, the quality of InGaN can be improved.

[0112] It is preferable that the growth temperature of the well layer 16C be lower than the growth temperatures of the first strain relaxation layer 16A and the second strain relaxation layer 16B. This is to suppress thermal damage to the first strain relaxation layer 16A and the second strain relaxation layer 16B. Furthermore, it is preferable that the growth temperature of the second strain relaxation layer 16B be lower than the growth temperature of the first strain relaxation layer 16A.

[0113] It is preferable that the growth rate of the well layer 16C be slower than the growth rates of the first strain relaxation layer 16A and the second strain relaxation layer 16B. This allows for the formation of a higher quality well layer 16C. Furthermore, it is preferable that the growth rate of the second strain relaxation layer 16B be slower than the growth rate of the first strain relaxation layer 16A.

[0114] The In-gas ratio during the formation of the well layer 16C is preferably smaller than the In-gas ratio during the formation of the first strain relaxation layer 16A and the second strain relaxation layer 16B. This allows for the formation of the well layer 16C with higher quality.

[0115] By forming the well layer 16C in the manner described above, high-quality InGaN crystals can be obtained even with an In composition of 35% or more. In particular, it is possible to form InGaN with an In composition of 40% or more. Therefore, the well layer 16C can be formed with high quality, and the luminescence efficiency of the third active layer 16 can be increased.

[0116] The In composition of the composition gradient layer 16D is controlled by changing the gas phase ratio of the In source gas. This makes it easy to achieve the gradient of In composition shown in Figure 4. The gas phase ratio of the In source gas is the mole fraction of the In source gas relative to the group III source gas.

[0117] The growth temperature for the electron blocking layer 17 and the p-type layer 18 is preferably 500 to 950°C. This is to suppress thermal damage to the first active layer 12, the second active layer 14, and the third active layer 16. A higher growth temperature is preferable for improving the crystallinity of the electron blocking layer 17 and the p-type layer 18, more preferably 600 to 900°C, and even more preferably 700 to 900°C.

[0118] Next, a portion of the surface of the p-type layer 18 is dry-etched until it reaches the undoped intermediate layer 15A of the second intermediate layer 15 to form the first groove 30, and then dry-etched until it reaches the undoped intermediate layer 13A of the first intermediate layer 13 to form the second groove 31 (see Figure 10, step S2 in Figure 8).

[0119] Next, electron blocking layers 19A to 19C are formed on the p-type layer 18, on the undoped intermediate layer 15A of the second intermediate layer 15 exposed by the first groove 30, and on the undoped intermediate layer 13A of the first intermediate layer 13 exposed by the second groove 31, by MOCVD. Then, p-type layers 20A to 20C are formed on the electron blocking layers 19A to 19C by MOCVD (see Figure 11, step S3 in Figure 8). Note that the p-type layers 20A to 20C are not p-type at this stage, but will become p-type later, so they are referred to as such.

[0120] The growth temperature of the electron blocking layers 19A to 19C is preferably 950°C or lower. This is because the first active layer 12, the second active layer 14, and the third active layer 16 contain InGaN, and this temperature is used to suppress thermal damage to the InGaN. More preferably, the temperature is 900°C or lower. Furthermore, the growth temperature of the electron blocking layers 19A to 19C is preferably 750°C or higher, and more preferably 800°C or higher.

[0121] The growth temperature for the p-type layers 20A to 20C is preferably 650 to 1000°C, more preferably 700 to 950°C, and even more preferably 750 to 900°C.

[0122] Next, a portion of the surface of the p-type layer 20C is dry-etched until it reaches the n-type layer 11 to form a third groove 32 (see Figure 12, step S4 in Figure 8). Then, the n-side electrode 21 is formed on the n-type layer 11 exposed at the bottom of the third groove 32, and the p-side electrodes 22A to 22C are formed on the p-type layers 18, 20A, and 20B. The light-emitting element of the first embodiment is thus manufactured.

[0123] 5. Experimental Results Next, the experimental results relating to the first embodiment will be described. The light-emitting element 1 according to the first embodiment was fabricated, and a voltage was applied between the p-side electrode 22A and the n-side electrode 21 to cause the third active layer 16 to emit light. Figure 13 is a graph showing the emission spectrum of the third active layer 16 of the light-emitting element 1. Figure 14 is a graph showing the relationship between the current density of the current injected into the third active layer 16 of the light-emitting element 1 and the peak wavelength of the emission of the third active layer 16. Figure 15 is a graph showing the relationship between the current density of the current injected into the third active layer 16 of the light-emitting element 1 and the full width at half maximum (FWHM) of the emission spectrum of the third active layer 16.

[0124] As shown in Figures 13 and 14, it was found that the higher the current injected into the third active layer 16, the more the peak wavelength of emission from the third active layer 16 shifts to the shorter wavelength side. It was also found that a low current injected into the third active layer 16 resulted in red emission, while a high current resulted in yellow emission. Furthermore, as shown in Figure 15, it was found that the larger the wavelength shift to the shorter wavelength side, the larger the full width at half maximum. Also, as shown in Figure 13, the emission intensity differs by about 100 times between the case of red emission with a current of 1 mA and the case of yellow emission with a current of 100 mA. A difference of about 100 times in emission intensity can be matched by PWM control without changing the emission wavelength.

[0125] (Other transformation forms) In the first embodiment of the light-emitting element, three active layers (first active layer 12, second active layer 14, and third active layer 16) are provided, each emitting blue, green, and yellow-to-red light respectively. However, the present invention is not limited to this, and it is sufficient to have two or more active layers with different emission wavelengths. Furthermore, in the first embodiment, the emission wavelength can be selected between yellow and red, but it is not limited to this. However, from the viewpoint of expanding the color gamut, it is preferable to set the wavelength shift amount to 20 nm or more. For example, the wavelength can be selected between green and yellow. In this case, the In composition and thickness of the well layer in the second active layer 14 are set so that yellow light is emitted when the current injected into the second active layer 14 is low, and green light is emitted when the current is high.

[0126] Although the light-emitting element 1 in the first embodiment was of the flip-chip type, the present invention is not limited to this and can also be applied to the face-up type. Furthermore, when a conductive material is used as the substrate 10, a vertical structure may be used.

[0127] (Second Embodiment) The method for controlling the emission color in the first embodiment is also applicable to light-emitting elements with a single active layer. In the second embodiment, an example of a light-emitting element with a single active layer and selectable emission wavelengths between yellow and red is described.

[0128] Figure 16 is a cross-sectional view showing the configuration of a light-emitting element in the second embodiment, and is a cross-sectional view perpendicular to the main surface of the substrate. As shown in Figure 16, the light-emitting element in the second embodiment is a face-up type and includes a substrate 100, an n-type layer 101, a first superlattice layer 102, a second superlattice layer 103, a third superlattice layer 104, an n-type intermediate layer 105, a fourth superlattice layer 106, a well layer 107, a composition gradient layer 108, a first barrier layer 109, a second barrier layer 110, a third barrier layer 111, an electron blocking layer 112, a p-type contact layer 113, a transparent electrode 114, a p-side electrode 115, and an n-side electrode 116.

[0129] In Embodiment 1, the light-emitting element is of the face-up type, but it may also be of the flip-chip type. Furthermore, if a conductive material such as GaN is used as the substrate 100, a vertical structure may be used.

[0130] The substrate 100 and the n-type layer 101 are the same as the substrate 10 and the n-type layer 11 in the first embodiment, respectively.

[0131] The first superlattice layer 102 is a semiconductor layer provided on the n-type layer 101. The first superlattice layer 102 is a superlattice structure in which group III nitride semiconductor thin films of different compositions are alternately stacked. For example, GaN and InGaN, or two InGaNs with different In compositions. The average In composition of the first superlattice layer 102 is, for example, 2 to 10%. The number of pairs in the superlattice structure is, for example, 3 to 30. It may be undoped, or Si may be 1 × 10⁻¹⁶ 17 ~100×10 17 cm -3 It may be doped to a certain extent. The first superlattice layer 102 can alleviate the strain in the well layer 107.

[0132] The second superlattice layer 103 is a semiconductor layer provided on the first superlattice layer 102. The second superlattice layer 103 has a superlattice structure similar to that of the first superlattice layer 102. However, the In composition is different; the average In composition of the second superlattice layer 103 is higher than the average In composition of the first superlattice layer 102, for example, 2-15%. The number of pairs in the superlattice structure is, for example, 3-30. It may be undoped, or Si can be 1 × 10⁻¹⁶ 17 ~100×10 17 cm -3 It may be doped to a certain extent. The second superlattice layer 103 can further alleviate the strain in the well layer 107.

[0133] Instead of the second superlattice layer 103, a quantum well structure may be used in which the wavelength corresponding to the bandgap energy of the well layer is near ultraviolet to blue (for example, a wavelength of 380 to 480 nm). Similar to the case of the superlattice structure, the strain of the well layer 107 can be relaxed. The quantum well structure may be either SQW or MQW, but SQW is preferred because it is thicker. Even with the quantum well structure, since the n-type intermediate layer 105 exists on top of the second superlattice layer 103, actual light emission does not occur.

[0134] The third superlattice layer 104 is a semiconductor layer provided on the second superlattice layer 103. The third superlattice layer 104 has a superlattice structure similar to that of the first superlattice layer 102. However, the In composition is different; the average In composition of the third superlattice layer 104 is higher than the average In composition of the second superlattice layer 103, for example, 2-20%. The number of pairs in the superlattice structure is, for example, 3-30. It may be undoped, or Si can be 1 × 10⁻¹⁶ 17 ~100×10 17 cm -3 It may be doped to a certain extent. The third superlattice layer 104 can further alleviate the strain in the well layer 107.

[0135] Instead of the third superlattice layer 104, a quantum well structure may be used in which the wavelength corresponding to the bandgap energy of the well layer is blue-green to yellow-green (for example, wavelengths of 480 to 580 nm). Similar to the superlattice structure, the strain of the well layer 107 can be relaxed. The quantum well structure may be either SQW or MQW, but SQW is preferred because it is thicker. Even with the quantum well structure, since the n-type intermediate layer 105 exists on top of the third superlattice layer 104, actual light emission does not occur.

[0136] As described above, by providing three superlattice structures—a first superlattice layer 102, a second superlattice layer 103, and a third superlattice layer 104—and gradually increasing the In composition, the strain is gradually relieved, preventing the occurrence of defects.

[0137] The n-type intermediate layer 105 is a semiconductor layer provided on the third superlattice layer 104. The n-type intermediate layer 105 is a layer made of n-type GaN or InGaN. If InGaN is used, the In composition is, for example, 15% or less. By providing the n-type intermediate layer 105, the first superlattice layer 102, the second superlattice layer 103, and the third superlattice layer 104 can be prevented from emitting light.

[0138] The fourth superlattice layer 106 is a layer provided on the n-type intermediate layer 105. The fourth superlattice layer 106 has a superlattice structure similar to that of the first superlattice layer 102. However, the In composition is different; the average In composition of the third superlattice layer 104 is greater than or equal to the average In composition of the first superlattice layer 102, and less than or equal to the average In composition of the second superlattice layer 103. The average In composition is, for example, 2-10%. The number of pairs in the superlattice structure is, for example, 1-30. It may be undoped, or Si may be 1 × 10⁻⁶ 17 ~100×10 17 cm -3 It may be doped to a certain extent. The fourth superlattice layer 106 can further alleviate the strain in the well layer 107. In addition, the fourth superlattice layer 106 also functions as an n-side barrier layer for the well layer 107.

[0139] The first strain relaxation layer 16A and the second strain relaxation layer 16B in the first embodiment may be provided instead of, or in addition to, the fourth superlattice layer 106. As will be described later, strain can be efficiently relaxed. Only one of the first strain relaxation layer 16A and the second strain relaxation layer 16B may be provided.

[0140] The well layer 107 is a layer provided on the fourth superlattice layer 106. The composition gradient layer 108 is a semiconductor layer provided in contact with the well layer 107. The first barrier layer 109 is a semiconductor layer provided in contact with the composition gradient layer 108. The second barrier layer 110 is a semiconductor layer provided in contact with the first barrier layer 109. The third barrier layer 111 is a semiconductor layer provided in contact with the second barrier layer 110. The well layer 107, composition gradient layer 108, first barrier layer 109, second barrier layer 110, and third barrier layer 111 are the same as the well layer 16C, composition gradient layer 16D, first barrier layer 16E, second barrier layer 16F, and third barrier layer 16G in the first embodiment, respectively.

[0141] In the second embodiment, the well layer 107 is a single SQW structure, but it may also be an MQW structure with two or more well layers 107. In this case, a composition gradient layer 108 is provided on each well layer 107. The number of pairs is preferably 1 to 5, and more preferably 1 to 3.

[0142] The electron blocking layer 112 is a p-type semiconductor layer provided on the third barrier layer 111. The electron blocking layer 112 is a layer that blocks electrons injected from the n-type layer 101 in order to efficiently confine them to the well layer 107. Furthermore, by making the electron blocking layer 112 p-type, holes can be efficiently injected into the well layer 107, creating a larger barrier to electrons and enhancing the electron blocking function. The Mg concentration of the electron blocking layer 112 is 1 × 10⁻⁶. 19 ~100×10 19 cm -3 It is best to do so. Furthermore, the electronic block layer 112 may be undoped.

[0143] The electron blocking layer 112 may be a single layer of GaN or AlGaN, or a structure in which two or more of AlGaN, GaN, and InGaN are stacked, or a structure in which only the composition ratio is changed. It may also be a superlattice structure. A superlattice structure can block electrons more efficiently. Examples of superlattice structures include a structure in which p-AlGaN and p-InGaN are stacked alternately, or a structure in which p-AlGaN and p-GaN are stacked alternately.

[0144] The thickness of the electron blocking layer 112 is, for example, 2 to 50 nm, preferably 2 to 25 nm.

[0145] The p-type contact layer 113 is a p-type semiconductor layer provided on the electron block layer 112. The p-type contact layer 113 is composed of a first layer and a second layer, in that order from the electron block layer 112 side.

[0146] The first layer is preferably made of p-GaN or p-InGaN. The thickness of the first layer is preferably 10 to 500 nm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm. The Mg concentration of the first layer is 1 × 10⁻⁶ 19 ~100×10 19 cm -3It is preferable to do so. The second layer is preferably p-GaN or p-InGaN. The thickness of the second layer is preferably 2 to 50 nm, more preferably 4 to 20 nm, and even more preferably 6 to 10 nm. The Mg concentration of the second layer is 1 × 10⁻⁶ 20 ~100×10 20 cm -3 It would be best to do so.

[0147] A recess 117 is provided on the surface of the p-type contact layer 113. The recess 117 is deep enough to reach the n-type layer 101. The n-type layer 101 is exposed at the bottom of the recess 117.

[0148] The transparent electrode 114 is an electrode provided on the p-type contact layer 113. The transparent electrode 114 is made of a transparent conductive material, such as ITO, IZO, ICO, or ZnO.

[0149] The p-side electrode 115 is an electrode provided on the transparent electrode 114. For example, it may be made of Ni / Au.

[0150] The n-side electrode 116 is an electrode provided on the bottom surface of the recess 117. For example, it is made of Ti / Al.

[0151] In the second embodiment, as in the first embodiment, the light-emitting element can selectively emit light at any wavelength between yellow and red by changing the amount of current injected into the well layer 107. [Explanation of Symbols]

[0152] 10: Circuit board 11:N-type layer 12: 1st active layer 13: First Meso-Place 14:Second active layer 15: Second Meso-Marginal Layer 16: 3rd active layer 17, 19A~19C: Electron Block Layer 18, 20A~20C: p-type layer 21:n side electrode 22A~22C:p side electrode

Claims

1. A method for controlling the light emission color of a light-emitting element, The light-emitting element is An n-type layer made of an n-type group III nitride semiconductor, A first active layer made of a group III nitride semiconductor formed on the n-type layer, An intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, A second active layer made of a group III nitride semiconductor formed in a part of the intermediate layer, A first p-type layer is formed on the second active layer and is made of a p-type group III nitride semiconductor, A second p-type layer is formed on the intermediate layer in a region where the second active layer is not formed, and is made of a p-type group III nitride semiconductor. The first active layer emits light at a first wavelength, When a predetermined first current is injected into the second active layer, it emits light at a second wavelength longer than the first wavelength, and when a second current greater than the first current is injected, it emits light at a third wavelength longer than the first wavelength and shorter than the second wavelength. A method for controlling the emission color of a light-emitting element, wherein the emission wavelength of the second active layer is controlled to any wavelength from the second wavelength to the third wavelength by controlling the current injected into the second active layer between the first current amount and the second current amount.

2. The method for controlling the emission color of a light-emitting element according to claim 1, wherein the difference between the second wavelength and the third wavelength is 20 nm or more.

3. A method for controlling the emission color of a light-emitting element according to claim 1, wherein the second emission wavelength is red and the third wavelength is yellow.

4. The method for controlling the emission color of a light-emitting element according to any one of claims 1 to 3, wherein the thickness of the well layer of the second active layer is 3.5 nm or more and 7.0 nm or less.

5. A method for controlling the emission color of a light-emitting element according to claim 1, wherein the emission intensity of the second active layer is controlled by PWM control of the current injected into the second active layer.

6. Light-emitting element and The device includes a control device for controlling the light-emitting color of the light-emitting element, The light-emitting element is An n-type layer made of an n-type group III nitride semiconductor, A first active layer made of a group III nitride semiconductor formed on the n-type layer, An intermediate layer made of an n-type or undoped group III nitride semiconductor formed on the first active layer, A second active layer made of a group III nitride semiconductor formed in a part of the intermediate layer, A first p-type layer is formed on the second active layer and is made of a p-type group III nitride semiconductor, A second p-type layer is formed on the intermediate layer in a region where the second active layer is not formed, and is made of a p-type group III nitride semiconductor. The first active layer is configured to emit light at a first wavelength. The second active layer is configured to emit light at a second wavelength longer than the first wavelength when a predetermined first current is injected, and to emit light at a third wavelength longer than the first wavelength and shorter than the second wavelength when a second current greater than the first current is injected. The light-emitting device includes a current control unit that controls the emission wavelength of the second active layer to any wavelength from the second wavelength to the third wavelength by controlling the current injected into the second active layer between the first current amount and the second current amount.

7. The light-emitting device according to claim 6, wherein the difference between the second wavelength and the third wavelength is 20 nm or more.

8. The light-emitting device according to claim 6, wherein the second wavelength is red and the third wavelength is yellow.

9. The light-emitting device according to any one of claims 6 to 8, wherein the thickness of the well layer of the second active layer is 3.5 nm or more and 7.0 nm or less.

10. The light-emitting device according to claim 6, wherein the control device has a PWM circuit that controls the light emission intensity of the second active layer by PWM control of the current injected into the second active layer.

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