CN117174794A

CN117174794A - Light-emitting element

Info

Publication number: CN117174794A
Application number: CN202310644954.5A
Authority: CN
Inventors: 奥野浩司; 五所野尾浩一; 大矢昌辉
Original assignee: Toyoda Gosei Co Ltd
Current assignee: Toyoda Gosei Co Ltd
Priority date: 2022-06-02
Filing date: 2023-06-01
Publication date: 2023-12-05

Abstract

The present invention relates to a light emitting element. The first intermediate layer is a semiconductor layer arranged on the first active layer and is positioned between the first active layer and the second active layer. The first intermediate layer has a structure in which an undoped layer and an n-type layer are stacked in this order from the first active layer side. The second intermediate layer is a semiconductor layer arranged on the second active layer and is positioned between the second active layer and the third active layer. The second intermediate layer has a structure in which an undoped layer and an n-type layer are laminated in this order from the second active layer side.

Description

Light-emitting element

Technical Field

The present disclosure relates to a light emitting element.

Background

In recent years, high definition of displays has been pursued, and attention has been paid to micro LED displays in which 1 pixel is a micro LED of the order of 1 to 100 μm. Various full-color systems are known, for example, a system in which 3 active layers that emit blue, green, and red light are sequentially stacked on the same substrate. In this case, in order to drive the active layers individually, an intermediate layer needs to be formed between the active layers.

Prior art literature

Patent literature

Patent document 1: japanese patent No. 5854419

Patent document 2: japanese patent laid-open No. 6-209122

Disclosure of Invention

However, when each active layer is driven separately, it is difficult to perform uniform control because of differences in drive voltage, current injection efficiency, and reverse current due to differences in pn junction distance. Further, it is difficult to independently control 2 kinds of active layers laminated via intermediate layers.

Accordingly, one of the objects of the present disclosure is: the difference in diode characteristics when driving each active layer is suppressed, and the light emission characteristics are controlled independently for each active layer.

In addition, the intermediate layer must be formed after the active layer is laminated. Therefore, the intermediate layer needs to be formed at a low temperature to avoid thermal damage to the active layer. However, if the intermediate layer is formed at a low temperature, there are problems as follows: the quality of the intermediate layer and the surface flatness deteriorate until the quality of the active layer formed thereon also deteriorates.

Accordingly, another object of the present disclosure is to improve the surface flatness of the intermediate layer.

In addition, inGaN having a high In composition ratio is required for emitting green light and red light. However, high quality InGaN cannot be formed due to strain caused by lattice mismatch.

Accordingly, it is another object of the present disclosure to improve the quality of the active layer.

In order to emit red light by InGaN, the In composition needs to be about 40%. However, in the method of patent document 1, it is difficult to obtain high-quality InGaN when the In composition is high.

Accordingly, another object of the present disclosure is to improve the quality of group IIIA nitride semiconductors having an In composition of 35% or more.

A first aspect of the present disclosure is a light-emitting element including a group IIIA nitride semiconductor, including:

an n-layer made of an n-type group IIIA nitride semiconductor,

a first active layer provided on the n layers and having a predetermined emission wavelength,

an intermediate layer provided on the first active layer and having a structure in which an undoped layer made of an undoped group IIIA nitride semiconductor and an n-type layer made of an n-type group IIIA nitride semiconductor are laminated in order from the first active layer side,

a second active layer provided on the intermediate layer and having a different emission wavelength from the first active layer,

a trench reaching the undoped layer from the second active layer side,

a first p-layer formed of a p-type group IIIA nitride semiconductor and provided on the second active layer,

a second p layer formed of a p-type group IIIA nitride semiconductor and provided on the undoped layer exposed at the bottom surface of the trench,

a first p-electrode disposed on the first p-layer, and

and a second p-electrode disposed on the second p-layer.

A second aspect of the present disclosure is a light-emitting element including a group IIIA nitride semiconductor, including:

an n-layer made of an n-type group IIIA nitride semiconductor,

an intermediate layer formed on the first active layer and composed of an In-containing group IIIA nitride semiconductor, and

the intermediate layer has an In composition so as not to absorb the band gap of light emitted from the first active layer and the second active layer.

A third aspect of the present disclosure is a light-emitting element including a group IIIA nitride semiconductor, including:

an n-layer made of an n-type group IIIA nitride semiconductor,

an intermediate layer disposed on the first active layer,

a second active layer provided on the intermediate layer and having a longer emission wavelength than the first active layer,

a groove reaching the intermediate layer from the second active layer side,

A second p-layer formed of a p-type group IIIA nitride semiconductor and provided on the intermediate layer exposed at the bottom surface of the trench,

a first p-electrode disposed on the first p-layer, and

a second p-electrode disposed on the second p-layer,

the second active layer has a structure in which a strain relief layer having a quantum well structure and adjusting the thickness of the well layer so as not to emit light, and a light-emitting layer having a quantum well structure and emitting light are laminated in this order from the intermediate layer side,

the wavelength of the strain relief layer corresponding to the band edge energy of the well layer is set to be shorter than the emission wavelength of the light-emitting layer.

According to the first aspect of the present disclosure, the difference in light emission characteristics when the respective active layers are driven separately can be suppressed.

According to the second aspect of the present disclosure, the surface flatness of the intermediate layer can be improved.

According to the third aspect of the present disclosure, the quality of the active layer can be improved.

Drawings

Fig. 1 is a diagram showing a configuration of a light-emitting element according to a first embodiment.

Fig. 2 is a diagram showing a structure of a light-emitting element according to a modification.

Fig. 3 is a diagram showing a structure of a light-emitting element according to a modification.

Fig. 4 is a diagram showing an equivalent circuit of the light-emitting element of the first embodiment.

Fig. 5 is a diagram showing a process for manufacturing the light-emitting element according to the first embodiment.

Fig. 6 is a diagram showing a process for manufacturing the light-emitting element according to the first embodiment.

Fig. 7 is a diagram showing a process for manufacturing the light-emitting element according to the first embodiment.

Fig. 8 is a diagram showing a process for manufacturing the light-emitting element according to the first embodiment.

Fig. 9 is a diagram showing a configuration of a light-emitting element according to the second embodiment.

Fig. 10 is a diagram showing a structure of a light-emitting element according to the third embodiment.

Fig. 11 is a diagram showing the structure of the light-emitting element of experimental example 1.

Fig. 12 is an AFM image obtained by photographing the surface of the third active layer 18.

Fig. 13 is a graph showing a relationship between a driving current and external quantum efficiency.

Fig. 14 is a graph showing an emission spectrum.

Fig. 15 is a graph showing an emission spectrum.

Fig. 16 is a graph showing an emission spectrum.

Fig. 17 is a graph showing an emission spectrum.

Fig. 18 is an AFM image obtained by photographing the surface of the third active layer 18.

Fig. 19 is a graph showing a relationship between a driving current and external quantum efficiency.

Fig. 20 is a diagram showing a structure of a light-emitting element according to the fourth embodiment.

Fig. 21 is a diagram showing an equivalent circuit of the light-emitting element of the fourth embodiment.

Fig. 22 is a diagram showing a structure of a light-emitting element according to the fifth embodiment.

Fig. 23 is an AFM image of the well layer surface of the quantum well structure layer 518C when the growth rate is changed.

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.

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.

Symbol description

10: substrate board

11: n layer

12: ESD layer

13: substrate layer

14: first active layer

15. 215, 415: a first intermediate layer

16. 316: second active layer

17. 217, 417: a second intermediate layer

18. 318: third active layer

19: protective layer

20A to 20C: regrowth layer

21A to 21C, 421A to C, 521: electron blocking layer

22A-22C, 522: p layer

23: n electrode

24A to 24C: p electrode

215A, 217A: undoped layer

215B, 217B: n-type layer

316A: strain relief layer

316B, 318C, 518C: quantum well structure layer

318A, 518A: first strain relief layer

318B, 518B: second strain relief layer

518: active layer

Detailed Description

1. First mode

A light-emitting element composed of a group IIIA nitride semiconductor comprises: an n-type semiconductor device includes an n-type layer made of an n-type group IIIA nitride semiconductor, a first active layer provided on the n-type layer and having a predetermined emission wavelength, an intermediate layer provided on the first active layer and having a structure in which an undoped group IIIA nitride semiconductor and an n-type layer made of an n-type group IIIA nitride semiconductor are laminated in this order from the first active layer side, a second active layer provided on the intermediate layer and having an emission wavelength different from that of the first active layer, a trench reaching the undoped layer from the second active layer side, a first p-type layer provided on the second active layer and made of a p-type group IIIA nitride semiconductor, a second p-type layer provided on the undoped layer exposed on the bottom surface of the trench, a first p-electrode provided on the first p-type layer, and a second p-electrode provided on the second p-type layer.

The thickness of the intermediate layer is 150nm or less, and the thickness of the undoped layer and the n-type layer may be 10nm or more.

The intermediate layer is made of an group IIIA nitride semiconductor containing In, and the In composition may be set so as not to absorb the band gap of the light emitted from the first active layer and the second active layer.

the wavelength of the strain relief layer corresponding to the band edge energy of the well layer may be set shorter than the emission wavelength of the light-emitting layer.

A method for manufacturing a light-emitting element composed of a group IIIA nitride semiconductor comprises: the method comprises a step of forming an n-layer made of an n-type group IIIA nitride semiconductor, a step of forming a first active layer having a predetermined emission wavelength on the n-layer, a step of forming an intermediate layer having a structure in which an undoped group IIIA nitride semiconductor and an n-type layer made of an n-type group IIIA nitride semiconductor are laminated in this order from the first active layer side, and a growth temperature of the intermediate layer is 700 to 1000 ℃, a step of forming a second active layer having an emission wavelength different from that of the first active layer on the intermediate layer, a step of forming a groove reaching the undoped layer from the second active layer side, a step of forming a first p-layer and a second p-layer made of a p-type group IIIA nitride semiconductor on the second active layer and the undoped layer exposed to the bottom surface of the groove, respectively, and a step of forming a first p-electrode and a second p-electrode on the first p-layer and the second p-layer, respectively.

2. Second mode

A light-emitting element composed of a group IIIA nitride semiconductor comprises: an n-type group IIIA nitride semiconductor layer, a first active layer provided on the n-type group IIIA nitride semiconductor layer and having a predetermined emission wavelength, an intermediate layer provided on the first active layer and made of an In-containing group IIIA nitride semiconductor layer, and a second active layer provided on the intermediate layer and having an emission wavelength different from that of the first active layer. The intermediate layer has an In composition so as not to absorb the band gap of light emitted from the first active layer and the second active layer.

In addition, it may have: a groove reaching the intermediate layer from the second active layer side, a first p layer formed of a p-type group IIIA nitride semiconductor and provided on the second active layer, a second p layer formed of a p-type group IIIA nitride semiconductor and provided on the intermediate layer exposed at the bottom surface of the groove, a first p electrode provided on the first p layer, and a second p electrode provided on the second p layer.

The intermediate layer may have a structure in which a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer are stacked in this order from the first active layer side, the second layer may have a p-type impurity concentration higher than that of the first layer, the third layer may have an n-type impurity concentration higher than that of the fourth layer, and the second layer and the third layer may form a tunnel junction structure, and the intermediate layer may include: 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, and an electrode provided on the fourth layer exposed on the bottom surface of the groove. The presence of a regrowth interface can be avoided, and deterioration of device characteristics can be suppressed.

The In composition of the second layer and the third layer may be higher than the In composition of the first layer and the fourth layer. The probability of tunnel effect due to the tunnel junction structure can be further improved. In addition, the In composition of the second layer may be higher than that of the third layer. The second layer may be thinner than the first layer Yu Shangshu, and the third layer may be thinner than the fourth layer Yu Shangshu.

The intermediate layer may be InGaN. The In composition of the intermediate layer may be 10% or less. The intermediate layer may be GaN doped with In.

A method for manufacturing a light-emitting element composed of a group IIIA nitride semiconductor comprises: the method comprises a step of forming an n-layer composed of an n-type group IIIA nitride semiconductor, a step of forming a first active layer having a predetermined emission wavelength on the n-layer, a step of forming an intermediate layer composed of an In-containing group IIIA nitride semiconductor on the first active layer at a growth temperature of 700 to 1000 ℃, and a step of forming a second active layer having an emission wavelength different from that of the first active layer on the intermediate layer. The intermediate layer has an In composition so as not to absorb the band gap of light emitted from the first active layer and the second active layer.

In addition, it may have: a step of forming a groove reaching the intermediate layer from the second active layer side, a step of forming a first p layer and a second p layer made of a p-type group IIIA nitride semiconductor on the second active layer and on the intermediate layer exposed on the bottom surface of the groove, and a 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 may be formed by stacking a p-type first layer, a p-type second layer, an n-type third layer, and an n-type fourth layer in this order from the first active layer side, wherein the second layer has a p-type impurity concentration higher than that of the first layer, the third layer has an n-type impurity concentration higher than that of the fourth layer, and the second layer and the third layer form a tunnel junction structure, and the intermediate layer may include: a step of forming a p-layer on the second active layer, a step of forming a groove extending from the p-layer side to the fourth layer, a step of forming a p-electrode on the p-layer, and a step of forming an electrode on the fourth layer exposed on the bottom surface of the groove.

In the method for manufacturing a light-emitting element including a group IIIA nitride semiconductor, the In composition of the second layer and the third layer may be higher than the In composition of the first layer and the fourth layer. In addition, the In composition of the second layer may be higher than that of the third layer. The second layer may be made thinner than the first layer Yu Shangshu, and the third layer may be made thinner than the fourth layer Yu Shangshu. In addition, 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.

In the method for manufacturing a light-emitting element made of a group IIIA nitride semiconductor, the In composition of the intermediate layer may be 10% or less. In addition, the intermediate layer may be InGaN. In addition, the intermediate layer may be GaN doped with In.

3. Third mode

A light-emitting element composed of a group IIIA nitride semiconductor comprises: an n-type group IIIA nitride semiconductor layer, a first active layer provided on the n-type group IIIA nitride semiconductor layer and having a predetermined emission wavelength, an intermediate layer provided on the first active layer, a second active layer provided on the intermediate layer and having an emission wavelength longer than that of the first active layer, a groove reaching the intermediate layer from the second active layer side, a first p-type group IIIA nitride semiconductor layer provided on the second active layer and having a p-type group IIIA nitride semiconductor layer provided on the intermediate layer exposed on the bottom surface of the groove, a second p-type group IIIA nitride semiconductor layer provided on the intermediate layer, a first p-electrode provided on the first p-layer, and a second p-electrode provided on the second p-layer.

The second active layer has a structure in which a strain relief layer having a quantum well structure and adjusting the thickness of the well layer so as not to emit light and a light-emitting layer having a quantum well structure and emitting light are laminated in this order from the intermediate layer side. The wavelength of the strain relief layer corresponding to the band edge energy of the well layer is set to be shorter than the emission wavelength of the light-emitting layer.

The wavelength of the strain relief layer corresponding to the band edge energy of the well layer may be set to be equal to the emission wavelength of the first active layer.

The wavelength of the strain relief layer corresponding to the band edge energy of the well layer may be set to be 40 to 100nm shorter than the emission wavelength of the light-emitting layer.

The strain relief layer may have an SQW structure.

The ratio of the thickness of the first active layer to the thickness of the second active layer may be 30% or less.

A method for manufacturing a light-emitting element composed of a group IIIA nitride semiconductor comprises: the method comprises a step of forming an n-layer made of an n-type group IIIA nitride semiconductor, a step of forming a first active layer having a predetermined light emission wavelength on the n-layer, a step of forming an intermediate layer made of a group IIIA nitride semiconductor on the first active layer at a growth temperature of 700 to 1000 ℃, a step of forming a second active layer having a light emission wavelength longer than that of the first active layer on the intermediate layer, a step of forming a groove reaching the intermediate layer from the second active layer side, a step of forming a first p-layer and a second p-layer made of a p-type group IIIA nitride semiconductor on the second active layer and the intermediate layer exposed to the bottom surface of the groove, and a step of forming a first p-electrode and a second p-electrode on the first p-layer and the second p-layer, respectively.

The second active layer is formed by stacking a strain relief layer, which is a quantum well structure and which adjusts the thickness of the well layer so as not to emit light, and a light-emitting layer, which is a quantum well structure and which emits light, in this order from the intermediate layer side. The wavelength of the strain relief layer corresponding to the band edge energy of the well layer is set to be shorter than the emission wavelength of the light-emitting layer.

The strain relief layer may have an SQW structure.

4. Fourth aspect of the invention

The method for producing a group IIIA nitride semiconductor is a method for producing a group IIIA nitride semiconductor In which an In composition is 35% or more by MOCVD, wherein the growth temperature is 550 to 700 ℃, the growth rate is 0.8nm/min or less, and the In solid-phase ratio/In gas ratio is 0.75 to 1, thereby forming the group IIIA nitride semiconductor.

The partial pressure of the N source gas may be set to 0.15 to 0.2atm. The VIII ratio may be 30000 to 80000. In addition, the In vapor phase ratio may be 40% or more. In addition, the partial pressure of Ga raw material gas may be set to 1X 10 ^－6 ～3×10 ^－6 atm, the partial pressure of the In raw material gas is set to 1X 10 ^－6 ～3×10 ^－6 atm。

The method for manufacturing a light-emitting element is a method for manufacturing a light-emitting element composed of a group IIIA nitride semiconductor having a quantum well structure layer with a light-emitting color of yellow to red, and the well layer of the quantum well structure layer is formed by the method for manufacturing a group IIIA nitride semiconductor.

In addition, it may have: a first strain relief layer forming step of forming a first strain relief layer having a quantum well structure and a thickness of the well layer adjusted so as not to emit light and corresponding to a wavelength of blue at the band edge energy of the well layer, a second strain relief layer forming step of forming a second strain relief layer having a thickness of the well layer adjusted so as not to emit light and corresponding to a wavelength of green at the band edge energy of the well layer, and a quantum well structure layer forming step of forming the quantum well structure layer on the second strain relief layer.

In addition, the growth temperature of the well layer of the quantum well structure layer may be lower than the growth temperature of the first strain relief layer and the second strain relief layer. In addition, the growth temperature of the second strain relief layer may be lower than the growth temperature of the first strain relief layer.

In addition, the growth rate of the well layer of the quantum well structure layer may be made slower than the growth rates of the first strain relief layer and the second strain relief layer. In addition, the growth rate of the second strain relief layer may be made slower than the growth rate of the first strain relief layer.

In addition, the In gas phase ratio at the time of forming the well layer of the quantum well structure layer may be made smaller than the In gas phase ratio at the time of forming the first strain relief layer and the second strain relief layer.

The growth rate of the barrier layer of the quantum well structure layer stacked after formation of the well layer of the quantum well structure layer may be equal to or higher than the growth temperature of the well layer. The growth temperature of the barrier layer of the quantum well structure layer stacked after the formation of the well layer of the quantum well structure layer may be the same as the growth temperature of the well layer.

5. First embodiment

5-1. Structure of light-emitting element

Fig. 1 is a diagram showing a configuration of a light-emitting element according to a first embodiment. The light emitting element of the first embodiment can emit blue light, green light, and red light, respectively. The light emitting element of the first embodiment is a flip chip type that extracts light from the back surface side of a substrate, and is packaged on a package substrate (not shown) in a face-down (face-down) manner. The first embodiment has a structure in which 1 pixel is 1 chip, but may be a monolithic structure. In other words, the element structure of the first embodiment may be Micro LED display elements arranged in a matrix on the same substrate.

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

The substrate 10 is a growth substrate for growing a group IIIA nitride semiconductor. For example, sapphire, si, gaN, etc.

The n-layer 11 is an n-type semiconductor provided on the substrate 10 through a low temperature buffer layer and a high temperature buffer layer (not shown). However, the buffer layer may be provided as needed, and the buffer layer may not be provided in the case where the substrate is GaN or the like. The n-layer 11 is, for example, n-GaN, n-AlGaN, or the like. Si concentration is, for example, 1X 10 ¹⁸ ～100×10 ¹⁸ cm ^－3 。

The ESD layer 12 is a semiconductor layer provided on the n layer 11, and is provided to improve electrostatic withstand voltage. The ESD layer 12 may be omitted as long as it is provided as necessary. The ESD layer 12 is, for example, gaN, inGaN, or AlGaN undoped or doped with Si at a low concentration.

The underlayer 13 is a semiconductor layer having a superlattice structure provided on the ESD layer 12, and is a layer for relaxing lattice strain of the semiconductor layer formed on the underlayer 13. The base layer 13 may be provided as needed, and may be omitted. The underlayer 13 is formed by alternately stacking group IIIA nitride semiconductor thin films (for example, 2 of GaN, inGaN, alGaN) having different compositions, and has a logarithmic number of, for example, 3 to 30. Can be undoped or doped with 1×10 ¹⁷ ～100×10 ¹⁷ cm ^－3 Left and right Si. In addition, the superlattice structure is not required as long as the strain can be relaxed. The material may be any material having a small difference in lattice constant at the hetero interface 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 of a SQW or MQW structure provided on the base layer 13. The light-emitting wavelength is blue and is 430-480 nm. The first active layer 14 has a structure in which 1 to 7 pairs of barrier layers made of AlGaN and well layers made of InGaN are alternately stacked. More preferably 1 to 5 pairs, and 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 as to be able to control light emission from the first active layer 14 and light emission from the second active layer 16, respectively. In addition, the first active layer 14 is protected from etching damage when the second trench 31 is formed.

The material of the first intermediate layer 15 is a group IIIA nitride semiconductor containing In, and may be InGaN, for example. The surface flatness can be improved by suppressing the roughness of the surface of the first intermediate layer 15 by the In-based surfactant effect. In addition, lattice strain can be relaxed. The In composition (molar ratio of In to the entire group IIIA metal of the group IIIA nitride semiconductor) of the first intermediate layer 15 may be set so as not to absorb the band gap of the light emitted from the first active layer 14 and the second active layer 16. The In composition is preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less. If the In composition is more than 10%, the surface roughness of the first intermediate layer 15 may be caused. In is arbitrarily set as long as it is larger than 0%, and may be a doping level (a level at which mixed crystals are not formed). For example, the In concentration is 1X 10 ¹⁴ cm ^－3 ～1×10 ²² cm ^－3 Is a GaN of (C).

In addition, impurities may be doped in the first intermediate layer 15. Preferably an n-type impurity. For example, the Si concentration may be 1×10 ¹⁷ ～1000×10 ¹⁷ cm ^－3 Preferably 10X 10 ¹⁷ ～100×10 ¹⁷ cm ^－3 More preferably 20X 10 ¹⁷ ～80×10 ¹⁷ cm ^－3 。

The thickness of the first intermediate layer 15 is preferably 20 to 150nm. If it is thicker than 150nm, it may become a cause of surface roughness of the first intermediate layer 15. In addition, if it is thinner than 20nm, it may be difficult to control the depth of the second trench 31 within the first intermediate layer 15 when forming the second trench 31 to be described later. More preferably 30 to 100nm, still more preferably 50 to 80nm.

The second active layer 16 is a light emitting layer of a SQW or MQW structure provided on the first intermediate layer 15. The light-emitting wavelength is green and is 510-570 nm. The second active layer 16 has a structure in which 1 to 7 pairs of barrier layers made of GaN and well layers made of InGaN are alternately stacked. More preferably 1 to 5 pairs, and still more preferably 1 to 3 pairs. In addition, it is preferably equal to or less than the number of pairs of the first active layers 14, more preferably less than the number of pairs of the first active layers 14.

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 provided so as to be able to control the light emission from the second active layer 16 and the light emission from the third active layer 18, respectively. In addition, the second active layer 16 is also protected from etching damage when forming the third groove 32 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. In addition, the second intermediate layer 17 may be doped with impurities in the same manner as the first intermediate layer 15. The thickness of the second intermediate layer 17 may be the same as the thickness of the first intermediate layer 15, and the thickness of the first intermediate layer 15 and the thickness of the second intermediate layer 17 may be the same. However, it is preferable to be thinner than the first intermediate layer 15, and the in composition is also larger than the first intermediate layer 15. This is because the second active layer 16 that emits green light is more susceptible to thermal damage than the first active layer 14 that emits blue light, and the influence of strain at the interface becomes greater.

The third active layer 18 is a light emitting layer of a SQW or MQW structure provided on the second intermediate layer 17. The light-emitting wavelength is red and 590-700 nm. The third active layer 18 has a structure in which 1 to 7 pairs of barrier layers made of InGaN and well layers made of InGaN are alternately stacked. More preferably 1 to 5 pairs, and still more preferably 1 to 3 pairs. In addition, it is preferably equal to or less than the logarithm of the second active layer 16, more preferably less than the logarithm of the second active layer 16.

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 AlGaN, gaN, inGaN, etc., as long as it is a material having a wider band gap than the well layer of the third active layer 18. The thickness of the protective layer 19 is preferably 2.5 to 50nm, more preferably 5 to 25nm. The protective layer 19 may be doped with impurities or Mg. In this case, the Mg concentration may be 1×10 ¹⁸ ～1000×10 ¹⁸ cm ^－3 。

A part of the region of the protective layer 19 is etched to provide grooves, and a third groove 32 reaching the second intermediate layer 17 from the protective layer 19, a second groove 31 reaching the first intermediate layer 15, and a first groove 30 reaching the n-layer 11 are provided.

The regrowth layers 20A to 20C are respectively provided on the protective layer 19, on the second intermediate layer 17 exposed at the bottom surface of the third trench 32, and on the first intermediate layer 15 exposed at the bottom surface of the second trench 31. The regrowth layers 20A to 20C have the same structure as the protective layer 19.

The electron blocking layers 21A to 21C are semiconductor layers provided on the regrowth layers 20A to 20C, respectively, and are layers for blocking electrons injected from the n-layer 11 in the first active layer 14, the second active layer 16, and the third active layer 18 with high efficiency. The electron blocking layer may be a single layer of GaN or AlGaN, or may be a structure in which 2 or more of AlGaN, gaN, inGaN are stacked, or a structure in which only the composition ratio is changed. In addition, the superlattice structure may also be used. The thickness of the electron blocking layers 21A to 21C is preferably 5 to 50nm, more preferably 5 to 25nm. The Mg concentration of the electron blocking layers 21A to 21C may be 1X 10 ¹⁹ ～100×10 ¹⁹ cm ^－3 。

The p layers 22A to 22C are semiconductor layers provided on the electron blocking layers 21A to 21C, respectively, and are composed of a first layer and a second layer in this order from the electron blocking layer 21 side. The first layer is preferably p-GaN, p-InGaN. The thickness of the first layer is preferably 10 to 500nm, more preferably 10 to 200nm, and still more preferably 10 to 100nm. The Mg concentration of the first layer may be 1×10 ¹⁹ ～100×10 ¹⁹ cm ^－3 . The second layer is preferably p-GaN, p-InGaN. The thickness of the second layer is excellentThe wavelength is selected to be 2 to 50nm, more preferably 4 to 20nm, still more preferably 6 to 10nm. The second layer may have a Mg concentration of 1×10 ²⁰ ～100×10 ²⁰ cm ^－3 。

In the first embodiment, the regrowth layers 20A to 20C and the electron blocking layers 21A to 21C, p and the layers 22A to 22C are separately provided, but may be continuous (see fig. 2). In this case, a regrowth layer, an electron blocking layer, and a p-layer are formed on the side surface of the third trench 32 and the side surface of the second trench 31, but the operation of the device is hardly affected. The reason for this is as follows. If the p-electrodes 24, A, p, 24, B, p, 24C are sufficiently spatially separated, respectively, the resistance of the p-layer connecting the p-electrodes 24, A, p, 24, B, p, 24C is very high and little current flows. Further, since the mobility of holes is low, holes do not spread laterally from the region in contact with the electrode, but flow mainly longitudinally through the pn junction directly under the electrode. Therefore, even if the regrowth layers 20A to 20C and the electron blocking layers 21A to 21C, p layers 22A to 22C are continuous, there is no influence on the operation of the element. That is, when a current flows through the p-electrode 24A, a current flows directly under the p-electrode 24A, and as a result, the active layer directly under the p-electrode 24A emits light, and almost no current flows through the active layer directly under the p-electrodes 24B and 24C, and light is emitted.

As shown in fig. 3, an insulating film 27 may be provided on the side surface of the third groove 32 and the side surface of the second groove 31. The insulating film 27 is formed by leaving a mask for selectively growing the regrowth layers 20A to 20C and the electron blocking layers 21A to 21C, p and the electron blocking layers 22A to 22C.

The n-electrode 23 is an electrode provided on the n-layer 11 exposed at the bottom surface of the first trench 30. In the case where 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.

The p-electrodes 24A to 24C are electrodes provided on the 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.

5-2. Operation of light emitting element

The operation of the light emitting element of the first embodiment will be described. In the light-emitting element of the first embodiment, the third active layer 18 can emit red light by applying a voltage between the p-electrode 24A and the n-electrode 23, the second active layer 16 can emit green light by applying a voltage between the p-electrode 24B and the n-electrode 23, and the first active layer 14 can emit blue light by applying a voltage between the p-electrode 24C and the n-electrode 23. In addition, 2 or more of blue light, green light, and red light may be emitted simultaneously. In this way, in the light-emitting element of the first embodiment, blue light, green light, and red light can be controlled by selecting an electrode to which a voltage is applied, and the light-emitting element can be used as 1 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 1 element, and full-color light emission can be realized by 1 element. Accordingly, the size of 1 element can be made very small for a full-color light emitting element of 1 pixel manufactured by preparing blue, green, and red LEDs and arranging them on the same substrate. Further, according to the configuration of the first embodiment, the step of preparing and arranging the blue, green, and red LEDs, respectively, can be omitted, and the manufacturing cost can be greatly reduced, and a full-color light-emitting element and a light-emitting display using the full-color light-emitting element can be realized at very low cost.

Here, in the first embodiment, since the first intermediate layer 15 and the second intermediate layer 17 contain In, the surface planarity of the first intermediate layer 15 and the second intermediate layer 17 can be improved by the surfactant effect of In, and the surface planarity of the second active layer 16 and the third active layer 18 can also be improved. In addition, the lattice strain generated by the difference in lattice constants between the underlayer 13 and the first active layer 14 can be relaxed. As a result, according to the light-emitting element of the first embodiment, the light-emitting efficiency can be improved.

5-3. Method for manufacturing light-emitting element

Next, a process for manufacturing the light-emitting element according to the first embodiment will be described with reference to the drawings.

First, a substrate 10 is prepared, and hydrogen, nitrogen, and ammonia as needed are added thereto, and the substrate is heat-treated.

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

The growth temperature of the first active layer 14 is preferably 700 to 950 ℃. The crystal quality can be improved and the luminous efficiency can be improved. The first active layer 14 is composed of a well layer and a barrier layer, and 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. At different temperatures, the growth temperature of the well layer is preferably lower than the growth temperature of the barrier layer.

The growth temperature of the first intermediate layer 15 is preferably 700 to 1000 ℃. This is to suppress thermal damage to the first active layer 14. In addition, if the temperature is lower than 700 ℃, pits and point defects due to threading dislocation are likely to occur. More preferably 800 to 950 ℃, still more preferably 850 to 950 ℃.

The growth temperature of the second active layer 16 is preferably 650 to 950 ℃. The crystal quality can be improved and the luminous efficiency can be improved. The second active layer 16 is composed of a well layer and a barrier layer, and 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. At different temperatures, the growth temperature of the well layer is preferably lower than the growth temperature of the barrier layer. In addition, 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, it is preferable that the growth temperature of the second intermediate layer 17 is lower than that of the first intermediate layer 15. This is because the second active layer 16 that emits green light is more susceptible to thermal damage than the first active layer 14 that emits blue light, and the influence of strain at the interface becomes large.

The growth temperature of the third active layer 18 is preferably 500 to 950 ℃. The crystal quality can be improved and the luminous efficiency can be improved. The third active layer 18 is composed of a well layer and a barrier layer, and 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. At different temperatures, the growth temperature of the well layer is preferably lower than the growth temperature of the barrier layer. In addition, 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 ℃. This is to suppress thermal damage to the first, second, and third active layers 14, 16, 18. In order to improve the crystallinity of the protective layer 19, the growth temperature is preferably 600 to 900 ℃, more preferably 700 to 900 ℃.

Next, a part of the surface of the protective layer 19 is dry-etched until reaching the second intermediate layer 17 to form the third groove 32, and then dry-etched until reaching the first intermediate layer 15 to form the second groove 31 (see fig. 6). The third grooves 32, 31 are preferably etched to an intermediate thickness of the second intermediate layer 17, the first intermediate layer 15.

Next, the regrowth layers 20A to 20C are formed on the protective layer 19, on the second intermediate layer 17 exposed by the third trench 32, and on the first intermediate layer 15 exposed by the second trench 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. 2. As shown in fig. 3, the regrowth layers 20A to 20C may be formed separately by forming the insulating film 27 on the side surfaces of the third trench 32 and the second trench 31 and selectively growing the regrowth layers 20A to 20C using the insulating film as a mask.

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

Next, p layers 22A to 22C are formed on the electron blocking layers 21A to 21C (see fig. 7). The growth temperature of the p-layers 22A to 22C is preferably 650 to 1000 ℃. More preferably 700 to 950 ℃, still more preferably 750 to 900 ℃.

Next, a part of the region of the surface of the p-layer 22C is dry etched until reaching the n-layer 11, thereby forming a first trench 30 (see fig. 8). Then, n-electrode 23 is formed on n-layer 11 exposed at the bottom surface of first trench 30, and p-electrodes 24A to 24C are formed on p-layers 22A to 22C. Thereby manufacturing the light emitting element of the first embodiment.

6. Second embodiment

As shown in fig. 9, the light-emitting element according to the second embodiment is obtained by replacing the first intermediate layer 15 and the second intermediate layer 17 with the first intermediate layer 215 and the second intermediate layer 217 in the light-emitting element according to the first embodiment.

The first intermediate layer 215 has a structure in which an undoped layer 215A, n type layer 215B is stacked in this order from the first active layer 14 side. The undoped layer 215A, n type layer 215B is composed of the same material except for impurities and is GaN or InGaN. The same material as the first intermediate layer 15 of the first embodiment is preferable. Undoped layer 215A is undoped and n-type layer 215B is Si doped. The Si concentration of the n-type layer 215B is preferably 1×10 ¹⁷ ～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. Namely, it is preferably 20 to 150nm. The thickness of the undoped layer 215A is preferably 10nm or more. This is to achieve control of the etching depth and to avoid etching damage to the first active layer 14. The thickness of the n-type layer 215B is preferably 10nm or more. This is to control the light emission characteristics of each active layer independently. The n-type layer 215B may modulate doped Si, and a portion of the region of the n-type layer 215B may be an undoped region.

The second intermediate layer 217 has a structure in which an undoped layer 217A, n type layer 217B is laminated in this order from the second active layer 16 side. Undoped layer 217A, n type layer 217B has the same structure as undoped layer 215A, n type layer 215B. In other words, the undoped layer 217A, n type layer 217B is made of the same material except for impurities and is GaN or InGaN. The undoped layer 217A is undoped, and the n-type layer 217B is Si-doped. However, it is preferable to be thinner than the first intermediate layer 215, and the in composition is also larger than that of the first intermediate layer 215. The reason is the same as in the case of the second intermediate layer 17. In other words, the second active layer 16 that emits green light is more susceptible to thermal damage than the first active layer 14 that emits blue light, and the influence of strain at the interface becomes larger.

The third trench 32 is a depth of the undoped layer 217A reaching the second intermediate layer 217. Thus, the second active layer 16 emits light by removing the n-type layer 217B of the second intermediate layer 17 under the p-electrode 24B to avoid the n-type layer from being located on the second active layer 16. In addition, the second trench 31 reaches the depth of the undoped layer 215A of the first intermediate layer 215. For the same reason, the n-type layer 215B of the first intermediate layer 15 is removed under the p-electrode 24C to avoid the n-type layer from being located on the first active layer 14, thereby causing the first active layer 14 to emit light.

Here, the distance between pn junctions will be described. The pn junction distance corresponds to the film thickness depleted at zero bias. The total film thickness of an undoped or low-doped active layer sandwiched between a p-layer having a high concentration of acceptor impurities and an n-layer having a high concentration of donor impurities corresponds to an LED.

When the first and second intermediate layers 215 and 217 are undoped, the distance between pn junctions (the thickness of the depletion layer) corresponds to the distance from the electron blocking layer 21A highly doped with acceptor impurities to the n-layer 11 highly doped with donor impurities in the region under the p-electrode 24A, that is, the film thickness including the first and second active layers 14 and 16, the third active layer 18, and the first and second intermediate layers 15 and 17. The distance from the electron blocking layer 21B highly doped with acceptor impurities to the n-layer 11 at the p-electrode 24B corresponds to the film thickness including the first active layer 14, the second active layer 16, and a part of the first intermediate layer 15 and the second intermediate layer 17. In addition, the distance from the electron blocking layer 21C highly doped with acceptor impurities to the n-layer 11 at the p-electrode 24C corresponds to the film thickness including the first active layer 14 and a part of the first intermediate layer 15.

Therefore, the pn-junction distances are different in these 3 cases, respectively, resulting in different driving voltages, current injection efficiencies, and reverse currents. When it is desired to apply a voltage to the p-electrode 24A to cause the third active layer 18 to emit light, carriers of electrons and holes may be 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 apply a voltage to the p-electrode 24B to cause the second active layer 16 to emit light, the first active layer 14 may also emit light.

In the second embodiment, such a problem is solved by the structure of the intermediate layer. In other words, in the second embodiment, the first intermediate layer 15 is 2 layers of the undoped layer 215A and the n-type layer 215B doped with the donor impurity at a high concentration, the second intermediate layer 17 is 2 layers of the undoped layer 217A and the n-type layer 217B doped with the donor impurity at a high concentration, and the n-type layers 215B and 217B are doped with Si to be n-type.

Therefore, the pn-junction distance becomes a distance from the electron blocking layer 21A to the n-type layer 217B of the second intermediate layer 217 in the region under the p electrode 24A, a distance from the electron blocking layer 21B to the n-type layer 215B of the first intermediate layer 215 in the region under the p electrode 24B, and a distance from the electron blocking layer 21C to the n-layer 11 in the region under the p electrode 24C. That is, the pn-junction distance under all electrodes corresponds to the total film thickness including 1 active layer and the undoped layer in the intermediate layer without including a plurality of active layers.

Here, by appropriately controlling the thicknesses of the undoped layer 215A of the first intermediate layer 215 and the undoped layer 217A of the second intermediate layer 17, the pn-junction distances can be equalized in these 3 cases. As a result, in these 3 cases, variations in the drive voltage, current injection efficiency, and reverse current can be suppressed, and uniform control can be realized.

In these 3 cases, since each of the pn junctions includes only 1 first active layer 14, second active layer 16, and third active layer 18, the n-type layer of the intermediate layer serves as a barrier layer for holes, and holes are not easily injected into the lower active layer beyond the n-type layer of the intermediate layer. As a result, light emission other than the active layer located between the pn junctions and intended to emit light can be suppressed.

7. Third embodiment

As shown in fig. 10, in the light-emitting element of the third embodiment, 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 in the light-emitting element of the first embodiment.

The second active layer 316 has a structure in which a strain relief layer 316A and a quantum well structure layer (light-emitting layer) 316B of SQW or MQW are laminated in this order from the second intermediate layer 15 side. The quantum well structure layer 316B has the same structure as the second active layer 16 of the first embodiment.

The strain relief layer 316A is a SQW structure in which a barrier layer, a well layer, and a barrier layer are sequentially stacked, and is a quantum well structure in which the thickness of the well layer is adjusted to be thin in order to avoid light emission. For example, light emission can be avoided by making the thickness of the well layer 1nm or less. The barrier layer is AlGaN, and the well layer is InGaN. The wavelength of the strain relief layer 316A corresponding to the band edge energy of the well layer may be shorter than the emission wavelength of the quantum well structure layer 316B, and for example, 400 to 460nm if the emission wavelength of the second active layer 16 is 500 to 560 nm. Preferably 40 to 100nm shorter than the emission wavelength of the quantum well structure layer 316B. In this case, the growth temperature of the strain relief layer 316A is 700 to 800 ℃.

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

The control of the band-end energy of the well layer of the strain relief layer 316A may be controlled by the thickness of the well layer. That is, the thickness of the well layer of the strain relief layer 316A is made sufficiently thin to raise the energy of the sub-band (subband) in the well, thereby increasing the band edge energy. Thus, the emission wavelength of the quantum well structure layer 316B can be shorter than that of the quantum well structure layer. The growth temperature is arbitrary, and the quantum well structure layer 316B may be grown at the same growth temperature.

Further, if the film thickness of the well layer of the strain relief layer 316A is made thinner, the sub-band is further increased, and the energy difference from the barrier layer becomes smaller. I.e., near the band end energy of the barrier layer. As a result, it becomes difficult to enclose carriers in the well layer of the strain relief layer 316A, and light emission is not easily performed, thereby functioning as a part of the barrier layer of the quantum well structure layer 316B, and also obtaining the effect of strain relief. In this way, by forming the strain relief layer 316A having a well layer with a carrier blocking worse than that of the quantum well structure layer 316B, the strain relief layer 316A that does not emit light can be formed.

In short, the material and layer structure of the strain relief layer 316A may be set so that the effective lattice constant of the entire strain relief 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 relief layer 316A does not emit light.

The strain relief layer 316A may have an MQW structure in which a barrier layer and a well layer are laminated in a layer of 2 pairs or more, but the second active layer 316 is preferably an SQW structure because it is thick.

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

The ratio of the thickness of the first active layer 14 to the thickness of the second active layer 316 is preferably set to 30% or less. The strain of the quantum well structure layer 316B can be relaxed more effectively, and the pn-junction distance can be made constant under the p-electrodes 24A to 24C, so that the device characteristics under the p-electrodes 24A to 24C can be made uniform.

The third active layer 318 has a structure in which a first strain relief layer 318A, a second strain relief layer 318B, and a quantum well structure layer 318C of SQW or MQW are stacked in this order from the second intermediate layer 17 side. 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 the same structure as the strain relief layer 316A of the second active layer 316. The wavelength of the first strain relief layer 318A corresponding to the band edge energy of the well layer may be shorter than the emission wavelength of the quantum well structure layer 316B, for example, 400 to 460nm.

As for the second strain relief layer 318B, the wavelength of the band-edge energy of the second strain relief layer 318B corresponding to the well layer is shorter than the emission wavelength of the quantum well structure layer 318C, and longer than the wavelength of the first strain relief layer 318A corresponding to the band-edge energy of the well layer. For example, 510 to 570nm. Otherwise, the same as the first strain relief layer 318A.

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

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 preferably set to 30% or less. The strain of the quantum well structure layer 318C can be relaxed more effectively, and the distance between pn junctions is constant at the respective p-electrodes 24A to 24C, so that the device characteristics at the respective p-electrodes 24A to 24C can be made uniform.

By providing the first strain relief layer 318A and the second strain relief layer 318B in this manner, the strain can be relieved stepwise, and the strain of the quantum well structure layer 318C stacked thereon can be effectively relieved. As a result, the quality of the well layer of the quantum well structure layer 318C can be improved.

The first and second strain relaxing layers 318A and 318B are used to relax the strain in 2 stages in the third active layer 318, but 3 or more strain relaxing layers may be provided to relax the strain in 3 or more stages. In addition, the second active layer 316 may have a plurality of strain-relieving layers 316A to relieve strain stepwise.

The first active layer 14 may be provided with a strain relief layer in the same manner. In this case, the growth temperature of the strain-relieving layer is, for example, 800 to 900 ℃.

8. Modification examples of the first to third embodiments

The light-emitting element of the present embodiment has 3 active layers, i.e., the first active layer 14, the second active layer 16, and the third active layer 18, but may be applied to a structure having 2 or more active layers having different emission wavelengths. The emission color is not limited to blue, green, and red, and may be any emission wavelength.

The light emitting element of the present embodiment preferably controls light emission by PWM driving by a PWM circuit. The light intensity can be easily controlled by the pulse width and the pulse period, and also the wavelength shift due to the difference in the drive current can be suppressed.

9. Experimental results

Next, experimental results relating to the present embodiment will be described.

9-1. Experiment 1

A light-emitting element (see fig. 11, hereinafter referred to as a light-emitting element of experimental example 1) was produced in which the second intermediate layer 17 and the third active layer 18 were omitted from the light-emitting element of the first embodiment, the regrowth layer 20B, the electron blocking layer 21B, p, the 22B, p electrode 24B were omitted, the first intermediate layer 215 of the second embodiment was used in place of the first intermediate layer 15, and the second active layer 316 of the third embodiment was used in place of the second active layer 16. The first intermediate layer 215 is InGaN having an In composition of 5%. The wavelength of the strain relief layer 316A of the second active layer 316 corresponding to the band edge energy of the well layer is the same as the emission wavelength of the first active layer 14, and has an SQW structure.

Fig. 12 is an AFM image obtained by photographing the surface of the second active layer 316 of the light-emitting element of experimental example 1. In fig. 12, the upper layer shows a range of 10 μm square, and the lower layer shows a range of 2 μm square. For comparison, the case (experimental example 2) was also shown in which the first intermediate layer 215 was GaN, except that it was the same as experimental example 2. Referring to fig. 12, in experimental example 1, the pit density was lower than that in experimental example 2. Further, the surface flatness RMS was in the range of 10 μm square, the experimental example 1 was 0.88nm, the experimental example 2 was 2.6nm, and in the range of 2 μm square, the experimental example 1 was 0.78nm, the experimental example 2 was 3.1nm, and in either case, the experimental example 1 was smaller than the experimental example 2. As a result, it was found that In the first intermediate layer 215 acts as a surfactant, and thus the surface flatness of the first intermediate layer 215 is improved, and the surface flatness and crystal quality of the second active layer 316 thereon are also improved.

Fig. 9 is a graph showing a relationship between a driving current and external quantum efficiency for the light emitting elements of experimental examples 1 and 2. The external quantum efficiency is a case where a voltage is applied to the p-electrode 24B to cause the second active layer 316 to emit light. According to fig. 9, the external quantum efficiency of experimental example 1 is higher than that of experimental example 2. From this, it can be seen that: the external quantum efficiency is improved by the improvement of the crystal quality of the second active layer 316.

9-2. Experiment 2

The light-emitting element of the first embodiment (light-emitting element shown in fig. 1, hereinafter referred to as the light-emitting element of experimental example 3) in which the light-emitting wavelength of the first active layer 14 was 430nm, the light-emitting wavelength of the second active layer 16 was 520nm, and the light-emitting wavelength of the third active layer 18 was 630nm was subjected to current injection into the p-electrode 24A, and the light-emitting spectrum was measured. The Si concentration of the n-type layer 215B, n type layer 217B was 1×10 ¹⁸ cm ^－3 、2×10 ¹⁸ cm ^－3 、3×10 ¹⁸ cm ^－3 Is a spectrum of 3. For comparison, the light emission spectrum was also measured when the n-type layer 215 and B, n type layer 217B was replaced with undoped one.

FIGS. 14 to 17 are graphs showing light emission spectra, and FIG. 14 is a graph showing Si concentration of 3X 10 ¹⁸ cm ^－3 In the case of (2X 10) in FIG. 15 ¹⁸ cm ^－3 In the case of (1X 10), FIG. 16 ¹⁸ cm ^－3 Fig. 17 shows an undoped case. As can be seen from fig. 17: in the undoped case, not only the third active layer 18 emits red light, but also the first active layer 14 emits blue light, which is weak and of blue light intensity. On the other hand, according to fig. 14 to 16, in the case of Si doping, the red light is equal to or stronger than the blue light, and the higher the Si concentration, the lower the intensity of the blue light is emitted. Although the decrease in intensity of emitted blue light also slightly occurs in place of the second active layer 16, according to fig. 14, if the Si concentration is sufficiently high, the intensity of emitted green light also decreases. As a result, it was found that by introducing the Si-doped n-type layer 215B, n-type layer 217B into the first intermediate layer 15 and the second intermediate layer 17, light emission from the active layers (the first active layer 14 and the second active layer 16) other than the third active layer 18, which is an active layer that is desired to emit light, can be suppressed.

9-3. Experiment 3

Fig. 18 is an AFM image obtained by photographing 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 relief layer 316A is not provided in the second active layer 316 in experimental example 2. In FIG. 16, the upper layer shows a range of 10 μm square, and the lower layer shows a range of 2 μm square. According to FIG. 18, the surface flatness RMS was in the range of 10 μm square, the test example 2 was 2.6nm, the test example 4 was 3.8nm, and in the range of 2 μm square, the test example 2 was 3.1nm, the test example 4 was 3.3nm, and in any case, the test example 2 was smaller than the test example 4. Namely, the surface flatness is improved. The results showed that: by introducing the strain relief layer 316A into the second active layer 316, the strain of the quantum well structure layer 316B thereon is relieved, and the surface flatness and crystal quality are improved.

Fig. 19 is a graph showing a relationship between a driving current and external quantum efficiency for the light emitting elements of experimental examples 2 and 4. The external quantum efficiency is a case where a voltage is applied to the p-electrode 24A to cause the second active layer 316 to emit light. According to fig. 19, the external quantum efficiency of experimental example 2 was higher than that of experimental example 4. From this, it can be seen that: by relaxing the strain of the second active layer 316, the surface flatness and crystal quality are improved, and the external quantum efficiency is improved.

10. Fourth embodiment

10-1. Structure of light-emitting element

Fig. 20 is a view showing the structure of the light-emitting element of the fourth embodiment, and is a cross-sectional view of a surface perpendicular to the main surface of the substrate. As shown in fig. 20, the light-emitting element according to the fourth embodiment is obtained by changing a part of the structure of the light-emitting element according to the first embodiment as follows. The same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

According to fig. 20, a first intermediate layer 415 and a second intermediate layer 417 are provided instead of the first intermediate layer 15 and the second intermediate layer 17. The protective layer 19, the regrowth layers 20A to 20C, and the electron blocking layers 21A to 21C, p, 22A to 22C are omitted, the electron blocking layer 421 to A, p, 422 is provided on the third active layer 18, and the p-electrode 24A is provided on the p-layer 422. In other words, the light emitting element of the fourth embodiment has no regrowth layer. The first electrode 424B is provided on the first intermediate layer 415 exposed on the bottom surface of the second trench 31, and the second electrode 424C is provided on the second intermediate layer 417 exposed on the bottom surface of the third trench 32. Further, the electron blocking layers 421B and 421C are interposed 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 blocking layer 421C is a p-type layer disposed on the first active layer 14, and is located between the first active layer 14 and the first intermediate layer 15. The electron blocking layer 421C is similar to the electron blocking layers 21A to 21C except that it is not a regrown layer and is continuously grown 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 this order from the first active layer 14 side, and the fourth layer 415D is exposed at the bottom surface of the second groove 31. 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 over the electron blocking layer 421C. In order to efficiently emit light from the first active layer 14, the first active layer 14 is preferably sandwiched between a p-type layer and an n-type layer, and the first layer 415A is preferably provided as the p-type contact layer.

The material of the first layer 415A is the same as the first intermediate layer 15 in the first embodiment except for impurities. That is, the group IIIA nitride semiconductor containing In may be InGaN, for example. The surface flatness can be improved by suppressing roughness of the surface of the first intermediate layer 415 by the In-based surfactant effect. Further, lattice strain can be relaxed. The In composition of the first intermediate layer 415 may be set so as not to absorb the band gap of the light emitted from the first active layer 14, the second active layer 16, and the third active layer 18.

The In composition of the first layer 415A is preferably 10% or less, more preferably 5% or less, and further preferably 2% or less. If the In composition is more than 10%, the surface roughness of the first intermediate layer 415 may be caused. If In is more than 0%, the doping level (level at which mixed crystals are not formed) may be arbitrary. For example, the In concentration is 1X 10 ¹⁴ cm ^－3 ～1×10 ²² cm ^－3 Is a GaN of (C).

The first layer 415A is a p-type half doped with Mg as a p-type impurityA conductor. For example, the Mg concentration may be 1×10 ¹⁸ ～1×10 ²⁰ cm ^－3 Preferably 5X 10 ¹⁸ ～1×10 ²⁰ cm ^－3 More preferably 1X 10 ¹⁹ ～1×10 ²⁰ cm ^－3 . Mg is preferably doped as described above, although it may also be undoped. The first layer 415A may be doped with polarization having a gradient In composition In the thickness direction. In which case it may be undoped. In addition, mg may be doped into the third layer 415C by Mg diffusion from the electron blocking layer 421C which is a lower layer of the first layer 415A. In this case, the Mg concentration of the electron blocking layer 421C may be 1×10 ¹⁹ ～1×10 ²¹ cm ^－3 Is not limited in terms of the range of (a).

The thickness of the first layer 415A is preferably 10 to 300nm. If it is thicker than 300nm, it may cause roughness of the surface of the first intermediate layer 415. In addition, if it is thinner than 10nm, there is a possibility that the light emission efficiency of the first active layer 14 cannot be sufficiently improved. More preferably 20 to 200nm, still more preferably 30 to 100nm.

The second layer 415B is a semiconductor layer provided over the first layer 415A. A tunnel junction structure is formed by lamination of 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 that of the first layer 415A and the fourth layer 415D, and In this case, it is preferably higher than that of the first layer 415A and the fourth layer 415D. The probability of tunnel effect due to the tunnel junction structure can be further improved. The preferred 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 as a p-type impurity. Mg concentration of 1×10 ²⁰ ～1×10 ²¹ cm ^－3 . The Mg concentration of the second layer 415B is higher than that of the first layer 415A.

The thickness of the second layer 415B is 5 to 50nm. If this range is used, the tunneling probability of the tunnel junction structure can be sufficiently increased. More preferably 5 to 35nm, still more preferably 5 to 20nm. In addition, the thickness of the second layer 415B is preferably thinner than that of the first layer 415A.

The third layer 415C is a semiconductor layer provided over the second layer 415B. A tunnel junction structure is formed by stacking the second layer 415B on the third layer 415C. By this tunnel junction structure, a current flows from the n-type third layer 415C to the p-type second layer 415B by tunneling, 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 that of the first layer 415A and the fourth layer 415D, and In this case, it is preferably higher than that of the first layer 415A and the fourth layer 415D. The probability of tunnel effect due to the tunnel junction structure can be further improved. In addition, the In composition of the third layer 415C may be different from that of the second layer 415B. In this case, the In composition of the third layer 415C is preferably lower than that 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 as an n-type impurity. Si concentration of 1X 10 ²⁰ ～1×10 ²¹ cm ^－3 。

A layer co-doped with Si and Mg may be intentionally or naturally present near the junction interface of the second layer 415B and the third layer 415C. Mg is likely to remain in the furnace due to the memory effect, and therefore Mg can be doped in the third layer 415C and the fourth layer 415D. Here, mg concentration of the third layer 415C and the fourth layer 415D is required to be lower than the respective Si concentrations.

The thickness of the third layer 415C is 1 to 30nm. If this range is used, the tunneling probability of the tunnel junction structure can be sufficiently increased. More preferably 2 to 25nm, still more preferably 5 to 20nm. In addition, the thickness of the third layer 415C is preferably thinner than that of the fourth layer 415D.

As described above, the band gap of the second layer 415B and the third layer 415C forming the tunnel junction structure becomes small due to the inclusion of In, and the tunnel effect probability becomes high. A layer may be further 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 for suppressing Mg of the second layer 415B from diffusing to the third layer 415C may be provided.

The fourth layer 415D is a semiconductor layer provided over the third layer 415C. In order to efficiently emit light from the second active layer 16, the second active layer 16 is preferably sandwiched between a p-type layer and an n-type layer, and the fourth layer 415D is preferably provided as the n-type contact layer. In addition, this is a layer for avoiding exposure of the second groove 31 to the third layer 415C when forming the second groove.

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

The fourth layer 415D is an n-type semiconductor doped with Si as an n-type impurity. For example, the Si concentration may be 1×10 ¹⁷ ～1×10 ²⁰ cm ^－3 Preferably 1X 10 ¹⁸ ～1×10 ¹⁹ cm ^－3 More preferably 2X 10 ¹⁸ ～8×10 ¹⁸ cm ^－3 . 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 500nm. If it is thicker than 500nm, it may cause roughness of the surface of the first intermediate layer 415. In addition, if it is thinner than 10nm, there is a possibility that the light emission efficiency of the second active layer 16 cannot be sufficiently improved. In addition, it may be difficult to control the depth of the second groove 31 within the fourth layer 415D when forming the second groove 31. More preferably 10 to 200nm, still more preferably 10 to 100nm. The thickness of the fourth layer 415D may be different from the thickness of the first layer 415A.

The electron blocking 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 blocking layer 421B is similar to the electron blocking layers 21A to 21C except that it is not a regrown layer and is continuously grown 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 stacked in this order from the second active layer 16 side, and the fourth layer 417D is exposed at the bottom surface of the third trench 32. 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, the second layer 417B, the third layer 417C, and the fourth layer 417D are the same as the first layer 415A, the second layer 415B, the third layer 415C, and the fourth layer 415D of the first intermediate layer 415, respectively. A tunnel junction structure is formed by stacking the second layer 417B and the third layer 417C, and a current flows from the n-type third layer 417C to the p-type second layer 417B by tunnel effect, so that holes are supplied 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 those of the first intermediate layer 15 and the second intermediate layer 17 in embodiment 1 are obtained. In other words, the surface flatness can be improved, and the lattice strain can be relaxed.

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

The electron blocking layer 421A is a p-type layer provided on the third active layer 18. The electron blocking layer 421A is similar to the electron blocking layers 21A to 21C except that it is not a regrown layer and is continuously grown on the third active layer 18.

The p-layer 422 is a layer provided on the electron blocking layer 421A. The p-layer 422 is similar to the p-layer 22A except that it is not a regrown layer and is grown continuously over the electron blocking layer 421A.

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

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

In the light-emitting element according to 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 according to the third embodiment, respectively. In this case, the strain relief layer 316A of the second active layer 316 functions as a buffer layer for Mg to diffuse from the first intermediate layer 415 to the quantum well structure layer 316B. The first strain relief layer 318A and the second strain relief layer 318B of the third active layer 318 function as buffer layers for Mg diffusion from the second intermediate layer 417 to the quantum well structure layer 318C. Therefore, a decrease in light emission efficiency can be suppressed.

The various modifications described in the first to third embodiments can 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 may have a tunnel junction structure as it is, or the first intermediate layer 415 may have a structure in which the regrowth layer 20C and the electron blocking layer 21C, p layer 22C are provided in place of the first intermediate layer 15 of the first embodiment, as in the first embodiment.

Such a constitution has the following advantages. The first active layer 14 that emits blue light has high light emission efficiency, and even if the light emission efficiency is reduced due to regrowth, there is no significant obstacle. On the other hand, the second active layer 16 that emits green light has low light emission efficiency, and it is desirable to avoid as much as possible the decrease in light emission efficiency caused by the regrowth. Therefore, if the element region for emitting blue light is formed by groove formation and regrowth as in the first embodiment, and the element region for emitting green light is formed by a tunnel junction structure as in the fourth embodiment, variations in emission efficiency of blue, green, and red can be reduced.

10-2. Operation of light emitting element

The operation of the light emitting element of the fourth embodiment will be described. In the light-emitting element according to 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. In addition, green light may be emitted from the second active layer 16 by applying a voltage between the first electrode 424B and the second electrode 424C. In addition, blue light may be emitted from the first active layer 14 by applying a voltage between the second electrode 424C and the n electrode 23.

Further, 2 or more of blue, green, and red may be emitted simultaneously. Specifically, the voltage is applied as follows. When all of blue, green, and red are emitted, a voltage is applied between the p-electrode 24A and the n-electrode 23. When green and red are simultaneously emitted, a voltage is applied between the p-electrode 24A and the second electrode 424C. When blue and green are simultaneously emitted, a voltage is applied between the first electrode 424B and the n-electrode 23. When blue and red are simultaneously emitted, 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 way, in the light-emitting element according to the fourth embodiment, blue light, green light, and red light can be controlled by selecting electrodes to which voltages are applied, and the light-emitting element can be used as 1 pixel of a display.

Fig. 21 shows an equivalent circuit of the light-emitting element of the fourth embodiment. The light emitting element according to the fourth embodiment is equivalent to a structure in which red LEDs, first tunnel junctions (reverse tunnel diodes), green LEDs, second tunnel junctions, and blue LEDs are connected in columns, and electrodes are drawn out from connection portions between the red LEDs and the first tunnel junctions and connection portions between the green LEDs and the second tunnel junctions. The light-emitting element of the fourth embodiment is also configured such that blue, green, and red LEDs are formed in 1 element, similarly to the light-emitting element of the first embodiment, and full-color light emission can be realized by 1 element.

10-3. Method for manufacturing light-emitting element

Next, a process for manufacturing the light-emitting element according to the fourth embodiment will be described.

First, the substrate 10 is prepared and heat-treated in the same manner as in the first embodiment. Then, a buffer layer, an n layer 11, an ESD layer 12, a base layer 13, a first active layer 14, an electron blocking layer 421C, a first intermediate layer 415, a second active layer 16, an electron blocking layer 421B, a second intermediate layer 417, a third active layer 18, and an electron blocking layer 421A, p layer 422 are formed on the substrate 10 in this order from the substrate 10 side by the MOCVD method.

The growth temperatures of the first intermediate layer 415 and the second intermediate layer 417 are in the same range as the first intermediate layer 15 and the second intermediate layer 17 in the first embodiment. It is preferable that the growth temperature of the second intermediate layer 417 is lower than the growth temperature of the first intermediate layer 415. This is because the second active layer 16 that emits green light is more susceptible to thermal damage than the first active layer 14 that emits blue light, and the influence of strain at the interface becomes large.

In the formation of 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 further improve the tunnel effect in the tunnel junction in order to improve crystallinity. In addition, in the formation of the second intermediate layer 417, the growth temperature of the second layer 417B and the third layer 417C is preferably lower than the growth temperature of the first layer 417A and the fourth layer 417D.

Next, a part of the region of the surface of the p-layer 422 is dry-etched until reaching the fourth layer 417D of the second intermediate layer 417 to form the third trench 32, dry-etched until reaching the fourth layer 415D of the first intermediate layer 415 to form the second trench 31, and dry-etched until reaching the n-layer 11 to form the first trench 30.

Next, n-electrode 23 is formed on n-layer 11 exposed at the bottom surface of first trench 30, p-electrode 24A is formed on p-layer 422, first electrode 424B is formed at the bottom surface of third trench 32, and second electrode 424C is formed at the bottom surface of second trench 31. 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 by the same process as the n-electrode 23. Thereby manufacturing the light emitting element of the fourth embodiment.

As described above, the light emitting element of the fourth embodiment does not require the electron blocking layer or the regrowth layer of the p layer by providing the tunnel junction structure in the first intermediate layer 415 and the second intermediate layer 417. Since the regrowth interface causes etching damage, contamination with impurities by exposure to the atmosphere, and thermal damage by regrowth, there is a possibility that the regrowth interface between pn may deteriorate the device characteristics. However, since the light-emitting element of the fourth embodiment has no regrowth layer, there is no regrowth interface between pn's, and thus such a problem does not occur.

In the first to fourth embodiments, inGaN is used as the well layer in the quantum well structure layer 318C of the third active layer 18 and the third active layer 318, but a group IIIA nitride semiconductor doped with Eu (europium), particularly GaN, may be used. In this case, the light may be made to emit red light, and the emission wavelength may be about 620nm. When Eu-doped GaN is used, since strain relaxation of the active layer is not required, the first strain relaxing layer 318A and the second strain relaxing 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.

Likewise, group IIIA nitride semiconductors doped with Pr (praseodymium), in particular GaN, may also be used. Can be used as a material emitting red light.

As well layers in the quantum well structure layers 316B of the second active layers 16 and 316, group IIIA nitride semiconductors doped with Tb (terbium), in particular GaN, may be used. In this case, the light may be emitted green.

As the well layer in the first active layer 14, a group IIIA nitride semiconductor doped with Tm (thulium), particularly GaN, may be used. In this case, blue light may be emitted.

11. Fifth embodiment

11-1. Structure of light-emitting element

Fig. 22 is a view showing the structure of the light-emitting element of the fifth embodiment, and is a cross-sectional view of a surface perpendicular to the main surface of the substrate. The light-emitting element of the fifth embodiment has light-emitting colors of yellow to red, and includes a substrate 510, an n-layer 511, a base layer 513, an active layer 518, an electron blocking layer 521, a p-layer 522, an n-electrode 523, and a p-electrode 524, as shown in fig. 22.

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

The base layer 513 is preferably a laminate of a superlattice structure layer and a high-concentration n-type GaN layer. The superlattice structure layer is preferably formed by alternately stacking n-type InGaN and n-type GaN, and the number of pairs is, for example, 3 to 30.Si concentration is, for example, 1X 10 ¹⁷ ～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 ～1×10 ¹⁹ cm ^－3 . Further, the high-concentration n-type GaN layer is preferably in contact with the active layer 518.

The active layer 518 is a layer disposed on the base layer 513. The active layer 518 has a structure in which a first strain relief layer 518A, a second strain relief layer 518B, and a quantum well structure layer 518C of SQW or MQW are stacked in this order from the base layer 513 side.

The first and second strain relief layers 518A and 518B are similar to the first and second strain relief layers 318A and 318B in the third active layer 318 according to the third embodiment. As in the third embodiment, the first and second strain relaxing layers 518A and 518B are provided to stepwise relax the strain, so that the strain of the quantum well structure layer 518C stacked thereon can be effectively relaxed. As a result, the quality of the well layer of the quantum well structure layer 518C can be improved. The first strain relief layer 518A and the second strain relief layer 518B are preferably SQW.

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

The quantum well structure layer 518C is a light emitting layer of a SQW or MQW structure provided on the second strain relief layer 518B. The light-emitting wavelength is yellow-red and 560-700 nm. The third active layer 18 is formed by alternately stacking 1 to 7 pairs of well layers made of InGaN and barrier layers made of InGaN having an In composition lower than that of the well layers. More preferably 1 to 5 pairs, and still more preferably 1 to 3 pairs. In addition, it is preferably equal to or less than the logarithm of the second active layer 16, more preferably less than. Most preferred is SQW. The well layer of the quantum well structure layer 518C is InGaN having an In composition of 35% or more.

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

The p-layer 522 is a layer provided on the electron blocking layer 521. The p-layer 522 is the same as the p-layer 422 of the fourth embodiment.

A portion of the p-layer 522 is etched to provide a trench reaching the n-layer 11, and an n-electrode 523 is provided on the n-layer 11 exposed at the bottom surface of the trench. The material of the n-electrode 523 is the same as that of the n-electrode 23. In addition, a p-electrode 524 is disposed on the p-layer 522. The material of the p-electrode 524 is the same as that of the p-electrodes 24A to 24C.

11-2. Method for manufacturing light-emitting element

Next, a process for manufacturing the light-emitting element according to the fifth embodiment will be described.

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

The growth temperature of the electron blocking layer 521 and the p layer 522 is preferably 935 ℃. This is to suppress thermal damage to the active layer 518 and to suppress a decrease in light emission efficiency. The lower limit of the growth temperature is, for example, 600 ℃. More preferably 650 to 900 ℃. In addition, the growth temperature of the p-layer 522 is preferably higher than that of the electron blocking layer 521.

Next, a trench reaching the n-layer 11 is formed by dry etching a predetermined region of the p-layer 522, an n-electrode 523 is formed on the bottom surface of the trench, and a p-electrode 524 is formed on the p-layer 522. Thereby manufacturing the light emitting element of the fifth embodiment.

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 having an In composition of 35% or more, and it is difficult to obtain a high-quality crystal. The inventors have conducted intensive studies and developments to obtain high-quality InGaN having an In composition of 35% or more, and as a result, have found a method for obtaining high-quality InGaN. The method will be described below.

The growth temperature of the quantum well structure layer 518C is 700 ℃ or lower. The lower limit of the growth temperature is, for example, 550 ℃. By setting the growth temperature to a value around the decomposition temperature (630 ℃) of InN, decomposition and re-evaporation of InN can be suppressed, and InGaN having a high In composition (In particular, an In composition of 35% or more) can be formed. Preferably 650 ℃ or less, more preferably 610 to 650 ℃, still more preferably 620 to 640 ℃, and most preferably 625 to 635 ℃.

The growth rate of the quantum well structure layer 518C is 0.8nm/min or less. This is to suppress surface roughness, abnormal growth, and liquid droplets (droplets) caused by insufficient migration of raw material atoms at low growth temperatures. The droplets are caused by the formation of blocks of In on the crystal surface. Preferably 0.75nm/min or less, more preferably 0.7nm/min or less, and still more preferably 0.5nm/min or less. The lower limit of the growth rate is not particularly limited, and if the growth rate is too low, the formation of the quantum well structure layer 518C takes time, and thus is preferably 0.05nm/min or more.

The In solid phase ratio/In gas phase ratio is 0.75-1. Here, the In gas ratio is a molar ratio of In the raw material gas In the formation of InGaN to all group IIIA metals. The In solid phase ratio is a molar ratio of In all group IIIA metals In the InGaN crystal formed. The In solid phase ratio/In gas phase ratio can be controlled by the growth temperature, in gas phase ratio, VIII ratio, etc. By setting the In solid phase ratio/In gas phase ratio In such a range, abnormal growth and droplet formation of InGaN can be suppressed. The In solid phase ratio/In gas ratio is more preferably 0.85 to 1, and still more preferably 0.9 to 1.

By setting the growth temperature, growth rate, in solid phase ratio/In vapor phase ratio In the above-described ranges, even InGaN having an In composition of 35% or more can be obtained as a high-quality crystal. Since the growth temperature is reduced to 700 ℃ or lower as described above, the ammonia decomposition efficiency becomes low, migration of the raw material atoms is difficult to occur, and it is difficult to obtain high-quality InGaN.

The In gas phase ratio is preferably 40% or more. The In solid phase ratio/In gas phase ratio can be easily controlled within the above range, and abnormal growth and droplet formation of InGaN can be suppressed. The In gas phase ratio is preferably 55% or less.

The partial pressure of the Ga raw material gas is preferably 1X 10 ^－6 ～3×10 ^－6 The partial pressure of the In raw material gas is preferably 1X 10 ^－6 ～3×10 ^－6 and (5) 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).

The growth rate of the barrier layer of the quantum well structure layer 518C may be equal to or faster than the growth rate of the well layer of the quantum well structure layer 518C. In addition, the growth temperature of the barrier layer of the quantum well structure layer 518C may be equal to or higher than the growth temperature of the well layer of the quantum well structure layer 518C. In the case of higher temperature, the second barrier layer may be laminated by forming the first barrier layer at a temperature equal to the growth temperature of the well layer and then raising the temperature to 2 to 20 nm. This prevents the well layer having a high In composition from thermally decomposing during the temperature rise. The first barrier layer and the second barrier layer may be InGaN having an In composition lower than that of the well layer. Of course, gaN, alGaN, alGaInN may be used, or a combination thereof may be used.

The partial pressure of the N source gas is preferably 0.15 to 0.2atm. Can inhibit H generated by ammonia decomposition ₂ And the InN is decomposed and re-evaporated, so that the quality of InGaN can be improved. The nitrogen of the carrier gas is not an N source gas.

The VIII ratio (molar ratio of ammonia to group IIIA metal source gas) is preferably 30000 to 80000. If the ratio is 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 and second strain relief layers 518A and 518B. This is to suppress thermal damage to the first and second strain relief layers 518A and 518B. In addition, the growth temperature of the second strain relief layer 518B is preferably lower than the growth temperature of the first strain relief layer 518A.

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

The In gas phase ratio at the time of forming the quantum well structure layer 518C is preferably smaller than the In gas phase ratio at the time of forming the first strain relief layer 518A and the second strain relief 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 can be obtained for InGaN having an In composition of 35% or more, and In particular, inGaN having an In composition of 40% or more can be formed as a red light emitting material. 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 IIIA nitride semiconductor that emits red light with high light emission efficiency can be realized.

12. Modification of the fifth embodiment

The active layer 518 of the light emitting element of the fifth embodiment may be used as the third active layers 18 and 318 of the light emitting elements of the first to fourth embodiments.

The InGaN formation method according to the fifth embodiment can be used not only for a light emitting element but also for InGaN such as a solar cell and a photocatalyst.

Further, according to the fifth embodiment, not only the quality of InGaN having an In composition of 35% or more but also the quality of the group IIIA nitride semiconductor having an In composition of 35% or more can be improved. For example, the quality of AlGaInN having an In composition of 35% or more can be improved.

13. Experimental results

Next, experimental results relating to the fifth embodiment will be described.

13-1. Experiment 4

The growth rate is changed to form the quantum well structure layer 518C. The growth temperature was 637 ℃, in gas phase ratio was 47.5%, and ammonia flow rate was 27slm. The VIII ratios were 48000, 27000 and 20000, and the growth rates were 0.48nm/min, 0.72nm/min and 0.96nm/min, respectively. The In solid phase ratios were 42.0%, 40.0%, 41.0%, and 88.4%, 84.2%, 86.3%, respectively.

Fig. 23 is an AFM image of the well layer surface of the quantum well structure layer 518C when the growth rate is changed. The surface of the InGaN layer has the same film thickness of 2-3 nm as the actual well layer. Fig. 23 (a) shows the growth rate of 0.48nm/min, fig. 23 (b) shows the growth rate of 0.72nm/min, and fig. 23 (c) shows the growth rate of 0.96nm/min.

According to FIG. 23 (a), in the case of a growth rate of 0.48nm/min, droplets were hardly seen on the surface of the well layer, and the density of droplets was 1X 10 ⁷ cm ^－2 The diameter of the droplet is about 30nm.

In addition, according to (b) in FIG. 23, in the case of the growth rate of 0.72nm/min, more droplets were observed on the surface of the well layer than in the case of the growth rate of 0.48nm/min, and the density of the droplets was 1X 10 ⁸ cm ^－2 The diameter of the droplet is about 30nm.

In addition, according to (c) in FIG. 23, in the case of the growth rate of 0.96nm/min, more droplets were observed on the surface of the well layer than in the case of the growth rate of 0.72nm/min, the size was also large, and the density of the droplets was 4X 10 ⁸ cm ^－2 The diameter of the droplet is about 50nm.

From this result, it can be seen that: in order to reduce the droplet, the growth rate of InGaN is preferably 0.75nm/min or less, more preferably 0.5nm/min.

13-2. Experiment 5

The quantum well structure layer 518C is formed by changing In solid phase ratio/In gas phase ratio. The growth temperature was 637 ℃, the growth rate was 0.48nm/min, and the ammonia flow rate was 27slm. The VIII ratios were 40000, 48000 and 51000, and the in gas ratios were 57%, 52.5%, 47.5% and 45%, respectively. The In solid phase ratio was 42.0%, and the In solid phase ratio/In gas phase ratio was 73.7%, 80.0%, 88.4%, 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. Fig. 24 (a) shows the case where the In solid phase ratio/In gas ratio is 73.7%, fig. 24 (b) shows the case where the In solid phase ratio/In gas ratio is 80.0%, fig. 24 (c) shows the case where the In solid phase ratio/In gas ratio is 88.4%, and fig. 24 (d) shows the case where the In solid phase ratio/In gas ratio is 93.3%.

According to FIG. 24 (a), in the case where the In solid phase ratio/In gas ratio was 73.7%, many droplets were observed on the surface of the well layer, the size was also large, and the density of the droplets was 7.5X10 ⁷ cm ^－2 The diameter of the droplet is about 130nm.

Further, according to (b) In fig. 24, when the In solid phase ratio/In gas ratio is 80.0%, the well layer surface has fewer droplets and a smaller size than 73.7%. The density of the droplets was 5.0X10 ⁷ cm ^－2 The diameter of the droplet is about 80nm.

Further, according to (c) In fig. 24, when the In solid phase ratio/In gas ratio is 88.4%, the well layer surface has fewer droplets and a smaller size than In the case of 80.0%. The density of the droplets was 1.0X10 ⁷ cm ^－2 The diameter of the droplet is about 30nm.

In addition, according to (d) In fig. 24, when the In solid phase ratio/In gas ratio was 93.3%, no droplet was observed on the surface of the well layer.

From this result, it can be seen that: the In solid phase ratio/In gas phase ratio is preferably 0.75 or more, more preferably 0.85 or more, and still more preferably 0.9 or more.

13-3. Experiment 6

The partial pressure of ammonia is changed to form the quantum well structure layer 518C. The growth temperature was 637 ℃. The flow rates of the carrier gas (nitrogen) were set to three stages of 142slm, 130slm, and 110slm, and the flow rates of the ammonia corresponding to these three stages were 15slm, 27slm, and 47slm, respectively, and the partial pressures of the ammonia were 0.096atm, 0.172atm, and 0.299atm. The VIII ratios were 27000, 48000 and 85000, respectively, and the in gas ratios were 47.5%. In either case, the growth rate was 0.48nm/min, the In solid phase ratio was 40%, 42%, 40%, and the In solid phase ratio/In gas ratio was 84.2%, 88.4%, 84.2%, respectively.

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

According to (a) in fig. 25, in the case where the partial pressure of ammonia is 0.096atm, droplets are seen on the surface of the well layer. The density of the droplets was 5.0X10 ⁷ cm ^－2 The diameter of the droplet is about 50nm.

In addition, according to (b) of fig. 25, in the case where the ammonia partial pressure is 0.172atm, although droplets are seen on the surface of the well layer, the droplets are small and small in size as compared with the case where the ammonia partial pressure is 0.096 atm. The density of the droplets was 1.0X10 ⁷ cm ^－2 The diameter of the droplet is about 30nm.

In addition, according to (c) of fig. 25, in the case where the partial pressure of ammonia is 0.299atm, more droplets are seen on the surface of the well layer than in the case where the partial pressure of ammonia is 0.172atm, and the size is also larger. The density of the droplets was 5.0X10 ⁷ cm ^－2 The diameter of the droplet is about 50nm.

From the results, it is found that the partial pressure of ammonia is preferably 0.15 to 0.2atm. It is also found that the VIII ratio is preferably 30000 to 80000.

Industrial applicability

The light emitting element of the present disclosure can be used for a full-color display or the like.

Claims

1. A light-emitting element comprising a group IIIA nitride semiconductor, comprising:

an n-layer made of an n-type group IIIA nitride semiconductor,

a first active layer disposed on the n layers and having a prescribed emission wavelength,

an intermediate layer provided on the first active layer and having a structure in which an undoped layer made of an undoped group IIIA nitride semiconductor and an n-type layer made of an n-type group IIIA nitride semiconductor are stacked in order from the first active layer side,

A second active layer disposed on the intermediate layer and having a different emission wavelength than the first active layer,

a trench reaching the undoped layer from the second active layer side,

a first p-layer provided on the second active layer and made of a p-type group IIIA nitride semiconductor,

a second p-layer formed of a p-type group IIIA nitride semiconductor and provided on the undoped layer exposed at the bottom of the trench,

a first p-electrode disposed on the first p-layer, and

and a second p-electrode disposed on the second p-layer.

2. The light-emitting element according to claim 1, wherein a thickness of the intermediate layer is 150nm or less, and wherein a thickness of the undoped layer and the n-type layer is 10nm or more.

3. The light-emitting element according to claim 1 or 2, wherein the intermediate layer is composed of an group IIIA nitride semiconductor containing In, and wherein an In composition is set so as not to absorb a band gap of light emitted from the first active layer and the second active layer.

4. The light-emitting element according to claim 1 or 2, wherein the second active layer has a structure in which a strain relief layer which is a quantum well structure and adjusts a thickness of the well layer so as not to emit light, and a light-emitting layer which is a quantum well structure and emits light are laminated in this order from the intermediate layer side,

The wavelength of the strain relief layer corresponding to the band edge energy of the well layer is set shorter than the emission wavelength of the light-emitting layer.

5. A light-emitting element comprising a group IIIA nitride semiconductor, comprising:

an n-layer made of an n-type group IIIA nitride semiconductor,

an intermediate layer provided on the first active layer and made of an In-containing group IIIA nitride semiconductor, and

the intermediate layer has an In composition so as not to absorb the band gap of the light emitted from the first active layer and the second active layer.

6. The light-emitting element according to claim 5, wherein the light-emitting element has:

a groove reaching the intermediate layer from the second active layer side,

a first p-electrode disposed on the first p-layer, and

And a second p-electrode disposed on the second p-layer.

7. The light-emitting element according to claim 5, wherein 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 stacked in this order from the first active layer side,

the second layer has a p-type impurity concentration higher than that of the first layer, the third layer has an n-type impurity concentration higher than that of the fourth layer, the second layer and the third layer form a tunnel junction structure,

and has:

a p-layer disposed on the second active layer,

slots reaching the fourth layer from the p-layer side,

a p-electrode disposed on the p-layer, and

and an electrode disposed on the fourth layer exposed at the bottom surface of the groove.

8. The light-emitting element according to claim 7, wherein an In composition of the second layer and the third layer is higher than an In composition of the first layer and the fourth layer.

9. The light-emitting element according to claim 7 or 8, wherein an In composition of the second layer is higher than an In composition of the third layer.

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

11. The light-emitting element according to any one of claims 5 to 7, wherein the intermediate layer is InGaN.

12. The light-emitting element according to any one of claims 5 to 7, wherein an In composition of the intermediate layer is 10% or less.

13. The light-emitting element according to any one of claims 5 to 7, wherein the intermediate layer is GaN doped with In.

14. A light-emitting element comprising a group IIIA nitride semiconductor, comprising:

an n-layer made of an n-type group IIIA nitride semiconductor,

an intermediate layer disposed on the first active layer,

a groove reaching the intermediate layer from the second active layer side,

a first p-electrode disposed on the first p-layer, and

a second p-electrode disposed on the second p-layer,

The second active layer has a structure in which a strain relief layer having a quantum well structure and adjusting the thickness of the well layer so as not to emit light and a light-emitting layer having a quantum well structure and emitting light are laminated in this order from the intermediate layer side,

15. The light-emitting element according to claim 14, wherein a wavelength of the strain-relaxing layer corresponding to a band-edge energy of the well layer is set to be equal to an emission wavelength of the first active layer.

16. The light-emitting element according to claim 14 or 15, wherein a wavelength of the strain relief layer corresponding to a band edge energy of the well layer is set to be 40 to 100nm shorter than an emission wavelength of the light-emitting layer.

17. The light-emitting element according to claim 14 or 15, wherein the strain relief layer is a SQW structure.

18. The light-emitting element according to claim 14 or 15, wherein a ratio of a thickness of the first active layer to a thickness of the second active layer is 30% or less.