Light-emitting element

Abstract

The invention provides a light-emitting element with improved carrier injection efficiency. The light-emitting element has a first semiconductor layer (Alx1Iny1Ga1-x1-y1N), a second semiconductor layer (Alx2Iny2Ga1-x2-y2N), a third semiconductor layer (Alx3Iny3Ga1-x3-y3N), and a fourth semiconductor layer (Alx4Iny4Ga1-x4-y4N) in this order, the second semiconductor layer and the third semiconductor layer contain a p-type impurity, the thickness of the second semiconductor layer is smaller than that of the third semiconductor layer, and the thickness of the fourth semiconductor layer is smaller than that of the third semiconductor layer. The Al composition ratio of the second semiconductor layer is greater than any one of the Al composition ratio of the first semiconductor layer, the Al composition ratio of the third semiconductor layer, and the Al composition ratio of the fourth semiconductor layer, and the Al composition ratio of the third semiconductor layer is greater than any one of the Al composition ratio of the first semiconductor layer and the Al composition ratio of the fourth semiconductor layer.

Description

Technical Field

[0001] The present invention relates to a light emitting element. Background Art

[0002] Laser elements using nitride semiconductors are used as light sources for high-power vehicle headlights and laser processing machines. In order to efficiently operate high-power laser elements, it is important to improve the carrier injection efficiency of the laser element. One of the reasons for reducing the carrier injection efficiency is the phenomenon that the electrons injected into the active layer are thermally excited and overflow to the p-side semiconductor layer. In order to suppress the overflow of electrons to the p-side semiconductor layer, an electron blocking layer having a larger band gap than the p-side semiconductor layer is inserted between the active layer and the p-side semiconductor layer.

[0003] A structure having a peak of the aluminum (Al) composition ratio in a region of the electron blocking layer close to the active layer is known (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2023-010171 Summary of the invention

[0005] <Problems to be Solved by the Invention>

[0006] The present invention provides a light-emitting element with improved carrier injection efficiency.

[0007] <Methods used to solve problems>

[0008] In one embodiment, the light emitting element includes a first semiconductor layer, a second semiconductor layer, a third semiconductor layer and a fourth semiconductor layer in sequence.

[0009] The first semiconductor layer is Al x1 In y1 Ga 1-x1-y1 N (0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1),

[0010] The second semiconductor layer is Al x2 In y2 Ga 1-x2-y2 N (0≤x2≤1, 0≤y2≤1, 0≤x2+y2≤1),

[0011] The third semiconductor layer is Al x3 In y3 Ga 1-x3-y3 N (0≤x3≤1, 0≤y3≤1, 0≤x3+y3≤1),

[0012] The fourth semiconductor layer is Al x4 In y4 Ga 1-x4-y4N (0 ≤ x4 ≤ 1, 0 ≤ y4 ≤ 1, 0 ≤ x4 + y4 ≤ 1),

[0013] The second semiconductor layer and the third semiconductor layer contain p-type impurities,

[0014] The thickness of the second semiconductor layer is less than the thickness of the third semiconductor layer,

[0015] The Al composition ratio x2 of the second semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer, the Al composition ratio x3 of the third semiconductor layer, and the Al composition ratio x4 of the fourth semiconductor layer,

[0016] The Al composition ratio x3 of the third semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer and the Al composition ratio x4 of the fourth semiconductor layer.

[0017] <Advantages of the Invention>

[0018] According to the present invention, a light-emitting element with improved carrier injection efficiency can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic cross-sectional view of the light-emitting element.

[0020] Figure 2 is a schematic diagram showing the distribution of the Al composition ratio from the first semiconductor layer to the fourth semiconductor layer of the light-emitting element according to the embodiment.

[0021] Figure 3 is an HAADF-STEM (high-angle annular dark field scanning transmission electron microscope) image of the fabricated light-emitting element.

[0022] Figure 4 is a graph showing the Al composition ratio from the first semiconductor layer to the fourth semiconductor layer.

[0023] Figure 5 is a schematic diagram of a configuration example having a peak in the Al composition ratio in a region of the active layer far from the electron blocking layer as a comparative example.

[0024] Figure 6 is a graph showing the slope efficiency with respect to current of the light-emitting elements of the example and the comparative example.

[0025] REFERENCE SIGNS LIST

[0026] 1 Substrate

[0027] 3 n-side semiconductor layer

[0028] 10Semiconductor laser element

[0029] 11First semiconductor layer

[0030] 12 Second semiconductor layer

[0031] 13Third semiconductor layer

[0032] 14Fourth semiconductor layer

[0033] 15 Active layer

[0034] 17 n-side electrode

[0035] 18 p-side electrode

[0036] x1 Al composition ratio of the first semiconductor layer

[0037] x2 Al composition ratio of the second semiconductor layer

[0038] x3 Al composition ratio of the third semiconductor layer

[0039] x4 Al composition ratio of the fourth semiconductor layer. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments for implementing the present invention will be described with reference to the accompanying drawings. The following description is intended to implement the technical idea of ​​the present invention. Unless otherwise specified, the present invention is not limited to the following description. In each figure, components with the same function are sometimes marked with the same reference numerals. In order to facilitate the description or understanding of the main points, they can be divided into implementation modes, but the configurations shown in different implementation modes or implementation modes can be partially replaced or combined. In the implementation modes described below, matters different from the above-mentioned implementation modes are mainly described, and repeated descriptions of matters common to the above-mentioned implementation modes can be omitted. The size, positional relationship, etc. of the components shown in each figure are sometimes exaggerated for the sake of clarity.

[0041] <Implementation Method>

[0042] Figure 1 1 is a schematic cross-sectional view of a light emitting element according to an embodiment. The light emitting element is, for example, a semiconductor laser element. In addition, the light emitting element is, for example, a light emitting diode. Hereinafter, a semiconductor laser element 10 will be described as an example of a light emitting element. Figure 1The cross section in is a cross section orthogonal to the resonance direction of the semiconductor laser element 10. The semiconductor laser element 10 is provided with an n-side semiconductor layer 3 on a substrate 1, and has an active layer 15, a first semiconductor layer 11, a second semiconductor layer 12, a third semiconductor layer 13 and a fourth semiconductor layer 14 in order on the n-side semiconductor layer 3. The first semiconductor layer 11 is located on the side opposite to the n-side semiconductor layer 3 across the active layer 15, and is composed of, for example, GaN or AlGaN. The second semiconductor layer 12 is located between the first semiconductor layer 11 and the third semiconductor layer 13, and is a high Al composition layer having the highest Al composition ratio among the first semiconductor layer 11 to the fourth semiconductor layer 14. The third semiconductor layer 13 has a higher Al composition ratio than the fourth semiconductor layer 14, and can be used as, for example, an electron blocking layer for the fourth semiconductor layer 14. In this case, at least a portion of the second semiconductor layer 12 can also be included in the electron blocking layer. The fourth semiconductor layer 14 is a layer closest to the p-side contact layer, and can be, for example, a p-side optical guiding layer. The second semiconductor layer 12 and the third semiconductor layer 13 disposed between the first semiconductor layer 11 and the fourth semiconductor layer 14 have a larger band gap energy than the first semiconductor layer 11 and the fourth semiconductor layer 14 , and form a barrier to electrons at the lower end of the conduction band.

[0043] The semiconductor laser element 10 is formed of a nitride semiconductor. The first semiconductor layer 11 is Al x1 In y1 Ga 1-x1-y1 N (0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1). The second semiconductor layer 12 is Al x2 In y2 Ga 1-x2-y2 N (0≤x2≤1, 0≤y2≤1, 0≤x2+y2≤1). The third semiconductor layer 13 is Al x3 In y3 Ga 1-x3-y3 N (0≤x3≤1, 0≤y3≤1, 0≤x3+y3≤1). The fourth semiconductor layer 14 is Al x4 In y4 Ga 1-x4-y4 N (0≤x4≤1, 0≤y4≤1, 0≤x4+y4≤1). The second semiconductor layer 12 and the third semiconductor layer 13 contain p-type impurities. The thickness of the second semiconductor layer 12 is smaller than the thickness of the third semiconductor layer 13. The Al composition ratio x2 of the second semiconductor layer 12 is greater than any one of the Al composition ratio x1 of the first semiconductor layer 11, the Al composition ratio x3 of the third semiconductor layer 13, and the Al composition ratio x4 of the fourth semiconductor layer 14. The Al composition ratio x3 of the third semiconductor layer 13 is greater than any one of the Al composition ratio x1 of the first semiconductor layer 11 and the Al composition ratio x4 of the fourth semiconductor layer 14.

[0044] As the substrate 1, a GaN substrate is used in Embodiment 1. The +c plane (0001) plane of the GaN substrate is used as the main plane, and the first semiconductor layer 11, the second semiconductor layer 12, the third semiconductor layer 13, and the fourth semiconductor layer 14 are grown on the +c plane. Here, the case where "the +c plane is the main plane" includes an offset within ±1°. By using a substrate with the +c plane as the main plane, mass productivity can be improved. On the back side of the substrate 1, an n-side electrode 17 is provided. An n-type impurity can be added to the substrate 1 to serve as a contact layer.

[0045] The n-side semiconductor layer 3 and the active layer 15 are arranged between the substrate 1 and the first semiconductor layer 11. The n-side semiconductor layer 3 is formed of AlGaN, and a binary, ternary or quaternary nitride semiconductor can be used. The n-side semiconductor layer 3 may include more than one n-side semiconductor layer, for example, an n-side cladding layer and an n-side optical guiding layer. The n-side cladding layer has a larger band gap energy than the n-side optical guiding layer. In order to suppress light absorption, the n-side optical guiding layer is preferably undoped or has a lower concentration of n-type impurities than the n-side cladding layer. Here, "undoped" refers to the case where no impurities are intentionally added to form a film, which means that the impurity concentration is 1×10 16 cm -3 The following or substantially no impurities.

[0046] An undoped AlInGaN light confinement layer may be provided at the interface region between the n-side semiconductor layer 3 and the active layer 15, i.e., the uppermost layer of the n-side semiconductor layer 3. In order to effectively confine light in the active layer in the stacking direction, the In composition ratio y1 of the undoped light confinement layer is preferably less than 0.05.

[0047] (First Semiconductor Layer 11)

[0048] The first semiconductor layer 11 is provided between the active layer 15 and the second semiconductor layer 12 as a part of the p-side semiconductor layer. x1 In y1 Ga 1-x1-y1 N (0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1). The first semiconductor layer 11 is provided, for example, for the purpose of confining light in the active layer 15. The first semiconductor layer 11 is formed into a film by being undoped, for example. The composition ratios x1 and y1 are determined in such a way as to effectively confine light in the active layer 15. The In composition ratio y1 of the first semiconductor layer 11 may be 0. In this case, the refractive index of the first semiconductor layer 11 is reduced, and the light shielding performance can be improved.

[0049] The uppermost layer of the first semiconductor layer 11 may be a barrier layer or a well layer. From the viewpoint of suppressing electron overflow to the fourth semiconductor layer 14 close to the p-side contact layer and promoting hole diffusion to the active layer 15, the uppermost layer of the first semiconductor layer 11 may be a well layer.

[0050] (Second Semiconductor Layer 12 and Third Semiconductor Layer 13)

[0051] The second semiconductor layer 12 and the third semiconductor layer 13 are provided between the first semiconductor layer 11 and the fourth semiconductor layer 14. The second semiconductor layer 12 is provided on the side closer to the n-side semiconductor layer 3 than the third semiconductor layer 13, and is composed of Al x2 In y2 Ga 1-x2- y2 The third semiconductor layer 13 is arranged on a side closer to the fourth semiconductor layer 14 than the second semiconductor layer 12 and is composed of Al x3 In y3 Ga 1-x3-y3 N (0≤x3≤1, 0≤y3≤1, 0≤x3+y3≤1). The second semiconductor layer 12 and the third semiconductor layer 13 can be used as electron blocking layers. The Al composition ratio x2 of the second semiconductor layer 12 is greater than any one of the Al composition ratio x1 of the first semiconductor layer 11, the Al composition ratio x3 of the third semiconductor layer 13, and the Al composition ratio x4 of the fourth semiconductor layer 14. In addition, the thickness of the second semiconductor layer 12 is less than the thickness of the third semiconductor layer 13. By reducing the thickness of the second semiconductor layer 12 having a relatively high Al composition ratio, the activation energy of the p-type impurity contained in the second semiconductor layer 12 becomes smaller, thereby increasing the Hall concentration. In addition, the use of the second semiconductor layer 12 and the third semiconductor layer 13 can reduce electron overflow, thereby improving the carrier injection efficiency. In addition, the In composition ratio y2 of the second semiconductor layer 12 can be 0. In this case, the refractive index of the second semiconductor layer 12 is reduced, thereby improving the performance of confining light. In addition, the In composition ratio y3 of the third semiconductor layer 13 can be 0. In this case, the refractive index of the third semiconductor layer 13 is reduced, so that the performance of confining light can be improved.

[0052] The thickness of the second semiconductor layer 12 is, for example, greater than 0.5 nm and less than or equal to 2.5 nm. By making the second semiconductor layer 12 thicker than 0.5 nm, electron overflow can be effectively reduced. In addition, by setting the thickness of the second semiconductor layer 12 to be less than or equal to 2.5 nm, the increase in the operating voltage can be reduced. For example, the total thickness of the second semiconductor layer 12 and the third semiconductor layer 13 is greater than 5 nm and less than or equal to 30 nm. By making the total thickness of the second semiconductor layer 12 and the third semiconductor layer 13 greater than 5 nm, the possibility of the p-type impurities added in the fourth semiconductor layer 14 diffusing into the active layer 15 can be reduced. By setting the total thickness of the second semiconductor layer 12 and the third semiconductor layer to be less than or equal to 30 nm, the movement of holes in the third semiconductor layer 13 or the second semiconductor layer 12 is not easily hindered, thereby reducing the increase in the forward voltage. For example, p-type impurities such as Mg can be added to the third semiconductor layer 13. In this case, the p-type impurity concentration in the third semiconductor layer 13 is less than the p-type impurity concentration in the fourth semiconductor layer 14 close to the p-side contact layer. By adding p-type impurities to the third semiconductor layer 13, the hole injection efficiency from the fourth semiconductor layer 14 to the first semiconductor layer 11 can be improved. In addition, by making the p-type impurity concentration in the third semiconductor layer 13 lower than the p-type impurity concentration in the fourth semiconductor layer 14 near the p-side contact layer, the light loss in the third semiconductor layer 13 can be reduced.

[0053] Even in the case where the second semiconductor layer 12 is not doped and formed into a film, p-type impurities (for example, Mg) can diffuse from the third semiconductor layer 13 to the second semiconductor layer 12. When the Al composition ratio x2 of the second semiconductor layer 12 is increased in order to reduce the overflow of electrons from the first semiconductor layer 11 to the fourth semiconductor layer 14 on the p-side, there is a tendency that the activation degree of the p-type impurities decreases and the series resistance increases. Therefore, by making the second semiconductor layer 12 with a larger Al composition ratio x2 have a thickness that makes it difficult for the activation degree of the p-type impurities to be reduced, the injection of holes from the fourth semiconductor layer 14 to the first semiconductor layer 11 and the active layer 15 can be less hindered, thereby reducing the increase in the driving voltage. The thickness of the second semiconductor layer 12 that makes it difficult for the activation degree of the p-type impurities to be reduced is, for example, less than or equal to 2.5nm.

[0054] (Fourth Semiconductor Layer 14)

[0055] The fourth semiconductor layer 14 is a semiconductor layer to which p-type impurities are added. x4 In y4 Ga 1-x4- y4N (0≤x4≤1, 0≤y4≤1, 0≤x4+y4≤1), and a binary, ternary or quaternary nitride semiconductor can be used according to the composition of x4 and y4. In the fourth semiconductor layer 14, for example, Mg is added as a p-type impurity. The In composition ratio y4 of the fourth semiconductor layer 14 can be 0. In this case, the refractive index of the fourth semiconductor layer 14 is reduced, thereby improving the light shielding performance.

[0056] The first semiconductor layer 11, the second semiconductor layer 12, the third semiconductor layer 13, and the fourth semiconductor layer 14 are processed into the shape of the ridge portion 16. Figure 1 In the cross section, due to the change in the lateral refractive index of the ridge 16, that is, the insulating film 19, Al x4 In y4 Ga 1-x4-y4 N (0≤x4≤1, 0≤y4≤1, 0≤x4+y4≤1), the dielectric change of the insulating film 19, the light in the active layer 15 is confined in the lateral direction. A p-side electrode 18 is provided on the upper surface of the ridge 16. A p-side contact layer may be provided at the interface between the fourth semiconductor layer 14 and the p-side electrode 18. The p-side contact layer contains p-type impurities at a concentration higher than that of any layer of the fourth semiconductor layer 14. The first semiconductor layer 11 is adjacent to the second semiconductor layer 12. The second semiconductor layer 12 is adjacent to the third semiconductor layer 13. The third semiconductor layer 13 is adjacent to the fourth semiconductor layer 14. By making the layers continuous, the structure for reducing the rise in the operating voltage of the semiconductor laser element 10 can be accommodated in a narrow space.

[0057] (Distribution of Al composition ratio from the first semiconductor layer to the fourth semiconductor layer)

[0058] Figure 2The distribution of the Al composition ratio from the first semiconductor layer 11 to the fourth semiconductor layer 14 of the semiconductor laser element 10 of the embodiment is shown. The horizontal axis represents the position in the stacking direction, and the closer to the n side the right side is. The vertical axis represents the Al composition ratio. Among the first semiconductor layer 11 to the fourth semiconductor layer 14, the Al composition ratio x2 of the second semiconductor layer 12 is the highest. The Al composition ratio x2 is, for example, greater than or equal to 0.4 and less than or equal to 0.8 (denoted as "40%≤x2≤80%" in the figure), preferably greater than or equal to 0.45 and less than or equal to 0.75. Since the Al composition ratio x2 of the second semiconductor layer 12 is greater than or equal to 0.4, it can effectively prevent the electrons from overflowing at the lower end of the conduction band. Generally, the higher the Al composition ratio, the larger the band gap and the higher the electron blocking effect, but Al inactivates the p-type impurities. When the Al composition ratio x2 exceeds 0.8, due to the inactivation of the p-type impurities, the contact resistivity between the second semiconductor layer 12 and the active layer becomes higher, and the driving voltage may increase. Therefore, the Al composition ratio x2 of the second semiconductor layer 12 is preferably greater than or equal to 0.4 and less than or equal to 0.8.

[0059] The Al composition ratio x3 of the third semiconductor layer 13 is less than the Al composition ratio x2 of the second semiconductor layer 12. The Al composition ratio x3 of the third semiconductor layer 13 is greater than the Al composition ratio x1 of the first semiconductor layer 11 and the Al composition ratio x4 of the fourth semiconductor layer 14. The third semiconductor layer 13 is a compositionally inclined layer. The Al composition ratio x3 of the third semiconductor layer 13 slowly decreases from the side close to the second semiconductor layer 12 as it approaches the side close to the fourth semiconductor layer 14, and decreases sharply at the boundary with the fourth semiconductor layer 14. The composition inclination of the third semiconductor layer 13 starts from the boundary between the second semiconductor layer 12 and the third semiconductor layer 13. Thus, the rise in the operating voltage caused by the third semiconductor layer 13 can be reduced. From the boundary between the third semiconductor layer 13 and the fourth semiconductor layer 14, the absolute value of the rate of change of the Al composition ratio toward the position where the Al composition ratio x4 in the fourth semiconductor layer 14 shows the minimum value is greater than the absolute value of the rate of change of the Al composition ratio of the third semiconductor layer 13. In other words, in the third semiconductor layer 13, the Al composition ratio x3, which decreases slowly from the boundary with the second semiconductor layer 12 to the vicinity of the boundary with the fourth semiconductor layer 14, decreases sharply at the boundary with the fourth semiconductor layer 14, and the distribution of the Al composition ratio changes in a step-like manner. According to this configuration, the electron blocking effect in the third semiconductor layer 13 can be enhanced.

[0060] The Al composition ratio in the region closest to the second semiconductor layer 12 in the third semiconductor layer 13 is 25%±5%. The Al composition ratio in the region closest to the fourth semiconductor layer 14 in the third semiconductor layer 13 is 18%±5% under the condition that it is less than the Al composition ratio near the boundary with the second semiconductor layer 12. The Al composition ratio at the point closest to the fourth semiconductor layer 14 in the third semiconductor layer 13 is greater than the Al composition ratio x4 of the fourth semiconductor layer 14. According to this configuration, the electron blocking effect in the third semiconductor layer 13 can be enhanced. When the thickness of the third semiconductor layer 13 is, for example, 10 nm, the Al composition ratio x3 slowly decreases throughout the thickness range.

[0061] The absolute value of the rate of change of the Al composition ratio x2 from the position where the Al composition ratio in the second semiconductor layer 12 shows the maximum value to the boundary between the second semiconductor layer 12 and the third semiconductor layer 13 is greater than the absolute value of the rate of change of the Al composition ratio x3 of the third semiconductor layer 13. According to this configuration, the electron blocking effect in the second semiconductor layer 12 can be enhanced. In addition, the absolute value of the rate of change of the Al composition ratio from the boundary between the first semiconductor layer 11 and the second semiconductor layer 12 to the position where the Al composition ratio in the second semiconductor layer 12 shows the maximum value is greater than the absolute value of the rate of change of the Al composition ratio x3 in the third semiconductor layer 13. In other words, in the second semiconductor layer 12, the Al composition ratio x2 increases sharply near the boundary with the first semiconductor layer 11, and the Al composition ratio x2 decreases sharply near the boundary with the third semiconductor layer 13. According to this configuration, the electron blocking effect in the second semiconductor layer 12 can be enhanced. However, the amount of change (absolute value) of the Al composition ratio is smaller than the amount of change on the third semiconductor layer 13 side.

[0062] The Al composition ratio x4 of the fourth semiconductor layer 14 is greater than 1% and less than or equal to 10%. According to this configuration, light loss caused by Al can be reduced. The fourth semiconductor layer 14 can be used as a p-side light guiding layer, for example. The p-side light guiding layer has a lower refractive index than the first semiconductor layer 11 and a larger band gap than the first semiconductor layer 11.

[0063] exist Figure 2 In the example, the Al composition ratio x1 of the first semiconductor layer 11 is greater than or equal to 1% and less than or equal to 10%. According to this configuration, the light loss caused by Al can be reduced. x1 In y1 Ga 1-x1-y1When the first semiconductor layer 11 is formed by N (0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1), the target oscillation wavelength can be designed by adjusting the Al composition ratio x1 and the In composition ratio y1. The Al composition ratio x1 of the first semiconductor layer can be appropriately adjusted to a range of 1 / 50 or more and 1 / 5 or less of the peak Al composition ratio x2 of the second semiconductor layer 12.

[0064] By having the semiconductor laser element 10 Figure 2 The distribution of the Al composition ratio shown can suppress the overflow of electrons from the first semiconductor layer 11 to the fourth semiconductor layer 14, and can make the injection of holes from the fourth semiconductor layer 14 to the first semiconductor layer 11 less obstructed, thereby improving the carrier injection efficiency. With the improvement of the carrier injection efficiency, the output under the same injection current can be increased with less current oscillation, thereby improving the power conversion efficiency.

[0065] It should be noted that the band gap energies of the first semiconductor layer 11, the second semiconductor layer 12, the third semiconductor layer 13, and the fourth semiconductor layer 14 may have the following relationship. That is, the band gap energy of the second semiconductor layer 12 is higher than the band gap energies of the first semiconductor layer 11, the third semiconductor layer 13, and the fourth semiconductor layer 14. In addition, the band gap energy of the third semiconductor layer 13 is higher than the band gap energies of the first semiconductor layer 11 and the fourth semiconductor layer 14. The band gap energy of the third semiconductor layer 13 gradually decreases from the side close to the second semiconductor layer 12 as it approaches the side close to the fourth semiconductor layer 14.

[0066] (Sample preparation and evaluation)

[0067] based on Figure 2 The distribution of Al composition ratio in the sample of the semiconductor laser element 10 was produced. The n-side semiconductor layer 3 with a thickness of 3 μm was formed on the GaN substrate. Ammonia, trimethylaluminum (TMA), trimethylgallium (TMG) and monosilane were used as raw material gases to grow silicon-doped AlGaN.

[0068] After the n-side semiconductor layer 3 is formed, the active layer 15 and the first semiconductor layer 11 are grown. The average Al composition ratio x1 of the first semiconductor layer 11 is 4.5%.

[0069] After forming the first semiconductor layer 11, the second semiconductor layer 12 is formed. The second semiconductor layer 12 can be used as a part of the electron blocking layer. Ammonia, TMA and TMG are used to form an Al2O3 layer with a thickness of about 1.0 nm. 0.5 Ga 0.5 The second semiconductor layer 12 of N.

[0070] Next, ammonia, TMA, TMG and bis(cyclopentadienyl)magnesium (Cp 2The third semiconductor layer 13 is formed by using Mg doped AlGaN to form the third semiconductor layer 13. The third semiconductor layer 13 is arranged on the side closer to the p-side contact layer than the second semiconductor layer 12, and can be used as a part of the electron blocking layer. For example, the third semiconductor layer 13 is formed with a thickness of 9.0 nm using Mg doped AlGaN. 2 The Al composition ratio x3 of the third semiconductor layer 13 in the thickness direction is adjusted by gradually reducing the flow rate of TMA starting from Mg. The Al composition ratio immediately after the formation of the third semiconductor layer 13 begins, that is, the Al composition ratio near the boundary with the second semiconductor layer 12 is set to 25%. Thereafter, the flow rate of TMA is gradually reduced so that the Al composition ratio on the outermost surface of the third semiconductor layer 13 is 18%. Thus, a film having Figure 2 The second semiconductor layer 12 and the third semiconductor layer 13 have an Al composition ratio distribution.

[0071] Next, ammonia, TMA, TMG and Cp 2 Mg forms a Mg-doped fourth semiconductor layer 14. The fourth semiconductor layer 14 is a p-side semiconductor layer close to the p-side contact layer, and includes a p-side optical guide layer, a p-side cladding layer, a p-side contact layer, etc. The average value of the Al composition ratio x4 of the fourth semiconductor layer 14 is, for example, 4.5%. Thus, a stack including the first semiconductor layer 11 to the fourth semiconductor layer 14 is formed on the substrate 1.

[0072] An etching mask is formed in a predetermined region on the fourth semiconductor layer 14, and a portion between the fourth semiconductor layer 14 and the first semiconductor layer 11 is removed by dry etching. Then, the mask is removed to obtain Figure 1 The ridge shape. An insulating film 19 is formed to cover the entire surface of the fourth semiconductor layer 14. The insulating film 19 on the upper surface of the ridge 16 is removed to form a p-side electrode 18 on the upper surface of the fourth semiconductor layer 14. The p-side electrode 18 is formed of a good conductor such as gold, platinum, titanium, aluminum, or an alloy thereof. Depending on the application, the p-side electrode 18 can be used as a transparent electrode such as ITO. In addition, an n-side electrode 17 is formed on the back side of the substrate 1. The n-side electrode 17 is formed of a good conductor such as gold, platinum, titanium, aluminum, or an alloy thereof.

[0073] Figure 3 is a HAADF-STEM image of the fabricated sample. Figure 3 The up and down direction of the image is Figure 1 The stacking direction is consistent. Figure 3 The lower side is the first semiconductor layer 11, and the upper side is the fourth semiconductor layer 14. The second semiconductor layer 12 having a high Al composition ratio is confirmed to exist between the third semiconductor layer 13 and the first semiconductor layer 11. The second semiconductor layer 12 can function as a part of the electron blocking layer together with the third semiconductor layer 13.

[0074] Figure 4 Represents the measured value of the Al composition ratio from the first semiconductor layer 11 to the fourth semiconductor layer 14. The horizontal axis represents the position [nm] in the depth direction from the fourth semiconductor layer 14 forming the ridge 16 toward the first semiconductor layer 11, and the vertical axis represents the Al composition ratio [Atom %]. The Al composition ratio is measured by secondary ion mass spectrometry (SIMS). The left end (0nm) of the horizontal axis is the position in the fourth semiconductor layer 14 at 5nm from the boundary between the third semiconductor layer 13 and the fourth semiconductor layer 14, and the right end (22nm) is the position in the first semiconductor layer 11 at 7nm from the boundary between the first semiconductor layer 11 and the second semiconductor layer. Sputter an ion beam, and repeat the mass analysis of the secondary ions generated in the order of the fourth semiconductor layer 14, the third semiconductor layer 13, the second semiconductor layer 12, and the first semiconductor layer 11 to measure the composition ratio in the depth direction.

[0075] At the interface between the second semiconductor layer 12 and the first semiconductor layer 11, which are located from 14nm to 15nm, the Al composition ratio changes sharply from 50% to 4.5%. Since the composition value of Al is switched between the first semiconductor layer 11 and the second semiconductor layer 12 during the sample preparation process, the change in the Al composition ratio becomes discontinuous and changes sharply. At the interface between the second semiconductor layer 12 and the third semiconductor layer 13, which are located between 12nm and 14nm, the composition value of Al changes from 50% to 25%. Similarly, between the second semiconductor layer 12 and the third semiconductor layer 13, the Al composition ratio changes sharply due to the switching of the composition value of Al during the sample preparation process. In the third semiconductor layer 13, which is located between 5nm and 12nm, the Al composition ratio changes continuously from 18% to 25%. At the interface between the third semiconductor layer 13 and the fourth semiconductor layer 14, which are located near 5nm, the Al composition ratio changes sharply from 18% to 4.5%. During the sample preparation process, when the fourth semiconductor layer 14 is formed on the third semiconductor layer 13, the Al composition ratio changes sharply due to the switching of the composition value of Al. Due to Figure 4 The Al composition ratio in the sample is continuously measured by SIMS, which may also include measurement errors. Therefore, there is a tilt in the distribution diagram of the Al composition ratio, but the measured values ​​are consistent with Figure 2 The design values ​​are very consistent.

[0076] like Figure 3 and Figure 4 As shown in FIG. 1 , when the Al composition ratio of the second semiconductor layer 12 is made the highest, the energy barrier at the lower end of the conduction band on the boundary side with the first semiconductor layer 11 becomes higher. Figure 4From the measured distribution diagram of the Al composition ratio in the stacking direction, it can be seen that the overflow of electrons to the fourth semiconductor layer 14 is effectively reduced. It can be considered that by adopting this structure, electrons are effectively blocked, thereby reducing the occurrence of carrier loss due to non-radiative recombination in the electron blocking layer.

[0077] As a comparative example, Figure 5 An example of a structure having a peak of the Al composition ratio in a region near the boundary between the electron blocking layer and the p-side semiconductor layer near the p-side contact layer is shown. In this figure, the n-side of the stacking direction of the horizontal axis is the side near the active layer, and the p-side is the side near the p-side contact layer. The region having the peak of the Al composition ratio corresponds to the electron blocking layer. The electron blocking layer contains p-type impurities such as Mg. In the layer of the first semiconductor layer closest to the electron blocking layer, the change in the Al composition ratio discontinuously rises to 2% at the boundary between the first semiconductor layer and the electron blocking layer.

[0078] In the electron blocking layer, the Al composition ratio changes from 2% to 35% as it moves away from the outermost surface of the first semiconductor layer 11. In the electron blocking layer of the comparative example, the peak value (35%) of the Al composition ratio is located in the region farthest from the active layer in the electron blocking layer, and the Al composition ratio decreases sharply in the region farther from the active layer than this region. In the comparative example, the Al composition ratio in the layer farther from the active layer based on the position showing the peak value of the Al composition ratio is 4.5%, which is the same as the fourth semiconductor layer 14 of the embodiment.

[0079] exist Figure 5 In the comparative example of , the energy barrier at the lower end of the conduction band of the electron blocking layer having the peak of the Al composition ratio is formed in the region farthest from the active layer in the electron blocking layer, and decreases while tilting toward the active layer. It can be considered that in this structure, the electrons injected into the active layer undergo non-radiative recombination in the electron blocking layer before reaching the region having the peak of the Al composition ratio, thereby causing carrier loss.

[0080] Figure 6 The figure shows the slope efficiency of the semiconductor laser elements of the embodiment and the comparative example. The horizontal axis represents the injection current [mA], and the vertical axis represents the ratio of the increase in light output to the current (dL / dI). The ratio of the increase in light output to the injection current is the slope efficiency. Even if the injection current increases, the semiconductor laser element of the embodiment maintains an almost constant light output. In contrast, in the semiconductor laser element of the comparative example, the slope efficiency decreases in the high current region. This is because the electrons injected into the active layer flow to the p-side, which is not conducive to the generation of light.

[0081] According to the semiconductor laser device 10 of the embodiment,

[0082] (a) making the thickness of the second semiconductor layer 12 smaller than the thickness of the third semiconductor layer 13,

[0083] (b) the Al composition ratio x2 of the second semiconductor layer 12 is made larger than any one of the Al composition ratio x1 of the first semiconductor layer 11 , the Al composition ratio x3 of the third semiconductor layer 13 , and the Al composition ratio x4 of the fourth semiconductor layer 14 ;

[0084] (c) making the Al composition ratio x3 of the third semiconductor layer 13 larger than either the Al composition ratio x1 of the first semiconductor layer or the Al composition ratio x4 of the fourth semiconductor layer,

[0085] Can improve carrier injection efficiency.

[0086] By making the absolute value of the change rate of the Al composition ratio from the first semiconductor layer 11 to the second semiconductor layer 12 larger than the absolute value of the change rate of the Al composition ratio of the third semiconductor layer 13 , it is possible to effectively prevent the overflow of electrons to the p-side.

[0087] By making the absolute value of the change rate of the Al composition ratio from the second semiconductor layer 12 to the third semiconductor layer 13 larger than the absolute value of the change rate of the Al composition ratio of the third semiconductor layer 13 , it is possible to effectively prevent the overflow of electrons to the p-side.

[0088] By making the thickness of the second semiconductor layer 12 greater than or equal to 0.5 nm and less than or equal to 2.5 nm, the increase in driving voltage can be reduced. By making the Al composition ratio of the first semiconductor layer 11 and the fourth semiconductor layer 14 greater than or equal to 1% and less than or equal to 10%, the reduction in hole injection efficiency can be suppressed, thereby improving conductivity.

[0089] The embodiments of the present invention may include the following configurations, for example.

[0090] (Item 1)

[0091] A light emitting element comprises a first semiconductor layer, a second semiconductor layer, a third semiconductor layer and a fourth semiconductor layer in sequence,

[0092] The first semiconductor layer is Al x1 In y1 Ga 1-x1-y1 N (0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1),

[0093] The second semiconductor layer is Al x2 In y2 Ga 1-x2-y2 N (0≤x2≤1, 0≤y2≤1, 0≤x2+y2≤1),

[0094] The third semiconductor layer is Alx3 In y3 Ga 1-x3-y3 N (0≤x3≤1, 0≤y3≤1, 0≤x3+y3≤1),

[0095] The fourth semiconductor layer is Al x4 In y4 Ga 1-x4-y4 N (0≤x4≤1, 0≤y4≤1, 0≤x4+y4≤1),

[0096] The second semiconductor layer and the third semiconductor layer contain p-type impurities,

[0097] The thickness of the second semiconductor layer is smaller than the thickness of the third semiconductor layer,

[0098] The Al composition ratio x2 of the second semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer, the Al composition ratio x3 of the third semiconductor layer, and the Al composition ratio x4 of the fourth semiconductor layer,

[0099] The Al composition ratio x3 of the third semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer and the Al composition ratio x4 of the fourth semiconductor layer.

[0100] (Item 2)

[0101] The light-emitting element according to item 1, wherein

[0102] The Al composition ratio x3 of the third semiconductor layer decreases from the second semiconductor layer toward the fourth semiconductor layer.

[0103] An absolute value of a change rate of the Al composition ratio from a boundary between the third semiconductor layer and the fourth semiconductor layer to a position where the Al composition ratio in the fourth semiconductor layer shows a minimum value is greater than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

[0104] (Item 3)

[0105] The light-emitting element according to item 1 or 2, wherein

[0106] An absolute value of a change rate of the Al composition ratio from a boundary between the first semiconductor layer and the second semiconductor layer to a position where the Al composition ratio in the second semiconductor layer shows a maximum value is greater than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

[0107] (Item 4)

[0108] The light-emitting element according to any one of items 1 to 3, wherein

[0109] An absolute value of a change rate of the Al composition ratio from a position where the Al composition ratio in the second semiconductor layer shows a maximum value to a boundary between the second semiconductor layer and the third semiconductor layer is larger than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

[0110] (Item 5)

[0111] The light-emitting element according to any one of items 1 to 4, wherein

[0112] The thickness of the second semiconductor layer is greater than 0.5 nm and less than or equal to 2.5 nm.

[0113] (Item 6)

[0114] The light-emitting element according to any one of items 1 to 5, wherein

[0115] The sum of the thicknesses of the second semiconductor layer and the third semiconductor layer is greater than 5 nm and less than or equal to 30 nm.

[0116] (Item 7)

[0117] The light-emitting element according to any one of items 1 to 6, wherein

[0118] An Al composition ratio x2 of the second semiconductor layer is greater than or equal to 40% and less than or equal to 80%.

[0119] (Item 8)

[0120] The light-emitting element according to any one of items 1 to 7, wherein

[0121] An Al composition ratio x1 of the first semiconductor layer is greater than or equal to 1% and less than or equal to 10%.

[0122] (Item 9)

[0123] The light-emitting element according to any one of items 1 to 8, wherein

[0124] An Al composition ratio x4 of the fourth semiconductor layer is greater than or equal to 1% and less than or equal to 10%.

[0125] (Item 10)

[0126] The light-emitting element according to any one of items 1 to 9, wherein

[0127] The third semiconductor layer and the fourth semiconductor layer contain first conductivity type impurities,

[0128] An amount of the first conductive type impurity included in the third semiconductor layer is smaller than an amount of the first conductive type impurity included in the fourth semiconductor layer.

Claims

1. A light-emitting element, comprising, in sequence, a first semiconductor layer, a second semiconductor layer, a third semiconductor layer and a fourth semiconductor layer, The first semiconductor layer is Al x1 In y1 Ga 1-x1-y1 N, where 0≤x1≤1, 0≤y1≤1, 0≤x1+y1≤1, The second semiconductor layer is Al x2 In y2 Ga 1-x2-y2 N, where 0≤x2≤1, 0≤y2≤1, 0≤x2+y2≤1, The third semiconductor layer is Al x3 In y3 Ga 1-x3-y3 N, where 0≤x3≤1, 0≤y3≤1, 0≤x3+y3≤1, The fourth semiconductor layer is Al x4 In y4 Ga 1-x4-y4 N, where 0≤x4≤1, 0≤y4≤1, 0≤x4+y4≤1, The second semiconductor layer and the third semiconductor layer contain p-type impurities, The thickness of the second semiconductor layer is smaller than the thickness of the third semiconductor layer, The Al composition ratio x2 of the second semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer, the Al composition ratio x3 of the third semiconductor layer, and the Al composition ratio x4 of the fourth semiconductor layer, The Al composition ratio x3 of the third semiconductor layer is greater than any one of the Al composition ratio x1 of the first semiconductor layer and the Al composition ratio x4 of the fourth semiconductor layer.

2. The light-emitting element according to claim 1, wherein The Al composition ratio x3 of the third semiconductor layer decreases from the second semiconductor layer toward the fourth semiconductor layer. An absolute value of a change rate of the Al composition ratio from a boundary between the third semiconductor layer and the fourth semiconductor layer to a position where the Al composition ratio in the fourth semiconductor layer shows a minimum value is greater than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

3. The light-emitting element according to claim 1 or 2, wherein: An absolute value of a change rate of the Al composition ratio from a boundary between the first semiconductor layer and the second semiconductor layer to a position where the Al composition ratio in the second semiconductor layer shows a maximum value is greater than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

4. The light-emitting element according to any one of claims 1 to 3, wherein An absolute value of a change rate of the Al composition ratio from a position where the Al composition ratio in the second semiconductor layer shows a maximum value to a boundary between the second semiconductor layer and the third semiconductor layer is larger than an absolute value of a change rate of the Al composition ratio x3 of the third semiconductor layer.

5. The light-emitting element according to any one of claims 1 to 4, wherein The thickness of the second semiconductor layer is greater than 0.5 nm and less than or equal to 2.5 nm.

6. The light-emitting element according to any one of claims 1 to 5, wherein The sum of the thicknesses of the second semiconductor layer and the third semiconductor layer is greater than 5 nm and less than or equal to 30 nm.

7. The light-emitting element according to any one of claims 1 to 6, wherein An Al composition ratio x2 of the second semiconductor layer is greater than or equal to 40% and less than or equal to 80%.

8. The light-emitting element according to any one of claims 1 to 7, wherein An Al composition ratio x1 of the first semiconductor layer is greater than or equal to 1% and less than or equal to 10%.

9. The light-emitting element according to any one of claims 1 to 8, wherein An Al composition ratio x4 of the fourth semiconductor layer is greater than or equal to 1% and less than or equal to 10%.

10. The light-emitting element according to any one of claims 1 to 9, wherein The third semiconductor layer and the fourth semiconductor layer contain first conductivity type impurities, An amount of the first conductive type impurity included in the third semiconductor layer is smaller than an amount of the first conductive type impurity included in the fourth semiconductor layer.

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