Nitride semiconductor light-emitting element and method for manufacturing nitride semiconductor light-emitting element

Abstract

To provide a technique for obtaining ohmic characteristics of an n-side electrode on an N-polar surface.SOLUTION: The nitride semiconductor light-emitting element 1 includes an n-side electrode 42, a contact layer 41 on which the n-side electrode 42 is laminated, and an n-AlGaN layer 40 on which the contact layer 41 is laminated, and the contact layer 41 uses GaN and is laminated on an N-polar surface of the n-AlGaN layer 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitride semiconductor light-emitting device and a method for manufacturing the nitride semiconductor light-emitting device. [Background technology]

[0002] Patent Document 1 discloses a nitride semiconductor light-emitting device in which a nitride semiconductor is stacked on a sapphire substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-177965 Summary of the Invention [Problem to be solved by the invention]

[0004] AlGaN-based ultraviolet light-emitting devices are fabricated using AlN and AlGaN-based nitride semiconductor crystals grown on an insulating sapphire or AlN substrate. However, the use of an insulating substrate results in a structure in which the p-side and n-side electrodes of the device are formed on the wafer surface, causing current to flow horizontally, resulting in uneven current distribution in the light-emitting region and high electrical resistance. This leads to problems such as reduced light-emitting efficiency, a smaller light-emitting region, and increased driving voltage. To address these issues, it is extremely effective to use a vertical conduction structure device in which current flows vertically through the crystal.

[0005] For GaN-based light-emitting devices, a vertically conducting thin-film device structure can be fabricated by using laser lift-off (LLO) technology to peel GaN-based nitride semiconductor crystals from sapphire substrates and then forming an n-side electrode on the exposed surface (N (nitrogen) polarity face). This method was used to fabricate vertically conducting AlGaN-based nitride semiconductor crystal devices. To fabricate vertically conducting devices, AlGaN-based nitride semiconductor crystals with a p-side electrode formed on the surface are eutectic-bonded to a support using metals such as Au and Sn, and then peeled from the sapphire substrate using LLO technology. An n-side electrode is then formed on the exposed surface. To prevent cracks from forming in the crystal, the heat treatment temperature after n-side electrode formation must be below 300°C. For the n-side electrode of N-polar AlGaN, we investigated V / Al / Ti / Au electrodes, which have proven successful on AlGaN metal polarity faces, and Cr / Ni / Au and Ti / Pt / Au electrodes, which provide ohmic characteristics without alloying with metal polarity faces or N-polarity faces of GaN in GaN-based devices. As a result, within the constraint of a heat treatment temperature of 300°C or less, the most favorable results were obtained with a Ti / Pt / Au electrode, but its characteristics were Schottky. It was found that it was difficult to obtain ohmic characteristics with the electrode modifications described above. For this reason, a technology was desired to obtain ohmic characteristics for the n-side electrode on the N-polarity surface by modifying parts other than the electrode.

[0006] The present invention has been made in view of the above-described conventional circumstances, and an object to be achieved is to provide a technique for obtaining ohmic characteristics of an n-side electrode on an N-polarity surface. [Means for solving the problem]

[0007] The nitride semiconductor light-emitting device of the first invention is An n-side electrode, a contact layer on which the n-side electrode is laminated; an AlGaN layer on which the contact layer is laminated; Equipped with The contact layer is made of at least one of GaN and AlGaN and is laminated on the N-polar surface of the AlGaN layer.

[0008] The method for manufacturing a nitride semiconductor light-emitting device according to the second invention includes the steps of: An n-side electrode, a contact layer on which the n-side electrode is laminated; an AlGaN layer on which the contact layer is laminated; A method for manufacturing a nitride semiconductor light-emitting device comprising: The contact layer is deposited on the N-polar surface of the AlGaN layer using an ECR sputtering apparatus.

[0009] This configuration significantly improves the IV characteristics between the AlGaN layer on the N-polarity surface and the n-side electrode via the contact layer. Here, the ECR sputtering device is a device that can generate ECR (Electron Cyclotron Resonance) plasma and perform sputtering using the ECR plasma. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing the structure of the nitride semiconductor light-emitting device of Example 1, which has been improved. [Figure 2] 1A to 1C are schematic diagrams illustrating steps for manufacturing the nitride semiconductor light-emitting device of Example 1. [Figure 3] FIG. 1 is a schematic diagram showing an ECR sputtering apparatus. [Figure 4] FIG. 2 is a schematic diagram showing the structure of a sample for measuring IV characteristics in a contact layer. [Figure 5] FIG. 1 is a plan view of each sample for TML measurement. [Figure 6] 1 is a graph showing IV characteristics of a contact layer using GaN and a contact layer using AlGaN. [Figure 7] 10 is a graph showing IV characteristics in the case of a contact layer using GaN, a contact layer using AlGaN, and a case where no contact layer is provided. [Figure 8]10 is a graph showing the results of a simulation of the light intensity distribution at a wavelength of 300 nm in an element when the thickness of a contact layer using GaN is changed. [Figure 9] 10 is a graph showing the results of a simulation of the light intensity distribution at a wavelength of 270 nm in an element when the thickness of a contact layer using GaN is changed. [Figure 10] 10 is a graph showing the simulation results of the light intensity distribution at a wavelength of 300 nm in an element when the thickness of a contact layer using AlGaN is changed. [Figure 11] 10 is a graph showing the simulation results of the light intensity distribution at a wavelength of 270 nm in an element when the thickness of the contact layer using AlGaN is changed. [Figure 12] 10 is a graph showing the results of a simulation of the light intensity distribution at a wavelength of 300 nm in an element when the thickness of each of AlGaN and GaN is changed in a contact layer in which AlGaN and GaN are stacked. DETAILED DESCRIPTION OF THE INVENTION

[0011] A preferred embodiment of the present invention will now be described.

[0012] In the nitride semiconductor light-emitting device of the present invention, the thickness of the contact layer using GaN in the stacking direction can be greater than 0 nm and not greater than 75 nm, in which case an n-side electrode can be in ohmic contact with the contact layer.

[0013] In the nitride semiconductor light-emitting device of the present invention, the thickness of the contact layer using AlGaN in the stacking direction can be greater than 0 nm and not greater than 50 nm, in which case an n-side electrode can be in ohmic contact with the contact layer.

[0014] In the nitride semiconductor light emitting device of the present invention, the AlN mole fraction of the contact layer can be smaller than that of the AlGaN layer, in which case the n-side electrode can be in ohmic contact with the contact layer.

[0015] The AlN mole fraction of the contact layer of the nitride semiconductor light emitting device of the present invention may be greater than 0 and not greater than 0.5. In this case, ohmic characteristics are easily achieved in the IV characteristics between the contact layer and the n-side electrode.

[0016] In the nitride semiconductor light-emitting device of the present invention, the contact layer may be formed by stacking GaN on the surface of AlGaN, in which case the GaN prevents the surface of the AlGaN from being exposed, thereby suppressing oxidation of Al in the AlGaN and enabling an n-side electrode to make good ohmic contact with the contact layer.

[0017] In the nitride semiconductor light-emitting device of the present invention, when the thickness of the AlGaN in the stacking direction is 50 nm, the thickness of the GaN in the stacking direction may be 10 nm to 50 nm, when the thickness of the AlGaN in the stacking direction is 75 nm, the thickness of the GaN in the stacking direction may be 10 nm to 30 nm, and when the thickness of the AlGaN in the stacking direction is 100 nm, the thickness of the GaN in the stacking direction may be 10 nm. In this case, the n-side electrode can be in ohmic contact with the contact layer without affecting the light intensity distribution in the nitride semiconductor light-emitting device.

[0018] Next, a first embodiment of the nitride semiconductor light emitting device of the present invention will be described with reference to the drawings.

[0019] Example 1 [Configuration of nitride semiconductor light-emitting element] As shown in FIG. 1, the nitride semiconductor light-emitting element 1 of Example 1 includes a support 31, a metal layer 32, an insulating layer 33, a p-side electrode 43, a semiconductor layer 34, a contact layer 41, and an n-side electrode 42.

[0020] A sintered body formed by firing fine powder of AlN is used for the support 31. The thickness of the support 31 is, for example, 400 μm.

[0021] The metal layer 32 is laminated on the support 31. For example, the metal layer 32 has a gold-tin eutectic layer and a titanium-platinum layer. The gold-tin eutectic layer is laminated on a titanium-platinum-gold layer (not shown) laminated on the surface of the support 31. The gold-tin eutectic layer is an alloy of Au and Sn and is formed by eutectic bonding. A titanium-platinum layer is also laminated on the surface of the gold-tin eutectic layer. The titanium-platinum layer is formed by laminating two pairs of Ti and Pt alternately.

[0022] The insulating layer 33 is laminated on the surface of the titanium-platinum layer. The insulating layer 33 is formed of, for example, Al2O3. An opening 33A is formed in the insulating layer 33, penetrating the layer in the film thickness direction. The p-side electrode 43 is laminated on the surface of the metal layer 32 within the opening 33A formed in the insulating layer 33. The p-side electrode 43 is formed by laminating Ni, Pt, and Au.

[0023] The semiconductor layer 34 includes a p-GaN layer 35, a p-AlGaN layer 36, a cladding layer 37, an electron blocking layer 38, a light-emitting layer 39, and an n-AlGaN layer 40, which is an AlGaN layer. The semiconductor layer 34 is manufactured by crystal growth using MOVPE (metal organic vapor phase epitaxy). The upward surface of the semiconductor layer 34 in FIG. 1 is an N-polar surface, and the downward surface is a metal polar surface.

[0024] The p-GaN layer 35 is deposited so as to cover the surfaces of the insulating layer 33 and the p-side electrode 43. Mg is added to the p-GaN layer 35. For example, the thickness of the p-GaN layer 35 is 10 nm.

[0025] The p-AlGaN layer 36 is deposited so as to cover the surface of the p-GaN layer 35. The p-AlGaN layer 36 is doped with Mg as a p-type impurity. The p-AlGaN layer 36 has an AlN mole fraction of 0 at the interface with the p-GaN layer 35 and an AlN mole fraction of 0.6 at the surface. The p-AlGaN layer 36 has a composition gradient in which the AlN mole fraction varies from 0 to 0.6 in the thickness direction. The thickness of the p-AlGaN layer 36 is, for example, 75 nm.

[0026] The cladding layer 37 is laminated on the surface of the p-AlGaN layer 36. The cladding layer 37 is made of AlGaN. The cladding layer 37 has an AlN molar fraction of 0.6 at the interface with the p-AlGaN layer 36 and an AlN molar fraction of 0.9 at the surface. The cladding layer 37 has a composition gradient in which the AlN molar fraction varies from 0.6 to 0.9 in the thickness direction. The thickness of the cladding layer 37 is, for example, 320 nm.

[0027] The electron blocking layer 38 is laminated on the surface of the cladding layer 37. The electron blocking layer 38 is made of AlGaN. The AlN mole fraction in the electron blocking layer 38 is 1.0. The thickness of the electron blocking layer 38 is, for example, 5 nm.

[0028] The light-emitting layer 39 includes a second guide layer 39C, a double quantum well active layer 39B, and a first guide layer 39A. The second guide layer 39C is formed on the surface of the electron blocking layer 38. The second guide layer 39C is made of AlGaN. The AlN mole fraction in the second guide layer 39C is 0.45. The thickness of the second guide layer 39C is, for example, 50 nm.

[0029] The double quantum well active layer 39B is laminated on the surface of the second guide layer 39C. The double quantum well active layer 39B is formed by laminating two pairs of an active layer (with an AlN molar fraction of 0.35) having a thickness of 4 nm and a barrier layer (with an AlN molar fraction of 0.45) having a thickness of 8 nm.

[0030] The first guide layer 39A is stacked on the surface of the double quantum well active layer 39B. The first guide layer 39A is made of AlGaN. The AlN mole fraction in the first guide layer 39A is 0.45. The thickness of the first guide layer 39A is, for example, 50 nm.

[0031] The n-AlGaN layer 40 is stacked on the surface of the first guide layer 39A. The n-AlGaN layer 40 is doped with Si as an n-type impurity. The AlN mole fraction in the n-AlGaN layer 40 is 0.62. The thickness of the n-AlGaN layer 40 is, for example, 2.5 μm.

[0032] The contact layer 41 is laminated on the N-polar surface of the n-AlGaN layer 40. The contact layer 41 is made of GaN. The contact layer 41 is not doped with n-type impurities or p-type impurities.

[0033] The n-side electrode 42 is laminated on the surface of the contact layer 41. The n-side electrode 42 is formed by laminating Ti, Pt, and Au. The nitride semiconductor light-emitting element 1 is configured in this manner.

[0034] [Method of manufacturing nitride semiconductor light-emitting device] An example of a manufacturing method for the nitride semiconductor light-emitting element 1 will be described. First, an AlN layer 72 is deposited to a thickness of 1550 nm on a sapphire substrate 70 having a C-plane surface and an AlN layer 71 deposited on the surface, using MOCVD (see FIG. 2(A)). Next, a 420 nm SiO2 layer (not shown) is deposited on the surface of the AlN layer 72 using a sputtering device. Then, a resist is applied to the surface of the SiO2 layer to form a resist film, and a fine pattern with a pitch of 1000 nm and a diameter of 500 nm is formed in the resist film using a nanoimprinting device. Next, the exposed SiO2 layer is dry-etched with CF4 gas using an ICP dry etching device, and subsequently, the residue of the SiO2 layer is removed using buffered hydrofluoric acid. Next, the surface side of the AlN layer 72 is dry-etched to a depth of 300 nm using Cl2 gas, and the SiO2 layer and resist film used as a mask are removed using buffered hydrofluoric acid. A plurality of protrusions 72A with a pitch of approximately 1000 nm, a diameter of approximately 450 nm, and a height of approximately 300 nm are formed on the surface of the AlN layer 72. Then, a u-AlGaN layer 73 with an AlN mole fraction of 0.68 is deposited to a thickness of 5 μm by MOCVD, and each layer of the semiconductor layer 34, from the n-AlGaN layer 40 to the p-GaN layer 35, is deposited thereon in this order.

[0035] Next, an insulating layer 33 is stacked on the p-GaN layer 35 and an opening 33A is formed in the insulating layer 33. Then, a p-side electrode 43 is formed in the opening 33A, a metal layer 32 is stacked, and the support 31 is joined to the metal layer 32 (see FIG. 2(B)).

[0036] Next, the back surface of the sapphire substrate 70 (i.e., the surface opposite to the surface on which the semiconductor layer 34 is stacked) is mirror-polished, and the sapphire substrate 70 is peeled off from the semiconductor layer 34 using a laser lift-off (LLO) method. Thereafter, the AlN layer 72, the u-AlGaN layer 73, and the n-AlGaN layer 40 are polished by CMP to expose the n-AlGaN layer 40 of the semiconductor layer 34, and the exposed surface is finished to be smooth (see FIG. 2(C)).

[0037] Then, a contact layer 41 is deposited on the smooth surface of the n-AlGaN layer 40 (see FIG. 2(D)). The contact layer 41 is deposited using an ECR sputtering apparatus 100 manufactured by JSW Afty (see FIG. 3). As shown in FIG. 3, the ECR sputtering apparatus 100 includes a film formation chamber 100A, a magnetron sputtering source 100B, and an ECR sputtering plasma source 100D. The film formation chamber 100A is provided with an inlet 100E and an outlet 100F. Ar gas and N2 (nitrogen) gas can be introduced into the film formation chamber 100A via the inlet 100E. The outlet 100F can discharge the Ar gas and N2 gas that have flowed into the film formation chamber 100A to the outside. A fixing table 100G is provided in a hanging manner within the film formation chamber 100A, and a semiconductor layer 34 having a support 31 bonded thereto is attached to the lower end of the fixing table 100G. The smoothly finished surface of the n-AlGaN layer 40 of the semiconductor layer 34 faces downward.

[0038] Magnetron sputtering source 100B operates by receiving power from sputtering power supply 100C. Magnetron sputtering source 100B uses a magnetron sputtering method to eject particles P from target 100H placed in film formation chamber 100A. GaN crystal is used for target 100H.

[0039] The ECR sputtering plasma source 100D can generate an ECR (Electron Cyclotron Resonance) plasma F.

[0040] The semiconductor layer 34, to which the support 31 is bonded, is attached to the support table 100G of the ECR sputtering apparatus 100. The semiconductor layer 34, to which the support 31 is bonded, is not heated. Ar gas is introduced into the film formation chamber 100A through the inlet 100E. The Ar gas inflow rate is, for example, 40 sccm. Then, GaN particles P are knocked out from the target 100H by the magnetron sputtering source 100B. Simultaneously, ECR plasma F is generated by the ECR sputtering plasma source 100D. The ECR plasma F flows toward the semiconductor layer 34, which is fixed to the support table 100G. When the GaN particles P reach the flow of the ECR plasma F, they are carried by the flow of the ECR plasma F toward the semiconductor layer 34 and are deposited on the surface of the n-AlGaN layer 40. In this way, the GaN particles P are deposited on the surface of the n-AlGaN layer 40 to a predetermined thickness, forming a contact layer 41. The semiconductor layer 34, to which the support 31 is bonded, is not actively heated by a heater or the like. However, the semiconductor layer 34 to which the support 31 is bonded is heated at a relatively low temperature of about 115° C. Therefore, the semiconductor layer 34 to which the support 31 is bonded can be laminated with the contact layer 41 while minimizing damage caused by heat.

[0041] Next, an n-side electrode 42 is deposited on the surface of the contact layer 41 by vapor deposition (see FIG. 2(D)). After that, a portion of the semiconductor layer 34 is removed to expose the metal layer 32, and a p-side electrode is deposited on the exposed surface of the metal layer 32 (not shown). In this way, the nitride semiconductor light-emitting element 1 is completed.

[0042] [Evaluation of IV characteristics in GaN contact layers] Next, to confirm the characteristics of the contact layer 41 deposited using the ECR sputtering apparatus 100, a sample was first prepared by providing the contact layer 41 on a sapphire substrate 70 (see FIG. 4A). The I-V characteristics of the contact layer 41 were measured using an electrode pattern for TLM (Transmission Line Model) measurements. In FIG. 4A, the contact layer 41 is deposited on the sapphire substrate 70 to a thickness of approximately 108 nm, and two n-side electrodes 42 are deposited at a distance S between them. Six samples with the structure shown in FIG. 4A were prepared by varying the distance S between the two n-side electrodes 42 in 5-μm increments from 5 μm to 30 μm. Specifically, as shown in FIG. 5, when each sample is viewed from above, the n-side electrode 42 is divided into an outer portion 42A and an inner portion 42B by a circular gap. The surface of the contact layer 41 is exposed through the circular gap. The n-side electrode 42 is formed by laminating Ti, Pt, and Au.

[0043] FIG. 6 shows the IV characteristics of each sample in which the contact layer 41 is laminated on the sapphire substrate 70. The solid line graphs in FIG. 6 show the IV characteristics of the contact layer 41 using GaN. The dotted line graphs in FIG. 6 will be described later. Each solid line graph is a straight line in which the current and voltage are directly proportional to each other. The slope of each solid line graph varies depending on the distance S between the two n-side electrodes 42. Specifically, the slope of the sample in which the distance S is 5 μm is the steepest, and the slope becomes gentler as the distance S increases, with the slope of the sample in which the distance S is 30 μm being the gentlest. In other words, it was found that ohmic characteristics can be obtained by the n-side electrode 42 (Ti / Pt / Au) formed on the surface of the contact layer 41 using GaN. The specific contact resistance between the contact layer 41 using GaN and the n-side electrode 42 was 2.9×10 -4 Ω cm 2 It was.

[0044] Next, samples were fabricated in which a contact layer 41 was laminated so as to cover the entire surface of the n-AlGaN layer 40 that was the uppermost layer on the semiconductor layer 34, and the contact layer 41 in the region where the n-side electrode 42 was not laminated was removed (see FIG. 4(B)). The I-V characteristics of one of the samples were measured, and the results are shown in FIG. 7. For comparison, a sample was also fabricated in which two n-side electrodes 42 were laminated directly on the surface of the n-AlGaN layer 40 without the contact layer 41, and the I-V characteristics of this sample were also measured. Note that the distance S between the two n-side electrodes 42 in each sample whose I-V characteristics were measured and shown in FIG. 7 was 30 μm.

[0045] For the sample in which the contact layer 41 using GaN was stacked (solid line in FIG. 7), the intercept where the approximation line of the rising part of the graph intersects with the line indicating a current value of 0 mA was approximately 0.5 V. For the sample in which the two n-side electrodes 42 were stacked directly on the surface of the n-AlGaN layer 40 (dashed line in FIG. 7), the intercept where the approximation line of the rising part of the graph intersects with the line indicating a current value of 0 mA was approximately 2.3 V.

[0046] 6 and 7, it was found that ohmic characteristics were obtained when a GaN-based contact layer 41 was deposited so as to cover the entire surface of the sapphire substrate 70 (the structure shown in FIG. 4(A)). In contrast, it was found that Schottky characteristics were obtained when the contact layer 41 in the region where the n-side electrode 42 was not deposited was removed (the structure shown in FIG. 4(B)). This is thought to be due to the heterobarrier at the interface between the GaN-based contact layer 41 and the n-AlGaN layer 40, which exhibits Schottky characteristics. However, it was found that the degree of Schottky characteristics was smaller than in a structure without the contact layer 41. From the above results, it was found that the drive voltage can be reduced by depositing a GaN-based contact layer 41 on the surface of the N-polarity n-AlGaN layer 40.

[0047] [Light intensity distribution when a GaN contact layer is stacked] Next, we investigated the light intensity distribution at a wavelength of 300 nm in the nitride semiconductor light-emitting element 1 on which a GaN-based contact layer 41 was stacked. Stacking a GaN-based contact layer 41, which has a higher refractive index than the n-AlGaN layer 40, on the surface of the n-AlGaN layer 40 may affect the light intensity distribution in the nitride semiconductor light-emitting element 1. For this reason, we used STR's SiLENe Laser Edition ver. 6.5 to simulate the light intensity distribution in the nitride semiconductor light-emitting element 1. Six thicknesses of the GaN-based contact layer 41 (0 nm, 50 nm, 75 nm, 100 nm, 125 nm, and 150 nm) were stacked on the surface of an n-AlGaN layer 40 with a thickness of 2500 nm. The light intensity distributions for each of these are shown in FIG. 8.

[0048] As shown in Figure 8, when a contact layer 41 using GaN is stacked on the surface of an n-AlGaN layer 40, it was found that when the thickness is 0 nm, 50 nm, or 75 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, when it is 100 nm or 125 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39 and a peak in TE2 occurs at the position of the contact layer 41, and when it is 150 nm, the peak in TE2 overlaps with the position of the light-emitting layer 39 and the peak in TE1 overlaps with the position of the contact layer 41.

[0049] Next, a simulation of the light intensity distribution at a wavelength of 270 nm in the nitride semiconductor light-emitting element 1 on which the GaN-based contact layer 41 was stacked was performed using STR's SiLENe Laser Edition ver. 6.5. The light intensity distribution for each of six thicknesses (0 nm, 50 nm, 75 nm, 100 nm, 125 nm, and 150 nm) of the GaN-based contact layer 41 stacked on the surface of an n-AlGaN layer 40 with an AlN mole fraction of 0.75 and a thickness of 2500 nm is shown in FIG.

[0050] 9, it was found that when the thickness of the contact layer 41 using GaN was 0 nm, 50 nm, or 75 nm, the peak of TE1 (fundamental mode) overlapped with the position of the light-emitting layer 39, and when the thickness was 100 nm, 125 nm, or 150 nm, the peak of TE1 (fundamental mode) overlapped with the position of the light-emitting layer 39 and a peak in TE2 appeared at the position of the contact layer 41. This tendency was also observed when the thickness of the n-AlGaN layer 40 was 1000 nm.

[0051] From the results of the graphs for TE1, TE2, and TE3 at wavelengths of 300 nm and 270 nm, it was found that when the thickness of GaN-based contact layer 41 is between 0 nm and 75 nm, it does not affect the light intensity distribution in nitride semiconductor light-emitting element 1, but when it is 100 nm or more, it has a significant effect on the light intensity distribution. Therefore, the thickness of GaN-based contact layer 41 is preferably between 0 nm and 75 nm, and more preferably between 0 nm and 50 nm. It is believed that a similar tendency will be observed at wavelengths other than 300 nm and 270 nm.

[0052] Next, the effects of the above embodiment will be described.

[0053] The nitride semiconductor light-emitting element 1 includes an n-side electrode 42, a contact layer 41 on which the n-side electrode 42 is stacked, and an n-AlGaN layer 40 on which the contact layer 41 is stacked, and the contact layer 41 is made of GaN and is stacked on the N-polarity face of the n-AlGaN layer 40. With this configuration, the n-side electrode 42 can be in ohmic contact with the contact layer 41. Although a slight barrier appears between the contact layer 41 and the n-AlGaN layer 40, the IV characteristics can be significantly improved compared to when the contact layer 41 is not present.

[0054] The thickness of the contact layer 41 made of GaN in the stacking direction is greater than 0 nm and not greater than 75 nm. With this configuration, the n-side electrode 42 can be in ohmic contact with the contact layer 41 without affecting the light intensity distribution in the nitride semiconductor light-emitting element 1. Although a slight barrier appears between the contact layer 41 and the n-AlGaN layer 40, the IV characteristics can be significantly improved compared to when the contact layer 41 is not present.

[0055] The method for manufacturing a nitride semiconductor light-emitting device includes an n-side electrode 42, a contact layer 41 on which the n-side electrode 42 is stacked, and an n-AlGaN layer 40 on which the contact layer 41 is stacked, and the contact layer 41 is stacked on the N-polarity surface of the n-AlGaN layer 40 using an ECR sputtering apparatus. This configuration makes it possible to avoid excessive heating of the semiconductor layer 34 when stacking the contact layer 41, thereby minimizing thermal damage to the semiconductor layer 34 and making the IV characteristics between the contact layer and the n-side electrode on the N-polarity surface ohmic. Although a slight barrier appears between the contact layer 41 and the n-AlGaN layer 40, the IV characteristics can be significantly improved compared to when the contact layer 41 is not present.

[0056] <Example 2> [Contact layer using AlGaN] To reduce the heterobarrier at the interface between the GaN contact layer 41 and the n-AlGaN layer 40, we investigated the use of AlGaN for the contact layer 41. When depositing AlGaN as the contact layer 41 on the surface of the n-AlGaN layer 40, a GaN crystal was placed as the target 100H, and an Al target was placed in the ECR sputtering plasma source 100D of the ECR sputtering apparatus 100 to simultaneously deposit AlN and GaN on the surface of the n-AlGaN layer 40. The AlN mole fraction of the n-AlGaN layer 40 was 0.62. The AlN mole fraction of the AlGaN contact layer 41 was 0.5 and the GaN mole fraction was 0.5. The semiconductor layer 34 to which the support 31 was bonded was not heated. Ar gas and N gas were then introduced into the deposition chamber 100A via the inlet 100E. For example, the Ar gas inflow rate was 40 sccm, and the N gas inflow rate was 1.5 sccm.

[0057] To confirm the characteristics of the contact layer 41 using AlGaN deposited using the ECR sputtering apparatus 100, a sample was first prepared by providing the contact layer 41 on a sapphire substrate 70 (see FIG. 4A). The IV characteristics of the contact layer 41 were measured using an electrode pattern for TLM measurement. The thickness of the contact layer 41 was approximately 240 nm. Six samples with the structure shown in FIG. 4A were prepared by varying the distance S between the two n-side electrodes 42 in 5-μm increments from 5 μm to 30 μm. Specifically, as shown in FIG. 5, when viewed from above, the n-side electrode 42 is divided into an outer portion 42A and an inner portion 42B by a circular gap. The surface of the contact layer 41 is exposed through the circular gap. The n-side electrode 42 is formed by laminating Ti, Pt, and Au.

[0058] FIG. 6 shows the IV characteristics of each sample in which the contact layer 41 is laminated on the sapphire substrate 70. The dotted line graphs in FIG. 6 show the results for the contact layer 41 using AlGaN. Each dotted line graph is a straight line in which the current and voltage are directly proportional to each other. The slope of each dotted line graph varies depending on the distance S between the two n-side electrodes 42. Specifically, the slope of the sample in which the distance S is 5 μm is the steepest, and the slope becomes gentler as the distance S increases, with the slope of the sample in which the distance S is 30 μm being the gentlest. In other words, it was found that ohmic characteristics can be obtained by the n-side electrode 42 (Ti / Pt / Au) formed on the surface of the contact layer 41 using AlGaN. The specific contact resistance between the contact layer 41 using AlGaN and the n-side electrode 42 is 3.8×10 -4 Ω cm 2 It was.

[0059] Next, samples were fabricated in which a contact layer 41 was laminated so as to cover the entire surface of the n-AlGaN layer 40 that was the uppermost layer on the semiconductor layer 34. The contact layer 41 in the region where the n-side electrode 42 was not laminated was removed (see FIG. 4(B)). The I-V characteristics of one of the samples were measured, and the results are shown in FIG. 7. In the sample in which the contact layer 41 using AlGaN was laminated and the I-V characteristics shown in FIG. 7 were measured, the distance S between the two n-side electrodes 42 was 30 μm. The sample in which the contact layer 41 using AlGaN was laminated (dotted line in FIG. 7) showed a linear characteristic in which the current and voltage were approximately directly proportional to each other.

[0060] 6 and 7, it was found that ohmic characteristics can be obtained when the contact layer 41 using AlGaN is laminated so as to cover the entire surface of the sapphire substrate 70 (structure shown in FIG. 4(A)). It was also found that ohmic characteristics can be obtained when the contact layer 41 in the region where the n-side electrode 42 is not laminated is removed (structure shown in FIG. 4(B)). From the above results, it was found that ohmic contact can be achieved and the driving voltage can be reduced by laminating the contact layer 41 using AlGaN on the surface of the n-polarity n-AlGaN layer 40.

[0061] [Light intensity distribution when stacking a contact layer using AlGaN] Next, we investigated the light intensity distribution at a wavelength of 300 nm within a device in which an AlGaN contact layer 41 was stacked. If an AlGaN (AlN mole fraction 0.5, GaN mole fraction 0.5) contact layer 41, which has a higher refractive index than the n-AlGaN layer 40, were stacked on the surface of the n-AlGaN layer 40, it could potentially affect the light intensity distribution within the device. Therefore, we used SiLENe Laser Edition ver. 6.5 to simulate the light intensity distribution within the device. Figure 10 shows the light intensity distribution when six different thicknesses of an AlGaN contact layer 41 (0 nm, 50 nm, 75 nm, 100 nm, 125 nm, and 150 nm) were stacked on the surface of a 2500 nm-thick n-AlGaN layer 40.

[0062] As shown in Figure 10, when an AlGaN contact layer 41 is stacked on the surface of the n-AlGaN layer 40, the peak of TE1 (fundamental mode) coincides with the light-emitting layer 39 when the thickness is 0 nm, 50 nm, 75 nm, or 100 nm. When the thickness is 125 nm, the peak of TE1 (fundamental mode) coincides with the light-emitting layer 39, and the peaks of TE3 are closer to the contact layer 41. When the thickness is 150 nm, the peak of TE1 (fundamental mode) coincides with the light-emitting layer 39, and the peaks of TE2 and TE3 occur closer to the contact layer 41. That is, when the thickness of the AlGaN contact layer 41 is between 0 nm and 100 nm, it does not affect the light intensity distribution within the device. However, when the thickness is 150 nm or more, it significantly affects the light intensity distribution. This tendency was also observed when the thickness of the n-AlGaN layer 40 is 1000 nm.

[0063] Next, a simulation of the light intensity distribution at a wavelength of 270 nm in the nitride semiconductor light-emitting element 1 on which the contact layer 41 using AlGaN was stacked was performed using STR's SiLENe Laser Edition ver6.5. The light intensity distribution for each of six thicknesses (0 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm) of the AlGaN contact layer 41 stacked on the surface of an n-AlGaN layer 40 with an AlN mole fraction of 0.75 and a thickness of 2500 nm is shown in FIG.

[0064] As shown in Figure 11, when the thickness of the contact layer 41 using AlGaN is 0 nm or 50 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, when it is 75 nm or 100 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39 and a peak in TE2 occurs at the position of the contact layer 41, and when it is 125 nm or 150 nm, the peak of TE1 (fundamental mode) overlaps with the position of the contact layer 41 and a peak in TE2 occurs at the position of the light-emitting layer 39.

[0065] From the results of the graphs for TE1, TE2, and TE3 at wavelengths of 300 nm and 270 nm, it was found that when the thickness of the contact layer 41 using AlGaN is between 0 nm and 50 nm, it does not affect the light intensity distribution in the nitride semiconductor light-emitting element 1, but when it is 100 nm or more, it has a significant effect on the light intensity distribution. Therefore, the thickness of the contact layer 41 using AlGaN is preferably between 0 nm and 50 nm. It is believed that a similar tendency will be observed at wavelengths other than 300 nm and 270 nm.

[0066] The thickness of the contact layer 41 using AlGaN in the stacking direction is greater than 0 nm and not greater than 50 nm. With this configuration, the n-side electrode 42 can be in ohmic contact with the contact layer 41 without affecting the light intensity distribution in the nitride semiconductor light-emitting element 1, and ohmic characteristics can be obtained without any barrier appearing between the contact layer 41 and the n-AlGaN layer 40, thereby significantly improving the IV characteristics.

[0067] In Example 2, the AlN mole fraction of the contact layer 41 was 0.5, but the AlN mole fraction of the contact layer 41 may be smaller than the AlN mole fraction of the n-AlGaN layer 40 on which the contact layer 41 is stacked, and preferably the Al mole fraction of the contact layer 41 is greater than 0 and equal to or less than 0.5. This configuration makes it easy to achieve ohmic characteristics between the contact layer 41 and the n-side electrode 42.

[0068] Example 3 [Study on AlGaN and GaN contact layers] The results of Example 2 demonstrate that stacking an AlGaN contact layer 41 on the surface of the n-AlGaN layer 40 enables ohmic contact with the n-side electrode 42 and reduces the drive voltage. However, the AlGaN contact layer 41 exposes Al atoms on its surface, raising concerns about the oxidation of the exposed Al atoms. Therefore, a simulation of the light intensity distribution at a wavelength of 300 nm was performed using SiLENe Laser Edition ver. 6.5. This simulation involved stacking four AlGaN thicknesses (50 nm, 75 nm, 100 nm, and 125 nm) on the surface of the 2500 nm-thick n-AlGaN layer 40, and then stacking three GaN thicknesses (10 nm, 30 nm, and 50 nm) on each AlGaN thickness. A total of 12 patterns were examined.

[0069] As shown in FIG. 12, when the thickness of AlGaN is 50 nm, the peak of TE1 (fundamental mode) overlaps with the position of light emitting layer 39 when the thickness of GaN is 10 nm, 30 nm, or 50 nm.

[0070] When the AlGaN thickness is 75 nm, it was found that when the GaN thickness is 10 nm or 30 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and when the GaN thickness is 50 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and peaks in TE2 and TE3 appear at the position of the contact layer 41.

[0071] When the thickness of the AlGaN is 100 nm, it was found that when the thickness of the GaN is 10 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and when the thickness of the GaN is 30 nm or 50 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and peaks in TE2 and TE3 appear at the position of the contact layer 41.

[0072] When the AlGaN thickness is 125 nm, it was found that when the GaN thickness is 10 nm or 30 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and the peaks in TE2 and TE3 occur at the position of the contact layer 41, and when the GaN thickness is 50 nm, the peak of TE1 (fundamental mode) overlaps with the position of the light-emitting layer 39, and the peak in TE2 occurs at the position of the contact layer 41.

[0073] That is, when a contact layer 41 in which AlGaN and GaN are stacked is used, if the AlGaN thickness is 50 nm, a GaN thickness of 10 nm or more and 50 nm or less does not affect the light intensity distribution in the nitride semiconductor light-emitting element 1, if the AlGaN thickness is 75 nm, a GaN thickness of 10 nm or more and 30 nm or less does not affect the light intensity distribution in the nitride semiconductor light-emitting element 1, and if the AlGaN thickness is 100 nm, a GaN thickness of 10 nm does not affect the light intensity distribution in the nitride semiconductor light-emitting element 1. Furthermore, if the AlGaN thickness is 125 nm, it was found that changing the GaN thickness does affect the light intensity distribution in the nitride semiconductor light-emitting element 1.

[0074] The contact layer 41 is formed by stacking GaN on the surface of AlGaN. With this configuration, the GaN prevents the surface of the AlGaN from being exposed, and the n-side electrode 42 can be in good ohmic contact with the contact layer 41 while suppressing oxidation of Al in the AlGaN.

[0075] In the case of the contact layer 41 using AlGaN and GaN, when the thickness of AlGaN in the stacking direction is 50 nm, the thickness of GaN in the stacking direction is 10 nm to 50 nm, when the thickness of AlGaN in the stacking direction is 75 nm, the thickness of GaN in the stacking direction is 10 nm to 30 nm, and when the thickness of AlGaN in the stacking direction is 100 nm, the thickness of GaN in the stacking direction is 10 nm. With this configuration, the n-side electrode 42 can be in ohmic contact with the contact layer 41 without affecting the light intensity distribution in the element.

[0076] The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention. (1) Unlike the above embodiment, a GaN crystal target may be placed in an ECR sputtering plasma source to deposit a contact layer using GaN. (2) In the above embodiment, sintered AlN, which does not have cleavage properties, is used, but cleavable SiC, Si, etc. may also be used as the support. (3) In the above embodiment, the crystals are grown by stacking using the MOVPE method, but this is not limiting and other methods such as MOCVD, MBE, sputtering, and LPEE may also be used to grow the crystals by stacking. (4) The ECR sputtering device may be any device other than that used in this example, as long as it can generate ECR plasma. (5) In the above embodiment, the contact layer is not doped with n-type impurities, but the contact layer may be doped with n-type impurities. [Explanation of symbols]

[0077] 1: Nitride semiconductor light emitting device 40: n-AlGaN layer (AlGaN layer) 41: Contact layer 42:n side electrode

Claims

1. an n-side electrode; a contact layer on which the n-side electrode is laminated; an AlGaN layer on which the contact layer is stacked; Equipped with The contact layer is made of at least one of GaN and AlGaN and is stacked on an N-polarity face of the AlGaN layer.

2. 2. The nitride semiconductor light-emitting device according to claim 1, wherein the thickness of said contact layer using GaN in the stacking direction is greater than 0 nm and not more than 75 nm.

3. 2. The nitride semiconductor light-emitting device according to claim 1, wherein the thickness of said contact layer using AlGaN in the stacking direction is greater than 0 nm and not more than 50 nm.

4. The nitride semiconductor light-emitting device according to claim 3 , wherein the AlN mole fraction of said contact layer is smaller than the AlN mole fraction of said AlGaN layer.

5. The nitride semiconductor light-emitting device according to claim 3 , wherein the AlN mole fraction of said contact layer is greater than 0 and not more than 0.

5.

6. The nitride semiconductor light-emitting device according to claim 1 , wherein said contact layer is formed by stacking said GaN on a surface of said AlGaN.

7. When the thickness of the AlGaN in the stacking direction is 50 nm, the thickness of the GaN in the stacking direction is 10 nm or more and 50 nm or less, When the thickness of the AlGaN in the stacking direction is 75 nm, the thickness of the GaN in the stacking direction is 10 nm or more and 30 nm or less, 7. The nitride semiconductor light-emitting device according to claim 6, wherein when the thickness of said AlGaN in the stacking direction is 100 nm, the thickness of said GaN in the stacking direction is 10 nm.

8. an n-side electrode; a contact layer on which the n-side electrode is laminated; an AlGaN layer on which the contact layer is stacked; A method for manufacturing a nitride semiconductor light-emitting device comprising: The method for manufacturing a nitride semiconductor light-emitting device, wherein the contact layer is deposited on the N-polarity surface of the AlGaN layer using an ECR sputtering apparatus.

Images