Nitride semiconductor device

Abstract

The nitride semiconductor device of the present invention includes: an n-side nitride semiconductor layer; an active layer provided on the n-side nitride semiconductor layer and including a plurality of well layers made of a nitride semiconductor and a plurality of barrier layers made of a nitride semiconductor; and a p-side nitride semiconductor layer provided on the active layer. The plurality of well layers successively have, starting from the n-side nitride semiconductor layer side: a first intermediate layer having a bandgap smaller than that of the barrier layer and containing Al, Ga, and N; a second intermediate layer having a bandgap energy smaller than that of the first intermediate layer and containing Ga and N; and a light-emitting layer having a bandgap energy smaller than that of the first intermediate layer and emitting ultraviolet light containing Ga and N. The film thickness of the first intermediate layer is smaller than those of the second intermediate layer and the light-emitting layer. Among the plurality of barrier layers, the barrier layer disposed between the second intermediate layer and the light-emitting layer is doped with an n-type impurity.

Description

Technical Field

[0001] The present invention relates to a nitride semiconductor device. Background Art

[0002] In recent years, the development of light-emitting devices that emit ultraviolet light has been in progress. For example, Patent Document 1 discloses a light-emitting device having a multi-quantum well structure suitable for emitting deep ultraviolet light. In addition, near-ultraviolet light-emitting devices are also being developed for resin curing or various sensing detections.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-175005

[0006] Problems to be Solved by the Invention

[0007] Such nitride semiconductor devices that emit ultraviolet light have been improved to enhance their characteristics, such as light emission output, etc., but their characteristics have not been sufficiently improved. Summary of the Invention

[0008] Accordingly, an object of the present invention is to provide a nitride semiconductor device that emits ultraviolet light with a high light emission output.

[0009] The nitride semiconductor device of the present invention includes:

[0010] an n-side nitride semiconductor layer;

[0011] an active layer provided on the n-side nitride semiconductor layer and having a plurality of well layers made of a nitride semiconductor and a plurality of barrier layers made of a nitride semiconductor;

[0012] a p-side nitride semiconductor layer provided on the active layer,

[0013] the plurality of well layers sequentially include, from the n-side nitride semiconductor layer side:

[0014] a first intermediate layer having a smaller bandgap than the barrier layer and containing Al, Ga, and N;

[0015] a second intermediate layer having a smaller bandgap energy than the first intermediate layer and containing Ga and N;

[0016] a light-emitting layer having a smaller bandgap energy than the first intermediate layer and emitting ultraviolet light containing Ga and N,

[0017] the film thickness of the first intermediate layer is thinner than those of the second intermediate layer and the light-emitting layer,

[0018] Among the plurality of barrier layers, the barrier layer disposed between the second intermediate layer and the light-emitting layer is doped with an n-type impurity.

[0019] Advantages of the Invention

[0020] The nitride semiconductor device according to an embodiment of the present invention can provide a nitride semiconductor device that emits ultraviolet light with a high light emission output. Description of the Drawings

[0021] Figure 1 It is a cross-sectional view showing the structure of a nitride semiconductor device according to an embodiment of the present invention disposed on a substrate.

[0022] Figure 2 It shows Figure 1 a diagram of the multiple quantum well structure of the nitride semiconductor device shown.

[0023] Figure 3 It shows Figure 2 a diagram of the bandgap energy of the multiple quantum well structure shown.

[0024] Figure 4 It is a cross-sectional view of a first substrate prepared in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0025] Figure 5 It is a cross-sectional view when an n-side nitride semiconductor layer is formed on the upper surface of the first substrate prepared in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0026] Figure 6 It is a cross-sectional view when an active layer is formed on the n-side nitride semiconductor layer formed on the upper surface of the first substrate in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0027] Figure 7 It is a cross-sectional view of a first wafer in which a p-side nitride semiconductor layer is formed on the active layer formed via the n-side nitride semiconductor layer on the upper surface of the first substrate in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0028] Figure 8 It is a cross-sectional view when a resist for forming a second electrode is formed on the p-side nitride semiconductor layer of the first wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0029] Figure 9 It is a cross-sectional view when a metal film for forming a second electrode is formed on the p-side nitride semiconductor layer of the first wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0030] Figure 10This is a cross-sectional view when forming a second electrode with a specified shape by removing a resist formed on the p-side nitride semiconductor layer of the first wafer together with a metal film formed on the resist in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0031] Figure 11 This is a cross-sectional view when forming a resist on a second electrode in order to form an insulating film between the second electrodes on the p-side nitride semiconductor layer of the first wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0032] Figure 12 This is a cross-sectional view when an insulating film is formed between the second electrodes on the p-side nitride semiconductor layer of the first wafer and on the resist in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0033] Figure 13 This is a cross-sectional view when forming a second electrode and an insulating film on the p-side nitride semiconductor layer of the first wafer by removing the resist together with the insulating film formed on the resist in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0034] Figure 14 This is a cross-sectional view when forming a metal layer on the second electrode and the insulating film formed on the p-side nitride semiconductor layer of the first wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0035] Figure 15 This is a cross-sectional view when preparing a second substrate having a metal layer formed on one surface and bringing the first wafer into opposition to the second substrate in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0036] Figure 16 This is a cross-sectional view when bonding the first wafer and the second substrate by bonding the metal layers to each other in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0037] Figure 17 This is a cross-sectional view of a second wafer manufactured in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0038] Figure 18 This is a cross-sectional view when removing a part of the nitride semiconductor element of the manufactured second wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0039] Figure 19 This is a cross-sectional view when forming a first electrode with a specified pattern on the n-side nitride semiconductor layer of the second wafer in the method for manufacturing a light-emitting device according to an embodiment of the present invention.

[0040] Figure 20 It is a diagram showing a multi - quantum well structure of a nitride semiconductor device representing a modified example of the present invention. Detailed implementation manners

[0041] Hereinafter, implementation manners and examples for implementing the present invention will be described with reference to the accompanying drawings. In addition, the nitride semiconductor devices described below are contents for embodying the technical idea of the present invention, and the present invention is not limited to the following contents unless otherwise specified.

[0042] In each of the drawings, components having the same function are sometimes denoted by the same reference numerals. For the sake of easy explanation of the key points or understanding, for convenience, they are sometimes shown separately as implementation manners or examples, but partial replacement or combination can be made for the structures shown in different implementation manners or examples. In the following implementation manners and examples, descriptions of the same content as that described above are omitted, and only the differences are described. In particular, the same functions and effects of the same structures are not repeatedly mentioned in each implementation manner or example. The sizes and positional relationships of the components shown in each drawing are sometimes exaggerated for clear explanation.

[0043] A semiconductor structure for a light - emitting diode has an n - type n - side nitride semiconductor layer, a p - type p - side nitride semiconductor layer, and an active layer provided between the n - side nitride semiconductor and the p - side nitride semiconductor. In addition, the active layer uses, for example, a multi - quantum well structure including a plurality of well layers. Generally, in a light - emitting diode that emits ultraviolet light and in which the active layer includes a plurality of well layers, there is a tendency that the well layers located on the p - side nitride semiconductor layer side in the plurality of well layers contribute to light emission, and the well layers located on the n - side nitride semiconductor layer side do not contribute to light emission. In addition, the well layers located on the n - side nitride semiconductor layer side may absorb (self - absorb) the light emitted from the well layers located on the p - side nitride semiconductor layer side, deteriorating the light extraction efficiency.

[0044] Then, as factors affecting the light emission output of the nitride semiconductor device, the inventors focused on the recombination probability of electrons and holes, the lattice relaxation of the crystal in the semiconductor layer, and the self - absorption of light by the semiconductor layer and conducted in - depth research.

[0045] The inventors first studied a method for reducing the self - absorption of light in a plurality of well layers. The self - absorption of light by the well layer decreases as the band - gap energy of the semiconductor layer constituting the well layer increases. Then, the inventors studied reducing the self - absorption of light in the active layer by making the band - gap energy of the non - light - emitting - contributing well layer (intermediate layer) located on the n - side nitride semiconductor layer side larger than the band - gap energy of the light - emitting - contributing well layer located on the p - side nitride semiconductor layer side.

[0046] It is expected that nitride semiconductor devices having a plurality of well layers with such a structure exhibit a higher light emission output than conventional nitride semiconductor devices, but in fact, a sufficiently high light emission output cannot be obtained.

[0047] The present inventors have repeatedly studied this result and speculated that the reason why the light emission output cannot be sufficiently increased is that lattice relaxation of the crystal between the light-emitting layer, which is a well layer contributing to light emission, and the intermediate layer hinders the improvement of the light emission output because of the difference in composition between the light-emitting layer and the intermediate layer. Based on this speculation, when the present inventors disposed a second intermediate layer having a smaller band gap than the first intermediate layer between the light-emitting layer and the intermediate layer (first intermediate layer) to suppress lattice relaxation, the light emission output could be increased as compared with the case where there was no second intermediate layer.

[0048] In the above-described nitride semiconductor device including, in order from the n-side nitride semiconductor layer side, a first intermediate layer having a larger band gap energy, a second intermediate layer having a band gap energy smaller than that of the first intermediate layer, and a light-emitting layer, as a result of research to obtain a higher light emission output, the following findings were obtained.

[0049] (1) By making the film thickness of the first intermediate layer thinner than those of the second intermediate layer and the light-emitting layer, self-absorption of light emitted from the light-emitting layer in the first intermediate layer can be more effectively suppressed.

[0050] (2) By doping an n-type impurity in the barrier layer between the light-emitting layer and the second intermediate layer, recombination in the light-emitting layer can be further promoted.

[0051] Here, considering the recombination probability of electrons and holes, the light-emitting layer is preferably a layer containing Ga and N, and a prescribed light emission wavelength is set mainly by adjusting the composition ratio of In, Ga, and N.

[0052] In addition, the band gap energy of the first intermediate layer is preferably a layer containing Al, Ga, and N, and is made larger than the band gap energy of the light-emitting layer mainly by adjusting the composition ratio of Al, Ga, and N. Thereby, self-absorption of the first intermediate layer can be effectively suppressed.

[0053] Furthermore, the second intermediate layer is a layer containing Ga and N, and has a band gap energy smaller than that of the first intermediate layer mainly by adjusting the composition ratio of Ga and N.

[0054] The nitride semiconductor device of the present invention is completed based on the above insights, and includes: an n-side nitride semiconductor layer; an active layer provided on the n-side nitride semiconductor layer and including a plurality of well layers made of nitride semiconductor and a plurality of barrier layers made of nitride semiconductor; and a p-side nitride semiconductor layer provided on the active layer. Moreover, the plurality of well layers sequentially have, starting from the n-side nitride semiconductor layer side: a first intermediate layer having a bandgap smaller than that of the barrier layer and containing Al, Ga, and N; a second intermediate layer having a bandgap energy smaller than that of the first intermediate layer and containing Ga and N; and a light-emitting layer having a bandgap energy smaller than that of the first intermediate layer and emitting ultraviolet light containing Ga and N. The film thickness of the first intermediate layer is smaller than those of the second intermediate layer and the light-emitting layer, and among the plurality of barrier layers, the barrier layer disposed between the second intermediate layer and the light-emitting layer is doped with an n-type impurity.

[0055] Embodiment

[0056] Hereinafter, a method for manufacturing a nitride semiconductor device of the present embodiment and a light-emitting device including the nitride semiconductor device will be described with reference to the drawings.

[0057] 1. Nitride semiconductor device

[0058] Figure 1 FIG. is a cross-sectional view showing the structure of the nitride semiconductor device 1 of the present embodiment disposed on the second substrate 22.

[0059] As Figure 1 shown, the nitride semiconductor device 1 of the present embodiment is disposed on the second substrate 22. The nitride semiconductor device 1 includes, in order from the second substrate 22 side, a p-side nitride semiconductor layer 13, an active layer 12, and an n-side nitride semiconductor layer 11. A first electrode 31 is electrically connected to the n-side nitride semiconductor layer 11. A second electrode 32 is electrically connected to the p-side nitride semiconductor layer 13. The nitride semiconductor device 1 is bonded to the second substrate 22 via a metal layer 40. Thus, for example, by using a conductive semiconductor substrate or a substrate made of metal as the second substrate 22, power can be supplied to the nitride semiconductor device 1 via the second substrate 22. With such a structure, the nitride semiconductor device 1 can emit light by applying a voltage between the first electrode 31 and the second electrode 32. The light emitted by the nitride semiconductor device 1 is mainly emitted from the surface side of the n-side nitride semiconductor layer 11 where the first electrode 31 is provided.

[0060] Hereinafter, the nitride semiconductor device 1 of the present embodiment will be described in detail.

[0061] (n-side nitride semiconductor layer)

[0062] The n-side nitride semiconductor layer 11 is, for example, a nitride semiconductor doped with an n-type impurity such as Si. The n-side nitride semiconductor layer 11 may be composed of a single layer or may be composed of multiple layers. Additionally, for example, the n-side nitride semiconductor layer 11 may partially include an undoped semiconductor layer. Here, the undoped semiconductor layer refers to a layer grown without adding an n-type impurity during growth. For example, it may also contain inevitable impurities mixed in from adjacent layers by diffusion or the like.

[0063] (p-side nitride semiconductor layer)

[0064] The p-side nitride semiconductor layer 13 is, for example, a nitride semiconductor doped with a p-type impurity such as Mg. The p-side nitride semiconductor layer 13 may be composed of a single layer or may be composed of multiple layers. Additionally, for example, the p-side nitride semiconductor layer 13 may partially include an undoped semiconductor layer.

[0065] (Active layer)

[0066] The active layer 12 includes a plurality of well layers made of a nitride semiconductor and a plurality of barrier layers made of a nitride semiconductor. As Figure 2 shown, the multi-quantum well structure of the present embodiment sequentially includes, from the n-side nitride semiconductor layer 11 side: a first layer portion 2 including a plurality of first intermediate layers 6 and a plurality of barrier layers 5, a second layer portion 3 including a second intermediate layer 8 and an n-type impurity-doped barrier layer 7, and a third layer portion 4 including a light-emitting layer 10 and an undoped barrier layer 9 without doped impurities.

[0067] (First layer portion)

[0068] The first layer portion 2 is a portion where the first intermediate layer 6 and the barrier layer 5 are alternately stacked. The barrier layer 5 is disposed on the n-side nitride semiconductor layer 11, the first intermediate layer 6 is disposed on the barrier layer 5, and then the barrier layer 5 and the first intermediate layer 6 are alternately stacked, and the barrier layer 5 is disposed on the uppermost layer. The first layer portion 2 of the present embodiment includes 4 barrier layers 5 and 3 first intermediate layers 6. Additionally, as Figure 3 shown, the barrier layer has a larger bandgap energy than the well layer. This is the same in the following second layer portion 3 and third layer portion 4.

[0069] The barrier layer 5 is a nitride semiconductor layer containing Al, Ga, and N. The nitride semiconductor layer containing Al, Ga, and N is, for example, a ternary compound. The general formula of the barrier layer 5 is, for example, Al a Ga 1－aN (0 < a < 1). The mixed crystal ratio of Al in the barrier layer 5 is preferably 0.05 ≤ a ≤ 0.15. The film thickness of the barrier layer 5 is, for example, 10 nm or more and 50 nm or less, preferably 20 nm or more and 40 nm or less. The barrier layer 5 of the first layer portion 2 may be doped with n-type impurities in the same manner as the n-type impurity-doped barrier layer 7 of the second layer portion 3 described later. Alternatively, a part of the plurality of barrier layers 5 may be a barrier layer doped with n-type impurities, and another part may be a barrier layer not doped with n-type impurities. By doping the barrier layer 5 of the first layer portion 2 with n-type impurities, similar to the n-type impurity-doped barrier layer 7 of the second layer portion 3 described later, the recombination probability in the light-emitting layer 10 can be increased.

[0070] The first intermediate layer 6 is a nitride semiconductor layer containing Al, Ga, and N. As Figure 3 shown, the first intermediate layer 6 has a larger bandgap energy than the second intermediate layer 8 and the light-emitting layer 10. The first intermediate layer 6 is, for example, a ternary compound or a quaternary compound. The general formula of the first intermediate layer 6 is, for example, Al b In c Ga 1－b－c N (0 < b < 1, 0 ≤ c < 1, b + c < 1). The mixed crystal ratio of Al in the first intermediate layer 6 is preferably 0.03 ≤ b ≤ 0.1. In addition, the content of In in the first intermediate layer 6 is preferably 0 ≤ c ≤ 0.03. By making the first intermediate layer 6 have such a composition, the absorption of light emitted from the light-emitting layer 10 can be suppressed. Different from the light-emitting light-emitting layer 10, the first intermediate layer 6 is a substantially non-light-emitting non-light-emitting well layer.

[0071] The film thickness of the first intermediate layer 6 is thinner than that of the second intermediate layer 8 and the light-emitting layer 10. By having such a film thickness, self-absorption of the first intermediate layer 6 can be effectively suppressed. The film thickness of the first intermediate layer 6 is, for example, 2 nm or more and 10 nm or less, preferably 3 nm or more and 7 nm or less.

[0072] The first intermediate layer 6 having the above bandgap energy and film thickness functions as a buffer layer for growing the light-emitting layer 10 described later with good crystallinity, and can suppress the absorption of light emitted from the light-emitting layer 10.

[0073] (Second layer portion)

[0074] The second layer portion 3 is a part formed by laminating one second intermediate layer 8 and one n-type impurity-doped barrier layer 7. The second intermediate layer 8 is disposed on the barrier layer 5 disposed at the uppermost layer of the first layer portion 2, and the n-type impurity-doped barrier layer 7 is disposed on the second intermediate layer 8.

[0075] The n-type impurity-doped barrier layer 7 in the second layer portion 3 is a nitride semiconductor layer containing Al, Ga, and N doped with an n-type impurity. The n-type impurity-doped barrier layer 7 is, for example, a ternary compound. The composition of the n-type impurity-doped barrier layer 7 may also be the same as that of the above-described barrier layer 5. In addition, the film thickness of the n-type impurity-doped barrier layer 7 is, for example, 20 nm or more and 40 nm or less. The n-type impurity is, for example, Si. The concentration of the n-type impurity in the n-type impurity-doped barrier layer 7 is, for example, 1×10 17 atoms / cm 3 or more and 1×10 19 atoms / cm 3 or less. By forming the n-type impurity-doped barrier layer 7 adjacent to the light-emitting layer 10, the recombination probability of holes injected from the p-side nitride semiconductor layer 13 and electrons injected via the n-type impurity-doped barrier layer 7 in the light-emitting layer 10 can be increased compared to the case where an undoped barrier layer is provided between the first intermediate layer 6 and the second intermediate layer. In addition, as a result of increasing the recombination probability in the light-emitting layer 10, injection of holes into the second intermediate layer 8 and the first intermediate layer 6 can be suppressed, and a structure in which the second intermediate layer 8 and the first intermediate layer 6 substantially do not emit light can be formed.

[0076] The second intermediate layer 8 is a nitride semiconductor layer containing Ga and N, and preferably a nitride semiconductor layer containing In, Ga, and N. In addition, as Figure 3 shown, the second intermediate layer 8 has a smaller bandgap energy than the first intermediate layer 6. The general formula of the second intermediate layer 8 is, for example, In d Ga 1－d N (0≤d<1). The In content of the second intermediate layer 8 is preferably less than the In content of the light-emitting layer 10. Thereby, the bandgap energy of the second intermediate layer 8 is made greater than the bandgap energy of the light-emitting layer 10, and absorption of light emitted from the light-emitting layer 10 by the second intermediate layer 8 can be suppressed. The In content of the second intermediate layer 8 is preferably 0≤d≤0.03. Different from the light-emitting light-emitting layer 10, the second intermediate layer 8 is a substantially non-light-emitting non-light-emitting well layer like the above-described first intermediate layer 6.

[0077] When the bandgap energy of the second intermediate layer 8 is made substantially the same as the bandgap energy of the light-emitting layer 10, it is preferable that the film thickness of the second intermediate layer 8 is thinner than the film thickness of the light-emitting layer 10. Thereby, absorption of light emitted from the light-emitting layer 10 by the second intermediate layer 8 can be suppressed. By thinning the film thickness of the second intermediate layer 8, self-absorption of the second intermediate layer 8 can be suppressed. The film thickness of the second intermediate layer 8 is thicker than that of the first intermediate layer 6. The film thickness of the second intermediate layer 8 is, for example, 5 nm or more and 20 nm or less, and preferably 10 nm or more and 18 nm or less.

[0078] The second intermediate layer 8 having the above-described bandgap energy and film thickness suppresses lattice relaxation of crystals generated between the first intermediate layer 6 and the later-described light-emitting layer 10. Here, lattice relaxation is a phenomenon in which strain is dispersed by generating dislocations at the boundary portions of crystals having different lattice constants. On the other hand, there is a tendency for the crystallinity to decrease due to the generation of dislocations due to lattice relaxation. Thus, in the nitride semiconductor device of the present embodiment, by providing the second intermediate layer 8, the crystallinity reduced by laminating the first intermediate layer 6 made of an Al-containing nitride semiconductor can be restored.

[0079] (Third layer portion)

[0080] The third layer portion 4 is a portion in which one light-emitting layer 10 and one undoped barrier layer 9 are laminated. The light-emitting layer 10 is disposed on the n-type impurity-doped barrier layer 7 of the second layer portion 3, and the undoped barrier layer 9 is disposed on the light-emitting layer 10.

[0081] The undoped barrier layer 9 in the third layer portion 4 is a nitride semiconductor layer not doped with n-type impurities. The undoped barrier layer 9 is, for example, a ternary compound. The undoped barrier layer 9 may have the same composition as the above-described barrier layer 5 and n-type impurity-doped barrier layer 7. The film thickness of the undoped barrier layer 9 is thicker than that of the barrier layer 5 and the n-type impurity-doped barrier layer 7. The film thickness of the undoped barrier layer 9 is, for example, 30 nm or more and 50 nm or less. Since the undoped barrier layer 9 does not contain n-type impurities, holes moving from the p-side nitride semiconductor layer 13 pass through the undoped barrier layer 9 and move to the light-emitting layer 10. Therefore, holes can be efficiently supplied to the light-emitting layer 10, and the light-emitting efficiency of the light-emitting layer 10 can be improved.

[0082] The light-emitting layer 10 is a nitride semiconductor layer containing Ga and N and emits ultraviolet light. In the present specification, ultraviolet light means light having a wavelength of 400 nm or less. The general formula of the light-emitting layer 10 is, for example, In e Ga 1－e N (0 ≤ e < 1). The content of In is preferably 0 ≤ e ≤ 0.05. The light-emitting layer 10 having such a composition emits ultraviolet light. The peak wavelength of the light emitted by the light-emitting layer 10 is, for example, 365 nm or more and 400 nm or less. As an example of the peak wavelength of the light-emitting layer 10, it is about 365 nm or about 385 nm. In addition, as Figure 3 shown, the light-emitting layer 10, for example, has substantially the same bandgap energy as the second intermediate layer 8. In addition, by making the light-emitting layer 10 contain Al or the like, the peak wavelength of the light-emitting layer 10 can be, for example, 250 nm or more and 365 nm or less. When the light-emitting layer 10 is, for example, Al f Ga 1－f N (0 < f < 1), the content of Al can be 0 < f ≤ 0.6.

[0083] The film thickness of the light-emitting layer 10 is equal to or greater than the film thickness of the second intermediate layer 8. The film thickness of the light-emitting layer 10 is, for example, 10 nm or more and 18 nm or less. The light-emitting layer 10 having such a film thickness can promote the recombination of electrons and holes.

[0084] 2. Method for manufacturing a light-emitting device

[0085] Next, a method for manufacturing a light-emitting device including the nitride semiconductor element of the present embodiment will be described.

[0086] (First wafer preparation process)

[0087] In the first wafer preparation process, as Figure 4 shown, a first substrate 21 made of, for example, sapphire is prepared. Then, as Figure 5 shown, an n-side nitride semiconductor layer 11 including an n-type contact layer and an n-type cladding layer is formed in sequence from the first substrate 21 side by growing, for example, an n-type contact layer and an n-type cladding layer on the first substrate 21. Alternatively, the n-side nitride semiconductor layer 11 may be formed on the first substrate 21 via a buffer layer.

[0088] Next, as Figure 6 shown, an active layer 12 is formed on the n-side nitride semiconductor layer 11. The active layer 12 is formed by the following process.

[0089] First, a barrier layer 5 is grown on the n-side nitride semiconductor layer 11 using a source gas containing an Al source gas, a Ga source gas, and an N source gas (barrier layer growth process). When the composition of the barrier layer 5 is, for example, AlGaN, the barrier layer 5 can be formed by setting the flow rate of the Al source gas in the range of 1 to 2 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, and the flow rate of the N source gas in the range of 5 to 10 slm.

[0090] Next, a first intermediate layer 6 is grown on the barrier layer 5 using a source gas containing an Al source gas, an In source gas, a Ga source gas, and an N source gas (first intermediate layer growth process). When the composition of the first intermediate layer 6 is, for example, AlInGaN, the first intermediate layer 6 can be formed by setting the flow rate of the Al source gas to 0.2 to 1.5 sccm, the flow rate of the In source gas in the range of 0.1 to 25 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, and the flow rate of the N source gas in the range of 5 to 10 slm.

[0091] By alternately repeating the barrier layer growth process and the first intermediate layer growth process, a first layer portion 2 having a plurality of barrier layers 5 and first intermediate layers 6 is formed. In addition, the process of forming the first layer portion 2 ends in the barrier layer growth process.

[0092] Next, a second intermediate layer 8 is grown on the barrier layer 5 using source gases containing an In source gas, a Ga source gas, and an N source gas (second intermediate layer growth process). When the composition of the second intermediate layer 8 is, for example, InGaN, the second intermediate layer 8 can be formed by setting the flow rate of the In source gas in the range of 0.1 to 25 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, and the flow rate of the N source gas in the range of 5 to 10 slm.

[0093] Next, an n-type impurity-doped barrier layer 7 is grown on the second intermediate layer 8 using source gases containing an Al source gas, a Ga source gas, an N source gas, and an n-type impurity source gas (n-type impurity-doped barrier layer growth process). When the composition of the n-type impurity-doped barrier layer 7 is, for example, AlGaN and the n-type impurity is Si, the n-type impurity-doped barrier layer 7 can be formed by setting the flow rate of the Al source gas in the range of 1 to 2 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, the flow rate of the N source gas in the range of 5 to 10 slm, and the doping amount of the n-type impurity in the range of 1×10 17 atoms / cm 3 above and 1×10 19 atoms / cm 3 below.

[0094] By performing the second intermediate layer growth process and the n-type impurity-doped barrier layer growth process, a second layer portion 3 having the second intermediate layer 8 and the n-type impurity-doped barrier layer 7 is formed.

[0095] Next, a light-emitting layer 10 is grown on the n-type impurity-doped barrier layer 7 using source gases containing an In source gas, a Ga source gas, and an N source gas (light-emitting layer growth process). When the composition of the light-emitting layer 10 is, for example, InGaN or GaN, the light-emitting layer 10 can be formed by setting the flow rate of the In source gas in the range of 0 to 45 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, and the flow rate of the N source gas in the range of 5 to 10 slm.

[0096] Next, an undoped barrier layer 9 is grown on the light-emitting layer 10 using source gases containing an Al source gas, a Ga source gas, and an N source gas (undoped barrier layer growth process). When the composition of the undoped barrier layer 9 is, for example, AlGaN, the undoped barrier layer 9 can be formed by setting the flow rate of the Al source gas in the range of 1 to 2 sccm, the flow rate of the Ga source gas in the range of 30 to 50 sccm, and the flow rate of the N source gas in the range of 5 to 10 slm.

[0097] By performing a light-emitting layer growth process and an undoped barrier layer growth process, a third layer portion 4 having a light-emitting layer 10 and an undoped barrier layer 9 is formed.

[0098] Then, on the active layer 12 having the first layer portion 2, the second layer portion 3, and the third layer portion 4, for example, by growing a p-type cladding layer and a p-type contact layer, a p-side nitride semiconductor layer 13 including a p-type cladding layer and a p-type contact layer is sequentially formed from the active layer 12 side. Through such a process, as Figure 7 shown, a first wafer 100 having a semiconductor structure 1a with an n-side nitride semiconductor layer 11, an active layer 12, and a p-side nitride semiconductor layer 13 formed on a first substrate 21 is prepared.

[0099] (Second Wafer Preparation Process)

[0100] In the second wafer preparation step, first, a second electrode 32 having a predetermined pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100 as follows.

[0101] Initially, as Figure 8 shown, a resist 51 is formed on the p-side nitride semiconductor layer 13 of the first wafer 100. Here, for example, the resist 51 is formed on a portion of the p-side nitride semiconductor layer 13 where the second electrode is not formed.

[0102] Next, as Figure 9 shown, a metal film (32, 32a) containing Ag, for example, is formed on the entire upper surface of the p-side nitride semiconductor layer 13. Thereby, the second electrode 32 is formed on the p-side nitride semiconductor layer 13 where the resist 51 is not formed.

[0103] Then, as Figure 10 shown, the resist 51 and the metal film 32a formed on the resist 51 are removed together.

[0104] As described above, the second electrode 32 having a predetermined pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100.

[0105] Here, a method of forming the second electrode 32 having a predetermined pattern by a lift-off process is described. However, the lift-off process may not be used. For example, a metal film may be formed on the entire upper surface of the p-side nitride semiconductor layer 13 without forming the resist 51, a resist may be formed on the metal film, and the metal film may be removed using the resist as a mask, thereby forming the second electrode 32 having a predetermined pattern.

[0106] Next, as Figure 11 shown, a resist 52 is formed on the second electrode 32. After forming the resist 52, as Figure 12As shown, an insulating film 35a is formed on a portion of the p-side nitride semiconductor layer 13 where the second electrode 32 is not formed and on the resist 52. Then, as Figure 13 shown, the resist 52 and the insulating film 35a formed on the resist 52 are removed together. In this way, an insulating film 35 is formed on the portion of the p-side nitride semiconductor layer 13 where the second electrode 32 is not formed. The insulating film 35 is provided, for example, at a cutting position CL described later. By configuring in this way, a structure can be formed in which the second electrode 32 is not exposed from the side surface of the light-emitting device by the insulating film 35. As a result, a short circuit on the side surface of the light-emitting device can be suppressed, and the reliability can be improved.

[0107] Next, as Figure 14 shown, a metal layer 40a is formed on the second electrode 32 and the insulating film 35 formed on the p-side nitride semiconductor layer 13. In addition, as Figure 15 shown, a second substrate 22 having a metal layer 40b formed on one surface is prepared, and the metal layer 40b and the metal layer 40a are bonded together. Thus, as Figure 16 shown, the second substrate 22 is bonded to the p-side nitride semiconductor layer 13 via the second electrode 32 and the insulating film 35. After the second substrate 22 is bonded, as Figure 17 shown, the first substrate 21 is removed. As described above, the second substrate 22 is bonded to the p-side nitride semiconductor layer 13 of the first wafer 100, and the first substrate 21 of the first wafer 100 is removed. For example, the removal of the first substrate 21 is performed by laser lift-off, in which laser is irradiated near the interface between the first substrate 21 and the n-side nitride semiconductor layer 11 to separate the first substrate 21 from the n-side nitride semiconductor layer 11. Alternatively, it is performed by wet etching using a solution capable of etching the first substrate 21. As described above, the semiconductor structure 1a formed on the first substrate 21 is transferred to the second substrate 22 via the metal layer 40, the second electrode 32, and the insulating film 35. In this way, as Figure 17 shown, a second wafer 200 having the semiconductor structure 1a in which the n-side nitride semiconductor layer 11 is exposed on the surface is prepared on the second substrate 22. That is, in the second wafer 200, on the second substrate 22, the p-side nitride semiconductor layer 13, the active layer 12, and the n-side nitride semiconductor layer 11 are sequentially stacked from the second substrate 22 side via the metal layer 40, the second electrode 32, and the insulating film 35. Here, the second substrate 22 is preferably a silicon substrate made of Si. By making the second substrate 22 a silicon substrate, the second substrate 22 can be easily divided in a cutting process described later.

[0108] (Nitride semiconductor element separation process)

[0109] Next, as Figure 18As shown, by removing a part of the semiconductor structure 1a of the second wafer 200, it is separated into a plurality of nitride semiconductor elements 1. Through this process, the semiconductor structure 1a is separated corresponding to each light-emitting device obtained in the subsequent cutting process. The removal of a part of the semiconductor structure 1a is performed by dry etching such as reactive ion etching, for example.

[0110] (First electrode formation process)

[0111] Next, on the n-side nitride semiconductor layer 11 of the second wafer 200 shown in Figure 19 a first electrode 31 having a predetermined pattern is formed. Similar to the formation method of the above-described second electrode 32, the first electrode 31 can be formed by a lift-off process or an etching process using a resist.

[0112] (Cutting process)

[0113] Finally, the second wafer 200 on which the first electrode 31 is formed is divided into individual light-emitting devices of a desired size. This division is performed by cutting or the like along the Figure 19 predetermined cutting position CL shown in

[0114] 3. Modification example of nitride semiconductor element

[0115] Hereinafter, a modification example of the nitride semiconductor element 1 will be described.

[0116] The third layer portion 4 of the nitride semiconductor element 1 in the above-described embodiment includes one light-emitting layer 10 and one undoped barrier layer 9, but is not limited thereto, and may include a plurality of light-emitting layers 10 and a plurality of undoped barrier layers 9. For example, as shown in Figure 20 a nitride semiconductor element 101 according to a modification example of the present invention includes a third layer portion 104 including three light-emitting layers 10 and three undoped barrier layers 9. In addition, among the plurality of undoped barrier layers 9, the film thickness of the undoped barrier layer 9 in contact with the p-side nitride semiconductor layer 13 may be thicker than that of the other undoped barrier layers 9.

[0117] Furthermore, the first layer portion 2 of the nitride semiconductor element 1 described above includes four barrier layers 5 and three first intermediate layers 6, but the number of first intermediate layers 6 included in the first layer portion 2 is not limited thereto. For example, the first layer portion 2 may include one first intermediate layer 6, or may include two or four or more first intermediate layers 6. Moreover, the number of barrier layers 5 may also vary according to the number of first intermediate layers 6.

[0118] Example

[0119] Example 1

[0120] The nitride semiconductor element of Example 1 was fabricated as follows.

[0121] First, prepare a first substrate 21 made of sapphire, and grow an n-type contact layer and an n-type cladding layer thereon to successively form an n-side nitride semiconductor layer 11 including the n-type contact layer and the n-type cladding layer from the first substrate 21 side.

[0122] Next, stack a barrier layer 5 made of Al 0.095 Ga 0.905 N and containing an n-type impurity and a first intermediate layer 6 made of Al 0.03 In 0.005 Ga 0.965 N on the n-side nitride semiconductor layer 11. In this embodiment, four barrier layers 5 and three first intermediate layers 6 respectively disposed between the four barrier layers 5 are formed. The film thickness of the barrier layer 5 is grown to a thickness of 29 nm, and the thickness of the first intermediate layer 6 is grown to 5 nm. The flow rates of the respective source gases when growing the barrier layer 5 are: the Al source gas is set to 1.5 sccm, the Ga source gas is set to 38.7 sccm, and the N source gas is set to 7 slm. In addition, the n-type impurity contained in the barrier layer 5 is Si, and the doping amount of Si is set to 1×10 18 atoms / cm 3 ³. The flow rates of the respective source gases when growing the first intermediate layer 6 are: the Al source gas is set to 0.2 sccm, the In source gas is set to 6 sccm, the Ga source gas is set to 43.6 sccm, and the N source gas is set to 7 slm.

[0123] Next, stack a second intermediate layer 8 made of In 0.005 Ga 0.995 N and an n-type impurity-doped barrier layer 7 made of Al 0.095 Ga 0.905 N and containing Si as an n-type impurity on the barrier layer 5. The thickness of the second intermediate layer 8 is grown to a thickness of 15 nm, and the film thickness of the n-type impurity-doped barrier layer 7 is grown to 29 nm. The flow rates of the respective source gases when growing the second intermediate layer 8 are: the In source gas is set to 16 sccm, the Ga source gas is set to 43.6 sccm, and the N source gas is set to 7 slm. The flow rates of the respective source gases when growing the n-type impurity-doped barrier layer 7 are: the Al source gas is set to 1.5 sccm, the Ga source gas is set to 38.7 sccm, and the N source gas is set to 7 slm. In addition, the n-type impurity contained in the n-type impurity-doped barrier layer 7 is Si, and the doping amount of Si is set to 1×10 18 atoms / cm 3 ³.

[0124] Next, stack a second intermediate layer 8 made of In 0.005 Ga0.995 A light-emitting layer 10 composed of N and Al 0.095 Ga 0.905 An undoped barrier layer 9 composed of N. The thickness of the light-emitting layer 10 is grown to 15 nm, and the film thickness of the undoped barrier layer 9 is grown to 40 nm. The flow rates of the respective source gases when growing the light-emitting layer 10 are as follows: the In source gas is set to 16 sccm, the Ga source gas is set to 43.6 sccm, and the N source gas is set to 7 slm. The flow rates of the respective source gases when growing the undoped barrier layer 9 are as follows: the Al source gas is set to 1.5 sccm, the Ga source gas is set to 38.7 sccm, and the N source gas is set to 7 slm.

[0125] After forming the thus-grown active layer 12, a p-side nitride semiconductor layer 13 including a p-type cladding layer and a p-type contact layer is formed, thereby preparing the first wafer 100.

[0126] Next, a second electrode 32 having a specified pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100 and transferred onto the second substrate 22 via the metal layer 40. Then, the first substrate 21 is removed, thereby forming a first electrode 31 having a specified pattern on the n-side nitride semiconductor layer 11.

[0127] For the nitride semiconductor device of Example 1 formed as described above, the light emission output when a current of 1000 mA flows is evaluated.

[0128] As a result, the light emission output of the nitride semiconductor device of Example 1 is 1605.4 mW.

[0129] Example 2

[0130] In the nitride semiconductor device of Example 1, except that the film thickness of the first intermediate layer 6 is grown to 8 nm, the nitride semiconductor device of Example 2 is fabricated in the same manner as the nitride semiconductor device of Example 1.

[0131] For the nitride semiconductor device of Example 2 fabricated as described above, the light emission output when a current of 1000 mA flows is 1576.0 mW.

[0132] Example 3

[0133] In the nitride semiconductor device of Example 1, except that the film thickness of the second intermediate layer 8 is grown to 8 nm, the nitride semiconductor device of Example 3 is fabricated in the same manner as the nitride semiconductor device of Example 1.

[0134] For the nitride semiconductor device of Example 3 fabricated as described above, the light emission output when a current of 1000 mA flows is 1594.3 mW.

[0135] Example 4

[0136] In the nitride semiconductor device of Example 1, when growing the first intermediate layer 6, the flow rates of the source gases are as follows: the Al source gas is set to 0.4 sccm, the In source gas is set to 6 sccm, the Ga source gas is set to 43.6 sccm, the N source gas is set to 7 slm, and the composition of the first intermediate layer 6 is set to Al 0.045 In 0.005 Ga 0.95 N. Except for this, the nitride semiconductor device of Example 4 is fabricated in the same manner as the nitride semiconductor device of Example 1.

[0137] For the nitride semiconductor device of Example 4 fabricated as described above, the light emission output when a current of 1000 mA flows through it is 1614.2 mW.

[0138] Example 5

[0139] In the nitride semiconductor device of Example 1, when growing the first intermediate layer 6, the flow rates of the source gases are as follows: the Al source gas is set to 0.6 sccm, the In source gas is set to 6 sccm, the Ga source gas is set to 43.6 sccm, the N source gas is set to 7 slm, and the composition of the first intermediate layer 6 is set to Al 0.06 In 0.005 Ga 0.935 N. Except for this, the nitride semiconductor device of Example 5 is fabricated in the same manner as the nitride semiconductor device of Example 1.

[0140] For the nitride semiconductor device of Example 5 fabricated as described above, the light emission output when a current of 1000 mA flows through it is 1595.6 mW.

[0141] Reference Example 1

[0142] In the nitride semiconductor device of Example 1, except that the first intermediate layer 6 is composed of In 0.005 Ga 0.995 N and the film thickness is grown to 15 nm, the nitride semiconductor device of Reference Example 1 is fabricated in the same manner as the nitride semiconductor device of Example 1. When growing the first intermediate layer 6 composed of In 0.005 Ga 0.995 N, the flow rates of the respective source gases are as follows: the In source gas is set to 16 sccm, the Ga source gas is set to 43.6 sccm, and the N source gas is set to 7 slm.

[0143] For the nitride semiconductor device of Reference Example 1 fabricated as described above, the light emission output when a current of 1000 mA flows through it is 1523.2 mW.

[0144] Reference Example 2

[0145] In addition to the nitride semiconductor device of Example 1, except that the second intermediate layer 8 is composed of Al 0.03 In 0.005 Ga 0.965 N and the film thickness is grown to 5 nm, the nitride semiconductor device of Reference Example 2 is fabricated in the same manner as the nitride semiconductor device of Example 1. When growing the second intermediate layer 8 composed of Al 0.03 In 0.005 Ga 0.965 N, the flow rates of the respective source gases are as follows: the Al source gas is set to 0.2 sccm, the In source gas is set to 6 sccm, the Ga source gas is set to 43.6 sccm, and the N source gas is set to 7 slm.

[0146] For the nitride semiconductor device of Reference Example 2 fabricated as described above, the light emission output when a current of 1000 mA flows is 1572.0 mW.

[0147] The results of Examples 1 to 5 and Reference Examples 1 and 2 are shown in Table 1. In Table 1, the film thickness of the first intermediate layer 6 is represented as film thickness T1, and the film thickness of the second intermediate layer 8 is represented as film thickness T2.

[0148]

[0149] Example 1 Example 2 Example 3 Example 4 Example 5 Reference Example 1 Reference Example 2 Luminescence output [mW] 1605.4 1576.0 1594.3 1614.2 1595.6 1523.2 1572.0 Film thickness T1 [nm] 5 8 5 5 5 15 5 Film thickness T2 [nm] 15 15 8 15 15 15 5

[0150] From these results, it can be seen that the nitride semiconductor devices of Examples 1 to 5 having a structure in which the band gap energy of the first intermediate layer 6 is larger than the band gap energies of the second intermediate layer 8 and the light emitting layer 10, and the film thickness of the first intermediate layer 6 is thinner than the film thicknesses of the second intermediate layer 8 and the light emitting layer 10 show a higher light emission output than the nitride semiconductor devices of Reference Examples 1 and 2. In addition, it can be seen that by making the film thickness of the first intermediate layer 6 thinner, a high light emission output can be obtained. Furthermore, it can also be seen that as the Al source gas during the growth of the first intermediate layer 6 increases or decreases from a certain value, the light emission output tends to decrease.

[0151] It can be seen that the light emission output of the nitride semiconductor device of Reference Example 1 in which the first intermediate layer 6 and the second intermediate layer 8 are composed of InGaN is lower than that of the nitride semiconductor devices of Examples 1 to 5. This is considered to be because the self-absorption of the first intermediate layer 6 is more than that of the nitride semiconductor devices of Examples 1 to 5. In addition, it can be seen that the light emission output of the nitride semiconductor device of Reference Example 2 in which the first intermediate layer 6 and the second intermediate layer 8 are composed of AlInGaN is lower than that of the nitride semiconductor devices of Examples 1 to 5. This is considered to be due to the influence caused by the failure to obtain the effect of suppressing lattice relaxation caused by the second intermediate layer 8.

[0152] As described above, the embodiments and examples of the present invention have been explained. However, the disclosed content can also be changed in the detailed parts of the composition, and changes in the combination or order of elements in the embodiments and examples can be achieved without departing from the scope and spirit of the claimed invention.

[0153] Symbol Explanation

[0154] 1, 101: Nitride semiconductor element

[0155] 1a: Semiconductor structure

[0156] 2: First layer portion

[0157] 3: Second layer portion

[0158] 4, 104: Third layer portion

[0159] 5: Barrier layer

[0160] 6: First intermediate layer

[0161] 7: n-type impurity doped barrier layer

[0162] 8: Second intermediate layer

[0163] 9: Undoped barrier layer

[0164] 10: Light emitting layer

[0165] 11: n-side nitride semiconductor layer

[0166] 12: Active layer

[0167] 13: p-side nitride semiconductor layer

[0168] 21: First substrate

[0169] 22: Second substrate

[0170] 31: First electrode

[0171] 32: Second electrode

[0172] 35: Insulating film

[0173] 100: First wafer

[0174] 200: Second wafer

Claims

1. A nitride semiconductor device, comprising: An n-side nitride semiconductor layer; An active layer disposed on the n-side nitride semiconductor layer, having a plurality of well layers made of a nitride semiconductor and a plurality of barrier layers made of a nitride semiconductor; A p-side nitride semiconductor layer disposed on the active layer, The plurality of well layers sequentially have, starting from the n-side nitride semiconductor layer side: A first intermediate layer having a bandgap smaller than that of the barrier layer and containing Al, Ga, and N; A second intermediate layer having a bandgap energy smaller than that of the first intermediate layer and containing Ga and N; A light-emitting layer having a bandgap energy smaller than that of the first intermediate layer and emitting ultraviolet light containing Ga and N, The film thickness of the first intermediate layer is thinner than those of the second intermediate layer and the light-emitting layer, Among the plurality of barrier layers, the barrier layer disposed between the second intermediate layer and the light-emitting layer is doped with an n-type impurity, The film thickness of the first intermediate layer is 3 nm or more and 7 nm or less, The film thickness of the second intermediate layer is 10 nm or more and 18 nm or less, The film thickness of the light-emitting layer is 10 nm or more and 18 nm or less.

2. The nitride semiconductor device according to claim 1, wherein The plurality of well layers include a plurality of the first intermediate layers.

3. The nitride semiconductor device according to claim 1 or 2, wherein The bandgap energy of the second intermediate layer is substantially the same as that of the light-emitting layer, The film thickness of the second intermediate layer is thinner than that of the light-emitting layer.

4. The nitride semiconductor device according to any one of claims 1 to 3, wherein The light-emitting layer and the second intermediate layer contain In, The content of In in the second intermediate layer is less than the content of In in the light-emitting layer.

5. The nitride semiconductor device according to any one of claims 1 to 4, wherein The first intermediate layer is AlGaN or AlInGaN, The second intermediate layer is GaN or InGaN, The light-emitting layer is GaN or InGaN.

6. The nitride semiconductor device according to any one of claims 1 to 5, wherein The barrier layer contains Al, Ga, and N.

7. The nitride semiconductor device according to any one of claims 1 to 6, wherein The film thickness of the barrier layer disposed between the second intermediate layer and the light-emitting layer is 20 nm or more and 40 nm or less.

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