Nitride semiconductor devices

Abstract

To provide a nitride semiconductor element capable of emitting ultraviolet light with improved light-emitting output.SOLUTION: A nitride semiconductor element comprises an n-side nitride semiconductor layer 11, an active layer 12 provided on the n-side nitride semiconductor layer and including a plurality of well layers composed of a nitride semiconductor and a plurality of barrier layers composed of a nitride semiconductor, and a p-side nitride semiconductor layer 13 provided on the active layer. The plurality of well layers comprises, in order from the n-side nitride semiconductor layer side, a first intermediate layer 6 having a smaller bandgap than the barrier layers and containing Al, Ga, and N, a second intermediate layer 8 having smaller bandgap energy than the first intermediate layer and containing Ga and N, and a light-emitting layer 10 having smaller bandgap energy than the first intermediate layer and emitting ultraviolet light including Ga and N. A film thickness of the first intermediate layer is thinner than film thicknesses of the second intermediate layer and the light-emitting layer. Among the plurality of barrier layers, the barrier layer 7 arranged between the second intermediate layer and the light-emitting layer is doped with an n-type impurity.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, the development of light-emitting elements that emit ultraviolet light has been actively promoted. For example, Patent Document 1 discloses a light-emitting element having a multiple quantum well structure suitable for emitting deep ultraviolet light. In addition, near-ultraviolet light-emitting elements are also being developed for use in resin curing and various sensing applications. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-175005 A Summary of the Invention [Problem to be solved by the invention]

[0004] Although improvements have been made to such nitride semiconductor elements that emit ultraviolet light in order to improve their characteristics, such as light emission output, the characteristics have not yet been sufficiently improved.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a nitride semiconductor device that emits ultraviolet light with high light output. [Means for solving the problem]

[0006] The nitride semiconductor device according to the present invention comprises: an n-side nitride semiconductor layer; an active layer provided on the n-side nitride semiconductor layer, the active layer including 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 provided on the active layer, The plurality of well layers are, in order from the n-side nitride semiconductor layer side, a first intermediate layer having a band gap smaller than that of the barrier layer and containing Al, Ga, and N; a second intermediate layer having a band gap energy smaller than that of the first intermediate layer and containing Ga and N; a light emitting layer that has a band gap energy smaller than that of the first intermediate layer, contains Ga and N, and emits ultraviolet light; the first intermediate layer has a thickness smaller than that of the second intermediate layer and that of the light-emitting layer; Of 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. Effect of the Invention

[0007] According to the nitride semiconductor device according to one embodiment of the present invention, it is possible to provide a nitride semiconductor device that emits ultraviolet light with high light emission output. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a configuration of a nitride semiconductor device according to an embodiment of the present invention, which is disposed on a substrate. [Diagram 2] FIG. 2 is a diagram showing a multiple quantum well structure of the nitride semiconductor device shown in FIG. [Diagram 3] FIG. 3 is a diagram showing band gap energy of the multiple quantum well structure shown in FIG. 2. [Figure 4] 2 is a cross-sectional view of a first substrate prepared in a manufacturing method for a light emitting device according to one embodiment of the present invention. [Diagram 5] 3 is a cross-sectional view showing a state where an n-side nitride semiconductor layer is formed on an upper surface of a prepared first substrate in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 6] 3 is a cross-sectional view showing a state where an active layer is formed on an n-side nitride semiconductor layer formed on an upper surface of a first substrate in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 7]1 is a cross-sectional view of a first wafer in which a p-side nitride semiconductor layer is formed on an active layer formed on an n-side nitride semiconductor layer on the upper surface of a first substrate in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 8] 4 is a cross-sectional view showing a state where a resist for forming a second electrode is formed on a p-side nitride semiconductor layer of a first wafer in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 9] 4 is a cross-sectional view showing a state where a metal film for forming a second electrode is formed on a p-side nitride semiconductor layer of a first wafer in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 10] FIG. 11 is a cross-sectional view showing a state in which a resist formed on a p-side nitride semiconductor layer of a first wafer is removed together with a metal film formed on the resist to form a second electrode of a predetermined shape in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Figure 11] FIG. 2 is a cross-sectional view showing a state in which a resist is formed on a second electrode in order to form an insulating film between the second electrode and the p-side nitride semiconductor layer of the first wafer in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Figure 12] 4 is a cross-sectional view showing an insulating film formed between second electrodes on a p-side nitride semiconductor layer of a first wafer and on a resist in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 13] FIG. 11 is a cross-sectional view showing a state in which the resist is removed together with the insulating film formed on the resist, and a second electrode and an insulating film are formed on the p-side nitride semiconductor layer of the first wafer, in a manufacturing method for a light-emitting device of one embodiment of the present invention. [Figure 14] 4 is a cross-sectional view showing a state in which a metal layer is formed on a second electrode and an insulating film formed on a p-side nitride semiconductor layer of a first wafer in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 15] FIG. 11 is a cross-sectional view showing a state in which a second substrate having a metal layer formed on one surface thereof is prepared and the first wafer and the second substrate are placed opposite each other in a manufacturing method for a light emitting device according to one embodiment of the present invention. [Figure 16]10 is a cross-sectional view of a first wafer and a second substrate bonded together by bonding their metal layers together in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 17] 4 is a cross-sectional view of a second wafer produced in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 18] 4 is a cross-sectional view showing a state where a part of a nitride semiconductor element of a fabricated second wafer has been removed in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 19] 4 is a cross-sectional view showing a state where a first electrode having a predetermined pattern is formed on an n-side nitride semiconductor layer of a second wafer in a manufacturing method for a light emitting device according to one embodiment of the present invention. FIG. [Figure 20] FIG. 13 is a diagram showing a multiple quantum well structure of a nitride semiconductor device according to a modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the drawings. Note that the nitride semiconductor device described below is intended to embody the technical concept of the present invention, and unless otherwise specified, the present invention is not limited to the following. In each drawing, components having the same function may be given the same symbol. In consideration of the explanation or ease of understanding of the main points, the embodiments and examples may be shown separately for convenience, but partial replacement or combination of the configurations shown in different embodiments and examples is possible. In the embodiments and examples described below, descriptions of matters common to the above will be omitted, and only the differences will be described. In particular, similar effects due to similar configurations will not be mentioned in each embodiment or example. The size and positional relationship of the components shown in each drawing may be exaggerated to clarify the explanation.

[0010] The semiconductor structure used in the 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. The active layer may have a multiple quantum well structure including multiple well layers. In general, in a light-emitting diode that emits ultraviolet light and includes multiple well layers in the active layer, the well layer located on the p-side nitride semiconductor layer side among the multiple well layers tends to contribute to light emission, while the well layer located on the n-side nitride semiconductor layer side tends not to contribute to light emission. The well layer located on the n-side nitride semiconductor layer side may absorb (self-absorb) the light emitted by the well layer located on the p-side nitride semiconductor layer side, thereby possibly deteriorating the light extraction efficiency. The present inventors therefore conducted extensive research focusing on the recombination probability of electrons and holes, lattice relaxation of crystals in the semiconductor layer, and self-absorption of light by the semiconductor layer as factors that affect the light emission output of a nitride semiconductor element.

[0011] The present inventors first investigated a method for reducing the self-absorption of light in multiple well layers. The self-absorption of light by a well layer is reduced as the band gap energy of the semiconductor layer constituting the well layer increases. Therefore, the present inventors investigated reducing the self-absorption of light in the active layer by making the band gap energy of the well layer (intermediate layer) located on the n-side nitride semiconductor layer side and not contributing to light emission larger than the band gap energy of the well layer located on the p-side nitride semiconductor layer side and contributing to light emission.

[0012] It was expected that a nitride semiconductor device having multiple well layers configured in this way would exhibit a higher light emission output than conventional nitride semiconductor devices, but in reality it was not possible to obtain a sufficiently high light emission output.

[0013] The inventors of the present invention have further studied these results and speculated that the reason why the light emission output could not be sufficiently improved is that the lattice relaxation of the crystals between the light emitting layer and the intermediate layer, which occurs due to the difference in composition between the light emitting layer, which is a well layer that contributes to light emission, and the intermediate layer, inhibits the improvement of the light emission output. Based on this speculation, the inventors of the present invention arranged a second intermediate layer, which has a smaller band gap than the first intermediate layer, between the light emitting layer and the intermediate layer (first intermediate layer) in order to suppress the lattice relaxation, and were able to improve the light emission output compared to the case where the second intermediate layer was not provided.

[0014] As a result of further investigations into obtaining even higher light emission output in a nitride semiconductor element including, in order from the n-side nitride semiconductor layer side, a first intermediate layer having a large band gap energy, a second intermediate layer having a smaller band gap energy than the first intermediate layer, and a light emitting layer, the following findings were obtained. (1) By making the thickness of the first intermediate layer thinner than the thicknesses of the second intermediate layer and the light-emitting layer, self-absorption in the first intermediate layer of light emitted from the light-emitting layer can be more effectively suppressed. (2) By doping the barrier layer between the light-emitting layer and the second intermediate layer with an n-type impurity, recombination in the light-emitting layer can be further promoted.

[0015] Here, it is preferable that the light emitting layer is a layer containing Ga and N, taking into consideration the probability of recombination of electrons and holes, and that a predetermined emission wavelength is set by adjusting the composition ratio of In, Ga and N mainly. Moreover, it is preferable that the band gap energy of the first intermediate layer is made larger than that of the light emitting layer by making the first intermediate layer a layer containing Al, Ga, and N and adjusting the composition ratios mainly of Al, Ga, and N. This makes it possible to effectively suppress self-absorption by the first intermediate layer. Furthermore, the second intermediate layer is a layer containing Ga and N, and has a smaller band gap energy than the first intermediate layer by adjusting the composition ratio mainly of Ga and N.

[0016] The nitride semiconductor device according to the present invention has been made based on the above findings, 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 semiconductors and a plurality of barrier layers made of nitride semiconductors, and a p-side nitride semiconductor layer provided on the active layer. The plurality of well layers include, in order from the n-side nitride semiconductor layer side, a first intermediate layer having a smaller band gap than the barrier layer and including Al, Ga, and N, a second intermediate layer having a smaller band gap energy than the first intermediate layer and including Ga and N, and a light emitting layer having a smaller band gap energy than the first intermediate layer and including Ga and N, which emits ultraviolet light. The thickness of the first intermediate layer is smaller than the thicknesses of the second intermediate layer and the light emitting layer, and the barrier layer between the second intermediate layer and the light emitting layer among the plurality of barrier layers is doped with an n-type impurity.

[0017] Embodiment Hereinafter, a method for manufacturing the nitride semiconductor element and a light emitting device including the nitride semiconductor element according to the present embodiment will be described with reference to the drawings.

[0018] 1.Nitride semiconductor devices FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor device 1 according to this embodiment disposed on a second substrate 22. As shown in FIG.

[0019] As shown in FIG. 1, the nitride semiconductor device 1 according to this embodiment is disposed on a second substrate 22. The nitride semiconductor device 1 includes a p-side nitride semiconductor layer 13, an active layer 12, and an n-side nitride semiconductor layer 11 in this order from the second substrate 22 side. 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. Thereby, for example, by using a semiconductor substrate or a substrate made of metal having conductivity as the second substrate 22, it becomes possible to supply power to the nitride semiconductor device 1 via the second substrate 22. The nitride semiconductor device 1 having such a structure can emit light from the active layer 12 by applying a voltage between the first electrode 31 and the second electrode 32. The light emitted from the nitride semiconductor device 1 is mainly emitted from the surface side where the first electrode 31 of the n-side nitride semiconductor layer 11 is provided. Hereinafter, the nitride semiconductor device 1 of this embodiment will be described in detail.

[0020] <n-side nitride semiconductor layer> 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 a plurality of layers. Further, the n-side nitride semiconductor layer 11 may partially include, for example, an undoped semiconductor layer. Here, the undoped semiconductor layer refers to a layer grown without adding an n-type impurity when growing, and may include unavoidable impurities mixed by diffusion or the like from an adjacent layer.

[0021] <p-side nitride semiconductor layer> 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 a plurality of layers. Further, the p-side nitride semiconductor layer 13 may partially include, for example, an undoped semiconductor layer.

[0022] <active layer> 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 shown in FIG. 2, the multiple quantum well structure according to the present embodiment includes 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 that is not doped with impurities, in this order from the n-side nitride semiconductor layer 11 side.

[0023] (First layer portion) The first layer portion 2 is a portion where the first intermediate layers 6 and the barrier layers 5 are alternately stacked. A barrier layer 5 is disposed on the n-side nitride semiconductor layer 11, and a first intermediate layer 6 is disposed on the barrier layer 5. Thereafter, the barrier layer 5 and the first intermediate layer 6 are alternately stacked, and a barrier layer 5 is disposed on the topmost layer. The first layer portion 2 according to the present embodiment includes four barrier layers 5 and three first intermediate layers 6. As shown in FIG. 3, the barrier layer has a larger bandgap energy than the well layer. This is the same for the following second layer portion 3 and third layer portion 4.

[0024] 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-a N (0 < a < 1). The mixing 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, and preferably 20 nm or more and 40 nm. The barrier layer 5 of the first layer portion 2 may be doped with an n-type impurity, similar to the n-type impurity-doped barrier layer 7 of the second layer portion 3 described later. Also, among the plurality of barrier layers 5, some may be barrier layers doped with an n-type impurity, and the other part may be barrier layers not doped with an n-type impurity. By doping the barrier layer 5 of the first layer portion 2 with an n-type impurity, the recombination probability in the light-emitting layer 10 can be increased, similar to the n-type impurity-doped barrier layer 7 of the second layer portion 3 described later.

[0025] The first intermediate layer 6 is a nitride semiconductor layer containing Al, Ga, and N. As shown in FIG. 3, the first intermediate layer 6 has a bandgap energy larger than that of 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. Also, 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, absorption of light emitted from the light-emitting layer 10 can be suppressed. Unlike the light-emitting layer 10 that emits light, the first intermediate layer 6 is a non-light-emitting well layer that substantially does not emit light. 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. By having such a film thickness, self-absorption by 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, and preferably 3 nm or more and 7 nm or less. The first intermediate layer 6 having the above-described bandgap energy and film thickness serves as a buffer layer for growing the light-emitting layer 10 described later with good crystallinity, and can suppress absorption of light emitted from the light-emitting layer 10.

[0026] (Second layer portion) The second layer portion 3 is a portion where one second intermediate layer 8 and one n-type impurity doped barrier layer 7 are stacked. The second intermediate layer 8 is disposed on the barrier layer 5 stacked on the top of the first layer portion 2, and the n-type impurity doped barrier layer 7 is disposed on the second intermediate layer 8.

[0027] 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 n-type impurities. 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 be the same as that of the barrier layer 5 described above. The thickness of the n-type impurity doped barrier layer 7 is, for example, 20 nm to 40 nm. 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 More than 1×10 19 atoms / cm 3 The following is an example. By forming the n-type impurity-doped barrier layer 7 adjacent to the light emitting layer 10, the recombination probability in the light emitting layer 10 between holes injected from the p-side nitride semiconductor layer 13 and electrons injected via the n-type impurity-doped barrier layer 7 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. Furthermore, as a result of being able to increase the recombination probability in the light emitting layer 10, the 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 do not substantially emit light can be achieved.

[0028] 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. As shown in FIG. 3, the second intermediate layer 8 has a smaller band gap 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 lower than the In content of the light emitting layer 10. This makes the band gap energy of the second intermediate layer 8 larger than the band gap energy of the light emitting layer 10, and prevents the light emitted from the light emitting layer 10 from being absorbed by the second intermediate layer 8. The In content of the second intermediate layer 8 is preferably 0≦d≦0.03. Unlike the light emitting layer 10 which emits light, the second intermediate layer 8 is a non-luminescent well layer which does not substantially emit light, similar to the above-mentioned first intermediate layer 6. When the band gap energy of the second intermediate layer 8 is made to be approximately the same as the band gap energy of the light emitting layer 10, it is preferable to make the film thickness of the second intermediate layer 8 thinner than the film thickness of the light emitting layer 10. This makes it possible to suppress absorption of light emitted from the light emitting layer 10 by the second intermediate layer 8. By making the film thickness of the second intermediate layer 8 thinner, self-absorption by the second intermediate layer 8 is 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. The second intermediate layer 8 having the above-mentioned band gap energy and film thickness suppresses the lattice relaxation of the crystal occurring between the first intermediate layer 6 and the light emitting layer 10 described below. Here, lattice relaxation is a phenomenon in which dislocations are generated at the boundary portion of crystals with different lattice constants, thereby dispersing strain, but on the other hand, the occurrence of lattice relaxation tends to cause dislocations and reduce crystallinity. Therefore, in the nitride semiconductor device of this embodiment, by providing the second intermediate layer 8, it is possible to recover the crystallinity that was reduced by stacking the first intermediate layer 6 made of a nitride semiconductor containing Al.

[0029] (Third layer) The third layer 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 3, and the undoped barrier layer 9 is disposed on the light emitting layer 10.

[0030] The undoped barrier layer 9 in the third layer portion 4 is a nitride semiconductor layer that is 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 barrier layer 5 and the n-type impurity doped barrier layer 7 described above. The undoped barrier layer 9 has a thickness greater than the barrier layer 5 and the n-type impurity doped barrier layer 7. The undoped barrier layer 9 has a thickness of, for example, 30 nm or more and 50 nm or less. Since the undoped barrier layer 9 does not contain n-type impurities, holes that have moved 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 are efficiently supplied to the light emitting layer 10, and the light emitting efficiency of the light emitting layer 10 is improved.

[0031] The light-emitting layer 10 is a nitride semiconductor layer containing Ga and N, and emits ultraviolet light. In this 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. Examples of the peak wavelength of the light-emitting layer 10 are about 365 nm and about 385 nm. Further, as shown in FIG. 3, the light-emitting layer 10 has, for example, substantially the same bandgap energy as the second intermediate layer 8. Note that by including Al or the like in the light-emitting layer 10, 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. 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.

[0032] 2. Method for manufacturing a light-emitting device Next, a method for manufacturing a light-emitting device including the nitride semiconductor element of this embodiment will be described.

[0033] <First wafer preparation step> In the first wafer preparation step, as shown in FIG. 4, for example, a first substrate 21 made of sapphire is prepared. Then, as shown in FIG. 5, an n-type contact layer and an n-type cladding layer are grown on the first substrate 21 to form an n-side nitride semiconductor layer 11 including the n-type contact layer and the n-type cladding layer in this order from the first substrate 21 side. Note that the n-side nitride semiconductor layer 11 may be formed on the first substrate 21 via a buffer layer.

[0034] 6, the active layer 12 is formed on the n-side nitride semiconductor layer 11. The active layer 12 is formed by the following steps.

[0035] First, the barrier layer 5 is grown on the n-side nitride semiconductor layer 11 using source gases including an Al source gas, a Ga source gas, and an N source gas (barrier layer growth step). When the composition of the barrier layer 5 is, for example, AlGaN, the flow rates of the Al source gas, Ga source gas, and N source gas are set to 1 to 2 sccm, 30 to 50 sccm, and 5 to 10 slm, respectively, to form the barrier layer 5.

[0036] Next, a first intermediate layer 6 is grown on the barrier layer 5 using source gases including an Al source gas, an In source gas, a Ga source gas, and an N source gas (first intermediate layer growing step). 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 to 5 to 10 slm.

[0037] The barrier layer growth step and the first intermediate layer growth step are alternately repeated to form the first layer portion 2 having a plurality of barrier layers 5 and first intermediate layers 6. The step of forming the first layer portion 2 ends with the barrier layer growth step.

[0038] Next, the second intermediate layer 8 is grown on the barrier layer 5 using source gases including an In source gas, a Ga source gas, and an N source gas (second intermediate layer growing step). 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.

[0039] Next, the n-type impurity-doped barrier layer 7 is grown on the second intermediate layer 8 using source gases including Al source gas, Ga source gas, N source gas, and n-type impurity source gas (n-type impurity-doped barrier layer growing step). When the composition of the n-type impurity-doped barrier layer 7 is, for example, AlGaN and the n-type impurity is Si, the flow rate of the Al source gas is set in the range of 1 to 2 sccm, the flow rate of the Ga source gas is set in the range of 30 to 50 sccm, the flow rate of the N source gas is set in the range of 5 to 10 slm, and the doping amount of the n-type impurity is set to 1×10 17 atoms / cm 3 More than 1×10 19 atoms / cm 3 By setting the thickness within the following range, the n-type impurity doped barrier layer 7 can be formed.

[0040] By carrying out the second intermediate layer growing step and the n-type impurity doped barrier layer growing step, the second layer portion 3 having the second intermediate layer 8 and the n-type impurity doped barrier layer 7 is formed.

[0041] Next, the light emitting layer 10 is grown on the n-type impurity doped barrier layer 7 using source gases including an In source gas, a Ga source gas, and an N source gas (light emitting layer growing step). When the composition of the light emitting layer 10 is, for example, InGaN or GaN, the flow rate of the In source gas is set in the range of 0 to 45 sccm, the flow rate of the Ga source gas is set in the range of 30 to 50 sccm, and the flow rate of the N source gas is set in the range of 5 to 10 slm, whereby the light emitting layer 10 can be formed.

[0042] Next, the undoped barrier layer 9 is grown on the light emitting layer 10 using source gases including an Al source gas, a Ga source gas, and an N source gas (undoped barrier layer growing step). 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.

[0043] By carrying out the light emitting layer growing step and the undoped barrier layer growing step, the third layer portion 4 having the light emitting layer 10 and the undoped barrier layer 9 is formed.

[0044] Then, for example, a p-type cladding layer and a p-type contact layer are grown on the active layer 12 having the first layer portion 2, the second layer portion 3, and the third layer portion 4 to form a p-side nitride semiconductor layer 13 including the p-type cladding layer and the p-type contact layer in this order from the active layer 12 side. Through these steps, a first wafer 100 is prepared on a first substrate 21, in which a semiconductor structure 1a including an n-side nitride semiconductor layer 11, an active layer 12, and a p-side nitride semiconductor layer 13 is formed, as shown in FIG.

[0045] <Second wafer preparation process> In the second wafer preparation step, first, the second electrode 32 having a predetermined pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100, for example, in the following manner. 8, 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 to be formed. 9, a metal film (32, 32a) containing, for example, Ag is formed on the entire upper surface of the p-side nitride semiconductor layer 13. As a result, the second electrode 32 is formed on the p-side nitride semiconductor layer 13 on which the resist 51 is not formed. Then, as shown in FIG. 10, the resist 51 is removed together with the metal film 32a formed on the resist 51. In this manner, the second electrode 32 having a predetermined pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100. Here, a method for forming the second electrode 32 in a predetermined pattern by the lift-off process has been described. However, the second electrode 32 in a predetermined pattern may be formed without using the lift-off process, for example, by forming a metal film on the entire upper surface of the p-side nitride semiconductor layer 13 without forming the resist 51, forming a resist on the metal film, and removing the metal film using the resist as a mask.

[0046] Next, as shown in FIG. 11, a resist 52 is formed on the second electrode 32. After forming the resist 52, as shown in FIG. 12, an insulating film 35a is formed on the resist 52 and on a portion on the p-side nitride semiconductor layer 13 where the second electrode 32 is not formed. Then, as shown in FIG. 13, the resist 52 is removed together with the insulating film 35a formed on the resist 52. In this manner, the insulating film 35 is formed on the portion on the p-side nitride semiconductor layer 13 where the second electrode 32 is not formed. The insulating film 35 is provided, for example, on a cutting position CL described later. By disposing in this manner, the insulating film 35 can be configured so that the second electrode 32 is not exposed from the side surface of the light emitting device. As a result, the occurrence of a short circuit on the side surface of the light emitting device is suppressed, and the reliability can be improved.

[0047] Next, as shown in FIG. 14, 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. Separately, as shown in FIG. 15, 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 to each other. As a result, as shown in FIG. 16, 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, the first substrate 21 is removed as shown in FIG. 17. 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. The first substrate 21 is removed by, for example, laser lift-off, which irradiates a laser beam 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, the first substrate 21 is removed by wet etching using a solution capable of etching the first substrate 21. In the above manner, the semiconductor structure 1a formed on the first substrate 21 is transferred onto the second substrate 22 via the metal layer 40, the second electrode 32, and the insulating film 35. In this manner, as shown in FIG. 17, a second wafer 200 is prepared on the second substrate 22, the second wafer 200 being provided with the semiconductor structure 1a with the n-side nitride semiconductor layer 11 exposed on the surface. That is, in the second wafer 200, the p-side nitride semiconductor layer 13, the active layer 12, and the n-side nitride semiconductor layer 11 are laminated on the second substrate 22 in this order 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, and by using the silicon substrate as the second substrate 22, the second substrate 22 can be easily divided in a cutting process described later.

[0048] <Nitride semiconductor device isolation process> 18, the semiconductor structure 1a of the second wafer 200 is separated into a plurality of nitride semiconductor elements 1 by removing a portion of the semiconductor structure 1a. Through this process, the semiconductor structure 1a is separated so as to correspond to each light emitting device obtained in a cutting process described later. The removal of the portion of the semiconductor structure 1a is performed by dry etching such as reactive ion etching.

[0049] <First electrode formation process> Next, a first electrode 31 having a predetermined pattern is formed on the n-side nitride semiconductor layer 11 of the second wafer 200 shown in Fig. 19. The first electrode 31 can be formed by a lift-off process or an etching process using a resist, similar to the method for forming the second electrode 32 described above.

[0050] <Cutting process> Finally, the second wafer 200 on which the first electrodes 31 are formed is divided into individual light emitting devices of a desired size by dicing or the like along the predetermined cutting positions CL shown in FIG.

[0051] 3. Modifications of nitride semiconductor devices Modifications of the nitride semiconductor device 1 will now be described.

[0052] Although the third layer portion 4 in the nitride semiconductor device 1 of the embodiment described above includes one light emitting layer 10 and one undoped barrier layer 9, the present invention 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 FIG. 20, a nitride semiconductor device 101 of a modification according to the present invention includes a third layer portion 104 including three light emitting layers 10 and three undoped barrier layers 9. Furthermore, among the plurality of undoped barrier layers 9, the film thickness of the undoped barrier layer 9 provided in contact with the p-side nitride semiconductor layer 13 may be made thicker than the film thicknesses of the other undoped barrier layers 9.

[0053] Furthermore, although the first layer portion 2 in the nitride semiconductor device 1 described above includes four barrier layers 5 and three first intermediate layers 6, the number of first intermediate layers 6 included in the first layer portion 2 is not limited to this. 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. The number of barrier layers 5 may also vary depending on the number of first intermediate layers 6. EXAMPLES

[0054] Example 1. The nitride semiconductor device of Example 1 was fabricated as follows.

[0055] First, a first substrate 21 made of sapphire was prepared, and an n-type contact layer and an n-type cladding layer were grown thereon to form an n-side nitride semiconductor layer 11 including an n-type contact layer and an n-type cladding layer in that order from the first substrate 21 side.

[0056] Next, Al 0.095 Ga 0.905 A barrier layer 5 made of N and containing n-type impurities, and an Al 0.03 In 0.005 Ga 0.965 In this embodiment, four barrier layers 5 were formed, and three first intermediate layers 6 were disposed between the four barrier layers 5. The barrier layers 5 were grown to a thickness of 29 nm, and the first intermediate layers 6 were grown to a thickness of 5 nm. The flow rates of the source gases used for growing the barrier layers 5 were set as follows: Al source gas was set to 1.5 sccm, Ga source gas was set to 38.7 sccm, and N source gas was set to 7 slm. The n-type impurity contained in the barrier layers 5 was Si, and the doping amount of Si was 1×10 18 atoms / cm 3 The flow rates of the source gases for growing the first intermediate layer 6 were set as follows: Al source gas at 0.2 sccm, In source gas at 6 sccm, Ga source gas at 43.6 sccm, and N source gas at 7 slm.

[0057] Next, on the barrier layer 5, In 0.005 Ga 0.995 A second intermediate layer 8 made of N and Al 0.095 Ga 0.905The n-type impurity doped barrier layer 7, which is made of N and contains Si as an n-type impurity, was laminated one layer at a time. The second intermediate layer 8 was grown to a thickness of 15 nm, and the n-type impurity doped barrier layer 7 was grown to a thickness of 29 nm. The flow rates of the source gases used for growing the second intermediate layer 8 were set to 16 sccm for the In source gas, 43.6 sccm for the Ga source gas, and 7 slm for the N source gas. The flow rates of the source gases used for growing the n-type impurity doped barrier layer 7 were set to 1.5 sccm for the Al source gas, 38.7 sccm for the Ga source gas, and 7 slm for the N source gas. The n-type impurity contained in the n-type impurity doped barrier layer 7 was Si, and the doping amount of Si was 1×10 18 atoms / cm 3 It was set to be.

[0058] Next, on the n-type impurity doped barrier layer 7, In 0.005 Ga 0.995 A light-emitting layer 10 made of N and an Al 0.095 Ga 0.905 and an undoped barrier layer 9 made of N were laminated one by one. The light emitting layer 10 was grown to a thickness of 15 nm, and the undoped barrier layer 9 was grown to a thickness of 40 nm. The flow rates of the source gases used for growing the light emitting layer 10 were set as follows: In source gas was set to 16 sccm, Ga source gas was set to 43.6 sccm, and N source gas was set to 7 slm. The flow rates of the source gases used for growing the undoped barrier layer 9 were set as follows: Al source gas was set to 1.5 sccm, Ga source gas was set to 38.7 sccm, and N source gas was set to 7 slm.

[0059] After the active layer 12 was thus grown, a p-side nitride semiconductor layer 13 including a p-type cladding layer and a p-type contact layer was formed, and a first wafer 100 was prepared.

[0060] Next, the second electrode 32 having a predetermined pattern is formed on the p-side nitride semiconductor layer 13 of the first wafer 100, and transferred to the second substrate 22 via the metal layer 40. Thereafter, the first substrate 21 is removed, and the first electrode 31 having a predetermined pattern is formed on the n-side nitride semiconductor layer 11.

[0061] The nitride semiconductor device of Example 1 formed as described above was evaluated for light emission output when a current of 1000 mA was passed through it. As a result, the light emission output of the nitride semiconductor device of Example 1 was 1605.4 mW.

[0062] Example 2. The nitride semiconductor device of Example 2 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that in the nitride semiconductor device of Example 1, the first intermediate layer 6 was grown to a thickness of 8 nm. The nitride semiconductor device of Example 2 fabricated as described above had a light emission output of 1576.0 mW when a current of 1000 mA was passed through it.

[0063] Example 3. The nitride semiconductor device of Example 3 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that in the nitride semiconductor device of Example 1, the second intermediate layer 8 was grown to a thickness of 8 nm. The nitride semiconductor device of Example 3 fabricated as described above had a light emission output of 1594.3 mW when a current of 1000 mA was passed through it.

[0064] Example 4. In the nitride semiconductor device of Example 1, the flow rates of the source gases when growing the first intermediate layer 6 were set as follows: Al source gas was set at 0.4 sccm, In source gas was set at 6 sccm, Ga source gas was set at 43.6 sccm, and N source gas was set at 7 slm. The composition of the first intermediate layer 6 was Al. 0.045 In 0.005 Ga 0.95 A nitride semiconductor device of Example 4 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that N was used. The nitride semiconductor device of Example 4 fabricated as described above had a light emission output of 1614.2 mW when a current of 1000 mA was passed through it.

[0065] Example 5. In the nitride semiconductor device of Example 1, the flow rates of the source gases when growing the first intermediate layer 6 were set as follows: Al source gas was set to 0.6 sccm, In source gas was set to 6 sccm, Ga source gas was set to 43.6 sccm, and N source gas was set to 7 slm. The composition of the first intermediate layer 6 was Al. 0.06 In 0.005 Ga 0.935 A nitride semiconductor device of Example 5 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that N was used. The nitride semiconductor device of Example 5 fabricated as described above had a light emission output of 1595.6 mW when a current of 1000 mA was passed through it.

[0066] Reference example 1. In the nitride semiconductor device of Example 1, the first intermediate layer 6 is made of In 0.005 Ga 0.995 The nitride semiconductor device of Reference Example 1 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that the nitride semiconductor device was made of InN and grown to a film thickness of 15 nm. 0.005 Ga 0.995 The flow rates of the source gases used for growing the first intermediate layer 6 made of N were set as follows: In source gas was set to 16 sccm, Ga source gas was set to 43.6 sccm, and N source gas was set to 7 slm. The nitride semiconductor device of Reference Example 1 fabricated as described above had a light emission output of 1523.2 mW when a current of 1000 mA was passed through it.

[0067] Reference example 2. In the nitride semiconductor device of Example 1, the second intermediate layer 8 is made of Al 0.03 In 0.005 Ga 0.965 The nitride semiconductor device of Reference Example 2 was fabricated in the same manner as the nitride semiconductor device of Example 1, except that the AlN layer was grown to a thickness of 5 nm. 0.03 In 0.005 Ga 0.965 The flow rates of the source gases used to grow the second intermediate layer 8 made of N were set as follows: Al source gas at 0.2 sccm, In source gas at 6 sccm, Ga source gas at 43.6 sccm, and N source gas at 7 slm. The nitride semiconductor device of Reference Example 2 fabricated as described above had a light emission output of 1572.0 mW when a current of 1000 mA was passed through it.

[0068] The results of these 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. TIFF0007659213000001.tif19164

[0069] From these results, it was revealed that the nitride semiconductor devices of Examples 1 to 5, in which the band gap energy of the first intermediate layer 6 is larger than the band gap energy of the second intermediate layer 8 and the band gap energy of the light emitting layer 10, and the film thickness of the first intermediate layer 6 is smaller than the film thickness of the second intermediate layer 8 and the film thickness of the light emitting layer 10, exhibit higher light emission output than the nitride semiconductor devices of Reference Examples 1 and 2. It was also found that a higher light emission output can be obtained by making the film thickness of the first intermediate layer 6 thinner. Furthermore, it was found that the light emission output tends to decrease as the Al raw material gas when growing the first intermediate layer 6 is increased or decreased from a certain value. It was found that the nitride semiconductor device of Reference Example 1, in which the first intermediate layer 6 and the second intermediate layer 8 were made of InGaN, had a lower light emission output than the nitride semiconductor devices of Examples 1 to 5. This is believed to be due to the fact that more self-absorption by the first intermediate layer 6 occurred than in the nitride semiconductor devices of Examples 1 to 5. It was also found that the nitride semiconductor device of Reference Example 2, in which the first intermediate layer 6 and the second intermediate layer 8 were made of AlInGaN, had a lower light emission output than the nitride semiconductor devices of Examples 1 to 5. This is believed to be due to the fact that the effect of suppressing lattice relaxation by the second intermediate layer 8 was not obtained.

[0070] Although the embodiments and examples of the present invention have been described above, the disclosed contents may vary in details of the configuration, and the combination and order of elements in the embodiments and examples may be changed without departing from the scope and spirit of the claimed invention. [Explanation of symbols]

[0071] 1, 101 Nitride semiconductor devices 1a Semiconductor structure 2. First Layer 3. Second Layer 4, 104 Third Layer 5. Barrier Layer 6. The first middle class 7. n-type impurity doped barrier layer 8. The second middle class 9 Undoped barrier layer 10 Emitting layer 11 n-side nitride semiconductor layer 12 Active layer 13 p-side nitride semiconductor layer 21 First board 22 Second board 31 1st electrode 32 2nd electrode 35 Insulating film 100 1st wafer 200 2nd wafer

Claims

1. An n-side nitride semiconductor layer; an active layer provided on the n-side nitride semiconductor layer, the active layer including 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 provided on the active layer, The plurality of well layers are, in order from the n-side nitride semiconductor layer side, a first intermediate layer having a band gap smaller than that of the barrier layer and containing Al, Ga, and N; a second intermediate layer having a band gap energy smaller than that of the first intermediate layer and containing Ga and N; a light emitting layer that has a band gap energy smaller than that of the first intermediate layer, contains Ga and N, and emits ultraviolet light; Among the plurality of barrier layers, the barrier layer disposed between the light emitting layer and the p-side nitride semiconductor layer does not contain an n-type impurity, 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 barrier layer disposed between the second intermediate layer and the light emitting layer has a thickness of 20 nm or more and 40 nm or less; A nitride semiconductor device, wherein the second intermediate layer has a thickness of 10 nm or more and 18 nm or less.

2. A nitride semiconductor element as described in claim 1, wherein the thickness of the barrier layer arranged between the light-emitting layer and the p-side nitride semiconductor layer is greater than the thickness of the barrier layer arranged between the second intermediate layer and the light-emitting layer.

3. 3. The nitride semiconductor device according to claim 1, wherein the first intermediate layer has a thickness smaller than that of the second intermediate layer and that of the light emitting layer.

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

5. the band gap energy of the second intermediate layer is substantially the same as the band gap energy of the light emitting layer; 5. The nitride semiconductor device according to claim 1, wherein the second intermediate layer has a thickness smaller than a thickness of the light emitting layer.

6. the light emitting layer and the second intermediate layer contain In, 6. The nitride semiconductor device according to claim 1, wherein the In content of said second intermediate layer is smaller than the In content of said light emitting layer.

7. the first intermediate layer is AlGaN or AlInGaN; the second intermediate layer is GaN or InGaN; 7. The nitride semiconductor device according to claim 1, wherein the light emitting layer is made of GaN or InGaN.

8. The first intermediate layer has a thickness of 3 nm or more and 7 nm or less, 8. The nitride semiconductor device according to claim 1, wherein the light emitting layer has a thickness of 10 nm or more and 18 nm or less.

9. 9. The nitride semiconductor device according to claim 1, wherein the barrier layer contains Al, Ga and N.

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