Semiconductor light emitting device, method for fabricating semiconductor light emitting device, and contact structure

Abstract

To provide a light-emitting device that has an n-side contact structure capable of providing electric characteristics excellent over a wide Al composition range.SOLUTION: A light-emitting device comprises: an n type semiconductor layer which comprises group III nitride including Al as a group III constituent element; an active layer which includes group III nitride and can emit deep ultraviolet light; an n type contact layer of a group III nitride which includes Ga as a group III constituent element; an n type intermediate region of group III nitride including Ga and Al as group III constituent elements; and an n- electrode which includes metal. The n type intermediate region is provided between the n type contact layer and n type semiconductor layer, the n type contact layer is provided between the n type intermediate region and n- electrode, and the n type intermediate region has an Al composition X changing monotonously in a direction from the n type semiconductor layer to the n type contact layer, wherein the Al composition X of the n type intermediate region is equal to or larger than an Al composition Y of the n type contact layer, the Al composition Y of the n type contact layer is equal to or larger than zero, and the Al composition X of the n type intermediate region is equal to or less than an Al composition Z of the n type semiconductor layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a semiconductor light-emitting device, a method of manufacturing the semiconductor light-emitting device, and a contact structure.

Background Art

[0002] Patent Document 1 discloses an optical semiconductor element. This optical semiconductor element includes a composition gradient layer exposed by etching and an n-side electrode that makes direct contact with the composition gradient layer.

[0003] Patent Document 2 discloses a nitride semiconductor light-emitting element. This nitride semiconductor light-emitting element includes an n-contact layer and an Al y Ga 1-y N material layer (0 ≦ y ≦ 0.5, fixed Al composition) and an n-side electrode that makes direct contact with the Al y Ga 1-y N material layer.

[0004] Patent Document 3 discloses a nitride semiconductor ultraviolet light-emitting element. This nitride semiconductor ultraviolet light-emitting element has an n-type contact layer having an AlN molar fraction smaller than that of the n-type cladding layer and provided between the n-type cladding layer and the n electrode.

[0005] Patent Document 4 discloses a p-type cladding layer having a decreasing Al composition from an electron blocking layer toward a p-type contact layer.

[0006] Patent Document 5 discloses a nitride semiconductor light-emitting element. This nitride semiconductor light-emitting element includes a composition gradient layer having a decreasing Al composition y from a surface in contact with a carrier blocking layer toward a surface in contact with a second group-III nitride semiconductor layer.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

[0008] Semiconductor light-emitting devices using group III nitrides have an active layer including a GaN (gallium nitride) barrier layer and an InGaN well layer in the blue wavelength and longer wavelength regions, and are fabricated on a GaN template layer on a sapphire substrate or on a GaN substrate. On the other hand, in the ultraviolet wavelength region, the semiconductor light-emitting device has an active layer including, for example, an AlGaN barrier layer and an AlGaN well layer, and is fabricated on an AlN (aluminum nitride) template layer on a sapphire substrate or on an AlN substrate.

[0009] For example, when considering a blue semiconductor laser from an electrical aspect, a low resistance is provided to the n-type semiconductor by GaN doped with silicon. On the other hand, for the p-type semiconductor, a higher electrical resistance is provided compared to the n-type semiconductor due to the use of a magnesium dopant and AlGaN.

[0010] When considering a semiconductor light-emitting device that provides ultraviolet light, for example, light emission in the deep ultraviolet wavelength region, from an electrical aspect, magnesium is added to AlGaN having a larger Al composition compared to AlGaN of a blue semiconductor laser for the p-type semiconductor. For the n-type semiconductor, although silicon can continue to be used as a dopant, due to the use of an AlN template layer or an AlN substrate, the base semiconductor is changed from GaN to AlGaN or AlN having a high Al composition.

[0011] Comparing blue light-emitting devices and ultraviolet light-emitting devices from the perspective of n-type semiconductors, in blue light-emitting devices, especially semiconductor lasers, in order to achieve carrier confinement, the Al composition is increased from the GaN semiconductor of the substrate towards the active layer. On the other hand, in ultraviolet light-emitting devices, such as deep ultraviolet light-emitting diodes, the Al composition is decreased from the AlN semiconductor of the substrate towards the active layer for the Al composition that enables the emission wavelength of the active layer.

[0012] Thus, semiconductor light-emitting devices with deep ultraviolet wavelengths are developed in a material environment different from that of long-wavelength blue light-emitting devices.

[0013] Patent Document 1 discloses forming an n-side metal electrode that makes direct contact with a compositionally graded layer. In the optoelectronic device of Patent Document 1, the surface of the compositionally graded layer with which the n-side electrode makes contact is formed by etching. The manufacturing variation in the etching amount changes the Al composition of the surface of the compositionally graded layer with which the n-side metal electrode makes contact in-plane and from lot to lot.

[0014] Patent Document 2 discloses forming an n-side electrode so as to make direct contact with an AlGaN material layer with a fixed Al composition provided on an n-contact layer. Patent Document 3 discloses forming an n-side electrode so as to make direct contact with an n-type contact layer provided on an n-type cladding layer and having an AlN mole fraction smaller than that of the n-type cladding layer. Patent Document 4 teaches gradually decreasing the Al composition of a p-type cladding layer in order to improve the device lifetime. None of Patent Documents 2 to 4 teach an n-side compositionally graded layer.

[0015] In view of the above problems, an object of the present invention is to provide a semiconductor light-emitting device having an n-side contact structure that can provide good electrical characteristics in a wide range of Al compositions, a method of manufacturing a semiconductor light-emitting device, and a contact structure.

Means for Solving the Problems

[0016] A first aspect of the present invention is a semiconductor light-emitting device, the semiconductor light-emitting device comprising an n-type semiconductor layer including a group-III nitride semiconductor containing aluminum as a group-III constituent element, a p-type semiconductor layer provided on the n-type semiconductor layer, an active layer provided on the n-type semiconductor layer and including a group-III nitride semiconductor capable of generating deep ultraviolet light, an n-type contact layer of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium as a group-III constituent element, an n-type intermediate region of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium and aluminum as group-III constituent elements, and an n-electrode containing a metal, the n-type intermediate region being provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer being provided between the n-type intermediate region and the n-electrode, the n-type intermediate region having a monotonically changing (including changing in the same direction stepwise) Al composition X in a direction from the n-type semiconductor layer to the n-type contact layer, the Al composition X of the n-type intermediate region being equal to or greater than an Al composition Y of the group-III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer being equal to or greater than zero, the Al composition X of the n-type intermediate region being equal to or smaller than an Al composition Z of the n-type semiconductor layer, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer being arranged in order in a direction of an axis from the n-type intermediate region toward the n-electrode.

[0017] A second aspect according to the present invention is a method of manufacturing a semiconductor light-emitting device, the semiconductor light-emitting device including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer including a group-III nitride semiconductor capable of generating deep ultraviolet light, the method including growing, on a substrate, a first group-III nitride semiconductor layer including gallium and aluminum as group-III constituent elements for an n-type intermediate region; after growing the first group-III nitride semiconductor layer, growing, on the substrate, a second group-III nitride semiconductor layer including gallium as a group-III constituent element for an n-type contact layer; and after growing the second group-III nitride semiconductor layer, forming an n-electrode including a metal on the substrate, the n-type semiconductor layer including aluminum as a group-III constituent element, the n-type intermediate region being provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer being provided between the n-type intermediate region and the n-electrode, the n-type intermediate region having a monotonically changing Al composition X in a direction from the n-type semiconductor layer to the n-type contact layer, the Al composition X of the n-type intermediate region being equal to or greater than an Al composition Y of the group-III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer being equal to or greater than zero, the Al composition X of the n-type intermediate region being equal to or less than an Al composition Z of the n-type semiconductor layer, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer being sequentially arranged on the substrate in a direction of an axis from the n-type intermediate region to the n-electrode.

[0018] A third aspect of the present invention is a contact structure for a group-III nitride semiconductor device, the contact structure comprising: a substrate providing a group-III nitride main surface containing aluminum as a group-III constituent element; a semiconductor region in contact with the group-III nitride main surface and including one or more group-III nitride semiconductor layers; an n-type semiconductor layer of a group-III nitride semiconductor in contact with the semiconductor region; an n-type contact layer of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium as a group-III constituent element; an n-type intermediate region of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium and aluminum as group-III constituent elements; and an n-electrode containing a metal. The group-III nitride semiconductor of the n-type semiconductor layer contains aluminum as a group-III constituent element, the n-type semiconductor layer is provided between the substrate and the n-type intermediate region, the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the group-III nitride semiconductor of the n-type intermediate region has an Al composition X that monotonically changes in the direction from the n-type semiconductor layer to the n-electrode, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the group-III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer is not less than zero, and the Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer.

Advantages of the Invention

[0019] According to the above aspect of the present invention, a semiconductor light-emitting device having an n-side contact structure capable of providing good electrical characteristics in a wide range of Al compositions, a method of manufacturing a semiconductor light-emitting device, and a contact structure can be provided.

Brief Description of the Drawings

[0020]

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Embodiments for Carrying Out the Invention

[0021] Hereinafter, each embodiment for carrying out the present invention will be described with reference to the drawings. The same or similar components are denoted by the same or similar reference numerals, and redundant descriptions are omitted.

[0022] FIG. 1 is a drawing schematically showing a nitride device according to an embodiment of the present invention. FIG. 2 is a drawing showing an example of a nitride device according to an embodiment of the present invention. In FIG. 2, a cross-sectional line I-I showing the device cross-section of FIG. 1 is drawn. FIG. 3 is a drawing schematically showing a contact structure according to an embodiment of the present invention.

[0023] A nitride device is a light-emitting device having an active layer for light emission, such as a light-emitting diode (LED), a laser diode (LD), or a light source by electron beam excitation, which includes a group-III nitride. The n-type semiconductor layer can include a group-III nitride, and further, if necessary, the p-type semiconductor layer can include a group-III nitride. However, the nitride device is not limited to a light-emitting device and can include electronic devices not related to light emission, such as a high electron mobility transistor (HEMT), a photodetector (PD), a surface acoustic wave device, and a piezoelectric device. The group-III constituent elements include aluminum (Al), gallium (Ga), and indium (In). The group-III nitride is a compound of one or more group-III constituent elements (at least one of Al, Ga, and In) and nitrogen (N).

[0024] In the following description, the nitride device 110 has a light-emitting diode structure as an example, not a limitation, and the light-emitting diode operates as a semiconductor light-emitting device.

[0025] The nitride device 110 has a contact structure 111, and the contact structure 111 includes an n-type semiconductor layer 125, an n-type contact layer 127, an n-type intermediate region 129, and an n-electrode 131.

[0026] The n-type semiconductor layer 125 includes a group-III nitride semiconductor. The group-III nitride semiconductor of the n-type semiconductor layer 125 includes aluminum as a group-III constituent element. The n-type contact layer 127 is provided on the n-type semiconductor layer 125 and includes a group-III nitride semiconductor including gallium as a group-III constituent element. The n-type intermediate region 129 is provided on the n-type semiconductor layer 125 and includes a group-III nitride semiconductor including gallium and aluminum as group-III constituent elements. The n-electrode 131 includes a metal provided on the n-type semiconductor layer 125, the n-type intermediate region 129, and the n-type contact layer 127.

[0027] The n-type intermediate region 129 is provided between the n-type contact layer 127 and the n-type semiconductor layer 125. The n-type contact layer 127 is provided between the n-type intermediate region 129 and the n-electrode 131.

[0028] The group-III nitride semiconductor of the n-type intermediate region 129 can have an Al composition X that monotonically changes in the direction of the axis Ax1 in the direction from the n-type semiconductor layer 125 to the n-electrode 131. The monotonically changing Al composition does not increase in the direction from the n-type semiconductor layer 125 to the n-type contact layer 127. The Al composition X of the n-type intermediate region 129 is equal to or greater than the Al composition Y of the group-III nitride semiconductor of the n-type contact layer 127, and the Al composition Y of the n-type contact layer 127 is zero or greater. The Al composition X of the n-type intermediate region 129 is less than or equal to the Al composition Z of the n-type semiconductor layer 125.

[0029] According to the nitride device 110, the n-type intermediate region 129 having an Al composition X that monotonically changes in the direction from the n-type semiconductor layer 125 to the n-electrode 131 gives good electrical characteristics to the contact structure 111 for providing carriers to the n-type semiconductor layer 125. In the contact structure 111, the n-type intermediate region 129, the n-type contact layer 127, and the n-electrode 131 are arranged in this order. The Al composition Y of the n-type contact layer 127 is less than or equal to the Al composition X of any area of the n-type intermediate region 129. Also, the Al composition Z of the n-type semiconductor layer 125 is greater than or equal to the Al composition X of any area of the n-type intermediate region 129.

[0030] The n-type intermediate region 129 can have at least one of a graded composition GR and a stepped composition ST as shown in the Al composition profile Al-P of FIG. 1. The n-type intermediate region 129 may have an Al composition profile combining the graded composition GR and the stepped composition ST. In the graded composition GR and the stepped composition ST, the Al composition X of the n-type intermediate region 129 decreases in the direction from the n-type semiconductor layer 125 to the n-type contact layer 127 in at least a part of the n-type intermediate region 129. According to the nitride device 110, the monotonically changing Al composition X in the n-type intermediate region 129 is provided by the graded composition GR and the stepped composition ST.

[0031] By way of example rather than limitation, the Al composition X of the n-type intermediate region 129 can monotonically decrease in the direction from the n-type semiconductor layer 125 to the n-electrode 131 over the entire n-type intermediate region 129.

[0032] Specifically, the n-type intermediate region 129 can contain, for example, Al X Ga 1-X N, and can further contain indium as a group III constituent element. The Al composition X of the n-type intermediate region 129 decreases in the direction from the n-type semiconductor layer 125 to the n-type contact layer 127 over the entire n-type intermediate region 129. According to the nitride device 110, the n-type intermediate region 129 has an interface related to the n-type semiconductor layer 125 and an interface related to the n-type contact layer 127, and the Al composition X decreases from one of these interfaces toward the other interface.

[0033] The Al composition X of the n-type intermediate region 129 has a terminal Al composition at the interface related to the n-type contact layer 127. The terminal Al composition can be equal to or greater than the Al composition of the n-type contact layer 127 (where the Al composition includes zero). By way of example rather than limitation, an Al composition difference at this interface, for example, a composition difference of 30% or less, is acceptable in that the voltage rise at this interface is suppressed to approximately 0. Also, the terminal Al composition of the n-type intermediate region 129 can be, for example, 20% or more.

[0034] The Al composition X of the n-type intermediate region 129 has a starting Al composition at the interface related to the n-type semiconductor layer 125. The starting Al composition can be equal to or smaller than the Al composition of the n-type semiconductor layer 125. By way of non-limiting example, the starting Al composition of the n-type intermediate region 129 is often equal to the Al composition on the upper surface of the n-type semiconductor layer 125, whereby the change in electron concentration near the interface related to the n-type semiconductor layer 125 can be reduced. By way of non-limiting example, the Al composition difference at this interface, for example a composition difference of 30% or less, is acceptable in that the voltage rise at this interface is suppressed to almost zero. Unless otherwise stated as "by way of non-limiting example", numerical values usually allow a certain range and are shown by way of non-limiting example.

[0035] The n-type contact layer 127 can include at least one of n-type GaN, n-type AlGaN, and n-type InAlGaN. According to the nitride device 110, a gallium nitride-based semiconductor such as n-type GaN, n-type AlGaN, or n-type InAlGaN can be provided for the n-type contact layer 127. In this embodiment, the n-type contact layer 127 can be n-type GaN and / or n-type AlGaN, and its Al composition can be 0% to 40%. By way of non-limiting example, the n-type contact layer 127 can have a thickness of, for example, 10 to 1000 nm.

[0036] The group III nitride semiconductor of the n-type semiconductor layer 125 can include at least any one of AlN, AlGaN, and InAlGaN. According to the nitride device 110, AlN, AlGaN, or InAlGaN can be used as the base for the n-type contact layer 127 and the n-type intermediate region 129. In this embodiment, the n-type semiconductor layer 125 can include n-type AlGaN, and its Al composition can be in the range of 60% to 90%. Also, the Al composition on the upper surface of the n-type semiconductor layer 125 can be in the range of 60% to 90%. The n-type semiconductor layer 125 can have a thickness of, for example, 100 to 5000 nm.

[0037] By way of example and not limitation, the nitride device 110 can further include an active layer 114 and a p-type semiconductor layer 121. The active layer 114 and the p-type semiconductor layer 121 are provided on the n-type semiconductor layer 125 and the substrate 133.

[0038] The active layer 114 is capable of generating deep ultraviolet light and includes a group III nitride semiconductor provided on the substrate 133. The wavelength of the deep ultraviolet light can be in the range of 285 nm or less, and can be, for example, 200 nm or more.

[0039] Specifically, the active layer 114 can be composed of a single layer of AlGaN, or can have a single or multiple quantum well structures 114a. Specifically, the well layer 114b can include undoped AlGaN, and the barrier layer 114c can include undoped AlGaN. Either one or both of the well layer 114b and the barrier layer 114c may be doped with Si. The AlGaN of the barrier layer 114c has a larger bandgap than the AlGaN of the well layer 114b. The barrier layer 114c can include AlN if necessary.

[0040] According to the nitride device 110, for deep ultraviolet light with a wavelength of 285 nm or less, an active layer 114 with a high Al composition is required, and the current path to the active layer 114 is also formed by a group III nitride with a high Al composition. A good n-type contact structure 111 to the group III nitride with a high Al composition is provided by a combination of an n-type intermediate region 129, an n-type contact layer 127, and an n-electrode 131.

[0041] In addition, an n-type intermediate region 129 having a monotonically varying Al composition X in the direction from the n-type semiconductor layer 125 to the active layer 114 gives good electrical characteristics to the contact structure 111 for providing carriers to the active layer 114 through the n-type semiconductor layer 125. The Al composition Y of the n-type contact layer 127 is below the Al composition X of any area of the n-type intermediate region 129. Also, the Al composition Z of the n-type semiconductor layer 125 is above the Al composition X of any area of the n-type intermediate region 129.

[0042] If necessary, the nitride device 110 further includes a substrate 133, and the substrate 133 provides a group-III nitride main surface 133a containing aluminum as a group-III constituent element. The n-type semiconductor layer 125 is provided between the substrate 133 and the n-type intermediate region 129.

[0043] The n-type semiconductor layer 125 can have at least one of a layer with a monotonically changing graded composition (a structure identical or similar to GR) and a stepped composition (a structure identical or similar to ST) in the direction from the substrate 133 to the n-type contact layer 127 (or in the direction from the n-type contact layer 127 to the n-electrode 131). According to the contact structure 111, the n-type semiconductor layer 125 can have a monotonically changing Al composition, and the monotonically changing Al composition does not increase in the direction from the substrate 133 to the n-type contact layer 127. Also, the monotonically changing Al composition is provided by a graded composition and a stepped composition having an Al composition equal to or greater than the maximum value of the Al composition X in the n-type semiconductor layer 125. By way of non-limiting example, the n-type semiconductor layer 125 can have a monotonically decreasing Al composition in the direction from the substrate 133 to the n-type contact layer 127 (or in the direction from the n-type contact layer 127 to the n-electrode 131).

[0044] By way of non-limiting example, according to the contact structure 111, the n-type semiconductor layer 125 can have a single Al composition. In this case, the technical meaning of "single Al composition" should be determined in consideration of the variation in the measurement of the Al composition, and the variation in the measurement of the Al composition can be 5% or less, for example, in Auger electron spectroscopy. Alternatively, the nitride device 110 includes a semiconductor region 135 including one or more group-III nitride semiconductor layers, and the semiconductor region 135 is in contact with the group-III nitride main surface 133a. The group-III nitride semiconductor of the n-type semiconductor layer 125 is in contact with the main surface 135a of the semiconductor region 135.

[0045] According to the nitride device 110, an active layer 114 is provided on a substrate 133 as described above. The n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are arranged in order in the direction of the axis from the n-type intermediate region 129 toward the n-electrode 131.

[0046] The substrate 133, the n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are arranged in order in the direction of an axis Ax1 extending in the direction from the n-type contact layer 127 toward the n-electrode 131. In the contact structure 111, the n-type intermediate region 129, the n-type contact layer 127, and the n-electrode 131 are arranged in order. According to the contact structure 111, the nitride device 110 having the n-type semiconductor layer 125 closer to the substrate 133 than the p-type semiconductor layer 121 is given good electrical characteristics.

[0047] The substrate 133 mounts the n-type semiconductor layer 125, the active layer 114, the p-type semiconductor layer 121, the n-type contact layer 127, and the n-type intermediate region 129.

[0048] In the nitride device 110, the n-type contact layer 127 can have an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region 129. According to this nitride device 110, a group III nitride that is lattice-relaxed with respect to the n-type intermediate region 129 is provided in the n-type contact layer 127. Further, the n-type contact layer 127 that is lattice-relaxed with respect to the n-type intermediate region 129 can reduce the electrical resistance at the interface between the n-type contact layer 127 and the n-type intermediate region 129.

[0049] When the in-plane lattice constant of the n-type contact layer 127 is larger than the in-plane lattice constant of the n-type intermediate region 129, the carrier concentration at the interface between the n-type contact layer 127 and the n-type intermediate region 129 changes. More precisely, in the in-plane direction perpendicular to the axis from the n-type intermediate region 129 toward the n-electrode 131, the lattice constant of the n-type contact layer 127 is larger than the lattice constant of the n-type intermediate region 129.

[0050] The n-type contact layer 127 can have a lattice relaxation rate of 0.5 or more (50% or more) with respect to the n-type semiconductor layer 125. According to the nitride device 110, a group-III nitride having a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer 125 can be provided for the n-type contact layer 127. The magnitude of the lattice relaxation rate of the n-type contact layer 127 can change the carrier concentration at the interface between the n-type contact layer 127 and the n-type intermediate region 129. Also, the lattice relaxation rate of the n-type contact layer 127 with respect to the n-type semiconductor layer 125 may be greater than the lattice relaxation rate of the n-type intermediate region 129 with respect to the n-type semiconductor layer 125.

[0051] The substrate 133 can be a substrate including a group-III nitride containing aluminum as a group-III constituent element, and this substrate can be, for example, a single-crystalline aluminum nitride substrate. Alternatively, the substrate 133 includes a support 118 and a template layer 120. The support 118 has a main surface 118a made of a material different from that of the group-III nitride. The template layer 120 is made of a group-III nitride and is provided on the main surface 118a of the support 118. The template layer 120 can be, for example, an AlN template layer or an AlGaN template layer. The template layer 120 can cover the main surface 118a of the support 118 and include compressive strain. This compressive strain may be a source of the strain applied to the contact structure 111. The template layer 120 can be, for example, 2000 nm or less, for example, 500 nm.

[0052] By way of illustration and not limitation, the support 118 can include at least one of silicon, carbon, boron nitride (BN), aluminum oxide (sapphire), ceramic, silicon carbide, refractory metal, zirconia, tantalum carbide (TaC), ScAlMgO 4 and the like. For example, the support 118 can have a hexagonal crystal structure.

[0053] The active layer 114 is provided on the substrate 133 so as to generate light having a peak wavelength in the deep ultraviolet wavelength region of 285 nm or less, and can include AlGaN containing compressive strain.

[0054] The nitride device 110 can further include a nitride semiconductor region 116. The nitride semiconductor region 116 is provided between the substrate 133 and the active layer 114, and includes Al as a group III constituent element. The nitride semiconductor region 116 can include one or more n-type group III nitride semiconductor layers, and specifically includes an n-type semiconductor layer 125.

[0055] In this embodiment, the nitride semiconductor region 116 can include a first n-type semiconductor layer 122 and a second n-type semiconductor layer 124. The first n-type semiconductor layer 122 is provided between the substrate 133 and the active layer 114, and the second n-type semiconductor layer 124 is provided between the first n-type semiconductor layer 122 and the active layer 114. The n-type semiconductor layer 125 can be either one of the first n-type semiconductor layer 122 or the second n-type semiconductor layer 124, or both the first n-type semiconductor layer 122 and the second n-type semiconductor layer 124. For example, the first n-type semiconductor layer 122 can be provided between the substrate 133 and the n-type contact layer 127, and the first n-type semiconductor layer 122 can be provided between the substrate 133 and the n-type intermediate region 129.

[0056] By way of example and not limitation, the first n-type semiconductor layer 122 can include a group III nitride such as AlGaN or InAlGaN, and the second n-type semiconductor layer 124 can include a group III nitride such as AlGaN or InAlGaN.

[0057] By way of example and not limitation, the first n-type semiconductor layer 122 can have a first Al composition that is substantially equal to the second Al composition of the second n-type semiconductor layer 124. Alternatively, the first n-type semiconductor layer 122 can have a first Al composition that is greater than the second Al composition of the second n-type semiconductor layer 124.

[0058] By way of example and not limitation, the thickness of the first n-type semiconductor layer 122 may be greater than the thickness of the second n-type semiconductor layer 124. The thickness of the nitride semiconductor region 116 can be, for example, from 200 to 3000 nm. The film thickness of the second n-type semiconductor layer 124 can be from 10 to 200 nm, and preferably can be from 50 to 150 nm.

[0059] The nitride device 110 has a lower group III nitride laminate 113 located between the active layer 114 and the substrate 133, and an upper group III nitride laminate 115 located on the active layer 114.

[0060] In this embodiment, the lower group III nitride laminate 113 forms a junction 119a with the substrate 133 and can contain compressive strain caused by both or at least one of the compressive strain contained in the group III nitride of the substrate 133 and the lattice constant difference between the group III nitride of the substrate 133 and the lower group III nitride laminate 113. Further, the lower group III nitride laminate 113 forms a junction 119b with the active layer 114. The active layer 114 can contain compressive strain caused by both or at least one of the compressive strain contained in the group III nitride of the substrate 133 and the lattice constant difference between the group III nitride of the substrate 133 and the active layer 114. On the other hand, part or all of the upper group III nitride laminate 115 may be lattice relaxed. The upper group III nitride laminate 115 is provided on the active layer 114 and supplies carriers to the active layer 114.

[0061] In addition to the nitride semiconductor region 116, the lower group III nitride laminate 113 can include one or more group III nitride semiconductor layers. Specifically, the lower group III nitride laminate 113 can include a semiconductor region 135. The semiconductor region 135 can include a base layer, specifically an Al U Ga 1-U N layer 130 (U is greater than zero and X or more and 1 or less). The Al U Ga 1-U N layer 130 can be, for example, undoped and can be provided to cover the substrate 133.

[0062] The lower group-III nitride laminate 113 (and the semiconductor region 135) may include another underlying layer, specifically another Al V Ga 1-V N layer 132 (V is less than 1 and greater than 0.8. V is less than U). The Al V Ga 1-V N layer 132 can be, for example, undoped, and specifically, can be provided on the Al U Ga 1-U N layer 130.

[0063] In this embodiment, the nitride semiconductor region 116 forms a junction 119c with the Al V Ga 1-V N layer 132 (the main surface 135a of the semiconductor region 135). The Al V Ga 1-V N layer 132 forms a junction 119d with the Al U Ga 1-U N layer 130. In addition to the nitride semiconductor region 116, the lower group-III nitride laminate 113 is provided with an Al U Ga 1-U N layer 130 and an Al V Ga 1-V N layer 132. The nitride semiconductor region 116 has an Al composition smaller than that of the Al V Ga 1-V N layer 132 and greater than that of the well layer 114b.

[0064] The lower group-III nitride laminate 113 has a monotonically changing Al composition profile Al-P in the direction from the substrate 133 to the n-electrode 131. The monotonically changing Al composition profile Al-P means that when the Al composition of the main surface of the substrate 133 is greater than that of the well layer 114b, the Al composition of the lower group-III nitride laminate 113 does not increase from the substrate 133 to the active layer 114.

[0065] Next, the upper group-III nitride laminate 115 will be described. The upper group-III nitride laminate 115 can include, for example, an electron blocking layer 134, a p-type graded composition layer 136, and a p-type contact layer 138. The electron blocking layer 134, the p-type graded composition layer 136, and the p-type contact layer 138 (138a, 138b) can be sequentially provided on the active layer 114. When the electron blocking layer 134 is undoped, the p-type graded composition layer 136 and the p-type contact layer 138 function as a p-type semiconductor layer 121.

[0066] By way of example and not limitation, the upper group-III nitride laminate 115 can have the following configuration. Electron blocking layer 134: Undoped or Mg-doped AlN, thickness 7 nm. p-type graded composition layer 136: Undoped or Mg-doped graded composition AlGaN (Al composition: 0.9 to 0.4), thickness 15 nm. p-type contact layer 138a (first layer): Mg-doped GaN, thickness 120 nm. p-type contact layer 138b (second layer): High-concentration Mg-doped GaN, thickness 30 nm.

[0067] The nitride device 110 has a processed region 142 by etching. The processed region 142 by etching can include the upper side of the upper group-III nitride laminate 115, the active layer 114, and the nitride semiconductor region 116 (specifically, the upper side of the second n-type semiconductor layer 124 or the upper side of the second n-type semiconductor layer 124 and the first n-type semiconductor layer 122). In this embodiment, as shown in FIG. 2, the upper surface of the processed region 142 by etching can have a comb shape.

[0068] The nitride device 110 can further include a passivation film 144, and the passivation film 144 covers the processed region 142 by etching and the nitride semiconductor region 116. The passivation film 144 has a first opening 144a located on the upper surface of the processed region 142 by etching and a second opening 144b located on the upper surface of the n-type contact layer 127. The passivation film 144 is, for example, aluminum oxide (Al 2O 3 ) contains AlSiO or a silicon-based inorganic insulator. The silicon-based inorganic insulator can include, for example, silicon oxide (e.g., SiO 2 ), silicon nitride (e.g., Si 3 N 4 ), or silicon oxynitride (e.g., SiON).

[0069] The nitride device 110 can have a p - electrode 146. The p - electrode 146 is provided in the first opening 144a, and the n - electrode 131 is provided in the second opening 144b. The p - electrode 146 makes contact with the upper surface of the p - type contact layer 138. The n - electrode 131 makes contact with the upper surface of the n - type contact layer 127. By way of non - limiting example, the n - electrode 131 can include Ti / Al / Ni / Au (meaning Ti, Al, Ni, Au are laminated in this order), and the p - electrode 146 can include Ni / Au (meaning Au is laminated on Ni). In this embodiment, as shown in FIG. 2, the upper surface of the n - electrode 131 can have a comb shape, and the upper surface of the p - electrode 146 can have a comb shape.

[0070] The n - type semiconductor layer 125 includes a first region 125a and a second region 125b. The first region 125a and the second region 125b are arranged along a reference plane Ref that intersects the axis Ax1 extending from the n - type intermediate region 129 to the n - type contact layer 127. The active layer 114 and the p - type semiconductor layer 121 are provided on the second region 125b without being provided on the first region 125a. The n - electrode 131, the n - type contact layer 127, and the n - type intermediate region 129 are provided on a part of the first region 125a without being provided on the second region 125b. According to the nitride device 110, the n - type contact layer 127 and the n - type intermediate region 129 are selectively provided on the first region 125a, and the n - type contact layer 127 and the n - type intermediate region 129 are utilized for contact to the n - electrode 131.

[0071] Figures 4(a), 4(b), 5(a), 5(b), 6(a), 6(b), 7(a), and 7(b) are drawings showing the main steps of a method for fabricating the nitride device 110 according to the present embodiment. In the following description of the fabrication method, a light-emitting diode structure is fabricated as the nitride device 110. The light-emitting diode structure of the nitride device 110 includes an n-type semiconductor layer 125, an active layer 114, and a p-type semiconductor layer 121, and the active layer 114 includes a group-III nitride semiconductor capable of generating deep ultraviolet light. The n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are sequentially arranged on a substrate 133 in the direction of an axis Ax from an n-type intermediate region 129 toward an n-electrode 131.

[0072] As shown in the step of FIG. 4(a), an epitaxial wafer 162 is prepared. Preparing the epitaxial wafer 162 includes, for example, fabricating the epitaxial wafer 162 or obtaining the epitaxial wafer 162 by a method other than fabrication.

[0073] Fabricating the epitaxial wafer 162 can include the following steps.

[0074] In the step of FIG. 4(a), the epitaxial wafer 162 is fabricated. A substrate 150 for fabricating the epitaxial wafer 162 is prepared. The substrate 150 can be an AlN template including, for example, a 2-inch sapphire substrate. To fabricate the epitaxial wafer 162, a group-III nitride laminate 164 including a plurality of group-III nitride films is grown on the substrate 150. This growth can be performed, for example, by a metalorganic vapor phase epitaxy (MOVPE) method or a molecular beam epitaxy (MBE) method. In the following description, an MOVPE reactor 155a is adopted, and trimethylgallium (TMGa) and trimethylaluminum (TMAl) are used as the gallium precursor and the aluminum precursor, respectively. NH 3 is used as the nitrogen source.

[0075] The Group-III nitride laminate 164 includes semiconductor films for the lower Group-III nitride laminate 113 and the active layer 114. Specifically, the Group-III nitride laminate 164 has a nitride semiconductor region 166 and an active layer 168.

[0076] The nitride semiconductor region 166 is grown on the substrate 150. The nitride semiconductor region 166 includes a Group-III nitride semiconductor containing compressive strain. Specifically, a first n-type semiconductor layer 165 is grown on the substrate 150, and a second n-type semiconductor layer 167 is grown on the first n-type semiconductor layer 165. Each of the first n-type semiconductor layer 165 and the second n-type semiconductor layer 167 contains an n-type dopant (e.g., silicon) in this embodiment. In this embodiment, the first n-type semiconductor layer 165 is prepared as a semiconductor film for the n-type semiconductor layer 125.

[0077] After the growth of the nitride semiconductor region 166, the active layer 168 is grown. Specifically, the active layer 168 can contain AlGaN. The active layer 168 can be configured to generate light having a peak wavelength in a deep ultraviolet wavelength region of 285 nm or less. By way of example and not limitation, the active layer 168 can generate light up to a wavelength region of about 200 nm of deep ultraviolet light. By way of example and not limitation, the active layer 168 can contain InAlGaN that can generate light of a deep ultraviolet wavelength.

[0078] The nitride semiconductor region 166 and the active layer 168 are grown on the substrate 150 so as to form the following structure. The nitride semiconductor region 166 includes the first n-type semiconductor layer 165 and the second n-type semiconductor layer 167. The first n-type semiconductor layer 165 is provided between the substrate 150 and the active layer 168, and the second n-type semiconductor layer 167 is provided between the first n-type semiconductor layer 165 and the active layer 168. By way of example and not limitation, the second n-type semiconductor layer 167 can have a thickness smaller than the thickness of the first n-type semiconductor layer 165.

[0079] As already described, the active layer 168 can have a quantum well structure 168a. The quantum well structure 168a of the active layer 168 includes one or more well layers 168b and one or more barrier layers 168c.

[0080] The active layer 168 is grown on the nitride semiconductor region 166. Specifically, the active layer 168 has a structure including alternately stacked AlGaN well layers 168b and AlGaN barrier layers 168c. The AlGaN well layer 168b and the AlGaN barrier layer 168c each contain AlGaN having its respective Al composition. Specifically, the Al composition of the AlGaN well layer 168b is smaller than the Al composition of the AlGaN barrier layer 168c. The film thickness of the AlGaN well layer 168b may be 0.5 to 3.0 nm, more preferably 1.0 to 2.5 nm. The number of layers of the AlGaN well layer 168b may be, for example, 3 layers. The uppermost layer of the active layer 168 may be the AlGaN well layer 168b, and thus the electron blocking layer 174 may be in contact with the active layer 168. Also, the plurality of AlGaN well layers 168b can have equal film thicknesses and Al compositions to each other, or can have different film thicknesses and Al compositions to each other. For example, the uppermost AlGaN well layer 168b of the active layer 168 is in contact with the electron blocking layer 174, and this AlGaN well layer 168b can have a thinner film thickness than the other AlGaN well layers 168b. The emission wavelength of the active layer 168 may be 200 to 285 nm, more preferably 255 to 285 nm. The film thickness of the AlGaN well layer 168b may be 2 nm, the Al composition may be 0.42, and the Si dopant concentration may be 3×10 17 cm -3 It may be. Also, the film thickness of the AlGaN barrier layer 168c may be 3 nm, the Al composition may be 0.66, and the Si dopant concentration may be 5×10 17 cm -3 It may be. Exemplification of growth conditions of AlGaN for the active layer 168: Growth pressure: 40 kPa Substrate temperature: 1050 degrees Celsius

[0081] By way of example and not limitation, the thickness of the first n-type semiconductor layer 165 can be 800 nm or more, and the thickness of the second n-type semiconductor layer 167 can be less than 200 nm. The nitride semiconductor region 166 provides a low dislocation density and good flatness derived from the substrate 150 for the growth of the active layer 168.

[0082] In this embodiment, one or more group III nitride semiconductor layers can be grown prior to the growth of the nitride semiconductor region 166 and the active layer 168. In the group III nitride laminate 164, specifically, the semiconductor region 171 for the lower group III nitride laminate 113 can include the following semiconductor layers in addition to the nitride semiconductor region 166.

[0083] Specifically, an Al U Ga 1-U N layer 170 (U is greater than zero and not less than X and not more than 1) can be grown. The Al U Ga 1-U N layer 170 has an Al composition greater than that of the nitride semiconductor region 166. By way of example and not limitation, the Al U Ga 1-U N layer 170 can be undoped. Also, the Al U Ga 1-U N layer 170 can contain compressive strain.

[0084] Specifically, another Al U Ga 1-U N layer 172 (V is less than 1 and greater than 0.8. V is less than U) can be grown on the Al V Ga 1-V N layer 170. The Al V Ga 1-V N layer 172 has an Al composition greater than that of the nitride semiconductor region 166. The Al V Ga 1-V N layer 172 can contain compressive strain.

[0085] In addition to the nitride semiconductor region 166 and the active layer 168, the group III nitride laminate 164 is undoped AlU Ga 1-U N layer 170 and undoped Al V Ga 1-V can have an N layer 172.

[0086] Subsequently, a plurality of group-III nitride semiconductor layers 163 for the upper group-III nitride laminate 115 are grown on the active layer 168. Specifically, an electron blocking layer 174, a p-type graded composition layer 176, and a p-type contact layer 178 can be grown on the active layer 168 in this order. The group-III nitride laminate 164 can include the electron blocking layer 174, the p-type graded composition layer 176, and the p-type contact layer 178.

[0087] By this growth, an epitaxial wafer 162 is fabricated.

[0088] In the process of FIG. 4(b), if necessary, a groove 180a that defines the outer edge of the element of the light-emitting device is formed in the epitaxial wafer 162 by photolithography and etching. The etching is performed so as to reach the substrate 150 from the upper surface of the group-III nitride laminate 164, and the groove 180a is formed.

[0089] In the process of FIG. 5(a), a processed region 182 by etching is formed in the epitaxial wafer 162 by photolithography and etching to fabricate a substrate product SP1. The etching is performed so as to reach the nitride semiconductor region 166 (n-type semiconductor layer 125, or first n-type semiconductor layer 165, or second n-type semiconductor layer 167) from the upper surface of the group-III nitride laminate 164 so as to separate the active layer 168. The processed region 182 by etching is defined by a groove 180b. The groove 180b separates the plurality of group-III nitride semiconductor layers 163 and the active layer 168 for the upper group-III nitride laminate 115. By way of example and not limitation, the first n-type semiconductor layer 165 may appear at the bottom of the groove 180b. Instead of the first n-type semiconductor layer 165, the second n-type semiconductor layer 167 may appear at the bottom of the groove 180b.

[0090] In this embodiment, a group III nitride semiconductor film for the n-type intermediate region 169 and the n-type contact layer 171 is grown on the first n-type semiconductor layer 165 or the second n-type semiconductor layer 167. Specifically, the group III nitride semiconductor films of the n-type intermediate region 169 and the n-type contact layer 171 are formed by selective growth. In the following description, crystal growth using the MOVPE reactor 155b is adopted.

[0091] In the process of FIG. 5(b), a hard mask 173 for selective growth is formed on the substrate product SP1. The hard mask 173 includes a dielectric film, and the dielectric film is formed by a deposition method such as plasma CVD, thermal CVD, or sputtering. The dielectric film includes aluminum oxide (Al 2 O 3 ), AlSiO, or a silicon-based inorganic insulator. The silicon-based inorganic insulator can include, for example, silicon oxide (e.g., SiO 2 ), silicon nitride (e.g., Si 3 N 4 ), or silicon oxynitride (e.g., SiON). The hard mask 173 has an opening 173a located at the bottom of the groove 180b. For example, the hard mask 173 is fabricated by deposition of an inorganic film and processing of the inorganic film by photolithography and etching.

[0092] In the process of FIG. 5(b), after forming the hard mask 173, the substrate product SP1 is placed in the MOVPE reactor 155b, and growth for the n-type intermediate region 169 with a gradient Al composition is performed. The n-type intermediate region 169 is deposited on the III-nitride surface at the opening 173a of the hard mask 173. By this deposition, the n-type intermediate region 169 makes a junction with the underlying first n-type semiconductor layer 165 or second n-type semiconductor layer 167. In this growth, the supply amounts of the gallium precursor and the aluminum precursor are changed. Specifically, the gallium precursor, for example, trimethylgallium, is gradually increased; the aluminum precursor, for example, trimethylaluminum, is gradually decreased; or both. The Al composition of the n-type intermediate region 169 decreases in the direction from the nitride semiconductor region 166 to the active layer 168 (the direction of the axis Ax1 shown in FIG. 1). An n-type dopant is added during growth.

[0093] In the process of FIG. 6(a), after forming the hard mask 173, in this embodiment, following the growth of the n-type intermediate region 169, growth for the n-type contact layer 171 is performed. The n-type contact layer 171 is deposited on the n-type intermediate region 169 at the opening 173a of the hard mask 173. By this deposition, the n-type contact layer 171 makes a junction with the n-type intermediate region 169. The n-type contact layer 171 is typically n-type GaN or n-type AlGaN. The Al composition of the n-type contact layer 171 is zero or more and is below the minimum Al composition of the n-type intermediate region 169. An n-type dopant is added during growth.

[0094] In the process of FIG. 6(b), after the selective growth of the n-type intermediate region 169 and the n-type contact layer 171 is completed, it is taken out from the MOVPE reactor 155b. The hard mask 173 is removed by wet etching. At the bottom of the groove 180b, the stack 175 of the n-type intermediate region 169 and the n-type contact layer 171 remains. This stack 175 is separated from the processed region 182 by etching and makes a junction J1 with the first n-type semiconductor layer 165 or the second n-type semiconductor layer 167. Inside the stack 175, the n-type contact layer 171 makes a junction J2 with the n-type intermediate region 169.

[0095] In the process of FIG. 7(a), if necessary, the passivation film 184 is formed by a deposition method such as plasma CVD, thermal CVD, or sputtering. The passivation film 184 is fabricated by deposition of an inorganic film and processing of the inorganic film by photolithography and etching. The passivation film 184 has a first opening 184a located on the upper surface of the processed region 182 by etching, and a second opening 184b located on the upper surface of the stack 175 of the n-type intermediate region 169 and the n-type contact layer 171, that is, on the upper surface of the n-type contact layer 171. The passivation film 184 can contain, for example, a silicon-based inorganic insulator.

[0096] In the process of FIG. 7(b), after selective growth, electrodes, specifically a p-electrode 186 and an n-electrode 188, are formed. The p-electrode 186 is formed in the first opening 184a, and a heat treatment is performed after formation. The n-electrode 188 is formed in the second opening 184b, and a heat treatment is performed after formation. The n-electrode 188 can be fabricated following the fabrication of the p-electrode 186, or the p-electrode 186 can be fabricated following the fabrication of the n-electrode 188. The n-electrode 188 contacts the upper surface of the stack 175 of the n-type intermediate region 169 and the n-type contact layer 171, that is, contacts the n-type contact layer 171. The n-electrode 188 can have a stacked structure such as Ti / Au, Ti / Al / Ti / Au, Ti / Al / Ni / Au, V / Al / V / Au, or V / Al / Ni / Au. The p-electrode can contain, for example, materials such as Ni / Au, ITO.

[0097] By these processes, an example of the nitride device 110 is fabricated.

[0098] According to this fabrication method, the n-type intermediate region 169 having a monotonically changing Al composition X provides good electrical characteristics to the contact structure for supplying carriers to the active layer 168 through the nitride semiconductor region 166 for the n-type semiconductor layer 125.

[0099] The Al composition Y of the n-type contact layer 171 is equal to or less than the Al composition X in any area of the n-type intermediate region 169. Also, the Al composition Z of the nitride semiconductor region 166 for the n-type semiconductor layer 125 is equal to or greater than the Al composition X in any area of the n-type intermediate region 169.

[0100] (Example 1) The simulation related to the contact structure 111 will be described.

[0101] FIG. 8(a) is a drawing schematically showing an element structure (reference structure) having a contact structure of a direct contact structure. FIG. 8(b) is a drawing schematically showing a simulation model according to an experimental example. FIG. 9(a) is a drawing schematically showing a simulation model according to an experimental example. The simulation model according to the experimental example shown in FIG. 9(a) is different from the simulation model in FIG. 9(b) in that the n-type contact layer is GaN.

[0102] The element structure of the simulation model in FIG. 9(a) is different from the element structure shown in FIG. 8(a) in that a contact layer (n-GaN) and an intermediate layer with a gradient Al composition (n-type AlGaN, Al composition: 0% to 75% or 0% to 90%) are arranged between the n-electrode and the underlying n-type AlGaN (Al composition: 75% or 90%). The element structure of the simulation model in FIG. 8(b) is different from the element structure shown in FIG. 9(a) in that an intermediate layer with a constant Al composition (n-type AlGaN, Al composition: 0% to 70% or 0% to 80%) is arranged instead of the intermediate layer with a gradient Al composition (n-type AlGaN, Al composition: 0% to 75% or 0% to 90%). The intermediate layer with a gradient Al composition has a starting Al composition value at the interface of the underlying n-type AlGaN and a terminating Al composition value at the interface of the contact layer. The gradient Al composition of this intermediate layer linearly decreases from the starting Al composition value to the terminating Al composition value. In the element structure of the simulation model in FIG. 9(a), the n-electrode makes contact with the contact layer (n-GaN). This contact layer makes contact with the intermediate layer with a gradient Al composition (n-type AlGaN, Al composition: 0% to 75% or 0% to 90%). This intermediate layer makes contact with the underlying n-type AlGaN (Al composition: 75% or 90%).

[0103] The results shown subsequently are the voltage differences between the voltage required to pass a current of 100 A / cm2 between the n-electrode and the p-electrode of the element structure of each simulation model shown in FIGS. 8(b), 9(a), and 9(b), and the voltage required to pass a current of 100 A / cm2 between the n-electrode and the p-electrode of the element structure (reference structure) having the contact structure of the direct contact structure shown in FIG. 8(a). In the element structure (reference structure) having the contact structure of the direct contact structure shown in FIG. 8(a), the current is injected from the p-electrode and flows into the n-electrode through the p-type layer, the active layer, and the underlying n-type AlGaN. In the element structures of each simulation model shown in FIGS. 8(b), 9(a), and 9(b), the current is injected from the p-electrode and flows into the n-electrode through the p-type layer, the active layer, and the underlying n-type AlGaN, and further through the intermediate layer and the contact layer having a graded Al composition or a constant Al composition. Therefore, in the element structures of each simulation model shown in FIGS. 8(b), 9(a), and 9(b), due to the presence of the contact resistance at the interface between the underlying n-type AlGaN and the intermediate layer having a graded Al composition or a constant Al composition, the resistance in the intermediate layer having a graded Al composition or a constant Al composition, the contact resistance at the interface between the intermediate layer having a graded Al composition or a constant Al composition and the contact layer, and the resistance in the contact layer, the voltage required to pass a current of 100 A / cm 2 between the n-electrode and the p-electrode increases compared to the element structure (reference structure) having the contact structure of the direct contact structure shown in FIG. 8(a). This increase in voltage is the voltage difference shown as the calculation result of the simulation model. In both the reference structure and the element structure of the simulation model, the contact resistance between the n-electrode and the underlying n-type AlGaN, the contact resistance between the n-electrode and the contact layer, and the contact resistance between the p-electrode and the p-type layer are set to zero.

[0104] Figures 10(a) and 10(b) are graphs showing the calculation results of the simulation model in Fig. 9(a). The Al composition of the underlying n-type AlGaN is 75%. Figures 11(a) and 11(b) are graphs showing the calculation results of the simulation model in Fig. 8(b). The Al composition of the underlying n-type AlGaN is 75%. The simulations in Figs. 10(a) and 11(a) use a model in which the intermediate layer grows coherently with respect to the underlying n-type AlGaN. The simulations in Figs. 10(b) and 11(b) use a model in which the intermediate layer grows with complete relaxation (lattice relaxation rate of 100%) with respect to the underlying n-type AlGaN. In Figs. 10(a) and 10(b), the vertical axis of the graph indicates the final Al composition value of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the simulation model, the starting Al composition value is 75%. In Figs. 11(a) and 11(b), the vertical axis of the graph indicates the constant Al composition of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the graphs of Figs. 10(a) to 11(b), a plurality of solid lines are drawn together with numbers. The numbers represent voltage differences.

[0105] Comparing Figs. 10(a) and 10(b) with Figs. 11(a) and 11(b) respectively, the contact structure according to the embodiment in which the intermediate layer has a graded Al composition shows a low voltage rise in a wide Al composition range where the final Al composition of the graded Al composition intermediate layer is from zero. Specifically, in the result of Fig. 11(a), an area with a voltage of 0.5 volts or less does not occur. In the result of Fig. 11(b), an area with a voltage of 0.5 volts or less occurs only in a narrow Al composition range where the intermediate layer with a constant Al composition has a thin film thickness.

[0106] According to FIG. 10(a) showing a structure in which an intermediate layer with a graded Al composition grows coherently with respect to the underlying n-type AlGaN, in the structure where the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range where the terminal Al composition of the graded Al composition intermediate layer is from zero. By way of example and not limitation, in the range of a voltage rise of 3.0 volts or less, it is 15 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range from zero to 60%. In the range of a voltage rise of 0.5 volts or less, it is 30 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range from zero to 40%.

[0107] According to FIG. 10(b) showing a structure in which an intermediate layer with a graded Al composition grows completely relaxed with respect to the underlying n-type AlGaN, similarly, in the structure where the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range where the terminal Al composition of the graded Al composition intermediate layer is from zero. By way of example and not limitation, in the range of a voltage rise of 3.0 volts or less, it is 5 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range from zero to 45%. In the range of a voltage rise of 0.5 volts or less, it is 20 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range from zero to 20%.

[0108] FIGS. 12(a) and 12(b) show the voltage rise in the intermediate layer with a film thickness of 50 nm in the simulations of FIGS. 10(a) and 10(b), respectively. FIGS. 13(a) and 13(b) show the voltage rise in the intermediate layer with a film thickness of 50 nm in the simulations of FIGS. 11(a) and 11(b), respectively. In FIGS. 12(a) and 12(b), the vertical axis of the graph indicates the value of the voltage rise, and the horizontal axis indicates the terminal Al composition value of the graded Al composition intermediate layer. In FIGS. 13(a) and 13(b), the vertical axis of the graph indicates the value of the voltage rise, and the horizontal axis indicates a constant Al composition of the intermediate layer.

[0109] In FIGS. 12(a) and 12(b), the minimum values of the voltage rise are 0.014 volts and 0.015 volts, respectively, and are substantially constant in the range of low terminal Al composition values (40% or less in FIG. 12(a) and 20% or less in FIG. 12(b)). On the other hand, in FIGS. 13(a) and 13(b), the minimum values of the voltage rise are 0.788 volts and 0.767 volts, respectively. In the intermediate layer with a constant Al composition, the graph of the voltage rise has a convex-down shape.

[0110] FIGS. 14(a), 14(b), 14(c) and 14(d) are diagrams showing the carrier (electron) concentration in a contact structure including an inclined Al composition intermediate layer with a thickness of 10 nm, 20 nm, 30 nm and 50 nm, respectively, in the model of FIG. 10(a). The externally applied voltage is zero, and thus the current flowing between the n-electrode and the p-electrode is 0 A / cm 2 is. In any of the graphs, the terminal value of the Al composition is zero. In FIG. 14(a), electron depletion corresponding to about 1.3 eV in terms of energy occurs in the region of the inclined Al composition intermediate layer. In FIG. 14(b), electron depletion corresponding to about 0.8 eV in terms of energy occurs in the region of the inclined Al composition intermediate layer. In FIG. 14(c), slight electron depletion occurs in the region of the inclined Al composition intermediate layer. In FIG. 14(d), substantially no electron depletion occurs in the region of the inclined Al composition intermediate layer.

[0111] Figs. 15(a) and 15(b) are graphs showing the calculation results of the simulation model in Fig. 9(a). The Al composition of the underlying n-type AlGaN is 90%. Figs. 16(a) and 16(b) are graphs showing the calculation results of the simulation model in Fig. 8(b). The Al composition of the underlying n-type AlGaN is 90%. The simulations in Figs. 15(a) and 16(a) use a model in which the intermediate layer grows coherently with respect to the underlying n-type AlGaN. The simulations in Figs. 15(b) and 16(b) use a model in which the intermediate layer grows with complete relaxation (lattice relaxation rate of 100%) with respect to the underlying n-type AlGaN. In Figs. 15(a) and 15(b), the vertical axis of the graph indicates the final Al composition value of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the simulation model, the starting Al composition value is 90%. In Figs. 16(a) and 16(b), the vertical axis of the graph indicates a constant Al composition of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the graphs of Figs. 15(a) to 16(b), a plurality of solid lines are drawn together with numbers. The numbers represent voltage differences.

[0112] Comparing Figs. 15(a) and 15(b) with Figs. 16(a) and 16(b) respectively, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range starting from zero Al composition. Specifically, in the results of Fig. 16(a), no area with a voltage rise of 2.5 volts or less occurs. In the results of Fig. 16(b), an area with a voltage of 2.5 volts or less occurs only in a narrow Al composition range where the intermediate layer with a constant Al composition has a thin film thickness.

[0113] According to FIG. 15(a) showing a structure in which an intermediate layer with a graded Al composition grows coherently with respect to the underlying n-type AlGaN, in the structure where the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range where the terminal Al composition of the graded Al composition intermediate layer is zero. By way of non-limiting example, in the range of a voltage rise of 3.0 volts or less, it is 30 nm or more with respect to the film thickness of the intermediate layer, and the terminal value of the Al composition of the intermediate layer is in the range of 0% or more and 55% or less. In the range of a voltage rise of 1.0 volt or less, it is 35 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of 0 or more and 45% or less.

[0114] According to FIG. 15(b) showing a structure in which an intermediate layer with a graded Al composition grows completely relaxed with respect to the underlying n-type AlGaN, similarly, in the structure where the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range where the terminal Al composition of the graded Al composition intermediate layer is zero. By way of non-limiting example, in the range of a voltage rise of 3.0 volts or less, it is 10 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of 0% or more and 30% or less. In the range of a voltage rise of 1.0 volt or less, it is 25 nm or more with respect to the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of 0 or more and 20% or less.

[0115] The carrier concentration (not shown) of the contact structure (coherent growth) at several film thicknesses on the graph shown in FIG. 10(a) was examined. In the contact structure including an intermediate layer with a graded Al composition having a thickness of 20 nm and a terminal Al composition of 0%, in the region of the intermediate layer with the graded Al composition, a decrease in the electron concentration corresponding to a value exceeding 0.8 eV in energy conversion occurs. In the contact structure including an intermediate layer with a graded Al composition having a thickness of 20 nm and a terminal Al composition of 20%, in the region of the intermediate layer with the graded Al composition, a slight decrease in the electron concentration corresponding to about 0.4 eV in energy conversion occurs.

[0116] The carrier concentrations (not shown) of the contact structures (complete relaxation growth) at several film thicknesses on the graph shown in Fig. 10(b) were examined. In the contact structure including the intermediate layer with a thickness of 20 nm and a terminal Al composition of 0%, in the region of the intermediate layer with the inclined Al composition, there is a change in the electron concentration corresponding to about 0.2 eV in terms of energy, and there is substantially no decrease in the electron concentration (almost no electron depletion). In the contact structure including the intermediate layer with a thickness of 20 nm and a terminal Al composition of 20%, in the region of the intermediate layer with the inclined Al composition, a slight electron depletion corresponding to about 0.4 eV in terms of energy occurs.

[0117] Figs. 17(a) and 17(b) show the voltage rise in the intermediate layer with a film thickness of 50 nm in the simulations of Figs. 15(a) and 15(b), respectively. Figs. 17(c) and 17(d) show the voltage rise in the intermediate layer with a film thickness of 50 nm in the simulations of Figs. 16(a) and 16(b), respectively. In Figs. 17(a) and 17(b), the vertical axis of the graph indicates the value of the voltage rise, and the horizontal axis indicates the terminal Al composition value of the inclined Al composition intermediate layer. In Figs. 17(c) and 17(d), the vertical axis of the graph indicates the value of the voltage rise, and the horizontal axis indicates the constant Al composition of the intermediate layer.

[0118] In Figs. 17(a) and 17(b), the minimum values of the voltage rise are both 0 volts, respectively, and are almost constant in the range of low terminal Al composition values (40% or less in Fig. 17(a) and 20% or less in Fig. 17(b)). On the other hand, in Figs. 17(c) and 17(d), the minimum values of the voltage rise are 2.70 volts and 2.52 volts, respectively. In the intermediate layer with a constant Al composition, the graph of the voltage rise has a convex downward shape.

[0119] Figure 9(b) is a drawing schematically showing a simulation model according to an experimental example. The element structure of the simulation model in Figure 9(b) is different from the element structure shown in Figure 9(a) in that the contact layer is AlGaN. In response to this replacement, the intermediate layer with a graded Al composition (n-type AlGaN) has an Al composition range of 40% to 75%. The graded Al composition of this intermediate layer linearly decreases from the starting Al composition value to the ending Al composition value. The Al composition of the contact layer is 40%. In the element structure of the simulation model in Figure 9(b), the n-electrode makes contact with the contact layer (n-AlGaN). This contact layer makes contact with the intermediate layer with a graded Al composition. This intermediate layer makes contact with the underlying n-type AlGaN (Al composition: 75%).

[0120] Figure 18 is a graph showing the calculation results of the simulation model in Figure 9(b). The simulation in Figure 18 uses a model in which the intermediate layer and the contact layer are coherently grown with respect to the underlying n-type AlGaN. In Figure 18, the vertical axis of the graph indicates the ending value of the Al composition of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. A plurality of solid lines are drawn together with numbers in the graph of Figure 18. The numbers represent the voltage difference. In the simulation model, the starting Al composition value is 75%. The Al composition of the underlying n-type AlGaN is 75%.

[0121] According to the graph of FIG. 18 showing a structure in which an intermediate layer with a graded Al composition grows coherently with respect to the underlying n-type AlGaN, in the structure where the contact layer is n-AlGaN, the contact structure according to the example shows a low voltage rise in a wide Al composition range from 40% Al composition. By way of example and not limitation, the range of voltage rise of 1 volt or less is 3 nm or more with respect to the film thickness of the intermediate layer. Also, the end value of the Al composition of the intermediate layer is in the range of 40% or more and 60% or less. When the thickness of the intermediate layer with a graded composition is 15 nm or more, the voltage rise is almost zero. As a reference value, in a structure where an AlGaN contact layer with an Al composition of 40% grows coherently with an underlying n-type AlGaN with an Al composition of 75% and forms a direct junction, a voltage rise of about 1.3 volts occurs. By way of example and not limitation, in the structure where the contact layer is n-type AlGaN, the end value of the Al composition of the intermediate layer can be the same value as the Al composition value of the contact layer, or can be a value larger than the Al composition value of the contact layer. Also, the starting value of the Al composition of the intermediate layer can be the same value as the Al composition value of the underlying n-type AlGaN, or can be an Al composition value smaller than the Al composition value of the underlying n-type AlGaN.

[0122] In the structure of the simulation model of FIG. 9(b), the emission wavelength of the active layer is, for example, 280 nm. The n-electrode uses a structure in which Al, which exhibits a high reflectivity to deep ultraviolet light, directly contacts the contact layer. Since the Al composition of the contact layer is 40%, the contact layer is transparent to light with a wavelength of 280 nm. A part of the deep ultraviolet light emitted from the active layer passes through the contact layer and is reflected by the n-electrode. This reflected light is taken out of the device. This structure shows a high external quantum efficiency.

[0123] The results shown in FIGS. 10, 12, 14, 15, 17(a), 17(b), and 18 are substantially the same results if the discontinuity of the Al composition in the intermediate layer is small enough even when the Al composition of the graded Al composition intermediate layer in the simulation models shown in FIGS. 9(a) and 9(b) changes in a stepped manner rather than linearly.

[0124] (Example 2) Explain the measurement results regarding the contact structure. FIG. 19 is a drawing showing a device structure for an experiment related to the contact structure.

[0125] Both FIG. 19(a) and FIG. 19(b) show the epi-structure of the contact structure and the contact structure for electrical measurement. The epi-structure is fabricated by the following procedure. By MOVPE method, on an AlN template (omitted in the figure), an underlying n-type AlGaN, an inclined Al-composition intermediate layer (n-type AlGaN), and an n-GaN contact layer are continuously grown in sequence. The Al composition of the underlying n-type AlGaN is 75%, and the film thickness is 500 nm. The starting Al composition of the intermediate layer with an inclined Al composition is 75% (fixed), and three types of epi-structures were fabricated using 0%, 20%, and 40% as the terminal Al compositions. Also, two types of epi-structures were fabricated using 20 nm and 50 nm as the film thickness of the intermediate layer with an inclined Al composition. In any of the epi-structures, the film thickness of the contact layer is 200 nm. The reference epi-structure, as shown in FIG. 19(b), does not include an inclined Al-composition intermediate layer and includes an n-GaN contact layer directly grown on the underlying n-type AlGaN.

[0126] As shown in FIG. 19(a) and FIG. 19(b), electrodes are formed on the surface of the epi-structure using the vacuum evaporation method. On the epi-structure, a metal film for an electrode of Ti / Al / Ni / Au (thickness: 30 / 100 / 70 / 150 nm) is deposited. After depositing these metal films, N 2 In an atmosphere, heat treatment was performed at 800 degrees Celsius for 2 minutes.

[0127] To evaluate the contact resistance between the electrode and the contact layer, the electrode includes a circular electrode (inner electrode) and an annular electrode (outer electrode) surrounding it. The inner electrode and the outer electrode are formed such that the distance between them is at several values in the range of 2 to 48 μm. Electrical measurements were performed using the cTLM (circular transfer length method: cTLM) method.

[0128] Figures 19(c) and 19(d) show contact structures for electrical measurement. In an electrode epi-structure including an inner electrode and an outer electrode, a groove reaching the underlying n-type AlGaN is formed in the area between the inner electrode and the outer electrode using dry etching.

[0129] Figures 20(a) and 20(b) show the results of electrical measurement of the contact structure shown in Fig. 19(b). Fig. 20(a) shows the current-voltage (I-V) characteristics between two terminals of the inner electrode and the outer electrode of the contact structure shown in Fig. 19(b). Since the I-V curve is close to a straight line, it can be seen that the electrode and the contact layer form a good ohmic contact. Fig. 20(b) is a graph plotting the resistance value between two terminals obtained from Fig. 20(a) against the electrode spacing. The black dots (Experiment) in the graph indicate the measured values, and the dashed line (Fitting) indicates the fitting curve obtained by least-squares approximation from the experimental values using the following equation (1). Equation (1): R = Rsh / 2π{ln(r1 / r2)+Lt(1 / r1 + 1 / r2)} R: Resistance value between two terminals r1: Radius of the inner electrode r2: Radius of the outer electrode Rsh: Sheet resistance of the semiconductor layer Lt: Transmission length ln: Natural logarithm Rsh and Lt are fitting parameters. The characteristic contact resistance ρc between the electrode and the contact layer is obtained by the following equation (2). Equation (2): ρc = Rsh × Lt 2 The characteristic contact resistance ρc derived by fitting is ρc = 2.2×10 -4 Ω·cm 2 This shows that the contact resistance between the electrode and the contact layer is low by this experiment.

[0130] Figures 21(a) and 21(b) show the results of electrical measurements of the contact structure shown in Fig. 19(d). Fig. 21(a) shows the I-V characteristics between the two terminals of the inner electrode and the outer electrode of the contact structure shown in Fig. 19(d). Fig. 21(b) is a graph plotting the resistance value between the two terminals obtained from Fig. 21(a) against the electrode spacing. The I-V characteristics in Fig. 21(a) show rectification. Comparing this with the linear I-V characteristics shown in Fig. 20(a), it is presumed that this rectification characteristic occurs at the interface between the contact layer and the underlying n-type AlGaN. The dashed line shown in Fig. 21(b) was calculated using Equation (1). The resistance value (vertical axis) shown in Fig. 21(b) is the resistance value at a two-terminal current of 10 mA. The contact resistance derived from this graph using Equation (2) is ρc = 6.9×10 -2 Ω·cm 2 This is the case. It is presumed that this characteristic contact resistance ρc is the sum of the contact resistance at the electrode-contact layer interface, the resistance of the contact layer, and the contact resistance at the contact layer-underlying n-type AlGaN interface.

[0131] As already explained, the contact resistance at the electrode-contact layer interface is small. Also, the resistance of the contact layer is small. Therefore, the magnitude of the characteristic contact resistance ρc indicates that the contact resistance at the contact layer-underlying n-type AlGaN interface is large. The fact that the contact resistance at the contact layer-underlying n-type AlGaN interface is large means that the voltage rise at the contact layer-underlying n-type AlGaN interface is large.

[0132] Figures 22(a) and 22(b) show the results of electrical measurements of the contact structure shown in Fig. 19(a). In this contact structure, the film thickness of the inclined Al composition intermediate layer is 50 nm and the terminal Al composition is 0%. Fig. 22(a) shows the I-V characteristics between the two terminals of the inner electrode and the outer electrode of the contact structure shown in Fig. 19(a). Since the I-V curve is linear, the I-V characteristics in Fig. 22(a) show a good ohmic contact. Fig. 21(b) is a graph plotting the resistance value between the two terminals obtained from Fig. 22(a) against the electrode spacing. The dashed line was derived by fitting. The characteristic contact resistance ρc by fitting is ρc = 2.6×10-4 Ω·cm 2 which indicates that the contact resistance between the electrode and the contact layer is low.

[0133] Figures 23(a) and 23(b) show the results of electrical measurements of the contact structure shown in Figure 19(c). In this contact structure, the film thickness of the inclined Al composition intermediate layer is 50 nm, and the terminal Al composition is 0%. Figure 23(a) shows the I-V characteristics between two terminals of the inner electrode and the outer electrode of the contact structure shown in Figure 19(c). Since the I-V curve is linear, the I-V characteristics in Figure 23(a) do not show rectification. Figure 23(b) is a graph plotting the resistance value between two terminals obtained from Figure 23(a) against the electrode spacing. The broken line was derived by fitting. The characteristic contact resistance ρc by fitting is ρc = 2.9×10 -4 Ω·cm 2 is. This characteristic contact resistance ρc is presumed to be the sum of the contact resistance at the electrode-contact layer interface, the resistance of the contact layer, the contact resistance at the interface between the contact layer and the inclined Al composition intermediate layer, the resistance of the inclined Al composition intermediate layer, and the contact resistance at the interface between the inclined Al composition intermediate layer and the underlying n-type AlGaN. Since the contact resistance at the electrode-contact layer interface shown in Figure 22(b) is very close to the sum of the contact resistance at the electrode-contact layer interface shown in Figure 23(b) and the contact resistances of each layer and each interface of the contact layer-underlying n-type AlGaN, the contact resistances of each layer and each interface of the contact layer-underlying n-type AlGaN are small. That is, when this inclined Al composition intermediate layer is introduced, the voltage rise that occurs when current flows from the contact layer to the underlying n-type AlGaN is very small.

[0134] FIG. 24 is a graph showing the dependence of the specific contact resistance on the Al composition of the intermediate layer with a gradient Al composition for several film thicknesses. The vertical axis represents the specific contact resistance, and the horizontal axis represents the Al composition of the intermediate layer with a gradient Al composition. The specific contact resistance refers to the sum of the contact resistance at the layer interface of the electrode-contact and the contact resistances of each layer and each interface of the contact layer-substrate n-type AlGaN. Any contact structure having the characteristics shown in the graph has substantially the same contact resistance at the interface of the electrode-contact layer, the resistance of the contact layer, and the resistance of the intermediate layer with a gradient Al composition. Therefore, the difference in the specific contact resistance in the graph is considered to reflect the difference in the sum of the contact resistance at the interface of the contact layer-intermediate layer with a gradient Al composition and the contact resistance at the interface of the intermediate layer with a gradient Al composition-substrate n-type AlGaN. The small contact resistance at these interfaces means that the voltage rise that occurs when current flows from the contact layer to the substrate n-type AlGaN is small.

[0135] According to the results of FIG. 24, the following is shown. First, a thicker film thickness (50 nm) can contribute to the reduction of the specific contact resistance compared to a thinner film thickness (20 nm) of the intermediate layer with a gradient Al composition. Next, when the film thickness is thin (20 nm), the Al composition dependence of the specific contact resistance becomes large, and the minimum value is obtained when the terminal Al composition of the intermediate layer with a gradient Al composition is 20%. Also, when the film thickness is thick (50 nm), the Al composition dependence of the specific contact resistance becomes small, and the minimum value is obtained when the terminal Al composition of the intermediate layer with a gradient Al composition is 20%. These tendencies are the same as the results derived by simulation in the structure in which the intermediate layer with a gradient Al composition grows coherently with respect to the substrate n-type AlGaN shown in FIG. 10(a).

[0136] According to the experiment of Example 2, the results of the simulation in Example 1 are supported.

[0137] (Example 3) FIG. 25 is a drawing showing the measurement results of X-ray diffraction reciprocal lattice space mapping (XRD-RSM) of the epi structure (excluding electrodes) shown in FIG. 19(a). The epi structure includes an inclined Al composition intermediate layer with a starting Al composition of 75%, a terminal Al composition of 20%, and a film thickness of 50 nm. The XRD-RSM measurement was performed at (10-15) diffraction. From this mapping measurement, the in-plane lattice constant and the lattice constant in the direction perpendicular to the in-plane direction of each semiconductor layer in the epi structure are derived. The peak qc and the peak qm corresponding to each semiconductor layer correspond to the reciprocal of the lattice constant in the c-axis direction and the reciprocal of the lattice constant in the m-axis direction, respectively. For example, the AlN and AlGaN buffer layers are omitted in FIG. 19(a), and in the epi structure, the underlying n-type AlGaN is grown on these as a base. Since the peak qc values of the AlN and AlGaN buffer layers are larger than the peak qc value of the underlying n-type AlGaN, the lattice constant in the c-axis direction of the AlN homoepitaxial layer and the AlGaN buffer layer is smaller than the lattice constant in the c-axis direction of the underlying n-type AlGaN. On the other hand, since all of the AlN, AlGaN buffer layer, and underlying n-AlGaN have substantially the same peak qm value, the in-plane lattice constants of these layers are substantially equal. This indicates that the AlN, AlGaN buffer layer, and underlying n-type AlGaN are growing coherently.

[0138] In FIG. 25, qm of the peak corresponding to the inclined Al composition intermediate layer maintains a substantially constant value and is substantially the same value as qm of the peak corresponding to the underlying n-type AlGaN. This indicates that the inclined Al composition intermediate layer is growing coherently with the underlying n-type AlGaN. On the other hand, the peak corresponding to the inclined Al composition intermediate layer is shown as a measured value broadened in the qc direction at the same position as the peak qm value of the underlying n-type AlGaN. This reflects that the lattice constant in the c-axis direction is continuously changing in accordance with the continuous change of the Al composition of the inclined Al composition intermediate layer from 75% to 20%.

[0139] The absolute value of qm of the peak corresponding to the contact layer (n-GaN) is smaller than the absolute values of qm of AlN, the AlGaN buffer layer, the underlying n-type AlGaN, and the intermediate layer with a graded Al composition. This indicates that the in-plane lattice constant of the contact layer (n-GaN) is larger than that of the other semiconductor layers, and the contact layer (n-GaN) is lattice-relaxed. In Fig. 25, the lattice relaxation rate is estimated to be about 80%.

[0140] (Example 4) Figs. 26(a) to 26(f) are drawings showing differential interference microscope images of the surface of the epi-structure shown in Fig. 19(a). Specifically, Figs. 26(a) to 26(c) show the surface morphology of a contact structure having a graded Al composition intermediate layer with a thickness of 20 nm, and Figs. 26(d) to 26(f) show the surface morphology of a contact structure having a graded Al composition intermediate layer with a thickness of 50 nm. Figs. 26(a) and 26(d) show the surface morphology of a contact structure having a graded Al composition intermediate layer with starting and terminal Al compositions of 75% and 0%, respectively. Figs. 26(b) and 26(e) show the surface morphology of a contact structure having a graded Al composition intermediate layer with starting and terminal Al compositions of 75% and 20%, respectively. Figs. 26(c) and 26(f) show the surface morphology of a contact structure having a graded Al composition intermediate layer with starting and terminal Al compositions of 75% and 40%, respectively.

[0141] The surface morphologies of Figs. 26(b), 26(c), 26(e), and 26(f) are flatter than those of Figs. 26(a) and 26(d). According to this, it is presumed that the lattice relaxation of the graded Al composition intermediate layer is suppressed in the growth of AlGaN with an Al composition of 20% or more. Good surface flatness of the contact layer is preferable for electrode formation thereon and other processes. Therefore, it is desirable that the terminal Al composition value of the graded Al composition intermediate layer be 20% or more, which can provide good surface flatness.

[0142] Figure 27 is a drawing showing the I-V characteristics of a deep ultraviolet light-emitting diode. The dashed line "Reference" shows the characteristics of the structure shown in Fig. 8(a), and the solid line "Novel" shows the structure shown in Fig. 9(a), that is, in the structure of Fig. 8(a), a selective growth stack including an n-type AlGaN intermediate layer with a gradient Al composition and an n-type GaN contact layer is provided between the n-electrode and the underlying n-type AlGaN. The starting Al composition of the n-type AlGaN intermediate layer with a gradient Al composition is 75%, and the terminal Al composition is 20%. The thickness of the n-type AlGaN intermediate layer with a gradient Al composition is 50 nm. The Al composition of the underlying n-type AlGaN is 75%. The contact structure using the contact layer and the intermediate layer with a gradient Al composition has a low resistance from the n-electrode to the underlying n-type AlGaN. Comparing "Reference" with "Novel", at 2 100 A / cm

[0143] (Example 5) The technical background related to the contact structure will be described. The following technical matters are required for the Al composition of the underlying n-type AlGaN of the deep ultraviolet light-emitting diode.

[0144] First, the deep ultraviolet light from the active layer should be transmissible through the underlying n-type AlGaN. Specifically, when the emission wavelength is 285 nm, it is required that the underlying n-type AlGaN has an Al composition of 40% or more. When the emission wavelength is 265 nm, the underlying n-type AlGaN is required to have an Al composition of 60% or more. When the emission wavelength is 220 nm, the underlying n-type AlGaN is required to have an Al composition of 90% or more.

[0145] Second, the underlying n-type AlGaN should be grown coherently with respect to the underlying semiconductor. When the underlying n-type AlGaN is lattice relaxed and misfit dislocations occur, the crystal quality of the active layer deteriorates and the luminous efficiency decreases. In order to suppress the lattice relaxation of the underlying n-type AlGaN, the underlying n-type AlGaN is grown coherently with respect to the underlying AlN template or AlN substrate. For this purpose, typically, the Al composition of the underlying n-type AlGaN is desirably 50% or more, and more desirably 60% or more. From the viewpoint of coherent growth on AlN, the underlying n-type AlGaN preferably has a larger Al composition. When the AlN template contains compressive strain, the range of the Al composition of the underlying n-type AlGaN that can be grown coherently on the AlN template is narrower, that is, limited to a higher Al composition, than when the AlN template contains no strain or tensile strain.

[0146] Thirdly, electrons are drifted and spread in the in-plane direction in the underlying n-type AlGaN. The underlying n-type AlGaN is required to have high conductivity in order to spread electrons from the electrode in the plane. When the Al composition of the underlying n-type AlGaN exceeds 80%, its conductivity rapidly decreases. The Al composition of the underlying n-type AlGaN is desirably 80% or less. From the viewpoint of spreading electrons in the plane, the Al composition of the underlying n-AlGaN is preferably low.

[0147] Fourthly, the junction between the underlying n-type AlGaN and the n-electrode has a low contact resistance showing ohmic properties. When the contact between the underlying n-type AlGaN and the n-electrode shows a high contact resistance or the contact shows Schottky characteristics, the voltage drop at this contact increases, causing a decrease in the wall plug efficiency and an increase in heat generation. When the Al composition of the underlying n-type AlGaN is high, the contact resistance becomes high and it becomes difficult to form an ohmic contact. Therefore, the Al composition of the underlying n-type AlGaN is desirably 60% or less. From the viewpoint of good contact characteristics, the Al composition of the underlying n-type AlGaN is preferably low.

[0148] The Al composition of the underlying n-type AlGaN that simultaneously satisfies the above Item 2 and Item 4 is limited to a very narrow range. Therefore, it is difficult to form an underlying n-type AlGaN that can achieve a low contact resistance with a low n-electrode while suppressing a decrease in the light emission efficiency due to a decrease in the crystal quality of the active layer. In addition, in a device with a short emission wavelength, Item 1 imposes a more stringent requirement on the Al composition of the underlying n-type AlGaN than Item 2. In this case, Item 1 becomes related to the contact characteristics.

[0149] The deep ultraviolet light emitting diode shown in FIG. 27 includes a template layer 120 composed of AlN and an n-type semiconductor layer 125 composed of AlGaN. The full width at half maximum (XRC-FWHM) of the (0002) rocking curve of the template layer 120 made of AlN evaluated by X-ray diffraction measurement is 29 arcsec, and the (10-12) XRC-FWHM is 262 arcsec. The (0002) XRC-FWHM of the n-type semiconductor layer 125 made of AlGaN is 49 arcsec, and the (10-12) XRC-FWHM is 251 arcsec.

[0150] A typical form in this embodiment is shown below.

[0151] A first aspect according to the embodiment is a semiconductor light-emitting device, the semiconductor light-emitting device comprising: an n-type semiconductor layer including a group III nitride semiconductor containing aluminum as a group III constituent element; a p-type semiconductor layer provided on the n-type semiconductor layer; an active layer provided on the n-type semiconductor layer and including a group III nitride semiconductor capable of generating deep ultraviolet light; an n-type contact layer provided on the n-type semiconductor layer and including a group III nitride semiconductor containing gallium as a group III constituent element; an n-type intermediate region provided on the n-type semiconductor layer and including a group III nitride semiconductor containing gallium and aluminum as group III constituent elements; and an n-electrode containing a metal, wherein the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, an Al composition X of the n-type intermediate region is equal to or greater than an Al composition Y of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or less than an Al composition Z of the n-type semiconductor layer, the Al composition X of the n-type intermediate region monotonically changes in a direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a gradient composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a part of the n-type intermediate region, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are arranged in order in a direction of an axis from the n-type intermediate region to the n-electrode.

[0152] According to the semiconductor light-emitting device, the n-type intermediate region having the Al composition X that monotonically changes in a direction from the n-type semiconductor layer to the n-type contact layer imparts good electrical characteristics to a contact structure for providing carriers to the active layer through the n-type semiconductor layer.

[0153] The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. Also, the Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

[0154] In the semiconductor light-emitting device according to the first embodiment, the n-type intermediate region has at least one of a gradient composition and a stepped composition in which the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer in at least a part of the n-type intermediate region.

[0155] According to the semiconductor light-emitting device, the monotonically changing Al composition in the n-type intermediate region is provided by the gradient composition and the stepped composition.

[0156] In the semiconductor light-emitting device according to the first embodiment, the n-type intermediate region contains Al X Ga 1-X N, and the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer over the entire n-type intermediate region.

[0157] According to the semiconductor light-emitting device, the n-type intermediate region has an interface related to the n-type semiconductor layer and an interface related to the n-type contact layer, and the Al composition X decreases from one interface to the other interface.

[0158] In the semiconductor light-emitting device according to the first embodiment, the n-type contact layer contains any one of n-type GaN, n-type AlGaN, or n-type InAlGaN.

[0159] According to the semiconductor light-emitting device, an n-type GaN, n-type AlGaN, or n-type InAlGaN of a gallium nitride-based semiconductor can be provided in the n-type contact layer.

[0160] In the semiconductor light-emitting device according to the first embodiment, the in-plane lattice constant of the n-type contact layer is equal to or larger than the in-plane lattice constant of the n-type intermediate region.

[0161] According to the semiconductor light-emitting device, the n-type contact layer is provided with a group-III nitride that is lattice-relaxed with respect to the n-type intermediate region. The n-type contact layer that is lattice-relaxed with respect to the n-type intermediate region can reduce the electrical resistance at the interface between the n-type contact layer and the n-type intermediate region.

[0162] In the semiconductor light-emitting device according to the first aspect, the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer.

[0163] According to the semiconductor light-emitting device, the n-type contact layer can be provided with a group-III nitride having a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer.

[0164] In the semiconductor light-emitting device according to the first aspect, the group-III nitride semiconductor of the n-type semiconductor layer contains either AlN or AlGaN.

[0165] According to the semiconductor light-emitting device, AlN or AlGaN can be used as the base for the n-type contact layer and the n-type intermediate region.

[0166] In the semiconductor light-emitting device according to the first aspect, the wavelength of the deep ultraviolet light is in the range of 285 nm or less.

[0167] According to the semiconductor light-emitting device, for deep ultraviolet light with a wavelength of 285 nm or less, an active layer with a high Al composition is required, and the current path to the active layer is also formed of a group-III nitride with a high Al composition. A good n-side contact structure for the group-III nitride with a high Al composition is provided by the combination of the n-type intermediate region, the n-type contact layer, and the n-electrode.

[0168] The semiconductor light-emitting device according to the first aspect further includes a substrate that provides a III-nitride main surface containing aluminum as a group-III constituent element, and the substrate mounts the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region, and the substrate includes a substrate containing a III-nitride containing aluminum as a group-III constituent element, or a support made of a material different from the III-nitride, and an AlN template layer or an AlGaN template layer provided on the main surface of the support.

[0169] According to the semiconductor light-emitting device, an active layer is provided on the substrate as described above.

[0170] In the semiconductor light-emitting device according to the first aspect, the difference between the Al composition Y of the n-type contact layer and the Al composition X of the n-type intermediate region is 0.3 or less at the interface between the n-type contact layer and the n-type intermediate region, and the difference between the Al composition X of the n-type intermediate region and the Al composition Z of the n-type semiconductor layer can be 0.3 or less at the interface between the n-type intermediate region and the n-type semiconductor layer.

[0171] According to the semiconductor light-emitting device, the above-described Al composition difference can provide good electrical characteristics to the semiconductor light-emitting device.

[0172] A second embodiment according to the present invention is a method for manufacturing a semiconductor light-emitting device, the semiconductor light-emitting device including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer including a group-III nitride semiconductor capable of generating deep ultraviolet light, the method including growing, on a substrate, a first group-III nitride semiconductor layer for an n-type intermediate region including gallium and aluminum as group-III constituent elements; after growing the first group-III nitride semiconductor layer, growing, on the substrate, a second group-III nitride semiconductor layer for an n-type contact layer including gallium as a group-III constituent element; and after growing the second group-III nitride semiconductor layer, forming an n-electrode including a metal on the substrate, the n-type semiconductor layer including aluminum as a group-III constituent element, the n-type intermediate region being provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer being provided between the n-type intermediate region and the n-electrode, an Al composition X of the n-type intermediate region being equal to or greater than an Al composition Y of the n-type contact layer, the Al composition Y of the n-type contact layer being equal to or greater than zero, the Al composition X of the n-type intermediate region being equal to or less than an Al composition Z of the n-type semiconductor layer, the Al composition X of the n-type intermediate region changing monotonically in a direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region having at least one of a gradient composition and a stepped composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a part of the n-type intermediate region, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer being arranged in order on the substrate in a direction of an axis extending from the n-type intermediate region to the n-electrode.

[0173] According to this manufacturing method, the n-type intermediate region having an Al composition X that changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer provides good electrical characteristics to the contact structure for supplying carriers to the active layer through the n-type semiconductor layer. The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. Also, the Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

[0174] In the method for manufacturing a semiconductor light-emitting device according to the second embodiment, the n-type intermediate region contains Al X Ga 1-X N, and the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer over the entire n-type intermediate region.

[0175] According to this manufacturing method, the n-type intermediate region has an interface related to the n-type semiconductor layer and an interface related to the n-type contact layer, and the Al composition X decreases from one of these interfaces to the other interface.

[0176] In the method for manufacturing a semiconductor light-emitting device according to the second embodiment, the in-plane lattice constant of the n-type contact layer is equal to or larger than the in-plane lattice constant of the n-type intermediate region.

[0177] According to this manufacturing method, a group-III nitride that is lattice-relaxed with respect to the n-type intermediate region can be provided in the n-type contact layer.

[0178] In the method for manufacturing a semiconductor light-emitting device according to the second embodiment, the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer.

[0179] According to this manufacturing method, a group-III nitride having a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer can be provided in the n-type contact layer.

[0180] In the method for manufacturing a semiconductor light-emitting device according to the second embodiment, the n-type contact layer contains any one of n-type GaN, n-type AlGaN, or n-type InAlGaN.

[0181] According to this manufacturing method, n-type GaN, n-type AlGaN, or n-type InAlGaN, which are nitride-based semiconductors, can be provided in the n-type contact layer.

[0182] In the method of manufacturing a semiconductor light-emitting device according to the second embodiment, the n-type intermediate region has a gradient composition and a stepped structure in which the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer in at least a part of the n-type intermediate region.

[0183] According to the manufacturing method, the monotonically changing Al composition in the n-type intermediate region is provided by the gradient composition and the stepped structure.

[0184] In the method of manufacturing a semiconductor light-emitting device according to the second embodiment, the wavelength of the deep ultraviolet light is in the range of 285 nm or less.

[0185] According to the manufacturing method, for deep ultraviolet light with a wavelength of 285 nm or less, an active layer with a high Al composition is required, and the current path to the active layer is also formed of group III nitrides with a high Al composition. A good n-side contact structure to the group III nitrides with a high Al composition is provided by the combination of the n-type intermediate region, the n-type contact layer, and the n-electrode.

[0186] In the method of manufacturing a semiconductor light-emitting device according to the second embodiment, the substrate provides a main surface of a group III nitride containing aluminum as a group III constituent element, and the substrate mounts the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region. The substrate includes a substrate containing a group III nitride containing aluminum as a group III constituent element, or a support made of a material different from the group III nitride, and a template layer of AlN or a template layer of AlGaN provided on the main surface of the support.

[0187] According to the manufacturing method, an active layer is provided on the substrate as described above.

[0188] The third aspect according to the embodiment is a contact structure, and the contact structure is a contact structure for a group-III nitride semiconductor device, and includes a substrate providing a group-III nitride main surface containing aluminum as a group-III constituent element, a semiconductor region in contact with the group-III nitride main surface and including one or more group-III nitride semiconductor layers, an n-type semiconductor layer of a group-III nitride semiconductor in contact with the semiconductor region, an n-type contact layer of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium as a group-III constituent element, an n-type intermediate region of a group-III nitride semiconductor provided on the n-type semiconductor layer and containing gallium and aluminum as group-III constituent elements, and an n-electrode containing a metal. The group-III nitride semiconductor of the n-type semiconductor layer contains aluminum as a group-III constituent element. The n-type semiconductor layer is provided between the substrate and the n-type intermediate region. The n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer. The n-type contact layer is provided between the n-type intermediate region and the n-electrode. The Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer. The Al composition Y of the n-type contact layer is equal to or greater than zero. The Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer. The Al composition X of the n-type intermediate region monotonically changes in the direction from the n-type semiconductor layer to the n-type contact layer. The n-type intermediate region has at least one of a gradient composition and a step composition in which the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer in at least a part of the n-type intermediate region.

[0189] According to the contact structure, the n-type intermediate region having the Al composition X that monotonically changes in the direction from the n-type semiconductor layer to the n-electrode gives good electrical characteristics to the contact structure for providing carriers to the n-type semiconductor layer. In the contact structure, the n-type intermediate region, the n-type contact layer, and the n-electrode are arranged in this order. The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. Also, the Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

[0190] The contact structure according to the third embodiment further includes a p-type semiconductor layer provided on the substrate and an active layer including a group III nitride semiconductor provided on the substrate and capable of generating deep ultraviolet light, and the substrate, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are arranged in order in the direction of the axis extending from the n-type contact layer to the n-electrode.

[0191] According to the contact structure, good electrical characteristics are given to a semiconductor device having an n-type semiconductor layer closer to the substrate than the p-type semiconductor layer. In the contact structure, the n-type intermediate region, the n-type contact layer, and the n-electrode are arranged in this order.

[0192] In the contact structure according to the third embodiment, the n-type semiconductor layer has at least one of a gradient composition and a staircase structure that monotonically changes in the direction from the substrate to the n-type contact layer.

[0193] According to the contact structure, the n-type semiconductor layer can have a monotonically changing Al composition, and the monotonically changing Al composition is provided by a gradient composition and a staircase structure having an Al composition below the maximum value of the Al composition X.

[0194] In the contact structure according to the third embodiment, the n-type semiconductor layer has a single Al composition.

[0195] According to the contact structure, the n-type semiconductor layer can have a single Al composition. The technical meaning of "single Al composition" is determined in consideration of the variation in the measurement of the Al composition.

[0196] The present invention is not limited to the above-described embodiments, and various modifications can be made and implemented without departing from the gist of the present invention. And all of them are included in the technical idea of the present invention.

Explanation of reference numerals

[0197] 110 ··· Nitride device, 111 ··· Contact structure, 113 ··· Lower group III nitride laminate, 114 ··· Active layer, 114a ··· Quantum well structure, 114b ··· Well layer, 114c ··· Barrier layer, 115 ··· Upper group III nitride laminate, 116 ··· Nitride semiconductor region, 118 ··· Support, 118a ··· Main surface, 119a, 119b, 119c, 119d ··· Bonding, 120 ··· Template layer, 121 ··· p-type semiconductor layer, 122 ··· First n-type semiconductor layer, 124 ··· Second n-type semiconductor layer, 125 ··· n-type semiconductor layer, 125a ··· First region, 125b ··· Second region, 127 ··· n-type contact layer, 129 ··· n-type intermediate region, 130 ··· Al U Ga 1-U N layer, 131 ··· n-electrode, 132 ··· Al V Ga 1-V N layer, 133 ··· Substrate, 133a ··· Group III nitride main surface, 134 ··· Electron blocking layer, 135 ··· Semiconductor region, 135a ··· Main surface, 136 ··· p-type graded composition layer, 138, 138a, 138b ··· p-type contact layer, 142 ··· Processed region by etching, 144 ··· Passivation film, 144a, 144b ··· Opening, 146 ··· p-electrode, 150 ··· Substrate, 155a, 155b ··· MOVPE reactor, 162 ··· Epitaxial wafer, 163 ··· Group III nitride semiconductor layer, 164 ··· Group III nitride laminate, 165 ··· First n-type semiconductor layer, 166 ··· Nitride semiconductor region, 167 ··· Second n-type semiconductor layer, 168 ··· Active layer, 168a ··· Quantum well structure, 168b ··· Well layer, 168c ··· Barrier layer, 169 ··· n-type intermediate region, 170 ··· Al U Ga 1-U N layer, 171 ··· n-type contact layer, 172 ··· Al V Ga 1-VN layer, 173... hard mask, 173a... opening, 174... electron blocking layer, 175... contact stack, 176... p-type graded composition layer, 178... p-type contact layer, 180a, 180b... trench, 182... processed region by etching, 184... passivation film, 184a, 184b... opening, 186... p-electrode, 188... n-electrode, ρc... specific contact resistance.

Claims

1. 1. A semiconductor light emitting device, comprising: an n-type semiconductor layer including a Group III nitride semiconductor containing aluminum as a Group III constituent element; a p-type semiconductor layer provided on the n-type semiconductor layer; an active layer including a group III nitride semiconductor provided on the n-type semiconductor layer and capable of generating deep ultraviolet light; an n-type contact layer made of a Group III nitride semiconductor containing gallium as a Group III constituent element provided on the n-type semiconductor layer; an n-type intermediate region of a Group III nitride semiconductor including gallium and aluminum as Group III constituent elements provided on the n-type semiconductor layer; an n-electrode comprising a metal; Equipped with the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region; the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero; the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer; the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region, The n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged in the direction of an axis from the n-type intermediate region toward the n-electrode. Semiconductor light emitting device.

2. The n-type intermediate region is Al Ｘ G １－Ｘ Contains N, the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer throughout the n-type intermediate region; 10. The semiconductor light emitting device of claim 1.

3. The n-type contact layer includes any one of n-type GaN, n-type AlGaN, and n-type InAlGaN.

3. A semiconductor light emitting device according to claim 1 or 2.

4. The wavelength of the deep ultraviolet light is in the range of 285 nm or less. A semiconductor light emitting device according to any one of claims 1 to 3.

5. The semiconductor device further includes a substrate providing a Group III nitride primary surface including aluminum as a Group III constituent element, the substrate includes the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region; The substrate is a substrate including a Group III nitride having aluminum as a Group III constituent element, or a substrate including a support made of a material other than Group III nitride, and an AlN template layer or an AlGaN template layer provided on a primary surface of the support. A semiconductor light emitting device according to any one of claims 1 to 4.

6. a difference between the Al composition Y of the n-type contact layer and the Al composition X of the n-type intermediate region is 0.3 or less at an interface between the n-type contact layer and the n-type intermediate region, a difference between the Al composition X of the n-type intermediate region and the Al composition Z of the n-type semiconductor layer is 0.3 or less at an interface between the n-type intermediate region and the n-type semiconductor layer; A semiconductor light emitting device according to any one of claims 1 to 5.

7. 1. A method of fabricating a semiconductor light emitting device, the semiconductor light emitting device comprising an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer comprising a Group III nitride semiconductor capable of generating deep ultraviolet light, the method comprising: growing a first Group III nitride semiconductor layer for an n-type intermediate region on the substrate, the first Group III nitride semiconductor layer including gallium and aluminum as Group III constituent elements; growing, on the substrate, a second Group III nitride semiconductor layer for an n-type contact layer, the second Group III nitride semiconductor layer containing gallium as a Group III constituent element, after growing the first Group III nitride semiconductor layer; forming an n-electrode containing a metal on the substrate after growing the second Group III nitride semiconductor layer; Equipped with the n-type semiconductor layer contains aluminum as a group III constituent element, the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region; the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero; the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer; the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region, The n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged on the substrate in the direction of an axis from the n-type intermediate region to the n-electrode. A method for making a semiconductor light emitting device.

8. The n-type intermediate region is Al Ｘ G １－Ｘ Contains N, the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer throughout the n-type intermediate region; A method for making the semiconductor light emitting device of claim 7.

9. The n-type contact layer includes any one of n-type GaN, n-type AlGaN, and n-type InAlGaN; A method for making a semiconductor light emitting device according to claim 7 or claim 8.

10. The wavelength of the deep ultraviolet light is in the range of 285 nm or less. A method for making a semiconductor light emitting device according to any one of claims 7 to 9.

11. the substrate provides a Group III nitride primary surface containing aluminum as a Group III constituent element; the substrate includes the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region; The substrate includes a substrate including a group III nitride including aluminum as a group III constituent element, or a substrate including a support body made of a material different from group III nitride, and an AlN template layer or an AlGaN template layer provided on a primary surface of the support body. A method for making a semiconductor light emitting device according to any one of claims 7 to 10.

12. 1. A contact structure for a Group III nitride semiconductor device, comprising: a substrate providing a Group III nitride primary surface containing aluminum as a Group III constituent element; a semiconductor region in contact with the Group III nitride primary surface and including one or more Group III nitride semiconductor layers; an n-type semiconductor layer of a Group III nitride semiconductor in contact with the semiconductor region; an n-type contact layer made of a Group III nitride semiconductor containing gallium as a Group III constituent element provided on the n-type semiconductor layer; an n-type intermediate region of a Group III nitride semiconductor including gallium and aluminum as Group III constituent elements provided on the n-type semiconductor layer; an n-electrode comprising a metal; Equipped with the Group III nitride semiconductor of the n-type semiconductor layer contains aluminum as a Group III constituent element, the n-type semiconductor layer is provided between the substrate and the n-type intermediate region, the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region; the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero; the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer; the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region; Contact structure.

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