Patent Description:
Nowadays, semiconductor light emitting devices such as light emitting diodes and laser diodes that emit blue light have been in practical use. Development of light emitting devices that output deep ultraviolet light having a shorter wavelength has also been pursued. A light emitting device for emitting deep ultraviolet light includes an aluminum gallium nitride (AlGaN) based n-type clad layer, active layer, p-type clad layer, etc. stacked successively on a substrate. Deep ultraviolet light emitted by the active layer is output from a light extraction surface of the substrate (see, for example, patent document <NUM>).

<CIT> discloses a semiconductor light-emitting element provided with a plurality of dent parts on the light taking-out surface.

<CIT> discloses a semiconductor light emitting device which includes at least one concave on a light extraction surface.

<CIT> and <CIT> disclose a semiconductor light emitting element which includes a cone-shaped structure formed on a light extraction surface and having a first portion with a first angle of inclination of a side surface and a second portion with a second angle of inclination of a side surface smaller than the first angle.

<CIT> discloses LEDs having light extraction structures on or within the LED to increase its efficiency.

<CIT> discloses an LED chip having light extraction structures.

It is known that the external quantum efficiency of deep ultraviolet light output via the light extraction surface of the substrate of a deep ultraviolet light emitting device is as low as several % and that the shorter the wavelength of emitted light, the lower the external quantum efficiency (see, for example, non-patent document <NUM>).

In this background, one illustrative purpose of the present invention is to provide a technology of increasing the light extraction efficiency of semiconductor light emitting devices.

An aspect of the present invention relates to a semiconductor light emitting device as defined by claim <NUM>.

According to the present invention, the concave-convex structure provided by forming a plurality of cone-shaped parts in an array on the light extraction surface inhibits total reflection of light occurring inside the light extraction surface and increases the efficiency of light output from the light extraction surface. Further, by configuring the angle of inclination of the side surface of the cone-shaped part to vary in stages and configuring the height of the second portion having a smaller angle of inclination to be larger than the height of the first portion having a larger angle of inclination, the light extraction efficiency is suitably improved. Thus, the light extraction efficiency is suitably improved according to the embodiment.

The height of the second portion may be not less than <NUM>% and not more than <NUM>% of a height of the cone-shaped part.

The first angle may be not less than <NUM>° and not more than <NUM>°, and the second angle may be not less than <NUM>° and not more than <NUM>°.

A difference between the first angle and the second angle may be <NUM>° or larger.

A proportion of an area occupied by the plurality of cone-shaped parts per a unit area of the light extraction surface may be not less than <NUM>% and not more than <NUM>% in a plan view of the light extraction surface.

In a cross-sectional view perpendicular to a direction of height of the cone-shaped part, the first portion may have a hexagonal shape or a shape intermediate between a hexagon and a circle, and the second portion may have a shape closer to a circle than the first portion.

The semiconductor light emitting device may include: a base structure including at least one of a sapphire (Al<NUM>O<NUM>) layer and an aluminum nitride (AlN) layer; and a light emitting structure formed on the base structure and including an aluminum gallium nitride (AlGaN)-based or a gallium nitride (GaN)-based semiconductor layer that emits ultraviolet light of a wavelength of not less than <NUM> and not more than <NUM>. The light extraction layer may be the sapphire (Al<NUM>O<NUM>) layer, the Ain layer or a silicon oxide (SiOx) layer, or a silicon nitride layer (SiNx) or an aluminum oxide layer (Al<NUM>O<NUM>) of the base structure.

Another aspect of the present invention relates to a method of manufacturing a semiconductor light emitting device as defined by claim <NUM>.

The method is directed to manufacturing a semiconductor light emitting device including a light extraction layer having a light extraction surface and comprises: forming a mask having an array pattern on the light extraction layer; and etching the mask and the light extraction layer from above the mask. The etching includes first dry-etching for dry-etching the mask and the light extraction layer until the entirety of the mask is removed and second dry-etching for further dry-etching the light extraction layer after the mask is removed. A plurality of cone-shaped parts are formed in an array on the light extraction surface in the first dry-etching, and the plurality of cone-shaped parts are further etched in the second dry-etching to form the cone-shaped part having a first portion having a first angle of inclination of a side surface and a second portion having a second angle of inclination of a side surface smaller than the first angle.

According to the present invention, the cone-shaped parts of a shape in which the angle of inclination of the side surface varies in stages can be formed, by further performing the second dry-etching step after the cone-shaped parts are formed by the first dry-etching step. Thus, according to the present invention,
the light extraction surface for which the higher light extraction efficiency is even higher can be manufactured easily.

According to the present invention, the light extraction efficiency of semiconductor light emitting devices is improved.

A detailed description will be given of embodiments to practice the present invention with reference to the drawings. Same numerals are used in the description to denote same elements and a duplicate description is omitted as appropriate. To facilitate the understanding, the relative dimensions of the constituting elements in the drawings do not necessarily mirror the relative dimensions in the actual apparatus.

<FIG> is a cross sectional view schematically showing a configuration of a semiconductor light emitting device <NUM> according to the embodiment. The semiconductor light emitting device <NUM> includes a base structure <NUM> and a light emitting structure <NUM>. The base structure <NUM> includes a substrate <NUM>, a first base layer <NUM>, and a second base layer <NUM>. The light emitting structure <NUM> includes an n-type clad layer <NUM>, an active layer <NUM>, an electron block layer <NUM>, a p-type clad layer <NUM>, a p-side electrode <NUM>, and an n-side electrode <NUM>.

The semiconductor light emitting device <NUM> is a semiconductor light emitting device configured to emit "deep ultraviolet light" having a central wavelength of about <NUM> or shorter. To output deep ultraviolet light having such a wavelength, the active layer <NUM> is made of an aluminum gallium nitride (AlGaN)-based semiconductor material having a band gap of about <NUM> eV or larger. In this embodiment, the case of emitting deep ultraviolet light having a central wavelength of about <NUM> or shorter is specifically discussed.

In this specification, the term "AlGaN-based semiconductor material" mainly refers to a semiconductor material containing aluminum nitride (AlN) and gallium nitride (GaN) and shall encompass a semiconductor material containing other materials such as indium nitride (InN). Therefore, "AlGaN-based semiconductor materials" as recited in this specification can be represented by a composition In<NUM>-x-yAlxGayN (<NUM>≤x+y≤<NUM>, <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>). The AlGaN-based semiconductor material shall contain AlN, GaN, AlGaN, indium aluminum nitride (InAlN), indium gallium nitride (InGaN), or indium aluminum gallium nitride (InAlGaN).

Of "AlGaN-based semiconductor materials", those materials that do not substantially contain AlN may be distinguished by referring to them as "GaN-based semiconductor materials". "GaN-based semiconductor materials" mainly contain GaN or InGaN and encompass materials that additionally contain a slight amount of AlN. Similarly, of "AlGaN-based semiconductor materials", those materials that do not substantially contain GaN may be distinguished by referring to them as "AlN-based semiconductor materials". "AlN-based semiconductor materials" mainly contain AlN or InAlN and encompass materials that additionally contain a slight amount of GaN.

The substrate <NUM> is a sapphire (Al<NUM>O<NUM>) substrate. The substrate <NUM> may be an aluminum nitride (AlN) substrate in one variation. The substrate <NUM> includes a first principal surface 22a and a second principal surface 22b opposite to the first principal surface 22a. The first principal surface 22a is a principal surface that is a crystal growth surface. For example, the first principal surface 22a is the (<NUM>) plane of the sapphire substrate. The second principal surface 22b is a principal surface that is the light extraction surface and is formed with a micro-concave-convex structure (texture structure) <NUM> of a submicron scale. The detail of the concave-convex structure <NUM> will be described later.

The substrate <NUM> has a thickness t of <NUM> or larger. For example, the substrate <NUM> has a thickness of about <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The thickness t of the substrate <NUM> is twice the height hA of the concave-convex structure <NUM> or larger. Typically, the thickness t is ten times the height hA of the concave-convex structure <NUM> or larger. Therefore, the height hB from the first principal surface 22a of the substrate <NUM> to a boundary surface 22c bordering the concave-convex structure <NUM> is larger than the height hA of the concave-convex structure <NUM> and twice the height hA of the concave-convex structure hA or larger.

The first base layer <NUM> and the second base layer <NUM> are stacked on the first principal surface 22a of the substrate <NUM>. The first base layer <NUM> is a layer made of an AlN-based semiconductor material and is, for example, an AlN(HT-AlN) layer gown at a high temperature. The second base layer <NUM> is a layer made of an AlGaN-based semiconductor material and is, for example, an undoped AlGaN(u-AlGaN) layer.

The substrate <NUM>, the first base layer <NUM>, and the second base layer <NUM> function as a foundation layer (template) to form the n-type clad layer <NUM> and the layers above. These layers also function as a light extraction layer for extracting the deep ultraviolet light emitted by the active layer <NUM> outside and transmit the deep ultraviolet light emitted by the active layer <NUM>. It is preferred that the first base layer <NUM> and the second base layer <NUM> be made of an AlGaN-based or AlN-based material having an AlN ratio higher than that of the active layer <NUM> so as to increase the transmittance for the deep ultraviolet light emitted by the active layer <NUM>. It is further preferred that the first base layer <NUM> and the second base layer <NUM> be made of a material having a lower refractive index than the active layer <NUM>. It is also preferred that the first base layer <NUM> and the second base layer <NUM> be made of a material having a higher refractive index than the substrate <NUM>. Given that the substrate <NUM> is a sapphire substrate (the refractive index n<NUM>=about <NUM>) and the active layer <NUM> is a made of an AlGaN-based semiconductor material (the refractive index n<NUM>=about <NUM>-<NUM>), for example, it is preferred that the first base layer <NUM> and the second base layer <NUM> be made of an AlN layer (the refractive index n<NUM>=about <NUM>) or an AlGaN-based semiconductor material (the refractive index n<NUM>=about <NUM>-<NUM>) having a relatively higher AlN composition ratio.

The n-type clad layer <NUM> is an n-type semiconductor layer provided on the second base layer <NUM>. The n-type clad layer <NUM> is made of an n-type AlGaN-based semiconductor material. For example, the n-type clad layer <NUM> is an AlGaN layer doped with silicon (Si) as an n-type impurity. The composition ratio of the n-type clad layer <NUM> is selected to transmit the deep ultraviolet light emitted by the active layer <NUM>. For example, the n-type clad layer <NUM> is formed such that the molar fraction of AlN is <NUM>% or higher, and, preferably, <NUM>% or higher. The n-type clad layer <NUM> has a band gap larger than the wavelength of the deep ultraviolet light emitted by the active layer <NUM>. For example, the n-type clad layer <NUM> is formed to have a band gap of <NUM> eV or larger. The n-type clad layer <NUM> has a thickness of about <NUM> ~ <NUM>. For example, the n-type clad layer <NUM> has a thickness of about <NUM>.

The active layer <NUM> is formed in a partial region on the n-type clad layer <NUM>. The active layer <NUM> is made of an AlGaN-based semiconductor material and has a double heterojunction structure by being sandwiched by the n-type clad layer <NUM> and the electron block layer <NUM>. The active layer <NUM> may form a monolayer or multilayer quantum well structure. The quantum well structure like this can be formed by building a stack of a barrier layer made of an undoped AlGaN-based semiconductor material and a well layer made of an undoped AlGaN-based semiconductor material. To output deep ultraviolet light having a wavelength of <NUM> or shorter, the active layer <NUM> is formed to have a band gap of <NUM> eV or larger. For example, the AlN composition ratio of the active layer <NUM> is selected so as to output deep ultraviolet light having a wavelength of <NUM> or shorter.

The electron block layer <NUM> is formed on the active layer <NUM>. The electron block layer <NUM> is a layer made of a p-type AlGaN-based semiconductor material and is exemplified by an undoped AlGaN layer. The electron block layer <NUM> is formed such that the molar fraction of AlN is <NUM>% or higher, and, preferably, <NUM>% or higher. The electron block layer <NUM> may be formed such that the molar fraction of AlN is <NUM>% or higher or may be made of an AlN-based semiconductor material that does not substantially contain GaN. The electron block layer <NUM> may be made of an AlGaN-based semiconductor material or an AlN-based semiconductor material doped with magnesium (Mg) as a p-type impurity. The electron block layer <NUM> has a thickness of about <NUM> ~ <NUM>. For example, the electron block layer <NUM> has a thickness of about <NUM> - <NUM>.

The p-type clad layer <NUM> is formed on the electron block layer <NUM>. The p-type clad layer <NUM> is a layer made of a p-type AlGaN-based semiconductor material and is exemplified by a Mg-doped AlGaN layer. The composition ratio of the p-type clad layer <NUM> is selected such that the molar fraction of AlN in the p-type clad layer <NUM> is lower than that of the electron block layer <NUM>. The p-type clad layer <NUM> has a thickness of about <NUM> ~ <NUM>. For example, the p-type clad layer <NUM> has a thickness of about <NUM> - <NUM>.

The p-side electrode <NUM> is provided on the p-type clad layer <NUM>. The p-side electrode <NUM> is made of a material capable of establishing ohmic contact with the p-type clad layer <NUM>. For example, the p-side electrode <NUM> is formed by a nickel (Ni)/gold (Au) stack structure.

The n-side electrode <NUM> is provided on the n-type clad layer <NUM>. For example, the n-side electrode <NUM> is a Ti/Al-based electrode and is formed by, for example, a titanium (Ti)/Al/Ti/Au or Ti/Al/Ni/Au stack structure.

The concave-convex structure <NUM> is formed on the second principal surface (also referred to as the light extraction surface) 22b of the substrate <NUM> that is the light extraction layer. The concave-convex structure <NUM> inhibits reflection or total reflection on the second principal surface 22b and increases the light extraction efficiency of deep ultraviolet light output from the second principal surface 22b. The concave-convex structure <NUM> has a plurality of cone-shaped parts <NUM> formed in an array on the light extraction surface. The cone-shaped part <NUM> is made of the same material as the substrate <NUM>. For example, the cone-shaped part <NUM> is made of sapphire (Al<NUM>O<NUM>) or aluminum nitride (AlN).

The cone-shaped part <NUM> has a first portion <NUM> having a relatively large angle of inclination of the side surface and a second portion <NUM> having a relatively small angle of inclination of the side surface. The first portion <NUM> is located toward the bottom of the cone-shaped part <NUM> (toward the top of the plane of paper of <FIG>), and the second portion <NUM> is located toward the apex of the cone-shaped part <NUM> (toward the bottom of the plane of paper of <FIG>).

Referring to <FIG>, the concave-convex structure <NUM> is formed on substantially the entirety of the second principal surface 22b. The concave-convex structure <NUM> may be formed only in a restricted area on the second principal surface 22b. For example, the concave-convex structure <NUM> may be formed only in an inner region C1 of the second principal surface 22b and may not be formed in an outer region C2. The size of the outer region C2 is not limited to a particular size. For example, the outer region C2 extends in a range of about <NUM> ~ <NUM>.

<FIG> is a cross-sectional view schematically showing a configuration of the concave-convex structure <NUM> and represents a partial enlarged view of <FIG> is oriented upside down relative to <FIG>. The plurality of cone-shaped parts <NUM> (52a, 52b, 52c) are arranged at a predetermined pitch p. The pitch p of the cone-shaped parts <NUM> is defined as a distance between apexes <NUM> of adjacent cone-shaped parts <NUM> (e.g., 52b and 52c). The cone-shaped parts <NUM> is formed such that the pitch p between adjacent cone-shaped parts <NUM> is not less than <NUM> and not more than <NUM>, and, for example, not less than <NUM> and not more than <NUM>.

The plurality of cone-shaped parts <NUM> are formed to have a substantially uniform height hA. The height hA of the cone-shaped part <NUM> is not less than <NUM> and not more than <NUM> and, preferably, not less than <NUM> and not more than <NUM>. The height hA of the cone-shaped part <NUM> is not less than <NUM> times and not more than <NUM> times and, preferably, not less than <NUM> times and not more than <NUM> times the pitch p of the cone-shaped part <NUM>. Given that the pitch p of the cone-shaped parts <NUM> is <NUM>, for example, the height h of the cone-shaped part <NUM> is not less than <NUM> and not more than <NUM> and, preferably, not less than <NUM> and not more than <NUM>. The height hA of the cone-shaped part <NUM> may have certain (e.g., <NUM>% ~ <NUM>%) variability.

The cone-shaped part <NUM> has the first portion <NUM> having a first angle θ<NUM> of inclination of the side surface and the second portion <NUM> having a second angle θ<NUM> of inclination of the side surface. The first portion <NUM> is a portion including a bottom <NUM> of the cone-shaped part <NUM>, and the second portion <NUM> is a portion including the apex <NUM> of the cone-shaped part <NUM>. The first angle θ<NUM> of the first portion <NUM> is an angle formed by the side surface of the cone-shaped part <NUM> and the boundary surface 22c that could be seen as the bottom surface of the cone-shaped part <NUM> and is an angle of inclination of the side surface at the bottom <NUM> of the cone-shaped part <NUM>. Meanwhile, the second angle θ<NUM> of the second portion <NUM> is an angle of inclination of the side surface near the boundary between the first portion <NUM> and the second portion <NUM>.

Comparing the first angle θ<NUM> with the second angle θ<NUM>, the first angle θ<NUM> is larger than the second angle θ<NUM> (i.e., θ<NUM>>θ<NUM>). Therefore, the cone-shaped part <NUM> is shaped such that the inclination of the side surface is gentler near the apex <NUM> than near the bottom <NUM>. The first angle θ<NUM> is <NUM>° or larger and, preferably, not less than <NUM>° and not more than <NUM>°. The second angle θ<NUM> is <NUM>° or smaller and, preferably, not less than <NUM>° and not more than <NUM>°. An angle difference Δθ (θ<NUM>-θ<NUM>) between the first angle θ<NUM> and the second angle θ<NUM> is preferably <NUM>° or larger, and more preferably, <NUM>° or larger or <NUM>° or larger.

In the cone-shaped part <NUM>, the height h<NUM> of the second portion <NUM> is larger than the height h<NUM> of the first portion <NUM>. In accordance with the present invention, the height h<NUM> of the second portion <NUM> is not less than <NUM> times and not more than <NUM> times the height h<NUM> of the first portion <NUM> and, preferably, <NUM> times the height h<NUM> or larger. For example, the height h<NUM> of the second portion <NUM> is about twice ~ three times the height h<NUM> of the first portion <NUM>. Therefore, the height h<NUM> of the second portion <NUM> preferably occupies <NUM>% or larger of the total height hA of the cone-shaped part <NUM> and, more preferably, occupies <NUM>% - <NUM>% of the total height hA. Also, the height h<NUM> of the second portion <NUM> is preferably <NUM>% or smaller than the total height hA of the cone-shaped part, and the first portion <NUM> occupies a certain proportion (<NUM>% or larger).

The side surface of each of the first portion <NUM> and the second portion <NUM> of the cone-shaped part <NUM> illustrated has a constant angle of inclination, and the side surface is formed to be straight in a cross-sectional view of <FIG> perpendicular to the boundary surface 22c. However, the angle of inclination of the side surface of the first portion <NUM> and the second portion <NUM> may not be constant, and the side surface may be shaped such that the angle of inclination varies gradually. For example, the first portion <NUM> may be shaped such that the angle of inclination θ<NUM> is substantially constant, and the second portion <NUM> may be shaped such that the angle of inclination θ<NUM> grows gradually smaller toward the apex <NUM>. For example, the side surface of the second portion <NUM> may be convexly curved outward from the cone-shaped part <NUM>.

<FIG> is a top view schematically showing a configuration of the concave-convex structure <NUM> and schematically shows an arrangement of the plurality of cone-shaped parts <NUM> of <FIG> corresponds to an A-A cross section of <FIG>. The plurality of cone-shaped parts <NUM> are arranged in a triangular grid pattern as illustrated. In a plan view of the light extraction surface 22b, the outer profile of the cone-shaped part <NUM> has a shape similar to a hexagon and has a shape intermediate between a hexagon and a circle. The term "a shape intermediate between a hexagon and a circle" refers to a shape in which the profile line is substantially located in a region between a hexagon and an inscribed circle thereof and refers to a shape produced by rounding the corners of a heptagon or a polygon having a larger number of corners (e.g., octagon, dodecagon, icositetragon) or of a hexagon or a polygon having a larger number or corners. For example, the cone-shaped part may be shaped such that <NUM>% or larger or, preferably, <NUM>% or larger of the area between a hexagon and an inscribed circle thereof is located inside the profile line. In the case of "a shape intermediate between a hexagon and a circle" like this, the area occupied will be larger than the area of the reference circle (e.g., the inscribed circle). Thus, by causing the outer profile of the cone-shaped part <NUM> to be similar to a hexagon to present "a shape intermediate between a hexagon and a circle", the proportion of the area occupied by the plurality of cone-shaped parts <NUM> per a unit area in a plan view of the second principal surface 22b is increased accordingly. Provided that the circular cone-shaped parts <NUM> are arranged in a hexagonal close packed pattern, for example, the proportion of the area occupied would be approximately <NUM>%. By causing the outer profile of the cone-shaped parts <NUM> to be similar to a hexagon, the proportion can be increased to <NUM>% or higher.

The cone-shaped part <NUM> may be shaped such that the plan view of the second principal surface 22b, i.e., the cross section perpendicular to the direction of height of the cone-shaped part <NUM> varies in the direction of height. For example, the cross-sectional shape of the first portion <NUM> perpendicular to the direction of height may be different from the cross-sectional shape of the second portion <NUM> perpendicular to the direction of height. The cross-sectional shape of the first portion <NUM> perpendicular to the direction of height may be a shape intermediate between a hexagon and a circle, and the cross-sectional shape of the second portion <NUM> perpendicular to the direction of height may have a shape closer to a circle than the first portion. For example, the cross-sectional shape of the second portion <NUM> perpendicular to the direction of height may have corners more rounded and having smaller curvature (i.e., larger radius of curvature) than those of the cross sectional-shape of the first portion <NUM> perpendicular to the direction of height. The shape difference between the first portion <NUM> and the second portion <NUM> may be defined by the circularity. For example, a determination as to whether a shape is relatively similar to a circle may be made by referring to a difference between the maximum radius of curvature and the minimum radius of curvature defined in the JIS standard (JISB0621-<NUM>). In this case, the second portion <NUM> may be have a shape with a smaller circularity than the first portion <NUM>.

Preferably, the gap between adjacent cone-shaped parts <NUM> (e.g., 52a, 52b) is small, and the width or diameter ϕ of the cone-shaped part <NUM> is preferably nearly equal to the pitch p of the adjacent cone-shaped parts <NUM>. The diameter ϕ of the cone-shaped part <NUM> is configured to be <NUM> times the pitch p or larger and, preferably, <NUM> times the pitch p or larger. By configuring the diameter ϕ of the cone-shaped part <NUM> to be <NUM> times the pitch p or larger, the proportion of the plurality of cone-shaped parts <NUM> occupying a unit area in a plan view of the second principal surface 22b is ensured to be <NUM>% or higher.

A description will now be given of a method of manufacturing the semiconductor light emitting device <NUM>. <FIG> is a flowchart showing a method of manufacturing the semiconductor light emitting device <NUM>. First, a light emitting device provided with a light extraction layer is prepared (S10), and a resin mask of an array pattern is formed on the light extraction layer (S12). Subsequently, a first dry-etching step is performed to dry-etch the mask and the light extraction layer from the above mask and etch the mask and the layer until the entirety of the mask is removed (S14). Subsequently, a second dry-etching step is performed to further dry-etch the light extraction surface after the mask is removed in the first dry-etching step (S16). In the embodiment, the first dry-etching step to remove the mask and the second dry-etching step to overetch the layer after the mask is removed are performed.

In the step of preparing the light emitting device, the substrate <NUM> not formed with the concave-convex structure <NUM> is prepared, and the first base layer <NUM>, the second base layer <NUM>, the n-type clad layer <NUM>, the active layer <NUM>, the electron block layer <NUM>, and the p-type clad layer <NUM> are stacked successively on the first principal surface 22a of the substrate <NUM>. The second base layer <NUM>, the n-type clad layer <NUM>, the active layer <NUM>, the electron block layer <NUM>, and the p-type clad layer <NUM> made of an AlGaN-based semiconductor material or a GaN-based semiconductor material can be formed by a well-known epitaxial growth method such as the metalorganic vapor phase epitaxy (MOVPE) method and the molecular beam epitaxy (MBE) method.

Subsequently, portions of the active layer <NUM>, the electron block layer <NUM>, and the p-type clad layer <NUM> stacked on the n-type clad layer <NUM> are removed to expose a partial region of the n-type clad layer <NUM>. For example, portions of the active layer <NUM>, the electron block layer <NUM>, and the p-type clad layer <NUM> may be removed by forming a mask, avoiding a partial region on the p-type clad layer <NUM>, and performing reactive ion etching or dry etching using plasma, thereby exposing a partial region of the n-type clad layer <NUM>.

The n-side electrode <NUM> is then formed on the partial region of the n-type clad layer <NUM> exposed, and the p-side electrode <NUM> is formed on the p-type clad layer <NUM>. The metal layers forming the p-side electrode <NUM> and the n-side electrode <NUM> may be formed by a well-known method such as electron beam deposition and sputtering.

The concave-convex structure <NUM> is then formed on the second principal surface 22b of the substrate <NUM>. <FIG> schematically show steps of manufacturing the concave-convex structure <NUM> and shows a step of processing a processed surface 60c of the light extraction layer <NUM> in which the concave-convex structure <NUM> has yet been formed. The light extraction layer <NUM> is a layer in which the light extraction surface should be formed and is a layer corresponding to the substrate <NUM> of the semiconductor light emitting device <NUM> shown in <FIG>.

<FIG> shows a step of forming a mask <NUM> on the light extraction layer <NUM>. For example, the processed surface 60c of the light extraction layer <NUM> is the (<NUM>) plane (c plane) of the sapphire substrate. The mask <NUM> includes an array pattern corresponding to the cone-shaped parts <NUM> of the concave-convex structure <NUM> and includes a plurality of columns <NUM> arranged in an array. The plurality of columns <NUM> arranged in a triangular grid pattern, and each column has a prism or cylinder shape. The column <NUM> may be provided with a slight taper angle and may be shaped in a truncated pyramid or a truncated cone. For example, the mask <NUM> is formed by a resist resin by using the nanoimprinting technology. The method of forming the mask <NUM> is not limited to any particular method, and the mask <NUM> may be formed by using a lithographic technology based on exposure or electron-beam printing.

The mask <NUM> is formed such that the pitch pc of adjacent columns <NUM> is identical to the pitch p of the cone-shaped parts <NUM>. The height hc of the column <NUM> is determined based on the height h<NUM> of a cone-shaped part <NUM> formed in the first dry-etching step (see <FIG>, the detail will be described later) and the ratio between the etching rates of the light extraction layer <NUM> and the mask <NUM>. Denoting the etching rate of the light extraction layer <NUM> by e and the etching of the mask <NUM> by ec, the height h of the column <NUM> is determined by an expression hc≈h<NUM>*ec/e. The height hc of the column <NUM> may be slightly larger than the value given by the above expression or larger than the value h<NUM>*ec/e by about <NUM>% ~ <NUM>%. The diameter ϕc of the column <NUM> is smaller than the pitch pc of the columns <NUM> and is, for example, about <NUM>% ~ <NUM>% of the pitch pc. The diameter ϕc of the column <NUM> may be smaller than the diameter ϕ of the cone-shaped part <NUM> ultimately formed.

A dry-etching process is then performed from above the mask <NUM>. Reactive ion etching (RIE) may be used as a method of dry-etching the light extraction layer <NUM> and the mask <NUM>. More specifically, plasma etching using inductive coupling plasma (ICP) may be used. The gas species used in plasma etching is not limited to any particular type, but it is preferred to use a chlorine-based gas such as chlorine (Cl<NUM>) and boron trichloride (BCl<NUM>) as an etching gas. By using an etching gas like the above, it is possible to suitably etch sapphire or aluminum nitride forming the light extraction layer <NUM> and etch the resist resin forming the mask <NUM>.

<FIG> schematically shows the dry-etched light extraction layer <NUM> and the mask <NUM> and shows a state in the middle of the first dry-etching step described above. In the first dry-etching step, the column <NUM> is isotropically etched from above and from side. As the etching step proceeds, the height hc and the diameter ϕc of the column <NUM> grow smaller. Meanwhile, those portions of the light extraction layer <NUM> located below the mask <NUM> that are not covered with the mask <NUM> are etched. Since the covered area of the column <NUM> is reduced toward the center of the column <NUM> with time, the area of the light extraction layer <NUM> that is etched grows larger with time. As a result, the etching volume in the direction of depth of the light extraction layer <NUM> varies depending on the distance from the center of the column <NUM> with the result that the cone-shaped part <NUM> having an inclined surface <NUM> and similar to a truncated cone or a truncated pyramid is formed below the mask <NUM>. The cone-shaped part <NUM> is formed at a position corresponding to the array pattern of the mask <NUM> and is formed in a position corresponding to each of the plurality of columns <NUM>.

<FIG> schematically shows the dry-etched light extraction layer <NUM> and the mask <NUM> and shows a state that occurs immediately before the first dry-etching step is terminated. As the dry-etching step is allowed to proceed from the state shown in <FIG>, the column <NUM> grows even smaller, and the entirety of the mask <NUM> is ultimately removed from the light extraction layer <NUM>. The light extraction layer <NUM> is etched such that the width (diameter) of the apex <NUM> of the cone-shaped part <NUM> becomes even smaller. As a result, the cone-shaped part <NUM> having a pointed apex <NUM> and similar to a cone or a pyramid in shape is formed.

The height h<NUM> of the cone-shaped part <NUM> formed in the first dry-etching step corresponds to the etching volume (also called the first etching volume) in the direction of depth by which the light extraction layer <NUM> is etched in the first dry-etching step and is given by an expression h<NUM>=hc*e/ec, where hc denotes the initial height of the mask <NUM>, e denotes the etching rate of the light extraction layer <NUM>, and ec denotes the etching rate of the mask <NUM>.

It is preferred that the cone-shaped part <NUM> be shaped in the first dry-etching step such that the aspect ratio h<NUM>/p<NUM> of the height h<NUM> relative to the pitch p<NUM> is <NUM> or larger, and, more preferably, <NUM> or larger. Given that the pitch p<NUM> of the cone-shaped part <NUM> is <NUM>, for example, the height h<NUM> of the cone-shaped part <NUM> is preferably <NUM> or larger. By configuring the aspect ratio of the cone-shaped part <NUM> to be <NUM> or larger after the first dry-etching step, the aspect ratio h/p of the cone-shaped part <NUM> formed after the second dry-etching step may be of a suitable value (e.g., not less than <NUM> and not more than <NUM>).

Unlike the cone-shaped part <NUM> shown in <FIG> described above, the cone-shaped part <NUM> after the first dry-etching step is formed such that the inclined surface <NUM> has a constant angle of inclination θ<NUM>. In other words, the cone-shaped part <NUM> after the first dry-etching step does not have the first portion and the second portion in which the angle of inclination varies in stages. The angle of inclination θ<NUM> of the inclined surface <NUM> of the cone-shaped part <NUM> after the first dry-etching step is, for example, <NUM>° or larger, or <NUM>° or larger, though the angle may depend on the aspect ratio described above. Typically, the angle of inclination θ<NUM> of the inclined surface <NUM> is smaller than the first angle θ<NUM> and larger than the second angle θ<NUM> (i.e., θ<NUM>>θ<NUM>>θ<NUM>).

<FIG> is a top view schematically showing a configuration of a plurality of cone-shaped parts <NUM> shown in Fig. 7b (e.g., 66a, 66b, 66c) and shows a case where the cylindrical column <NUM> is used as the mask <NUM>. <FIG> corresponds to a B-B cross section of <FIG>. As shown in the figures, the outer profile of the cone-shaped part <NUM> after the first dry-etching step has a circular shape corresponding to the shape of the column <NUM> in a plan view of the processed surface 60c. A gap d<NUM> (=p<NUM>-ϕ<NUM>) is found between the plurality of cone-shaped parts <NUM>, and the magnitude of the gap d<NUM> is, for example, about <NUM>% ~ <NUM>% of the pitch p<NUM>. Providing the gap d<NUM> in the first dry-etching step secures a large aspect ratio (typically <NUM> or larger) of the cone-shaped part <NUM> as formed.

In the embodiment, the second dry-etching step for dry-etching the light extraction layer <NUM> further is performed after the entirety of the mask <NUM> is removed in the first dry-etching step. The second dry-etching step is a step with substantially the same etching condition as the first dry-etching step and is performed in continuation of the first dry-etching step. In other words, the second dry-etching step is performed to follow the first dry-etching step while the light emitting device remains housed in the etching process chamber. In one variation, the second dry-etching step may be performed in isolation from the first dry-etching step, or a certain addition process may be performed between the first dry-etching step and the second dry-etching step. Further, the processing conditions of the first dry-etching step and the second dry-etching step may differ. For example, processing conditions like etching gas, etching rate, etc. may differ.

<FIG> is a cross-sectional view schematically showing a structure of the plurality of cone-shaped parts <NUM> formed after the second dry-etching step. By further dry-etching the conical cone-shaped part <NUM> shown in <FIG>, the cone-shaped part <NUM> having the first portion <NUM> and the second portion <NUM> with different angles of inclination is formed. The second dry-etching step is performed in the absence of the mask <NUM> and is a so-called maskless, free-running dry-etching process.

When the second dry-etching step is started, the apex <NUM> of the cone-shaped part <NUM> is pointed so that the electric field applied during plasma etching tends to be concentrated on the apex <NUM>, causing the etching rate near the apex <NUM> to be relatively high. This is considered to result in the neighborhood of the apex <NUM> being etched more heavily and the second portion <NUM> having a relatively small angle of inclination θ<NUM> being formed toward the apex <NUM>.

In the second dry-etching step, the reaction product produced by dry-etching could be randomly attached (re-attached) to the surface of the light extraction layer <NUM>. Since the etching rate near a bottom <NUM> of the cone-shaped part <NUM> shown in <FIG> is relatively low as compared to the rate near the apex <NUM>, it is considered to be easy for the reaction product produced by dry-etching to be attached to the neighborhood of the bottom <NUM>. This is considered to result in a larger amount of the reaction product attached to the neighborhood of the bottom <NUM> of the cone-shaped part <NUM>, a larger diameter ϕ of the cone-shaped part <NUM> after the second dry-etching than the diameter ϕ<NUM> of the cone-shaped part <NUM> shown in <FIG>, and reduction in the gap d<NUM> between adjacent cone-shaped parts <NUM>. In this way, the first portion <NUM> having the relatively larger angle of inclination θ<NUM> as compared to that of the second portion <NUM> is formed. Further, the cone-shaped part <NUM> having an outer profile similar to a hexagon than a circle is formed in a plan view of the processed surface 60c, and the proportion of the area occupied by the plurality of cone-shaped parts <NUM> per a unit area will be larger than that of the cone-shaped parts <NUM> shown in <FIG>.

The shape of the cone-shaped part <NUM> formed after the second dry-etching step is suitably controlled by adjusting the shape of the cone-shaped part <NUM> before the second dry-etching step and the etching volume hD of the second dry-etching step. More specifically, the aspect ratio h/p of the cone-shaped part <NUM> after the second dry-etching step is configured to be of a suitable value by configuring the aspect ratio h<NUM>/p<NUM> of the cone-shaped part <NUM> before the second dry-etching step to be of a certain value or larger. Further, the cone-shaped part <NUM> in which the height h<NUM> of the first portion <NUM> is larger than the height h<NUM> of the second portion <NUM> can be formed by configuring the etching volume hD in the second dry-etching step to be within a certain range.

<FIG> are electron microscope images of the concave-convex structure <NUM> according one example. <FIG> shows an concave-convex structure corresponding to the cone-shaped part <NUM> after the first dry-etching step and shows a constant angle of inclination of the side surface of the cone-shaped part. <FIG> show an concave-convex structure corresponding to the cone-shaped part <NUM> after the second dry-etching step and shows that the angle of inclination of the side surface of the cone-shaped part varies depending on the position in the direction of height. For ease of understanding, the first portion <NUM> and the second portion <NUM> of the cone-shaped part <NUM> are indicated in <FIG> by broken lines.

In the first example shown in <FIG>, the pitch p is about <NUM>, the diameter ϕ is about <NUM>, the height is about <NUM>, and the angle of inclination θ of the inclined surface is about <NUM>°. The aspect ratio h/p is about <NUM>, and the proportion of the area occupied by the plurality of cone-shaped parts per a unit area is about <NUM>%. The first example exhibited an improvement of about <NUM>% in light output over a light emitting device not provided with an concave-convex structure.

In the second example shown in <FIG>, the pitch p is about <NUM>, the diameter ϕ is about <NUM>, the height h is about <NUM>, the aspect ratio h/p is about <NUM>, and the proportion of the area occupied by the plurality of cone-shaped parts per a unit area is about <NUM>%. The height h<NUM> of the first portion is about <NUM>, and the angle of inclination θ<NUM> of the first portion is about <NUM>°. The height h<NUM> of the second portion is about <NUM>, and the angle of inclination θ<NUM> of the second portion is about <NUM>°. The proportion of the height of the second portion h<NUM>/hA is about <NUM>%, and the angle difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> is about <NUM>°. The second example exhibited an improvement of about <NUM>% in light output over a light emitting device not provided with an concave-convex structure.

In the third example shown in <FIG>, the pitch p is about <NUM>, the diameter ϕ is about <NUM>, the height h is about <NUM>, the aspect ratio h/p is about <NUM>, and the proportion of the area occupied by the plurality of cone-shaped parts per a unit area is about <NUM>%. The height h<NUM> of the first portion is about <NUM>, and the angle of inclination θ<NUM> of the first portion is about <NUM>°. The height h<NUM> of the second portion is about <NUM>, and the angle of inclination θ<NUM> of the first portion is about <NUM>°. The proportion of the height of the second portion h<NUM>/hA is about <NUM>%, and the angle difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> is about <NUM>°. The third example exhibited an improvement of about <NUM>% in light output over a light emitting device not provided with an concave-convex structure.

In the fourth example shown in <FIG>, the pitch p is about <NUM>, the diameter ϕ is about <NUM>, the height h is about <NUM>, the aspect ratio h/p is about <NUM>, and the proportion of the area occupied by the plurality of cone-shaped parts per a unit area is about <NUM>%. The height h<NUM> of the first portion is about <NUM>, and the angle of inclination θ<NUM> of the first portion is about <NUM>°. The height h<NUM> of the second portion is about <NUM>, and the angle of inclination θ<NUM> of the second portion is about <NUM>°. The proportion of the height of the second portion h<NUM>/hA is about <NUM>%, and the angle difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> is about <NUM>°. The fourth example exhibited an improvement of about <NUM>% in light output over a light emitting device not provided with an concave-convex structure.

In the fifth example shown in <FIG>, the pitch p is about <NUM>, the diameter ϕ is about <NUM>, the height h is about <NUM>, and the aspect ratio h/p is about <NUM>. The proportion of the area occupied by the plurality of cone-shaped parts per a unit area is about <NUM>%. The height h<NUM> of the first portion is about <NUM>, and the angle of inclination θ<NUM> of the first portion is about <NUM>°. The height h<NUM> of the second portion is about <NUM>, and the angle of inclination θ<NUM> of the second portion is about <NUM>°. The proportion of the height of the second portion h<NUM>/hA is about <NUM>%, and the angle difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> is about <NUM>°. The fifth example exhibited an improvement of about <NUM>% in light output over a light emitting device not provided with an concave-convex structure.

<FIG> is a graph showing a relationship between the proportion of the height h<NUM> of the second portion <NUM> of the concave-convex structure <NUM> according to the examples and the light output. As illustrated, the light output is improved by increasing the proportion of the height of the second portion <NUM>. The graph reveals that the light output is suitably improved by configuring the proportion of the height of the second portion <NUM> to be <NUM>% or larger, i.e., by configuring the height h<NUM> of the second portion <NUM> to be larger than the height h<NUM> of the first portion <NUM>. The graph also shows that the rate of improvement in light output tends to drop when the proportion of the height of the second portion <NUM> exceeds <NUM>%, i.e., when the height h<NUM> of the second portion <NUM> is far more than twice the height h<NUM> of the first portion <NUM>. Therefore, the height h<NUM> of the second portion <NUM> is around twice the height h<NUM> of the first portion <NUM> is in accordance with the present invention not less than <NUM> times and not more than three times the height h<NUM> of the first portion.

<FIG> is a graph showing a relationship between the difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> of the concave-convex structure <NUM> according to the examples and the light output. The figure reveals that the light output is improved by increasing the difference Δθ between the first angle θ<NUM> and the second angle θ<NUM> and that the light output is suitably improved by configuring the angle difference Δθ to be <NUM>° or larger.

<FIG> is a graph showing a relationship between the proportion of the area occupied by the concave-convex structure <NUM> according to the examples and the light output. The graph also shows the values of aspect ratio h/p of the concave-convex structure <NUM>. The graph reveals that the light output is suitably improved by controlling the aspect ratio h/p to be <NUM> or smaller and, at the same time, increasing the proportion of the area occupied by the cone-shaped part <NUM>, instead of preferentially increasing the aspect ratio h/p of the concave-convex structure <NUM>. For example, a higher light output is obtained by configuring the aspect ratio h/p of the concave-convex structure <NUM> to be <NUM> and the proportion of the area to be about <NUM>% rather than by configuring the aspect ratio h/p of the concave-convex structure <NUM> to be <NUM> and the proportion of the area to be about <NUM>%. Therefore, the light output is suitably improved by configuring the proportion of the area to be <NUM>% or larger at the cost of somewhat smaller aspect ratio (e.g., not less than <NUM> and not more than <NUM>). Further, by configuring the shape of the outer profile of the cone-shaped part <NUM> to be similar to a hexagon, the proportion of the area is configured to be <NUM>% or larger, with the result that the light output is suitably improved even if the aspect ratio h/p is <NUM> or smaller.

According to the embodiment, the light output of the concave-convex structure <NUM> is improved by configuring the height h<NUM> of the second portion <NUM> having a smaller angle of inclination of the side surface to be larger than the height h<NUM> of the first portion <NUM> having a larger angle of inclination of the side surface. It should be noted that such an advantage is directly opposite to what we expected. We also determined the correlation between the heights h<NUM>, h<NUM> of the first portion <NUM> and the second portion <NUM> and the light output of the concave-convex structure <NUM> by numerical computation (simulation) and found out a result opposite to that of the embodiment described above. In other words, the numerical computation showed an increase in the light output by configuring the height h<NUM> of the first portion <NUM> to be larger than the height h<NUM> of the second portion. While the reason for the difference between the light output value of the concave-convex structure <NUM> determined by the numerical computation and the light output value of the concave-convex structure <NUM> actually manufactured is unknown, the difference is considered to result from the impact from multipath reflection and multiple scattering inside the concave-convex structure <NUM>, the impact from the variation in the shape and size of the individual cone-shaped parts <NUM> of the concave-convex structure <NUM> manufactured.

The variation in the shape and size of the individual cone-shaped parts <NUM> of the concave-convex structure <NUM> is considered to be due to the variation in the shape of the mask <NUM> (column <NUM>) formed on the light extraction layer <NUM>. The shape of the cone-shaped part <NUM> discussed above is greatly affected by the etching volume in the second dry-etching step after the column <NUM> of the mask <NUM> is removed. Therefore, the variation in the shape of the mask <NUM> results in a shift between points of time of start of the second dry-etching step, and the shift could cause a difference in the shape of the cone-shaped parts <NUM>. For example, formation of the mask <NUM> using a common deposition device creates the variation of about ±<NUM>% in the film thickness within the plane, which creates the variation of a maximum of <NUM>% in the film thickness of the mask <NUM>. Further, the dry-etching selection ratio between the mask <NUM> and the light extraction layer <NUM> is about <NUM> ~ <NUM> so that the variation of about <NUM>% ~ <NUM>% in the film thickness of the mask <NUM> is created in the cone-shaped parts <NUM>. Further, the variation in the etching volume in the dry-etching step of about ±<NUM>% is created within the plane. Consequently, given that initial film thickness hc of the mask <NUM> is <NUM> and the cone-shaped part <NUM> of the height h<NUM> of <NUM> is formed after the first dry-etching step, for example, the variation of about <NUM> is created in the height hA of the cone-shaped parts <NUM> as a sum of the variation caused by the mask <NUM> (maximum of about <NUM>) and the variation in the dry-etching step (maximum of about <NUM>).

The amount of variation in the height of the cone-shaped parts <NUM> described above represents about <NUM> - <NUM>% of the height hA of the cone-shaped parts <NUM> ultimately formed and could occur randomly within the plane of the light extraction surface. In this embodiment, the diffraction effect obtained by uniformly shaping the cone-shaped parts <NUM> is not positively utilized so that it is unlikely that the extraction efficiency drops due to the variation in the shape of the cone-shaped parts <NUM>. Rather, the variation in the shape of the plurality of cone-shaped parts <NUM> and resultant variation in the orientation of light that can be extracted in the individual cone-shaped parts <NUM> are expected to provide the advantage of enabling light in various direction to be extracted in the concave-convex structure <NUM> as a whole. Thus, significant benefit and advantage that could not be expected from the result based on numerical computation are realized according to the embodiment.

According to the embodiment, the proportion of the area occupied by the ultimate cone-shaped parts <NUM> is increased by forming the cone-shaped part <NUM> of a high aspect ratio in the first dry-etching step and then performing the second dry-etching step. It can therefore be said that the aspect ratio of the cone-shaped part <NUM> and the proportion of the occupied area are in a trade-off in this embodiment. In the related art, the concave-convex shape of a high aspect ratio has been considered desirable for improvement of the light output using an concave-convex structure. It has been considered important to increase the aspect ratio of the concave-convex structure as much as possible. However, our finding demonstrated that improvement in the light output is realized by increasing the proportion of the area occupied by the concave-convex shape to <NUM>% or larger at the cost of somewhat smaller aspect ratio (e.g., not less than <NUM> and not more than <NUM>). Also, further improvement in the light output is realized by configuring the outer profile of the first portion <NUM> of the cone-shaped part <NUM> to have a shape similar to a hexagon to increase the proportion of the area occupied by the concave-convex shape to <NUM>% or larger. Thus, the embodiment provides the semiconductor light emitting device <NUM> in which the light output from the light extraction surface is improved and the external output efficiency is higher than in the related art.

According to the embodiment, only one type of mask need be used to form the cone-shaped part <NUM> having the first portion <NUM> and the second portion <NUM> so that the manufacturing steps are simplified, and the manufacturing cost is reduced. In the related art, an attempt to form an concave-convex shape with a graded inclination has required application of a plurality of types of masks suited to the concave-convex shape sought to be formed and so has required the number of steps corresponding to the number of types of masks used. Meanwhile, according to the embodiment, only one type of mask need be used, and the first dry-etching step and the second dry-etching step may be performed continuously. Therefore, the number manufacturing steps is reduced. Thus, according to the embodiment, the light extraction efficiency of the semiconductor light emitting device <NUM> is improved, while also preventing the manufacturing cost from being increased.

Described above is an explanation based on an exemplary embodiment. The embodiment is intended to be illustrative only and it will be understood by those skilled in the art that various design changes are possible and various modifications are possible and that such modifications are also within the scope of the present invention.

In the embodiment described above, the concave-convex structure <NUM> is shown as being formed on the second principal surface 22b of the substrate <NUM>. In one variation, the concave-convex structure <NUM> may be formed on a further layer formed on the second principal surface 22b of the substrate. For example, a third base layer may be formed on the second principal surface 22b, and the concave-convex structure <NUM> may be formed on the third base layer. The third base layer is preferably made of a material having a lower refractive index than the active layer <NUM> and a higher refractive index than the substrate <NUM> for the wavelength of the deep ultraviolet light emitted by the active layer <NUM>. Given that the substrate <NUM> is made of sapphire (the refractive index n<NUM>=about <NUM>) and the active layer <NUM> is a made of an AlGaN-based semiconductor material (the refractive index n<NUM>=about <NUM> ~ <NUM>), it is desirable that the third base layer be made of AlN (the refractive index n<NUM>=about <NUM>) or an AlGaN-based semiconductor material having a relatively higher AlN composition ratio (the refractive index n<NUM>=about <NUM> ~ <NUM>). The third base layer may be made of silicon nitride (SiNx, the refractive index n<NUM>=about <NUM> ~ <NUM>), silicon oxynitride (SiON), silicon oxide (SiO<NUM>), or aluminum oxide (Al<NUM>O<NUM>). It is preferred that the third base layer have a high transmittance for the deep ultraviolet light emitted by the active layer <NUM> and be configured to have an internal transmittance of <NUM>% or higher.

The method of forming the cone-shaped part <NUM> having the first portion <NUM> and the second portion <NUM> by using one type of mask has been described in the embodiment, but the method of manufacturing the cone-shaped part <NUM> is not limited to the method described above, and an alternatively method may be used. For example, the cone-shaped part <NUM> having the first portion <NUM> and the second portion <NUM> may be formed by combining two or more types of mask. Alternatively, different types of mask may be applied to a plurality of dry-etching steps. For example, the second etching step may be performed by applying the second type of mask after the first etching step using the first type of mask.

In the embodiment and the variations, a description is given of a case of forming the concave-convex structure <NUM> on the light extraction layer after the light emitting structure <NUM> is formed. In a further variation, the light emitting structure <NUM> may be formed after the concave-convex structure <NUM> is formed on the light extraction layer. For example, the substrate <NUM> on which the concave-convex structure <NUM> is formed in advance may be prepared, and the light emitting structure <NUM> may be formed on the substrate.

In the embodiment and the variations, a description is given of a case of forming the concave-convex structure <NUM> in the semiconductor light emitting device <NUM> for outputting deep ultraviolet light. In a further variation, the concave-convex structure <NUM> described above may be applied to a semiconductor light emitting device for outputting light other than deep ultraviolet light. For example, the concave-convex structure <NUM> may be applied to a light emitting device for outputting ultraviolet light of <NUM> ~ <NUM> or a light emitting device for outputting blue light of <NUM> ~ <NUM>. Further, the concave-convex structure <NUM> may be applied to a light emitting device for outputting visible light such as green light, yellow light, and red light or to a light emitting device for outputting infra-red light.

semiconductor light emitting device, <NUM>. base structure, <NUM>. substrate, 22a. first principal surface, 22b. second principal surface, 28b. light extraction surface, <NUM>. light emitting structure, <NUM>. concave-convex structure, <NUM>. cone-shaped part, <NUM>. first portion, <NUM>. second portion, <NUM>. bottom, <NUM>. light extraction layer, <NUM>.

Claim 1:
A semiconductor light emitting device (<NUM>) including a light extraction layer (<NUM>) having a light extraction surface (22b), a plurality of cone-shaped parts (<NUM>) formed in an array being provided on the light extraction surface, wherein
the cone-shaped part has a first portion (<NUM>) having a first angle (θ<NUM>) of inclination of a side surface and a second portion (<NUM>) having a second angle (θ<NUM>) of inclination of a side surface smaller than the first angle, and
the second portion (<NUM>) is closer to an apex (<NUM>) of the cone-shaped part (<NUM>) than the first portion and has a larger height (h<NUM>) than a height (h<NUM>) of the first portion (<NUM>), characterized in that
the height (h<NUM>) of the second portion (<NUM>) is not less than <NUM> times and not more than <NUM> times the height (h<NUM>) of the first portion (<NUM>).