AU2016200996B2 - Light-emitting element - Google Patents

Abstract

OF THE DISCLOSURE A light-emitting element includes: a sapphire substrate having a c-plane at a main surface thereof; and a semiconductor layer provided at the main surface side of the sapphire substrate. The sapphire substrate includes a first unit including a first region, a second region, and a third region, wherein, when viewed from the main surface side, the three regions together have a shape ofa regular hexagon thatis evenly divided into the three regions such that each region has a shape of a rhombus; and a plurality of second units disposed to be aligned with each side of the first unit, the second unit having mirror symmetry relative to the first unit. The first unit and the second units are arranged to make a space at the center of the unit. 74a

Description

LIGHT-EMITTING ELEMENT BACKGROUND OF THE INVENTION

Field of the Invention

[0001]

The present disclosure relates to light-emitting elements.

Description of the Related Art

[0002]

In general, a light-emitting element (light-emitting

diode: LED) including a semiconductor, such as a nitride

semiconductor, is usually configured by stacking an n-type

semiconductor layer, an active layer, and a p-type

semiconductor layer over a sapphire substrate in this order.

To improve light extraction efficiency of the light-emitting

element, some techniques are conventionally proposed that

involve previously forming elongated concave portions or a

composite structure of elongated concave and convex portions

on a sapphire substrate (see JP 2008-53385 A, JP 2008-91942 A,

and JP 2012-114204 A).

[0002A]

Reference to any prior art in the specification is not

an acknowledgement or suggestion that this prior art forms part

of the common generalknowledge in any jurisdiction or that this

prior art could reasonably be expected to be combined with any other piece of prior art by a skilled person in the art.

[0003]

SUMMARY OF THE INVENTION

[0004]

Certain embodiments of the present invention may provide

a light-emitting element that has a semiconductor layer

exhibiting excellent crystal orientation while being capable

of further reducing a dislocation density.

[0005]

In order to address the foregoing matter, a

light-emitting element according to one aspect of the present

disclosure is provided which includes: a sapphire substrate

having a c-plane at a main surface thereof; and a semiconductor

layer provided on a side of the main surface of the sapphire

substrate, wherein the sapphire substrate includes: a first

unit including a first region, a second region, and a third

region, which are produced by partitioning the sapphire

substrate in such a manner as to evenly divide a regular hexagon

into three rhombuses as viewed from the main surface side, the

first region being partitioned by respective sides parallel to

a first m-axis and a second m-axis, the second region being

partitioned by respective sides parallel to the second m-axis

and a third m-axis, the third region being partitioned by

respective sides parallel to the first m-axis and the third m-axis; and a plurality of second units disposed to be aligned with each side of the first unit, at least one of the plurality of second units having mirror symmetry relative to the first unit with respect to an a-axis passing through an apex of the first unit, wherein the first unit includes: a plurality of first convex portions arranged in the first region, each of the first convex portions having, at an outer edge thereof, a side parallel to the first m-axis; a plurality of second convex portions arranged in the second region, each of the second convex portions having, at an outer edge thereof, a side parallel to the second m-axis; and a plurality of third convex portions arranged in the third region, each of the third convex portions having, at an outer edge thereof, a side parallel to the third m-axis, and wherein the first convex portion located closest to a center of the regular hexagon is disposed not to intersect a tangent line that is in parallel to the third m-axis andin contactwithanendon the center side ofthe secondconvex portion located closest to the center, and the second convex portion located closest to the center of the regular hexagon is disposed not to intersect a tangent line that is in parallel to the first m-axis and in contact with an end on the center side of the third convex portion located closest to the center.

[0006]

Alternatively, in order to address the foregoing matter,

a light-emitting element according to another aspect of the present disclosure may be provided which includes: a sapphire substrate; and a semiconductor layer provided on a side of a main surface of the sapphire substrate, wherein the sapphire substrate has on the main surface side, a plurality of first units and aplurality ofsecondunits, the first and secondunits having respective regular hexagonal regions, wherein the first unit includes a plurality of first convex portions provided in each of three rhombic regions formed by evenly dividing the regular hexagonal region into three, wherein the first convex portions in one rhombic region extend in parallel to one pair ofopposed sides and are arranged along the otherpair ofopposed sides, an extending direction forming an angle of 60 degrees with respect to another extending direction of the convex portions provided in two other adjacent rhombic regions, wherein the second unit has mirror symmetry relative to the first unit when defining, as a reference, a line parallel to a perpendicular bisector of one side included in the regular hexagonal region of the first unit, and wherein the regular hexagonal region of the first unit is formed by arranging the six second units for the one first unit, and six sides of the regular hexagonal region of the first unit are aligned with facing sides of respective regular hexagonal regions of the six second units.

[0007]

Accordingly, the light-emitting element in the embodiments of the present disclosure can have the semiconductor layer exhibiting excellent crystal orientation while being capable of further reducing the dislocation density.

4A

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Fig. 1 is a schematic cross-sectional view showing the

entire structure of a light-emitting element according to a

first embodiment.

Fig. 2A is a unit cell diagram schematically showing plane

orientations of a sapphire crystal in a sapphire substrate.

Fig. 2B is a plan view of a sapphire crystal structure

schematically showing the plane orientations of the sapphire

crystal in the sapphire substrate.

Fig. 3 is an enlarged plan view schematically showing a

part of the sapphire substrate in the light-emitting element

of the first embodiment.

Fig. 4A is an enlarged plan view schematically showing

convex portions formed at the substrate of the light-emitting

element in the first embodiment.

Fig. 4B is a schematic enlarged plan view for explaining

a first unit and a second unit each of which represents a group

of convex portions formed at the sapphire substrate of the

light-emitting element in the first embodiment.

Fig. 5A is a cross-sectional view taken along the line

X1-Xl of Fig. 4B, showing the convex portion formed at the

substrate of the light-emitting element in the first

embodiment.

Fig. 5B is a cross-sectional view taken along the line

X2-X2 of Fig. 4B, showing the convex portion formed at the

substrate of the light-emitting element in the first

embodiment.

Fig. 5C is a cross-sectional view taken along the line

X3-X3 of Fig. 4B, showing the convex portion formed at the

substrate of the light-emitting element in the first

embodiment.

Fig. 6is aplan view for explaining the relationship among

the first unit, the second unit, and respective distances

between the convex portions formed at the substrate of the

light-emitting element in the first embodiment.

Fig. 7 is a plan view for explaining a distance between

the convex portions located in the first and second units at

the substrate of the light-emitting element, as well as a

distance between sub-units in the first embodiment.

Fig. 8A is an explanatory diagram schematically showing

a cross-sectional resultant state of a crystalgrowth direction

of a nitride semiconductor and converging dislocations thereof

at the light-emitting element in the first embodiment.

Fig. 8B is an explanatory diagram schematically showing

another cross-sectional midway state of a crystal growth

direction of the nitride semiconductor and converging

dislocations thereof at the light-emitting element in the first

embodiment.

Fig. 9A is a schematic cross-sectional view showing the state of a mask formation step while omitting illustration of a part of the sapphire substrate in order to form the convex portions at the substrate of the light-emitting element in the first embodiment.

Fig. 9B is a schematic cross-sectional view showing a

midstream of an etching step while omitting illustration of a

part of the substrate in order to form the convex portions at

the sapphire substrate of the light-emitting element in the

first embodiment.

Fig. 9C is a schematic cross-sectional view showing the

end of the dry etching in the etching step while omitting

illustration of a part of the substrate in order to form convex

portions at the sapphire substrate of the light-emitting

element in the first embodiment.

Fig. 9D is a schematic diagram showing a manufacturing

process of the light-emitting element in the first embodiment,

specifically, a schematic cross-sectional view of the state of

a buffer layer formed in a buffer layer formation step while

omitting illustration of a part of the substrate.

Fig. 9E is a schematic diagram showing another

manufacturing process of the light-emitting element in the

first embodiment, specifically, a schematic cross-sectional

view of a midstream of a semiconductor growth step while

omitting illustration of a part of the substrate.

Fig. 9F is a schematic diagram showing another manufacturing process of the light-emitting element in the first embodiment, specifically, a schematic cross-sectional view ofanother midstreamof the semiconductor growth step while omitting illustration of a part of the substrate.

Fig. 9G is a schematic diagram showing another

manufacturing process of the light-emitting element in the

first embodiment, specifically, a schematic cross-sectional

view of the state of a semiconductor layer provided in the

semiconductor layer growth step while omitting illustration of

a part of the substrate.

Fig. 9H is a schematic diagram showing another

manufacturing process of the light-emitting element in the

first embodiment, specifically, a plan view showing an example

of the light-emitting element having electrodes formed after

the semiconductor layer growth step.

Fig. 91 is a schematic diagram showing another

manufacturing process of the light-emitting element in the

first embodiment, specifically, a cross-sectional view taken

along the line X4-X4 of Fig. 9H showing the example of the

light-emitting element having the electrodes formed after the

semiconductor layer growth step.

Fig. 10A is a schematic plan view showing the arrangement

state of convex portions formed at a sapphire substrate in a

structure of a comparative example for the first embodiment.

Fig. 10B is a schematic plan view showing the state of crystal growth of a nitride semiconductor layer in a thickness of 2 pm on the sapphire substrate in the structure of the comparative example for the first embodiment.

Fig. 10C is a schematic plan view showing the state of crystal

growth of a nitride semiconductor layer in a thickness of 3.5

pm on the sapphire substrate in the structure of the comparative

example for the first embodiment.

Fig. 10D is a schematic plan view showing the state of

crystal growth of a nitride semiconductor layer in a thickness

of 4.5 pm on the sapphire substrate in the structure of the

comparative example for the first embodiment.

Fig. 11A is a schematic plan view showing the arrangement

state of convex portions formed at a sapphire substrate in the

first embodiment.

Fig. 11B is a schematic plan view showing the state of

crystal growth of a nitride semiconductor layer in a thickness

of 2 pm on the sapphire substrate in the first embodiment.

Fig. 11C is a schematic plan view showing the state of

crystal growth of a nitride semiconductor layer in a thickness

of 3.5 pm on the sapphire substrate in the first embodiment.

Fig. 11D is a schematic plan view showing the state of

crystal growth of a nitride semiconductor layer in a thickness

of 4.5 pm on the sapphire substrate in the first embodiment.

Fig. 12 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of the light-emitting element according to a second embodiment.

Fig. 13 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of the

light-emitting element according to a third embodiment.

Fig. 14 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of the

light-emitting element according to a fourth embodiment.

Fig. 15 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of a

light-emitting element in a first modified example of the first

to fourth embodiments.

Fig. 16 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of a

light-emitting element in a secondmodified example of the first

to fourth embodiments.

Fig. 17 is an enlarged plan view schematically showing

convex portions formed at the sapphire substrate of a

light-emitting element in a third modified example of the first

to fourth embodiments.

DETAILED DESCRITION OF THE EMBODIMEN

[0009]

A light-emitting element and a manufacturing method therefor

according to each of embodiments will be described with

reference to the accompanying drawings. The drawings referred in the description below schematically illustrate the respective embodiments. Some drawings emphasize the scale, interval, positional relationship, and the like of eachmember, or omit the illustration of the member. In the description below, the same names or reference characters denote the same or similar member in principle, and thus a detailed redundant description thereof will be omitted as appropriate.

[00101

<First Embodiment>

[Light-Emitting Element Structure]

A light-emitting element according to a first embodiment

will be described as the structure of a nitride semiconductor

element as an example with reference to Figs. 1 to 7. A

light-emitting element 1 has a laminated structure including

a sapphire substrate 10, a buffer layer 20, and a nitride

semiconductor layer 30 that are stacked in this order.

[00111

As shown in Figs. 1 and 3, the sapphire substrate 10 is

for growing a nitride semiconductor (e.g., GaN) while

supporting the nitride semiconductor layer 30. The sapphire

substrate 10 has, at its upper surface on a c-plane side as a

main surface side, a plurality of convex portions 11 formed in

an elongated shape in the plan view. The sapphire substrate

has a thickness, for example, of 50 pm to 300 pm as a whole,

including the convex portions 11 (first convex portions 11A, secondconvexportions11B, and thirdconvexportions11C). The first to third convex portions 11A to 11C will be regarded as the convex portions 11 when collectively being explained.

[0012]

The convex portion 11 can form the nitride semiconductor

layer 30 that has a reduced dislocation density and exhibits

excellent crystal orientation as a result of improving the

flatness when growing crystals of a nitride semiconductor on

the sapphire substrate 10. Here, as shown in Figs. 2A and 2B,

the sapphire substrate 10 is formed of a sapphire crystal SC

having a hexagonal crystal structure, and has a c-plane ((0001)

surface) as a main surface. Note that the "c-plane" as used

in the present specification may include a surface that is

slightly inclined by an off angle relative to the c-plane. The

off angle is, for example, approximately 3° or less. The

above-mentioned convex portion 11 is formed at the surface on

the c-plane side as the main surface. Referring to the unit

cell diagram, the sapphire crystal SC has six m-planes as side

surfaces of a hexagonal cylinder, and three a-planes

respectively perpendicular to the ai axis, the a 2 axis, and the

a 3 axis, that is, a first a-plane, a second a-plane, and a third

a-plane, in addition to the c-plane. The direction

perpendicular to the m-plane is the m-axis direction. The

m-axis directions include three directions respectively

extending and displaced by 30 degrees relative to the ai axis, the a 2 axis, and the a3 axis. The m axes are respectively positioned in parallel to the first to third a-planes, and hereinafter referred to as a first m axis Sal, a second m axis

Sa2, and a third m axis Sa3, respectively.

[0013]

As illustrated in Figs. 3 and 4A, all convex portions 11

have the same shape. The predetermined number of convex

portions 11 (for example, three to five convex portions; four

convex portions in Fig. 3) are formed to be arranged in parallel

at predetermined intervals along any one of the first m axis

Sal, the second m axis Sa2, and the third m axis Sa3. The convex

portions 11 (first to third convex portions 11A to 11C) are

preferably placed, for example, at an interval (with the

shortest distance therebetween) of 0.3 pm to 4 pm in the

longitudinal direction and transverse direction. The length

in the longitudinal direction of the convex portion 11 (whole

core length Li) and the length in the transverse direction (core

diameter Da) are preferable set in a range of 5 pm to 25 pm,

and in a range of 1 pm to 5 pm, respectively. The height of

the convex portion 11is preferably set, for example, in a range

of 0.5 pm to 2.5 pm.

In the convex portion 11, the length in the longitudinal

direction of the elongated shape in the plan view (length in

parallel to each of the m axes Sal to Sa3) is preferably three

or more times (more preferably, 6 to 15 times, or 5 to 12 times) as long as that in the transverse direction (length perpendicular to each of the m axes Sal to Sa3). The convex portion 11 has both ends in the longitudinal direction formed in the substantially same shape. Here, the convex portion 11 has a linear part with both ends thereof formed in a semicircular shape in the plan view. Note that the length of the linear part in the longitudinal direction of the convex portion 11 is defined as a core length L2, and the length of the convex portion

11 from one end to the other thereof is defined as the whole

core length L. Here, the convex portion 11 is formed in such

a manner that the ratio of the core length L2 to the whole core

length Li is, for example, in a range of 1:1.05 to 1.6.

The convex portions 11 have, as their sides 11a to 11c,

the linear parts positioned at their outer edges in parallel

to the m axes Sal to Sa3, respectively. For example, the first

convex portion 11A is formed to have the opposed linear sides

11a in parallel to the first m axis Sal, and arc outer edges

located at both ends of the sides 11a in the plan view. The

first convex portion 11A is positioned to form an angle of 60

degrees with respect to the extending directions of the second

convex portion 11B and the third convex portion 11C. Note that

the second convex portion 11B and the third convex portion 11C

have the substantially same structure, and thus a detailed

description thereof is made below.

[00141

As shown in Figs. 5A to 5C, the convex portion 11 has its

section with a sharpened and not flat upper part thereof in the

transverse direction (direction perpendicular to a

corresponding one of the maxes Sal to Sa3). Thatis, the convex

portion 11 is formed to have an apex with a triangle

cross-sectional shape in the transverse direction extending

from a predetermined position in height to the apex. Thismeans

that the convex portion 11 is formed in a domical shape that

has its side surfaces inclined relative to the c axis, which

is an axis perpendicular to the upper surface of the sapphire

substrate 10.

The total number of convex portions 11 is determined

depending on the area of the sapphire substrate 10, taking into

consideration the interval between the respective convex

portions 11 and the length of each convex portion 11. For

example, the convex portions 11 are evenly distributed across

the entire surface of the sapphire substrate 10.

[0015]

In the first embodiment, as shown in Figs. 3 and 4A, the

convex portions 11 include the first convex portions 11A

disposed along the first m axis Sal, the second convex portions

11B disposed along the second m axis Sa2, and the third convex

portions 11C disposed along the third m axis Sa3. A group of

first convex portions llA (first convex portion group) is

referred to as a first sub-unit SUl; a group of second convex portions 11B (second convex portion group) is referred to as a second sub-unit SU2; and a group of third convex portions 11C

(third convex portion group) is referred to as a third sub-unit

SU3.

[0016]

The first convex portions 11A are disposed in a first

region Arl as one of virtual rhombic regions obtained by evenly

dividing an virtual regular hexagon into three pieces; the

second convex portions 11B are disposed in a second region Ar2

as another rhombicregionmentioned above; and the third convex

portions 11C are disposed in a third region Ar3 as the

above-mentioned remaining rhombic region. The first region

Arl with the first convex portions 11A formed therein, the

second region Ar2 with the second convex portions 11B formed

therein, and the third region Ar3 with the third convexportions

11C formed therein are gathered together to form the virtual

hexagonal region, which is defined as a first unit KU. That

is, the first unit KU is evenly divided into three regions,

namely, the first region Arl to the third region Ar3. The first

convex portions 11A to the third convex portions 11C have

three-fold rotational symmetry in the first unit KU.

[0017]

The first region Arl is set as a rhombic region disposed

in the first unit KU having the regular hexagon, the rhombic

region having its sides in parallel to the first m axis Sal and the second m axis Sa2. The second region Ar2 is set as a rhombic region disposed in the first unit KU having the regular hexagon, the rhombic region having its sides in parallel to the second m axis Sa2 and the third m axis Sa3. The third region Ar3 is set as a rhombic region disposed in the first unit KU having the regular hexagon, the rhombic region having its sides in parallel to the first m axis Sal and the third m axis Sa3.

[0018]

As shown in Figs. 3 and 4B, the sapphire substrate 10 is

configured to form a unit pattern by the first unit KU and a

second unit TU that has mirror symmetry with respect to the first

unit KU. The unit pattern is formed by combining the

arrangement of the first, second, and third regions Arl, Ar2,

and Ar3 ofthe first unitKUformingone virtualregular hexagon,

with the second unit TU which has mirror symmetry relative to

the firstunit and forms anothervirtualregularhexagon. Here,

in the combination of the first unit KU and the second unit TU,

each side of the virtual regular hexagon of the first unit KU

is aligned with one side of the corresponding virtual regular

hexagon of the second unit TU, thereby forming the unit pattern.

[0019]

Note that the regular hexagons virtually partitioned by

the first unit KU and the second unit TU are formed by virtual

reference lines for positioning the first convex portions 11A

to the third convex portions 11C, but not actually formed on the substrate. The rhombuses imaginarily partitioned as the first regionArl to the thirdregionAr3, or as the firstsub-unit

SUl to third sub-unit SU3 are formed by the virtual reference

lines but not actually formed on the substrate.

[0020]

The relationship of the mirror (mirror image) symmetry

between the first unit KU and the second unit TU means that as

shown in Fig. 4B, the first region Arl to third region Ar3 of

the virtual-regular-hexagonal first unit KU positioned on one

side via a symmetry axis MG are positioned to overlap with the

first region Arl to third region Ar3 of the

virtual-regular-hexagonal second unit TU, which are positioned

mirror-symmetrically, when the first unit is copied as the

mirror image on the other side of the symmetry axis MG. Then,

the second unit TU is moved in parallel to itself from the apex

as a starting point, whereby the second unit TU is aligned with

each side of the first unit KU. For example, as shown in Fig.

3, a side Hal of the first unit KU is aligned with a side Hb6

of the second unit TU. Likewise, a side Ha2 is aligned with

a side Hb5; a side Ha3 with a side Hb4; a side Ha4 with a side

Hb3; a side Ha5 with a side Hb2; and a side Ha6 with a side Hbl.

[0021]

Here, the first unit KU is displaced to have mirror

symmetry with its apex as the starting point and then moved in

parallel to itself to make alignment of the respective sides between the first and secondunits. The same goes for the second unit TU that has mirror symmetric with respect to the first unit

KU one side of which is parallel to the symmetry axis MG. That

is, the second unit TU should have the mirror symmetry with

respect to the first unit KU, regarding the arrangement

relationship of the first region Arl to third region Ar3. Note

that the second unit TU obtained by setting one side of the first

unit KU parallel to the symmetry axis MG is displaced by an angle

of 30 degrees and moved in parallel to itself, so that the sides

Hbl to Hb6 are aligned to the respective sides Hal to Ha6 of

the first unit UK to thereby form the unit pattern as mentioned

above. As shown in Fig. 4B, in the second unit TU, the first

convex portion llA has mirror symmetry to that of the first unit,

and the inclination direction of the first convex portion is

set to form an inclination angle along the second m axis as

illustrated in the figure. Further, in the second unit TU, the

second convex portion 11B has mirror symmetry to that of the

first unit, and the inclination direction of the second convex

portion is set to form an inclination angle along the first m

axis as illustrated in the figure.

In other words, the second unit TU has the mirror symmetry

with respect to the first unit KU when defining, as a reference,

a straight line parallel to a perpendicular bisector of one side

included in the regular hexagonal region of the first unit KU

(in which the convex portion 11 is arranged to be rotated by

180 degrees with respect to the reference straight line).

Further, six second units TU are arranged for one first unit

KU such that each of the six sides Hal to Ha6 of the regular

hexagonal region of the one first unit KU is aligned with one

of the sides Hbl to Hb6 of the regular hexagonal regions of the

six second units TU.

As shown in Fig. 4B, in the secondunit TU, the first convex

portion 11A has mirror symmetry to that of the first unit, and

the inclination direction of the first convex portion is set

to form an inclination angle along the second m axis as

illustrated in the figure. Further, in the second unit TU, the

second convex portion 11B has mirror symmetry to that of the

first unit, and the inclination direction of the second convex

portion is set to form an inclination angle along the first m

axis as illustrated in the drawing.

[0022]

As illustrated in Figs. 3 and 4A, the plurality of first

convex portions 11A are respectively formed along the first m

axis Sal to form the same shape. The first convex portions 11A

in the first unit KU extend along the first m axis Sal to form

an elongated shape in the first rhombic region Ar as one of

three regions obtained by evenly dividing the regular hexagon

virtually formed. The first convex portions 11A are arranged

in parallel at equal intervals such that one ends of the four

first convex portions and other ends thereof are aligned along the second m axis Sa2.

That is, the first convex portions 11A extend in parallel

to a pair of opposed sides of the rhombic region as the first

region Arl, and arranged at equalintervals along the other pair

of opposed sides thereof. The first convex portions 11A

disposed in the first region Ar are arranged such that the

extending direction thereof forms 60 degrees with respect to

the extending directions of the convex portions 11B and 11C

provided in the second and third regions Ar2 and Ar3, which are

two other rhombic regions adjacent to the first region.

The four first convex portions 11A are collectively

regarded as the first sub-unit SU1, and arranged in the first

regionArl while being spacedby a first distance dalanda fourth

distance dsl. In the first sub-unit SUl, the first convex

portions 11A are arranged such that their ends on one side are

aligned along one side of the regular hexagon, while their other

ends on the other side are spaced from the second region Ar2

side by the first distance dal set as a predetermined distance,

and aligned along the same second m axis Sa2. Note that the

fourth distance dsl is a distance between the first convex

portion 11A positioned the farthest from the central point side

of the virtual regular hexagon and the corresponding one side

ofthe regularhexagonin the first regionArl. Here, the fourth

distance dsl is set substantially the same as that between the

adjacent first convex portions 11A.

[00231

Thus, as shown in Fig. 4A, the first distance dal between

the other ends of the first convex portions 11A and the second

region Ar2 is configured to be uniform across the four first

convexportions11A. Aregion ofthe substrate for continuously

keeping the first distance dal in the substantially constant

range along the secondmaxis Sa2 is formed toovercome the third

convex portion 11C located closest to the center of the regular

hexagon in the third region Ar3 and to reach the third convex

portion11Clocatedsecond closest to the center. Inparticular,

in the first region Arl, the first convex portion 11A closest

to the center of the regular hexagon is spaced apart from the

end of the second convex portion 11B closest to the center

thereof so as not to intersect a tangent line Ya2 directed toward

the first region Arl, in parallel to the third m axis Sa3. In

the center of the unit, a region continuously extending along

the second m axis Sa2 can be formed from the first region Arl

to the third regionAr3 with the first distance dalkept constant.

The tangent line Ya2 is a virtual line that is in parallel to

the third m axis Sa3 and in contact with the end of the second

convex portion 11B.

[0024]

The second convex portions 11B in the first unit KU extend

along the second m axis Sa2 to form an elongated shape in the

second rhombic region Ar2 as one of three regions obtained by evenly dividing the regular hexagon virtually formed. The second convex portions 11B are arranged in parallel at equal intervals such that one ends of the four second convex portions and other ends thereof are aligned along the third m axis Sa3.

Thatis, the second convexportions11Bextendinparallel

to a pair of opposed sides of the rhombic region as the second

region Ar2, and arranged at equalintervals along the other pair

of opposed sides thereof. The second convex portions 11B

disposed in the second region Ar2 are arranged such that the

extending direction thereof forms 60 degrees with respect to

the extending directions of the convex portions 11A and 11C

provided in the first and third regions Arl and Ar3, which are

two other rhombic regions adjacent to the second region.

The four second convex portions 11B are collectively

regarded as the second sub-unit SU2, and arranged in the second

region Ar2 while being spaced by a second distance da2 and a

fifth distance ds2. In the second sub-unit SU2, the second

convex portions 11B are arranged such that their ends on one

side are aligned along one side of the regular hexagon, while

their other ends on the other side are spaced from the third

region Ar3 side by the predetermined distance and aligned along

the same third m axis Sa3. Note that the fifth distance ds2

is a distance between the second convex portion 11B positioned

farthest from the central point side of the virtual regular

hexagon and the corresponding one side of the regular hexagon in the second region Ar2. Here, the fifth distance ds2 is set substantially the same as the interval between the adjacent second convex portions 11B.

[0025]

Thus, as shown in Fig. 4A, the second distance da2 between

the other ends of the second convex portions 11B and the third

region Ar3 is configured to be uniform across the four second

convexportions11B. Aregion ofthe substrate for continuously

keeping the second distance da2 in the substantially constant

range along the third m axis Sa3 is formed to overcome the first

convex portion 11A located closest to the center of the regular

hexagon in the first region Arl and to reach the first convex

portion11Alocatedsecondclosest to the center. Inparticular,

in the second region Ar2, the second convex portion 11B closest

to the center of the regular hexagon is spaced apart from the

end of the third convexportion11C closest to the center thereof

so as not to intersect a tangent line Ya3 directed toward the

second region Ar2, in parallel to the first m axis Sal. Thus,

in the center of the unit, the region continuously extending

along the third m axis Sa3 can be formed from the second region

Ar2 to the first region Arl with the second distance da2 kept

constant. The tangent line Ya3 is a virtual line that is in

parallel to the first m axis Sal and in contact with the end

of the third convex portion 11C.

[0026]

The third convex portions 11C in the first unit KU extend

along the third m axis Sa3 to form an elongated shape in the

third rhombic region Ar3 as one of three regions obtained by

evenly dividing the regular hexagon virtually formed. The

third convex portions 11C are arranged in parallel at equal

intervals such that one ends of the four third convex portions

and other ends thereof are aligned along the first m axis Sal.

That is, the third convex portions 11C extend in parallel

to a pair of opposed sides of the rhombic region as the third

region Ar3, and arranged at equalintervals along the other pair

of opposed sides thereof. The third convex portions 11C

disposed in the third region Ar3 are arranged such that the

extending direction thereof forms 60 degrees with respect to

the extending directions of the convex portions 11A and 11B

provided in the first and second regions Arl and Ar2, which are

two other rhombic regions adjacent to the third region.

The four third convex portions 11C are collectively

regarded as the third sub-unit SU3, and arranged in the third

region Ar3 while being spaced by a third distance da3 and a sixth

distance ds3. In the third sub-unit SU3, the third convex

portions 11C are arranged such that their ends on one side are

aligned along one side of the regular hexagon, while their other

ends on the other side are spaced from the first region Arl side

by the predetermined distance and aligned along the same first

m axis Sal. Note that the sixth distance ds3 is a distance between the third convex portion 11C positioned farthest from the central point side of the virtual regular hexagon and the corresponding one side of the regular hexagon in the third region Ar3. Here, the sixth distance ds3 is set substantially the same as that between the adjacent third convex portions 11C.

[0027]

Thus, as shown in Fig. 4A, the third distance da3 between

the other ends of the third convex portions 11C and the first

region Arl is configured to be uniform across the four third

convex portions 11C. Aregion of the substrate for continuously

keeping the third distance da3 in the substantially constant

range along the first m axis Salis formed to overcome the second

convex portion 11B located closest to the center of the regular

hexagon in the second region Ar2 and to reach the second convex

portion 11B located second closest to the center. In particular,

in the third region Ar3, the third convex portion 11C closest

to the center of the regular hexagon is spaced apart from the

end of the first convex portion 11Aclosest to the center thereof

so as not to intersect a tangent line Yal directed toward the

third region Ar3, in parallel to the second m axis Sa2. Thus,

in the center of the unit, the region continuously extending

along the first m axis Sal can be formed from the third region

Ar3 to the second region Ar2 with the third distance da3 kept

constant. The tangent line Yal is a virtual line that is in

parallel to the second m axis Sa2 and in contact with the end of the first convex portion 11A.

[0028]

In the first unit KU and the second unit TU, at least two

of the first convex portion 11A, second convex portion 11B, and

third convex portion 11C, which are closest to the center of

the virtual regular hexagon should be arranged spaced not to

intersect a corresponding one of the tangent line Yal, tangent

line Ya2, and tangent line Ya3. For example, even if the first

convex portion 11A is disposed to make the first distance dal

narrow while abutting against with the tangent line Ya2, the

second convex portion 11B and the third convex portion 11C

should be arranged spaced from the tangent line Yal or the

tangent line Ya3. The same goes for the second convex portion

11B and the third convex portion 11C.

That is, in the first unit KU and the second unit TU, the

first convex portion 11A located closest to the center of the

regular hexagon is disposed not to intersect the tangent line

Ya2 that is in parallel to the third m axis Sa3 in contact with

the end on the center side of the second convex portion 11B

closest to the center. Further, in the first unit KU and the

second unit TU, the second convex portion 11B located closest

to the center of the regular hexagonis disposednot tointersect

the tangent line Ya3 that is in parallel to the first m axis

Sal and in contact with the end on the center side of the third

convex portion 11C closest to the center.

[00291

As shown in Figs. 6 and 7, in the first unit KU and the

second unit TU, the first convex portions 11A are arranged

spaced by the first distance dal and the fourth distance dsl

in the first region Arl; the second convex portions 11B are

arranged spaced by the second distance da2 and the fifth

distance ds2 in the second region Ar2; and the third convex

portions 11C are arranged spaced by the third distance da3 and

the sixth distance ds3 in the third region Ar3. Thus, the first

convex portions 11A to the third convex portions 11C are

arranged at substantially equal intervals present in each unit

pattern.

[0030]

As shown in Fig. 7, the first unit KU and the second unit

TU are configured such that the intervals between the convex

portions 11 are substantially equal in the center regions CEl

and CE2 of the virtual regular hexagon, as well as in the

respective regions SE between the apexes of the virtual regular

hexagons by revising an interval between the convex portions

significantly different from those in other regions.

Therefore, the first unit KU and the second unit TU have

such a unit pattern that the crystal growth rate of the nitride

semiconductor, such as GaN, is equalized in a plane of the

sapphire substrate 10, compared to the conventional structure

(in other words, the dislocation density of the nitride semiconductor layer 30 being grown tends to be reduced, and the crystal orientation of the nitride semiconductor layer 30 is improved).

[0031]

In the arrangement pattern of the convex portions 11,

there are six apex-parts where the first and second units KU

and TUare opposed toeachother. Regarding the above-mentioned

sub-unit or the unit of regions, in some of the six apex-parts

where the units are opposed to each other, the facing apexes

of the four virtual rhombic sub-units are butted against one

another, while in the others of the six apex-parts, the facing

apexes of the five virtual rhombic sub-units are butted against

one another. In the center of the unit, the facing apexes of

the three virtual rhombic sub-units are butted against one

another (in the conventional structure, for example, see Fig.

A; in Fig. 10A, there are only two types of apex butting parts,

specifically, the butting part of six apexes, and the butting

partofthree apexes). Thatis, by the use ofsuchaunitpattern

in the first unit KU and the second unit TU, the number of apexes

butted against one another is set to differ depending on the

positions of the virtual apexes for each sub-unit or in units

of region, which can easily adjust the intervals of the convex

portions 11.

[0032]

As shown in Figs. 5A to 5C, the first convex portion 11A to the third convex portion 11C has a cross-sectional shape in the transverse direction that has its upper part sharpened and not flat, so that the number of penetration dislocations appearing at the surface of the nitride semiconductor can be decreased. Note that if the convex portion 11 has the cross-sectional shape with a flat top surface, such as a trapezoid shape (not shown), the nitride semiconductor also grows from the flat top surface (c-plane). Since the nitride semiconductor growing from the top surface barely grows in the lateraldirection, a plurality of dislocations generated in the growth direction does not converge, resulting in an increase in dislocation density at the surface of the nitride semiconductor. In contrast, as mentioned above, when there is no flat top surface in the cross-sectional shape of the convex portion 11, the growth from the top part of the convex portion

11 is suppressed, permitting the nitride semiconductor to grow

in the lateral direction. Thus, the convex portions 11 allows

the plurality of dislocations generatedin the growth direction

to converge, reducing the dislocation density.

[0033]

In the crystal growth, a relatively stable crystal plane

tends to appear as the facet surface. Crystals of the hexagonal

nitride semiconductor (e.g., GaN) grows while setting a plane

slightly inclined relative to the m-plane of the nitride

semiconductor as the facet surface. Thus, if the tip end in the longitudinal direction of the convex portion 11 has a semicircular shape in the planer view, the respective facet surfaces can grow substantially in the uniform width, so that the crystals of the nitride semiconductor can be butted against and bonded to each other toward the center of the semicircular shape. In the crystalgrowth of the nitride semiconductor, the nitride semiconductor grows mainly from the c-plane (flat surface without having the convex portions 11) of the sapphire substrate 10, whereby the crystals can be uniformly grown also in the lateral direction to be abutted against and bonded to each other above the convex portion 11 (note that referring to

Figs. 8A and 8B, the detailed description of dislocations will

be given later.)

[0034]

Returning to Fig. 1, the description of the structure of

the light-emitting element 1 will be continued. The buffer

layer 20 serves to buffer a difference in lattice constant

between the sapphire substrate 10 and the nitride semiconductor

grown on the sapphire substrate 10. The buffer layer 20 is

formed between the sapphire substrate 10 and the nitride

semiconductor layer 30. The buffer layer 20 includes, for

example, AlN, AlGaN, etc. The buffer layer 20 can be formed

by sputtering, for example, under predetermined conditions in

a buffer layer formation step of the manufacturing method as

mentioned later. The buffer layer 20 is a layered shape that covers the sapphire substrate 10, for example, as shown in Fig.

1, but may partly expose the sapphire substrate 10.

[0035]

The nitride semiconductor layer 30 serves as a light

emission portion of the light-emitting element 1 and is formed

using a nitride semiconductor, such as InxAlyGaix-yN (0 X, 0

K Y, X + Y 1). As illustrated in Fig. 1, the nitride

semiconductor layer 30is formed over the c-plane (main surface)

of the sapphire substrate 10 via the buffer layer 20, and has

a laminated structure including an n-type semiconductor layer

31, an active layer 32, and a p-type semiconductor layer 33 that

are stacked from the bottom in this order. The active layer

32 has a quantum well structure, for example, with a well layer

(light-emission layer) and a barrier layer.

[0036]

Here, referring to Figs. 8A and 8B, the crystal growth

and dislocation willbe described. In the use of a flat sapphire

substrate 10 with no convex portions 11formed thereon, crystals

of the nitride semiconductor cannot grow in the lateral

direction. However, as mentioned above, in the use of the

above-mentioned sapphire substrate 10 with the convex portions

11 formed thereon, crystals of the nitride semiconductor can

also grow in the lateral direction during the crystal growth.

Since dislocations basically proceed in the crystal growth

direction, as shown in Figs. 8A and 8B, the nitride semiconductor grows in the lateral direction toward the convex portion 11, whereby the dislocations of the nitride semiconductor also proceed in the lateral direction toward above the convex portion 11. Above the convex portion 11, the nitride semiconductors are butted against each other, also causing convergence of the dislocations to make a closed loop or the like. As a result, the dislocations are less likely to appear on the surface of the final surface of the nitride semiconductor. Note that in Figs. 8Aand 8B, the crystal growth proceeds from the state shown in Fig. 8B to that shown in Fig.

8A over time.

[0037]

In this way, the crystals of the nitride semiconductor

are gradually butted against and bonded to each other with the

facet surface kept exposed, which decreases the number of

dislocations, leading to a decrease in dislocation density of

the nitride semiconductor layer 30. At this time, as

illustrated by the change from the state of Fig. 8B to that of

Fig. 8A, the longer the time during which the nitride

semiconductor exposes the facet surface (the thicker the grown

layer with the facet surface exposed), the more likely the

dislocations are to converge, which can easily decrease the

number of dislocations. By configuring the unit pattern of the

convex portions 11 as mentioned above, the dislocations can

converge in a shorter time, thus enabling the crystal growth to achieve a flat surface in a position closer to the sapphire substrate 10, compared to the case in the related art. As shown in Figs. 8A and 8B, the proceeding direction of dislocations during the crystal grow in the lateral direction is one direction, but can change in midstream. For example, the dislocations proceed upward in the early stage, and then laterally or obliquely upward in the midstream.

[0038]

The convex portion 11 has its outer edge in the

longitudinal direction shaped to extend in the direction

forming an angle along the corresponding one of the first m axis

Sal to the third m axis Sa3 of the sapphire substrate 10, so

that the crystal growth rate is adjusted until the crystals of

the nitride semiconductor are butted against and bonded to each

other above the convex portion 11 to achieve the flat surface

in a short time. Now, a description will be given of GaN by

way of example, which is one of typical nitride semiconductors.

[0039]

Crystals of the hexagonal GaN grow with the upward

direction set as the c-axis direction. Regarding the lateral

direction, crystals are less likely to grow in the m-axis

direction, compared to the a-axis direction. Thus, crystals

tend to grow while maintaining the facet surface having its base

aligned with the line of intersection between the c-plane of

the sapphire substrate 10 and a surface equivalent to the m-plane of the GaN (surface perpendicular to the c-plane of the sapphire substrate 10) in the plan view. At this time, the m-plane of GaN is positioned along the same flat surface as the a-plane of the sapphire substrate 10. That is, GaN tends to grow while maintaining the facet surface which has, as its base, the line aligned with the a-plane of the sapphire substrate 10 the planview. Then, the elongated convex portions 11having the outer edges extending in the longitudinal direction are arranged at the surface of the sapphire substrate 10 along a surface different from the m-plane of the sapphire substrate

(typically, a-plane). Thus, the outer edge extending in the

longitudinal direction of the convex portion 11 is not aligned

with the a-plane of GaN, and the base of the facet surface is

in parallel to the outer edge extending in the longitudinal

direction of the convex portion 11.

[0040]

As a result, as compared to the case in which the outer

edge of the convex portion 11 extending in the longitudinal

direction is aligned with the a-plane of the GaN, that is, the

case in which the base of the facet surface is non-parallel with

respect to the outer edge extending in the longitudinal

direction of the convex portion 11, the growth rate of GaN in

the transverse direction of the convex portion 11 becomes slow.

Thus, above the convex portion 11, it takes more time to grow

crystals in the lateral direction than to grow crystals in the upward direction, and dislocations are easily permitted to converge, which can reduce the dislocation density. When the direction in which the nitride semiconductor easily grows

(a-axis direction of GaN) is identical to the transverse

direction of the convex portion 11, the crystals of the nitride

semiconductor growing from both sides in the transverse

direction of the convexportion 11are butted against and bonded

to each other across a wide range. When the grown crystals are

butted against each other, new dislocations might occur. For

this reason, the transverse direction of the convex portions

11 are positioned to be displaced from the a-axis direction of

GaN in which the nitride semiconductor tends to easily grow

(here, the longitudinal direction of the convex portion 11 of

the sapphires substrate 10 is disposed along each of the m axes

of the sapphire substrate 10), so that the crystals of the

nitride semiconductor grown from both sides in the longitudinal

direction of the convex portion11are butted against and bonded

to each other, thereby suppressing occurrence of new

dislocations.

[0041]

In the light-emitting element 1, as mentioned above, the

facet surface of the nitride semiconductor is aligned with the

outer edge of the convex portion 11 extending in the

longitudinal direction, whereby crystals of the nitride

semiconductor gradually grow from the vicinity of their tip ends to converge near the center of the convex portion 11. Thus, in the plan view, above the convex portion 11, an area at the center of the convex portion 11 in the longitudinal direction where the dislocations remain becomes small (narrow) and further the dislocation density also tends to be small. In contrast, for example, when the outer edge extending in the longitudinal direction of the convex portion 1 is positioned in the direction exceeding a range of ±100from each m axis of the sapphire substrate 10 (for example, when the longitudinal direction of the convex portion is aligned with a direction perpendicular to the direction of the first m axis Sal), the outer edges extending in the longitudinal direction of the convex portion 11 are not aligned with the facet surface of the nitride semiconductor. As a result, the crystals of the nitride semiconductor are almost simultaneously butted against and bonded to each other in the vicinity of the center line of the convex portion 11 in the longitudinal direction, and will not be able to grow in the lateral direction any more.

[0042]

By using such a unit pattern in the first unit KU and the

second unit TU, a difference in growth rate of the nitride

semiconductor in the plane of the sapphire substrate 10 can be

reduced (the flatness of the nitride semiconductor can be

improved during the crystalgrowth), thereby further decreasing

the dislocation density of the nitride semiconductor layer 30, compared to the case in which an interval between adjacent convex portions 11 in the first unit KU and the second unit TU is narrow. Together with this, the crystal growth of the nitride semiconductor layer 30 can also be improved. For example, if an interval at the center of the unit cannot be adjusted, even though an interval between the units is secured, the further flatness during the crystalgrowthcannot be ensured.

The unit pattern is formed by positioning the second unit TU

having the mirror symmetry relative to the first unit KU to widen

the arrangement of the center of the unit (with a space in the

im axis direction of the sapphire substrate), thereby ensuring

further flatness.

[0043]

The light-emitting element 1 with the above-mentioned

structure in the first embodiment includes the nitride

semiconductor layer 30 with the low dislocation density that

is grown from the sapphire substrate 10 with the elongated

convex portions 11, and thus can improve the temperature

property. The term "improvement of the temperature property"

as used herein means that a change in output is small when the

atmospheric temperature is increased. For example, assuming

that an optical output from the light-emitting element 1 is set

to 1 while being driven under the normal-temperature atmosphere

(for example, at 25°C), the optical output from the light

emitting element 1 while being driven under the high-temperature atmosphere (for example, at 100°C) is decreased to become lower than 1, but this decrease of the optical output is small.

[00441

Such improvement of the temperature property is supposed

to be due to reduction in trapped electrons caused by the

dislocations because the dislocation density is decreased. in

more details, the dislocation density of, particularly, the

active layer 32 of the nitride semiconductor layer 30 is lowered

to thereby improve the temperature property. The dislocation

density of the active layer 32 can be determined by the density

of dislocations appearing at the surface of the n-type

semiconductor layer 31 as the underlayer. Thus, especially,

the dislocation density of the surface of the n-type

semiconductor layer 31 is preferably decreased.

Normally, in light-emitting elements, as the dislocation

density is decreased, the temperature property is improved, but

Vf is increased, and the optical output is lowered (that is,

the forward voltage (Vf) and the optical output (Po) are

degraded.) However, the light-emitting element 1 with the

structure of the present disclosure can also improve the crystal

orientation, thereby reducing the forward voltage (Vf) while

maintaining or improving the temperature property, thus

improving the optical output (Po). Together with this, the

light-emitting element 1 can also improve its luminous efficiency.

[0045]

[Manufacturing method for light-emitting element]

A manufacturing method for the light-emitting element 1

in the first embodiment willbe described with reference to Figs.

9A to 91. Note that a description will be given of the

manufacturing method for a light-emitting element 2, in which

an externalconnection electrode is added to the light-emitting

element 1. The cross-sectional views of the substrate

illustrate sections taken along the longitudinal direction

through the center of the third convex portion located closest

to the center point of the first unit KU.

[0046]

First, the manner of forming the convex portion 11 on the

main surface of the sapphire substrate will be described. The

convex portion 11 is formed at the sapphire substrate by

performingamask formation step shownin Fig. 9A, andan etching

step shown in Figs. 9B and 9C in this order.

In the mask formation step, a mask M is formed on the

sapphire substrate 10. In the mask formation step,

specifically, as shown in Fig. 9A, for example, SiO 2 or

photoresist is deposited at the surface on the c-plane side of

the sapphire substrate 10 and then patterned, thereby forming

a plurality of elongated masks M that cover regions where the

convex portions 11 are to be formed.

[00471

The etching step involves etching the sapphire substrate

10. In the etching step, specifically, as shown in Figs. 9B

and 9C, the sapphire substrate 10 with the mask M disposed

therein is dry-etched to thereby form a plurality of convex

portions11inside the firstunitKUand the secondunit TUhaving

virtual regular hexagonal shape, at the surface on the c-plane

side of the sapphire substrate 10. Each of the convex portions

11 has an elongated shape that extends along a corresponding

one of the first m axis Sal, the second m axis Sa2, and the third

m axis Sa3.

[0048]

In this embodiment, material that is less susceptible to

etching than the substrate is used as material for the mask M,

whereby in a first etching step, the mask M on the sapphire

substrate 10 is also etched. In this case, not only the upper

surface but also the side surfaces of the mask M are gradually

etched to reduce the diameter of the mask M. The top part of

convex portion 11 over the sapphire substrate 10 is etched into

a domical shape, such as a semicircular shape, with its upper

end sharpened, in the front view. If the convex portion 11 has

its upper surface (c-plane) formed in some shape, the nitride

semiconductor might grow from the upper surface. For this

reason, the upper end of the convex portion withno upper surface,

such as in a hemispherical shape, is preferably formed in a sharpened shape.

[0049]

Specific ways for the dry etching suitable for use can

include, for example, vapor-phase etching, plasma etching, and

reactive ion etching. At this time, examples of etching gas

include C1 2 , SiCl 4 , BC1 3 , HBr, SF 6 , CH 4 , CH 2 F 2 , CHF 3 , C 4 F8 , CF 4

, and Ar of inert gas.

[0050]

A manufacturing method for the light-emitting element 1

will be described below.

In the manufacturing method for the light-emitting

element 1, after forming the convex portions 11 (first convex

portion 11A to third convex portion 11C) at the sapphire

substrate 10 mentioned above, further, a buffer layer formation

step shownin Fig. 9Dand a semiconductor layer growthstep shown

in Figs. 9E and 9F are performed in this order.

[0051]

In the buffer layer formation step, the buffer layer 20

is formed over the sapphire substrate 10. Specifically, as

shown in Fig. 9D, the buffer layer formation step involves

forming the buffer layer 20, for example, by sputtering, over

the sapphire substrate 10 with the convex portions 11 formed

thereat. The buffer layer formation step can also be omitted,

but should be preferably performed. For example, as shown in

Fig. 9D, the buffer layer 20 has a layered shape that covers the sapphire substrate 10, but does not necessarily cover the sapphire substrate completely in the layered shape and may partially expose the sapphire substrate 10 in a patchy manner by decreasing the layer thickness.

[0052]

In the semiconductor layer growth step, the nitride

semiconductor layer 30 is grown over the surface of the sapphire

substrate 10 on the side with the convex portions 11 formed,

thereby forming a light-emitting element structure.

Specifically, in the semiconductor layer growth step, as shown

in Figs. 9E to 9F, crystals for the n-type semiconductor layer

31 are grown over the surface on the c-plane side of the sapphire

substrate 10 with the convex portions 11 via the buffer layer

20. At this time, the n-type semiconductor layer 31 grows in

the upward direction and lateral direction from an area between

the convex portions 11 to cover the convex portions 11. Until

the convex portions 11 are completely covered, the nitride

semiconductor included in the n-type semiconductor layer 31

grows over the surface of the sapphire substrate 10 while

maintaining an inclined growth surface (facet surface). When

the n-type semiconductor layer 31 grows, the dislocations

converge as already mentioned with reference to Figs. 8A and

8B, whereby the dislocations can be reduced, compared to the

related art structure.

[00531

Subsequently, as shown in Fig. 9G, the active layer 32

is grown on the n-type semiconductor layer 31, and further the

p-type semiconductor layer 33 is formed thereon, thereby

forming the light-emitting element structure including the

active layer 32. Note that until the crystals of the nitride

semiconductor are bonded together above the convex portion 11,

an non-doped nitride semiconductor layer with no impurities

added may be grown, and then n-type impurities may be added to

grow the n-type nitride semiconductor layer. At least until

the crystals ofthe nitride semiconductormaybe bonded together

above the convex portions 11, more preferably, the nitride

semiconductor made of GaN continues to be grown.

[0054]

Through the steps mentioned above, as shown in Fig. 9G,

the light-emitting element 1 with no electrode can be

manufactured.

Next, Figs. 9H and 91 show specific examples of a

manufacturing method for the light-emitting element 2 that

includes the light-emitting element 1 equipped with the

external connection electrode. The light-emitting element 2

shown in Figs. 9H and 91 includes the sapphire substrate 10 with

the convex portions 11, and the n-type semiconductor layer 31,

the active layer 32, and p-type semiconductor layer 31 that are

provided over the sapphire substrate. The n-type

semiconductor layer 33 is partly exposed and provided with an n-side electrode 40. A translucent electrode (for example,

ITO) and a p-side electrode 60 are provided at the surface of

the p-type semiconductor layer 33. After the semiconductor

layer growth step mentioned above, an electrode formation step

is performed, so that the light-emitting element 2 including

the light-emitting element 1 equipped with these electrodes can

be manufactured.

[00551

That is, first, partial regions of the p-type

semiconductor layer 33 and the active layer 32 are removed by

dry etching and the like to expose a part of the n-type

semiconductor layer 31. Then, the n-side electrode 40 is formed

over an exposed part of the n-type semiconductor layer 31, the

translucent electrode 50 is formed over the p-type

semiconductor layer 33, and the p-type electrode 60 is formed

over the translucent electrode 50, whereby the light-emitting

element 2 can be manufactured as shown in Figs. 9H and 91. Note

that after the above-mentioned semiconductor layer growth step,

a singulation step may be performed which involves dividing the

above-mentioned light-emitting element structure and the

sapphire substrate 10 into singulated elements. At this time,

the electrode formation step is performed after the

semiconductor layer growth step and before the singulation

step.

[0056]

In the manufacturing method for the light-emitting

element 1 in this way, the convex portions 11 formed at the

sapphire substrate10have their topparts formednot to be flat,

and extend along the respective m axes. The convex portions

11 are arranged within either the first unit KU or the second

unit TU as the virtual regular hexagon and arranged at

predetermined intervals in each unit. Thus, the manufacturing

method for the light-emitting element 1 can reduce a difference

in growth rate of the nitride semiconductor in the plane of the

sapphire substrate 10 (or improve the flatness of the nitride

semiconductor during the growth step), thereby decreasing the

dislocation density of the nitride semiconductor layer 30.

Together with this, the crystal growth of the nitride

semiconductor layer 30 can be improved. Thus, the

light-emitting element 1 with the structure of the present

disclosure can also improve the crystal orientation, thereby

reducing the forward voltage (Vf) while maintaining or

improving the temperature property, thus improving the optical

output (Po). Additionally, the light-emitting element 1 can

also improve its luminous efficiency.

[0057]

Then, the features of the substrate will be described.

The description will be given of the flatness during crystal

growth by comparing a unit pattern that has only a first unit

KU with convex portions 11 arranged at small intervals in the center of the unit as shown in Figs. 10A to 10D, with another unit pattern that is formed by positioning the second unit TU to have the mirror symmetry relative to the first unit KU to widen the center of the unit for arrangement as shown in Figs.

11A to 11D. Referring to Figs. 10A to 10D, an interval between

the ends of the convex portions 1011 at the center of a PB region

is narrow, leading to a state in which the region continuing

in each m-axis direction is small (or a state in which the ends

of the convex portions 11 overcome the tangent lines Yal to Ya3).

Referring to Figs. 10A to 10D, which are schematic diagrams that

are made based on a scanning electron microscope (SEM)

photograph, a description will be given of an example of GaN

grown on the sapphire substrate with convex portions 1011 as

a Comparative Example. Referring to Figs. 11A to 11D, which

are schematic diagrams that are made based on a scanning

electron microscope (SEM) photograph, a description will be

given of an example of GaN grown on the sapphire substrate with

the elongated convex portions 11 as the first embodiment.

[0058]

Each of the convex portion 11 and the convex portion 1011

had a length in the longitudinal direction of about 10 pm, a

length in the transverse direction of about 2.6 pm, and a height

of about 1.4 pm. The convex portion 11 and the convex portion

1011 were formed to have their outer edges in the longitudinal

direction extending along one of the firstmaxis Sal, the second m axis Sa2, and the third m axis Sa3 of the sapphire substrate.

The thickness of the GaN was approximately 2 pm in Figs. lOB

and 11B, approximately 3.5 pm in Figs. 10C and 11C, and

approximately 4.5 pm in Figs. 10D and 11D. Note that GaN was

deposited by setting the flow rate of TMG supplied as gallium

raw material gas, for example, to 20 sccm until the GaN film

had a thickness of about 2 pm, and then to 60 sccm. As other

process conditions, until the thickness of the deposited GaN

film reached about 2 pm, the pressure was set to 1 atm, and a

V/III ratio was set to about 2000, and thereafter, the pressure

was set 1 atm, and a V/III ratio was set to about 1500. The

sapphire substrate having-+c-plane asitsmain surface was used.

Over the main surface of the sapphire substrate, AlGaN was

deposited in a thickness of about 20 nm as the buffer layer,

and then GaN was deposited thereon.

[0059]

By comparison between the position designated by PA and

the position designated by PB in the drawing, the following is

shown. That is, referring to Figs. 10B to 10D, only the first

units KU are provided with the convex portions 1011 disposed

densely at the center of the unit. Thus, when the thickness

of the grown crystals of GaN is 4.5 pm, the state of crystal

growth differs between thepositions PAand PB. In otherwords,

as shown in Fig. 10D, in the position PA, the crystals grow fast,

thus making the crystal surface already flat, while in the position PB, the crystals grow slower than that in the position

PA because of no space in ±a axis direction (±m axis direction

of the sapphire substrate) of GaN, which is more likely to grow,

thus making the surface of GaN still recessed.

[0060]

In contrast, referring to Fig. llA, the first unit KU and

the second unit TU take the specific unit pattern while the ends

of the convex portions 11 at the center of the unit are spaced

apart from each other (in a state where the ends of the convex

portions 11 do not overcome the respective tangent lines Yal

to Ya3). Thus, as shown in Figs. 11B to llD, when the thickness

of the grown crystals of GaN is 4.5 pm, the surface of the GaN

becomes substantially flat in both positions PA and PB. That

is, the space is formed at the center of the unit in the ±a-axis

direction of GaN (in the ±m-axis direction of the sapphire

substrate), and the specific unit pattern of the first unit and

second unit is used, whereby the crystal growth rate becomes

substantially equalacross the entire substrate, thus achieving

the flat structure in which GaN is grown with the uneven surface

state suppressed.

[0061]

In a Comparative Example, a wafer is prepared by allowing

the nitride semiconductor layer to grow on the sapphire

substrate with the convex portions 11 arranged in the manner

represented by PB of Fig. 10A. Further, in an Example of the invention, a wafer is prepared by allowing the nitride semiconductor layer to grow on the sapphire substrate with the convex portions 1011 arranged in the manner represented by PB of Fig. 11A. In the respective center regions of the prepared wafers in Comparative Example and Example, an full width at half maximum (FWHM) of X-ray rocking curve (XRC) at (002) surface and the number of pits caused by threading dislocations were measured. The results thereof are shown in Table 1.

[0062]

In each of the Comparative Example and the Example, when

intended to measure the FWHM of XRC at the (002) surface, an

n-type semiconductor layer, an active layer, and a p-type

semiconductor layer were grown in this order over the structure

shown in Fig. 10C or 11C to form a nitride semiconductor layer,

and then the nitride semiconductor layer was measured for the

FWHM of XRC.

When intended to measure the number of pits caused by the

threading dislocations, an n-type semiconductor was grown on

the structure shown in Fig. 10C or 11C to form a nitride

semiconductor layer, and further GaN for measurement was grown

on the nitride semiconductor layer. Then, the number of pits

were measured in a range of 10 pm x 10 pm from the upper surface

of the nitride semiconductor layer. Note that to simply measure

the dislocation density in measurement of the number of pits,

the GaN was dared to be further grown on the n-type semiconductor layer under conditions in which the crystal growth in the lateral direction became slow, causing pits to occur from the dislocations as starting points, which allows an operator to view the dislocation as the pit from the upper surface of the nitride semiconductor layer.

[0063]

[Table 1]

FWHM of XRC at Number of pits caused (002) surface by threading (arcsec) dislocations (pieces) 211 Comparative Example 70

Example 197 58

[0064]

As shown in Table 1, it is found that the FWHM of XRC at

the (002) surface in Example having the structure of the convex

portions11shownin Fig.11Ais smaller than thatin Comparative

Example having the structure of the convex portions 1011 shown

in Fig. 10A, and that the dislocation density in Example is

smaller than that in Comparative Example based on the result

of the number of pits caused by the threading dislocations.

[0065]

Next, GaN was grown on the sapphire substrate having the

structure of the convex portions 1101 shown in Fig. 10A as

Comparative Example, and on the sapphire substrate having the structure of the convex portions 11 shown in Fig. 11A as Example to thereby forma wafer having a laminated structure ofan n-type semiconductor layer, an active layer, and a p-type semiconductor layer in this order. The wafer was singulated into light-emitting elements. In the light-emitting element sampled in each of Comparative Example and Example, a forward voltage (Vf), an optical output (Po), a power conversion efficiency (WPE), and a temperature property were measured, and the results thereof are shown in Table 2. Note that the values shown in Table 2 were obtained by measurement on samples of the light-emitting elements taken from the center regions of the wafers and on which the electrodes were formed, in both

Comparative Example and Example.

The temperature property was calculated based on a

mathematical formula 1 below from an optical output (Po) at

atmospheric temperature of 100°C and an optical output (Po) at

atmospheric temperature of 25°C by allowing the current of 65

mA to flow through the light-emitting element. As the value

of the temperature property becomes higher, the decrease in

optical output is reduced relative to the change in temperature

(which means the excellent temperature property).

[0066]

[Equation 1]

Optical output at 100OC (Po) Temperature property[%]= x 100 ••• Formula (1) Optical output at 25°C (Po)

[0067]

[Table 2]

Forward Optical Power conversion Temperature voltage output efficiency WPE property Vf (V) Po (mW) (%) (%) Comparative 2.93 133.5 70.0 90.6 Example

Example 2.90 134.1 71.2 91.7

[0068]

As shown in Table 2, it is found that the light-emitting

element structure in Example having the convexportions11shown

in Fig. 11A has a smaller forward voltage (Vf), a larger optical

output (Po), a higher power conversion efficiency (WPE), and

a larger temperature property than those of the light-emitting

element in Comparative Example having the convex portions 1011

shown in Fig. 10A. That is, the light-emitting element 1 with

the structure of the present disclosure can also improve the

crystal orientation, thereby reducing the forward voltage (Vf)

while maintaining or improving the temperature property, and

improving the optical output (Po). Together with this, the light-emitting element 1 can also improve its luminous efficiency.

[0069]

While the light-emitting element 1 and the manufacturing

method therefor according to the first embodiment have been

specifically described above, the spirit of the present

disclosure is not limited to the description above and must be

widely interpreted based on the description in the accompanied

claims. It is apparent that various modifications and changes

can be made to these descriptions and are included in the spirit

of the invention.

The second to fourth embodiments and modified examples

1 to 3 will be described below with reference to Figs. 12 to

17. Referring to Figs. 12 to 16, differences in the arrangement

structure of convex portions from those of the first embodiment

will be mainly described. Light-emitting elements in the

second to fourth embodiments to be described later have the

substantially same structure and manufacturing method as that

of the light-emitting element 1 in the first embodiment, except

for the structure of the convex portions of the sapphire

substrate, and a description thereof will be omitted.

[00701

<Second Embodiment>

As shown in Fig. 12, the first convex portions 11A to third

convex portions 11C in a light-emitting element according to the second embodiment are configured such that a first distance dal to a third distance da3 and a fourth distance dsl to a sixth distance ds3 are set larger, and the intervals between the adjacent first convex portions11A, between the adjacent second convex portions 11B, and between the third convex portions 11C are wider, than the structure shown in Fig. 3. In the light-emitting element configured in this way, the first convex portions 11A to the third convex portions 11C of the sapphire substrate 10A take the specific unit pattern of the first unit

KU and the second unit TU, and the respective intervals and/or

distances are widened by 20% to 40%, compared to the structure

shown in Fig. 3. Thus, the light-emitting element can more

easily ensure the flatness when the semiconductor layer is

completely grown. Note that when the interval between the

convex portions 11 shown in Fig. 3 is set, for example, to 3

pm as the reference, the interval between the convex portions

11 shown in Fig. 12 is set in a range of 3.6 to 4.2 pm. Note

that the expression "each of the intervals is widened by 20 to

%" as used herein means that an average of the intervals is

widened or increased by 20 to 40% in an allowable range when

defining the average as a reference value. That is, each of

the intervals is preferably set to the upper limit of the

allowable range with respect to the reference value.

[0071]

In the light-emitting element with the above-mentioned structure in the second embodiment, the outer edges in the longitudinal direction of the convex portions 11 disposed at the sapphire substrate 10A are arranged to extend along the respective m axes of the sapphire substrate 10A and formed such that the setting interval between the adjacent outer edges is wider by 20 to 40% than the reference value. This increases the time for the nitride semiconductor to grow in the lateral direction during the crystal growth of the nitride semiconductor. Thus, the dislocations occurring during the crystal growth of the nitride semiconductor tend to converge in a narrow range, resulting in a decrease in dislocation density of the nitride semiconductor layer 30. Further, the light-emitting element in the second embodiment can also improve the crystal orientation, thereby reducing the forward voltage (Vf) while maintaining or improving the temperature property, thus improving the optical output (Po). Together with this, the light-emitting element can also enhance the luminous efficiency.

[00721

<Third Embodiment>

As shown in Fig. 13, in the planer view of a sapphire

substrate 10B ofa light-emittingelement according to the third

embodiment, three convex portions 111 are disposed in each of

the virtual rhombic regions at the surface on the c-plane side

of the sapphire substrate 10B such that the outer edge in the longitudinaldirection of the convex portion extends along each m axis. Specifically, the convex portions 111 include first convex portions 111A each having its outer edge in the longitudinal direction of the elongated shape extending along the first m axis Sal, second convex portions 111B each having its outer edge in the longitudinal direction of the elongated shape extending along the second m axis Sa2, and third convex portions 111C each having its outer edge in the longitudinal direction of the elongated shape extending along the third m axis Sa3.

[0073]

Here, in the first to third convex portions 111A to 111C,

the interval between the respective adjacent convex portions

is set to be equal to or more than a core diameter of the

corresponding convex portion. Note that a pitch Pc between the

convex portions 111 (when drawing a center line through the

center of the core diameter of each convex portion along the

longitudinal direction of the convex portion, the distance to

the center line of another adjacent convex portion) is set to

exceed the core diameter Da. In the first convex portions 111A

to the third convex portions 111C, the interval and pitch Pc

between the convex portions are set wider, and the first

distance dal to the third distance da3 and the fourth distance

dsl to the sixth distance ds3 are also set wider depending on

the interval between the convex portions. Here, the first convex portions 111A to the third convex portions 111C are set such that the ratio of the core diameter Da to the whole core length Li is in a range of 1:5 to 6 by way of example.

Furthermore, the relationship between the core diameter Da and

the pitch Pc is set to 1:2 by way of example.

[0074]

In the light-emitting element with the above-mentioned

structure according to the third embodiment, a distance between

the convex portion 111 formed on the sapphire substrate 10B and

a flat part thereof with no convex portion 111 is appropriately

adjusted, which increases the time for the nitride

semiconductor to grow in the lateral direction during the

crystal growth, easily causing dislocations generated during

the crystal growth to converge in a narrow range, resulting in

a decrease in dislocation density of the nitride semiconductor

layer 30. Further, the light-emitting element in the third

embodiment can also improve the crystal orientation, thereby

reducing the forward voltage (Vf) while maintaining or

improving the temperature property to improve the optical

output (Po). Together with this, the luminous efficiency can

be improved.

[0075]

<Fourth Embodiment>

As shown in Fig. 14, in the plan view of a sapphire

substrate 10C of a light-emitting element in the fourth embodiment, five convex portions 211 extend along each m axis in the corresponding virtual rhombic region to be arranged at predetermined intervals, at the surface on the c-plane side of the sapphire substrate 10C. Specifically, the first-unit convex portions 211 include first convex portions 211A each having its outer edge in the longitudinal direction of the elongated shape extending along the first m axis Sal, second convex portions 211B each having its outer edge in the longitudinal direction of the elongated shape extending along the secondmaxis Sa2, and third convexportions 211Ceachhaving its outer edge in the longitudinal direction of the elongated shape extending along the third m axis Sa3. The first convex portions 211A to the third convex portions 211C are set such that the ratio of the core diameter Da to the whole core length

Ll is 1:11.5, and such that the ratio of the core diameter Da

to the pitch Pc is 1:2.5.

[00761

In this way, even if the ratio of the core diameter Da

to the whole core length Ll is smaller than that in the structure

shown in Fig. 3, the convex portions 211 are configured to take

the specific unit patter of the first unit KU and the second

unit TU and to make a space at the center of the unit. Thus,

like the embodiments mentioned above, the light-emitting

element can also improve the crystal orientation, thereby

reducing the forward voltage Vf while maintaining or improving the temperature property to improve the optical output.

Togetherwith this, the luminous efficiency can alsobe enhanced.

While the second to fourth embodiments have described above that

the number of convex portions formed in each virtual rhombic

region is set to three to five, the number of convex portions

may be six or seven or more.

[0077]

While the above first to fourth embodiments have

described that in the sapphire substrates 10 to 10C for the

nitride semiconductor element, the convex portions 11, 111, and

211 in the elongated shape are arranged in such a manner as to

align both ends of the adjacent convex portions with eachother.

For example, as shown in Figs. 15 to 17, the convex portions

may be disposed within the first region Arl to the third region

Ar3 such that parts or all of both ends of the adjacent convex

portions are displaced. The structure of the convex portion

11of the sapphire substrate 10 shown in Fig. 3 willbe described

below as a typical one. However, other embodiments have the

same function effects. In the description below, the location

of the third convex portion llc in the first unit KU located

closest to the center thereof is changed by way of example.

Alternatively, the location(s) of another or other third convex

portion(s) 11c, or the location(s) of one or some of the first

convex portions 11A or second convex portions 11B may be

changed.

[0078]

<First Modified Example>

As shown in Fig. 15, the first convex portions 11A to the

third convex portions 11Cof the first unit KUmay partly include,

for example, a convex portion 11d (convex portion hatched in

the figure) that is arranged by displacing one end of one third

convex portion 11C with respect to the other convex portions.

The convex portion 1ld is formed only in the first unit KU and

not in the second unit TU. That is, in the second unit TU, the

arrangement of the first region Arl to the third region Ar3 is

required to have mirror symmetry, whereas in the first unit,

the arrangement of the first convex portions 11A to the third

convex portions 11C, including the convex portion lid disposed

in the unit does not have the mirror symmetry.

[0079]

As shown in Fig. 15, when viewing an entirety of the unit

pattern composed of the first unit KU of the arrangement of the

first convex portions 11A to the third convex portions 11C,

including the convex portion lid, as well as the second unit

TU of the arrangement of the first convex portions 11A to the

third convexportions11C, not including the convexportionld,

the same unit patternis repeated with the first unit KUcentered.

The convex portion 11d is provided by displacing the third

convex portion 11C located closest to the center of the first

unit KU with respect to the other third convex portions 11C.

The convex portion 11d is disposed to be abutted against and

intersect the tangent line Yal. Note that the second distance

da2 leads from the second region Ar2 to the first region Arl,

whereby the region or space at the center of the first unit KU

is widely ensured. Therefore, as mentioned above, even when

the convex portions 11 include the convex portion lid in such

a sapphire substrate 10, this modified example includes the

specific unit pattern of the first unit KU and the second unit

TU as well as the region at the center of the unit. Thus, like

the embodiments described above, as compared to the related art

structure, the light-emitting element can improve the crystal

orientation, thereby reducing the forward voltage (Vf) while

remaining or improving the temperature property to improve the

light output (Po) . Together with this, the luminous efficiency

can also be improved.

[00801

<Second Modified Example>

As shown in Fig. 16, in the first unit KU and the second

unit TU, one of the third convex portions 11C may be disposed

as a convex portion ile (convex portion hatched in the figure)

to have its end displaced with respect to the other third convex

portions 11C. Here, the second unit TU including the

arrangement of the convex portion lie has the mirror symmetry

relative to the first unit KU. Even though there is the convex

portion lie having its one end displaced with respect to the other convex portions, in the first unit KU and the second unit

TU in this way, the uniform arrangement is achieved as a whole

for each unit pattern, in which the sides of the second units

TU are aligned with the respective sides of one first unit KU.

Therefore, as mentioned above, even though the convex portions

11 include the convex portion lle in such a sapphire substrate

, this modified example includes the specific unit pattern

of the first unit KU and the second TU as well as the region,

or space at the center part of the unit. Thus, like the

embodiments or example described above, as compared to the

related art structure, the light-emitting element can improve

the crystal orientation, thereby reducing the forward voltage

(Vf) while remaining or improving the temperature property to

improve the light output (Po) . Together with this, the luminous

efficiency can also be improved.

[0081]

<Third Modified Example>

Further, as shown in Fig. 17, the first unit KU may be

configured such that the first convex portions 11A disposed in

the first region Arl, the second convex portions 11B disposed

in the second region, and the third convex portions11C disposed

in the third region Ar3 may be disposed in different

arrangements for each region. Referring to Fig. 17, the first

distance dal to the third distance da3 are the maximumdistances.

In the unit pattern, one side of the second unit TU that has the mirror symmetry relative to the arrangement of the first convex portion 11A to the third convex portion 11C in the first unit KU may be aligned with each side of the first unit KU.

Further, for example, the second unit TU with the structure

shownin Fig. 3, whichdiffers fromthe first unitin arrangement

of the first convex portions 11A to the third convex portions

11C, may be configured to be aligned with each side of the first

unit KU shown in Fig. 17.

[0082]

As shown in Fig. 17, even though the respective ends of

the first convex portions 11A to the third convex portions 11C

in the first units KU are positioned in different patterns, the

same arrangement of the convex portions 11 is repeated every

unit that includes the first unit KU and the second units TU

disposed around the first unit KU as the center. Therefore,

as mentioned above, even with the arrangement of the convex

portions 11in the sapphire substrate 10, this modified example

includes the specific unit pattern of the first unit KU and the

second TU as well as the region at the center part of the unit.

Thus, like the embodiments described above, as compared to the

structure of the related art, the light-emitting element can

improve the crystal orientation, thereby reducing the forward

voltage (Vf) while remaining or improving the temperature

property to improve the light output (Po). Together with this,

the luminous efficiency can also be improved.

[0083]

The light-emitting elements in the respective

embodiments described above may have the following structures.

That is, in the sapphire substrate, as long as the convex

portions canbe arranged along the respective maxesin the first

region Arl to the third region Ar3, as shown in Figs. 3, and

12 to 17, the ends of the convex portions are aligned with each

other, or alternativelymaynot partly or completelybe aligned.

Inotherwords, in the firstunitKU, twoofthree convexportions

located closest to the center of the regular hexagon are spaced

apart from each other without intersecting a facing one of the

tangent lines Yal to Ya3, and the other convex portion may be

disposed to form any of the first distance dal to the third

distance da3. The use of the unit pattern including the first

unit KU and the second unit TU that has the mirror symmetry

relative to the first unit can reduce the forward voltage (Vf),

improving the temperature property, and also improving the

power conversion efficiency (WPE) in the light-emittingelement,

as described above.

The unit pattern of the first unit and the second unit

maybe configured to align each side of the regular hexagon of

the second unit with the side of the regular hexagon of the first

unit.

[0084]

Note that in the sapphire substrate, the convex portions

11 are arranged for each unit along the corresponding m axis.

Thus, another convex portion 11is disposed on an extended line

in the longitudinal direction, which can suppress the leak of

light in the transverse direction, thereby achieving light

distribution characteristics close to those of a Lambertian.

As shown in Figs. 3 and 12 to 17, both ends of each of

the convex portions 11, 111, and 211 are semicircular and have

substantially the same shape. However, the shapes ofthe convex

portions 11, 111, and 211 are not limited thereto.

Further, the convexportions11, 111, and211maybe formed

to protrude upward from the c-plane and sharpened from a

predetermined position in the height direction at an angle 0

with respect to a ridge line via an inclined surface. Thus,

like the above-mentioned convex portions 11, 111, and 211,

during crystal growth of the nitride semiconductor, the crystal

growth from above the convex portion 12 is suppressed, causing

the nitride semiconductor togrowin the lateraldirection. The

dislocations generated in the growth direction are allowed to

converge, resultingin a decrease in the number ofdislocations.

When forming the inclined surface, dry etching is

performed, followed by wet etching, so that the inclined surface

can be formed to be inclined toward the top part of each of the

convex portions 11, 111, and 211.

[0085]

Alternatively, in the first unit KU and the second unit

TU of the light emitting elements 1 and 2, one of two other

rhombic regions (second region Ar2 and third region Ar3) other

than the first regionArl mayinclude aplurality ofthird convex

portions 11c that have their ends aligned along the extending

direction of the first convex portion 11A (111A, 211A). One

third convex portion 11C (111C, 211C) located closest to the

center of the regular hexagonalregion (first unit KUand second

unit TU) may be arranged not to intersect the tangent line Ya3

that is in contact with the end on the center side of the first

convex portion 11A (111A, 211A) located closest to the center,

as well as in parallel to the direction of arrangement of the

first convex portion 11A (111A, 211A).

[00861

Further, the above-mentioned light-emitting elements 1

and 2 may be configured as described below. The other of the

above-mentioned two other rhombic regions (second region Ar2

and third region Ar3) may include a plurality of second convex

portions 11B (111B, 211B) that have their ends aligned along

the extending direction of the third convex portion 11C (111C,

211C). One second convex portion 11B (111B, 211B) located

closest to the center of the regular hexagonal region (first

unit KU and second unit TU) may be arranged not to intersect

the tangent line that is in contact with one end on the center

side of the third convex portion 11C (111C, 211C) located

closest to the center, as well as in parallel to the direction in which the third convex portion 11C (111C, 211C) is disposed.

The terms "space" and "interval" are each used above

depending on the described position, but substantially imply

the same meaning.

[0086A]

By way of clarification and for avoidance of doubt, as

used herein and except where the context requires otherwise,

the term "comprise" and variations of the term, such as

"comprising", "comprises" and "comprised", are not intended to

exclude further additions, components, integers or steps.

Description of Reference Numerals

[0087]

1, 2 light-emitting element

, 10A, 10B, 10C, 10D sapphire substrate (substrate for

nitride semiconductor element)

11, 111, 211 convex portion

11A, 111A, 211A first convex portion

11B, 111B, 211B second convex portion

11C, 111C, 211C third convex portion

buffer layer

nitride semiconductor layer (semiconductor layer)

31 n-type semiconductor layer

32 active layer

33 p-type semiconductor layer n-side electrode translucent electrode p-side electrode

M mask

SC sapphire

Claims (9)

What is claimed is:

1. A light-emitting element, including:

a sapphire substrate having a c-plane at a main surface

thereof; and

a semiconductor layer provided on a side of the main

surface of the sapphire substrate,

wherein the sapphire substrate includes:

a first unit including a first region, a second

region, and a third region, wherein, when viewed from the main

surface side, the three regions together have a shape of a

regular hexagon that is evenly divided into the three regions

such that each region has a shape of a rhombus, the first region

being partitioned by sides that are respectively parallel to

a first m-axis and a second m-axis, the second region being

partitioned by sides that are respectively parallel to the

second m-axis and a third m-axis, the third region being

partitionedby sides that are respectivelyparallelto the first

m-axis and the third m-axis; and

a plurality of second units disposed to be aligned

with respective sides of the first unit, at least one of the

plurality of second units having mirror symmetry relative to

the first unit with respect to an a-axis passing through an apex

of the first unit,

wherein the first unit includes: a plurality of first convex portions arranged in the first region, each of the first convex portions having, at an outer edge thereof, a side parallel to the first m-axis; a plurality of second convex portions arranged in the second region, each of the second convex portions having, at an outer edge thereof, a side parallel to the second m-axis; and a plurality of third convex portions arranged in the third region, each of the third convex portions having, at an outer edge thereof, a side parallel to the third m-axis, wherein the first convex portion located closest to a center of the regular hexagon does not intersect a tangent line that is in parallel to the third m-axis and in contact with an endon a center side ofthe second convexportion located closest to the center, and wherein the second convex portion located closest to the center of the regular hexagon is disposed not to intersect a tangent line that is in parallel to the first m-axis and in contact with an end on a center side of the third convex portion located closest to the center.

2. The light-emitting element according to claim 1,

wherein the first convexportions are arrangedwitha same

pitch therebetween and have a plurality of ends thereof aligned

with a same line parallel to the second m-axis, wherein the second convex portions are arranged with a same pitch therebetween while having a plurality ofends thereof aligned with a same line parallel to the third m-axis, and wherein the third convexportions are arrangedwitha same pitch therebetween while having a plurality of ends thereof aligned with a same line parallel to the first m-axis.

3. The light-emitting element according to claim 1 or claim

2,

wherein the first convex portions are arranged to be

spaced by a first distance in the first region, the first

distance being set as a predetermined distance on a side of the

second region,

wherein the second convex portions are arranged to be

spaced by a second distance in the second region, the second

distance being set as a predetermined distance on a side of the

third region,

wherein the third convex portions are arranged to be

spaced by a third distance in the third region, the third

distance being set as a predetermined distance on a side of the

first region, and

wherein the first distance, the second distance, and the

third distance are the same.

4. The light-emitting element according to any one of the preceding claims, wherein the first convex portion located farthest from the center of the hexagon is disposed to be spaced from a perimeter line of the hexagon that is parallel to the first m-axis of the hexagon by a fourth distance, wherein the second convex portion located farthest from the center of the hexagon is spaced from a perimeter line of the hexagon that is parallel to the second m-axis of the hexagon by a fifth distance, wherein the third convex portion located farthest from the center of the hexagon is spaced from a perimeter line of the hexagon that is parallel to the third m-axis of the hexagon by a sixth distance set as a prescribed distance, and wherein the fourth distance, the fifth distance, and the sixth distance are the same.

5. The light-emitting element according to any one of the

preceding claims, wherein the first convex portion, the second

convex portion, and the third convex portion have three-fold

rotational symmetry.

6. The light-emitting element according to any one of the

preceding claims, wherein the first convex portions, the second

convex portions, and the third convex portions are disposed in

equal numbers of three to five in the first region, the second region, and the third region, respectively.

7. The light-emitting element according to any one of the

preceding claims, wherein each of the first convex portion, the

second convex portion, and the third convex portion has a length

in a direction parallel to the first m-axis twice or more times

as large as that in a direction perpendicular to the first

m-axis.

8. The light-emitting element according to any one of the

preceding claims, wherein each of the first convex portion, the

second convex portion, and the third convex portion has a shape

with an upper part of a cross-section thereof sharpened, the

cross-section being taken along a direction perpendicular to

the first m-axis.

9. The light-emittingelement according toanyone ofclaims

1 to 7, wherein each of the first convex portion, the second

convex, and the third convex portion is configured such that

a tip end thereof in a direction parallel to the first m-axis

is semicircular in a plan view.