JP2001189531A - Semiconductor substrate and semiconductor light- emitting device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN semiconductor substrate having high quality and a semiconductor light-emitting device and its manufacturing method. SOLUTION: In the semiconductor light-emitting device, a structure in which GaN thick films 106 are laminated on the first substrate in which a GaN low- temperature buffer layer 102, a GaN layer 103 and a selective growth mask 104 composed of SiO2 are formed sequentially on a sapphire substrate 101 is formed. The GaN thick films 106 are grown selectively on the surfaces of the GaN layer 103 exposed in opening sections 105 by an MOCVD method, and growth is further continued, and the thick films are also grown in the lateral direction on the surface of the selective growth mask 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor substrate, a semiconductor light emitting device and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a blue LED is a red or green LED.
Although the brightness was lower than that of the ED, there was a problem in practical use. However, in recent years, in a GaN-based compound semiconductor represented by the general formula InAlGaN, the crystal growth technology has been improved by using a low-temperature AlN buffer layer or a low-temperature GaN buffer layer. And a low-resistance p-type semiconductor layer doped with Mg were obtained, so that a high-brightness blue LED was put to practical use, and a semiconductor laser that did not reach practical use but continually oscillated at room temperature was realized. .

In general, when a high-quality semiconductor layer is epitaxially grown on a substrate, it is necessary that the substrate and the semiconductor layer have substantially the same lattice constant and thermal expansion coefficient. However, with respect to GaN-based semiconductors, there is no substrate in the world that satisfies these simultaneously.

[0004] At present, attempts have been made to produce bulk GaN single crystals, but only a few millimeters have been obtained, and they are still far from practical use.

[0005] Therefore, in the case of a GaN-based device, a crystal element is generally grown using a heterogeneous substrate having a lattice constant and a thermal expansion coefficient that are significantly different from those of a GaN-based semiconductor such as sapphire, MgAl ₂ O ₄ spinel, or SiC, thereby producing a laser device. are doing.

However, when a heterogeneous substrate is used, there are problems such as crystal defects, formation of an end face of an optical resonator, formation of an electrode, and heat dissipation, and a practical laser device has not yet been manufactured.

Hereinafter, these problems will be briefly described. Regarding crystal defects, when crystal growth is performed using a heterogeneous substrate having a lattice constant and a thermal expansion coefficient that are significantly different from those of GaN-based semiconductors such as sapphire, MgAl ₂ O ₄ spinel, and SiC, dislocations introduced due to lattice mismatching Density of 10 ⁸ or more
It is very large at 10 ¹⁰ cm ^-2 and GaN
It is difficult to grow a crystal having a quality necessary for producing a practical semiconductor laser, such as generation of distortion and cracks due to a difference from a thermal expansion coefficient of the system semiconductor.

Further, regarding the formation of the optical resonator end face, since the cleavage planes of the heterosubstrate and the GaN-based compound semiconductor do not always coincide with each other, they are parallel and cleaved by a cleavage method like a conventional AlGaAs-based laser. It has been difficult to form a smooth optical resonator end face.

Therefore, in the case of the GaN system, the end face of the optical resonator is manufactured by a method such as cracking a GaN-based crystal by dry-etching or thinly polishing a substrate such as sapphire and cleaving the substrate.

Here, the method using dry etching is complicated because the manufacturing process requires steps such as formation of a dry etching mask, dry etching, and mask removal. Furthermore, since the dry etching technology of the GaN-based compound semiconductor has not been established yet, the formed resonator mirror has unevenness such as vertical streaks and is formed in a tapered shape.
Parallelism and perpendicularity were not yet enough. In addition, when the resonator mirror was formed by dry etching, the substrate remained as a terrace in front of the end face of the resonator mirror, so that light was reflected by the terrace, and the beam shape did not become a single peak.

Further, a substrate such as sapphire is polished thinly,
In the method of forming the optical resonator facet by cleaving the substrate to break the GaN-based crystal, the optical resonator facet has large irregularities due to a shift in the cleavage face between the GaN-based crystal and the substrate. Therefore, the threshold current of the laser was increased.

Further, regarding the formation of the electrodes, since the sapphire substrate generally used is insulative, the electrodes cannot be taken from the back surface of the substrate. Therefore, the electrodes are formed on the element surface, and the conventional AlGaAs
There is a problem that mounting such as forming an electrode on the back surface of a substrate and die bonding cannot be performed like a laser of an s type or the like, and further, a chip area is increased by a space of the electrode. In addition, since dry etching for exposing the n-type layer is required for forming the n-side electrode,
The manufacturing process of the laser element has been complicated.

As for heat dissipation, the life is extremely short in high-temperature operation or high-power operation due to the poor thermal conductivity of a sapphire substrate generally used.

In order to solve the above problems, a technique for manufacturing a GaN substrate with a high quality GaN thick film having a low defect density has been developed.

For example, JP-A-10-326912, JP-A-10-326751, and JP-A-10-3
JP-A-12971 and JP-A-11-4048 disclose:
A technique has been disclosed in which GaN is selectively grown on a heterogeneous substrate using a mask and crystal growth is continued to embed the mask to form a flat GaN thick film over the entire surface of the substrate.

FIG. 12 is a view for explaining a method of manufacturing a GaN thick film substrate disclosed in Japanese Patent Application Laid-Open No. 10-312971. Referring to FIG. 12, first, a III-V compound semiconductor film 12 such as GaN is laminated on a heterogeneous substrate 11 such as sapphire, and several μm of SiO ₂ or the like is further formed thereon.
A mask 14 having an m width is formed, and a growth region 13 for selectively growing a III-V compound semiconductor such as GaN is formed (FIG. 12A).

Next, a III-
A facet structure 15 is manufactured by selectively growing a group V compound semiconductor (FIG. 12B).

When the growth of the group III-V compound semiconductor is further continued, the facet 15 grows laterally and the mask 14
Cover the top (FIG. 12 (c)).

As the growth continues, the adjacent III-V
The group 15 compound semiconductors 15 are united and the grooves are filled (FIG. 12).
(D)).

As the growth is further continued, the surface of the group III-V compound semiconductor 15 is flattened, and
A group V compound semiconductor thick film is formed (FIG. 12E).

According to the techniques disclosed in the above-mentioned publications, the density of threading dislocations generated at the substrate interface is high in the portion of the crystal layer selectively grown on a heterogeneous substrate, but the crystal layer is formed in a lateral direction on the mask. In the laterally grown portion, the density of threading dislocations has been drastically reduced, resulting in a high-quality crystal. Furthermore, by repeating selective growth and lateral growth on this, over the entire surface of the wafer,
A high-quality GaN thick film with few dislocations can be formed. Further, according to this technology, a thick G of 100 μm or more is used.
Even if aN is grown, cracks due to a difference in thermal expansion coefficient do not occur, so that a GaN thick film having a thickness usable as a substrate can be grown even if a heterogeneous substrate is removed.

In the techniques disclosed in the above publications, finally, the GaN substrate is formed by removing the dissimilar substrate and the mask in order to solve the problems of the optical resonator end face, electrode formation, and heat dissipation. Removal of the dissimilar substrate and the mask material depends on a method utilizing polishing or thermal shock.

JP-A-10-312971 and JP-A-11-4048 disclose a GaN-based semiconductor laser manufactured by laminating a laser structure on a GaN substrate from which a different kind of substrate and a mask material are removed. I have.

FIG. 13 is a view showing a semiconductor laser disclosed in JP-A-11-4048. In FIG. 13, a nitride semiconductor substrate (GaN substrate) 40 is formed by growing Si-doped GaN thickly on a sapphire substrate via a selective growth mask, similarly to the process shown in FIG. Then, the selective growth mask is polished and removed, leaving only the Si-doped GaN substrate.

In the semiconductor laser shown in FIG. 13, a nitride semiconductor layer having a laser structure is grown on the GaN substrate 40. The lamination structure of the laser is n-type GaN
Buffer layer 41 of n-type In _0.1 Ga _0.9
Crack preventing layer 42 made of N, n-type Al _0.2 Ga _0.8 N
-Side cladding layer 43 made of / GaN superlattice, n-type Ga
N-side light guide layer 44 made of N, In _0.05 Ga _0.95 N /
Active layer 45 having an In _0.2 Ga _0.8 N multiple quantum well structure, p-side cap layer 46 made of p-type Al _0.3 Ga _0.7 N, p-type G
p-side light guide layer 47 made of aN, p-type Al _0.2 Ga _0.8
P-side cladding layer 48 of N / GaN superlattice, p-type G
It is formed by sequentially laminating p-side contact layers 49 made of aN.

Then, a part of the p-side contact layer 49 and a part of the p-side cladding layer 48 are dry-etched to form a ridge stripe having a width of 4 μm. The position where the ridge stripe is formed is the crystal portion immediately above the selective growth mask. Since the sapphire substrate and the selective growth mask have been removed, a mark serving as a starting point is placed on the GaN substrate before growing the nitride semiconductor device. A p-side electrode 51 made of Ni / Au is formed on the ridge stripe.
Is formed, and an n-side electrode 53 made of Ti / Al is formed on the back surface of the n-type GaN substrate. The end face of the laser resonator is formed by cleaving the M-plane of the n-type GaN substrate.

Other techniques for producing a GaN thick film substrate include, for example, Japanese Patent Application Laid-Open Nos. 7-202265 and
A technique disclosed in Japanese Patent Application Publication No. 165498 is known. In this technique, a buffer layer made of ZnO is formed on a sapphire substrate, a GaN-based semiconductor is grown thereon, and then the buffer layer is dissolved and removed. Then, the substrate and the GaN-based semiconductor are separately manufactured.

JP-A-10-229218 discloses a first wafer having a GaN-based semiconductor formed on a first substrate and a second wafer having a GaN-based semiconductor formed on a second substrate. And bonding the first and second wafers so that the respective GaN-based semiconductors are in close contact with each other, and then polishing and removing the first substrate and the second substrate. I have.

[0029]

As described above, a high-quality GaN-based compound on a heterogeneous substrate such as sapphire can be obtained by the technology of a low-temperature buffer layer and the technology of manufacturing a low-defect substrate by a combination of selective growth and lateral growth. The semiconductor crystal can be grown, and the life of the GaN-based semiconductor laser is prolonged during low-power operation near room temperature. Moreover,
A GaN substrate is manufactured, and by using this substrate, G
Improvements in characteristics of aN-based semiconductor lasers are expected.

However, a large-area, high-quality GaN substrate that can be industrially used has not been realized yet. As a result, a practical laser that operates at a high output has not yet been realized.

Also, JP-A-10-326912,
JP-A-10-326751, JP-A-10-312
In the method of manufacturing a GaN substrate disclosed in Japanese Patent Application Laid-Open No. 971 and Japanese Patent Application Laid-Open No. 11-4048, no crack occurs even when a thick GaN is grown. Warpage occurs. For this reason,
It is difficult to uniformly polish a heterogeneous substrate having a diameter of about 2 inches over the entire surface. Even if a high-quality GaN thick film is grown on a substrate having a diameter of about 2 inches, a 10 mm Large GaN
A substrate could not be made. That is, it is difficult to produce a large-area GaN substrate by the conventional method of polishing and removing the substrate. In addition, due to the warpage, defects are introduced into the GaN layer in the process of polishing a heterogeneous substrate, thereby deteriorating the crystallinity and increasing the threshold current density of the semiconductor laser fabricated thereon. Laser characteristics are not always good.

Further, Ga formed by removing a heterogeneous substrate is used.
On the N substrate, a region having a very high defect density and a region having a low defect density are formed at intervals of several μm. Therefore, it is difficult to accurately manufacture a laser element in a narrow region having a low defect density. Was not good either.

Further, after bonding the first and second wafers so that the respective GaN-based semiconductors are in close contact with each other, the first substrate and the second substrate are removed.
In the method disclosed in Japanese Patent No. 229218, the substrate and the G
Due to the difference in the coefficient of thermal expansion from the aN-based semiconductor, when the GaN is grown to a large thickness, the wafer warps. Therefore, in the case of a large-area wafer, the GaN-based semiconductor may not completely adhere to the entire surface of the wafer. In addition, cracks may occur in the process of close contact. In addition, since the first substrate and the second substrate are polished and removed, two expensive substrates are used for manufacturing one GaN substrate, resulting in a high cost.

In addition, Japanese Patent Application Laid-Open Nos. 7-202265 and 7-1995 produce a GaN substrate that does not require polishing and removal of the substrate.
In the technique disclosed in JP-A-165498, it takes a very long time to dissolve and remove the buffer layer made of ZnO as a thin film, and it is difficult to put it into practical use.

On the other hand, in the method of separating different kinds of substrates using thermal shock, the problem of introducing defects due to thermal shock is the same as in polishing, and it is difficult to produce a high-quality GaN substrate. .

An object of the present invention is to provide a high-quality GaN-based semiconductor substrate, a semiconductor light-emitting device, and a method for manufacturing the same.

[0037]

In order to achieve the above object, according to the first aspect of the present invention, there is provided at least a region where GaN, which is isolated and surrounded by a region where GaN is not directly grown, selectively grows, is provided. On one formed first substrate, G
In a semiconductor substrate on which aN is crystal-grown, GaN grown from a region where GaN is selectively grown also grows in a lateral direction, and also grows on a surface of a region where GaN is not directly grown.

According to a second aspect of the present invention, there is provided the semiconductor substrate according to the first aspect, wherein the first region and the second region adjacent to the first region are formed as regions where GaN is selectively grown. However, when formed on the first substrate, the GaN crystal grown from the first region is not in contact with another GaN crystal grown from the second region adjacent to the first region. And

According to a third aspect of the present invention, there is provided a semiconductor substrate according to the first or second aspect, wherein the GaN is formed on the GaN grown laterally on the surface of the region where GaN is not directly grown. It is characterized in that the nitride semiconductor laminated structure is formed by lamination.

According to a fourth aspect of the present invention, in the semiconductor light emitting device according to the third aspect, the group III nitride semiconductor laminated structure and GaN grown laterally on the surface of the region where GaN is not directly grown are: It is characterized by being separated from the first substrate.

According to a fifth aspect of the present invention, in the semiconductor light emitting device according to the third aspect, GaN of the semiconductor substrate comprises:
The region of the first substrate that is C-axis oriented on the first substrate and where GaN is selectively grown is <1-100
It is characterized by having an optical resonator surface formed by cleaving the (1-100) plane of the group III nitride semiconductor laminated structure.

According to a sixth aspect of the present invention, in the semiconductor light emitting device of the fourth aspect, GaN grown laterally on the surface of the region where GaN is not directly grown has n-type or p-type conductivity. An ohmic electrode for injecting a current into the semiconductor light emitting device is formed on the surface of the group III nitride semiconductor multilayer structure and on the GaN surface on the opposite side.

According to a seventh aspect of the present invention, there is provided a semiconductor substrate according to the first or second aspect, wherein the GaN is formed on the GaN grown laterally on the surface of the region where the GaN is not directly grown. After the nitride semiconductor laminated structure is laminated and the surface side of the group III nitride semiconductor laminated structure formed on the semiconductor substrate is attached to the support, the light emitting device structure is formed.
A state in which a group I nitride semiconductor multilayer structure and GaN grown laterally on the surface of a region where GaN does not grow directly are separated from a first substrate, and a group III nitride semiconductor multilayer structure is attached to a support. And a step of depositing an electrode material on the back side of GaN.

According to a further aspect of the present invention, there is provided a semiconductor substrate according to the first or second aspect, wherein the GaN grown laterally on the surface of the region on which GaN is not directly grown is a group III light-emitting device. After laminating the nitride semiconductor laminated structure and attaching the surface side of the group III nitride semiconductor laminated structure formed on the semiconductor substrate to the support, the selectively grown GaN of the semiconductor substrate is separated from the first substrate And removing the first substrate from the back surface of the first substrate.

[0045]

Embodiments of the present invention will be described below with reference to the drawings.

The semiconductor substrate of the present invention comprises a first substrate on which at least one region where GaN selectively grows, which is isolated and surrounded by a region where GaN does not directly grow, is formed. The grown GaN is characterized in that GaN grown from a region where GaN selectively grows also grows laterally, and also grows on the surface of the region where GaN does not grow directly.

Here, the first substrate does not mean only a heterogeneous substrate, but a structure in which a region where GaN is selectively grown and a region where GaN is not directly grown are formed on the outermost surface. For example, on a sapphire substrate,
GaN buffer layer deposited at low temperature, G deposited at high temperature
The first substrate is also a structure in which an aN layer is sequentially stacked, and a region where GaN is selectively grown and a region where GaN is not directly grown are formed on the surface thereof.

The region where GaN is selectively grown is formed, for example, by growing a GaN thin film on a substrate such as sapphire and then depositing a mask material such as SiO ₂ or SiN and patterning it by a method such as photolithography. Is opened to expose the surface of the GaN thin film.
A region where GaN crystal grows selectively can be formed on the surface of the N thin film, and a region where crystal growth does not directly occur can be formed on the surface of the mask material. Ga on a substrate such as sapphire
An N thin film is grown and patterned by etching or the like to expose the surface of the substrate such as sapphire, and the exposed sapphire substrate surface is formed as a region where crystal growth does not directly occur. Can be produced as a region where GaN crystal grows. Further, a mask material such as SiO ₂ or SiN is deposited on a substrate such as sapphire, patterned by a method such as photolithography to open a window, and after exposing the substrate surface such as sapphire,
A GaN buffer layer can be deposited at a low temperature, and GaN can be grown at a high temperature on the GaN buffer layer. In this case, an exposed substrate surface such as sapphire can be formed as a region where GaN selectively grows. In addition, there is a method of forming a region where GaN is selectively grown by damaging the surface of a substrate such as sapphire, but these methods are not particularly limited.

In the semiconductor substrate of the present invention as described above, a GaN crystal grown from a region where GaN is selectively grown on the first substrate is a GaN crystal grown on a conventional heterogeneous substrate.
The dislocation density is high like the crystal, but the crystal part grown laterally from it, that is, GaN around the selective growth region
The dislocation density is significantly reduced in the GaN crystal portion formed on the region where is not directly grown. Therefore, G formed on the region where the GaN is not directly grown around the selective growth region.
By using the aN crystal part in a region where a stacked structure such as a semiconductor light emitting element structure is grown, a high-quality crystal with few dislocations can be grown. That is, it is possible to provide a semiconductor substrate capable of manufacturing a high-quality group III nitride semiconductor light emitting device (for example, a semiconductor laser) with high yield.

Further, in the present invention, a first region and a second region adjacent to the first region are formed on the first substrate as regions where GaN is selectively grown. In this case, the GaN crystal grown from the first region is not in contact with another GaN crystal grown from the second region adjacent to the first region.

As described above, by adopting a structure in which adjacent GaN crystals are not in contact with each other, warping of the wafer due to a difference in thermal expansion coefficient between a heterogeneous substrate and a GaN thick film, which has conventionally been a problem, is almost eliminated. That is, high quality III
It is possible to provide a large-area semiconductor substrate having no warp on which group III nitride crystals can be grown.

In other words, in the semiconductor substrate of the present invention, there is no warpage of the substrate caused by a difference in thermal expansion coefficient between the substrate and the GaN thick film, and a high-quality crystal in which threading dislocations are reduced by lateral growth. The area of the part can be increased. Therefore, a decrease in yield due to warpage of the substrate during device fabrication is suppressed. In addition, high-quality crystal growth can be achieved over a wider area than before.

The shape and area ratio of the selective growth region and the region that does not grow directly are not particularly limited.
For the purpose of the semiconductor substrate of the present invention for crystal growth of an aN-based semiconductor and fabrication of a semiconductor light emitting device, it is desirable that the size of a region to be selectively grown be as small as possible and the size of a region not directly grown be increased. In addition, the width of GaN grown on the region that is not directly grown is not particularly limited as long as a light emitting element can be formed. However, from the viewpoint of chip division and mounting, preferably 100 μm or more, and more preferably 300 μm or more. It is better to Further, there is no particular limitation on the thickness of GaN of the semiconductor substrate. However, when the element is manufactured by separating GaN from the first substrate, Ga is used.
The thickness of N is preferably 80 μm or more.

The method of growing GaN is not particularly limited, and MOCVD, HVPE, and other methods can be used.

FIG. 1 is a diagram (plan view) showing one configuration example of a semiconductor substrate according to the present invention. FIG. 2 is a sectional view taken on line AA of FIG.
It is sectional drawing in a line. As shown in FIG. 2, this semiconductor substrate has a G substrate on a sapphire substrate 101 on which a GaN low-temperature buffer layer 102, a GaN layer 103, and a selective growth mask 104 made of SiO ₂ are sequentially formed.
The structure is such that the aN thick film 106 is laminated.

Here, the selective growth region (the region where GaN is selectively grown) is the Ga region exposed at the mask opening 105.
The area on the surface of the N layer 103 where GaN is not directly grown is the surface of the selective growth mask 104 made of SiO ₂ .

The sapphire substrate 101 is, for example,
It has a diameter of 2 inches and a thickness of about 300 μm with the C-plane (0001) as the main surface.

The GaN low-temperature buffer layer 102
It is deposited to a thickness of about 50 nm at a temperature of 520 ° C. by MOCVD. In addition, the GaN layer 103 has a MOCV
The crystal is grown at a temperature of 1050 ° C. to a thickness of about 1 μm by Method D. The selective growth mask 104 is formed by depositing SiO ₂ to a thickness of about 200 nm by a plasma CVD method, forming a striped stripe pattern as shown in FIG. It is manufactured by opening a strip-shaped opening 105 in SiO ₂ with an aqueous solution to expose the surface of the GaN layer 103 and removing the resist. The dimensions of the opening 105 of this stripe pattern are 10 μm in the X direction and 12 mm in the Y direction (maximum value at the center).
Are formed at a repetition pitch of 700 μm in the X direction, and are arranged in four rows at an interval of 700 μm in the Y direction.

The GaN thick film 106 has an MO
GaN layer 10 exposed at opening 105 by CVD
After the selective growth on the surface of No. 3, the growth is further continued and the lateral growth is also performed on the surface of the selective growth mask 104.
The GaN thick film 106 has a thickness of about 150 μm and grows in a lateral direction with a width of about 300 μm on one side. Seen from the top, it is a strip-shaped GaN thick film as shown in FIG. Also, as can be seen from FIGS.
The N thick films 106, 106 are not in contact.

A semiconductor light emitting device (for example, a semiconductor laser) can be manufactured using the semiconductor substrate as described above. In this case, the semiconductor light emitting device of the present invention forms a light emitting device structure on GaN grown laterally on the surface of the region of the semiconductor substrate of the present invention where GaN is not directly grown.
A group I nitride semiconductor multilayer structure is formed by stacking. Here, in the present invention, the structure and manufacturing method of the group III nitride semiconductor laminated structure (light emitting element structure) are not particularly limited.

FIG. 3 is a diagram (perspective view) showing a configuration example of the semiconductor light emitting device of the present invention, and FIG. 4 is a cross-sectional view taken along a plane perpendicular to the light emitting direction. That is, FIGS. 3 and 4 show the semiconductor light emitting device formed in the portion B surrounded by the dotted line in FIG. In the examples of FIGS. 3 and 4, the semiconductor light emitting device is configured as a semiconductor laser.

In the examples shown in FIGS. 3 and 4, the semiconductor laser is a semiconductor substrate (101, 102, 103,
On the GaN thick film 106 grown laterally on the surface of the mask material 104 of (104, 106), a laminated structure (light emitting element structure (laser structure in the example of FIGS. 3 and 4)) 1000 is crystal-grown. Is formed.

That is, as a light emitting element structure (laser structure), n-type GaN doped with Si to have a low resistance is used.
On the thick film 106, an n-type Al _0.2 Ga _0.8 N clad layer 10
7, n-type GaN optical guide layer 108, In _0.05 Ga _0.95 N
/ In _0.15 Ga _0.85 N quantum well active layer 109, p-type Ga
The laminated structure 1000 including the N light guide layer 110, the p-type Al _0.2 Ga _0.8 N clad layer 111, and the p-type GaN cap layer 112 is formed by changing the p-type GaN cap layer 112 from the p-type Al
_The current confining ridge waveguide structure 116 is formed by dry etching while leaving a part of the _0.2 Ga _0.8 N cladding layer 111 in a stripe shape.

Optical resonator surfaces 1001 and 1002 are formed perpendicular to the ridge waveguide structure 116 and the active layer 109. The optical resonator surfaces 1001 and 1002 are etched by the dry etching until the stacked structure 1000 reaches the n-type GaN thick film 106. On the surface of the n-type GaN thick film 106 exposed by the dry etching, an n-side ohmic electrode 115 is formed.

An insulating film (SiO ₂ ) 113 is formed on the surface of the laminated structure 1000 other than the portion where the n-side ohmic electrode 115 is formed. An opening is formed in the insulating film (SiO ₂ ) 113 on the ridge 116, and the p-type GaN cap layer 11 exposed through the opening is formed.
2, a p-side ohmic electrode 114 is formed.

The laminated structure 1000 has the MOCV
Crystal growth can be performed by method D. Further, the n-side ohmic electrode 115 can be formed by evaporating Ti / Al, and the p-side ohmic electrode 114 can be formed of Ta / Ti /
It can be formed by evaporating Au.

In the semiconductor light emitting device (semiconductor laser) having such a configuration, carriers are injected into the active layer 109 by injecting a current into the p-side ohmic electrode 114 and the n-side ohmic electrode 115 to emit light. Amplification of light occurs, and laser beams 1101 and 1102 are emitted from the optical resonator surfaces 1001 and 1002.

In the above-described semiconductor light emitting device, since there is no problem of warpage of the semiconductor substrate, it is not necessary to divide the substrate into small pieces, and a large number of semiconductor laser structures can be manufactured at once on a large area substrate. Therefore, a low-cost semiconductor light emitting device (semiconductor laser) can be provided.

Further, in the conventional GaN substrate, since the region having a low dislocation density is narrow, a laser element must be manufactured with high accuracy in a region having a width of several μm, which is a factor that lowers the laser yield. However, since the semiconductor substrate of the present invention has a wider area of a high-quality crystal part in which lateral dislocations are reduced by lateral growth than the conventional GaN substrate, the position accuracy of the device formation region is higher than that of the conventional GaN substrate. Can have a large margin. Therefore, a high-performance laser can be manufactured with high yield. Since a laser can be easily manufactured in a region having a low dislocation density, a long-life laser can be manufactured.

In the above-described semiconductor light emitting device (for example, a semiconductor laser), a group III nitride semiconductor laminated structure and a GaN
GaN grown laterally on the surface of the region where GaN does not grow directly
Can be separated from the first substrate to form a semiconductor light emitting device (for example, a semiconductor laser). Also in this case, in the present invention, the structure and manufacturing method of the group III nitride semiconductor laminated structure (light emitting element structure) are not particularly limited.

The method of separating the group III nitride semiconductor laminated structure and the GaN grown laterally on the surface of the region where GaN is not directly grown from the first substrate is not particularly limited. Since the GaN grown in the direction is not strongly bonded to the region below the GaN, the GaN grown in the lateral direction is obtained by, for example, cutting the selectively grown portion and the horizontally grown portion by dicing or the like. GaN
And the group III nitride semiconductor laminated structure formed thereon can be easily separated from the first substrate.

As described above, in the semiconductor light emitting device (semiconductor laser) of the present invention fabricated on the semiconductor substrate of the present invention,
Furthermore, in order to separate a semiconductor laser from a heterogeneous substrate, it is possible to separate the heterogeneous substrate without using polishing or thermal shock as in the related art, so that distortion or defects introduced when polishing or applying thermal shock are generated. , A long-life laser with good characteristics can be provided.

FIG. 5 is a diagram (perspective view) showing another configuration example of the semiconductor light emitting device of the present invention, and FIG. 6 is a sectional view taken along a plane perpendicular to the light emitting direction. That is, FIGS. 5 and 6 show the semiconductor light emitting device formed in the portion B surrounded by the dotted line in FIG. 5 and 6, the semiconductor light emitting device is configured as a semiconductor laser.

In the examples shown in FIGS. 5 and 6, the semiconductor laser of the semiconductor laser shown in FIGS. 3 and 4 is grown laterally on the surface of the region where the GaN is not directly grown and the group III nitride semiconductor laminated structure 1000. GaN 106 is separated from the first substrate (101, 102, 103, 104). Here, the laminated structure 1000 has the same configuration as that shown in FIGS.

In the semiconductor laser shown in FIGS. 5 and 6, a light emitting element structure (laser structure) is first formed in a portion B surrounded by a dotted line in FIG. 2 in the same manner as shown in FIGS. Dicing from the surface of the GaN crystal layer 106 grown on the selective growth mask 104 to the sapphire substrate 101 in parallel to the opening 105 of the selective growth mask 104, and as shown in FIGS. And the light emitting element structure are separated from the first substrate (from the sapphire substrate 101 to the selective growth mask 104).

In the semiconductor lasers shown in FIGS. 5 and 6, p
-Side ohmic electrode 114 and n-side ohmic electrode 11
By injecting a current into the active layer 109, carriers are injected into the active layer 109, light emission and light amplification occur, and laser light 1101, 1102 from the optical resonator surfaces 1001, 1002.
Is emitted.

In the semiconductor lasers shown in FIGS. 5 and 6, the first substrate (from the sapphire substrate 101 to the selective growth mask 104) is removed from the semiconductor laser shown in FIGS. And high output operation becomes possible.
That is, as compared with a GaN-based semiconductor laser having sapphire or the like having a lower thermal conductivity than GaN as the first substrate,
It has good heat dissipation and slows down even during high-temperature, high-power operation and has a long life.

Each of the semiconductor light emitting devices described above (for example, the semiconductor laser shown in FIGS. 3 and 4 or the semiconductor laser shown in FIGS. 5 and 6)
GaN (GaN layer 106 in the examples of FIGS. 3, 4, 5, and 6) of a semiconductor substrate that is crystal-grown on the first substrate is, for example, formed on the first substrate. C
The region of the first substrate on which the GaN is selectively grown and which is axially oriented has a stripe shape along the <1-100> direction of the GaN, and has a group III nitride semiconductor multilayer structure (1-1).
00) having an optical resonator surface formed by cleaving the surface.

FIG. 7 is a diagram (perspective view) showing a more specific configuration example of the semiconductor light emitting device of the present invention, and FIG. 8 is a sectional view taken along a plane perpendicular to the light emitting direction. That is, FIG.
FIG. 8 shows a semiconductor light emitting device formed in a portion B surrounded by a dotted line in FIG. In the examples of FIGS. 7 and 8, the semiconductor light emitting device is configured as a semiconductor laser.

In the examples shown in FIGS. 7 and 8, the semiconductor laser is the semiconductor substrate (101, 102, 103,
104, 105, 106) on the GaN thick film 106 grown laterally on the surface of the mask material 104.
Are formed by crystal growth. However,
In the semiconductor lasers of FIGS. 7 and 8, the opening 105 of the mask material 104 is formed of the first group III nitride semiconductor of <1-100.
> It has a stripe shape along the direction.

In the semiconductor lasers shown in FIGS. 7 and 8, first, as shown in FIGS. 3 and 4, a light emitting element structure (laser structure) is formed in a portion B surrounded by a dotted line in FIG. Dicing from the surface of the GaN crystal layer 106 grown on the selective growth mask 104 to the sapphire substrate 101 in parallel with the opening 105 of the selective growth mask 104, the GaN crystal layer 106 and the light emitting element structure are connected to the first substrate. (From the sapphire substrate 101 to the selective growth mask 104). Then, as shown in FIGS. 7 and 8, by cleaving the (1-100) plane, the optical resonator planes 1001 and 1002 can be formed. That is,
The optical resonator surfaces 1001 and 1002 are perpendicular to the current confinement ridge waveguide structure 116 along the <1-100> direction (1
It is formed by cleaving the (-100) plane.

Also in the semiconductor lasers of FIGS. 7 and 8, p
-Side ohmic electrode 114 and n-side ohmic electrode 11
By injecting a current into the active layer 5, carriers are injected into the active layer 109, light emission and light amplification occur, and laser light 1101, 110 2 is emitted from the optical resonator surfaces 1001, 1002.
2 is emitted.

In the semiconductor lasers shown in FIGS. 7 and 8, the GaN of the semiconductor substrate is C-axis oriented on the first substrate, and the region where the GaN of the first substrate selectively grows is <1 of GaN.
−100>, and has an optical resonator surface formed by cleaving the (1-100) plane of the group III nitride semiconductor multilayer structure. A resonator mirror having good smoothness and parallelism can be easily formed without requiring a complicated manufacturing process. In addition, since it is not a resonator mirror made by forcibly cleaving different kinds of substrates such as sapphire with different cleavage directions, it is smoother in the atomic order, scattering loss is reduced than before, and laser oscillation is performed at a low threshold. Can be done. In addition, the beam shape is unimodal, and the beam quality is good.
A group III nitride semiconductor laser can be provided.

Further, the semiconductor light emitting device described above (for example,
In the semiconductor lasers shown in FIGS. 5 and 6 and the semiconductor lasers shown in FIGS. 7 and 8, the GaN layer 106 grown laterally on the surface of the region where GaN is not directly grown has n-type or p-type conductivity. In this case, an ohmic electrode for injecting a current into the semiconductor light emitting device (semiconductor laser) may be formed on the surface of the laminated structure (light emitting device structure (laser structure)) constituting the semiconductor light emitting device (semiconductor laser). , On the opposite side of the GaN layer 106.

In this case, compared with the case where the p and n electrodes are formed on the same surface, face-down mounting in which the semiconductor laser side is mounted on a heat sink material can be easily performed, and the heat radiation efficiency at the time of a large output operation can be achieved. Can be higher. Therefore, a semiconductor light emitting device (semiconductor laser) capable of high-temperature and large-output operation can be realized.

Each of the above semiconductor light emitting devices (semiconductor lasers) can be manufactured, for example, by the following method.
That is, for example, GaN grown laterally on the surface of a region where GaN is not directly grown has n-type or p-type conductivity, and an ohmic electrode for injecting current into the semiconductor light emitting device is formed of a group III nitride semiconductor. The surface of the laminated structure,
When each is formed on the opposite GaN surface,
A group III nitride semiconductor multilayer structure forming a light emitting element structure is stacked on GaN grown laterally on a surface of a region of the semiconductor substrate where GaN does not directly grow, and a group III nitride semiconductor stack formed on the semiconductor substrate is formed. After adhering the surface side of the structure to the support, the group III nitride semiconductor laminated structure forming the light emitting element structure and GaN grown laterally on the surface of the region where GaN does not directly grow are separated from the first substrate. Separated and bonded with a group III nitride semiconductor laminated structure on a support,
It can be manufactured by depositing an electrode material on the back side of aN.

Here, the support may be of any material, shape, etc. as long as the structure of the light-emitting element (laser crystal) does not fall apart after the first substrate is separated and can support the structure of the light-emitting element. Can be used. For example, metals, glass, organic substances, and the like can be used as the material.
In addition, the method of attaching to the support is not particularly limited.

As described above, according to the above-described manufacturing method, the first substrate is separated in a state where the first substrate is adhered to the support. Is less damaged, and the yield is improved. That is, since the light emitting element (laser) chip can be collectively handled with the chip attached to the support, the light emitting element (laser) chip can be set collectively with the chip attached to the support in a holder such as a vacuum evaporation apparatus. Time and labor can be saved as compared with a case where the substrate and the light emitting element structure are separated to separate the light emitting element chips, and then the individual chips are set one by one in the holder. Therefore, the cost for manufacturing a light-emitting element can be reduced.

Specifically, as a method for separating the first substrate,
A group III nitride semiconductor multilayer structure forming a light emitting element structure is stacked on GaN grown laterally on a surface of a region of the semiconductor substrate where GaN does not directly grow, and a group III nitride semiconductor stack formed on the semiconductor substrate is formed. After adhering the surface side of the structure to the support, cutting from the back surface of the first substrate so as to divide the selectively grown GaN of the semiconductor substrate and the first substrate,
By removing the first substrate, the first substrate can be separated.

In this case, since the first substrate can be separated without polishing, the first substrate can be separated without introducing defects due to polishing.

The method of separating the first substrate is not particularly limited, and may be a method of polishing or a method of separating the selectively grown GaN of the semiconductor substrate from the first substrate as described above. Alternatively, an arbitrary method such as a method of removing the first substrate by cutting from the back surface of the first substrate or another method can be used.

FIG. 9 is a diagram showing an example of a manufacturing process of a semiconductor light emitting device (semiconductor laser) of the present invention (particularly, a diagram showing an example of a process from separation of a first substrate to formation of an electrode).

In the process example shown in FIG. 9, first, a laminated structure (light-emitting device structure (laser structure)) 1000 is formed in a portion B surrounded by a dotted line in FIG.
Next, the side on which the light emitting element structure is formed is adhered to an adhesive sheet 5000 for dicing (FIG. 9A), and dicing for separating the sapphire substrate 101 and the selective growth mask 104 is performed (FIG. 9B). )). That is, in the process example of FIG. 9, an adhesive sheet 5000 for dicing is used as a support. Dicing is performed so as to cut in parallel with the opening 105 of the selective growth mask until the GaN crystal layer 106 grown in the selective growth mask opening 105 is reached from the back surface of the sapphire substrate 101.

Then, the light emitting element structure 1000 is separated from the first substrate (from the sapphire substrate 101 to the selective growth mask 104) (FIG. 9C).

Then, the entire pressure-sensitive adhesive sheet 5000 is set on a vacuum deposition machine, and the n-side electrode 115 is vacuum-deposited (FIG. 9).
(D)). Thereafter, the GaN crystal 106 on which the light emitting element structure 1000 is formed is removed from the adhesive sheet 5000,
After heat treatment to form ohmic electrode 115, (1
The (-100) plane is cleaved to form an optical resonator surface (FIG. 9E).

Thus, for example, a semiconductor light emitting device (semiconductor laser) as shown in FIGS. 10 and 11 can be manufactured. FIG. 10 is a perspective view of the semiconductor laser, and FIG.
1 is a cross-sectional view of a plane perpendicular to the light emission direction. FIG.
0, in the example of FIG. 11, the light emitting element structure (laser structure)
N-type GaN thick film 10 doped with Si to reduce resistance
6, an n-type Al _0.2 Ga _0.8 N clad layer 107, an n-type GaN optical guide layer 108, In _0.05 Ga _0.95 N / In
_0.15 Ga _0.85 N quantum well active layer 109, p-type GaN optical guide layer 110, p-type Al _0.2 Ga _0.8 N cladding layer 11
1. Stacked structure 10 composed of p-type GaN cap layer 112
00 from the p-type GaN cap layer 112 to the p-type Al _0.2
Etching is performed while leaving the Ga _0.8 N cladding layer 111 halfway in the form of a stripe, and the current constriction ridge waveguide structure 11 is formed.
6 is produced. In other words, this semiconductor laser is a mask material 104 of the semiconductor substrate shown in FIGS.
It is formed by a laminated structure 1000 grown on the GaN thick film 106 grown laterally on the surface. However,
The opening of the mask material 104 has a stripe shape along the <1-100> direction of GaN.

An insulating film (SiO ₂ ) 113 is formed on the surface of the laminated structure (light emitting element structure), and an opening is formed in the insulating film (SiO ₂ ) 113 on the ridge 116. A p-side ohmic electrode 114 is formed on the surface of the p-type GaN cap layer exposed at the opening. On the back surface of the n-type GaN thick film 106, an n-side ohmic electrode 115 is formed. The n-side ohmic electrode 115 can be formed by evaporating Ti / Al.
The p-side ohmic electrode 114 can be formed by evaporating Ta / Ti / Au.

Optical resonator surfaces 1001 and 1002 are formed perpendicular to the ridge 116 and the active layer 109.
The optical resonator surfaces 1001 and 1002 are, as described above, <
Current constriction ridge waveguide structure 1 along 1-100> direction
It is formed by cleaving a (1-100) plane perpendicular to 16.

10 and 11, the p-side ohmic electrode 114 and the n-side ohmic electrode 115
By injecting a current into the active layer 109, carriers are injected into the active layer 109, and light emission and light amplification are caused.
001 and 1002, laser beams 1101 and 1102
Is emitted.

[0100]

As described above, according to the first aspect of the present invention, at least one region where GaN, which is isolated and surrounded by regions where GaN does not directly grow, selectively grows is formed. GaN grown from a region where GaN selectively grows also grows in a lateral direction on a semiconductor substrate on which GaN is crystal-grown on the first substrate.
Provides a semiconductor substrate capable of producing high-quality III-nitride crystals, particularly high-quality III-nitride semiconductor light-emitting devices (eg, semiconductor lasers) with good yields, since they are also grown on the surface of regions where direct growth does not occur. it can.

According to the second aspect of the present invention, in the semiconductor substrate according to the first aspect, the first region and the second region adjacent to the first region are provided as GaN selective growth regions. When the region is formed on the first substrate,
Since there is no contact between the GaN crystal grown from the first region and the other GaN crystal grown from the second region adjacent to the first region, there is no warpage capable of growing a high-quality group III nitride crystal. A large-area semiconductor substrate can be provided.

According to the third aspect of the present invention, a light emitting element structure is formed on GaN grown laterally on the surface of a region of the semiconductor substrate of the first or second aspect where GaN is not directly grown. Since the group III nitride semiconductor multilayer structure is formed by lamination, a high quality and low cost group III nitride semiconductor light emitting device can be provided.

According to the fourth aspect of the present invention, in the semiconductor light emitting device according to the third aspect, the group III nitride semiconductor laminated structure and the GaN grown laterally on the surface of the region where GaN is not directly grown. However, since it is configured to be separated from the first substrate, it is possible to provide a group III nitride semiconductor light emitting device having excellent heat dissipation characteristics and a long life at low cost.

According to a fifth aspect of the present invention, in the semiconductor light emitting device according to the third aspect, the Ga of the semiconductor substrate is
N is C-axis oriented on the first substrate, and the area of the first substrate where GaN is selectively grown is <1-10 of GaN.
0> direction, and has an optical resonator surface formed by cleaving the (1-100) plane of the group III nitride semiconductor multilayer structure. A nitride semiconductor light emitting device (semiconductor laser) can be provided.

According to the sixth aspect of the present invention, in the semiconductor light emitting device according to the fourth aspect, GaN grown laterally on the surface of the region where GaN is not directly grown is made of n-type or p-type conductive material. And an ohmic electrode for injecting a current into the semiconductor light emitting device has a surface of the group III nitride semiconductor laminated structure and a GaN surface on the opposite side,
Since each is formed, further, face-down mounting technology can be easily achieved, and high-temperature, large-output operation is possible.
A group I nitride semiconductor light emitting device can be provided.

According to the seventh aspect of the present invention, a light emitting device structure is formed on GaN grown laterally on the surface of a region of the semiconductor substrate of the first or second aspect where GaN is not directly grown. After laminating the group III nitride semiconductor laminated structure, and attaching the surface side of the group III nitride semiconductor laminated structure formed on the semiconductor substrate to the support, the group III nitride semiconductor laminated structure forming the light emitting element structure In the state where GaN grown laterally on the surface of the region where GaN is not directly grown is separated from the first substrate, and a group III nitride semiconductor laminated structure is attached to a support, an electrode is formed on the back side of GaN. The method includes a step of depositing a material, and separates the first substrate in a state where the first substrate is attached to the support. Therefore, even after the light-emitting element (laser) chip is separated, individual chips are not separated and the chip is damaged. Less yield Even better.

According to the eighth aspect of the present invention, a light emitting element structure is formed on GaN grown laterally on the surface of a region of the semiconductor substrate of the first or second aspect where GaN is not directly grown. After stacking the group III nitride semiconductor multilayer structure, and attaching the surface side of the group III nitride semiconductor multilayer structure formed on the semiconductor substrate to the support, the selectively grown GaN of the semiconductor substrate and the first substrate Cutting from the back surface of the first substrate so as to divide the first substrate, and removing the first substrate. Since the first substrate can be separated without polishing, introduction of a defect by polishing And the first substrate can be separated.

[Brief description of the drawings]

FIG. 1 is a diagram showing one configuration example of a semiconductor substrate according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a diagram (perspective view) showing a configuration example of a semiconductor light emitting device of the present invention.

4 is a cross-sectional view of the semiconductor light emitting device of FIG. 3 taken along a plane perpendicular to the light emission direction.

FIG. 5 is a diagram (perspective view) showing a configuration example of a semiconductor light emitting device of the present invention.

6 is a cross-sectional view of the semiconductor light emitting device of FIG. 5 in a plane perpendicular to the light emission direction.

FIG. 7 is a diagram (perspective view) showing a configuration example of a semiconductor light emitting device of the present invention.

8 is a cross-sectional view of the semiconductor light emitting device of FIG. 7 in a plane perpendicular to the light emission direction.

FIG. 9 is a diagram illustrating an example of a manufacturing process of a semiconductor light emitting device (semiconductor laser) of the present invention (particularly, a diagram illustrating an example of a process from separation of a first substrate to formation of an electrode).

FIG. 10 is a diagram (perspective view) showing a configuration example of a semiconductor light emitting device of the present invention.

11 is a cross-sectional view of the semiconductor light emitting device of FIG. 10 taken along a plane perpendicular to the light emission direction.

FIG. 12 is a diagram for explaining a conventional method of manufacturing a GaN thick film substrate.

FIG. 13 is a diagram showing a conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 101 Sapphire substrate 102 GaN low-temperature buffer layer 103 GaN layer 104 Selective growth mask 105 Mask opening 106 GaN thick film 107 n-type Al _0.2 Ga _0.8 N clad layer 108 n-type GaN optical guide layer 109 In _0.05 Ga _0.95 N / In _0.15 Ga _0.85
N quantum well active layer 110 p-type GaN optical guide layer 111 p-type Al _0.2 Ga _0.8 N cladding layer 112 p-type GaN cap layer 113 insulating film (SiO ₂ ) 114 p-side ohmic electrode 115 n-side ohmic electrode 116 ridge conductor Waveguide structure 1000 Laminated structure 1001,1002 Optical resonator surface 1101,1102 Laser light 5000 Adhesive sheet

Continuation of the front page F term (reference) 5F041 AA40 CA04 CA05 CA34 CA40 CA82 CA85 CA92 5F073 AA13 AA74 CA07 CB22 DA31 DA35

Claims (8)

[Claims] 1. A semiconductor substrate in which GaN is crystal-grown on a first substrate in which at least one region in which GaN selectively grows is surrounded by regions in which GaN does not grow directly In the above, GaN grown from the region where GaN selectively grows also grows in the lateral direction,
A semiconductor substrate characterized in that it also grows on the surface of a region where does not grow directly. 2. The semiconductor substrate according to claim 1, wherein G
When the first region and the second region adjacent to the first region are formed on the first substrate as the region where the aN selectively grows, the GaN grown from the first region is formed. Other G grown from the crystal and the second region adjacent to the first region
A semiconductor substrate, which is not in contact with an aN crystal. 3. A group III nitride semiconductor laminated structure forming a light emitting element structure is laminated on GaN grown laterally on a surface of a region of the semiconductor substrate according to claim 1 or 2 on which GaN is not directly grown. A semiconductor light emitting device characterized by comprising: 4. The semiconductor light emitting device according to claim 3, wherein the group III nitride semiconductor laminated structure and GaN grown laterally on a surface of a region where GaN is not directly grown are separated from the first substrate. A semiconductor light emitting device characterized by comprising: 5. The semiconductor light emitting device according to claim 3, wherein GaN of the semiconductor substrate is C-axis oriented on the first substrate, and a region of the first substrate where GaN selectively grows, It has a stripe shape along the <1-100> direction of GaN, and has a (1-10)
0) A semiconductor light emitting device having an optical resonator surface formed by cleaving a surface. 6. The semiconductor light emitting device according to claim 4, wherein the GaN grown laterally on the surface of the region where GaN is not directly grown has n-type or p-type conductivity. A semiconductor light emitting device, wherein ohmic electrodes for injecting a current are formed on the surface of the group III nitride semiconductor laminated structure and on the GaN surface on the opposite side, respectively. 7. A group III nitride semiconductor multilayer structure forming a light emitting element structure is laminated on GaN grown laterally on the surface of a region of the semiconductor substrate according to claim 1 where GaN does not grow directly. After attaching the surface side of the group III nitride semiconductor laminated structure formed on the semiconductor substrate to the support, the group III nitride semiconductor laminated structure forming the light emitting element structure and the surface of the region where GaN is not directly grown are formed. A step of separating the GaN grown in the lateral direction from the first substrate and depositing an electrode material on the backside of the GaN in a state where the group III nitride semiconductor laminated structure is attached to the support. A method for manufacturing a semiconductor light-emitting element, comprising: 8. A group III nitride semiconductor multilayer structure forming a light emitting device structure is laminated on GaN grown laterally on the surface of a region of the semiconductor substrate according to claim 1 or 2, on which GaN is not directly grown. After attaching the surface side of the group III nitride semiconductor laminated structure formed on the semiconductor substrate to the support, the first substrate is separated from the selectively grown GaN of the semiconductor substrate and the first substrate. A method for manufacturing a semiconductor light emitting device, comprising a step of cutting from a back surface and removing a first substrate.