JP2002335049A - Semiconductor substrate for gallium nitride based devices - Google Patents

Abstract

(57) [PROBLEMS] To provide a nitride semiconductor device which can be manufactured at a high yield by relaxing warpage of a substrate during manufacturing and has good device characteristics. A first semiconductor substrate for forming a plurality of gallium nitride-based semiconductor devices, the first substrate being grown with lateral growth on a heterogeneous substrate made of a material different from a gallium nitride-based compound semiconductor. The semiconductor device includes a plurality of first regions including a nitride semiconductor layer and a plurality of second regions including a second nitride semiconductor layer grown substantially only in the vertical direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate for a gallium nitride based device, and more particularly to a gallium nitride based semiconductor substrate for forming a gallium nitride based semiconductor light emitting device.

[0002]

2. Description of the Related Art A laser device using a nitride semiconductor mainly oscillates a laser beam having a short wavelength of blue to violet, and various uses thereof such as an optical disk device are under study. The continuous oscillation of this laser device has been realized and put into practical use in recent years, but the characteristics of the device are not sufficiently satisfactory in its application, and further improvement in device characteristics is required. In addition, an LED using a nitride semiconductor element can emit light in the ultraviolet region to red, and can be used for various elements such as a light receiving element and a transistor.

[0003] In such a nitride semiconductor device, an element structure is formed on a different kind of substrate mainly made of a different material from the nitride semiconductor via an underlayer such as a buffer layer. But,
Among the above elements, L which needs to be driven with a large current and high output
In D and high output type LEDs, crystal defects, particularly dislocation densities such as threading dislocations, are a major factor in determining device characteristics. This is because, when the dislocation density is increased, the element characteristics are deteriorated under the above-mentioned large current and high output driving, and it is difficult to obtain a practically usable element. Therefore, in such a nitride semiconductor device, a nitride semiconductor layer formed using lateral growth such as ELOG is used as an underlayer, and an element structure is formed on the underlayer. Since a substrate having a good dislocation density is used, the above problem can be solved. Alternatively, after forming a nitride semiconductor substrate using lateral growth such as ELOG on a heterogeneous substrate, the heterogeneous substrate may be removed to form a nitride semiconductor single substrate.

However, in a nitride semiconductor substrate using lateral growth such as ELOG on a heterogeneous substrate as described above, a thick nitride semiconductor is formed on the heterogeneous substrate. Warpage occurs.

[0005]

As described above, the EL
When a nitride semiconductor film formed by lateral growth such as OG or a nitride semiconductor grown thereon is used as a substrate, the wafer is warped and is difficult to handle in a device manufacturing process. Becomes This is because, in the case of a warped wafer, the anisotropic etching has a curved surface, so that the accuracy of the etching is inferior, and this may cause defective products even when dividing the wafer to take out chips. Therefore, an object of the present invention is to provide a semiconductor substrate for a gallium nitride-based device having a nitride semiconductor layer using lateral growth and having a small warpage of the substrate, in order to solve the above problem. Another object of the present invention is to provide a nitride semiconductor device which facilitates the manufacture of the device, improves the yield, and has better device characteristics.

[0006]

In order to achieve the above object, a first gallium nitride based semiconductor substrate according to the present invention is a semiconductor substrate for forming a plurality of gallium nitride based semiconductor elements. The semiconductor substrate includes a plurality of first regions each including a first nitride semiconductor layer grown along with lateral growth on a heterogeneous substrate made of a material different from the gallium nitride-based compound semiconductor. And a plurality of second regions including a second nitride semiconductor layer grown only in the vertical direction. The first gallium nitride-based device semiconductor substrate according to the present invention configured as described above has a plurality of first gallium nitride-based element semiconductor substrates each including a first nitride semiconductor layer grown with lateral growth.
Since there are regions and a plurality of second regions each including a second nitride semiconductor layer grown substantially only in the vertical direction, the material between the heterogeneous substrate and the first region is formed. The stress caused by bending the substrate caused by the difference can be reduced by the second region, so that the warpage of the substrate can be reduced.

Further, a second semiconductor substrate for a gallium nitride based device according to the present invention is a semiconductor substrate for forming a plurality of gallium nitride based semiconductor light emitting devices, and each of the semiconductor substrates is accompanied by a lateral growth. A plurality of first regions including a first nitride semiconductor layer grown by growth and a plurality of second regions including a second nitride semiconductor layer grown by growth substantially only in the vertical direction. It is characterized by becoming. The second gallium nitride-based device semiconductor substrate according to the present invention configured as described above has a plurality of first nitride semiconductor layers each including a first nitride semiconductor layer grown with lateral growth.
Since it has a region and a plurality of second regions each including a second nitride semiconductor layer grown by growth only substantially in the vertical direction, for example, a stress generated during manufacturing that bends the substrate is applied to the second region. Since it can be alleviated by the region, the warpage of the substrate can be reduced.

In the first and second gallium nitride based semiconductor substrates according to the present invention, the first regions are separated by the second regions so as to correspond to the respective gallium nitride based semiconductor light emitting devices. It is preferable that the warpage of the substrate can be reduced more effectively. Each of the first regions is a region for forming a gallium nitride based semiconductor light emitting device.

In the first and second gallium nitride based semiconductor substrates according to the present invention, the first region and the second region may be formed in parallel and alternately with each other.

In the case where a laser diode is formed as the gallium nitride based semiconductor light emitting device using the first and second gallium nitride based semiconductor substrates according to the present invention, each of the first regions includes at least each of the respective lasers. Preferably, it is formed so as to be located immediately below the optical waveguide region of the diode.

In the first and second gallium nitride based semiconductor substrates according to the present invention, each of the first regions may include a selective growth mask made of a material that does not substantially grow a nitride semiconductor. In this case, the selective growth mask preferably has an opening formed on a buffer layer made of a gallium nitride-based compound semiconductor formed on the heterogeneous substrate and exposing a part of the surface of the buffer layer. The first nitride semiconductor layer is laterally grown on the selective growth mask from the buffer layer exposed through the opening.

In the first and second gallium nitride based semiconductor substrates according to the present invention, a portion of the buffer layer exposed by the opening is removed by etching to form a recess, and The nitride semiconductor layer may be grown from the side surface of the recess.

In the first and second gallium nitride based semiconductor substrates according to the present invention, it is preferable that the first nitride semiconductor layer is made of GaN.

In the first and second gallium nitride based semiconductor substrates according to the present invention, it is more preferable that the first nitride semiconductor layer is made of undoped GaN.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a semiconductor substrate 19 for a gallium nitride based device according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 2A and 2B, a semiconductor substrate 19 for a gallium nitride-based element of the present embodiment is formed on a heterogeneous substrate 10 made of sapphire, with a buffer layer 12 interposed between nitride semiconductors made of GaN. A substrate on which the layer 13 has been grown, which is used to form a plurality of gallium nitride based semiconductor light emitting devices. Here, in particular, the gallium nitride-based device semiconductor substrate of the present embodiment has a first region 1 and a second region 2, and the first region 1 is made of GaN grown with lateral growth. Semiconductor layer 13b made of GaN including second semiconductor layer 13a formed by growth substantially only in the vertical direction.
It is characterized by including.

Specifically, in the gallium nitride-based device semiconductor substrate 19 of the present embodiment, each of the first regions 1 is a gallium nitride-based semiconductor light-emitting device to be formed on the gallium nitride-based device semiconductor substrate 19. It is separated by the second region 2 so as to correspond to the element. In the present invention, it is not necessary that each of the first regions 1 is separated from the gallium nitride-based device semiconductor light emitting device in a one-to-one correspondence. For example, as shown in FIG. The first region corresponding to the semiconductor light emitting device for a gallium nitride-based device formed side by side in the direction may be formed as a continuous linear region. In this case, the first region 1 and the second region 2 It is formed in parallel and alternately.

In the gallium nitride-based element semiconductor substrate 19 of the embodiment thus configured, each of the first regions 1 has a nitride semiconductor layer 13a having good crystallinity grown along with the lateral growth. So that a nitride semiconductor layer can be grown thereon with good crystallinity,
The characteristics of the gallium nitride based semiconductor light emitting device constituted by the nitride semiconductor layer can be improved. In addition, heterogeneous substrate 1
9 and the nitride semiconductor layer 13 have different physical properties due to the difference in their materials. Therefore, as shown in FIGS. 9A and 9B, stress is applied so as to curve the substrate. However, in this embodiment, Since the first region 1 and the second region 2 are formed as described above, as shown in FIGS. 9C and 9D, the nitride semiconductor with lateral growth over the entire surface of the heterogeneous substrate 10 is formed. The stress for bending the substrate can be reduced as compared with the case where the layer is formed.

That is, in the first region 1, since the nitride semiconductor layer 13a has good crystallinity, the stress for bending the substrate increases. On the other hand, since the nitride semiconductor layer 13b in the second region 2 is formed by growth substantially only in the vertical direction (the direction perpendicular to the surface of the heterogeneous substrate), it is accompanied by lateral growth. The number of crystal defects increases as compared to the grown nitride semiconductor layer 13a having good crystallinity.
As a result, in the second region 2, the stress that causes the substrate to bend due to a difference in material between the heterogeneous substrate 10 and the nitride semiconductor layer 13b is reduced due to the poor crystallinity of the nitride semiconductor layer 13b, and the substrate is bent. Is alleviated.

As described above, in the gallium nitride-based device semiconductor substrate 19 according to the embodiment of the present invention, the first region 1 having the nitride semiconductor layer 13a having good crystallinity as described above is continuously formed. Instead, the first region 1 and the second region having a buffer effect of bending are alternately formed, so that the stress of bending the entire substrate is accompanied by uniform lateral growth on the heterogeneous substrate. The size can be reduced as compared with the case where a nitride semiconductor layer is formed. As a result, the semiconductor substrate for a gallium nitride-based device according to the embodiment of the present invention can reduce the curvature of the wafer without deteriorating the characteristics of the light-emitting device formed thereon. Breakage can be prevented, and a light-emitting element having good light-emitting characteristics can be manufactured with high yield.

Hereinafter, the gallium nitride based semiconductor substrate 19 and the laser device formed thereon according to the embodiment of the present invention will be described in more detail. The embodiment described below is based on In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1,
A laser element is formed by laminating a plurality of nitride semiconductor layers represented by 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) and having different compositions on a heterogeneous substrate 10. An active layer made of a nitride semiconductor containing In is formed between an n-side clad layer containing an n-type nitride semiconductor and a p-side clad layer containing a p-type nitride semiconductor so that an optical waveguide region of the device is formed. It has a basic structure located.

The method for growing a nitride semiconductor according to the present invention is not particularly limited. MOVPE (metal organic chemical vapor deposition), HVPE (halide vapor deposition), M
All known methods for growing nitride semiconductors, such as BE (Molecular Beam Epitaxy) and MOCVD (Metal Organic Chemical Vapor Deposition), can be applied, but the film thickness is 50 μm.
When growing the following nitride semiconductor, it is preferable to use the MOCVD method in which the growth rate can be easily controlled. In the case of growing a nitride semiconductor having a thickness of 50 μm or less, HVPE tends to be difficult to control the growth rate because the growth rate is high. However, HVPE has a relatively large thickness (for example, 50 μm or more). It is preferable to grow the nitride semiconductor layer because the growth rate is high and a thick nitride semiconductor layer can be formed in a short time.

(Different substrate 10) As the different substrate 10 in the present invention, a substrate made of a material different from a conventionally known nitride semiconductor as a substrate on which a nitride semiconductor can be grown can be used. Specifically (including 6H, 4H, and 3C), for example, C-plane, R-plane, and sapphire to either the main surface of the surface A, the insulating substrate such as spinel (MgA1 ₂ O _4), SiC , Zn
An oxide substrate lattice-matched with S, ZnO, GaAs, Si, and a nitride semiconductor may be used. Of the above-listed substrates, sapphire and spinel are used as the preferred heterosubstrate 10 in the present invention. Further, the heterogeneous substrate 10 may be off-angled as shown in FIG. 5. In particular, as shown in FIG. 11 can be grown with good crystallinity.

In this case, the off-angle is 0.1 ° to 0.5 ° so as to enable better nitride semiconductor crystal growth.
° is preferably set, more preferably 0.1 °
To 0.2 °. For example, a sapphire C-plane substrate
A substrate with an off-angle within the above range can be manufactured, and the substrate with the off-angle can be used in the present invention.

(Substrate Layer 11) In this embodiment, in order to easily grow a high-quality nitride semiconductor constituting a good element structure on the heterogeneous substrate 10,
_{In x Al y Ga 1-x-} y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0
A substrate layer 11 selected from nitride semiconductors represented by ≦ x + y ≦ 1) is provided. In the present embodiment, the substrate layer 11
Is a buffer layer 1 grown at a low temperature, as shown in FIG.
2 and the nitride semiconductor layer 13 grown on the buffer layer 12, and does not functionally constitute an element structure. This is a layer formed for easy growth.
Therefore, since the substrate layer 11 substantially functions as a part of the substrate, in this specification, a substrate formed by the heterogeneous substrate 10 and the substrate layer 11 is referred to as a gallium nitride-based element semiconductor substrate.

In order to effectively exhibit such a function, the nitride semiconductor layer 13 of the substrate layer 11 is preferably made of GaN which can form a good crystalline layer. A substrate layer 11 suitable for growing a nitride semiconductor having good crystallinity constituting the structure is obtained. When GaN is used as the nitride semiconductor layer 13, undoped (undoped) GaN
And G doped with n-type impurities such as Si, Ge, and S
Although any of aN may be used, undoped GaN is preferably used. When undoped GaN is used in this manner, a nitride semiconductor layer 13 having good crystallinity and excellent surface morphology can be formed as compared with the case where a nitride semiconductor having another composition is used. A favorable element structure can be formed.

As the buffer layer 11, specifically, AlN, GaN, AlGaN, InGaN, or the like is used.
m and a film thickness of 10 ° (angstrom) or more.

Here, in the present embodiment, when the substrate layer 11 is formed, selective growth is partially used to form the substrate layer 11.
And a portion grown without selective growth (nitride semiconductor 13b) and a portion grown without selective growth (nitride semiconductor 13b). The selective growth layer is specifically formed by forming a protective film on which a nitride semiconductor such as SiO ₂ hardly grows on the buffer layer 12 so that openings are formed at regular intervals, for example. Non-mask region (mask opening) where nitride semiconductor grows on 12
And a mask region, and the nitride semiconductor grown from the non-mask region grows in the lamination direction (vertical direction) as well as in the lateral direction (in the plane of the substrate). In this case, the nitride semiconductors grown from different non-mask regions are combined to form a film.

More specifically, as shown in FIG. 6A, a protective film 18 is formed on the buffer layer 12 so that openings are formed at a constant period, for example. The nitride semiconductor layer 13a is selectively grown from the portion, and the direction of lamination (open arrow in FIG. 6B) and the lateral direction (FIG.
A film is formed so as to cover the protective film 18 by the growth of (b). When grown in this manner, propagation of threading dislocations extending directly above heterogeneous substrate 10 is suppressed in accordance with the growth of the nitride semiconductor, and nitride semiconductor layer 1 having good crystallinity is obtained.
3a is formed. In the nitride semiconductor layer 13a having good crystallinity grown in this way, especially on the nitride semiconductor layer 13a on the protective film 18, penetration of threading dislocations extending from a heterogeneous substrate into the element can be prevented. It is possible to form a light emitting element having a good quality.

Such a growth method is known as LEO (Lateral).
Epitaxial Overgrowth, ELOG (Epitaxial Latera)
l OverGrowth) or the like, and various modifications are possible in addition to the methods exemplified above, and the modified methods can be applied to the present invention. For example, FIG. 6D shows an example in which the nitride semiconductor 13a is grown in two steps, and the crystallinity near the surface of the nitride semiconductor layer 13a is compared with that shown in FIG. 6C. It is a further improvement.

That is, the example shown in FIG.
(C) A protective film 18a having an opening is further formed on the nitride semiconductor 13a, and the nitride semiconductor 13a is grown again from the nitride semiconductor 13a located in the opening. In this example, the protective film 18a is
Is formed above the opening formed by the adjacent protective film 18 so as to open the upper part. By doing so, the second growth can be performed from the portion of the nitride semiconductor 13a grown first which is located on the protective film 18 having better crystallinity, so that the second growth of the nitride semiconductor 13a can be performed. This is because the crystallinity of the compound semiconductor 13a can be improved more than the nitride semiconductor 13a grown first.

As shown in FIGS. 6 (x) to 6 (z),
By forming irregularities on the buffer layer (nitride semiconductor layer) 12 grown on the heterogeneous substrate 10 and forming the protective film 18 on the upper surface of the convex portion, the convex portion serves as a mask region and the concave portion serves as a non-mask region. There is also a method of growing the buffer layer (nitride semiconductor layer) 12 in the lateral direction from the side surface of the concave portion (FIG. 6).
(Y)). According to this method, the nitride semiconductor 13a grown from the side surface of the adjacent concave portion (non-mask region) can be joined to the upper portion of the mask region convex portion, and the nitride semiconductor 13a covering the entire surface can be formed. In addition, FIG.
In (z), a mask is not provided on the bottom surface of the concave portion, and a mask 18 is provided on the surface of the convex portion to be a non-mask region and a mask region, respectively. However, a mask is also provided on the bottom surface of the concave portion to control the growth from the side surface of the concave portion. Alternatively, the lateral growth as shown in the figure can be performed without providing the mask 18 on the surface of the projection.

Here, the arrows shown in FIGS.
The white arrows indicate the film thickness direction, and the other arrows indicate the lateral growth of the nitride semiconductor. Also,
In the present invention, the mask region and the non-mask region are provided for selectively growing a nitride semiconductor on the surface of the substrate or the semiconductor layer. It is sufficient that the semiconductor is grown, whereby a nitride semiconductor by selective growth is formed with lateral growth. Specifically, it is sufficient that the growth of the nitride semiconductor is difficult (low growth rate) or almost impossible when the nitride semiconductor is grown as compared with the non-mask region. As described above, a mask region and a non-mask region are provided in a predetermined pattern on the substrate surface, and the mask region and the non-mask region are selectively grown along with the lateral growth in the substrate plane from the non-mask region. Layer is called a selective growth layer.

In the case where the selectively grown layer selectively grown along with the lateral direction is used as the nitride semiconductor layer 13a, In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1,
Although a nitride semiconductor represented by 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) can be used, GaN is preferably used, and undoped GaN is more preferably used. As described above, GaN is preferably used because GaN can be grown with the highest crystallinity among nitride semiconductors. The undoped layer is more preferable than the impurity-doped layer because the undoped layer has higher crystallinity. This is because it tends to be even better. The thickness of the nitride semiconductor layer 13a is:
It is sufficient that at least gallium nitride grown from the non-mask region covers the mask region and forms a flat surface, and is not limited to a specific range,
Preferably it is 5 μm or more and 30 μm or less, more preferably 1 μm or more.
The thickness is set to 0 μm or more and 15 μm or less. By being in this range, it is possible to form the nitride semiconductor layer 13a which is a selective growth layer having few dislocations and a flat and good surface.

The shape of a selective growth mask (having a mask region and a non-mask region) for selectively growing the nitride semiconductor 13a is formed in a stripe shape, a grid pattern, a dot shape, or the like on the substrate surface. can do. Among these shapes, a preferred shape is a stripe shape.
And the surface after film formation can be made flatter. Here, in the case of a stripe shape, the width of the mask region (stripe width, width of the upper part of the convex portion) is 1 μm or more and 20 μm or more.
The width of the non-mask region (stripe interval, width of the bottom of the concave portion) is preferably from 3 μm to 20 μm.
It is preferable to use a stripe shape having a size of 10 μm or less, preferably 10 μm to 19 μm. When the protective film is formed so as to have a stripe shape set in such a range, dislocations can be effectively reduced as compared with the case where a stripe-shaped protective film not set in the above range is formed. The surface condition can be improved.

Here, the surface of the substrate for growing gallium nitride in the non-mask region is preferably a nitride semiconductor. Further, as shown in FIGS. 6 (x) to 6 (z), in the case where the nitride semiconductor layer is provided with irregularities to form a selective growth layer, gallium nitride is grown from the side surfaces of the concave portions, so that the bottom surface of the concave portions is made of a different substrate. The surface of 10 may be exposed.

When a concave portion is provided in the buffer layer 12 on the substrate surface as a non-mask region, a specific method is as follows.
A desired concavo-convex shape can be formed by using an etching technique, a dicing technique, or the like. At this time, FIG.
As shown in (z), on the upper part of the convex part (the surface of the mask area),
By providing a protective film on which the nitride semiconductor is not grown or difficult to grow, the lateral growth (FIG. 6 (y)) of the nitride semiconductor from the side surface of the concave portion (non-mask region) is performed with respect to the growth on the upper portion of the convex portion. It is preferable to give priority to this, and although not shown, the protective film may be provided also on the bottom surface of the concave portion (non-mask region) to further promote the lateral growth. Conversely, the protective film 18 may not be provided, or a nitride semiconductor different from the nitride semiconductor 13a having the convex portion may be provided instead of the protective film 18. In this case, the side surface of the convex portion and the convex portion The nitride semiconductor grows from both the upper surface in both the lateral growth direction and the film thickness direction growth, and finally, the nitride semiconductor grown from the adjacent protrusions is combined to form a film.

As a material of a protective film on which a nitride semiconductor does not grow or is difficult to grow for forming a mask, a buffer layer (nitride semiconductor layer) when the surface of the nitride semiconductor 12 is modified by dry etching. Any material can be used as long as it can protect the material 12, such as an oxide, a metal, a fluoride, and a nitride. More specifically, silicon oxide (S
iO _x ), silicon nitride (Si _x N _y ), titanium oxide (Ti
O _X), an oxide such as zirconium oxide (ZrO _X), nitrides, or these multilayer films, it is possible to use a metal or the like. Among them, particularly preferred protective film materials include S
iO ₂ and SiN. The use of such a protective film is preferable in terms of selectivity during dry etching and suppression of diffusion into the nitride semiconductor.

As a method for forming these protective films, conventionally known vapor deposition techniques such as vapor deposition, sputtering, and CVD can be used. When the selective growth layer is formed using the protective film 18 in the form of a stripe, sapphire having a C-plane as a main surface, sapphire having a A-plane as a main surface, or spinel having a (111) plane as a main surface are different types. It is preferably used as a substrate. Hereinafter, the case of using different kinds of substrates will be described in more detail. In the case of using sapphire whose main surface is the C plane, the stripes in the mask region preferably have a longitudinal direction in a direction substantially perpendicular to the A plane of the sapphire. When the sapphire is off-angled from the C plane, the off-angle is in the range of 0.1 ° to 0.5 °, preferably in the range of 0.1 ° to 0.2 °.

When a sapphire substrate having the A-plane as the main surface is used to form a stripe-shaped mask, the longitudinal direction of the stripe in the mask region is determined by the R direction of the sapphire.
It is preferable to match the direction substantially perpendicular to the plane. Further, using a spinel substrate having the (111) plane as a main surface, the longitudinal direction of the stripe in the mask region is made substantially perpendicular to the (110) plane of the spinel (MgAl ₂ O ₄ ), or FIG. As shown in a), the direction is preferably inclined by θ from these perpendicular directions. This is because if the heterogeneous substrate and the stripe direction of the mask region are in the above combination, the in-plane of the substrate (first heterogeneous substrate)
(In a plane parallel to the main surface of the substrate), the growth of the nitride semiconductor has anisotropy, and the lateral growth of the selective growth layer (the direction perpendicular to the stripe direction) is a direction in which the growth of the nitride semiconductor is easy. This is because preferable ELOG growth is realized.
Here, θ is preferably in the range of 0.1 to 0.4 °.

As described above, by using the nitride semiconductor layer 13a as the selective growth layer made of gallium nitride, it is possible to prevent threading dislocations generated by using the heterogeneous substrate 10 from propagating to the element structure. . In addition, it is possible to form a good gallium nitride based semiconductor light emitting device substrate with good crystallinity and surface morphology of the nitride semiconductor layer 13a,
An element having good laser characteristics can be formed.
Further, since the selective growth layer involves the above-described lateral growth, generated dislocations are unevenly distributed according to the growth mode. Therefore, on the substrate layer surface and in the vicinity thereof,
There is a tendency for regions with high and low dislocation densities to occur,
When forming the laser element structure, it is preferable to form the laser element in a region having a low dislocation density in consideration of the distribution of the dislocation density.

More specifically, when a substrate layer as a selective growth layer is formed by using a protective film such as SiO _{2 in} the mask region, as shown in FIG. The vicinity of the central portion of the protective film 18 to which the grown nitride semiconductor 13a is bonded (portion indicated by reference numeral 26 in FIG. 8) and the region between and adjacent to the protective film 18 (the reference numeral 25 in FIG. Dislocations increase in the area shown in FIG. On the other hand, the region 24 is formed with the highest crystallinity on the protective film 18 located between the region 25 and the region 26 and excluding the portion 26 near the center of the protective film 18. Therefore, the element is configured such that an optical waveguide that requires a film with good crystallinity among the laser elements is located on this region 24. FIG. 8 is a cross-sectional view schematically showing a laser device formed on a semiconductor substrate for a gallium nitride-based device. In FIG. 8, layers denoted by reference numerals 14, 15, and 16 in FIG. Indicates an n-type layer, an active layer, and a p-type layer, respectively, and 22 indicates a ridge formed on the p-type layer 16. As shown in FIG. 8, in the laser device having the ridge structure, the laser device is provided so that the ridge is located above the region 24 having good crystallinity.

The region 24 having good crystallinity has a dislocation density of 1 × 10 ¹⁰ / cm ² or less, preferably 1 × 10 ¹⁰ / cm ^2.
8 / cm ² or less. In the regions 25 and 26 having good crystallinity, the dislocation density is 1 × 10 ¹⁰ / cm ^2.
As described above, when there are many defects, 1 × 10 ¹³ / cm ²
In some cases, this is the case.

When the nitride semiconductor layer 13a is formed by the method shown in FIGS. 6 (x) to 6 (y), the central portion of the non-mask region serving as the junction of the nitride semiconductor by lateral growth (FIG. Many dislocations are observed near the center of the recess). Therefore, by providing a laser element, particularly a region where an optical waveguide in the laser device is formed, so as to avoid the region having a high dislocation density, a laser device having good laser characteristics and excellent device reliability can be obtained. Can be configured. As described above, the crystallinity distribution on the surface of the selective growth region accompanied by lateral growth is inherited by the element structure grown thereon or the nitride semiconductor provided as a substrate on the selective growth layer.

As described above, in the present embodiment, when forming a gallium nitride-based semiconductor light emitting device substrate,
2 (a) and 2 (b), a selective growth method such as G is partially applied within the substrate plane to form a first region 1 where the substrate layer 11 is formed by selective growth on one wafer. (Also referred to as a selective growth region) and a second region 2 (also referred to as a film thickness growth region) that grows in a normal film thickness direction without performing selective growth are distributed in the plane. Conventionally, selective growth such as the above-described ELOG is formed on almost the entire surface of the wafer.

Next, the first region 1 configured as described above
The positional relationship between the element and the region forming the element will be specifically described. FIGS. 3 and 4 are plan views schematically illustrating the relationship between the selectively grown first region 1 and a region 4 in which an element structure is formed (hereinafter, referred to as an element region). (FIG. 4) and a sectional view (FIG. 3). As can be seen from FIG. 3, the selective growth region 1 needs to be provided at least in a part below the element region 4. In particular, as shown in the figure, the selective growth region 1 is preferably formed so as to be located below a region 3 through which a current flows when the element is driven (hereinafter referred to as a current drive region).

This is because, when a nitride semiconductor is grown on a substrate using selective growth such as ELOG, the nitride semiconductor grown by the selective growth has good crystallinity and a good surface. This is because a nitride semiconductor device having excellent device characteristics can be formed by forming a portion of the device region where the device actually operates to realize its function on a portion having good crystallinity. . Here, in the first region 1 that has been selectively grown, since the lateral growth is used, as described above, not all of the first region 1 has good crystallinity in the vicinity of the surface, and the first region 1 is shown in FIG. like,
The semiconductor substrate for a gallium nitride-based element includes a region 24 having good crystallinity and a region 2 having poor crystallinity as compared with the region 24.
5, 26 are distributed. Therefore, the element is configured such that an important portion for exhibiting the function of the element is located on the region 24 having good crystallinity.

<Selective growth region 1 and its modification> The selective growth region 1 in the present invention will be described below. As shown in FIG. 2, the selectively grown first region 1 is formed partially on the substrate (wafer), and has a rectangular shape in which stripes are cut off in the middle as shown in FIG. Can be formed in various patterns such as a stripe pattern or a grid pattern as shown in FIG. At this time, as shown in FIG. 2A, in a pattern in which a plurality of first regions 1 having a certain size are arranged on a substrate,
The shape of each first region 1 is rectangular, parallelogram,
Although it can be formed in any polygonal shape, it is preferably provided corresponding to the element region 4 and the element driving region 3.

The selectively grown first region 1 is shown in FIG.
(B) as shown in FIG.
As shown in FIG. 4, a part of the stripe can be formed in a state of being divided with an interval E provided. At this time, the interval E is not particularly limited, but is specifically 5 to 6
It may be 0 μm. Thus, the striped first
By cutting off the region 1, as shown in FIG. 2B, the warpage of the substrate can be reduced more favorably than the case where the stripe is provided from one end to the other end of the wafer. . This is because the first selectively grown stripes
This is because the formation of the region 1 causes a difference in the stress of the substrate between the stripe direction and a direction perpendicular thereto, and the relaxation of the warp of the substrate differs between the stripe direction and the direction perpendicular thereto.

However, as shown in FIG. 2A, when the first regions 1 are provided corresponding to the respective element forming regions, the direction dependency in the relaxation of the warpage stress of the substrate is reduced, and Good warpage mitigation can be realized in all directions. At this time, the interval between the first areas,
Optimum conditions, such as the length of the interval E at which the stripes are cut off, also depend on the thickness of the semiconductor layer and the thickness of the substrate. By providing the selectively grown first regions 1 in a matrix on the substrate, a two-dimensional warpage reduction effect can be expected.

In the present invention, when the selective growth region 1 is provided in any shape and pattern, as shown in FIG. 4, at least the region below the region where the optical waveguide is to be formed in the element region 4 is formed. It is preferable to provide the first region 1 that has been selectively grown. This is because the crystallinity of the optical waveguide affects the device characteristics. That is, as in the present invention, by using partial selective growth, a state in which warpage is relaxed is created, and in a state where warpage is small, a nitride semiconductor serving as a substrate is grown, so that growth is performed in a state where warpage is large. Thus, a nitride semiconductor substrate with a smaller warp can be obtained.

<Device Driving Region 3> In the present invention, as shown in FIG.
It is preferable that the first region 1 defined as a region through which the region 3 flows and selectively grown is provided at least below the element driving region 3. As described above, when the element driving region 3 through which a current flows is formed on the selective growth region 1 having excellent crystallinity, the element driving region 3 having good crystallinity can be formed. As a result, A nitride semiconductor device having excellent device characteristics can be manufactured. In the case of a laser device, the device driving region 3 is provided with a stripe-shaped ridge 22 in the region 3 and by forming a stripe-shaped p-electrode on the ridge as shown in FIG. The region 3 can be a region where a current flows, and
A stripe-shaped optical waveguide is formed immediately below the ridge in the element driving region 3.

In this manner, the optical waveguide is formed in the element driving region 3 having good crystallinity, so that the nitride semiconductor layer constituting the optical waveguide through which light is recombined and light is transmitted has good crystallinity. And the life of the device can be extended. As described above, the selectively grown first region 1 is preferably formed so as to be located below the waveguide region, and is formed at least immediately below the ridge portion 22.

<Element region 4> The element region 4 finally becomes 1
The elements are electrically insulated and arranged on a different kind of insulating substrate so that they can be driven independently as one element. In this state, the element region 4 corresponds to a chip region when the wafer is cut into chips. In the present invention, the element region 4
And the selective growth region 1 are formed so that at least a part thereof overlaps, for example, such that the current drive region overlaps with the selective growth region 1 (FIG. 4). Further, the present invention is not particularly limited to the shape of the element to be formed, the shape and the size of the element region,
It can be applied to various shapes and sizes.

Modified example. Further, in the present embodiment, a semiconductor substrate for a gallium nitride-based element including a heterogeneous substrate 10 has been described. However, the present invention is not limited to this. In FIG. It may be used as a semiconductor substrate for gallium-based devices. That is, after the nitride semiconductor layer 13 including the nitride semiconductor layer 13a grown along with the lateral growth of ELOG or the like is partially formed on the heterogeneous substrate 10, the nitride semiconductor including the heterogeneous substrate 10 is removed. The material semiconductor layer 13 itself may be used as a semiconductor substrate for a gallium nitride-based element. The warpage of the semiconductor substrate for a gallium nitride-based device manufactured as described above is also reduced as in the embodiment. As described above, in order to obtain the single substrate by removing the heterogeneous substrate 10, the above-described heterogeneous substrate 1 is used.
A relatively thick nitride semiconductor is grown on the substrate 0 and the heterogeneous substrate 10 is removed. In this case, the nitride semiconductor is formed to have a specific thickness of 50 μm or more. The heterogeneous substrate can be removed. Preferably, the nitride semiconductor is formed to have a thickness of 100 μm or more to remove the heterogeneous substrate.

In the gallium nitride device substrate of the above embodiment, the nitride semiconductor layer 13 is formed on the buffer layer 12.
However, the present invention is not limited to this. As shown in Example 1 described later, a base layer is grown on the buffer layer 12 and a protective film 18 is formed on the base layer. May be formed to grow the nitride semiconductor layer 13.

[0056]

Embodiments of the present invention will be described below. Example 1 Example 1 is an example in which a laser device having the structure shown in FIG. 10 is formed using the gallium nitride-based device semiconductor substrate shown in FIG. 1 and manufactured as follows. You. In the first embodiment, first, as a heterogeneous substrate 10 on which a nitride semiconductor is grown, a sapphire substrate having a thickness of 425 μm, 2 inches φ, a main surface of a C surface, and an orientation flat surface (hereinafter, referred to as an orientation flat surface) of an A surface. A substrate is prepared, and the wafer is set in a MOCVD reaction vessel.

First, the temperature is set to 510 ° C., and hydrogen is used as the carrier gas, ammonia and TMG (trimethylgallium) are used as the source gas, and G is deposited on the sapphire substrate 1.
a buffer layer (not shown) made of aN
It is grown to a thickness of 0 ° (angstrom). next,
The temperature was set to 1050 ° C., TMG and ammonia were used as source gases, and an underlayer made of undoped GaN was 2.5 μm.
It is grown to a thickness of m. After forming the underlayer, Si having an opening is formed on the underlayer as shown in FIG.
A protective film 18 made of O ₂ is formed, and gallium nitride is selectively grown through an opening to form a selective growth layer. As described above, the substrate layer 112 including the buffer layer, the underlayer, and the selective growth layer is formed.

The growth of the selective growth layer is shown in FIGS.
In the example of the first embodiment, the combined layer of the buffer layer and the underlayer corresponds to the buffer layer 12 in FIG. That is, the first embodiment
Then, after forming the underlayer, the wafer is taken out of the reaction vessel, placed in a CVD apparatus, and a protective film 18 is formed on the underlayer for selective growth (FIG. 6A). At this time,
As the protective film 18 serving as a mask region, as shown in FIG. 5, a stripe-shaped SiO ₂ film inclined at θ = 0.2 ° from a direction perpendicular to the orientation flat surface (A surface) of the sapphire substrate has a width of 5 μm. The protective film 18 is formed on the underlayer so that the interval (width of the opening) between the adjacent protective films 18 is 15 μm.

Here, in the first embodiment, the selective growth is partially applied, and the first region 1 to which the selective growth is applied and the second region to which the selective growth is not applied are alternately formed in a stripe shape. The width of the first region to which the selective growth is applied is 200 μm, and the width of the second region to which the selective growth is not applied is 1
The length is 60 μm, and the longitudinal direction of the stripe in the first region to which the selective growth is applied is formed so as to be substantially parallel to the cavity direction of a laser element to be formed later. At this time, as shown in FIG. 4, the first region is formed such that a region E where the selective growth region 1 is partially interrupted is formed in the stripe direction of the first region to be selectively grown. Specifically, 1
On each of the first regions 1, six element regions 4 are formed.

Then, the protective film 18 was formed on the underlayer as described above. However, the wafer was returned to the MOCVD reaction vessel, and the first region was formed at a temperature of 1050 ° C. using a source gas TMG and ammonia. In the region where the protective film 18 is not provided, undoped GaN is grown from the surface of the non-mask region where the protective film 18 is not provided, that is, the surface where the underlayer is exposed, so that the substrate layer is grown laterally so as to cover the mask region. In the region where the second region is to be formed, the substrate layer 112 is formed substantially only by vertical growth from the surface of the underlayer. In this way, the first region 1 with lateral growth (selective growth) and the second region 2 formed substantially only by vertical growth are grown to a thickness of 15 μm (FIG. 6B ), (C)), and a substrate layer 112 having a flat surface is formed (see FIG. 6 (c)).

In the growth of the selective growth layer, in the initial stage, the nitride semiconductor grows selectively only in the non-mask region. However, when the nitride semiconductor grows to a certain thickness, in addition to the growth in the thickness direction, the mask grows in the thickness direction. As a result of growing in the lateral direction (within the substrate plane) toward the protective film 18 in the region, the upper portion of the mask region is blocked by the laterally grown nitride semiconductor, so that the underlying layer has a flat surface with a thickness of 15 μm. A substrate layer 112 is formed. In the first embodiment, the first region 1 formed by selective growth by ELOG is partially formed in the substrate surface, so that the substrate is less warped as compared with the case where the first region 1 is selectively grown almost entirely in the substrate surface. A semiconductor substrate for a gallium nitride based device was obtained. At this time, the warpage of the wafer is
As shown in FIG. 7, a distance h from a horizontal position at a position away from the top of the warp (the center of the wafer) by a certain distance was measured and evaluated at a plurality of points. As a result, the distance ratio (h in Example 1) / (h in Comparative Example 1) is 10 to 15% as compared with the comparative example in which selective growth is performed over almost the entire surface of the substrate.
Of warpage was observed.

Next, in Example 1, a gallium nitride-based element semiconductor substrate having a substrate layer 112 formed on a heterogeneous substrate 10 thus manufactured is used, and the following layers are formed thereon. Thus, a laser device was formed. n
As the side contact layer 103, 3 μm of Si having a thickness of 4 μm is used.
GaN doped with × 10 ¹⁸ / cm ³ is formed. As the crack preventing layer 104, In _{0.06 having} a thickness of 0.15 μm is used.
Ga _0.94 N (may be omitted) is formed. The n-side cladding layer 105 has a superlattice structure having a total film thickness of 1.2 μm and an undoped Al _0.05 Ga film having a film thickness of 25 °.
And _0.95 N, laminated film thickness 25 Å, and GaN was 1 × 10 ¹⁹ / cm ³ doped with Si, an alternately. As the n-side light guide layer 106, undoped GaN having a thickness of 0.15 μm is formed. The active layer 107 has a multiple quantum well structure with a total film thickness of 550 °, and is Si doped In _0.05 Ga with a film thickness of 140 ° doped with Si at 5 × 10 ¹⁸ / cm ^3.
_0. A barrier layer composed of ₉₅ N (B), an undoped _In 0.13 _{Ga 0.8 7} well layer made of N with a thickness of 50Å and a (W), (B) - (W) - (B) - (W )-(B). As the p-side electron confinement layer 108, a film thickness of 100 ° and Mg of 1 × 10
²⁰ / cm ³ doped p-type Al _0.3 Ga _0.7 N is formed. 0.15 μm in thickness as the p-side light guide layer 109
A p-type GaN doped with m Mg at 1 × 10 ¹⁸ / cm ³ is formed. As the p-side cladding layer 110, a total film thickness of 0.4
5 μm superlattice structure, 25 ° thick undoped Al
_0.05 Ga _0.95 N and 1 × 1 Mg with a thickness of 25 °
0 ²⁰ / cm ³ doped p-type GaN are alternately stacked. As the p-side contact layer 111, a film thickness of 150
g is doped with 2 × 10 ²⁰ / cm ³ to form p-type GaN.

After forming each of the above layers, the wafer is taken out of the MOCVD apparatus, and the laminated semiconductor layers are finely processed by etching to form a resonator structure as a laser element. Specifically, first, an SIO ₂ film having a desired pattern is formed on the wafer surface (p-side contact layer 111 surface) by photolithography.
Etching is performed until the n-side contact layer 103 is exposed to provide an n-electrode formation surface. Next, a ridge stripe is formed in a region where the n-side contact layer 103 is not exposed. That is, on the surface of the p-side contact layer 111,
Forming a mask made of SiO _2, a mask made of a stripe-shaped SiO ₂ of width 1.8μm by a photolithography technique. Then, the p-side contact layer 111 and the p-side contact layer 111 are formed by RIE using SiCl ₄ gas.
The side cladding layer 110 and a part of the p-side light guide layer are removed by etching to form a ridge stripe.

After forming the ridge stripe, P
The wafer is transferred to the VD device and _TwoConsisting of a mask
Over the exposed surface of the ridge stripe formed from above
And Zr (mainly ZrO_Two) Of protective film 162
(Embedded layer) is formed to a thickness of 0.5 μm, and the wafer is treated with hydrofluoric acid.
Immersion in SiO_TwoMask is removed by lift-off method
I do.

As described above, the width of 1.8 μm for forming the striped waveguide region as shown in FIG.
The ridge stripe is formed to a depth where the p-side light guide layer has a thickness of 0.1 μm. Finally, the n-side contact layer 103 and the p-side contact layer 111 exposed by the etching
An n-electrode 121 made of Ti / Al on the surface, Ni
A p-electrode 120 of / Au (formed over the protective film 162 provided on the ridge stripe surface as shown in FIG. 10) is formed as shown in FIG.

Next, as shown in FIG. 10, extraction electrodes 122 and 123 electrically connected to the respective electrodes with a length of about 600 μm from the etching end face side serving as the resonator reflection face are interposed via the insulating film 164. Form. As shown in FIG. 4, as an etching step after the formation of the positive and negative electrodes, the semiconductor layer excluding the part to be the element region 4 is removed by etching, and a plurality of laser elements are provided on the surface of the heterogeneous substrate 10. Is obtained. At this time, the formed element region 4
Is formed almost perpendicular to the sapphire A surface, the length of the resonator is 600 μm, and the length of the element region 4 in the direction perpendicular to the direction is 675 μm.
It is.

Further, a plurality of element regions 4 are arranged at equal intervals as shown in FIG. 4 with a distance E in the resonator direction (width of the exposed first main surface) of 50 μm. At this time, the width of the element driving region 3 is about 200 μm, and the selective growth region is formed so as to cover it as shown in the figure. Further, as the resonator reflection surface, an etched end surface provided when the n-electrode formation surface is exposed may be used.
The substrate may be divided so as to be a face end face. Here, the etched end face is used as the resonator reflection face.

Subsequently, as a polishing step, the side (back side) of the sapphire substrate, which is a heterogeneous substrate, on which the element structure is not formed.
Is polished to a thickness of about 125 μm (solid line part in the figure) from a thickness of 425 μm (dotted line part in the figure) to make the heterogeneous substrate thinner. Next, the substrate is divided and chips are taken out. In the obtained laser element, continuous oscillation with an oscillation wavelength of 405 nm was confirmed at a room temperature at a threshold current density of 2.5 kA / cm ² and a threshold voltage of 4.5 V.

Example 2 In Example 1, after forming the underlayer, 100% of undoped GaN was deposited by HVPE.
formed with a thickness of μm, and further polished from the side of the different kind of substrate, and removed until the 100 μm layer has a thickness of 80 μm.
A nitride semiconductor substrate made of GaN is obtained, and an element structure similar to that of Example 1 is formed thereon to obtain a laser element.

[Comparative Example 1] In Example 1, when forming the underlayer, a stripe-shaped mask is formed on almost the entire surface of the substrate, and ELOG is grown on almost the entire surface to form the selective growth region 1. Other than using the formed nitride semiconductor substrate,
A laser device is obtained in the same manner as in the first embodiment. The nitride semiconductor substrate manufactured in this manner has a greater warpage of the substrate as compared with the first embodiment, and is inferior in accuracy due to the warpage of the substrate in etching when forming a ridge or the like, and in particular, the edge of the wafer. In this case, since the substrate surface is larger than the central part, etching defects are likely to occur.

[0071]

As described above, the first embodiment according to the present invention is described.
And the second gallium nitride-based element semiconductor substrate are respectively grown by a plurality of first regions including the first nitride semiconductor layer grown along with the lateral growth and growth substantially only in the vertical direction. Since the second region includes a plurality of second regions including the second nitride semiconductor layer, the stress for bending the substrate can be reduced by the second region, and the warpage of the substrate can be reduced. Therefore, according to the first and second gallium nitride-based semiconductor substrates for a device according to the present invention, the warpage of the substrate can be reduced, so that the yield can be improved during the manufacture of the device, and good device characteristics can be obtained. Can be provided.

[Brief description of the drawings]

FIG. 1A is a plan view of a gallium nitride-based device semiconductor substrate according to an embodiment of the present invention, and FIG. 1B is a plan view of a gallium nitride-based device semiconductor substrate according to an embodiment of the present invention. FIG.

FIG. 2 is a cross-sectional view taken along line XX ′ of FIG.

FIG. 3A is a cross-sectional view schematically illustrating a relationship between a selectively grown first region 1 and a device region 4 in which a device is formed in a semiconductor substrate for a gallium nitride-based device according to an embodiment;
(B) is sectional drawing which expands and shows a part of (a).

FIG. 4 is a plan view schematically showing a relationship between a selectively grown first region 1 and a device region 4 where a device is formed in the semiconductor substrate for a gallium nitride-based device of the embodiment.

FIG. 5 is a plan view showing an off-angle heterogeneous substrate that can be used in the present invention.

FIG. 6 is a schematic cross-sectional view illustrating selective growth accompanied by lateral growth of the present invention.

FIG. 7 is a schematic diagram showing a parameter h for evaluating the warpage of the substrate.

FIG. 8 is a schematic cross-sectional view showing distribution of a region with good crystallinity and a region with poor crystallinity in the selectively grown first region 1 of the present embodiment.

FIGS. 9A and 9B are side views showing how a substrate is curved when a uniform nitride semiconductor layer is formed on a heterogeneous substrate 10; FIGS. FIG. 5 is a side view showing a state in which the substrate is curved when a nitride semiconductor layer is formed by the first region 1 and the second region 2 as shown in FIG.

FIG. 10 is a cross-sectional view illustrating a configuration of a laser device according to a first embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 ... first area, 2 ... second area, 3 ... element driving area, 10 ... different substrate, 11,112 ... substrate layer, 12 ... buffer layer, 13 ... selectively grown nitride semiconductor layer , 14 ... n-type layer, 15 ... active layer, 16 ... p-type layer, 17 ... nitride semiconductor layer, 18 ... protective film, 20 ... p-electrode, 21 ... n-electrode, 22 ... ridge portion, 24 ... crystalline Good area, 25: poor crystallinity area, 101: substrate, 103: n-type contact layer, 104: crack preventing layer, 105: n-type cladding layer, 106: n-type light guide layer, 107: active layer, 108 ... p-type electron confinement layer, 109: p-type light guide layer, 110: p-type cladding layer, 111: p-type contact layer, 120: p-electrode, 121: n-electrode, 122: p-pad electrode, 123: n-pad electrode 163: Third protection (Buried layer), 164 ... insulating film.

Claims (9)

[Claims] 1. A semiconductor substrate for forming a plurality of gallium nitride-based semiconductor elements, wherein the semiconductor substrate is formed on a heterogeneous substrate made of a material different from a gallium nitride-based compound semiconductor, with respective lateral growth. A plurality of first regions including the grown first nitride semiconductor layer, and a plurality of second regions each including the second nitride semiconductor layer grown substantially only in the vertical direction. A gallium nitride-based device semiconductor substrate, comprising: 2. A semiconductor substrate for forming a plurality of gallium nitride based semiconductor devices, wherein the semiconductor substrate includes a plurality of first nitride semiconductor layers each including a first nitride semiconductor layer grown with lateral growth. A semiconductor substrate for a gallium nitride-based device, comprising: a region; and a plurality of second regions each including a second nitride semiconductor layer grown substantially only in a vertical direction. 3. The gallium nitride based device semiconductor substrate according to claim 1, wherein said first regions are separated by said second regions so as to correspond to said respective gallium nitride based semiconductor devices. 4. The semiconductor substrate for a gallium nitride-based element according to claim 1, wherein said first region and said second region are formed in parallel and alternately with each other. 5. The gallium nitride based semiconductor device is a laser diode, and each of the first regions is formed so as to be located at least immediately below an optical waveguide region of each of the laser diodes. 5. The semiconductor substrate for a gallium nitride based device according to one of the items 4. 6. Each of the first regions includes a selective growth mask made of a material on which a nitride semiconductor does not substantially grow, and the selective growth mask is formed of gallium nitride formed on the heterogeneous substrate. An opening formed on the buffer layer made of a base compound semiconductor and exposing a part of the surface of the buffer layer, wherein the first nitride semiconductor layer is exposed through the opening. The gallium nitride-based device semiconductor substrate according to claim 1, wherein the semiconductor substrate is grown laterally from the buffer layer on the selective growth mask. 7. The buffer layer according to claim 6, wherein a portion exposed by the opening is removed by etching to form a concave portion, and the first nitride semiconductor layer is grown from a side surface of the concave portion. A semiconductor substrate for a gallium nitride-based element as described in the above. 8. The semiconductor substrate for a gallium nitride-based element according to claim 1, wherein said first nitride semiconductor layer is made of GaN. 9. The semiconductor substrate for a gallium nitride-based device according to claim 8, wherein said first nitride semiconductor layer is made of undoped GaN.