JP2003069159A - Nitride semiconductor and manufacturing method thereof, and nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit cracks that are generated in a nitride semiconductor that grows when forming the nitride semiconductor on a substrate comprising the nitride semiconductor by crystal growth. SOLUTION: On a substrate 11 made of gallium nitride (GaN), a facet formation layer 12 comprising a nitride semiconductor containing at least aluminum is formed. A facet surface that inclines from a C surface is formed on the surface of the facet formation layer 12, and a selective growth layer 13 is subjected to horizontal growth from the inclined facet surface, thus allowing the selection growth layer 13 and an n-type cladding layer 14 that comprises an n-type AlGaN growing on the selection growth layer 13 to be subjected to lattice matching substantially, and, for example, obtaining a laser structure without any cracks by crystal growth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor and a manufacturing method thereof, and more particularly to a nitride semiconductor device which is expected to be applied to the field of optical information processing, etc., which is manufactured by the manufacturing method.

[0002]

2. Description of the Related Art A nitride semiconductor containing nitrogen (N) as a group V element has a relatively large band gap,
It is regarded as a promising material for short-wavelength light emitting devices. Among them, the general formula Al _x Ga _y In _z N (where, 0 ≦ x, y,
The gallium nitride-based compound semiconductor represented by z ≦ 1, x + y + z = 1) has been actively researched, and blue light emitting diode (LED) elements and green light emitting diode elements have already been put to practical use.

Further, in order to increase the capacity of an optical disk device, a short wavelength semiconductor laser device having an oscillation wavelength of about 400 nm is eagerly awaited, and a nitride semiconductor laser device using a gallium nitride-based compound semiconductor has attracted attention and is currently used. Then it is reaching the practical level.

A nitride semiconductor laser device is formed by crystal growth on a substrate made of gallium nitride (GaN), and a substrate (wafer) made of silicon (Si) or gallium arsenide (GaAs) can be manufactured. Have difficulty. Therefore, for example, IEICE TRANS.ELECTRON, VOL.E83-C, No.
4, PP.529-535 (2000), hydride vapor phase epitaxy (HV) on a sapphire substrate.
Gallium nitride (Ga) by a selective lateral overgrowth technique using a PE) method or a metal organic chemical vapor deposition (MOVPE) method.
A semiconductor layer made of N) is grown to a thickness of 100 μm or more, and then the sapphire substrate is removed to produce a substrate made of gallium nitride.

FIG. 12 shows a cross-sectional structure of a conventional gallium nitride based semiconductor laser device in which laser oscillation has been achieved.

As shown in FIG. 12, an n-type Al lattice-matched with the substrate 101 is formed on the substrate 101 made of GaN.
_An n-type contact layer 102 made of _0.015 Ga _0.985 N,
A crack suppressing layer 103 made of n-type Ga _0.95 In _0.05 N and having a thickness of about 0.1 μm, and n-type Al _0.15 Ga _0.85 N / G
n-type superlattice cladding layer 104 made of aN and n-type Ga
N-type optical guide layer 105 made of N, multiple quantum well (MQW) active layer 106 made of GaInN, and p-type Al
_A current blocking layer 107 made of _0.2 Ga _0.8 N and p-type G
p-type optical guide layer 108 made of aN and p-type Al _0.15 G
a p-type superlattice cladding layer 109 made of _0.85 N / GaN
And a p-type contact layer 110 made of p-type GaN are sequentially formed.

The conventional semiconductor laser device is characterized by having a crack suppressing layer 103 made of GaInN between the n-type contact layer 102 and the n-type superlattice cladding layer 104.

The crack suppressing layer 103 has the smallest lattice constant and the largest film thickness of the plurality of gallium nitride based semiconductor layers forming the laser structure including the active layer 106, and therefore cracks easily occur in the n-type super layer. The lattice strain generated between the lattice clad layer 104 and the n-type contact layer 102 lattice-matched with the substrate 101 is reduced, and cracks due to the lattice strain generated when forming the laser structure are suppressed.

[0009]

However, in the above-mentioned conventional gallium nitride based semiconductor laser device, the crack suppressing layer 103 for relaxing the lattice strain between the n-type contact layer 102 and the n-type cladding layer 104 is provided between them. Although provided, the precise relationship between the lattice constants of the two is not considered. Therefore, in order to suppress the cracks generated in the n-type superlattice cladding layer 104, there is no method other than adjusting the In composition and the film thickness thereof in the crack suppressing layer 103 and optimizing the growth conditions.

For example, the crack suppressing layer 103 is generally grown at a temperature lower by about 150 to 300 ° C. than the growth temperature of the semiconductor layer such as the n-type cladding layer 104. When the n-type cladding layer 104 and the n-type optical guide layer 105 are grown thereon, the temperature is raised, and the thermally unstable crack suppressing layer 103 is exposed to a temperature higher than its growth temperature. Crystal defects and dislocations are likely to occur in the crack suppression layer 103. Therefore, the crystallinity of the crack suppression layer 103 is not good, and the reproducibility during growth is poor, so that it is difficult to form the crack suppression layer 103 itself. As a result, defects and the like generated in the crack suppressing layer 103 are inherited also in the n-type superlattice cladding layer 104 grown on the crack suppressing layer 103, so that a laser structure having a high-quality semiconductor crystal layer is formed. Things are never easy.

If the crack suppressing layer 103 is provided between the n-type contact layer 102 and the n-type superlattice cladding layer 104, the crack suppressing layer 103 having poor crystallinity serves as a current path, so that the reverse breakdown voltage is low. There is also a problem that the element reliability during high output operation is deteriorated.

Moreover, the conventional crack suppressing layer 103 has an n-type lattice-matched to the substrate 101 made of gallium nitride.
The effect of suppressing cracks generated in the mold contact layer 102 cannot be expected.

When applied to a semiconductor laser device, particularly a readable and writable laser device for an optical disk, spontaneous emission light leaking from the active layer 106 during a low output operation during reading becomes a noise source. However, no consideration is given to the suppression of the spontaneous emission light in the conventional gallium nitride based semiconductor laser device.

In view of the above-mentioned conventional problems, the present invention is capable of suppressing cracks generated in a growing nitride semiconductor when a nitride semiconductor is formed on a substrate made of a nitride semiconductor by crystal growth. To aim.

[0015]

In order to achieve the above object, a nitride semiconductor according to the present invention is grown on a first semiconductor layer made of a first nitride semiconductor and a main surface of the first semiconductor layer. And a second semiconductor layer made of a second nitride semiconductor formed by the method, wherein the first semiconductor layer and the second semiconductor layer have different lattice constants in a plane parallel to the main surface. There is.

According to the nitride semiconductor of the present invention, although the second semiconductor layer is formed on the first semiconductor layer by growth, the lattice constants in the planes parallel to the respective principal planes are different from each other. ing. Here, as is well known, for example, a semiconductor light emitting device is formed by sandwiching an active layer and the clad layer having a composition with a larger forbidden band width and a smaller refractive index than the active layer. Often, a double heterojunction structure consisting of That is, in the case of a nitride semiconductor light emitting device, indium is generally added to the active layer and aluminum is added to the cladding layer. Aluminum (Al) has an atomic radius of gallium (G
It is smaller than a), so aluminum gallium nitride (A
lGaN) has a smaller lattice constant than gallium nitride (GaN). Therefore, for example, assuming that the first semiconductor layer is made of GaN and the second semiconductor layer is made of AlGaN epitaxially grown on the first semiconductor layer, the second semiconductor layer has a first semiconductor layer whose lattice constant is an underlayer. Even if it does not exactly match the lattice constant of
It grows so as to match the lattice constant of the semiconductor layer. As a result, in the clad layer that requires a relatively large film thickness in the laser structure, when the lattice strain exceeds the limit film thickness, cracks occur in the clad layer.

However, since the first semiconductor layer and the second semiconductor layer made of the nitride semiconductor according to the present invention have different lattice constants in a plane parallel to the main surface, the second semiconductor layer is a clad layer or the same. When the base layer is used, cracks do not occur in the second semiconductor layer even if the first semiconductor layer is a nitride semiconductor having a composition different from that of the second semiconductor layer.

The nitride semiconductor of the present invention is formed between the first semiconductor layer and the second semiconductor layer, and is composed of a third nitride semiconductor containing aluminum and having a plurality of facet surfaces different from each other on the surface thereof. It is preferable that a facet forming layer is further provided, and the second semiconductor layer is grown using the facet forming layer as a base layer.

As described above, since the second semiconductor layer is grown by using the facet forming layer formed on the surface and having a plurality of facet surfaces different from each other as the underlayer, the plane orientation different from that of the main surface of the first semiconductor layer is obtained. It also grows from the facets it has. As a result, the second semiconductor layer grows with a component in a direction parallel to the main surface of the first semiconductor layer, so-called lateral growth. Therefore, the lattice constant of the second semiconductor layer in the plane parallel to the main surface of the first semiconductor layer is compressed by the stress during growth and has a value different from the lattice constant of the first semiconductor layer.

In this case, it is preferable that one of the plurality of facet surfaces is a surface parallel to the main surface of the first semiconductor layer and the other surface is a surface inclined to the main surface. .

Further, in this case, the plane orientation of the first facet plane is the (0001) plane, and the plane orientation of the second facet surface is the {1-101} plane or the {1-102} plane. Is preferred. In the specification of the present application, the negative sign "-" attached to the Miller index of the plane orientation conveniently represents the inversion of one Miller index following the negative sign.

In the nitride semiconductor of the present invention, the first semiconductor layer is aluminum gallium indium nitride (Al _x
Ga _y In _z N (where, 0 ≦ x, y, z ≦ 1, x + y +
z = 1)), a nitrogen-containing compound crystal, sapphire, silicon carbide, or gallium arsenide.

The method for manufacturing a nitride semiconductor according to the present invention is
On the first semiconductor layer made of the first nitride semiconductor, a first
A first step of growing a facet forming layer made of a second nitride semiconductor containing aluminum at a temperature of 2 and a heat treatment of the facet forming layer at a second temperature higher than the first temperature. The second step of forming a plurality of facet planes having mutually different plane orientations on the surface of the facet forming layer, and on the heat treated facet forming layer,
A third step of growing a second semiconductor layer made of a third nitride semiconductor at a third temperature higher than the first temperature, wherein the first semiconductor layer and the second semiconductor layer are the first The lattice constants in the plane parallel to the main surface of the semiconductor layer are different from each other.

According to the method for manufacturing a nitride semiconductor of the present invention, the facet forming layer containing aluminum is grown on the first semiconductor layer at the first temperature, and then the first facet forming layer is formed on the facet forming layer. By performing the heat treatment at a second temperature higher than the temperature of 1, a plurality of facet planes having mutually different plane orientations are formed on the surface of the facet forming layer. Further, this heat treatment causes rearrangement of the crystal lattice in the facet forming layer, so that defects can be reduced. Therefore, the second semiconductor layer grown on the facet forming layer grows so that the lattice constant in the plane parallel to the substrate surface is different from that of the first semiconductor layer, so that the nitride semiconductor of the present invention can be obtained. it can.

In the method for manufacturing a nitride semiconductor of the present invention, it is preferable that the second step is performed in an atmosphere containing ammonia and hydrogen.

The partial pressure of hydrogen contained in the atmosphere in this case is preferably set to a value higher than or equal to the partial pressure of the carrier gas consisting of an inert gas excluding the hydrogen.

In the method for manufacturing a nitride semiconductor of the present invention, one of a plurality of facet planes has a plane orientation of (000
1) plane, and the other plane orientation is {1-101} plane or {1
It is preferably −102} plane.

The method for producing a nitride semiconductor of the present invention is the first
Of before the step, the first semiconductor layer, an aluminum gallium indium nitride _{(Al x Ga y In z N} ( where 0
≦ x, y, z ≦ 1, x + y + z = 1)), and further comprising a fourth step of growing on a substrate made of a compound crystal containing nitrogen, sapphire, silicon carbide, or gallium arsenide. Is preferred.

A nitride semiconductor device according to the present invention is formed on a first semiconductor layer made of a first nitride semiconductor and a main surface of the first semiconductor layer. A facet forming layer made of a second nitride semiconductor having a facet surface, a second semiconductor layer made of a third nitride semiconductor formed by growth on the facet forming layer, and grown on the second semiconductor layer. And a third semiconductor layer made of a fourth nitride semiconductor having a relatively large aluminum composition, wherein the first semiconductor layer and the second semiconductor layer have a lattice constant in a plane parallel to the main surface. Are different from each other, and the lattice constant of the second semiconductor layer is
It substantially matches the bulk state lattice constant of the third semiconductor layer.

According to the nitride semiconductor device of the present invention, the second semiconductor layer formed by growth on the facet forming layer of the present invention.
A semiconductor layer and a third semiconductor layer formed by growth on the second semiconductor layer and having a relatively large aluminum composition, wherein the second semiconductor layer has a lattice constant in a bulk state in the third semiconductor layer. Since it substantially matches the lattice constant of, even if the thickness of the third semiconductor layer is made relatively large,
No cracks occur in the third semiconductor layer.

The nitride semiconductor device of the present invention further comprises an active layer made of a fifth nitride semiconductor on the second semiconductor layer, and the size of the energy gap in the facet forming layer is oscillated from the active layer. It is preferable that the energy is smaller than the corresponding emission wavelength.

In the nitride semiconductor device of the present invention, it is preferable that no operating current flows in the facet forming layer.

In the nitride semiconductor device of the present invention, one face orientation of the plurality of facet faces is the (0001) face and the other face orientation is the {1-101} face or the {1-102} face.
It is preferably a surface.

In the nitride semiconductor device of the present invention, the first
The semiconductor layer is aluminum gallium indium nitride (A
l _x Ga _y In _z N (where, 0 ≦ x, y, z ≦ 1, x +
y + z = 1)), a compound crystal containing nitrogen, sapphire, silicon carbide, or gallium arsenide.

[0035]

(First Embodiment) First Embodiment of the Present Invention
Embodiments will be described with reference to the drawings.

FIG. 1A shows a sectional structure of the nitride semiconductor laser device according to the first embodiment of the present invention.

As shown in FIG. 1A, on a substrate 11 made of gallium nitride (GaN), for example, aluminum gallium indium nitride (Al _x Ga _y In _z N (where 0 <x ≦ 1,0 ≦ y, z ≦ 1, x + y + z = 1)). Undoped G is formed on the facet forming layer 12.
The selective growth layer 13 made of aN and silicon (S
i) as a dopant, an n-type contact layer 14 made of n-type GaN, an n-type clad layer 15 made of n-type Al _0.07 Ga _0.93 N, and an n-type optical guide layer 1 made of n-type GaN.
6, a multiple quantum well (MQW) active layer 17, and p-type Al using magnesium (Mg) as a p-type dopant, for example.
_The current blocking layer 18 made of _0.14 Ga _0.86 N and the p-type G
The p-type optical guide layer 19 made of aN, the p-type superlattice cladding layer 20, the p-type second contact layer 21 made of p-type GaN, and the p-type second contact layer 21 being doped at a higher concentration than the p-type second contact layer 21. p-type first contact layer 2 made of p-type GaN
2 and 2 are formed by sequential growth.

The MQW active layer 17 is, as shown in FIG. 1B, a three-layer well layer 17 made of gallium indium nitride (Ga _0.9 In _0.1 N) and having a thickness of about 3 nm.
a and a barrier layer 17b made of GaN and having a thickness of about 6 nm and formed between the well layers 17a.

The p-type superlattice cladding layer 20 is shown in FIG.
As shown in FIG. 1, each of the first layer 20a made of p-type aluminum gallium nitride (Al _0.14 Ga _0.86 N) and the second layer 20b made of GaN has a thickness of about 2.5 nm and has 140 periods. The layers are laminated, and the total thickness is about 700 nm. Here, the first layer 20a
The first layer 20a of the second layer 20b and the second layer 20b is a p-type semiconductor, but the present invention is not limited to this, and at least one of them may be a p-type semiconductor. Further, magnesium is used as the p-type dopant.

The n-type contact layer 14 is formed by etching the upper portion of the n-type contact layer 14 from the p-type first contact layer 22 to expose a part of the n-type contact layer 14. On the exposed surface,
For example, the n-side electrode 23 made of a laminated body of titanium (Ti) and aluminum (Al) is formed.

In addition, the p-type first contact layer 22, the p-type second contact layer 21, and the upper part of the p-type superlattice clad layer 20 are formed so that a stripe-shaped resonator structure is formed in the MQW active layer 17. The ridge portion 10 is formed by etching.

The upper surface of the ridge portion 10 is left with a width of about 3 μm to 5 μm, and both side surfaces of the mesa-shaped semiconductor layer reaching the ridge portion 10 and the n-type contact layer 14 are made of, for example, silicon oxide (SiO ₂ ). Is covered with a protective insulating film 24.

The exposed region from the protective insulating film 24 on the upper surface of the p-type first contact layer 22 is the current injection region of the laser element, and the upper surface and both side surfaces of the ridge portion 10 are in contact with the current injection region. For example, nickel (Ni)
The p-side electrode 25 is formed of a laminated body of gold and gold (Au).

The current block layer 18 has an Al composition of 0.14, and the A in the p-type superlattice cladding layer 20 is A.
Since the average composition of 1 is larger than 0.07, the band gap of the current blocking layer 18 is larger than that of the cladding layer 20. Therefore, the current blocking layer 18
Serves as a barrier layer that prevents electrons injected from the n-type contact layer 14 from leaking to the p-type optical guide layer 19 without being injected into the active layer 17.

Hereinafter, a method of manufacturing the nitride semiconductor laser device having the above structure will be described with reference to FIGS.
It demonstrates using (a) -FIG.2 (d).

Here, MO is used as an example of a crystal growth method.
The VPE method is used. The growth pressure of the nitride semiconductor may be a reduced pressure state lower than the atmospheric pressure (1 atm), a normal pressure state equivalent to the atmospheric pressure, or a pressurized state higher than the atmospheric pressure, and further suitable for each semiconductor layer. You may change to a suitable pressure. Further, as the carrier gas for introducing the group III source gas containing gallium or the like onto the substrate 11, an inert gas containing at least nitrogen (N ₂ ) or hydrogen (H ₂ ) is used.

First, as shown in FIG. 2A, a substrate 11 made of gallium nitride (GaN) having a (0001) plane (= C plane) in the plane orientation of the main surface is placed in a reaction chamber of a MOVPE apparatus. . Then, the growth temperature is set to about 550 ° C., and trimethylgallium (TM) which is a gallium source is formed on the substrate 11.
G), aluminum source trimethyl aluminum (TMA) and indium source trimethyl indium (TMI), and nitrogen source ammonia (NH).
₃ ) is introduced to form AlGaInN on the main surface of the substrate 11.
The prefacet forming layer 12A made of is grown. Here, since the prefacet forming layer 12A is grown at about 550 ° C., which is lower than the growth temperature of about 1000 ° C. for growing a normal nitride semiconductor, the prefacet forming layer 12 is grown.
The crystallinity of A is insufficient, and the surface morphology is also markedly uneven. However, the pre-facet forming layer 12A
Does not become polycrystalline because it grows on the substrate 11 made of GaN.

Next, as shown in FIG. 2B, the growth temperature is raised to about 1120 ° C., and ammonia (NH ₃ ) as a nitrogen source and hydrogen (H ₂ ) as a carrier gas and The prefacet forming layer 12A is heat-treated under the condition that the ratio with nitrogen (N ₂ ) is 1: 1: 1 or 2: 2: 1. Rearrangement of the crystal lattice occurs. Due to this rearrangement, the surface of the pre-facet forming layer 12A has one facet plane ((0001) plane) parallel to the substrate plane and another facet plane ({1-101} plane) inclined with respect to the substrate plane. Or a {1-102} plane).
Changes to. Due to such plane orientation, the surface of the facet forming layer 12 has a large number of hexagonal pyramids or hexagonal pyramid trapezoidal uneven shapes. The thickness of the facet forming layer 12 may be such that a hexagonal pyramid or a hexagonal pyramid can be formed, and is about 50 nm in the first embodiment. In addition, as an example of the composition of the facet forming layer 12,
When Al _0.1 Ga _0.9 N is used, the heat treatment time for this film thickness and composition is preferably about several minutes. The Al composition x of the facet forming layer 12 is preferably in the range of 0 <x <0.2. When x = 0, the above-mentioned facet surface is unlikely to occur, and when X ≧ 0.2, the facet forming layer 12 is not formed. The conductivity of 12 deteriorates.

Next, as shown in FIG. 2C, the growth temperature is set to about 1100 ° C., and TMG as a gallium source and ammonia as a nitrogen source are introduced onto the substrate 11 to form the facet forming layer 12. A selective growth layer 13 made of gallium nitride is grown thereon. At this time, the selective growth layer 13
Grow laterally from the {1-101} plane or the {1-102} plane that is formed on the surface of the facet forming layer 12 and is inclined with respect to the substrate surface. Further, the selective growth layer 13 is grown until the surface is flattened, and the state shown in FIG. 2D is obtained. The growth temperature of the selective growth layer 13 at this time is 1100 ° C.
The temperature is not limited to 900 ° C., but it depends on the pressure of the growth atmosphere.
It may be about 1300 ° C.

Next, as shown in FIG. 1A, on the selective growth layer 13, an n-type contact layer 14, an n-type cladding layer 15, an n-type optical guide layer 16, an MQW active layer 17, and a p-type. The cap layer 18, the p-type optical guide layer 19, the p-type superlattice cladding layer 20, the p-type second contact layer 21, and the p-type first contact layer 22 are sequentially grown. At this time, the respective semiconductor layers from the selective growth layer 13 to the p-type first contact layer 22 are crystal-grown so that the a-axis lattice constants are lattice-matched in the C plane.

Here, the growth temperature of the MQW active layer 17 is
The temperature is set to about 780 ° C. so that indium atoms (In) can be easily taken into the crystal.

In the present specification, the lattice constant when the semiconductor layer has a superlattice structure like the p-type superlattice clad layer 20 is the average value of the lattice constants of the layers forming the superlattice structure. There is. Further, in the present specification,
The term “substantially lattice matching” means a state in which, when semiconductor layers having different bulk lattice constants are stacked, the difference between lattice constants newly defined by lattice deformation due to stress is within ± 0.5%. Here, the bulk lattice constant refers to the original lattice constant of the bulk that is not subjected to thermal strain from the substrate or the like.

Next, by dry etching using, for example, chlorine (Cl ₂ ) gas as an etching gas, the p-type first contact layer 22, the p-type second contact layer 21, and the p-type superlattice cladding layer 21 are formed on the upper portions thereof. , The ridge portion 10 is formed. Subsequently, dry etching is performed from the lower portion of the p-type superlattice cladding layer 21 to the upper portion of the n-type contact layer 14 so as to include the ridge portion 10, and thus the n-type contact layer 14 is formed.
To expose.

Next, a stripe-shaped opening having a width of about 3 μm to 5 μm is formed on the upper surface of the p-type first contact layer 22 on the side surface of the ridge portion 10 and the side surface of the laminated body below it by the CVD method or the like. A protective insulating film 24 is deposited so as to have an appropriate opening on the exposed surface of the n-type contact layer 14.

Next, by a vapor deposition method or the like, the p-side electrode 25 is formed so as to include the opening of the ridge portion 10 in the protective insulating film 24.
Then, the n-side electrode 23 is formed on the exposed portion of the n-type contact layer 14 from the protective insulating film 24.
The order of forming the p-side electrode 25 and the n-side electrode 23 does not matter.

After that, the substrate 11 is cleaved so that the cavity facets are exposed to obtain the semiconductor laser device shown in FIG.

The p-side electrode 25 of the obtained semiconductor laser device
When a voltage is applied between the n-side electrode 23 and the n-side electrode 23, holes are injected from the p-side electrode 25 and electrons are injected from the n-side electrode 23 toward the MQW active layer 17. The injected holes and electrons generate a gain in the MQW active layer 17,
It has been confirmed that laser oscillation occurs at a wavelength of 405 nm.

The technical background of providing the facet forming layer 12 and its function will be described below.

[Technical Background of Facet Forming Layer] FIG. 3 shows the a-axis lattice constant of gallium nitride grown on a substrate made of gallium nitride (GaN) or sapphire and aluminum gallium nitride (A) lattice-matched to the lattice constant.
The relationship with the Al composition in the semiconductor layer made of (1GaN) is shown.

As shown in FIG. 3, the substrate made of GaN is a bulk crystal in a free-standing (freestanding) state, and its a-axis lattice constant is 3.189Å. Therefore, the AlGaN layer grown using the GaN substrate as a base layer cannot be lattice-matched with the GaN substrate without causing lattice distortion.

On the other hand, the lattice constant of the GaN layer grown by using the sapphire substrate as the base layer is sapphire whose coefficient of thermal expansion is larger than that of GaN, so that the lattice constant is a It is known that the axial lattice constant shrinks. Incidentally, the thermal expansion coefficient of gallium nitride is 5.59 × 10 ⁻⁶ / K, and the thermal expansion coefficient of sapphire is 7.5 × 10 ⁻⁶ / K.

The inventors of the present application have used a heterogeneous substrate (for example, sapphire) made of a material different from that of the semiconductor to be grown and a homogeneous substrate (for example, gallium nitride) made of the same material as the substrate for growing the nitride semiconductor. As a result of various studies, the following findings have been obtained.

First, the lattice constant of GaN grown and compressed on a sapphire substrate, which is a heterogeneous substrate, depends on growth conditions in a MOVPE device for growing a gallium nitride (GaN) semiconductor, such as the substrate temperature and the type of carrier gas. , Growth pressure, gas flow rate and temperature, and grown Ga
The first finding has been obtained that it depends sensitively on the crystallinity of N.

For example, the substrate temperature is sufficiently raised to about 1100 ° C., the temperature of the source gas is set to about 1020 ° C.,
When the sapphire substrate is sufficiently thermally expanded, a
The shaft is compressed more. In addition, gallium nitride (Ga
The a-axis lattice constants of N) and aluminum nitride (AlN) are 3.189Å and 3.112Å, respectively, and it is well known that by adding aluminum to gallium nitride, the lattice can be adjusted according to the composition of the added Al. The constant becomes smaller.

Therefore, by optimizing these growth conditions, the a-axis lattice constant of the GaN layer compressed by the sapphire substrate is about 0% to 10% in terms of the Al composition of aluminum gallium nitride. It is a finding that it can be adjusted within a range corresponding to a constant.

Therefore, when forming a laser structure made of a gallium nitride based semiconductor on a sapphire substrate, GaN is used.
By adjusting the growth conditions of the layer, it is possible to reduce the a-axis lattice constant of the GaN layer and make the lattice match with the a-axis lattice constant of the bulk state of the semiconductor layer made of AlGaN substantially without distortion.

Naturally, instead of the GaN layer, AlGaI
Even when the nN layer is grown on the sapphire substrate, GaN
Similar to the layer, the AlGaInN layer is subjected to compressive strain by the sapphire substrate and its a-axis lattice constant shrinks. As a result, G
By adjusting the growth conditions and the respective compositions of Al and In similarly to the aN layer, the AlGaInN layer is changed to AlGaInN.
It can be substantially lattice-matched to the a-axis lattice constant of the semiconductor layer made of N.

Instead of sapphire, silicon carbide (S
When a laser structure made of gallium nitride based semiconductor is formed on a substrate made of iC) or silicon (Si),
Since the coefficient of thermal expansion of silicon carbide or silicon is smaller than that of GaN, C, contrary to the case of sapphire,
It is known that the a-axis lattice constant is stretched by being subjected to stretching strain in the plane. By the way, the coefficient of thermal expansion of silicon carbide is 4.2.
× 10 ^-6 / K, the coefficient of thermal expansion of silicon is 3.59
It is × 10 ^-6 / K.

As described above, even when the GaN layer is subjected to extension strain, the growth conditions of the GaN layer are adjusted to reduce the elongation of the a-axis lattice constant of the GaN layer, thereby reducing Al.
It becomes possible to perform lattice matching with the bulk-state a-axis lattice constant of the semiconductor layer made of GaN substantially without distortion. Of course, the same effect can be obtained when the AlGaInN layer is grown on the substrate made of silicon carbide or silicon.

Needless to say, it is better that the lattice constant is as close as possible to the substantial lattice matching with the AlGaN layer. In addition, for example, in the laser structure, the AlGaN layer is a clad layer that has a larger forbidden band width and a smaller refractive index than the active layer and needs a relatively large film thickness.

On the other hand, when a semiconductor layer made of AlGaN having a bulk lattice constant smaller than that of GaN is grown on a GaN layer grown on the same kind of substrate made of gallium nitride (GaN), As is well known, as the Al composition increases, the lattice strain increases and cracks and defects increase, and it is difficult to obtain a laser structure that does not cause cracks.

[Function of Facet Forming Layer] In the first embodiment, as described above, the substrate 1 made of GaN is used.
The pre-facet forming layer 12A made of, for example, Al _0.1 Ga _0.9 N is grown on the substrate 1 at a growth temperature of about 550 ° C., and then heat treatment is performed at a temperature of about 1120 ° C. in an atmosphere containing ammonia and hydrogen. Further, the partial pressure of hydrogen in the atmosphere at this time is set to a value higher than or equal to the partial pressure of the carrier gas composed of nitrogen, for example.

By this heat treatment, rearrangement of crystal lattices occurs in the prefacet forming layer 12A, and, for example, the (0001) plane and the {1-101} plane or the {1-10] are formed on the surface thereof.
The facet forming layer 12 having a plane orientation different from the 2} plane is formed. The facet forming layer 12 is made of AlGaN.
, Which is an underlayer for obtaining the selective growth layer 13 made of GaN and having an a-axis lattice constant equivalent to that of the n-type cladding layer 14, for example.

The inventors of the present invention have found that the lateral growth of the selective growth layer 13 is selectively started from the facet plane inclined from the C plane of the facet formation layer 12, so that the selective growth layer 13 is parallel to the C plane of the selective growth layer 13. The second finding has been obtained that the in-plane lattice constant is compressed by the stress during growth and the a-axis lattice constant is contracted. Specifically, the a-axis lattice constant equivalent to that of the GaN layer that is compressed after being grown on the sapphire substrate described above, that is, 0 in terms of the Al composition of the AlGaN layer.
It is a finding that it is possible to grow a GaN layer (selective growth layer 13) having an a-axis lattice constant corresponding to a bulk lattice constant of about 10% to 10%.

In other words, the lattice constant of the GaN substrate 11 and the in-plane lattice constant (a-axis lattice constant) of the GaN layer (selective growth layer 13) grown on the substrate 11 are By interposing the facet forming layer 12, different values are obtained.

As a result, the GaN layer (selective growth layer 13)
And an AlGaN layer (n-type clad layer 1
4 and the p-type superlattice clad layer 20) can be substantially lattice-matched, and a laser structure free from cracks can be obtained by crystal growth.

Further, the heat treatment performed on the prefacet forming layer 12A at a temperature equal to or higher than the growth temperature also reduces crystal defects in the prefacet forming layer 12A itself, and as a result, the crystallinity of the facet forming layer 12 is reduced. And the crystallinity of the selective growth layer 13 and each semiconductor layer grown thereon can also be improved.

According to the second finding, in the first embodiment, AlGaIn is formed on the substrate 11 made of GaN.
By forming a facet forming layer 12 made of N and having a facet surface having a face orientation different from the substrate surface, and using the formed facet forming layer 12 as a base layer, a selective growth layer 13 made of GaN is grown on the facet forming layer 12. Selective growth layer 13
The a-axis lattice constant of is substantially lattice-matched to each a-axis lattice constant of the n-type cladding layer 14 and the p-type superlattice cladding layer 20.

With this structure, in the semiconductor laser device according to the first embodiment, it is possible to obtain a flat growth surface without cracks over the entire epitaxial growth layer on the substrate 11. As a result, the threshold current density during laser oscillation is reduced as compared with the semiconductor laser device according to the conventional example, and the yield during manufacturing is also significantly improved.

Moreover, the facet forming layer 12 according to the first embodiment has the crack suppressing layer 103 according to the conventional example of n.
Unlike the structure provided between the type contact layer 102 and the n-type superlattice cladding layer 104, the structure is provided between the substrate 11 and the selective growth layer 13. Therefore, the crack suppression layer 103 according to the conventional example is located in the current path, but the facet formation layer 12 according to the first embodiment is provided at a position deviated from the current path, so that the facet formation layer 12 has a defect. Even if occurs, the defect does not increase due to the current. Also, the facet forming layer 12
Is provided at a position distant from the MQW active layer 17, the n-type light guide layer 16 and the p-type light guide layer 19, so that the optical characteristics of the semiconductor layers 16, 17, 19 are not adversely affected. As a result, it is possible to improve the reverse breakdown voltage characteristic, prolong the service life during high-power operation, and improve the yield.

(Modified Example of First Embodiment) A modified example of the first embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows a cross-sectional structure of a nitride semiconductor laser device according to a modification of the first embodiment of the present invention. In FIG. 4, the same components as those shown in FIG. 1A are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 4, in this modification,
Substrate 11 made of undoped gallium nitride (GaN)
For example, silicon (Si), germanium (G
e) or n doped with an n-type dopant such as oxygen (O)
N-type substrate 31 made of gallium nitride having conductivity
To use.

In the method of manufacturing the semiconductor laser device according to the present modification, the n-type Al on which Si or the like is added is formed on the n-type substrate 31.
An n-type facet forming layer 32 made of GaInN is formed, and n-type Ga is formed on the formed n-type facet forming layer 32.
The selective growth layer 13 made of N is grown. Subsequently, the semiconductor layers from the n-type cladding layer 15 to the p-type first contact layer 22 are sequentially grown on the selective growth layer 13.

In this modification, the n-type substrate 31 having conductivity is used.
Therefore, it is not necessary to grow the n-type contact layer 14, and the etching step for exposing the n-type contact layer 14 is also unnecessary.

Instead, the n-side electrode 23 is formed on the surface of the n-type substrate 31 opposite to the facet forming layer 32. As a result, the p-side electrode 25 and the n-side electrode 23 are provided so as to face each other, and the current injected into the laser element flows substantially linearly in the laser element to cause laser oscillation.

Since the crystallinity of the n-type facet forming layer 32 is improved by the heat treatment at the growth temperature or higher performed when forming the n-type facet forming layer 32, the leak current due to the n-type facet forming layer 32 is sufficiently increased. It has been confirmed that it is suppressed and that the yield at the time of manufacturing is also improved.

Further, the facet forming layer 12 according to the first embodiment and the n-type facet forming layer 3 according to this modification.
By adjusting the Al composition, Ga composition, and In composition of the bandgap in Example 2 to be smaller than the bandgap of the MQW active layer 17, the facet forming layer 12 and the n-type facet forming layer 32 are the MQW active layer. 1
It becomes possible to absorb the spontaneous emission light emitted from 7. As a result, the spontaneous emission light emitted from the back surface of the substrate 11 or the n-type substrate 31 is suppressed, which is caused by the spontaneous emission light generated in the electronic element or the electronic device arranged around the semiconductor laser element. Noise can be reduced.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows a cross-sectional structure of a nitride semiconductor laser device according to the second embodiment of the present invention. In FIG. 5, the same components as those shown in FIG. 1A are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 5, the semiconductor laser device according to the second embodiment has a selective growth layer made of AlGaInN having a plurality of recessed portions 41a extending in stripes on the facet forming layer 12 made of AlGaInN. 41 is formed by growth. A mask film 42 made of, for example, silicon nitride (SiN _x ) is formed on the bottom surface and the wall surface of the recess 41a in the selective growth layer 41.

On the exposed surface of the selective growth layer 41 from the mask film 42, a lateral growth layer 43 of GaN is formed by growth, and the first embodiment is formed on the lateral growth layer 43. Similar to the embodiment, the n-type contact layer 14 to the p-type first contact layer 22 are sequentially formed by growth.

In the second embodiment, on the facet forming layer 12, a known selective lateral epitaxial growth method is used.
A selective growth layer 41 having a recess 41a that enables lateral overgrowth (ELOG) is formed, and the lateral long layer 43 is formed using the formed selective growth layer 41 as a base layer. As a result, as compared with the semiconductor laser device according to the first embodiment, the crystal defects in the epitaxial semiconductor layer are significantly reduced, thereby achieving high reliability of the semiconductor laser device.

A method of manufacturing the nitride semiconductor laser device having the above-described structure up to the selective growth layer will be described with reference to FIGS. 6 (a) to 6 (c).

First, as shown in FIG. 6A, MOVP
By the E method, the growth temperature is set to about 550 ° C. on the substrate 11 made of GaN, and TMG, TMA, and T which are group III sources are used.
By introducing MI and NH ₃ which is a group V source, the substrate 11
A prefacet forming layer made of AlGaInN is grown on the main surface of. Then, the substrate temperature is raised to about 1120 ° C., and the ratio of ammonia as a nitrogen source to hydrogen and nitrogen as a carrier gas is set to 1: 1: 1 or 2: 2: 1. By performing heat treatment on the pre-facet forming layer for several minutes under such conditions, the facet forming layer 12 having a facet surface parallel to the substrate surface and a facet surface inclined to the substrate surface is formed on the upper surface. Form.

Subsequently, the growth temperature is set to about 1100 ° C.,
A selective growth layer 41 made of AlGaInN is grown using the facet formation layer 12 as a base layer. At this time, the selective growth layer 41 is formed on the substrate surface (C
Since it grows from a facet plane different from the (plane), its a-axis lattice constant is smaller than the a-axis lattice constant of the substrate 11.

Next, using a lithography method, a resist pattern having stripe-shaped patterns each having a width of about 3 μm and extending in parallel at an interval of about 12 μm from each other on the selective growth layer 41 (FIG. (Not shown). Here, the direction in which the stripe extends is, for example, the <1-100> direction of the crystal zone axis. Then, the selective growth layer 41 is dry-etched by using the formed resist pattern as a mask.
A plurality of stripe-shaped convex portions formed of a plurality of recess portions 41a and a region sandwiched between the recess portions 41a. Then, a mask film 42 made of silicon nitride is deposited over the entire surface including the resist pattern and the convex portion on the selective growth layer 41 in which the recess portion 41a is formed by, for example, the ECR sputtering method. After that, the resist pattern is lifted off to remove the mask film 42 on the convex portion of the selective growth layer 41, thereby exposing the upper surface of the convex portion to obtain the state shown in FIG. 6B.

Next, as shown in FIG. 6C, M
The growth temperature is set to about 1000 ° C. by the OVPE method, and T
By selective lateral growth in which MG and NH ₃ are introduced onto the selective growth layer 41, the exposed surface of the convex portion in the selective growth layer 41 is used as a seed crystal, and GaN having a thickness of about 3 μm is formed thereon.
To grow the lateral growth layer 43.

Thereafter, as shown in FIG. 5, the n-type contact layer 14 to the p-type first contact layer 22 are grown on the lateral growth layer 43 in the same manner as in the first embodiment. Subsequently, dry etching for forming the ridge portion 10 and dry etching for exposing the n-type contact layer 14 are performed to form the protective insulating film 24, and then the p-side electrode 2 is formed.
5 and the n-side electrode 23 are sequentially formed.

Although GaN is used for the lateral growth layer 43, AlGaInN may be used. However, AlGaI
When nN is used, the compositions of Al and In are set to the a-axis lattice constant of the lateral growth layer 43 and the a-axis lattice constant of the n-type cladding layer 15.
It is necessary to adjust so that the axial lattice constant substantially matches.

(First Modification of Second Embodiment) A first modification of the second embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 shows a cross-sectional structure of a nitride semiconductor laser device according to a first modification of the second embodiment of the present invention. 7, the same components as those shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 7, in the first modification, instead of the substrate 11 made of undoped GaN, it is made of n-type gallium nitride to which an n-type dopant such as Si, Ge or O is added. N-type substrate 3 having conductivity
1 is used.

In the method of manufacturing the semiconductor laser device according to the first modification, the n-type A in which Si or the like is added to the n-type substrate 31 is used.
An n-type facet forming layer 32 made of 1GaInN is formed, and n-type Al is formed on the formed n-type facet forming layer 32.
A selective growth layer 41 made of GaInN is grown. Then, on the selective growth layer 41, a stripe-shaped recess 4 is formed.
1a is selectively formed, and a mask film 42 is further formed on the recess 41a. Then, the selective growth layer 41 is changed to n-type GaN.
The lateral growth layer 43 consisting of is selectively grown. Then, from the n-type contact layer 14 to the p-type first contact layer 2
Each semiconductor layer up to 2 is sequentially grown.

The first modification is a conductive n-type substrate 3
Since No. 1 is used, the etching process for exposing the n-type contact layer 14 is unnecessary.

Instead, the n-side electrode 23 is formed on the surface of the n-type substrate 31 opposite to the facet forming layer 32. As a result, the p-side electrode 25 and the n-side electrode 23 are provided so as to face each other, and the current injected into the laser element linearly flows through the laser element to cause laser oscillation.

Since the crystallinity of the n-type facet forming layer 32 is improved by the heat treatment at the growth temperature or higher performed when forming the n-type facet forming layer 32, the leak current due to the n-type facet forming layer 32 is sufficiently increased. It has been confirmed that it is suppressed and that the yield at the time of manufacturing is also improved.

Also, the facet forming layer 12 according to the second embodiment and the n-type facet forming layer 3 according to the first modification.
By adjusting the Al composition, Ga composition, and In composition of the bandgap in Example 2 to be smaller than the bandgap of the MQW active layer 17, the facet forming layer 12 and the n-type facet forming layer 32 are the MQW active layer. 1
It becomes possible to absorb the spontaneous emission light emitted from 7. As a result, the spontaneous emission light emitted from the back surface of the substrate 11 or the n-type substrate 31 is suppressed, which is caused by the spontaneous emission light generated in the electronic element or the electronic device arranged around the semiconductor laser element. Noise can be reduced.

Although silicon nitride is used for the mask film 42 provided on the selective growth layer 41, the material is not limited to this, and any material that does not substantially cause crystal growth of a nitride semiconductor thereon, such as, for example, oxidation is used. It may be silicon (SiO ₂ ) or silicon (Si).

(Second Modification of Second Embodiment) A second modification of the second embodiment of the present invention will be described below with reference to the drawings.

Of the method for manufacturing the nitride semiconductor laser device according to the second modification of the second embodiment of the present invention, the manufacturing method up to the lateral growth layer is referred to FIGS. 8A to 8C. While explaining.

First, as shown in FIG. 8A, the substrate 11
After the facet forming layer 12 is formed on the main surface of, the selective growth layer 41 is grown on the formed facet forming layer 12.

Next, as shown in FIG. 8B, a stripe-shaped resist pattern (not shown) is formed by a lithography method, and dry etching is performed on the upper part of the selective growth layer 41 using the formed resist pattern as a mask. Then, a plurality of recesses 41b having wall surfaces substantially vertical to the substrate surface are formed on the selective growth layer 41. Then, the resist pattern is removed, and subsequently, a mask film 42 made of silicon nitride is deposited on the upper surface of the selective growth layer 41 and the bottom surface of the recess 41b. At this time, the recess 4
The wall surface of 1b remains exposed.

Next, as shown in FIG. 8C, the lateral growth layer 4 is formed from the wall surface of the recess portion 41b in the selective growth layer 41.
3 is selectively grown to reduce its crystal defects.

As a third modification, the mask film 42 may not be provided in the recesses 41a and 41b in the second embodiment and each modification thereof.

Further, as a fourth modification, the selective growth layer 4
1 on the upper surface of the recess 1 in the selective growth layer growth 41,
A mask film 42 having a stripe-shaped opening is formed without providing 41 b, and subsequently, a lateral growth layer 43 is selectively grown from the exposed surface of the selective growth layer 41 from the mask film 42. The crystal defects of the lateral growth layer 43 may be reduced.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 9 shows a cross-sectional structure of a nitride semiconductor laser device according to the third embodiment of the present invention. In FIG. 9, the same components as those shown in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

In the second embodiment, the facet forming layer 12 is formed on the substrate 11, and then the lateral growth layer 43 is formed by the ELOG method. In the third embodiment, it is made of GaN. After the lateral growth layer 43 is formed on the substrate 11 by the ELOG method, the facet forming layer 12 is formed on the lateral growth layer 43.

As shown in FIG. 9, a stripe-shaped recess 11a is formed on the substrate 11, and the recess 11a is formed.
A mask film 42 is formed on the bottom surface and the wall surface of the.
Again, the direction in which the stripe extends is, for example, <1-100> of the crystal zone axis.

Lateral overgrowth layer 43 according to the third embodiment.
Are selectively grown from the top surface of the convex portion between the mask films 42 on the substrate 11. Therefore, in the facet forming layer 12 grown on the lateral growth layer 43, crystal defects are further reduced.

A method of manufacturing the nitride semiconductor laser device having the above-described structure up to the second selective growth layer will be described with reference to FIGS. 10 (a) to 10 (c). .

First, as shown in FIG. 10A, a width of about 3 μm and an interval of about 12 μm between adjacent ones are formed on a substrate 11 made of gallium nitride (GaN) by using a lithography method. A resist pattern (not shown) extending in parallel is formed. Subsequently, dry etching is performed on the substrate 11 using the formed resist pattern as a mask, so that a plurality of stripes including a plurality of recesses 11a and regions sandwiched between the recesses 11a are formed on the substrate 11. Forming a convex portion. Then, the recess 11a is formed by, for example, the ECR sputtering method.
A mask film 42 made of silicon nitride is deposited over the entire surface including the resist pattern and the protrusions on the substrate 11 on which the masks are formed. After that, the resist pattern is lifted off to remove the mask film 42 on the convex portion of the substrate 11 to expose the upper surface of the convex portion.

Next, as shown in FIG. 10B, MOV
By the PE method, the growth temperature is set to about 1000 ° C., and the convex portions on the substrate 11 are exposed by the selective lateral growth in which the group III source TMG and the group V source NH ₃ are introduced onto the substrate 11. The surface is a seed crystal and the thickness is about 3μ
A lateral growth layer 43 made of m GaN is grown.

Next, as shown in FIG. 10 (c), the growth temperature is set to about 550 ° C., TMG, TMA and TMI which are group III sources, and NH ₃ which is a group V source are introduced, and a lateral direction is introduced. A prefacet forming layer made of AlGaInN is grown on the growth layer 43. Subsequently, the substrate temperature is set to about 112
The prefacet is heated to 0 ° C., and the ratio of ammonia as a nitrogen source to hydrogen and nitrogen as a carrier gas is set to 1: 1: 1 or 2: 2: 1. By heat-treating the forming layer for several minutes, a facet forming layer 1 having a facet surface parallel to the substrate surface and a facet surface inclined to the substrate surface on the upper surface
Form 2.

Subsequently, the growth temperature is set to about 1100 ° C.,
A selective growth layer 13 made of AlGaInN is grown using the facet formation layer 12 as a base layer. At this time, the selective growth layer 13 is formed on the substrate surface (C
Since it grows from a facet surface different from the (plane), its a-axis lattice constant is smaller than the a-axis lattice constant of the lateral growth layer 43.

After that, as shown in FIG. 9, the n-type contact layer 14 to the p-type first contact layer 22 are grown on the selective growth layer 13 as in the first embodiment.
Subsequently, dry etching for forming the ridge portion 10 and dry etching for exposing the n-type contact layer 14 are performed to form a protective insulating film 24, and then a p-side electrode 25 and an n-side electrode 23 are sequentially formed.

Although GaN is used for the selective growth layer 13, AlGaInN may be used. However, AlGaI
When nN is used, it is necessary to adjust the composition of each of Al and In so that the a-axis lattice constant of the selective growth layer 13 and the a-axis lattice constant of the n-type cladding layer 15 substantially match.

Further, the lateral growth layer 43 may be grown by the same method as in the second, third and fourth modifications of the second embodiment.

(Modification of Third Embodiment) A modification of the third embodiment of the present invention will be described below with reference to the drawings.

FIG. 11 shows a cross-sectional structure of a nitride semiconductor laser device according to a modification of the third embodiment of the present invention. 11, the same components as those shown in FIG. 9 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 11, in this modified example, instead of the substrate 11 made of undoped GaN, conductivity made of n-type gallium nitride doped with an n-type dopant such as Si, Ge or O is used. Type n-type substrate 3
1 is used.

In the method of manufacturing the semiconductor laser device according to this modification, the recess 31a is selectively formed on the n-type substrate 31, and the lateral growth is performed on the n-type substrate 31 having the recess 31a. The layer 43 is formed by selective growth. After that, the n-type facet forming layer 32 made of n-type AlGaInN added with Si or the like is formed on the lateral growth layer 43, and the n-type facet forming layer 32 is formed on the formed n-type facet forming layer 32.
The selective growth layer 13 made of aN is grown. Subsequently, the semiconductor layers from the n-type cladding layer 15 to the p-type first contact layer 22 are sequentially grown on the selective growth layer 13.

In this modification, the n-type substrate 31 having conductivity is used.
Therefore, it is not necessary to grow the n-type contact layer 14, and the etching step for exposing the n-type contact layer 14 is also unnecessary.

Instead, the n-side electrode 23 is formed on the surface of the n-type substrate 31 opposite to the lateral growth layer 43. As a result, the p-side electrode 25 and the n-side electrode 23 are provided so as to face each other, and the current injected into the laser element linearly flows through the laser element to cause laser oscillation.

Since the crystallinity of the n-type facet forming layer 32 is improved by the heat treatment at the growth temperature or higher when forming the n-type facet forming layer 32, the leak current due to the n-type facet forming layer 32 is sufficiently increased. It has been confirmed that it is suppressed and that the yield at the time of manufacturing is also improved.

Also, the facet forming layer 12 according to the third embodiment and the n-type facet forming layer 32 according to the present modification.
By adjusting the Al composition, Ga composition, and In composition thereof to be smaller than that of the MQW active layer 17, the facet formation layer 1
2 and the n-type facet forming layer 32 are the MQW active layer 17
It becomes possible to absorb the spontaneous emission light emitted from. As a result, the spontaneous emission light emitted from the back surface of the substrate 11 or the n-type substrate 31 is suppressed, which is caused by the spontaneous emission light generated in the electronic element or the electronic device arranged around the semiconductor laser element. Noise can be reduced.

Although silicon nitride is used for the mask film 42 provided on the selective growth layer 41, the invention is not limited to this, and silicon oxide or silicon may be used, for example.

In the first to third embodiments and their modifications, the MOVPE method was used as the method for growing a nitride semiconductor, but the present invention is not limited to this, and the present invention is based on hydride vapor phase epitaxy (HVPE). Method or molecular beam epitaxy (MB
It can be applied to a crystal growth method capable of growing a nitride semiconductor layer such as the method E).

Although the laser structure made of a nitride semiconductor is formed on the substrate 11 made of gallium nitride (GaN), the substrate 11 is not limited to gallium nitride. For example, a bulk substrate made of a nitride semiconductor such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), or aluminum gallium indium nitride (AlGaInN) may be used. Furthermore, sapphire (single crystal Al ₂ O ₃ ), silicon carbide (SiC), silicon (S
The nitride semiconductor grown on the substrate i) or gallium arsenide (GaAs) may be used as a new substrate. That is, by providing the facet forming layer between the substrate and the active layer (laser structure), the first nitride semiconductor crystal layer having different lattice constants in the plane parallel to the substrate surface can be formed. It is sufficient that the first nitride semiconductor crystal layer and the cladding layer made of the second nitride semiconductor crystal layer grown on the first nitride semiconductor crystal layer are substantially lattice-matched.

Although the (0001) plane (C plane) is used as the main surface of the substrate 11 in each of the embodiments and the modifications thereof, it is not limited to the C plane as long as the lattice matching condition of the present invention is satisfied. Alternatively, a substrate having a main surface slightly inclined with respect to the C plane in the A plane or the M plane may be used.

Further, in the planes parallel to the respective growth planes of the first semiconductor layer located below the facet forming layer and the second semiconductor layer grown on the facet forming layer according to the present invention. The configuration in which the lattice constants are different from each other is not limited to gallium nitride based semiconductors. For example, boron nitride (BN) and nitride compound semiconductors such as a mixed crystal of BN and AlGaInN are generally effective.

Further, in each of the embodiments and the modified examples thereof, the configuration of the semiconductor laser device as the semiconductor device and the manufacturing method thereof have been described, but the present invention is not limited to the light emitting device and can be widely applied to the semiconductor device using the nitride semiconductor. You can

[0144]

According to the nitride semiconductor and the method for manufacturing the same according to the present invention, the first semiconductor layer and the second semiconductor layer have different lattice constants in a plane parallel to the main surface, so that the second semiconductor is obtained. When the layer is, for example, a clad layer or an underlying layer thereof, even if the first semiconductor layer is a nitride semiconductor having a composition different from that of the second semiconductor layer, the second semiconductor layer does not crack.

According to the nitride semiconductor device of the present invention,
A facet forming layer formed by growth on the first semiconductor layer is provided, and the lattice constant of the second semiconductor layer formed by growth on the facet forming layer is substantially equal to the bulk state lattice constant of the third semiconductor layer. Therefore, even if the thickness of the third semiconductor layer is made relatively large, cracks do not occur in the third semiconductor layer.

[Brief description of drawings]

FIG. 1A is a sectional view showing a structure of a nitride semiconductor laser device according to a first embodiment of the present invention. FIG. 2B is a partial structural cross-sectional view showing an active layer in the nitride semiconductor laser device according to the first embodiment of the present invention. (C)
FIG. 3 is a partial structural cross-sectional view showing a p-type superlattice cladding layer in the nitride semiconductor laser device according to the first embodiment of the present invention.

2A to 2D are structural cross-sectional views in order of the processes, showing a method for manufacturing a facet forming layer in a nitride semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a graph showing the concept of the present invention, which comprises an a-axis lattice constant in gallium nitride grown on a first gallium nitride or sapphire substrate and aluminum gallium nitride lattice-matched to the lattice constant. It is a graph which shows the relationship with Al composition in a semiconductor layer.

FIG. 4 is a structural cross-sectional view showing a nitride semiconductor laser device according to a modification of the first embodiment of the present invention.

FIG. 5 is a structural cross-sectional view showing a nitride semiconductor laser device according to a second embodiment of the present invention.

6A to 6C are facet forming layers in a nitride semiconductor laser device according to a second embodiment of the present invention,
FIG. 6 is a configuration cross-sectional view in process order showing a method for manufacturing a selective growth layer and a lateral growth layer.

FIG. 7 is a structural cross-sectional view showing a nitride semiconductor laser device according to a first modification of the second embodiment of the present invention.

FIGS. 8A to 8C show a method for manufacturing a facet forming layer, a selective growth layer and a lateral growth layer in a nitride semiconductor laser device according to a second modification of the second embodiment of the present invention. It is a structure sectional view in order of a process.

FIG. 9 is a structural cross-sectional view showing a nitride semiconductor laser device according to a third embodiment of the present invention.

10A to 10C are structural cross-sectional views in order of the processes, showing a method for manufacturing a lateral growth layer, a facet formation layer and a selective growth layer in a nitride semiconductor laser device according to a third embodiment of the present invention. It is a figure.

FIG. 11 is a structural cross-sectional view showing a nitride semiconductor laser device according to a modification of the third embodiment of the present invention.

FIG. 12 is a sectional view showing a structure of a conventional nitride semiconductor laser device.

[Explanation of symbols]

10 Ridge part 11 board 11a recess part 12 Facet forming layer 12A Prefacet forming layer 13 Selective growth layer 14 n-type contact layer 15 n-type clad layer 16 n-type optical guide layer 17 Multiple quantum well (MQW) active layer 17a Well layer 17b Barrier layer 18 Current blocking layer 19 p-type optical guide layer 20 p-type superlattice cladding layer 20a first layer 20b second layer 21 p-type second contact layer 22 p-type first contact layer 23 n-side electrode 24 Protective insulation film 25 p-side electrode 31 n-type substrate 31a recess part 32 n-type facet forming layer 41 Selective growth layer 41a recess part 41b recess 42 Mask film 43 Lateral growth layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ayumu Tsujimura             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Nobuyuki Otsuka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5F045 AA04 AB18 AC08 AC12 AC15                       AD09 AD15 AF02 AF04 AF09                       BB13 CA12 DA53 DA55 DB09                 5F073 AA13 AA45 AA47 AA51 AA74                       AA77 BA05 CA02 CB02 CB06                       DA05 EA27 EA29

Claims (15)

[Claims] 1. A first semiconductor layer made of a first nitride semiconductor, and a second semiconductor layer formed by growth on a main surface of the first semiconductor layer.
A second semiconductor layer made of a nitride semiconductor, wherein the first semiconductor layer and the second semiconductor layer have different lattice constants in a plane parallel to the main surface. . 2. A facet forming layer made of a third nitride semiconductor, which is formed between the first semiconductor layer and the second semiconductor layer, contains aluminum, and has a plurality of facet surfaces different from each other on the surface thereof. The nitride semiconductor according to claim 1, further comprising: the second semiconductor layer grown using the facet forming layer as a base layer. 3. One of the plurality of facet surfaces is a surface parallel to the main surface of the first semiconductor layer, and the other surface is a surface inclined with respect to the main surface. The nitride semiconductor according to claim 2, which is characterized in that. 4. The plane orientation of the one surface is a (0001) plane, and the plane orientation of the other surface is a {1-101} plane or a {1} plane.
4. The nitride semiconductor according to claim 3, which is a −102} plane. 5. The first semiconductor layer comprises aluminum gallium indium nitride (Al _x Ga _y In _z N (provided that 0
≦ x, y, z ≦ 1, x + y + z = 1)), a nitrogen-containing compound crystal, sapphire, silicon carbide, or gallium arsenide. Item 5. The nitride semiconductor according to any one of items 1 to 4. 6. A first step of growing a facet forming layer made of a second nitride semiconductor containing aluminum at a first temperature on a first semiconductor layer made of a first nitride semiconductor, A second step of forming a plurality of facet planes having mutually different plane orientations on the surface of the facet forming layer by performing heat treatment on the facet forming layer at a second temperature higher than the first temperature. And a third step of growing a second semiconductor layer made of a third nitride semiconductor on the heat-treated facet forming layer at a third temperature higher than the first temperature, The method for producing a nitride semiconductor, wherein the first semiconductor layer and the second semiconductor layer have different lattice constants in a plane parallel to the main surface of the first semiconductor layer. 7. The method for producing a nitride semiconductor according to claim 6, wherein the second step is performed in an atmosphere containing ammonia and hydrogen. 8. The partial pressure of hydrogen contained in the atmosphere is set to a value higher than or equal to the partial pressure of a carrier gas composed of an inert gas excluding the hydrogen. Manufacturing method of nitride semiconductor. 9. One of the plurality of facet planes has a (0001) plane orientation, and the other has a {1-10 plane orientation.
It is a 1} surface or a {1-102} surface, The manufacturing method of the nitride semiconductor of any one of Claims 6-8 characterized by the above-mentioned. 10. Before the first step, the first semiconductor layer is formed of aluminum gallium indium nitride (Al _x Ga _y In _z N (where 0 ≦ x, y, z ≦
1, x + y + z = 1)), a compound crystal containing nitrogen, sapphire, silicon carbide, or gallium arsenide, and a fourth step of growing on a substrate. 9. The method for manufacturing a nitride semiconductor according to any one of items 1 to 8. 11. A first semiconductor layer made of a first nitride semiconductor, and a second semiconductor layer formed on the main surface of the first semiconductor layer, containing aluminum, and having a plurality of facet surfaces different from each other on the upper surface thereof. A facet forming layer made of a nitride semiconductor, and a third facet formed by growth on the facet forming layer
A second semiconductor layer made of a nitride semiconductor, and a third semiconductor layer made of a fourth nitride semiconductor formed on the second semiconductor layer by growth and having a relatively large aluminum composition, The first semiconductor layer and the second semiconductor layer have different lattice constants in a plane parallel to the main surface, and the lattice constant of the second semiconductor layer is the lattice of the bulk state of the third semiconductor layer. A nitride semiconductor device, which substantially matches a constant. 12. An active layer made of a fifth nitride semiconductor is further provided on the second semiconductor layer, and a size of an energy gap in the facet forming layer is equal to an emission wavelength oscillated from the active layer. The nitride semiconductor device according to claim 11, which has a smaller energy than the corresponding energy. 13. The nitride semiconductor device according to claim 11, wherein an operating current does not flow in the facet forming layer. 14. One of the plurality of facet planes has a (0001) plane orientation, and the other plane orientation has {1-10.
The nitride semiconductor device according to claim 11, which is a 1} plane or a {1-102} plane. 15. The first semiconductor layer comprises aluminum gallium indium nitride (Al _x Ga _y In _z N (provided that
0 ≦ x, y, z ≦ 1, x + y + z = 1)), a nitrogen-containing compound crystal, sapphire, silicon carbide, or gallium arsenide. Any one of claims 11-14
A nitride semiconductor device according to item.