JP2000174392A - Nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that crystalline nonuniformity occurs in a face and to improve the reliability of an element in the conventional element. SOLUTION: A first nitride semiconductor layer 2 grown on the different type of substrate, a protection film 11, which is partially formed on the surface of the first nitride semiconductor layer 2, a selective growing layer 3 grown on the surface of the first nitride semiconductor layer 2 and a second buffer layer 4 containing a polycrystal on the layer are sequentially given between the different types of substrate and a light-emitting layer. Thus, crystalline in-face nonuniformity shown by an oblique line part is dissolved. Then, crystallinity becomes satisfactory in the respective layers stacked on the substrate. Even if a nitride semiconductor 5 grown on the second buffer layer 4 is AlGaN, satisfactory crystal is formed and an element characteristic and element reliability are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing
The present invention relates to a light emitting element having a double hetero structure having a cladding layer made of a nitride semiconductor containing 1 and an active layer containing In thereon.

[0002]

2. Description of the Related Art Conventionally, a semiconductor light emitting device having a short wavelength such as blue light is formed on a heterogeneous substrate by using a nitride semiconductor In _x Al _y Ga.
_1-xy N (0 ≦ x, 0 ≦ y, x + y ≦ 1) can be used for metalorganic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), halide vapor phase epitaxy (HDVPE), etc. It is epitaxially grown by a vapor phase growth method. As a structure of the laser element, a double hetero structure in which an active layer is sandwiched between n-type and p-type cladding layers having a large difference in refractive index as shown in FIG. 1 is employed. The active layer is mainly realized by InGaN, which is formed of AlGaN or Ga having a small refractive index.
Using N or the like as a cladding layer, light is confined in this region.

As described above, since the nitride semiconductor light emitting device uses a different kind of substrate, the crystallinity thereof is improved.
Various attempts have been made. As the attempt, there are various methods such as providing a buffer layer for alleviating a lattice constant difference from a heterogeneous substrate and a layer for preventing crystal defects from spreading during element driving. However, although there are some results, it is necessary to further improve the crystallinity and improve the reliability of the device.

In a laser device, in order to efficiently confine light in a waveguide, the thickness of a cladding layer is set as follows:
0.1 μm or more is required. Furthermore, in order to increase the refractive index difference from the InGaN active layer, the Al mixed crystal ratio of the AlGaN cladding layer must be increased.

[0005]

In order to improve the crystallinity of a nitride semiconductor laminated on a heterogeneous substrate, as shown in FIG. 4, the surface of the nitride semiconductor grown on the heterogeneous substrate is partially By providing the protective film 11 (FIG. 4A) and growing a nitride semiconductor in that state (FIG. 4B), growth in the plane direction was produced. The nitride semiconductor grown on the selective growth layer has good crystallinity, and the nitride semiconductor light-emitting device obtained by stacking each device structure by this method, for example, a laser device has a room temperature. Enabled continuous oscillation for more than 1,000 hours. However, inside the selective growth layer,
There is a characteristic distribution of crystallinity, and there is a difference in crystallinity between the shaded region in FIG. 1 and the other regions. Since the nitride semiconductor grown on the selective growth layer also inherits this distribution of crystallinity, there is a certain limit in the crystallinity of the semiconductor device obtained thereby, and the reliability is dramatically improved. Can not do.

Further, Al used for a cladding layer or the like is used.
When the Al mixed crystal ratio is increased, the nitride semiconductor layer containing
Cracks were severely generated, and it was not possible to grow with a film thickness sufficient to function as a cladding layer. here,
A nitride semiconductor grown due to lattice mismatch with a dissimilar substrate has a unique crystalline state due to internal strain and the like, and therefore the crystallinity of the grown layer greatly differs depending on the composition of the layer to be epitaxially grown. For example, if the nitride semiconductor is G
With aN, it is possible to grow a thick film while maintaining a certain degree of crystallinity. However, in the case of a mixed crystal of InGaN and AlGaN, even if the film thickness is small, a fatal defect occurs during the growth, As a result, the formation of the layers is extremely difficult. In particular, a nitride semiconductor layer containing Al is remarkable.
It is difficult to form even a film thickness of 1 μm, and a nitride semiconductor layer cannot be laminated thereon. For this reason,
Like the above-described selective growth layer, it is difficult to grow AlGaN on a layer having non-uniform in-plane distribution of crystallinity or a layer that inherits the tendency.

The present invention has been made to solve such a problem, and a selective growth layer provided for improving the crystallinity of a nitride semiconductor grown on a heterogeneous substrate includes:
Since there is non-uniform crystallinity accompanying this, it is necessary to form each element structure in a state where this is eliminated. In addition, by eliminating the adverse effects of providing such a selectively grown layer, a ternary mixed crystal AlGaN
It is an object of the present invention to provide a light emitting device in which a crystal is grown without generating cracks or the like even if the Al mixed crystal ratio is increased, and then a good nitride semiconductor layer is laminated.

[0008]

According to the nitride semiconductor light emitting device of the present invention, a good crystalline nitride semiconductor is grown by forming a low temperature growth buffer layer on a selective growth layer made of a nitride semiconductor. And a thicker A
A nitride semiconductor light emitting device having lGaN is also obtained.

That is, a light emitting device in which a nitride semiconductor layer including a light emitting layer is laminated on a heterogeneous substrate, wherein the first nitride grown on the heterogeneous substrate is located between the heterogeneous substrate and the light emitting layer. A semiconductor layer, a protection film partially formed on the surface of the first nitride semiconductor layer, and the first film via the protection film.
Characterized in that a selective growth layer grown on the surface of the nitride semiconductor layer and a second buffer layer containing polycrystal thereon are sequentially provided. Further, A is contacted on the buffer layer.
a third conductivity type layer made of l _x Ga ₁ -xN (0 <x ≦ 1), and more preferably, the third conductivity type layer has a thickness of 0.3 μm or more and a mixed crystal ratio. x is 0.05 or more, and the first conductivity type layer is GaN doped with an n-type impurity.

[0010]

FIG. 1 is a sectional view of a laser device according to one embodiment of the present invention, and the light emitting device of the present invention will be described based on the sectional view.

First, a first nitride semiconductor layer is grown on a heterogeneous substrate having a different lattice constant from the nitride semiconductor. Here, the first nitride semiconductor layer serves as a base for growing the selective growth layer. Further, as the substrate in the present invention, there are sapphire, spinel, and silicon carbide which are conventionally known, and the substrate used for other nitride semiconductors is not limited thereto. Further, a substrate in which the main surface of the substrate material is off-angled, and more preferably a substrate in which the main surface is off-angled in a step shape, can be used. As described above, it is preferable that the main surface of the heterogeneous substrate be off-angle because crystal defects are further reduced. Further, the first nitride semiconductor layer in the present invention may be composed of either a single-layer film or a multilayer film, regardless of the presence or absence of conductivity. Preferably, if the first nitride semiconductor layer grown as the underlayer has good crystallinity, the crystallinity of the nitride semiconductor grown thereon becomes good, so that undoped GaN is grown. Is preferred.

In the present invention, the method of growing a nitride semiconductor is not particularly limited, and may be MOVPE, MBE, HVP.
It can be grown by conventional methods known for growing nitride semiconductors such as E.

In the present invention, first, an underlayer of a selective growth layer
Grows a first nitride semiconductor layer,
Before growing the first nitride semiconductor layer,
Al _xGa_1-xN (0 <x ≦ 1), grown at low temperature
A buffer layer may be provided. This buffer layer
, Lattice mismatch between the substrate and the nitride semiconductor is reduced
And preferred. At this time, the growth temperature of the buffer layer
Is in the range of 200-900C. Light emitting device of the present invention
Has a structure without such a buffer layer on the substrate.
But it is preferable that a buffer layer is provided.
Thus, the crystallinity of the selectively grown layer is improved.

(Selective Growth Layer) The selective growth layer used in the nitride semiconductor light emitting device of the present invention will be described in detail below. 4 to 6 schematically show one embodiment of the selective growth layer, and a description will be given based on this specific example. In the figures, 1 is a heterogeneous substrate, 2 is a first nitride semiconductor layer, 3, 3
'Indicates a selective growth layer, and 11 and 12 indicate protective films.

As shown in the figure, a buffer layer is provided on a heterogeneous substrate, a first nitride semiconductor layer serving as an underlayer is then grown, and a protective film is partially provided on the surface thereof. A selective growth layer is grown.

In the present invention, the selective growth layer composed of the nitride semiconductor layer grown on the first nitride semiconductor layer partially provided with the protective film is specifically undoped (does not dope impurities). Ga in state, undope)
GaN doped with N and n-type impurities and GaN doped with Si can be used. The selective growth layer is
High temperature, specifically 900 ° C to 1100 ° C, preferably 1 ° C
It is grown on a heterogeneous substrate at 050 ° C., and the film thickness is not particularly limited, for example, 1 to 20 μm, preferably 2 to 10 μm
It is. When the film thickness of the selective growth layer is in the above range, the total film thickness of the selective growth layer and the underlayer is suppressed, and the warpage of the wafer (warpage in a state having a heterogeneous substrate) can be prevented.

As a material of the protective film, a material having a property that the nitride semiconductor does not grow or hardly grows on the surface of the protective film is preferably selected. For example, silicon oxide (Si)
O _x ), silicon nitride (Si _x N _y ), titanium oxide (Ti
O _X), an oxide such as zirconium oxide (ZrO _X), nitrides, or other of these multilayer films, it is possible to use a metal or the like having a 1200 ° C. or more melting point. These protective film materials have the property of withstanding the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C. and preventing the nitride semiconductor from growing or hardly growing on the surface thereof. To form a protective film material on a nitride semiconductor surface, for example, evaporation, sputtering,
A vapor deposition technique such as CVD can be used. Also,
In order to partially (selectively) form, a photomask having a predetermined shape is manufactured using a photolithography technique, and the material is vapor-phase-deposited through the photomask, whereby a predetermined shape is formed. Can be formed. The shape of the protective film is not particularly limited. For example, it can be formed in a dot, a stripe, a grid-like shape,
As will be described later, it is desirable to form a striped shape in a specific plane orientation. Further, it is preferable that the surface area of the protective film be larger than the surface area of the window portion because the nitride semiconductor grown thereon has less lattice defects.

The size of the protective film is not particularly limited. For example, when the protective film is formed in a stripe, the preferable stripe width is 0.5 to 100 μm, more preferably 1 to 50 μm.
It is desirable that the stripes be formed with a width of about m, and that the stripe pitch be smaller than the stripe width. In other words, making the surface area of the protective film larger than the window is
A nitride semiconductor layer with few crystal defects can be obtained.

Further, as a preferable mode for adjusting the surface area of the protective film and the window, it is preferable that the protective film is formed in a stripe shape and the width of the window is adjusted to 5 μm or less, more preferably, the width of the window (Ww). ) And the width (Ws) of the stripe-shaped first protective film, Ws / Ww, is adjusted so as to be 1 to 20. As described above, the width of the protective film and the window portion and Ws /
When the selective growth layer is grown by adjusting Ww, a nitride semiconductor with very few crystal defects and good crystallinity can be obtained.

The preferred value of the width of the window is 3 μm or less, more preferably 1 μm or less, and the lower limit is 0.1 μm.
1 μm or more. By adjusting the width of the window in this way,
A nitride semiconductor layer with less crystal defects can be obtained.

The width of the stripe-shaped protective film is within the above range, but particularly when the width of the window is 5 μm or less,
2 to 30 μm, preferably 5 to 20 μm,
More preferably, it is 5 to 15 μm. Within this range, a nitride semiconductor layer with few crystal defects can be obtained, which is preferable. The thickness of the stripe-shaped protective film is not particularly limited, but is, for example, 0.01 to 5 μm, and preferably 0.1 to 5 μm.
To 3 μm, and more preferably 0.1 to 2 μm. This range is preferable for obtaining the effect. Also,
Ratio Ws / Ww of width of window (Ww) and width of protective film (Ws)
Is 1 to 20, preferably 1 to 10. If it is 1 or less, crystal defects are likely to occur on the window and the protective film, and if it is 20 or more, the selective growth layer that grows on the protective film will not completely adhere and a cavity will be easily formed on the protective film.

As shown in FIG. 4, the selective growth layer grown through the protective film partially formed on the surface of the first nitride semiconductor starts growing from a window where no protective film is provided. When the thickness reaches a certain level, the nitride semiconductor 3 grows in a direction parallel to the plane, and the nitride semiconductor 3 grown from an adjacent window is connected to form a film. At this time, as shown in FIG. 6A, the crystal defects due to lattice mismatch with the substrate are likely to be influenced by the above-mentioned growth mode, and are bent and propagated mainly through the window through the window. Proliferates, but propagates in the thickness direction, but its density is greatly reduced. For this reason, when the selective growth layer has a certain thickness, almost no crystal defects reach the surface as shown in FIG. for that reason,
The surface of the selective growth layer grown with the film thickness in the range described above is:
Almost no crystal defects are observed. Further, due to the above-described growth of the selective growth layer in the plane direction, almost no crystal defects are formed even on the upper part of the protective film. Therefore, by growing a nitride semiconductor on the surface of the selective growth layer, an element having good crystallinity can be obtained.

FIG. 6 shows another embodiment of the selective growth layer.
(A) As shown in FIG.
(FIG. 6A), a protective film 12 is newly provided on the surface thereof, and a nitride semiconductor is further grown to provide a selective growth layer (FIG. 6B) in two stages. You can also. At this time, the protective film 12 formed on the surface of the first-stage selective growth layer 3 is replaced with the protective film 11 formed on the surface of the underlayer.
Is preferably formed so as to cover the upper part of the window provided by the method described above, since crystal defects extending from the window as shown in the figure can be prevented by the protective film 12 on the surface. This is to prevent the crystal defects from propagating and growing in the depth direction during device driving even if no crystal defects are formed at the time of growth, and the crystal defects from growing. For this reason, it is preferable that the protective film 12 formed on the surface of the first-stage selective growth layer 3 be formed wider than the window. Further, as still another embodiment, as shown in FIG. 5, irregularities are provided on the surface of the first nitride semiconductor on which the protective film is provided, for example, by etching or the like, and the exposed surfaces (surfaces of the convexes and concaves) are provided. Protective film 11 over almost the entire surface
', 11 are provided. By doing so, the nitride semiconductor is grown from the exposed end face, and the growth in the above-described plane direction is promoted, and as a result, crystal defects that propagate and amplify and extend from the underlying layer can be prevented, and A good selective growth layer can be formed. The selective growth layer of the present invention includes such an embodiment, and more specifically, a layer formed over many stages, a layer grown from the end face when the unevenness is provided, and a combination thereof. It was formed.

However, since this selective growth layer is formed in the growth mode as described above, as shown in FIG. 1, the upper part of the window (the area shown by oblique lines) and the upper part of the protective film (other than that) The crystallinity and orientation of the selective growth layer formed in the region (2) are different. This tendency is inherited by a nitride semiconductor grown in a normal growth mode without providing a protective film on the selective growth layer. Therefore, for example, in FIG. 2, the nitride semiconductor 6 on the selective growth layer 3 has the upper portion 3-a of the window portion and the upper portion 3 of the protective film.
-A, 6-a, 6 in-plane distribution of crystallinity inheriting the crystallinity of -b
-B. Further, the nitride semiconductor layers 7 grown thereon also have different in-plane crystallinity as 7-a and 7-b. For this reason, as shown in FIG. 2, while the crystallinity and orientation of the upper portion of the protective film are different from those of the upper portion of the window portion, the layers forming the element structure are stacked to form an element. That is, in the plane of the crystal, regions having different crystallinity and orientation are mixed, and the in-plane distribution is in a non-uniform state.

The reliability of the device obtained in this manner is improved by the improvement of the crystallinity due to the provision of the selective growth layer. Even if the reliability is improved by changing the composition or the like, there is a limit in a relatively close place. That is, although the crystallinity is improved by providing the selective growth layer, the reliability of the device obtained therefrom is limited. There was a tendency for the improvement in performance to reach a plateau.

It is an object of the present invention to prevent the adverse effects of providing such a selectively grown layer and obtain only the effect of improving the crystallinity. That is, as shown in FIG.
By providing the second buffer layer 4 containing a nitride semiconductor polycrystal on the selective growth layer, the above-mentioned non-uniformity of crystallinity is inherited by the nitride semiconductor grown on the selective growth layer. The effect of improving crystallinity is prevented by the layer grown thereon, thereby preventing the crystal growth. Therefore, only good crystallinity is inherited between the selective growth layer and the nitride semiconductor layer sandwiching the second buffer layer. In particular, in a light-emitting element, the crystallinity of a light-emitting layer such as an active layer greatly affects the light-emitting characteristics of the element. This has hindered improvement in device characteristics such as a decrease in threshold current density. In the present invention, since the above-described second buffer layer is interposed, the crystallinity of the light emitting layer is uniform in the plane, and the device characteristics are improved.

(Second Buffer Layer) After forming a selective growth layer via a protective film, a second buffer layer is formed as shown in FIG. A second buffer layer grown on the selective growth layer contains a polycrystalline nitride semiconductor;
Specifically, Al _x Ga _1-x grown at 200 to 900 ° C.
N (0 <x ≦ 1). This is because it is difficult to form a buffer layer at a temperature of 200 ° C. or lower, and a single crystal is formed at a temperature of 900 ° C. or higher. Preferably, when the temperature is in the range of 400 to 600 ° C., a buffer layer that works well can be formed, and the crystallinity of the third conductivity type layer to be grown next is improved. The second buffer layer is provided on the selective growth layer, but need not be formed in contact with the surface of the selective growth layer as shown in FIG. 3 and may be formed apart from the selective growth layer. . Preferably, by being provided in contact with the selective growth layer, it is possible to obtain only the effect of providing the above-mentioned second buffer layer, and particularly, to provide only a good crystallinity to the nitride semiconductor layer formed on the second buffer layer. , And a simple element structure contributes to an improvement in yield.

The composition of the second buffer layer is as follows:
Although not particularly limited, preferably, the composition or the mixed crystal ratio of the adjacent nitride semiconductor layer, the selective growth layer, or the third conductivity type layer is substantially the same, so that the crystallinity of the layer obtained by the growth is improved. There is a tendency. For example, when a second buffer layer made of GaN is formed on GaN doped with an n-type impurity as a selective growth layer, a third buffer layer formed is formed.
The crystallinity of the conductivity type layer is good, and the conductivity across the second buffer layer is also good. Making the composition and the mixed crystal ratio substantially the same means that the composition is made substantially the same regardless of the presence or absence of impurity addition.

Further, the film thickness is preferably 10 to 10
When the thickness is less than 10 °, the in-plane non-uniformity of the crystallinity is not completely solved, and the crystal may remain scattered in the plane. This is because good conductivity is hindered between the layers formed between the layers. More preferably, when the angle is 500 ° or less, good conductivity can be secured in driving the element.

Further, the nitride semiconductor layer provided between the selective growth layer and the second buffer layer may be a single layer or a multilayer film, and may be a layer having conductivity. Good, specifically, doped with p-type and n-type impurities. At this time, the composition of the nitride semiconductor is not particularly limited, but as a specific example, the nitride semiconductor was grown with Al _x Ga ₁ -xN (0 ≦ X ≦ 0.5) having an Al mixed crystal ratio X value of 0.5 or less. It is also preferable to use GaN having good crystallinity. As described above, the layer having conductivity is formed by the selective growth layer and the second layer.
By providing the second buffer layer between the first buffer layer and the second buffer layer, an element can be formed by utilizing the conductivity of the second buffer layer as described later.

(Third-Conductivity-Type Layer) In the present invention, the third-conductivity-type layer made of a nitride semiconductor layer provided in contact with the second buffer layer is not particularly limited and is determined by the layer structure of the element. This is a layer having properties. As described above, the third conductivity type layer and the lower layer located deeper than the second buffer layer ensure good conductivity, and further after the formation of the third conductivity type layer, that is, the third conductivity type. Since the crystallinity of a light-emitting layer such as an active layer grown on the layer becomes uniform in the plane, a light-emitting element having good element characteristics can be obtained.

In the present invention, the third conductivity type layer is made of AlGaN.
By having, the above-mentioned in-plane uniform crystallinity
The effect of the above is remarkable. At this time, the third conductivity type layer is
Al _xGa_1-xN (0 <x ≦ 1)
In particular, a layer that functions as a cladding layer to confine light
In order to achieve this, the film thickness must be at least 0.1 μm or more and A
1 is to increase the mixed crystal ratio. Specifically, the film thickness is thin
If there is not enough confinement, there is enough light confinement
It is preferable that the thickness be 0.3 μm or more.
You. Regarding the mixed crystal ratio of Al, the active layer (light emitting layer)
Is a guide layer between the active layer (light emitting layer) and the cladding layer
It is necessary to increase the difference between the refractive index and the like. concrete
Has a mixed crystal ratio x of 0.05 or more, more preferably 0.1
As described above, a sufficient refractive index difference is secured, and in addition,
Then, a sufficient function can be obtained in confining light.

Preferably, the selective growth layer is an n-type impurity-doped nitride semiconductor layer, and the third conductivity type layer is an n-type impurity-doped AlGaN layer. The problem that light is scattered to the n-side contact layer side in the device of the above can be solved.

The remarkable effect that can be achieved when the third conductivity type layer is AlGaN is that the light emitting element has a low-temperature buffer layer provided on a selective growth layer made of a nitride semiconductor, and a subsequent AlGaN layer is provided. It has good crystallinity and can be stacked thickly.

Conventionally, for example, Al having a mixed crystal ratio of 0.05 to 0.3 is replaced with Al having a thickness of 0.1 μm or more and less than 1 μm.
AlGaN, non-doped Ga
A desired film thickness was formed by alternately stacking tens of N each. This means that the layer containing Al is, for example, 0.1%.
This is because cracks often occur when the layer is grown even with a thickness of μm, and it is extremely difficult to grow the layer to a thickness larger than that. In the present invention, by growing via the second buffer layer, even if the film is grown to a thickness of, for example, 0.5 μm or more, cracks are not formed in the crystal, and the crystal is formed with good crystallinity. That is, in the present invention, the AlGaN layer in the element structure can be easily grown within the above-described thickness and mixed crystal ratio ranges, the degree of freedom in the layer configuration is dramatically improved, and the conventional AlGaN layer is formed. Since a complicated process for growing the crystal with good crystallinity can be omitted, the yield is improved.

It is not clear whether AlGaN having a relatively free mixed crystal ratio and thickness can be grown in this way. However, in addition to the above-described in-plane uniformity of crystallinity, the second buffer layer is different from a conventional buffer layer that alleviates lattice mismatch with a substrate, and has a nitride semiconductor in which strain or the like is inherent in the crystal. It is considered that the function of breaking the crystallographic orientation relationship of the GaN works. That is, a nitride semiconductor grown on a heterogeneous substrate having a different lattice constant is in a state in which a certain stress is applied to its crystal, and the nitride semiconductor grown thereon has different shapes and crystals depending on the composition. Grow with sex. Specifically, when growing a nitride semiconductor containing no Al, it is possible to form a film with a desired thickness in order to grow while maintaining a similar state. However, in AlGaN, this is called crack generation. Difficult to grow in shape. As described above, growing AlGaN (third conductivity type layer) on the nitride semiconductor via the second buffer layer of the present invention requires that the crystallographic relationship be broken to the extent that cracks are not generated. Seems to be that. However, on the other hand, by growing AlGaN, a part of the second buffer layer is crystallized, so that it seems that a certain degree of crystallographic relationship is maintained.

Accordingly, the selective growth layer and the third conductivity type formed with the second buffer layer interposed therebetween change the crystallographic relationship in the growth of the third conductivity type layer accompanied by cracks, On the other hand, as a light emitting element, the conductivity of both is maintained. Therefore, a light emitting layer such as an active layer to be further grown thereon also has good crystallinity, and sufficient light confinement is realized, so that a threshold current density is lowered and a laser device having high device reliability is obtained.

In the present invention, the impurities to be doped into each layer include p-type and n-type impurities. Specifically, the n-type impurities include, for example, Ge, S, Se and the like in addition to Si. Mg, Zn, Cd, C
a, Be, C and the like. By using a nitride semiconductor doped with these impurities for each layer, light-emitting elements having various element structures can be formed. For example, a first nitride semiconductor layer made of undoped GaN, a selective growth layer made of GaN doped with an n-type impurity, a second buffer layer made of undoped GaN, and an n-type impurity doped thereon. A structure in which a third conductivity type layer made of AlGaN is stacked. At this time, the n-type impurity is preferably Si and the p-type impurity is preferably Mg as an impurity to be doped into the nitride semiconductor, thereby exhibiting good n and p-type characteristics. Thus, the first nitride semiconductor layer, the selective growth layer, the second buffer layer, the third conductivity type layer,
Further, the impurity can be relatively freely added to the nitride semiconductor layer formed between the second buffer layer and the selective growth layer, and p and n-type impurities can be doped.

In the light emitting device of the present invention, the light emitting layer formed on the second buffer layer or the third conductivity type layer is
There is no particular limitation, and examples thereof include those made of a nitride semiconductor. Preferably, good light emission can be obtained as long as the layer is made of a nitride semiconductor layer containing In. Here, as described above, the nitride semiconductor layer containing In has better crystallinity than the conventional one having only the selective growth layer by adopting the configuration of the present invention.

The nitride semiconductor light-emitting device of the present invention has a structure in which after forming a selectively grown layer or after laminating each layer constituting an element structure, a heterogeneous substrate or the like is removed and an electrode is provided on the surface obtained by the removal. Is also good. At this time, the layer to be removed for providing the electrode on the back surface is not particularly limited, and has a depth that exposes a layer having good contact properties and becomes unnecessary together with the substrate, for example, a first nitride semiconductor. The electrode may be provided by removing the layer, the selective growth layer, or the like, or forming a layer in consideration of ohmic properties with the electrode on the surface after the removal.

[0041]

[Example 1] A sapphire substrate having a 2-inch φ and a C-plane as a main surface was prepared, and an MO was placed on the sapphire substrate.
A laser device made of a nitride semiconductor shown in FIG. 7 is manufactured by using the VPE method.

The sapphire substrate 1 was set in a reaction vessel, the temperature was set at 510 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) were used as source gases, and a buffer layer made of GaN was formed on the sapphire substrate 1. Is grown to a thickness of 200 °. After growing the buffer layer, T
Stopping only MG, raising the temperature to 1050 ° C.
When the temperature reaches 50 ° C., an undoped GaN layer 2 is grown to a thickness of 5 μm as a first nitride semiconductor layer using TMG, ammonia, and silane gas as source gases. A stripe-shaped photomask is formed on the surface of the GaN layer (first nitride semiconductor layer) 2 of the wafer in which the buffer layer and the GaN layer 2 are stacked, and the stripe width 1 is formed by a CVD apparatus.
A protective film 11 made of SiO ₂ having a thickness of 0 μm and a window portion of 8 μm is formed to a thickness of 0.1 μm (FIG. 4A). The stripe direction of the protective film 11 is a direction perpendicular to the sapphire A plane.

After the formation of the protective film 11, the wafer is transferred to a reaction vessel, and at 1050 ° C., a nitride semiconductor layer made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} Si using TMG and ammonia as source gases (selection). The growth layer) is grown to a thickness of 100 μm (FIG. 3).

(Second buffer layer 104)
3C, a second buffer layer made of undoped GaN is grown to a thickness of 200 ° on the surface of the selective growth layer 3 made of Si-doped GaN as shown in FIG.

(Third conductivity type layer; n-side cladding layer 105)
The selective growth layer 103 and the second buffer layer 104 shown in FIG.
Is formed, the temperature is raised to 1050 ° C., and n-type Al _0.2 G doped with 5 × 10 ¹⁸ / cm ³ of Si is used as the third conductivity type layer.
An n-side cladding layer made of a _0.8 N was grown to a thickness of 0.4 μm.

The wafer thus obtained was taken out of the reaction vessel, and the surface of the third conductivity type layer was observed under a microscope. As a result, no crack was generated and the mirror surface was uniform.

(N-side light guide layer 106) Following the third conductivity type layer, n-type GaN doped with 5 × 10 ¹⁸ / cm ^{3 of} Si
The n-side light guide layer 106 is grown to a thickness of 0.1 μm. The n-side light guide layer 106 functions as a light guide layer of an active layer, and is preferably used for growing GaN or InGaN, and is preferably formed to a thickness of usually 100 to 5 μm, more preferably 200 to 1 μm. The n-side light guide layer 106 is usually doped with an n-type impurity such as Si or Ge to have an n-type conductivity, but may be undoped. When a superlattice is used, at least one of the first layer and the second layer may be doped with an n-type impurity or may be undoped.

(Active Layer 107) Next, at 800 ° C., a well layer made of undoped In _0.2 Ga _0.8 N, 25 °
Barrier layer made of undoped In _0.01 Ga _0.99 N, 50 °
Are alternately stacked to grow an active layer 107 having a multiple quantum well structure (MQW) with a total film thickness of 175 °.

(P-side cap layer 108) Next, 1050
The band gap energy at p.
A p-side cap layer 108 of p-type Al _0.3 Ga _0.7 N doped with Mg at 1 × 10 ²⁰ / cm ³ , which is larger than the active layer 107, is grown to a thickness of 300 °. The p-side cap layer 7 is a layer doped with a p-type impurity. However, since the film thickness is small, it may be an i-type in which an n-type impurity is doped to compensate for carriers or an undoped type, and most preferably a p-type impurity. It is a layer doped with impurities. The thickness of the p-side cap layer 108 is 0.1 μm or less, more preferably 500 ° or less, and most preferably 300 ° or less.
Adjust to the following. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are easily formed in the p-type cap layer 108, and it is difficult to grow a nitride semiconductor layer having good crystallinity. When the AlGaN having a larger Al mixed crystal ratio is formed to be thinner, the LD element easily oscillates. For example, if the Y value is 0.2
In the case of the above Al _Y Ga ₁ -YN, it is desirable to adjust the angle to 500 ° or less. The lower limit of the thickness of the p-side cap layer 108 is not particularly limited, but is preferably formed to a thickness of 10 ° or more.

(P-side light guide layer 109) Next, the band gap energy is smaller than the p-side cap layer 108.
A p-side light guide layer 109 made of p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. This layer functions as a light guide layer of the active layer, and is preferably made of GaN or InGaN like the n-side light guide layer 106. This layer is also a p-side cladding layer 9
Also acts as a buffer layer when growing
By growing the layer to a thickness of 5 to 5 μm, more preferably 200 to 1 μm, it functions as a preferable light guide layer. This p-side light guide layer is usually doped with a p-type impurity such as Mg to have a p-type conductivity type, but it is not particularly necessary to dope the impurity. Note that the p-side light guide layer may be a superlattice layer. When a superlattice layer is formed, at least one of the first layer and the second layer may be doped with a p-type impurity or may be undoped.

(P-side cladding layer 110)
A first layer of p-type Al _0.2 Ga _0.8 N doped with × 10 ²⁰ / cm ^{3, 20} °, and a second layer of p-type GaN doped with Mg of 1 × 10 ¹⁹ / cm ³ , 20 ° alternately Then, a p-side cladding layer 110 composed of a superlattice layer having a total film thickness of 0.4 μm is grown. This layer acts as a carrier confinement layer similarly to the n-side cladding layer 105, and acts as a layer for lowering the resistivity on the p-type layer side by forming a superlattice structure. The thickness of the p-side cladding layer 110 is not particularly limited either, but is not less than 100 ° and not more than 2 μm.
More preferably, it is desirable to grow at a temperature of 500 ° or more and 1 μm or less. In particular, when a nitride semiconductor layer having a superlattice structure is used as a cladding layer, providing a superlattice layer on the p-layer side is more effective in reducing the threshold current. Further, when a p-type impurity is modulated and doped as in the case of the n-side cladding layer 105, the threshold value tends to decrease.

The superlattice layer is preferably at least on the p-side layer, and the presence of the superlattice layer on the p-side layer is preferable because the threshold value is further reduced.

In the case of a double hetero structure nitride semiconductor device having an active layer having a quantum well layer, Al having a thickness of 0.1 μm or less having a band gap energy larger than that of the active layer is in contact with the active layer. A p-side light guide layer having a smaller gap energy than the cap layer is provided at a position farther from the active layer than the cap layer, and a more active layer than the p-side light guide layer. It is very preferable to provide a p-side cladding layer made of a superlattice layer containing a nitride semiconductor containing Al having a band gap larger than that of the p-side light guide layer at a position away from the layer. In addition, since the band gap energy of the p-side cap layer is increased, electrons injected from the n-layer are blocked by this cap layer, and the electrons do not overflow the active layer, so that the leak current of the element is reduced. .

(P-side contact layer 111) Finally, Mg
Is grown to a thickness of 150 ° from p-type GaN doped with 2 × 10 ²⁰ / cm ³ . p
The side contact layer is 500 ° or less, more preferably 40 ° or less.
Adjusting the film thickness to 0 ° or less and 20 ° or more reduces the p-layer resistance, which is advantageous in lowering the threshold voltage.

After the reaction is completed, the wafer is annealed in a nitrogen atmosphere at 700 ° C.
Further lowering the resistance of the layer. After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 1, the uppermost p-side contact layer 111 and the p-side cladding layer 110 are etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm. I do. At this time, the ridge is formed such that the resonator direction of the obtained device is parallel to the step direction on the surface of the first nitride semiconductor (n-side contact layer 103).

After the formation of the ridge, as shown in FIG. 1, the p-side cladding layer 110 exposed on both sides of the ridge stripe is etched around the ridge stripe to form n
The surface of the n-side contact layer 103 where the electrode 115 is to be formed is exposed.

Next, a p-electrode 114 made of Ni / Au is formed on the entire surface of the ridge surface. Next, as shown in FIG.
An insulating film 113 made of SiO ₂ is formed on the surfaces of the p-side cladding layer 110 and the p-side contact layer 111 excluding the electrode 114, and the p-pad electrode 112 electrically connected to the p-electrode 114 via the insulating film 113 is formed. Form. On the other hand, on the surface of the n-side contact layer 103 exposed earlier, W and Al
An n-electrode 115 is formed.

After the electrodes are formed, the back surface of the sapphire substrate of the wafer is polished to a thickness of about 50 μm, and then the wafer is cleaved at the M-plane of sapphire to produce a bar having the cleaved surface as a resonance surface. On the other hand, a chip is separated by scribing a bar at a position parallel to the stripe-shaped electrodes to produce a laser element. FIG. 1 shows the shape of the laser element. When this laser element was oscillated at room temperature, the threshold current density was excellent, the yield of the element was improved as compared with the conventional laser element, and the life of the element was greatly improved.

[Example 2] As the second buffer layer, A
A nitride semiconductor laser device was obtained in the same manner as in Example 1, except that l _0.2 Ga _0.8 N was grown to a thickness of 200 °. In the obtained laser device, good oscillation was confirmed as in Example 1, and the threshold current and device life were also good in the same manner. The surface of the obtained n-side cladding layer is as good as in Example 1.

[Embodiment 3] The third conductivity type in the embodiment 1
As an n-side cladding layer, Si is 5 × 10 ¹⁸/cm
^ThreeDoped n-type Al_0.5Ga_0.7N is 0.5 μm thickness
And the surface was observed.
Was something. Same as Example 1 on this n-side cladding layer
Thus, a laser element was manufactured by laminating each layer. Get
The laser device obtained has the threshold current and the device
Good lifetime and high Al mixed crystal ratio
The light confinement efficiency increases, and the n-side contact layer
Due to the reduction of light leakage from
The pattern was good.

Example 4 After forming a protective film on the surface of the first nitride semiconductor layer in the same manner as in Example 1, undoped GaN was grown to a thickness of 50 μm, and the surface was wrapped to a mirror-like shape to protect it. As in the formation of the film 11, FIG.
(A) As shown in FIG.
A protective film 12 made of m ₃ Si ₃ N ₄ is formed with a thickness of 0.1 μm. After the formation of the protective film 12, the wafer was returned to the reaction vessel, and as shown in FIG. 6B, a selective growth layer 3 'made of undoped GaN was grown to a thickness of 50 μm. After forming the selective growth layer 3 ′, a nitride semiconductor layer made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} Si is grown to a thickness of 15 μm. After the second buffer layer is formed with a thickness of 200 °, the third conductivity type layers to p
The side contact layer was laminated, and each electrode was provided to obtain a laser device. The device life of the obtained laser device was improved as compared with that of Example 1, and when the crystal defects were observed after driving for 1000 hours, the second-stage selective growth layer 3 'shown in FIG. Crystal defects extending to
In addition, generation of a crystal result due to in-plane non-uniformity of crystallinity observed in a conventional light-emitting element was not observed.

[0062] In Example 5 Example 4, a GaN which is selectively grown layer 3 'was 1 × 10 ¹⁸ / cm ³ doped with Si, is grown directly second buffer layer over the selectively grown layers Except for this, a laser device was obtained in the same manner as in Example 4. The obtained laser device had device characteristics similar to those of Example 4. However, the crystallinity of AlGaN as the third conductivity type layer was slightly inferior to that of Example 4, but was different from that of the conventional device. There was no occurrence of cracks that greatly affected the growth and device characteristics.

[Comparative Example 1] Undoped GaN (first nitride
1 × 10 Si directly on the nitride semiconductor layer)¹⁸/cm ^ThreeDo
N-side contact layer with a thickness of 100 μm
After the growth, 5 × 10¹⁸
/cm^ThreeDoped n-type Al_0.2Ga_0.8N is 0.4 μm
It was grown to a film thickness. After forming the n-side cladding layer,
Observation of the entire surface reveals cracks and step breaks on the surface.
There were many occurrences and many cracks. Furthermore,
After the formation of the n-side cladding layer, the n-side
Light guide layer, active layer, p-side cap layer, p-side light guide
Layer, p-side cladding layer, p-side contact layer,
Then, a laser device was manufactured. About the obtained laser element
Most do not oscillate.
Occurred, and the device reliability was low.

[0064]

The nitride semiconductor light-emitting device of the present invention has a selective growth layer in the device structure or cannot be removed by a device using the same, and the nitride semiconductor light-emitting device in a plane which is a factor of deteriorating the crystallinity. Since the problem of non-uniform crystallinity has been solved, device characteristics such as device reliability have been improved. Further, since the problem has been solved, it is possible to easily form an AlGaN layer which has been conventionally difficult to grow,
An element provided with a thick film layer can be obtained without impairing crystallinity even if the mixed crystal ratio increases. As a result, for example, in the case of a laser element, the light is well confined in the waveguide, the threshold value is lowered, and the crystallinity is good, so that the reliability of the element is also high.

Further, as compared with the conventional method in which several tens of AlGaN and another layer are alternately stacked, the manufacturing is simplified, and the yield is greatly improved. The utility value is high.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a crystal morphology of a selective growth layer according to the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a mode of crystal growth via a selective growth layer in the present invention.

FIG. 3 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating one growth mode of a selective growth layer according to the present invention.

FIG. 5 is a schematic cross-sectional view illustrating one growth mode of a selective growth layer according to the present invention.

FIG. 6 is a schematic cross-sectional view illustrating one growth mode of a selective growth layer according to the present invention.

FIG. 7 is a schematic sectional view illustrating the structure of a nitride semiconductor laser device according to one embodiment of the present invention.

[Explanation of symbols]

 101 ... heterogeneous substrate 103 ... selective growth layer (n-side contact layer) 104 ... second buffer layer 105 ... third conductivity type layer (n-side cladding layer) 106 ... .. N-side light guide layer 107... Active layer 108... Cap layer 109... P-side light guide layer 110... P-side cladding layer 111. ... P pad electrode 113... Insulating film 114... P electrode 115... N electrode

Claims (3)

[Claims] 1. A light emitting device comprising a nitride semiconductor layer including a light emitting layer laminated on a heterogeneous substrate, wherein the first nitride grown on the heterogeneous substrate is between the heterogeneous substrate and the light emitting layer. A semiconductor layer, a protection film partially formed on the surface of the first nitride semiconductor layer, a selective growth layer grown on the surface of the first nitride semiconductor layer via the protection film, and And a second buffer layer containing polycrystal in order. 2. A semiconductor device according to claim 1, further comprising a third conductivity type layer in contact with said second buffer layer, wherein said third conductivity type layer is formed of Al _x Ga ₁ -xN (0
2. The nitride semiconductor light emitting device according to claim 1, wherein <x ≦ 1). 3. The nitride semiconductor light emitting device according to claim 2, wherein said third conductivity type layer has a thickness of 0.3 μm or more and said mixed crystal ratio x is 0.05 or more.