JP2001237492A - Semiconductor laser element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element and as manufacturing method thereof, where a resonator end surface of high flatness is provided for improved characteristics and reliability. SOLUTION: Related to a semiconductor laser element 100, layers 2-10 are sequentially formed on a sapphire substrate 1. The orientation of the resonator length of the semiconductor laser element 100 is <01-10>. On the end surfaces in <01-10> orientation of the layers 4-10, a GaN end surface regrowth layer 13, which comprises an undoped GaN with a surface (01-10) is formed. The surface (01-10) of the GaN end surface regrowth layer 13 constitutes the end surface of resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device and a method for manufacturing the same.

[0002]

2. Description of the Related Art GaN, InGaN, AlGaN, Al
A semiconductor laser device using a group III nitride semiconductor such as GaInN (hereinafter, referred to as a nitride semiconductor) is expected to be applied as a semiconductor laser device that emits light in a visible to ultraviolet region.

For example, when a GaN-based semiconductor laser device is manufactured, there is no GaN substrate.
GaN is formed on an insulating substrate such as sapphire (Al ₂ O ₃ ) having a different lattice constant from that of N by metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).
A system semiconductor layer is grown.

[0004]

In a conventional GaAs-based semiconductor laser device that emits infrared light or red light, the plane orientation of the substrate and the semiconductor layer on the substrate match. Therefore, the semiconductor layer can be cleaved together with the substrate on the surface where the substrate is easily cleaved. Therefore, it is possible to easily form a smooth resonator end face by cleavage.

On the other hand, also in the GaN-based semiconductor laser device, the surface which is easily cleaved coincides between the sapphire substrate and the GaN-based semiconductor layer. However, since the sapphire substrate and the GaN-based semiconductor layer have different lattice constants as described above, the plane orientations of the two are shifted by 30 °. For this reason, if the semiconductor layer is cleaved together with the substrate on a surface where the substrate is easily cleaved, the cleaved surface does not become a smooth surface, but becomes a rough surface with many irregularities. As described above, in the GaN-based semiconductor laser device, characteristics as a cavity end face cannot be obtained by cleavage of a sufficient end face. Further, when the resonator end face is formed by cleavage, an end face perpendicular to the direction of the resonator length cannot be obtained.

On the other hand, besides the method of forming the resonator end face by cleavage, there is a method of forming the resonator end face by dicing or etching. When the cavity facet of the GaN-based semiconductor laser device is formed by such a method, a smooth cavity facet can be obtained as compared with the case where the cavity facet is formed by cleavage.

However, when forming the cavity end face of the GaN-based semiconductor laser device by dicing, irregularities are formed on the end face by the blade of the blade. For this reason, it is difficult to form a smooth end face enough to obtain sufficient characteristics as a resonator end face.

According to the method of forming a resonator end face by etching utilizing a chemical reaction, a smoother resonator end face can be obtained as compared with the above-described cleavage and dicing methods.
However, when the resonator end face is formed by etching, it is difficult to obtain a resonator end face perpendicular to the direction of the resonator length.

As described above, in the GaN-based semiconductor laser device, it is necessary to produce a cavity end face that is sufficiently flat so that sufficient characteristics can be obtained as a cavity end face and is perpendicular to the direction of the cavity length. Is difficult. For this reason, in the manufactured GaN-based semiconductor laser device, the characteristics are degraded and the reliability is lowered.

An object of the present invention is to provide a semiconductor laser device having a cavity end face having good flatness and improved characteristics and reliability, and a method of manufacturing the same.

[0011]

According to the semiconductor laser device of the present invention, a first nitride-based semiconductor layer having an end face and including a light emitting layer is formed on a substrate. A second nitride-based semiconductor layer is formed on an end face of the nitride-based semiconductor layer described above, and the surface of the second nitride-based semiconductor layer forms a resonator end face.

In the semiconductor laser device according to the present invention, the surface of the second nitride-based semiconductor layer crystal-grown on the end face of the first nitride-based semiconductor layer constitutes the cavity end face. The end face of the resonator obtained by such crystal growth is smooth. Further, the second nitride-based semiconductor layer can be crystal-grown such that the surface is perpendicular to the direction of the cavity length of the semiconductor laser device. Therefore, a resonator end face perpendicular to the direction of the resonator length is formed.

Therefore, in the above-described semiconductor laser device having such a cavity end face, the device characteristics and reliability are improved.

The surface of the second nitride-based semiconductor layer is preferably perpendicular to the direction of the cavity length. in this case,
The cavity facet of the semiconductor laser device is perpendicular to the cavity length direction. As a result, efficient laser oscillation becomes possible, and the device characteristics of the semiconductor laser device are further improved.

[0015] The first and second nitride-based semiconductor layers may contain at least one of aluminum, gallium, indium, boron and thallium. Also, in this case,
The end face of the resonator is preferably perpendicular to the <01-10> direction of the first nitride semiconductor layer, and the surface of the second nitride semiconductor layer is preferably the (01-10) plane.

In this case, the direction of the cavity length of the semiconductor laser element is the <01-10> direction. Therefore, by making the surface of the second nitride-based semiconductor layer a (01-10) plane, the end face of the resonator becomes perpendicular to the direction of the resonator length.

According to the method of manufacturing a semiconductor laser device of the present invention, a step of forming a first semiconductor layer including a light emitting layer on a substrate; a step of forming a waveguide in the first semiconductor layer;
Forming a stripe-shaped groove extending in a direction perpendicular to the direction of the waveguide in a predetermined region of the semiconductor layer, and exposing an end face of the first semiconductor layer including the light-emitting layer in the groove; The method includes a step of forming a second semiconductor layer on an exposed end face of the first semiconductor layer, and a step of separating the first semiconductor layer together with the substrate along the groove.

In the method of manufacturing a semiconductor laser device according to the present invention, a second semiconductor layer is crystal-grown on an end face of the first semiconductor layer exposed in the groove, and the surface of the second semiconductor layer is made to have a cavity. End face. Since the surface of the crystal-grown second semiconductor layer is smooth, according to such a method of manufacturing a semiconductor laser device, a smooth cavity facet can be easily formed.

In this case, since the groove is formed in a direction perpendicular to the direction of the waveguide, the end face of the first semiconductor layer exposed in the groove is perpendicular to the direction of the waveguide. . For this reason, the second semiconductor layer formed on the end face of the first semiconductor layer is formed.
The surface of the semiconductor layer is perpendicular to the direction of the waveguide.
Therefore, a resonator end face perpendicular to the direction of the waveguide can be formed.

As described above, according to the above-described method for manufacturing a semiconductor laser device, a cavity end face that is smooth and perpendicular to the direction of the waveguide (the direction of the cavity length) can be formed. In the manufactured semiconductor laser device, the device characteristics and the reliability are improved.

The step of forming the second semiconductor layer includes the step of forming an insulating film on the surface of the first semiconductor layer excluding the end face of the first semiconductor layer exposed in the groove, and the step of excluding the region of the insulating film. Selectively growing a second semiconductor layer on an end face of the first semiconductor layer exposed in the groove.

In this case, since the second semiconductor layer does not grow in the region where the insulating film is formed, it is easy to select the region where the insulating film is not formed, that is, the end face of the first semiconductor layer exposed in the groove. It is possible to grow the second semiconductor layer effectively.

The first and second semiconductor layers are made of a group III nitride-based semiconductor, and the waveguide is formed by the <01-1> of the first semiconductor layer.
0> direction and the surface is (01-1)
It is preferable to form the second semiconductor layer so as to have the 0) plane. In this case, the surface of the second semiconductor layer is perpendicular to the waveguide. Therefore, a cavity end face perpendicular to the waveguide is obtained.

The surface of the second semiconductor layer may be set to the (01-10) plane by adjusting the supply amount of the group III raw material supplied at the time of forming the second semiconductor layer. In this case, the supply rate of the group III raw material is adjusted to adjust the growth rate of the second semiconductor layer. Thereby, the surface of the second semiconductor layer is set to (01-1)
0) plane.

[0025]

1 to 6 are schematic process diagrams showing a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

First, as shown in FIG. 1, the CV of the sapphire substrate 1 is formed by MOVPE (metal organic chemical vapor deposition).
AlGaN buffer layer 2, undoped GaN layer 3, undoped GaN layer 4, n-GaN contact layer 5, n-AlGaInN crack prevention layer 6, n
An AlGaN second cladding layer 7a, an n-GaN first cladding layer 7b, an MQW (multiple quantum well) light emitting layer 8 made of GaInN, a p-GaN first cladding layer 9a, pA
The 1GaN second cladding layer 9b and the p-GaN contact layer 10 are sequentially grown. The growth conditions for each of the layers 2 to 10 are as shown in Table 1.

[0027]

[Table 1]

In the source gases shown in Table 1, trimethyl aluminum (TMAl) is an aluminum source,
Trimethylgallium (TMGa) is a gallium source,
Trimethylindium (TMIn) is an indium source, and ammonia (NH ₃ ) is a nitrogen source. Silane gas (SiH ₄ ) is an n-type dopant gas, and cyclopentadienyl magnesium (Cp ₂ Mg) is a p-type dopant gas. In this case, Si is used as the n-type dopant, and Mg is used as the p-type dopant.
Is used.

The details of the growth of each of the layers 2 to 10 will be described below. After the AlGaN buffer layer 2 and the undoped GaN layer 3 are sequentially grown on the sapphire substrate 1, the wafer is once taken out of the reaction tube of the crystal growth apparatus. Then, an oxide film mask 2 having a plurality of stripe-shaped openings is formed by using a deposition technique such as an EB (electron beam) deposition method or a sputter deposition method and a photolithography technique.
0 is formed on the undoped GaN layer 3 as a selective growth mask. Then, the undoped GaN layer 3 is exposed in the opening of the oxide film mask 20.

In this embodiment, the oxide film mask 20 is made of SiO.
Consists of _two membranes. The width of the oxide film portion of the oxide film mask 20 is 1
And the width of the opening is 1 to 10 μm.
The stripe-shaped openings are formed such that the longitudinal direction is parallel to the <01-10> direction of GaN.

The GaN-based semiconductor is hexagonal,
[10-10] direction, [01-10] direction, [-1100] direction, [-1010] direction, [0-110] direction, and [1-1]
00] direction is an equivalent plane orientation. Here, these equivalent plane orientations are represented by the general notation <01-10>.

After the oxide film mask 20 is formed as described above, the wafer is returned to the reaction tube again and the undoped GaN
Grow layer 4. In this case, the undoped GaN layer 4 is selectively grown in the lateral direction (ELOG; Epitaxial Lateral Over G).
rowth).

That is, since GaN hardly grows on the oxide mask 20, the undoped GaN layer 4 does not grow on the oxide mask 20 in the initial stage of growth, and the undoped GaN layer exposed in the opening of the oxide mask 20. 3
Grow selectively on top. In this case, the undoped GaN layer 4 grows while forming a facet structure. As the growth proceeds, the undoped GaN layer 4 also grows in the lateral direction. Thereby, undoped G is also formed on oxide film mask 20.
An aN layer 4 is formed.

Here, with the lateral growth of the undoped GaN layer 4, a large number of threading dislocations propagated from the undoped GaN layer 3 are bent in a direction horizontal to the surface (C plane) of the sapphire substrate 1, that is, in a lateral direction. . Therefore, in GaN grown on the undoped GaN layer 3 exposed in the opening of the oxide film mask 20, threading dislocations propagating in the vertical direction can be reduced.

The thickness of the undoped GaN layer 4 required for all threading dislocations to bend in the horizontal direction is about the same as the width of the opening of the oxide film mask 20. Therefore, in this example, the undoped GaN layer 4 is grown to a thickness of about 1 to 10 μm, and all threading dislocations are bent in the lateral direction. Further, the growth of the undoped GaN layer 4 is continued until the facet structure is embedded and the surface is flattened.

As described above, in the undoped GaN layer 4 in the region on the undoped GaN layer 3, threading dislocations are bent in the horizontal direction, so that the dislocation density is reduced. In the undoped GaN layer 4 in the region on the oxide film mask 20,
Since threading dislocations propagated from the undoped GaN layer 3 are stopped at the oxide film mask 20, the dislocation density is reduced. Therefore, good crystallinity is realized in the undoped GaN layer 4.

On the flat undoped GaN layer 4 having a low dislocation density formed as described above, a semiconductor laser device structure is manufactured as follows.

When fabricating a semiconductor laser device structure, first, an n-GaN contact layer 5, an n-AlGaInN crack preventing layer 6, an n-GaN
-AlGaN second cladding layer 7a and n-GaN first cladding layer 7a
The cladding layer 7b is grown in order. Furthermore, n-GaN
On the first cladding layer 7b, five undoped GaN barrier layers and four undoped InGaN well layers with compressive strain are alternately grown to form an MQW light emitting layer 8 having a multiple quantum well (MQW) structure. Further, a p-GaN first cladding layer 9a, a p-AlGaN second cladding layer 9b, and a p-GaN contact layer 10 are sequentially grown on the MQW light emitting layer 8.

Subsequently, as shown in FIG. 2, a Ni mask (not shown) is formed on a predetermined region of the p-GaN contact layer 10 by using the EB vapor deposition method and the photolithography technique. By etching using this Ni mask, p-
GaN contact layer 10 to n-GaN contact layer 5
Is removed to expose an n-side electrode formation region of the n-GaN contact layer 5. Thereby, each layer 5
A mesa structure composed of 10 is formed. In this manner, a waveguide structure for confining light is manufactured, and a light waveguide is formed.

In this case, a mesa structure is formed so that the waveguide coincides with the <01-10> direction of the nitride semiconductor. The etching is performed by reactive ion etching (RIE) using, for example, CF ₄ as an etching gas.

A Ti film and an Al film are sequentially deposited on the exposed n-side electrode formation region of the n-GaN contact layer 5,
The side electrode 11 is formed. Further, a Ni film and an Au film are sequentially deposited on a predetermined region of the p-GaN contact layer 10,
The p-side electrode 12 is formed.

FIG. 3 shows a view of the wafer as viewed from the <11-20> direction. Next, a Ni mask (not shown) is formed in a predetermined region on the surface of the wafer by using the EB evaporation method and the photolithography technique. Here, on the surface of the wafer, a Ni mask is formed in a region excluding a band-like region having a constant width and a constant period along a direction perpendicular to the longitudinal direction of the opening of the oxide film mask 20.

Further, as shown in FIG. 4, using the above-mentioned Ni mask, the p-GaN contact layer 10 to the undoped GaN layer 4 and the n-GaN contact layer 5 in the strip region where the Ni mask is not formed are used. To undoped GaN layer 4 are etched. In this way,
Stripe-shaped grooves 15 having a width W of, for example, 20 μm are formed at a period of the resonator length, and the end faces of the layers 4 to 10 are exposed in the grooves 15.

In this case, the stripe-shaped grooves 15 are oriented in a direction perpendicular to the waveguide, that is, in the case of <1
1-20> direction.

In the GaN-based semiconductor, [11]
-20] direction, [-2110] direction, [-12-10] direction,
[-1-120] direction, [2-1-10] direction and [1-21] direction
0] direction is an equivalent plane orientation. Here, these equivalent plane orientations are represented by the general notation <11-20>.

The depth d of the groove 15 is set to be equal to or greater than that the waveguide is completely exposed at the end face in the groove 15. In this example, the depth d of the groove 15 is set so that the undoped GaN layer 4 is exposed at the end face in the groove 15.

After forming the stripe-shaped groove 15, the groove 1
An oxide film mask 30 is formed as a selective growth mask on the surface of the wafer excluding the end faces of the layers 4 to 10 exposed in the area 5 by using the EB evaporation method and the photolithography technique. In this example, the oxide film mask 30 is made of a SiO ₂ film and has a thickness of, for example, 2000 °.

FIG. 5 is a schematic partial sectional view in the <01-10> direction when the oxide film mask 30 is formed on the wafer as described above. As shown in FIG.
An oxide film mask 30 is formed on the N-contact layer 10, on the p-side electrode 12, and on the undoped GaN layer 4 exposed at the bottom of the groove 15.

Subsequently, as shown in FIG. 6, undoped GaN is selectively re-used by MOVPE in regions where the oxide film mask 30 is not formed, that is, in the end faces of the layers 4 to 10 exposed in the trenches 15. Let it grow. As a result, a GaN end face regrowth layer 13 having a thickness of several hundred Å, for example, 500 に is formed on the end faces of the layers 4 to 10 exposed in the groove 15.

In this embodiment, the surface of the GaN facet regrowth layer 13 constitutes the resonator facet of the semiconductor laser device. Thus, a striped resonator extending in the <01-10> direction is formed.

Here, when the GaN end face regrowth layer 13 is grown, the ratio of Ga to N is adjusted by adjusting the supply amount of Ga so that the growth rate of GaN becomes 2000 to 6000 ° / hour, for example, 4000 ° / hour. To a high state. In such a state, the growth rate of the GaN (01-10) plane is the lowest, and the growth of the other planes is promoted. Thereby, the GaN end face regrowth layer 13 having the (01-10) plane as the surface can be formed.

Since the GaN end face regrowth layer 13 formed as described above is formed by regrowth of undoped GaN, the surface is smooth. GaN end face regrowth layer 1
The surface roughness of No. 3 is at most 2 nm or less, and is expected to be about 2 to 3 atomic layers.

In the GaN end face regrowth layer 13, the surface can be easily changed to the (01-10) plane by adjusting the growth conditions as described above. Here, in this example, as described above, the waveguide is set to <01-1
0> direction, the GaN facet regrowth layer 13
Is perpendicular to the waveguide. In this case, GaN
The surface of the end face regrowth layer 13 is perpendicular to the surface of the sapphire substrate 1.

The oxide film mask 30 used as the selective growth mask may be removed after growing the GaN end face regrowth layer 13. Alternatively, the oxide film mask 30 may be used as an insulating protective film of the semiconductor laser device without being removed. In this example, the oxide film mask 30 is removed.

Finally, as shown in FIG. 7, the groove 15 is formed at the center of the groove 15 by dicing using the breaking technique or scribing using the breaking technique.
The sapphire substrate 1 along with each layer 2-4 along
Separate into individual semiconductor laser elements.

As described above, the direction of the resonator length is <0
The semiconductor laser device 100 having the (1-10) direction and the cavity facet formed by the (01-10) face of the GaN facet regrowth layer 13 is manufactured.

In the semiconductor laser device 100 manufactured by the above method, since the cavity facet is constituted by the GaN facet regrown layer 13, the cavity facet can be flattened at the atomic layer level. Further, a resonator end face perpendicular to the waveguide and perpendicular to the surface of the sapphire substrate 1 can be formed. Thereby, the semiconductor laser device 1
In the case of 00, it is possible to improve various characteristics of the device, such as improvement of light output, reduction of threshold value, improvement of light emission pattern, etc., and it is also possible to improve reliability.

In the semiconductor laser device 100, the undoped GaN layer 4 is formed by selective lateral growth. Therefore, in the undoped GaN layer 4 and each of the layers 5 to 10 formed thereon, the dislocation density is reduced, and excellent crystallinity is realized. Thereby,
In the semiconductor laser device 100, various characteristics and reliability of the device are further improved.

In the above description, the stripe-shaped groove 15 extending in the <11-20> direction is formed by etching (FIG. 4).
The stripe-shaped groove 15 may be formed by dicing or the like.

In consideration of mass productivity of the semiconductor laser device, it is preferable to form the groove 15 by dicing and etching, since it is possible to simultaneously process a plurality of device regions. Further, when manufacturing the semiconductor laser element 100, a process or the like for exposing the n-side electrode formation region is performed by etching. Therefore, it is particularly preferable to form the groove 15 by etching in consideration of the commonality of the process.

Although the sapphire substrate 1 is used in the above-described semiconductor laser device 100, a substrate made of a material other than sapphire may be used as long as each substrate can be grown to form a semiconductor laser device structure. You may. For example, a substrate made of SiC, spinel, Si, or the like may be used.

The structure of each of the layers 2 to 10 and 13 is not limited to the above, and it is sufficient if the layers 2 to 10 and 13 are made of a nitride semiconductor containing at least one of Ga, Al, In, B and Tl. Further, in the above description, the n-type layer and the p-type layer are sequentially formed on the substrate, but the p-type layer and the n-type layer may be sequentially formed on the substrate.

In the above description, the case where the method of manufacturing a semiconductor laser device according to the present invention is applied to a nitride-based semiconductor laser device has been described. The present invention is also applicable to devices such as GaAs-based semiconductor laser devices. Also in this case, the same effect as when the method of the present invention is applied to a nitride-based semiconductor laser device can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 2 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 3 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 4 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 5 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 6 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

FIG. 7 is a schematic view illustrating a method for manufacturing a semiconductor laser device according to one embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 AlGaN buffer layer 3, 4 Undoped GaN layer 5 n-GaN contact layer 6 n-AlGaInN crack prevention layer 7 an n-AlGaN second cladding layer 7 b n-GaN first cladding layer 8 MQW light emission Layer 9a p-GaN first cladding layer 9b p-AlGaN second cladding layer 10 p-GaN contact layer 13 GaN end face regrowth layer 15 groove 20,30 oxide film mask 100 semiconductor laser device

Claims (8)

[Claims] A first nitride-based semiconductor layer having an end face and including a light-emitting layer is formed on a substrate;
A second nitride-based semiconductor layer is formed on an end face of the nitride-based semiconductor layer, and a surface of the second nitride-based semiconductor layer forms a resonator end face. 2. The semiconductor laser device according to claim 1, wherein a surface of said second nitride-based semiconductor layer is perpendicular to a direction of a cavity length. 3. The semiconductor laser device according to claim 1, wherein the first and second nitride-based semiconductor layers include at least one of aluminum, gallium, indium, boron, and thallium. 4. The end face of the resonator is perpendicular to the <01-10> direction of the first nitride semiconductor layer, and the surface of the second nitride semiconductor layer is a (01-10) plane. The semiconductor laser device according to claim 1, wherein: 5. A step of forming a first semiconductor layer including a light emitting layer on a substrate; a step of forming a waveguide in the first semiconductor layer; and forming a waveguide in a predetermined region of the first semiconductor layer. Forming a stripe-shaped groove extending in a direction perpendicular to the direction of the waveguide and exposing an end face of the first semiconductor layer including the light-emitting layer in the groove; Manufacturing a semiconductor laser device, comprising: forming a second semiconductor layer on an end face of one semiconductor layer; and separating the first semiconductor layer together with the substrate along the groove. Method. 6. The step of forming the second semiconductor layer,
Forming an insulating film on a surface of the first semiconductor layer excluding an end face of the first semiconductor layer exposed in the groove; and forming the first film exposed in the groove excluding a region of the insulating film. 6. The method according to claim 5, further comprising the step of: selectively growing the second semiconductor layer on an end face of the semiconductor layer. 7. The first and second semiconductor layers are made of a group III nitride semiconductor, and the waveguide is formed in parallel with the <01-10> direction of the first semiconductor layer, and has a surface. 7. The method according to claim 5, wherein the second semiconductor layer is formed so as to have a (01-10) plane. 8. Supplying when forming the second semiconductor layer
8. The method of manufacturing a semiconductor laser device according to claim 7, wherein the surface of said second semiconductor layer is made to be a (01-10) plane by adjusting a supply amount of a group III raw material.