JP2003101156A - Semiconductor light-emitting device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting device in which a light- emitting element of multiple-wavelength is formed into monolithic, and to provide a manufacturing method therefor. SOLUTION: Semiconductor lasers LD1 and LD2 of different wavelength are integrally formed on a substrate 1 where an n-type GaN buffer layer 12 is formed on an n-type GaN substrate 11. An n-type AlGaN clad layer 2a on the LD1 side comprises a plane A which reflects a C-surface of the substrate, while an n-type AlGaN clad layer 2b on the LD2 side comprises a slope B. Over them, n-type GaN light-guide layers 3a and 3b, InGaN active layers 4a and 4b, p-type GaN light-guide layers 5a and 5b, p-type AlGaN clad layers 7a and 7b, and p-type contact layers 8a and 8b, are sequentially formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device in which light emitting elements of two different wavelengths are integrally formed on a substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, semiconductor lasers have been used in various fields such as home appliances, office automation equipment, communication equipment, and industrial measuring instruments. Particularly in recent years, development of short-wavelength semiconductor lasers has been focused on for the purpose of application to high-density optical disk recording and the like. For short wavelength semiconductor lasers, GaN, Al
A hexagonal compound semiconductor containing nitrogen (hereinafter simply referred to as a nitride semiconductor) such as GaN, InGaN, InGaAlN, or GaPN is used. Using such a nitride semiconductor, a short wavelength of up to 350 nm or less is possible,
Oscillation behavior at m has been reported. Regarding reliability,
It has been confirmed that LEDs have a life of 10,000 hours or more.

On the other hand, attempts have been made so far to make a semiconductor laser that oscillates monolithically at a wavelength of two or more wavelengths. When different wavelengths can oscillate with the same composition ratio of the light emitting material, it is possible to oscillate with different resonator structures and the like. However, when the two wavelengths are greatly different and it is difficult to oscillate them with the same composition ratio, separate steps are required to form the respective light emitting layers. Specifically, two light emitting layers are sequentially laminated or formed, or
When making one light emitting layer, mask the other light emitting layer area,
It is necessary to invert the mask again to create the other light emitting layer.

[0004]

As described above, in order to make a two-wavelength laser monolithically, the number of steps is large, the cost is high, and the yield is low. In particular, in a GaN-based nitride semiconductor, it is necessary to increase the In composition in order to obtain a long wavelength, but the In composition ratio is 25% or more,
At a wavelength of 450 nm or more, the semiconductor laser cannot oscillate due to the nonuniform In composition.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor light emitting device in which light emitting elements having a plurality of wavelengths are monolithically formed, and a manufacturing method thereof.

[0006]

SUMMARY OF THE INVENTION A semiconductor light emitting device according to the present invention is a hexagonal semiconductor device having a semiconductor substrate and a main surface of the semiconductor substrate having a plane parallel to the main surface and an inclined surface inclined from the main surface. A semiconductor layer made of crystal nitride, and I formed on the plane and the inclined surface of the semiconductor layer, respectively.
and a first light emitting layer and a second light emitting layer made of a hexagonal nitride semiconductor containing n in different composition ratios.

In the method for manufacturing a semiconductor light emitting device according to the present invention, a semiconductor layer made of hexagonal nitride is formed on a main surface of a semiconductor substrate so as to have a plane parallel to the main surface and an inclined surface inclined from the main surface. And a step of simultaneously forming first and second light emitting layers made of a hexagonal nitride semiconductor containing In at different composition ratios on the flat surface and the inclined surface of the semiconductor layer, respectively. And are included. In this case, the inclined surface of the semiconductor layer is formed by mesa etching after growing the semiconductor layer or by growing the semiconductor layer using a growth blocking mask.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a diagram showing a schematic configuration of a semiconductor laser device according to a first embodiment of the present invention. In this embodiment, two semiconductor lasers LD1 and LD2 having different wavelengths are integrated and formed on one semiconductor substrate 1. Here, the semiconductor substrate 1 is a hexagonal nitride semiconductor, and specifically, is an n-type GaN substrate 11 on which an n-type GaN buffer layer 12 is grown and formed.

The first semiconductor laser LD1 comprises a Si-doped n-type AlGaN on the buffer layer 12 of the semiconductor substrate 1.
Cladding layer 2a, n-type GaN optical waveguide layer 3a, InGaN
Active layer (multiple quantum well layer) 4a, p-type GaN optical waveguide layer 5
The Mg-doped p-type clad layer 6a is formed by being sequentially stacked. The second semiconductor laser LD2 includes an n-type AlGaN cladding layer 2b, an n-type GaN optical waveguide layer 3b, an InGaN active layer (multiple quantum well layer) 4b, and a p-type GaN optical waveguide layer on the buffer layer 12 of the semiconductor substrate 1. 5b, p
The mold clad layer 6b is formed by being sequentially laminated.

Here, n-type AlGaN cladding layers 2a and 2b, n-type GaN optical waveguide layers 3a and 3b, InGaN active layers (multiple quantum well layers) 4a and 4b, p-type GaN optical waveguide layers 5a and 5b, p-type. As will be described later, the cladding layers 6a and 6b are crystal-grown at the same time, and are separated by forming a groove 13 reaching the buffer layer 12 after the device is formed. However, in the semiconductor laser LD1, the upper surface of the n-type cladding layer 2a is formed with the same plane A as the main surface (c-plane) of the buffer layer 12, and the light emitting layer is formed on this, whereas the semiconductor laser LD1 is formed. In the LD2, the upper surface of the n-type cladding layer 2b is formed with the inclined surface B, so that the light emitting layer formed thereon also has the inclined surface.

P-type GaN contact layers 7a and 7b are formed on the surfaces of the p-type cladding layers 6a and 6b of the semiconductor lasers LD1 and LD2, and p-side electrodes 8a and 8b are formed on the p-type GaN contact layers 7a and 7b, respectively.
Are formed. The p-type contact layers 7a and 7b and the cladding layers 6a and 6b thereunder are mesa-etched for current confinement and lateral optical confinement. Board 1
A common n-side electrode 9 is formed on the back surface of the. Groove 13
Each of the semiconductor lasers LD1 and LD2 separated by
It is covered with a passivation film 14 made of an insulating film such as rO 2.

In this embodiment, the InGaN active layer 4a of the laser LD1 crystal-grown on the plane A and the InGaN active layer 4b of the laser LD2 crystal-grown on the inclined plane B have different In composition ratios. That is, specifically, the InGaN active layer 4 of the laser LD 2 grown on the inclined surface B.
The fact that the In composition ratio of b is high is used. As a result, the semiconductor laser LD2 can oscillate at a longer wavelength than the semiconductor laser LD1.

A specific manufacturing process of this embodiment will be described with reference to FIGS. MOCV for crystal growth
Method D is used. After pretreating the GaN substrate 11 with an organic solvent and an acid, the GaN substrate 11 is introduced into a growth chamber of a MOCVD apparatus and heated in a nitrogen atmosphere until the substrate temperature reaches 1030 ° C.
Before starting the growth, a small amount of hydrogen is flown before the raw material gas is flowed to remove the oxide film on the surface. After that, as shown in FIG. 2, an n-type buffer layer 12 is grown by a normal MOCVD growth method,
Gas switching is performed to grow the n-type AlGaN cladding layer 2.

After this, the substrate is once taken out from the growth chamber,
The cladding layer in the region of the second semiconductor laser LD2 is mesa-etched to form an inclined surface. Specifically, as shown by the broken line in FIG. 3, a mask 31 'that covers the two laser regions.
To form a mask 3 and its end gradually recedes to form a solid mask 3
Reactive ion etching is performed under the etching condition of 1 to form the inclined surface B on the cladding layer 2 in the region of the second semiconductor laser LD2. The etching conditions are set such that the extraction voltage of ions is set lower than that during normal mesa formation, and reactive etching is more dominant than sputtering. At this time, the tilt angle can be controlled by adjusting the extraction voltage of the ions.

After that, the substrate is again introduced into the MOCVD growth furnace, and as shown in FIG. 4, the n-type GaN optical waveguide layer 3, In
GaN active layer 4, p-type GaN optical waveguide layer 5, p-type AlGa
The N-clad layer 6 and the p-type contact layer 7 are sequentially formed.
Then, the substrate was taken out from the growth furnace, and as shown in FIG.
The p-side electrodes 8a and 8b are patterned on the p-type contact layer 7. At this time, the electrodes 8a and 8b are patterned using a mask that covers the electrodes 8a and 8b, and the p-type cladding layer 6 is subsequently mesa-etched. Subsequently, in order to isolate the elements from each other, as shown in FIG. 6, the groove 13 reaching the n-type buffer layer 12 is etched. Then, as shown in FIG. 1, a ZrO 2 film is formed as the passivation film 14 covering the side surface of the element. Finally GaN
After polishing the substrate 11 to a thickness of about 100 μm, the n-side electrode 9 is formed and the two semiconductor laser LDs are formed.
It is divided by dicing so that 1 and LD2 are included as a pair.

In this embodiment, depending on the angle of the inclined surface B forming the active layer of the second semiconductor laser LD2,
The amount of In contained in the active layer is controlled. Specifically, FIG. 7 shows the angle of an inclined surface (a surface perpendicular to the plane formed by the c-axis and the R-axis and inclined from the c-plane) and the In composition ratio of the InGaN layer formed on the inclined surface. It shows the relationship. This data is based on the growth conditions such that the In composition ratio of InGaN is 11% on the c-plane, specifically, the growth temperature of 85.
Trimethylindium (TMI) as a source gas at 0 ° C
And trimethylgallium (TMG) at a gas phase ratio of 0.9. Under this growth condition, a maximum In composition ratio of 45% is obtained on the inclined surface. When the growth conditions are changed to increase the In composition ratio on the c-plane, the amount of change of the In composition ratio at each angle with respect to the angle is further increased, and the In composition ratio on the c-plane is decreased. When performed under the conditions, the amount of change in the In composition ratio with respect to the angle becomes small.

Specifically, in this embodiment, in order to increase the In composition ratio of the active layer of the second semiconductor laser LD2 with a sufficient significant difference from that of the first semiconductor laser LD1, the inclination angle is set to be large. The setting is important. Figure 8
Referring to the hexagonal crystal axis shown in FIG. 2, the second semiconductor laser LD with the main surface of the semiconductor substrate 1 as the c-plane.
The inclined surface B of the active layer 2 is perpendicular to the plane formed by the c-axis and the R-axis, and the angle formed by the c-plane is 30 degrees or more to obtain an In composition ratio of 25 to 45%. Is preferred, which is preferable. Alternatively, it is preferable that the surface is perpendicular to the plane formed by the c-axis and the a-axis and the angle formed by the c-plane is 30 degrees or more.

When the device produced under such preferable conditions is operated, two semiconductor lasers LD1 and LD2 are obtained.
In both cases, continuous oscillation at room temperature was achieved at a threshold value of 35 mA. The oscillation wavelength of the first laser LD1 was 405 nm and that of the second laser was 450 nm. The operating voltage was 3.1 V, and the oscillation thresholds were almost the same. Reliability is 1 in an accelerated test with the temperature set at 70 ° C.
No deterioration was observed even after performing a reliability test equivalent to 0,000 hours.

Up to now, in InGaN semiconductor lasers, when the In composition is increased, the composition of In becomes non-uniform, that is, composition separation occurs, and the threshold current density tends to increase. It was found that the use of the present invention makes it possible to grow InGaN having a high In composition at a high growth temperature, suppress composition separation, and reduce the threshold current. It is considered that this is because the binding energy on the surface changes on the inclined surface B. In MOCVD growth, it is known that the growth normally proceeds with Ga polarity. However, it is considered that a bond corresponding to the opposite N-polarity is likely to occur on the inclined surface B, whereby the surface energy at the time of the bond is changed and In is likely to be incorporated. Alternatively, InGa
When N grows, it is in a state of competing etching and growth.
When the composition of n becomes large, it is easily etched,
It is considered that the etching rate becomes smaller on the inclined surface B.

As described above, according to this embodiment, an InGaN active layer having a higher In composition than the conventional one can be formed simultaneously with an active layer having a lower In composition, and a two-wavelength green nitride semiconductor laser which has not been mass-produced is obtained. Mass production is possible. Each semiconductor laser has only a partial surface treatment process before the formation of the active layer, and is basically the same as the process of making one semiconductor laser, and can realize a two-wavelength laser without complicated processes. it can.

The inclined surface B may be formed not by mesa etching but by a regrowth method using a mask. Specifically, as shown in FIG. 9, after partially growing the cladding layer 21 of the n-type AlGaN cladding layer 2, the substrate is taken out from the growth furnace and the SiO 2 mask 91 is patterned in a stripe shape. At this time, the mask 91 has an interval of 3
It is about 00 μm. This is again introduced into the growth furnace to grow the remaining clad layer 22. At this time, the clad layer 2
No. 2 grows only in a portion where the SiO 2 mask 91 is not present, and both end portions thereof become inclined surfaces B. After that, the substrate is taken out again, the SiO 2 mask is removed, and the same steps as the above steps are performed.

According to this method, the R surface can be formed as the inclined surface B. Intake of In on this surface is the largest, and the oscillation wavelength of the first laser LD1 is 405.
In the case of nm, the oscillation wavelength of the second laser LD2 is 530n.
m.

[Second Embodiment] FIG. 10 shows a schematic structure of a semiconductor laser device according to a second embodiment of the present invention. Parts corresponding to those of the previous embodiment shown in FIG. 1 are designated by the same reference numerals. In this embodiment, the light emitting layer portion on the second semiconductor laser LD2 side has a plane A having a step on both sides.
1 and A2, and an inclined surface B between these planes A1 and A2
Has a bent structure. Similar to the previous embodiment, the inclined surface B is a surface different from the c-plane, and the In composition ratio is high in this portion.

The first semiconductor laser LD1 comprises a Si-doped n-type AlGaN on the buffer layer 12 of the semiconductor substrate 1.
Cladding layer 2a, n-type GaN optical waveguide layer 3a, InGaN
Active layer (multiple quantum well layer) 4a, p-type GaN optical waveguide layer 5
The Mg-doped p-type clad layer 6a is formed by being sequentially stacked. The second semiconductor laser LD2 includes an n-type AlGaN cladding layer 2b, an n-type GaN optical waveguide layer 3b, an InGaN active layer (multiple quantum well layer) 4b, and a p-type GaN optical waveguide layer on the buffer layer 12 of the semiconductor substrate 1. 5b, p
The mold clad layer 6b is formed by being sequentially laminated.

As in the previous embodiment, n-type AlGaN
Cladding layers 2a and 2b, n-type GaN optical waveguide layers 3a and 3
b, InGaN active layers (multiple quantum well layers) 4a and 4b,
The p-type GaN optical waveguide layers 5a and 5b and the p-type cladding layers 6a and 6b are crystal-grown at the same time, and are separated by forming a groove 13 that reaches the buffer layer 12 after the element is formed. In the semiconductor laser LD1, the upper surface of the n-type cladding layer 2a is formed with the same plane A as the main surface (c-plane) of the buffer layer 12, and the light emitting layer is formed thereon, whereas in the semiconductor laser LD2. , The upper surface of the n-type clad layer 2b is formed with two planes A1 and A2 and an inclined surface B connecting these planes, and the light emitting layer formed thereon also has the same bending structure.

P-type GaN contact layers 7a and 7b are formed on the surfaces of the p-type cladding layers 6a and 6b of the semiconductor lasers LD1 and LD2, and p-side electrodes 8a and 8b are formed on the p-type GaN contact layers 7a and 7b, respectively.
Are formed. The p-type contact layers 7a and 7b and the cladding layers 7a and 7b thereunder are mesa-etched for current confinement and lateral optical confinement. Board 1
A common n-side electrode 9 is formed on the back surface of the. Groove 13
Each of the semiconductor lasers LD1 and LD2 separated by
It is covered with a passivation film 14 made of an insulating film such as rO 2.

Also in this embodiment, the InGaN active layer 4a of the laser LD1 crystal-grown on the plane A and the InGaN active layer 4b of the laser LD2 crystal-grown on the inclined plane B have different In composition ratios. That is, specifically, the InGaN active layer 4 of the laser LD 2 grown on the inclined surface B.
The fact that the In composition ratio of b is high is used. As a result, the semiconductor laser LD2 can oscillate at a longer wavelength than the semiconductor laser LD1.

A detailed description of the manufacturing process is omitted,
Basically, it is similar to the previous embodiment. In the case of this embodiment, the oscillation threshold of the first laser LD1 is 35 mA, whereas the oscillation threshold of the second laser LD2 is 20 mA, and single transverse mode oscillation is observed. This is a result of the bent structure that the light confinement effect and the current constriction effect are better than those of the previous embodiments.

In each of the above embodiments, the case where two semiconductor lasers having different wavelengths are formed on the same substrate has been described, but the present invention is not limited to this. For example, three or more semiconductor lasers can be integrated and formed. Further, in that case, if a plurality of inclined surfaces having different inclination angles are formed, it is possible to integrally form lasers having three or more kinds of oscillation wavelengths.
Further, the present invention is not limited to semiconductor lasers and can be similarly applied to light emitting diodes.

Further, in the embodiment, the InGaN-based semiconductor laser is used in which the In composition ratio is increased on the inclined surface, but InGaAlN, InAlN, I
Other In such as nGaBN, InBN, InGaAlBN
In a light emitting device having a hexagonal nitride semiconductor light emitting layer containing Al, the same effect is applied to a light emitting device having at least two light emitting layers made of hexagonal nitride semiconductor containing In at different composition ratios. it can.

[0031]

As described above, according to the present invention, it is possible to obtain a semiconductor light emitting device in which light emitting elements having a plurality of wavelengths are monolithically formed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a process up to formation of an n-type cladding layer according to the same embodiment.

FIG. 3 is a diagram showing a step of forming an inclined surface of the n-type cladding layer of the same embodiment.

FIG. 4 is a diagram showing steps up to formation of the p-type contact layer in the same embodiment.

FIG. 5 is a diagram showing a p-side electrode formation and mesa etching step of the same embodiment.

FIG. 6 is a diagram showing an element isolation groove forming step of the same embodiment.

FIG. 7 is a diagram showing a relationship between an inclination angle of a growth inclined surface of an InGaN layer and an In composition ratio.

FIG. 8 is a diagram showing a relationship between hexagonal crystal faces.

FIG. 9 is a diagram for explaining another method of forming an inclined surface.

FIG. 10 is a diagram showing a configuration of a semiconductor light emitting device according to another embodiment.

[Explanation of symbols]

LD1, LD2 ... Semiconductor laser, 1 ... Semiconductor substrate, 11
... n-type GaN substrate, 12 ... n-type GaN buffer layer, 2
a, 2b ... n-type AlGaN cladding layer, 3a, 3b ... n
-Type GaN optical waveguide layer, 4a, 4b ... InGaN active layer, 5
a, 5b ... p-type GaN optical waveguide layer, 6a, 6b ... p-type Al
GaN cladding layer, 7a, 7b ... P-type contact layer, 8
a, 8b ... P-side electrode, 9 ... N-side electrode, 13 ... Groove, 14 ...
Passivation film. A ... plane, B ... inclined surface.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiyuki Harada             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F term (reference) 5F041 AA12 CA23 CA34 CA40 CB29                 5F073 AA13 AA45 AA74 AB06 CA07                       DA05 DA25 DA30 EA04

Claims (5)

[Claims] 1. A semiconductor substrate, a semiconductor layer made of hexagonal nitride formed on a main surface of the semiconductor substrate with a plane parallel to the main surface and an inclined surface inclined from the main surface, and a semiconductor layer of the semiconductor layer. A semiconductor light emitting device comprising: a first light emitting layer and a second light emitting layer made of a hexagonal nitride semiconductor, the first light emitting layer and the second light emitting layer respectively formed on the flat surface and the inclined surface and containing In at different composition ratios. 2. The main surface of the semiconductor substrate is a c-plane, and the inclined surface of the semiconductor layer is perpendicular to a plane formed by the c-axis and the R-axis and has an angle of 30 degrees or more with the c-plane. 2. The semiconductor according to claim 1, which is one of a surface that is perpendicular to the plane formed by the c-axis and the a-axis and that forms an angle of 30 degrees or more with the c-plane. Light emitting device. 3. The semiconductor light emitting device according to claim 1, wherein the main surface of the semiconductor substrate is a c-plane, and the inclined surface of the semiconductor layer is an R-plane. 4. In the first and second light emitting layers, the In composition ratio of the second light emitting layer formed on the inclined surface is higher than that of the first light emitting layer formed on the flat surface. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a semiconductor light emitting device. 5. A step of forming a semiconductor layer made of hexagonal nitride on a main surface of a semiconductor substrate so as to have a plane parallel to the main surface and an inclined surface inclined from the main surface, I on the flat surface and the inclined surface, respectively.
and a step of simultaneously forming first and second light emitting layers made of a hexagonal nitride semiconductor containing n in different composition ratios from each other.