JP3697406B2 - Semiconductor light emitting device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device in which light emitting elements having two different wavelengths are integrally formed on a substrate, and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, semiconductor lasers have been used in various fields such as home appliances, OA 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. As the short wavelength semiconductor laser, a hexagonal compound semiconductor (hereinafter simply referred to as a nitride semiconductor) containing nitrogen such as GaN, AlGaN, InGaN, InGaAlN, GaPN or the like is used. Using such a nitride semiconductor, a short wavelength up to 350 nm or less is possible, and an oscillation operation at 400 nm has been reported. Regarding the reliability, it has been confirmed that the LED has a lifetime of 10,000 hours or more.
[0003]
On the other hand, attempts have been made to produce semiconductor lasers that oscillate monolithically at 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. However, when the two wavelengths are greatly different and it is difficult to oscillate them at the same composition ratio, a separate process is required to form each light emitting layer. Specifically, two light-emitting layers are sequentially stacked, or when one light-emitting layer is formed, the other light-emitting layer region is masked, and the mask is inverted again to create the other light-emitting layer. There is a need.
[0004]
[Problems to be solved by the invention]
As described above, making a two-wavelength laser monolithically requires a large number of processes, increases the cost, and decreases the yield. In particular, in a GaN-based nitride semiconductor, it is necessary to increase the In composition in order to obtain a long wavelength. However, if the In composition ratio is 25% or more and the wavelength is 450 nm or more, the semiconductor composition is uneven due to the nonuniformity of the In composition. Cannot oscillate.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor light emitting device in which light emitting elements having a plurality of wavelengths are formed monolithically and a method for manufacturing the same.
[0006]
[Means for Solving the Problems]
A semiconductor light-emitting device according to the present invention includes a semiconductor substrate, and a semiconductor layer made of hexagonal nitride formed on the main surface of the semiconductor substrate with a plane parallel to the main surface and an inclined surface inclined from the main surface; First and second light-emitting layers made of hexagonal nitride semiconductor, each of which is formed on the plane and the inclined surface of the semiconductor layer and contains In at different composition ratios, the plane and the inclined surface, And separating grooves formed in the first and second light-emitting layers and the semiconductor layer .
[0007]
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. a step, respectively on the plane and the inclined surface of the semiconductor layer, including at different composition ratio of in, and a step of simultaneously forming the first and second light-emitting layer composed of hexagonal nitride semiconductor, wherein the Forming a separation groove in the first and second light-emitting layers and the semiconductor layer so as to separate the flat surface and the inclined surface . In this case, the inclined surface of the semiconductor layer is formed by growing the semiconductor layer and then by mesa etching, or by growing the semiconductor layer using a growth prevention mask.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a schematic configuration of a semiconductor laser device according to an embodiment of the present invention. In this embodiment, two semiconductor lasers LD 1 and LD 2 having different wavelengths are integrally formed on one semiconductor substrate 1. Here, the semiconductor substrate 1 is a hexagonal nitride semiconductor. Specifically, an n-type GaN buffer layer 12 is grown on an n-type GaN substrate 11.
[0009]
The first semiconductor laser LD1 includes an Si-doped n-type AlGaN cladding layer 2a, an n-type GaN optical waveguide layer 3a, an InGaN active layer (multiple quantum well layer) 4a, and p-type GaN on the buffer layer 12 of the semiconductor substrate 1. The optical waveguide layer 5a and the Mg-doped p-type cladding layer 6a are sequentially laminated. 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 and a p-type cladding layer 6b are sequentially stacked.
[0010]
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, and p-type cladding layer 6a 6b are separated by forming a trench 13 that reaches the buffer layer 12 after device formation, as will be described later. 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 thereon, whereas the semiconductor laser In LD2, the upper surface of the n-type cladding layer 2b is formed with an inclined surface B, and thus the light emitting layer formed thereon also has an inclined surface.
[0011]
On the surfaces of the p-type cladding layers 6a and 6b of the semiconductor lasers LD1 and LD2, p-type GaN contact layers 7a and 7b are formed, and p-side electrodes 8a and 8b are formed respectively. The p-type contact layers 7a and 7b and the underlying cladding layers 6a and 6b are mesa-etched for current confinement and lateral light confinement. A common n-side electrode 9 is formed on the back surface of the substrate 1. Each of the semiconductor lasers LD1 and LD2 separated by the groove 13 is covered with a passivation film 14 made of an insulating film such as ZrO2.
[0012]
In this embodiment, the InGaN active layer 4a of the laser LD1 grown on the plane A and the InGaN active layer 4b of the laser LD2 grown on the inclined plane B have different In composition ratios. Specifically, the fact that the In composition ratio of the InGaN active layer 4b of the laser LD2 grown on the inclined surface B is increased is utilized. As a result, the semiconductor laser LD2 can oscillate at a longer wavelength than the semiconductor laser LD1.
[0013]
A specific manufacturing process of this embodiment will be described with reference to FIGS. The MOCVD method is used for crystal growth. After pre-treating the GaN substrate 11 with an organic solvent and an acid, the GaN substrate 11 is introduced into the growth chamber of the MOCVD apparatus, heated up in a nitrogen atmosphere until the substrate temperature reaches 1030 ° C., and a small amount of hydrogen is added before the growth starts. Before flowing the source gas, the surface oxide film is removed. Thereafter, as shown in FIG. 2, an n-type buffer layer 12 is grown by a normal MOCVD growth method, and gas switching is performed to grow an n-type AlGaN cladding layer 2.
[0014]
Thereafter, the substrate is once taken out of the growth chamber, and the clad layer in the region of the second semiconductor laser LD2 is mesa-etched to form an inclined surface. Specifically, as shown by a broken line in FIG. 3, a mask 31 ′ covering the two laser regions was formed, and the etching conditions were set such that the end portion gradually receded to become the solid mask 31. Reactive ion etching is performed to form an inclined surface B in the cladding layer 2 in the region of the second semiconductor laser LD2. The etching conditions are such that the ion extraction voltage is set lower than that during normal mesa formation so that reactive etching is dominant over sputtering. At this time, the inclination angle can be controlled by adjusting the ion extraction voltage.
[0015]
Thereafter, the substrate is again introduced into the MOCVD growth furnace, and as shown in FIG. 4, the n-type GaN optical waveguide layer 3, the InGaN active layer 4, the p-type GaN optical waveguide layer 5, the p-type AlGaN cladding layer 6, and the p-type. Contact layer 7 is formed sequentially. Then, the substrate is taken out from the growth furnace, and p-side electrodes 8a and 8b are patterned on the p-type contact layer 7 as shown in FIG. At this time, the electrodes 8a and 8b are patterned using a mask covering the electrodes 8a and 8b, and the p-type cladding layer 6 is subsequently mesa-etched. Subsequently, in order to separate the elements, the trench 13 reaching the n-type buffer layer 12 is etched as shown in FIG. Then, as shown in FIG. 1, a ZrO 2 film is formed as a passivation film 14 covering the element side surface.
Finally, after polishing the GaN substrate 11 to a thickness of about 100 μm, the n-side electrode 9 is formed and divided by dicing so as to include two semiconductor lasers LD1 and LD2 as a pair.
[0016]
In this embodiment, the amount of In contained in the active layer is controlled by the angle of the inclined surface B that forms the active layer of the second semiconductor laser LD2. Specifically, FIG. 7 shows the angle of the inclined surface (the 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. Showing the relationship. This data is based on growth conditions in which the In composition ratio of InGaN is 11% on the c-plane, specifically, a growth temperature of 850 ° C., and a gas phase of trimethylindium (TMI) and trimethylgallium (TMG) as source gases. When the ratio is 0.9. Under this growth condition, a maximum In composition ratio of 45% is obtained on the inclined surface. If the In composition ratio on the c-plane is increased by changing the growth conditions, the amount of change with respect to the angle of the In composition ratio at each angle is further increased, and the In composition ratio on the c-plane is reduced. If performed under the conditions, the amount of change with respect to the angle of the In composition ratio becomes small.
[0017]
Specifically, in this embodiment, in order to increase the In composition ratio of the active layer of the second semiconductor laser LD2 with a sufficiently significant difference from that of the first semiconductor laser LD1, the setting of the tilt angle is important. It is. Referring to the hexagonal crystal axis shown in FIG. 8, the main surface of the semiconductor substrate 1 is c-plane, and the inclined surface B of the active layer of the second semiconductor laser LD2 is c-axis and R-axis. And the angle formed by the c-plane is 30 degrees or more, which is preferable because an In composition ratio of 25 to 45% can be obtained. 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.
[0018]
When the element fabricated under such preferable conditions was operated, both the two semiconductor lasers LD1 and LD2 oscillated continuously at room temperature at a threshold of 35 mA. The oscillation wavelength was 405 nm for the first laser LD1 and 450 nm for the second laser. The operating voltage was 3.1 V, and the oscillation threshold values were almost the same. As for reliability, no deterioration was observed even when a reliability test corresponding to 100,000 hours was performed in an accelerated test with the temperature set at 70 ° C.
[0019]
Up to now, in InGaN-based semiconductor lasers, when the In composition is increased, non-uniform composition of the so-called composition separation occurs, and the threshold current density tends to increase. It has been found that when this invention is used, InGaN having a high In composition can be grown at a high growth temperature, the composition separation can be suppressed, and the threshold current can be lowered. The reason for this is considered that the binding energy at the surface changes on the inclined surface B. In MOCVD growth, it is known that growth proceeds normally with Ga polarity. However, it is considered that on the inclined surface B, a bond corresponding to the opposite N polarity is likely to occur as a bond, whereby the surface energy at the time of bonding is changed and In is likely to be taken in. Alternatively, the growth of InGaN is in an antagonistic state between etching and growth. When the In composition is increased, etching is facilitated, but the etching rate is considered to be reduced on the inclined surface B.
[0020]
As described above, according to this embodiment, an InGaN active layer having a higher In composition than before can be formed simultaneously with an active layer having a lower In composition, and a two-wavelength green nitride semiconductor laser that has not been mass-produced can be mass-produced. Each semiconductor laser can be realized as a two-wavelength laser without requiring a complicated process as it is basically different from the process of making one semiconductor laser, only by a part of the surface treatment process before forming the active layer. it can.
[0021]
The method of creating the inclined surface B may be a regrowth method using a mask, not mesa etching. Specifically, as shown in FIG. 9, after growing up to a partial cladding layer 21 of the n-type AlGaN cladding layer 2, the substrate is taken out of the growth furnace and the SiO2 mask 91 is patterned in a stripe shape. At this time, the mask 91 has an interval of about 300 μm. This is again introduced into the growth furnace, and the remaining cladding layer 22 is grown. At this time, the cladding layer 22 grows only in a portion where the SiO 2 mask 91 is not present, and both end portions thereof become inclined surfaces B. Thereafter, the substrate is taken out again, the SiO2 mask is removed, and the same process as the previous process is performed.
[0022]
According to this method, the R surface can be provided as the inclined surface B. In this plane, In is taken up most, and when the oscillation wavelength of the first laser LD1 is 405 nm, the oscillation wavelength of the second laser LD2 is 530 nm.
[0023]
[Embodiment 2]
FIG. 10 shows a schematic configuration of a semiconductor laser device according to the second embodiment of the present invention. Portions corresponding to those in FIG. 1 of the previous embodiment are denoted by the same reference numerals. In this embodiment, the light emitting layer portion on the second semiconductor laser LD2 side has a bent structure in which there are flat surfaces A1 and A2 having steps on both sides, and an inclined surface B is formed between these flat surfaces A1 and A2. . 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.
[0024]
The first semiconductor laser LD1 includes an Si-doped n-type AlGaN cladding layer 2a, an n-type GaN optical waveguide layer 3a, an InGaN active layer (multiple quantum well layer) 4a, and p-type GaN on the buffer layer 12 of the semiconductor substrate 1. The optical waveguide layer 5a and the Mg-doped p-type cladding layer 6a are sequentially laminated. 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 and a p-type cladding layer 6b are sequentially stacked.
[0025]
As in the previous embodiment, 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, and p-type GaN optical waveguide layers 5a and 5b. The p-type 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 element formation. 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 cladding layer 2b is formed with two planes A1 and A2 and an inclined surface B connecting them, and the light emitting layer formed thereon has a similar bent structure.
[0026]
On the surfaces of the p-type cladding layers 6a and 6b of the semiconductor lasers LD1 and LD2, p-type GaN contact layers 7a and 7b are formed, and p-side electrodes 8a and 8b are formed respectively. The p-type contact layers 7a and 7b and the underlying cladding layers 7a and 7b are mesa-etched for current confinement and lateral light confinement. A common n-side electrode 9 is formed on the back surface of the substrate 1. Each of the semiconductor lasers LD1 and LD2 separated by the groove 13 is covered with a passivation film 14 made of an insulating film such as ZrO2.
[0027]
Also in this embodiment, the InGaN active layer 4a of the laser LD1 grown on the plane A and the InGaN active layer 4b of the laser LD2 grown on the inclined surface B have different In composition ratios. Specifically, the fact that the In composition ratio of the InGaN active layer 4b of the laser LD2 grown on the inclined surface B is increased is utilized. As a result, the semiconductor laser LD2 can oscillate at a longer wavelength than the semiconductor laser LD1.
[0028]
Although a specific manufacturing process is omitted, it is basically the same as the previous embodiment. In the case of this embodiment, an oscillation threshold value of 20 mA was obtained for the second laser LD2 with respect to the oscillation threshold value of 35 mA of the first laser LD1, and single transverse mode oscillation was observed. This is a result that the optical confinement effect and the current confinement effect are better than those of the previous embodiment due to the bent structure.
[0029]
In each of the above embodiments, the case where two semiconductor lasers having different wavelengths are formed on the same substrate has been described. However, the present invention is not limited to this. For example, three or more semiconductor lasers can be integrated. In that case, if a plurality of inclined surfaces having different inclination angles are formed, lasers with three or more oscillation wavelengths can be integrally formed. Further, the present invention is not limited to the semiconductor laser and can be similarly applied to a light emitting diode.
[0030]
Further, in the embodiment, the InGaN-based semiconductor laser uses the fact that the In composition ratio increases on the inclined surface, but other In-containing hexagonal crystals such as InGaAlN, InAlN, InGaBN, InBN, and InGaAlBN are used. The light emitting device having a nitride semiconductor light emitting layer can be applied with the same effect to a light emitting device having at least two light emitting layers made of hexagonal nitride semiconductor containing In at different composition ratios.
[0031]
【The invention's effect】
As described above, according to the present invention, a semiconductor light emitting device in which light emitting elements having a plurality of wavelengths are monolithically formed can be obtained.
[Brief description of the 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 until formation of an n-type cladding layer according to the same embodiment;
FIG. 3 is a diagram showing a process of forming an inclined surface of the n-type cladding layer of the same embodiment.
4 is a diagram showing a process until formation of a p-type contact layer according to the embodiment. FIG.
FIG. 5 is a diagram showing a p-side electrode formation and mesa etching process according to the same embodiment;
FIG. 6 is a diagram showing an element isolation groove forming step according to the same embodiment;
FIG. 7 is a diagram showing the relationship between the inclination angle of the growth inclined surface of the InGaN layer and the In composition ratio.
FIG. 8 is a diagram showing the relationship of hexagonal crystal planes.
FIG. 9 is a view 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, 2a, 2b ... n-type AlGaN cladding layer, 3a, 3b ... n-type GaN optical waveguide layer, 4a, 4b ... InGaN active layer, 5a, 5b ... p-type GaN optical waveguide layer, 6a, 6b ... p-type AlGaN cladding layer, 7a, 7b ... p-type contact layer, 8a, 8b ... p-side electrode, 9 ... n-side electrode, 13 ... groove, 14 ... passivation film. A: plane, B: inclined surface.

Claims (7)

A semiconductor substrate;
A semiconductor layer made of hexagonal nitride formed on the main surface of the semiconductor substrate with a plane parallel to the main surface and an inclined surface inclined from the main surface;
First and second light-emitting layers made of hexagonal nitride semiconductors formed on the plane and the inclined surface of the semiconductor layer and containing In at different composition ratios;
A semiconductor light emitting device comprising: the first and second light emitting layers and a separation groove formed in the semiconductor layer so as to separate the flat surface and the inclined surface . The main surface of the semiconductor substrate is a c-plane, and the inclined surface of the semiconductor layer 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; 2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is any one of surfaces that are perpendicular to a plane formed by the c-axis and the a-axis and have an angle of 30 degrees or more with the c-plane. The semiconductor light-emitting device according to claim 1, wherein a main surface of the semiconductor substrate is a c-plane, and an inclined surface of the semiconductor layer is an R-plane.   The first and second light emitting layers are characterized in that 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 plane. Item 4. The semiconductor light-emitting device according to any one of Items 1 to 3. The semiconductor light emitting device according to claim 1, wherein the inclined surface is formed by etching the semiconductor layer in a region where the second light emitting layer is formed. Forming a semiconductor layer made of hexagonal nitride on the main surface of the semiconductor substrate so as to have a plane parallel to the main surface and an inclined surface inclined from the main surface;
Simultaneously forming first and second light-emitting layers made of hexagonal nitride semiconductor containing In at different composition ratios on the planar surface and the inclined surface of the semiconductor layer, respectively.
Forming a separation groove in the first and second light-emitting layers and the semiconductor layer so as to separate the flat surface and the inclined surface. . The method of manufacturing a semiconductor light emitting device according to claim 6, wherein the second light emitting layer formed on the inclined surface has a higher In composition ratio than the first light emitting layer formed on the plane. .

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