JP2000106470A - Semiconductor laser element and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a far field pattern from being disturbed due to reflection of laser light on the etching bottom face by laminating a semiconductor layer on a substrate and forming an electrode on an active layer and then making an isolation trench and forming a resonator face by etching. SOLUTION: A semiconductor laminate structure 200 laminated with a semiconductor layer is formed on a substrate 1 and a p-side electrode 10 is provided on an active layer formed on the substrate 1. An isolation trench 5b reaching the substrate 1 is made by half dicing perpendicularly in the elongating direction of the p-side electrode 10. Subsequently, a resonator end face is formed by etching and dicing is performed inclining the tooth of a dicer such that an acute angle is formed by the resonator end face and the trench 5b. According to the structure, a far field pattern is prevented from being disturbed due to reflection of laser light on the etching bottom face, and a defect being introduced into a semiconductor crystal at the time of making the isolation trench 5b can be prevented from having adverse effect on the element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a compound semiconductor laser device.

[0002]

2. Description of the Related Art A cavity surface in a semiconductor laser is generally formed by means such as cleavage, etching and polishing. When the resonator end face is formed by etching, the end face 30 of the resonator formed by etching and the end face 31 of the element are formed as shown in FIG.
Between the lengths L1 and L2 where the etched bottom surface is exposed.
And a pair of terrace-shaped regions 32a and 32b each having
Can be.

The lengths L1 and L2 of this region are determined by the distance between the division position at the time of element division and the end face of the resonator. For the length L1 of the region, for example, AlG
In an aAs-based compound semiconductor laser, Journal
al of Quantum Electronic
s, vol. 27, No.6, pp. 1319-pp. 1
No. 331 describes that it is necessary to suppress the thickness to 9 μm or less. This is because when L1 is longer than 9 μm, FIG.
This is because, as shown in (b), the laser light hits the etching bottom surface and is reflected, so that there is a problem that a stable far-field image cannot be obtained.

In order to avoid this problem, the gallium nitride based compound semiconductor laser device must be wrapped, cut or etched to remove part or all of the terrace-shaped region. For example, Japanese Patent Application Laid-Open No. 9-223844 discloses a technique for preventing laser light from being blocked.

In the device described in Japanese Patent Application Laid-Open No. 9-223844, a nitride semiconductor layer is grown on a substrate, and then the nitride semiconductor layer is etched to form a resonator surface on an etched surface. And cutting between opposing resonator surfaces. At this time, it is necessary to prevent the portion protruding from the resonator from touching the laser emission light from the resonator end face. Therefore, the cutting is performed at a position not touching the laser emission light from the resonator end face, or After cutting, the portion that comes into contact with the laser beam is further removed by lapping or the like.

[0006] In the present specification, the term "gallium nitride-based compound semiconductor" refers to gallium nitride (GaN).
a partially semiconductors replaced with another group III element, for _{example, Ga s Al t In 1-} st N (0 <s ≦ 1,0
≦ t <1, 0 <s + t ≦ 1), and includes a semiconductor in which a part of each constituent atom is replaced with an impurity atom or the like, or a semiconductor to which another impurity is added.

[0007]

However, with respect to a gallium nitride based compound semiconductor laser device, L1 is
It is not only necessary that the above-mentioned laser beam hit the etching bottom surface and be short enough to prevent its reflection.
That is, when dicing is used for element division, unless the length L is kept at a certain length or more, defects introduced into the semiconductor crystal during dicing gradually propagate to the vicinity of the active layer during driving of the element. However, the inventor has found for the first time that the reliability of the device is adversely affected, such as an increase in threshold current density and a decrease in external differential quantum efficiency. If dicing is performed in a state where the laminated structure of the portion to be diced is completely removed and the substrate is exposed, the effect is reduced, but the crystal defects introduced into the substrate still cause an interface between the substrate and the laminated structure. And eventually propagates in the vicinity of the active layer. Eventually, the reliability of the device is L1 regardless of whether or not the entire laminated structure at the site to be diced is removed.
Increases exponentially with the decrease of.

Therefore, L1 is not only required to be short enough to prevent the laser beam from hitting the bottom surface of the etching and preventing the laser beam from being reflected as described above. The field must be very small and long enough to have no practical effect on reliability.

For example, in the case of a gallium nitride based semiconductor laser device, L1 satisfying such conditions is 4 when the etching depth under the active layer is 3.0 μm and the laser beam emission angle is 30 degrees. It is 0.0 μm or more and 8.0 μm or less.

However, in the conventional device processing, it is very difficult to actually perform element division in a form that satisfies the conditions due to restrictions on processing accuracy. That is, for example, taking the example of scribing from the back surface of the substrate, which is a typical method of element division, the positional accuracy at which the scriber blade descends is at most ± several tens of μm, for example, the gallium nitride based semiconductor laser described above. In the case of an element, the position cannot be controlled to 4 μm or more and 8 μm or less. Also, even if the scriber's blade enters the designed scribe position without any deviation, the actual position of the blade on the back side of the substrate and the laminated structure on the surface of the substrate when stress is applied to the substrate afterwards The relative relationship with the position to be divided cannot be always kept constant. This point is particularly remarkable when the substrate is relatively hard and does not have cleavage, or when it is necessary to scribe on a surface that does not have cleavage according to a process requirement.

Also, in the case of dividing by dicing, the accuracy of the position where the blade of the dicer descends is still
It is at most several tens of μm, and it cannot be said that it is enough to perform actual element division in a form satisfying the condition. Further, even when the terrace-shaped region is removed by lapping, the above-described finished dimensions cannot be practically expected due to restrictions on grinding accuracy.

Further, if the terrace-like region can be removed by etching, this problem can be avoided to some extent. However, for example, sapphire, which is a typical substrate of a gallium nitride-based compound semiconductor laser device, needs to be removed by etching. However, it is very difficult in practice.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compound semiconductor laser device having a cavity end face formed by etching.
In order to prevent the outgoing light from being blocked by the terrace-shaped region, even if it is difficult to use etching as a means for removing the terrace-shaped region, crystal defects generated from the element dividing plane are transmitted to the active layer. An object of the present invention is to provide an element structure which does not cause deterioration in reliability and a manufacturing method thereof.

[0014]

According to a first aspect of the present invention, there is provided a method for manufacturing a semiconductor laser device, wherein a semiconductor layer is formed on a substrate, and a semiconductor layer is formed on the active layer. After forming the above electrode, a groove for element isolation is formed, and thereafter, a resonator surface is formed by etching.

According to a second aspect of the present invention, in the method of manufacturing a semiconductor laser device, an angle formed between the groove surface and the substrate surface on the light emitting surface side of the groove for element division is an acute angle.

According to a third aspect of the present invention, in the semiconductor laser device in which the cavity end face and the element dividing surface are located on different straight lines, the element dividing surface is located outside the light emission angle, and the semiconductor laser element is activated. It is characterized in that the layer is located at a position not affected by crystal defects from the element dividing plane.

According to a fourth aspect of the present invention, in the semiconductor laser device including the substrate and the semiconductor laminated structure on the substrate, the distance between the active layer end face and the element dividing surface is at least 4 μm, and H / tan θ (H is the resonance The height, θ, from the etching bottom surface to the active layer for producing the container is not more than a half-value width at which the light intensity becomes 1 / e ² ).

A semiconductor laser device according to a fifth aspect is characterized in that the semiconductor laser device is a nitride-based semiconductor laser device.

According to a sixth aspect of the present invention, there is provided a semiconductor laser device manufactured by the method of the first or second aspect.

Here, the angle between the groove surface and the substrate surface is an angle from the back surface of the substrate to the groove surface in a counterclockwise direction.

According to the present invention, there is provided a compound semiconductor laser device comprising a substrate and a laminated structure provided on the substrate, wherein the compound semiconductor laser device is formed between an end face of a resonator formed by etching and an element dividing surface. The length of the region on the side from which the laser light is extracted out of the pair of terrace-shaped regions where the etched bottom surface is exposed is made sufficiently short so that the optical path of the emitted laser light is not interrupted and the far-field image is disturbed. In addition, by making the crystal defects generated near the division plane at the time of element division propagate sufficiently near the active layer and making the element long enough not to affect the life of the element, that is, for example, a gallium nitride-based In the case of a compound semiconductor laser device, when the height from the etching bottom surface to the active layer is 3 μm, it is achieved by setting the height to 4 μm or more and 8 μm or less.

In such an element, a groove is formed by means such as a half die from the front surface side of the substrate before forming the resonator end face by etching, so that an exposure mask for forming the resonator can be aligned. By determining the position of the mask with respect to the end of the groove, it can be produced with good reproducibility.

The operation of the present invention is as follows. In the compound semiconductor laser device of the present invention, when a laser beam is emitted, a cavity formed between an end face of a cavity formed by etching and an end face of the element, a pair of terrace-shaped regions where an etched bottom surface is exposed, Since the length of the region on the light extraction side is sufficiently short, the laser light does not hit the etched bottom surface, causing no absorption or reflection, and a stable far-field image can be obtained. Further, since the length is sufficiently long, crystal defects generated in the vicinity of the division plane at the time of element division propagate to the vicinity of the active layer, and do not practically affect the life of the element.

[0024]

(Embodiment 1) A first embodiment of a compound semiconductor laser device according to the present invention will be described with reference to FIG. FIG. 1A schematically shows the semiconductor laser device of this embodiment. On the other hand, FIG.
FIG. 1C shows the semiconductor laser device of the present embodiment,
FIG. 3 is a diagram schematically illustrating a cross section when viewed from a direction A and a direction B indicated by arrows.

As shown in FIG. 1A, this semiconductor laser device is provided with a sapphire substrate 1, a semiconductor laminated structure 100 provided on the substrate, and a current (drive current) required for light emission. And a pair of electrodes 10 and 11.

This semiconductor multilayer structure 100 is shown in FIG.
As shown in the above, in order from the side close to the sapphire substrate 1,
n-type GaN buffer layer (4.0 μm thick) 40, n-type A
1 _0.1 Ga _0.9 N cladding layer (thickness 0.7 μm) 41, non-doped In _0.32 Ga _0.68 N active layer (thickness 40 °) 4
2. Mg-doped Al _0.1 Ga _0.9 N clad layer (thickness:
7 μm) 43 and a Mg-doped GaN contact layer (0.5 μm thickness) 44. Mg-doped Ga
The p-side electrode 10 is formed on the upper surface of the N-contact layer 44, and the n-side electrode 11 is formed on the partially exposed n-type GaN buffer layer 40. As shown in FIG.
The length La of the terrace region on the side from which the laser light is extracted is 5 μm.
m, the height Ha from the terrace region to the active layer 42 in the semiconductor multilayer structure 100 is 3.0 μm.

Hereinafter, a method for manufacturing the semiconductor laser device of FIG. 1 will be described with reference to FIGS. First, an organic metal compound vapor deposition method (MOCVD method) is used as shown in FIG.
As shown in (1), a semiconductor multilayer structure 100 is formed on a sapphire substrate 1. Next, after removing the substrate 1 from the MOCVD apparatus, thermal annealing at 800 ° C. is performed in an N ₂ atmosphere, thereby changing the Mg-doped layer to p-type. Next, after a photoresist is applied, a p-side electrode is formed by photolithography, as shown in FIG.
The photoresist 2 is patterned as shown in FIG. Next, the p-side electrode 10 is formed by a lift-off method as shown in FIG. 2C, a mask is formed by photolithography, and etching is performed to form one of the p-side electrodes 10 as shown in FIG. Remove the part.

Next, as shown in FIG. 3E, a groove 5a for element division reaching the substrate 1 is formed by half dicing perpendicular to the direction in which the p-side electrode 10 extends. Next, FIG.
As shown in (f), by photolithography,
A resist mask 3 for forming a resonator is formed on the semiconductor multilayer structure 100. At this time, when aligning the exposure mask for forming the resonator, a desired La, here 5
.mu.m, the difference between the design dimension of La and the actual finished dimension is different from that in the case where dicing is performed after the formation of the resonator end face, as in the conventional case. Significantly smaller, at most ± 1μ
m.

Thereafter, as shown in FIG. 4G, portions not covered with the resist mask 3 are selectively etched by dry etching. At this time, the etching is stopped when it is removed to 3.0 μm below the non-doped In _0.32 Ga _0.68 N active layer 42. The etching can be performed by, for example, RIE using Cl ₂ . Thereafter, as shown in FIG. 4H, the resist mask 3 is removed by using an appropriate etchant, for example, an organic solvent. Next, also by the photolithography method, as shown in FIG.
A resist mask 4 for forming a mesa stripe is formed. Thereafter, as shown in FIG. 5J, the resist mask 4 for forming the mesa stripe is formed by dry etching.
The portions not covered with are selectively etched. At this time, the etching is stopped when the n-type GaN buffer layer 40 is partially removed. The etching in this case can also be performed by, for example, RIE using Cl ₂ . Next, as shown in FIG. 5 (k), the resist mask 4 for forming the mesa stripe is removed, and as in the case of the p-side electrode 10, a photolithographic method and a lift-off method are used to form the resist mask 4 shown in FIG. As described above, the n-side electrode 11 is formed. Next, the back surface is polished to reduce the thickness of the substrate to about 200 μm.
Then, full dicing is performed from the layered structure 100 side to obtain a bar in which a plurality of elements are continuously connected in the direction in which the electrodes extend, as shown in FIG. Finally, FIG. 6 (n)
As described above, the substrate is broken at the groove 5a by the half dicing to obtain individual elements.

According to the method of this embodiment, at the time of alignment of the resist mask for forming the resonator, the position can be determined so as to obtain a desired La with respect to the end of the groove formed by dicing. The difference between the designed dimensions and the actual finished dimensions can be greatly reduced as compared with the case where dicing is performed after the formation of the resonator end face as in the related art. Therefore, the desired length of La
Semiconductor laser having good reproducibility can be produced. In addition, the nitride semiconductor laser device fabricated in such a manner showed a practically no problem level of reliability in various reliability tests.

In this embodiment, the etching depth at the time of forming the cavity end face is set to be 3.0 μm below the non-doped In _0.32 Ga _0.68 N active layer 42 so that a part of the n-type GaN buffer layer 40 remains. However, there is no problem if the etching is performed until the substrate is reached. In addition, although the mask at the time of etching is SiO ₂ , there is no problem with a photoresist mask or a metal mask. In addition, in order to form a groove for element division extending perpendicular to the direction in which the p-side electrode 10 extends, a groove can be formed from the front surface side of the substrate by, for example, blasting or a focused ion beam method (FIB) without dicing. Any method that can sufficiently secure the precision of the pitch of the groove to be formed can be applied without any problem.

In the first embodiment described above, the dicer blade at the time of dicing is inserted perpendicular to the substrate surface. However, the dicer blade is inclined with respect to the substrate surface.
It is possible to produce a nitride semiconductor laser device without providing any terrace-shaped region on the side from which laser light is extracted and without any practical problem in reliability. This is the second
An example will be described.

(Embodiment 2) A second embodiment of the compound semiconductor laser device according to the present invention will be described with reference to FIG. FIG. 7A schematically shows the semiconductor laser device of this embodiment. On the other hand, FIGS. 7B and 7C are cross-sectional views of the semiconductor laser device of the present example viewed from the directions A and B indicated by arrows in FIG. 7A, respectively. FIG.

As shown in FIG. 7A, this semiconductor laser device supplies a sapphire substrate 1, a semiconductor laminated structure 200 provided on the substrate 1, and a current (drive current) required for light emission. And a pair of electrodes 10 and 11.

The semiconductor multilayer structure 200 has an n-type GaN buffer layer (8.0 μm in thickness) 50 and an n-type A1 _0.1 Ga _0.9 N cladding layer (0.3 μm in thickness) in order from the side close to the sapphire substrate 1. 51, non-doped In _0.32 Ga _0.68
N active layer (thickness 30 °) 52, Mg-doped Al _0.1 Ga
_0.9 N clad layer (thickness: 0.3 μm) 53 and Mg
A doped GaN contact layer (3.0 μm thick) 54 is included.

A p-side electrode 10 is formed on the upper surface of the Mg-doped GaN contact layer 54, and a partially exposed n-type GaN
The n-side electrode 11 is formed on the buffer layer 50.

The terrace-shaped region is not provided on the laser light extraction side of the pair of resonator end faces, but is provided only on the other resonator end face side. The element dividing surface is not perpendicular to the substrate but is inclined at an angle of 45 degrees as shown in FIG. 7C. It is provided in such a direction as to protrude in the light emitting direction.

Hereinafter, a method of manufacturing the semiconductor laser device of FIG. 7 will be described. In the manufacturing method of the present embodiment, the first embodiment
The major difference is that the portion corresponding to FIG. 2E is not vertical in the groove for dividing the element as shown in FIG. First, the semiconductor multilayer structure 200 and the p-side electrode 10 are formed on the substrate in the same manner as in the first embodiment. So far,
This is the same as FIG. 2A to FIG. 3D in the first embodiment.

Next, as shown in FIG. 8E, a groove 5b for element division reaching the substrate 1 is formed by half dicing perpendicular to the direction in which the p-side electrode 10 extends. At this time, as shown in the figure, dicing is performed by inclining the teeth of the dicer so that the angle formed between the cavity end face formed by etching and the groove 5b is an acute angle, here 45 degrees.

Next, as shown in FIG. 8F, a resist mask 3 for forming a resonator is formed on the semiconductor multilayer structure 200 by photolithography. in this case,
At the time of alignment, the distance from the end of the groove 5b for element division formed by dicing to the end face of the resist mask 3 for forming a resonator is set to 10 μm. Thereafter, as shown in FIG. 8G, portions not covered with the resist mask 3 are selectively etched by dry etching. At this time, non-doped In _0.32 Ga _0.68
The etching is stopped when it has been removed to 7.0 μm below the N active layer 52. Etching is performed, for example, with Cl
₂ can be performed by RIE. Thereafter, individual elements are manufactured through the same steps as those in FIGS. 4H to 6N of the first embodiment.

As shown in FIG. 7, the compound semiconductor laser device thus manufactured has no terrace-shaped region on the side where the laser beam is taken out, so that the emitted light is not blocked and the device division surface As shown in FIG. 9, the distance from to the active layer is 5 μm even at the closest part.
Since the gap was at least μm, the generated crystal defects did not propagate to the active layer, and thus did not cause deterioration in reliability.

According to the method of this embodiment, at the time of aligning the resist mask for forming the resonator, the position of the mask can be determined with respect to the end of the groove formed by dicing. The difference from the dimensions can be greatly reduced as compared with the case where dicing is performed after the formation of the resonator end face as in the conventional case. Therefore, a semiconductor laser having a desired positional relationship between the active layer and the element dividing plane can be produced with good reproducibility.
Also, unlike the case of the first embodiment, the teeth are inclined at the time of half dicing, and the distance from the end of the groove formed by dicing to the resist mask for resonator formation, and the etching depth below the active layer By properly adjusting the thickness of the active layer, a terrace-shaped region cannot be formed on the laser light extraction side, and at the same time, defects introduced into the crystal during dicing do not affect the active layer. It is possible to increase the distance from the element dividing surface. The method used to form the groove for element division is not limited to dicing. For example, it is possible to form the groove with an inclination from the front surface side of the substrate, such as blast or FIB. Any method can be applied as long as it is a method that can sufficiently secure the accuracy of the above.

Although the angle at which the teeth are inserted at the time of the half die is set at 45 degrees, as shown in FIG. 9, it is possible to form a structure in which the distance from the element dividing surface to the active layer can be secured to 4 μm or more. For example, it is not limited to 45 degrees.

(Embodiment 3) In Embodiment 2 described above, the terrace-shaped region is provided only on the side of the pair of resonator end faces which is not the laser light extraction side. However, as shown in FIG. 10, even if a terrace-shaped region is provided also on the end face of the resonator on the side where the laser light is taken out, if it is designed so that the problem that the laser light hits and reflects on the terrace-shaped region does not occur. Of course, there is no problem.

Although the three embodiments have been described above, the substrate constituting the gallium nitride based compound semiconductor laser device of the present invention is not limited to those described here. That is, besides sapphire, for example, 6
H-SiC, GaN, ZnO, GaN, MgAl
₂ O ₄ , GaAs, LiAlO ₂ , LiGaO _{2 and the} like are also possible.

Although a metal organic chemical vapor deposition (MOCVD) method was used as a method for forming the laminated structure, there is no problem with other atom controlled growth methods such as MBE and HVPE.

Further, in the etching at the time of forming the cavity end face, the depth is set to be halfway of the n-type GaN buffer layer, but there is no problem if the etching is performed until the end face reaches the substrate. Although the mask is used as a mask when forming the cavity end face or when forming the mesa stripe, there is no problem with using a dielectric mask or a metal mask.

[0048]

According to the present invention, there is no disturbance of the far-field image caused by the laser beam hitting and reflecting on the etching bottom surface, and defects introduced into the semiconductor crystal when forming the element dividing grooves. However, while the device is being driven, it gradually propagates to the vicinity of the active layer, and does not adversely affect the reliability of the device such as an increase in threshold current density and a decrease in external differential quantum efficiency.
In addition, a large number of semiconductor laser devices having such a structure can be manufactured with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a first embodiment of a gallium nitride based compound semiconductor light emitting device of the present invention.

FIG. 2 is a process sectional view illustrating a method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

3 is a process sectional view illustrating the method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

FIG. 4 is a process sectional view illustrating the method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

FIG. 5 is a process sectional view illustrating the method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

6 is a process sectional view illustrating the method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

FIG. 7 is a schematic sectional view of a gallium nitride based compound semiconductor light emitting device according to a second embodiment of the present invention.

8 is a process sectional view illustrating the method for manufacturing the gallium nitride-based compound semiconductor light emitting device of FIG.

9 is a schematic cross-sectional view of the gallium nitride based compound semiconductor light emitting device of FIG.

FIG. 10 is a schematic sectional view of a gallium nitride based compound semiconductor light emitting device according to a third embodiment of the present invention.

FIG. 11 is a schematic sectional view of a conventional semiconductor laser.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 photoresist 3 resonator forming resist mask 4 mesa stripe forming resist mask 5a, 5b element dividing groove 10 p-side electrode 11 n-side electrode 30 resonator end face 31 element end face 32a, 32b terrace-shaped Region 33 Active layer 40, 50 n-type GaN buffer layer 41, 51 n-type AlGaN cladding layer 42, 52 non-doped InGaN active layer 43, 53 Mg-doped AIGaN clad layer 44, 54 Mg-doped GaN contact layer 100, 200 Semiconductor laminated structure

Claims (6)

[Claims] In a method of manufacturing a semiconductor laser device for manufacturing a resonator by etching, a semiconductor layer is stacked on a substrate, an electrode on an active layer is formed, a groove for element isolation is formed, A method for manufacturing a semiconductor laser device, wherein a resonator surface is formed by etching. 2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the groove for element division has an acute angle between the groove surface and the substrate surface on the light emitting surface side. 3. A semiconductor laser device in which an end face of a resonator and an element dividing plane are located on different straight lines, wherein the element dividing plane is located outside the light emission angle and the active layer is formed of a crystal defect from the element dividing plane. A semiconductor laser device, which is located at a position not affected by the above. 4. In a semiconductor laser device including a substrate and a semiconductor laminated structure on the substrate, a distance between an end surface of the active layer and an element dividing surface is 4 μm or more, and H / tan θ (H is a distance from an etching bottom surface for manufacturing a resonator to an active layer. Up to θ, the light intensity is 1
/ E ² ) or less. 5. The semiconductor laser device according to claim 4, wherein said semiconductor laser device is a nitride-based semiconductor laser device. 6. A semiconductor laser device manufactured by the manufacturing method according to claim 1.