JP2685818B2 - Semiconductor laser device - Google Patents

Description

The present invention relates to a semiconductor laser device using an InGaAlP-based semiconductor material, and more particularly to an internal current confinement type semiconductor laser device.

(Prior art) In recent years, chemical vapor deposition (hereinafter referred to as MOCV)
D method), it is possible to form InGaAlP on a GaAs substrate, and a visible light semiconductor laser using this technology has been attracting attention. InGaAlP materials are GaA
s Has the largest bandgap among III-V group mixed crystal semiconductors (excluding nitrides) under the condition of lattice matching with s substrate, 580 nm
It has the possibility of emitting light or lasing in the range of (yellow) to 690 nm (red).

FIG. 9 is a sectional view showing a conventional structure of an internal current confinement type semiconductor laser using the MOCVD method, in which 11 is an n-GaAs substrate, 12 is an n-GaAs buffer layer, 13 is an n-InGaAlP cladding layer, 14 is an InGaP active layer, 15 is a p-InGaAlP clad layer,
17 is an n-GaAs current blocking layer, 18 is a p-GaAs contact layer,
Reference numeral 19 is a stripe-shaped opening, 21 is a p-side electrode, and 22 is an n-side electrode. This laser is the first to the current blocking layer 17
This is achieved by using the MOCVD method for the second crystal growth and the second crystal growth of the contact layer 18 after forming the stripe-shaped opening 19. Then, the reverse injection by the current blocking layer 17 narrows the current injected into the double hetero structure portion in a stripe shape, thereby enabling laser oscillation.

However, this type of semiconductor laser has the following problems. That is, when the laser element is attached to the submount or the stem, the p-side-down method with the p-side electrode facing down is performed. At this time, the fusion material that fuses the laser element to the submount or the stem rises up on the side surface of the laser element, contacts the double hetero structure portion, and causes a problem of shorting the element. As a countermeasure against this, the thickness of the fusion material is reduced to reduce the rise of the fusion material.

The thickness of the contact layer is made thicker than the height at which the fusion material rises.

It is possible. However, if the thickness of the fusion material is reduced, the laser element may peel off. If the contact layer is too thick, the series resistance and thermal resistance of the laser element will increase, and the element characteristics will deteriorate.

(Problems to be solved by the invention) Conventionally, in order to prevent a short circuit of the laser element due to the rise of the fusion material, it is better to increase the thickness of the contact layer. However, the series resistance and thermal resistance of the laser element should be increased. It is better to reduce the thickness of the contact layer to reduce
There was a trade-off between them.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent a short circuit of a laser element without deteriorating element characteristics, and to provide a semiconductor with high yield and excellent reliability. It is to provide a laser device.

[Structure of the Invention] (Means for Solving the Problem) The gist of the present invention is to prevent deterioration of device characteristics and occurrence of short circuit by optimizing the film thickness of the contact layer.

That is, the present invention relates to a first conductivity type semiconductor substrate and a first conductivity type first substrate made of In _1-XY Ga _X Al _Y P (0 ≦ x <1,0 ≦ y <1) on the semiconductor substrate. A double heterojunction part formed by sequentially laminating a clad layer, an active layer, and a second clad layer of the second conductivity type, and a second heterojunction part formed on the double heterojunction part and partially provided with a stripe-shaped opening. 1 conductivity type Ga
In a semiconductor laser device comprising an As current blocking layer and a second conductivity type GaAs contact layer formed in the current blocking layer and an opening of the current blocking layer, the thickness of the current blocking layer is 0.5 μm or more. ， Set the impurity concentration to 1 × 10 ¹⁸ or more,
The thickness of the contact layer on the current blocking layer is 3.
The thickness is set to 3 to 3.7 μm.

(Operation) According to the present invention, it is possible to prevent deterioration of element characteristics and occurrence of short circuit by optimizing the film thickness of the contact layer. However, the range of the optimum film thickness is determined by the inventors of the present invention described below. It has been clarified by experiments and earnest research.

FIG. 4 shows a cross section in the vicinity of the current constriction portion. A GaAs current blocking layer 17 having a partial opening is formed on the uppermost portion (eg, clad layer) of the double hetero structure, and a GaAs contact layer is further formed thereon. 18 are formed. Current blocking layer 17
The opening width W is generally 5 to 7 μm, and the film thickness M is 0.5 to
0.7 μm, the impurity concentration is 1 × 10 ¹⁸ to 2 × 10 ¹⁸ cm ⁻³ . Here, the film thickness and impurity concentration of the current blocking layer 17 are determined by the breakdown voltage required for the current blocking layer 17, and this breakdown voltage may be made larger than the operating voltage of the laser (2.4 to 3 V). The M may be 0.5 μm or more and the impurity concentration may be 1 × 10 ¹⁸ cm ⁻³ or more. However, from the viewpoint of manufacturing, it is preferable that the film thickness is thin and the impurity concentration is low. Therefore, the upper limit of the film thickness M is set to 0.7 μm, and the upper limit of the impurity concentration is set to 2 × 10 ¹⁸ cm ⁻³ where doping is easy.

The inventors of the present invention have changed the film thickness of the contact layer 18 with the conditions regarding the current blocking layer 17 set as described above,
We investigated flatness characteristics, short-circuit characteristics, and operating temperature characteristics.
The results are shown in FIGS. 5 to 8.

FIG. 5 is a characteristic diagram showing changes in flatness with respect to film thickness. Here, the flatness is defined by the size of the step formed on the surface of the contact layer 18. The flatness 1 has almost no step, and the flatness 0 has the step substantially equal to the film thickness of the current blocking layer 17. It is in a state. When the film thickness L of the contact layer 18 is smaller than 3.3 μm, the flatness is deteriorated, and a concave portion reflecting the concave portion of the base is formed on the surface of the contact layer 18 as shown in FIG. 6 (a). When the film thickness L is 3.3 μm or more, the flatness is good and the surface of the contact layer 18 becomes substantially flat as shown in FIG. 6 (b). Further, as shown in FIG. 7, the short-circuit rate when the laser element is fused is substantially zero when the film thickness L is 3.3 μm or more, and the short-circuit rate rises when the film thickness L is smaller than 3.3 μm, and is 50 when the film thickness 2.5 μm. The short-circuit rate was over%.

On the other hand, the film thickness of the contact layer is also related to the maximum operating temperature of the laser device. That is, as the film thickness L of the contact layer 18 increases, the thermal resistance and series resistance of the element increase, and the element temperature, especially the temperature of the active layer 14, tends to increase. Then, when the temperature of the active layer 14 becomes higher than a certain value, the laser oscillation stops. FIG. 8 is a characteristic diagram showing changes in the maximum operating temperature of the laser element with respect to the film thickness L of the contact layer 18. When the film thickness L is 3.7 μm or less, the maximum operating temperature T _MAX is approximately constant 8
Although 0 ° C. can be obtained, when the film thickness L exceeds 3.7 μm, the operating temperature T _MAX gradually decreases.

Therefore, by defining the film thickness L of the contact layer 18 in the range of 3.3 to 3.7 μm, it is possible to flatten the contact layer 18 and prevent a short circuit due to the fusion material, and further prevent the maximum operating temperature from decreasing. It becomes possible to do.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser device according to an embodiment of the present invention. In the figure, 11 is an n-GaAs substrate, on which the n-GaAs buffer layer 12, thickness
0.6 μm n-In _0.5 Ga _0.15 Al _0.35 P first cladding layer 13,
In _0.5 Ga _0.25 Al _0.25 P active layer 14 with a thickness of 0.1 μm, thickness 0.6 μ
m p-In _0.5 Ga _0.15 Al _0.35 P second cladding layer 15, thickness 0.
A 05 μm p-InGaP cap layer 16 is formed. A 0.7 μm thick n-GaAs current blocking layer 17 having a stripe-shaped opening formed on the cap layer 16 and a 3.5 μm thick p-G
The aAs contact layer 18 is formed. Then, an AuZn film 21 which is a P-type electrode is deposited on the contact layer 18, and an AuGe film 22 which is an N-type electrode is deposited on the back surface of the substrate 11.

Next, regarding the method of manufacturing the semiconductor laser having the above structure,
This will be described with reference to FIG.

First, as shown in FIG. 2 (a), on the n-GaAs substrate 11
By the MOCVD method, n-GaAs buffer layer 12, n-InGaAlP clad layer 13, InGaAlP active layer 14, p-InGaAlP clad layer 15, p
The -InGaP cap layer 16 and the n-GaAs block layer (current blocking layer) 17 are continuously grown with the above-mentioned thickness and composition.
The growth temperature in the first crystal growth step was set at 700 ° C. in order to obtain good crystallinity of the double hetero junction (12, 16).

Then, using a photolithography technique, FIG.
As shown in, a stripe-shaped groove 19 is formed in the current blocking layer 17. At this time, n-GaAs is completely etched in the stripe portion, and p-InGaP is exposed on the surface.

Next, the processed substrate having the structure shown in FIG. 2 (b) is placed in the crystal growth furnace, and the p-GaAs contact layer 18 is grown by MOCVD as shown in FIG. 2 (c). In the second crystal growth step, dimethylzinc (DMZ) and PH ₃ which are impurity raw materials are allowed to flow in the growth furnace before the start of the growth of the regrown contact layer (before the temperature is raised) to grow the regrown layer. Raise to the growth temperature. The growth temperature of the regrown layer is the first
The temperature was set to 600 ° C., which was 100 ° C. lower than the growth temperature of the double heterojunction in the crystal growth step of the second time. The supply amount of DMZ was set to be the same as the supply amount of DMZ when p-InGaP was grown in the first crystal growth step.

After that, by depositing the electrodes 21 and 22 on the substrate side and the contact layer side, respectively, the internal current confinement type semiconductor laser having the structure shown in FIG. 1 is completed.

When current is injected into the laser element thus formed,
Due to the pn inversion layer formed by the n-GaAs current blocking layer 17, the injection current is limited to the current constriction portion. For this reason, light emission occurs in the active layer 14 substantially along the current constriction portion, and laser oscillation is also obtained. This laser device is mounted by a p-side-down method with the p-side electrode 21 facing down on a stem on which In having a thickness of 3 μm is vapor-deposited. In this case, the p-GaAs contact layer 18 is 3.5μ
Since it is thick as m, there is no problem that the fusion material rises and the laser element is short-circuited. Further, by setting the growth time of the p-GaAs contact layer 18 to within 2 hours and the growth temperature to 650 ° C. or lower, it is possible to suppress the diffusion of Zn into the n-GaAs current blocking layer 17 and to obtain good device characteristics. can get.

The present invention is not limited to the above-described embodiments. For example, the cap layer 16 formed on the double hetero junction is not always necessary and may be omitted. Further, as shown in FIGS. 3A and 3B, the cap layer 16 or the second cladding layer 15 exposed in the stripe-shaped opening 19 is ion-implanted with an impurity of the same conductivity type as that of the cladding layer 15 to diffuse the impurities. Region 31 may be formed to reduce the series resistance between contact layer 18 and the double heterojunction. Further, as shown in FIGS. 3C and 3D, a stripe-shaped recess 39 may be provided in the current blocking layer 17 instead of the opening 19 provided in the current blocking layer 17. In this case, the current blocking layer 17 in the recess 39 is ion-implanted with an impurity of the same conductivity type as that of the second cladding layer to provide the impurity diffusion region 31, so that the current is confined in a stripe shape.

Although Zn is used as the p-type impurity in the examples, a group III element such as magnesium or cadmium may be used instead. Further, the device structure is not limited to those shown in FIGS. 1 and 3, but can be applied to a device in which a regrowth layer needs to be formed after forming a double heterojunction portion.
In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, by setting the thickness of the contact layer in the range of 3.3 to 3.7 μm, it is possible to prevent the occurrence of a short circuit due to the rise of the fusion material. It is possible to realize a semiconductor laser device having high yield and excellent reliability because the increase in thermal resistance and series resistance can be suppressed to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a sectional view showing a manufacturing process of the laser of the above embodiment, and FIG. 4 is a sectional view for explaining a modified example, FIGS. 4 to 8 are diagrams for explaining the basic principle of the present invention, and FIG. 9 is a sectional view showing a conventional structure. 11 ... n-GaAs substrate, 12 ... n-GaAs buffer layer, 13 ...
... n-InGaAlP clad layer, 14 ... InGaAlP active layer, 15 ...
... p-InGaAlP clad layer, 16 ... p-InGaP cap layer, 17 ... n-GaAs current blocking layer, 18 ... p-GaAs contact layer, 19 ... aperture, 21, 22 ... electrodes.

Claims (3)

(57) [Claims] 1. A first conductivity type semiconductor substrate, and a first conductivity type first substrate made of In _1-XY Ga _X Al _Y P (0 ≦ x <1,0 ≦ y <1) on the semiconductor substrate. A double heterojunction part formed by sequentially laminating a clad layer, an active layer, and a second clad layer of the second conductivity type, and a second heterojunction part formed on the double heterojunction part and partially provided with a stripe-shaped opening. A semiconductor laser device comprising a GaAs current blocking layer of one conductivity type and a GaAs contact layer of a second conductivity type formed in the current blocking layer and an opening of the current blocking layer, wherein the thickness of the current blocking layer 0.5 μm or more, impurity concentration 1
A semiconductor laser device, wherein the thickness of the contact layer on the current blocking layer is set to 3.3 to 3.7 μm, and the thickness is set to × 10 ¹⁸ cm ⁻³ or more. 2. A first conductivity type semiconductor substrate, and a first conductivity type first substrate made of In _1-XY Ga _X Al _Y P (0 ≦ x <1,0 ≦ y <1) on the semiconductor substrate. A double heterojunction formed by sequentially laminating a clad layer, an active layer, and a second clad layer of the second conductivity type, and a second conductivity type In _1-Z Ga _Z formed on the double heterojunction part. A cap layer made of P (0 ≦ z <1), a GaAs current blocking layer of the first conductivity type having a stripe-shaped opening formed in a part of the cap layer,
In a semiconductor laser device comprising this current blocking layer and a GaAs contact layer of the second conductivity type formed in the opening of the current blocking layer, the current blocking layer has a film thickness of 0.5 μm or more and an impurity concentration of 1
A semiconductor laser device, wherein the thickness of the contact layer on the current blocking layer is set to 3.3 to 3.7 μm, and the thickness is set to × 10 ¹⁸ cm ⁻³ or more. 3. A semiconductor laser device according to claim 1, wherein the current blocking layer has a thickness of 0.7 μm or less and an impurity concentration of 2 × 10 ¹⁸ cm ⁻³ or less.