JPH01259589A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To provide a structure suitable for mass production by making an activated layer substantially flat at a region on a main groove near one end of a resonator and forming the thickness of the region near the end of the resonator thinner than that in the middle thereof. CONSTITUTION:An n-type GaAs layer which will serve as a current blocking layer 6 is grown on a p-type GaAs substrate 1. Then, V-shaped grooves are formed as a main stripe groove 2 and auxiliary stripe grooves 3 by means of photolithography and wet etching. On such a substrate, a first clad layer 5 composed of a p-type AlGaAs compound, an activated layer 4, a second clad layer 7 composed of an n-type AlGaAs compound, a cap layer 8 composed of an n-type GaAs compound to be made into electrodes and ohmic contacts are sequentially formed as laser operation layers. The thickness of the activated layer 4 on the main groove 2 is formed so that it can be thinner toward the ends of a resonator than the middle thereof. Accordingly, it is possible to prevent generation of defective thickness in the first clad layer, thereby improving the productivity of a high output semiconductor laser element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser device, and particularly to a semiconductor laser device capable of high output operation.

(Prior art) Conventionally, in order to increase the output power of semiconductor laser devices, dramatic destruction of the cavity facets (C, 0, D
:Catastrophe 0ptical Dam
In order to prevent this, the thickness of the active layer is reduced and light seeps into the cladding layer adjacent to the active layer, thereby reducing the optical density within the active layer and increasing the COD level. Laser elements are known.

However, in the case of an AJ2GaAs-based double heterostructure laser element, when the active layer thickness becomes approximately 0.05 μm or less, the required driving current tends to increase, and this is, for example, a constraint on actual crystal growth technology. This is due to an increase in light scattering loss caused by the uneven interface between the active layer and the cladding layer in contact with it.

Therefore, by setting the active layer thickness to about 0.05 μm or more near the center of the resonator, and configuring the active layer only near the end faces of the resonator to be thinner than the center of the resonator, it is possible to A structure that lowers the optical density of the resonator and prevents destruction of the resonator end face is generally known.

Furthermore, with such a structure, the optical density decreases in the thin region of the active layer near the cavity end face, and
Compared to the thicker part of the active layer in the center of the cavity, the injected carrier density is higher, so the gain spectrum shifts to shorter wavelengths, making it slightly transparent to the light generated in the center of the cavity. The so-called window effect can be expected to further increase the C, O, and D levels.

In this way, when realizing a structure in which the thickness of the active layer near the resonator end face is thinner than the layer thickness near the center of the resonator in a semiconductor laser with an internal stripe structure, the cross-sectional view shown in FIG. As shown, by providing sub-grooves 3 on both sides of the main stripe grooves 2 that contribute to light emission in a portion of the substrate crystal 1 corresponding to the vicinity of the cavity end face, the active layer 4 is curved downward within the sub-grooves 3. A structure has been proposed (Japanese Unexamined Patent Publication No. 49e).

This technique utilizes the following properties regarding the growth rate of liquid phase crystal growth.

■(The growth rate is slowest on the 100+ crystal plane, +111
+ Fastest on the crystal plane.

■Relationship between growth rate on a concave surface, growth rate on a flat surface, and growth rate on a convex surface.

From the above relationship, in FIG. 3, the active layer 4 grows on the downwardly curved surface in the sub-grooves 3, rather than on the upper surface of the first cladding 5 formed between the sub-grooves 3 and consisting of the (100) plane. Faster speed.

Therefore, As in the growth melt is quickly consumed inside the sub-groove 3, and As is diffused toward the sub-groove 3 from its surroundings.

As a result, in the range of As diffusion length around the sub-groove 3, A
The concentration of s is reduced, and the growth rate of the active layer 4 is suppressed. As is clear from this mechanism, the deeper the minor groove 3 is, the stronger the growth rate suppressing effect is, and the larger the cross-sectional area of the minor groove 3 is, the longer this effect lasts.

- In this structure, the shapes of the main groove 2 and the sub groove 3 are subject to the following restrictions.

(a) Under the conditions that the active layer 4 is flat on the main groove 2 and the active layer 4 hangs down into the sub-groove 3, the cross-sectional area of the main groove is equal to the cross-sectional area of the sub-groove.

(b) In order to obtain a strong growth rate suppressing effect, the active layer 4
is curved with a smaller radius of curvature. Therefore, the minor groove 3
make it deeper and narrower.

From the conditions (a) and (b) above, the relationship is that main groove depth ≦ minor groove depth, and in order to satisfy the condition that current flows in main groove 2 and does not flow in minor groove 3. In this case, the cross-sectional structure of the device as shown in FIG. 3 becomes inevitable.

In order to realize such a structure, as shown in FIG. 4(a), a groove 3a is formed in advance at a position corresponding to the sub-groove 3 of the substrate crystal 1, and then the current blocking layer 6 is formed into a flat and grooved shape. It is grown to a thickness of about 0.5 to 1 .mu.l in areas other than 3a (FIG. 4(b)). Then, the main groove 2 and the sub groove 3
(FIG. 4(c)), a final substrate is completed, and laser operating layers such as the first cladding layer 5, the active layer 4, the second cladding layer 7, and the cap layer are formed on this substrate.
Layers 8 are deposited in sequence.

(Problem to be Solved by the Invention) However, in order to grow a current blocking layer with a thickness of 1 μm or less flatly on a groove, it is necessary to rely on a liquid phase growth method which is inferior in mass production, and also requires liquid phase crystal growth. Since film thickness control using the growth method is inferior to that of vapor phase growth methods, etc., a decrease in yield is unavoidable, which poses a problem in mass production.

Further, in order to form the main groove and the sub-groove in accordance with the groove once filled with the current blocking layer, a mask alignment step is required twice, which increases the number of steps and causes a reduction in yield.

In addition, when performing LPE of the laser operating layer on the completed substrate, because the first cladding layer has a structure in which it hangs down in the sub-groove,
As shown in FIG. 5, a defect may occur in which the first cladding layer 5 is cut off at the edge 3b of the sub-groove 3. At this time, if the current blocking layer 6 is not made of an insulating crystal but uses a pn reverse junction, there is a problem in that it causes current leakage, which also causes a decrease in yield.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve manufacturing yield and provide a semiconductor laser device having a structure suitable for mass production.

[Structure of the Invention] (Means for Solving the Problems) A semiconductor laser element of the present invention includes a semiconductor substrate having a plane substantially coinciding with the f1001 crystal plane (in which a striped main groove is carved in the 1001 crystal direction; In this semiconductor laser device having a crystal layer for laser operation including an active layer formed on a semiconductor substrate, the active layer is formed in a substantially flat shape in a region above the main groove near the cavity end face, and
The region above the main groove is formed in a shape that protrudes toward the substrate side more than the other regions, and the layer thickness near the resonator end face is thinner than the layer thickness in the central region of the resonator. It is something to do.

(Function) By making the depth of the sub-stripe grooves shallower than the thickness of the current blocking layer, the steps of photolithography and groove etching before forming the current blocking layer become unnecessary. At the same time, since the current blocking layer is grown on a flat substrate crystal, M
It becomes possible to use methods such as OCVD. moreover,
Since the first cladding layer does not hang down into the sub-groove and forms a slope on the sub-groove, there is no need to worry about it being interrupted at the edge of the sub-groove. Since the active layer grows faster on the slope formed by the first cladding surface above the minor groove, As diffuses from above the main groove sandwiched between the two slopes, and as a result, the active layer on the main groove becomes thinner. As a result, the optical density within the active layer is reduced, and furthermore, the Windoν effect reduces optical absorption at the cavity end faces, making high-output operation possible.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Incidentally, the same parts as in FIG. 3 are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

FIG. 1(a) is a cross-sectional view of the laser device of the example near the cavity end face, FIG. 1(b) is a cross-sectional view of the central portion of the resonator, and FIG. 2 is a cross-sectional view of the semiconductor laser device of FIG. It is a figure for explaining a manufacturing process.

To fabricate the semiconductor laser device of this example, first, on a flat +1001 crystal plane p-type GaAs substrate (Zn-doped: carrier concentration lXl0 cab-') 1, an n-type GaAs layer of about 1 μm, which will become the current blocking layer 6, is deposited. (Te doped: 8xlOcm-') was grown as shown in Fig. 2(a).
Next, a V-shaped groove having a width of 3 μm and a depth of 1.3 μm, for example, is formed as the main stripe groove 2 by photolithography and wet etching (FIG. 2(b)).

Then, by the same method, a sub-stripe groove 3 having a width of 10 μl and a depth of 0.5 μl is formed (FIG. 2(C)).

At this time, since the sub-stripe grooves 3 are formed so as not to penetrate the current blocking layer 6, they do not contribute to light emission.

In this embodiment, the sub-groove 3-sub-groove 3 interval W is 20μ.
m, but the width and interval of the sub-grooves 3 are determined by the laser operating layer,
In particular, some adjustment is required depending on the LPE conditions of the first cladding layer.

On a substrate having the above parameters, a first cladding layer 5 consisting of p-type A f2 'GaO,350,65As, a p-type AJ2 GaO,0580,
Active layer 4 made of 944As, n-type AJ2 GaAs is O
A second cladding layer 7 made of 400,85 oxide and a cap layer 8 made of n-type GaAs for making ohmic contact with the electrode are grown in sequence.

Here, the thicknesses of the first cladding layer 6 and the active layer 4, which are important in terms of characteristics, are each 0.25 μm in the gain term region at the center of the cavity.
ttr s is 0.07 μm, and this value is equal to tel, t in FIG. 1(a), which is a cross-sectional view near the cavity end face.
Each corresponds closely to aa.

On the other hand, in the vicinity of the resonator end face, t a 1 =0.04 μm St c 2-0.
It was 15 μm. As a result, the relationships tcl > tC2 and ta2 > taa > tat were confirmed near the end faces, and the thickness of the active layer 4 on the main groove 2 was as follows compared to the central part of the resonator (Fig. 1(b)). We were able to create a structure in which the ends of the resonator are thinner.

P-side and n-side electrodes were formed on the thus produced multilayer structure wafer by a conventional method, and laser oscillation resonators were formed by cleavage and the wafer was divided into individual laser elements. This laser element has a diameter of 15 mm without end face coating.
A COD level of 0a+W or higher was recorded, and a high output operation of 1.5 to 2 times that of conventional high output laser elements was possible.

In this example, although no sub-groove is formed near the center of the resonator, the sub-groove-sub-groove interval W is widened near the center of the resonator.
Alternatively, it is clear that the same effect can be obtained by reducing the sub-groove volume near the center of the resonator.

Further, in the above-described embodiment, the sub-stripe grooves may be provided only on one side of the main stripe grooves, or a plurality of sub-stripe grooves may be formed on each of the left and right sides. Furthermore, it is also possible to realize this structure using materials other than GaA and eAs.

Further, the groove shape is not limited to the 7-shaped groove.

[Effects of the Invention] As explained above, according to the present invention, the structure is such that vapor phase growth can be used for crystal growth of the current blocking layer, which simplifies the process of forming the main stripe grooves and the substripe grooves. This makes it possible to prevent the occurrence of discontinuous defects in the first cladding layer, thereby improving the productivity of a high-power semiconductor laser device having an active layer that is thinner near the cavity end facets than at the cavity center.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of the vicinity of the cavity end face of a semiconductor laser device showing an embodiment of the present invention, FIG. 1(b) is a sectional view of the central part of the cavity, and FIG. Figure 3 is a cross-sectional view of a semiconductor laser element with a structure in which the active layer on the main groove is thinned by a conventional sub-groove, and Figure 4 is a diagram showing the substrate manufacturing process of the element, and Figure 4 is the substrate of the conventional semiconductor laser element shown in Figure 3. FIG. 5, which is a diagram showing the manufacturing process, is a diagram showing a growth failure of the first cladding layer in a conventional example. 1...Substrate crystal 2...Main groove 3...Sub-groove 4...Active layer 5...First cladding layer 6... ...Current blocking layer 7...Second cladding layer 8...Cap layer Applicant: Toshiba Corporation Patent attorney Satoshi Suyama - (a) 17th G3) (b) Figure 2 7 5, 22

Claims (1)

[Claims] A laser including a semiconductor substrate in which a striped main groove is carved in the {100} crystal direction in a plane that substantially coincides with the {100} crystal plane, and an active layer formed on the semiconductor substrate. In a semiconductor laser device having a crystal layer for operation, the active layer is formed in a substantially flat shape in a region above the main groove near the cavity end face, and in a region above the main groove closer to the substrate than other regions. 1. A semiconductor laser device, characterized in that it is formed in a protruding shape and configured such that the layer thickness near the end face of the resonator is thinner than the layer thickness in the central region of the resonator.