JPH0834334B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser device suitable for a light source for long-distance optical communication and a method for manufacturing the same, and more particularly to a semiconductor laser device that oscillates in a single transverse mode and is stable at a low current. The present invention relates to an operating semiconductor laser device and a manufacturing method thereof.

(Prior Art) A semiconductor laser device that oscillates in a wavelength region of 1 μm band (1.1 to 1.7 μm) has been actively studied as a light source for optical communication in the field of high-speed long-distance communication. This is because the propagation loss of the silica glass fiber for optical communication in this wavelength band is extremely low. In particular, a low-loss silica glass fiber using a high-purity material has no material dispersion in the wavelength range of 1.3 μm. Therefore, by using a semiconductor laser that emits a laser beam in this wavelength range, it is possible to achieve a high value exceeding 1 GHz · km. The cutoff frequency is obtained.

FIG. 5 shows a sectional view of a conventional semiconductor laser device used as a light source for 1.3 .mu.m band optical communication. This semiconductor laser device has an embedded double hetero structure.

As can be seen from FIG. 5, n-type In is formed on the semiconductor substrate 21.
P-clad layer 23, non-doped GaInAsP active layer 24, p-type InP
A mesa stripe-shaped multilayer film 31 having a double hetero structure in which the clad layer 25 is laminated in this order from the substrate 21 side is provided. Substrate in a region other than the region where the multilayer film 31 is provided
A buried layer in which the p-type InP current blocking layer 36 and the n-type InP current blocking layer 37 are stacked in this order from the substrate 21 side is provided on the 21. The embedded layer covers the side surface of the multilayer film 31. n-type InP current blocking layer 37 and p-type InP clad layer
On top of 25, p-type InP layer 38 and p-type GaInAsP contact layer
26 are stacked in this order from the substrate 21 side. p-type Ga
An AuZu electrode 28 is formed on the InAsP contact layer 26, and an AuGe electrode 29 is formed on the back surface of the substrate 21.

The semiconductor laser device shown in FIG. 5 is a multilayer film including the active layer 24.
31 sides are covered by a buried layer. For this,
Laser light that oscillates in a single transverse mode can be obtained. Also,
If a voltage is applied to the double heterostructure in the forward direction to oscillate laser light, it is provided in the buried layer.
A reverse bias is applied to the pn junction. Therefore, the reactive current flowing through the buried layer decreases, and the current concentrates in the multilayer film 31 and flows efficiently. Therefore, the oscillation threshold is lowered, and stable laser oscillation at low current is realized. However, the single transverse mode oscillation is realized, and the oscillation threshold (I
_th ) to a low value of about 20 mA or less, the active layer 24
It is necessary to set the width to about 1.5 μm to 2 μm.

Next, a conventional method of manufacturing the semiconductor laser device of FIG. 5 will be described.

First, the n-type InP clad layer 23, the non-doped GaInAsP active layer 24, and the p-type InP clad layer 25 are laminated in this order from the substrate 21 side on the semiconductor substrate 21 by the LPE method.

Next, an etching mask having a desired pattern is formed on the p-type InP clad layer 25 in order to form a portion in which the burying layer is buried in a later step, and then the p of the region not covered with the etching mask is formed. The type InP clad layer 25, the non-doped GaInAsP active layer 24, and the n-type InP clad layer 23 are etched. Thus, the InP clad layer 23, GaInAsP active layer
A mesa stripe-shaped multilayer film 31 including the InP clad layer 25 is formed on the substrate 21. The pattern of the etching mask at this time is important for determining the width of the active layer 24.

The p-type InP current blocking layer 36 and the n-type In layer are formed by LPE on the substrate 21 in the region where the InP clad layer 23, the GaInAsP active layer 24, and the InP clad layer 25 have been removed by the above etching.
The P current blocking layer 37 is laminated in this order from the substrate 21 side. At this time, the buried layer covers the side surface of the multilayer film 31, and moreover, the height of the interface (pn junction surface) between the p-type InP current blocking layer 36 and the n-type InP current blocking layer 37 is equal to that of the active layer 24. Try to match the height.

After removing the etching mask, the n-type InP current blocking layer 37
And the p-type InP layer 3 on the InP clad layer 25 by the LPE method.
8. The p-type GaInAsP contact layer 26 is laminated in this order from the substrate 21 side.

Then, an AuZu electrode 28 is formed on the p-type GaInAsP contact layer 26.
Then, an AuGe electrode 29 is formed on the back surface of the substrate 21.

(Problems to be Solved by the Invention) However, the above-described conventional technology has the following problems.

In order to form the active layer 24 having a predetermined width, a multi-layer film including the active layer 24 is formed on the entire surface of the substrate 21, and then a predetermined region of the multi-layer film is etched with high accuracy to obtain a multi-layer film having a predetermined width. film
A step of forming 31 is required. In order to stabilize the transverse mode of laser oscillation, it is necessary to control the deviation of the width of the active layer 24 from a predetermined value to about 0.1 μm or less. According to the above conventional technique, the multilayer film is formed by deeply etching a predetermined portion of the multilayer film formed on the entire surface of the wafer.
Since 31 is formed, it is difficult to accurately determine the width of the active layer 24 with such accuracy. Therefore, the width of the active layer 24 is greatly varied.

In addition, in order to reduce the reactive current, in the buried layer
The layer thickness of each layer must be controlled so that the height of the pn junction matches the height of the active layer. If a large deviation occurs between the height of the pn junction and the height of the active layer 24, the reactive current flowing through the buried layer without flowing through the active layer 24 increases. Therefore, the oscillation threshold of the semiconductor laser device becomes high.

Further, since a process such as an etching process is required between the crystal growing process for forming the double hetero structure and the crystal growing process for forming the buried layer, the process is complicated. Further, during the above crystal growth step, impurities may be mixed into the crystal layer from the atmosphere.

As described above, according to the conventional technique, a large number of semiconductor laser elements having deteriorated characteristics may be formed due to dimensional variations and the like generated during the manufacturing process.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a semiconductor laser device capable of controlling the width of an active layer with high accuracy and a method for manufacturing the same. is there.

Another object of the present invention is to provide a semiconductor laser device and a method for manufacturing the same, which does not require highly accurate control of the thickness of the buried layer.

(Means for Solving the Problems) A semiconductor laser device of the present invention includes a semiconductor substrate, a dielectric film formed on the semiconductor substrate, and a groove formed in the dielectric film and reaching the substrate. , A mesa-stripe-shaped laminated structure including an active layer provided on the substrate in the groove, and embedded layers provided on both side surfaces of the laminated structure, and the main surface of the substrate is (100 ) Plane, the groove is a groove along the <011> direction, the side surface of the laminated structure is a facet of the {111} plane, and the buried layer has a resistance higher than that of the laminated structure. Therefore, the above-mentioned purpose is achieved.

The manufacturing method of the present invention comprises a step of forming a dielectric film on a semiconductor substrate having a (100) plane as a main surface, and forming a groove along the <011> direction in the dielectric film so as to reach the substrate. And a step of selectively growing a mesa stripe-shaped laminated structure including an active layer only on the substrate in the groove,
Embedding the side surface of the laminated structure with a material having a higher resistance than that of the laminated structure, thereby achieving the above object.

(Example) Hereinafter, the present invention will be described with reference to Examples.

 FIG. 1 shows a sectional view of the first embodiment of the present invention.

An amorphous dielectric film (film thickness 0.2 to 0.5 μm) 2 made of a Si ₃ N ₄ film is provided on an n-type InP substrate 1 having a plane orientation (100). The dielectric film 2 is provided with a groove 10 having a width of 5 μm which reaches the substrate 1 along the [011] direction (resonator direction, perpendicular to the drawing). Since the groove 10 reaching the substrate 1 is provided in the dielectric film 2, a drive current flows between the electrodes via the groove 10.

On the substrate 1 in the groove 10, Si-doped n-type InP clad layer (layer thickness 2 μm, carrier concentration n to 1 × 10 ¹⁸ cm ⁻³ ) 3, non-doped GaInAsP active layer (layer thickness 0.15 μm, oscillation wavelength 1.3 μm).
m) 4, Zn-doped p-type InP clad layer (layer thickness 1 μm, carrier concentration p to 5 × 10 ¹⁷ cm ⁻³ ) 5, and Zn-doped p-type Ga
InAsP contact layer (layer thickness 0.1 μm, carrier concentration p ~ 1
A multi-layer film 11 having a mesa-stripe-shaped laminated structure in which × 10 ¹⁸ cm ⁻³ ) 6 are laminated in this order from the substrate 1 side is provided, and a double hetero structure is formed. Multilayer film 11
Is a (111) B plane, and the angle between the side and the surface of the substrate 1 is 54.7 degrees. Therefore, the width of the active layer 4 geometrically determined by this angle, the width of the groove 10 and the layer thickness of the p-type InP clad layer 3 is 2 μm.

An Fe-doped InP current blocking layer (resistivity 10 ⁵ Ω · cm or more) 7 having a higher resistance than the multilayer film 11 is provided as an embedded layer on the substrate 1 in the region other than the region where the multilayer film 11 is provided. It is provided so as to cover the side surface of the multilayer film 11.

An AuZn electrode 8 is provided on the high resistance InP current blocking layer and the p-type GaInAsP contact layer 6, and an AuGe electrode 9 is provided on the back surface of the substrate 1.
Are formed.

The semiconductor laser device according to the present embodiment has a mesa-stripe-shaped double hetero structure having side surfaces of (111) B-facet. The angle formed by the (111) B-facet and the surface of the substrate 1 is a crystallographically determined value (54.7 degrees). The mesa-stripe-shaped double hetero structure having the side surfaces of the (111) B-facet has the effect that it can be formed by selective growth using, for example, the MOCVD method, as described later.

Since the semiconductor laser device of the present embodiment is provided with the active layer 4 having a width having a small variation determined by this angle, the width of the groove 10 and the layer thickness of the n-type InP cladding layer 3, the oscillation transverse mode is stable. In addition, variations in characteristics between elements are reduced.

Further, since the buried layer is a high resistance layer and the dielectric layer 2 is provided between the buried layer and the substrate 1, the reactive current flowing through the buried layer is reduced.

Hereinafter, a method for manufacturing the semiconductor laser device shown in FIG. 1 will be described with reference to FIG.

First, a plasma is formed on the n-type InP substrate 1 having a plane orientation (100).
A dielectric film 2 made of a Si ₃ N ₄ film was formed by using the CVD method.
Next, a groove 10 having a width of 5 μm was formed in the dielectric film 2 along the [011] direction by a normal photo-etching process (FIG. 2 (a)). In addition, the depth of the groove 10 is equal to
The etching conditions were adjusted so that

Next, the multi-layer film 11 having the double terror structure was formed only on the substrate 1 in the groove 10 by selective growth using the MOCVD method (FIG. 2 (b)). At this time, crystal growth was prevented from occurring on the amorphous dielectric film 2. During crystal growth,
The n-type InP clad layer 3, the non-doped GaInAsP active layer 4, the p-type InP clad layer 5, and the p-type GaInAsP contact layer 6 were continuously grown in this order from the substrate 1 side by adjusting the gas species and the like. . At this time, the substrate temperature
The atmospheric pressure was maintained at 650 ° C and about 76 Torr. During this selective growth, there is a plane orientation dependence of the growth rate that crystal growth does not occur on the (111) B plane, and as a result, a (111) B plane facet is formed on the side surface of the multilayer film 11 after the growth. Was done. Thus, on the groove 10 along the [011] orientation, the multilayer film 11 having the upper surface which is the crystal growth surface as the (100) plane and the side surface along the groove 10 as the (111) B plane was formed.

Next, on the dielectric film 2 on which the multilayer film 11 was not grown,
The high resistance InP current blocking layer 7 was grown so as to cover the side surface of the multilayer film 11. During growth, the substrate temperature is about 550 ℃
The atmospheric pressure was maintained at 760 Torr (normal pressure). Under this growth condition, selective growth does not occur, so the multilayer film 11
Layers having almost the same thickness grew on both the top and the dielectric film 2 (FIG. 2 (c)). Since the dielectric film 2 is an amorphous film, the high resistance InP current blocking layer 7 grown thereon is
Is amorphous or polycrystalline.

The selective growth when the above-mentioned multilayer film is formed and the non-selective growth when the buried layer is formed are the temperature and the pressure in the same MOCVD device without taking out the wafer into the atmosphere. It was carried out continuously only by changing the growth conditions such as.

Next, after applying a polyimide resin PIQ (not shown) on the entire surface of the wafer, the polyimide resin PIQ and part of the high resistance InP current blocking layer 7 are etched back from the surface to the upper surface of the p-type GaInAsP contact layer 6. As a result, the wafer surface was flattened (FIG. 2 (d)).

Planarized high resistance InP current blocking layer 7 and p-type GaI
An AuZn electrode 8 was formed on the nAsP contact layer 6. Also,
An AuGe electrode 9 was formed on the back surface of the substrate 1 (FIG. 2 (e)). Thus, the semiconductor laser device of FIG. 1 was formed.

As described above, in this embodiment, the active layer 4 having a predetermined width is used.
In order to form the film with a high yield, the multi-layer film 11 including the active layer 4 was selectively grown on the groove 10 on the substrate 1 in the mesa stripe shape by the MOCVD method. Facets having a (111) B plane were formed on the side surfaces of the multilayer film 11 thus grown in a ridge shape. Since the angle formed by the (111) B-facet and the surface of the substrate 1 is a crystallographically determined value (54.7 degrees), the layer thickness of the n-type InP cladding layer 3 is adjusted with respect to the width of the groove 10. By doing so, the width of the active layer 4 could be controlled with high accuracy. Since the ridge-shaped multi-layered film 11 is formed in this manner, the step of deeply etching a predetermined portion of the multi-layered film formed on the entire surface of the wafer as in the conventional case is not necessary. For this reason, it was easy to suppress the deviation from this value to 0.1 μm or less, even though the design dimension of the width of the active layer 4 was about 2 μm. Therefore, the width of the active layer 4 can be controlled with good reproducibility, and the width of the active layer 4 is not greatly varied.

In addition, the above-mentioned selective growth and non-selective growth are carried out in the same MO.
Since the wafer was continuously processed in the CVD apparatus without being taken out into the atmosphere, the process was simplified and impurities were prevented from being mixed into the crystal layer from the atmosphere.

Further, since the high resistance InP current blocking layer 7 provided as the buried layer is a high resistance layer having no pn junction, it is not necessary to control the layer thickness with high accuracy. Therefore, the reactive current flowing through the buried layer does not increase due to the process variation, and the semiconductor laser device having a low oscillation threshold can be manufactured with high yield.

The second embodiment will be described below with reference to FIG.

In the second embodiment, the direction along the groove 10 is [01].

An amorphous dielectric film (film thickness 0.3 μm) 2 made of a Si ₃ N ₄ film is provided on an n-type InP substrate 1 having a plane orientation (100). The dielectric film 2 has a groove 1 with a width of 1.5 μm that reaches the substrate 1.
0 is provided along the [01] direction (resonator direction, perpendicular to the drawing). Since the direction along the groove 10 is [01], the angle formed by the (111) B plane, which is the side surface of the multilayer film 11 selectively growing in the groove 10, and the surface of the substrate 1 is crystallographically determined. It becomes a value (125.3 degrees). Therefore,
Unlike the case of the first embodiment, as shown in FIG.
In the second embodiment, the width of the active layer 4 is wider than the width of the groove 10. Also in this embodiment, the width of the active layer 4 can be controlled with high accuracy by adjusting the layer thickness of the n-type InP cladding layer 3 with respect to the width of the groove 10. Therefore, the same effect as that of the first embodiment can be obtained.

The third embodiment will be described below with reference to FIG. In the third embodiment, the steps up to the step of forming the multi-layer film 11 having the double hetero structure are the same as the steps of the first embodiment, so the steps after the step of forming the buried layer will be described.

In producing the third embodiment, after the multi-layer film 11 is formed by selective growth, the buried layer is formed on the substrate 1 in the region where the multi-layer film 11 is not formed by the same method as in the first embodiment. As a result, the high resistance InP current blocking layer 7 is grown so as to cover the side surface of the multilayer film 11. At this time, one of the differences from the first embodiment is that the layer thickness of the high resistance InP current blocking layer 7 is made smaller than the film thickness of the multilayer film 11.

After forming the high resistance InP current blocking layer 7, the high resistance InP is formed.
Ion implantation of p-type impurities is performed on a portion of the current block layer 7 located on the p-type GaInAsP contact layer 6. As a result, only that portion is a low resistance p-type diffusion layer.
Let's say 13.

Next, the SOG film 14 is formed on the wafer to flatten the wafer surface, and then the SOG film 14 is etched back from the surface to expose the surface of the p-type diffusion layer 13.

Finally, the AuZn electrode 8 is formed on the p-type diffusion layer 13 and the SOG film 14, and the AuGe electrode 9 is formed on the back surface of the substrate 1.

According to the semiconductor laser device of the present embodiment, it is possible to achieve stable single transverse mode oscillation with a low current, as in the other embodiments.

In this embodiment, the example in which the planarization is performed by using the SOG coating method and the etch back method together has been described.
It may be performed only by the coating method.

Further, as a method for forming the p-type diffusion layer 13, other doping method may be used in addition to the ion implantation method.

Although the GaInAsP-based semiconductor material is used in any of the above-described embodiments, the same effect can be obtained by using other materials such as AlGaAs-based and InGaAlP-based semiconductor materials.
Regarding the conductivity type of the semiconductor, the conductivity type of the embodiment may be reversed.

In the above embodiment, the direction along the groove is [011].
The case of [01] and the case of [01] have been described.
Other crystallographically equivalent directions indicated by 1> may be used.

(Effect of the Invention) As described above, the semiconductor laser device of the present invention has the mesa-stripe double hetero structure having the {111} face side surface and has the active layer whose width is adjusted to a desired value with high precision. As a result, the oscillation transverse mode is stable, and variations in characteristics between elements are reduced. Further, since the buried layer is a high resistance layer and the dielectric layer is provided between the buried layer and the substrate, the reactive current flowing through the buried layer is reduced and the oscillation threshold is reduced. .

According to the manufacturing method of the present invention, the active layer width can be controlled with good reproducibility and high resolution by selectively growing a double heterostructure multilayer film having a {111} face side surface in a groove on a substrate. . Therefore, there is no large variation in the active layer width. Therefore, a semiconductor laser device having an active layer of a predetermined width and stably operating in a single transverse mode can be formed with a high yield.

Further, the layer growth step for forming the double hetero structure and the layer growth step for forming the buried layer are continuously performed in the same device without performing an etching step between those steps. It can be carried out. For this reason, the process is simplified and impurities are suppressed from being mixed into the growth layer from the air atmosphere.

Further, it is not necessary to control the layer thickness of the buried layer with high precision,
Therefore, it is possible to manufacture a semiconductor laser device having a low oscillation threshold with a high yield without increasing the reactive current flowing through the buried layer due to the process variation in forming the buried layer.

Therefore, according to the present invention, it is possible to provide a semiconductor laser device that performs single transverse mode oscillation with a low current and is particularly suitable for a light source for long-distance optical communication with high yield.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIGS. 2 (a) to 2 (e) are sectional views for explaining a manufacturing method of the first embodiment, and FIG. 4 is a sectional view showing an embodiment of
FIG. 5 is a sectional view showing a third embodiment, and FIG. 5 is a sectional view showing a conventional example. 1 ... n-type InP substrate, 2 ... dielectric film, 3 ... n-type InP cladding layer, 4 ... non-doped GaInAsP active layer, 5 ... p
Type InP clad layer, 6 ... p type GaInAsP contact layer, 7
...... High resistance InP current blocking layer, 8 ...... AuZn electrode, 9 ...
… AuGe electrode, 10 …… groove, 11 …… multilayer film, 13 …… p-type diffusion layer, 14 …… SOG film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Okumura 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. Incorporated (72) Inventor Haruhisa Takiguchi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Co., Ltd. (56) Reference JP-A 1-239984 (JP, A) JP-A-62-244186 (JP) , A) JP-A-63-73690 (JP, A)

Claims (2)

[Claims] 1. A semiconductor substrate, a dielectric film formed on the semiconductor substrate, a groove formed in the dielectric film to reach the substrate, and provided in the groove on the substrate. A mesa stripe-shaped laminated structure including an active layer and buried layers provided on both side surfaces of the laminated structure, the main surface of the substrate being a (100) surface, and the groove being in a <011> direction. A semiconductor laser device in which the side surface of the laminated structure is a {111} facet and the buried layer has a resistance higher than that of the laminated structure. 2. A step of forming a dielectric film on a semiconductor substrate having a (100) plane as a main surface, and a step of forming a groove along the <011> direction on the dielectric film so as to reach the substrate. And a step of selectively growing a mesa-stripe-shaped laminated structure including an active layer only on the substrate in the groove, and a step of embedding a side portion of the laminated structure with a material having a higher resistance than the laminated structure. And a method for manufacturing a semiconductor laser device including: