JPH0156522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device, and more particularly to a buried heterostructure semiconductor laser device.

A fiber optic communication system consists of an optical fiber, a light source,
With remarkable progress in the development of optical receivers and various optical circuit components, they are rapidly entering the stage of practical application. In particular, in the combination of an optical fiber and a light source, a silica glass single mode optical fiber (SMF) has a transmission loss of 0.5 dB/
Km and ultra-low loss, and In _1-x Ga _x As _1-y P _y /
Since the emission wavelength of a laser diode (LD) made of InP-based mixed crystal is approximately 1.1 to 1.7 μm, In _1-x Ga _x As _1-y P _y /InP-based LD and silica glass-based SMF In combination, it has become possible to construct a long-distance, large-capacity optical fiber transmission system that can transmit data over 50 km without repeating.

As a light source for optical fiber transmission systems, laser diodes have characteristics such as small size, high efficiency, and direct modulation. High performance is required, including threshold current, fundamental transverse mode oscillation with high optical output, and the ability to operate at high temperatures. Semiconductor lasers with various structures have been manufactured to meet these requirements, but in particular, buried heterostructure semiconductor lasers (BHLDs) have a structure in which both the carrier and light are completely confined in the active layer. It is known that it exhibits good characteristics suitable as a light source for optical fiber communication systems because of its low oscillation threshold current, high temperature operation capability, and isotropic output beam.

Method 1 of manufacturing a buried heterostructure semiconductor laser
As one example, a device and manufacturing method using an InGaAsP-based mixed crystal material, which has an oscillation wavelength of about 1.1 to 1.7 μm and covers almost the entire low-loss wavelength region of a silica glass optical fiber, has been described (Hirao et al. Electronic Materials, Vol. 18, No. 12, pp. 58-61, published December 1, 1979). This BHLD has excellent characteristics, such as an oscillation wavelength of 1.3 μm, a low minimum oscillation threshold current of 20 mA, and the ability to operate at temperatures of about 50°C. However, as will be explained in detail later, in this type of BHLD, it is necessary to form a reverse mesa etching, which requires high-order If an attempt is made to narrow the active layer stripe width to 1 to 2 μm in order to suppress mode excitation, there is a drawback that if the active layer is deep, the accuracy of the width of the active layer stripe of the optical waveguide and the linearity in the length direction will be impaired. occured.

It is therefore an object of the present invention to alleviate the difficulties in manufacturing conventional BHLDs.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, the present invention provides a method for manufacturing a semiconductor laser device that does not require formation of reverse mesa etching.

According to the present invention, firstly, n made of InP
A first epitaxial growth step of stacking an n-conductivity type semiconductor layer including at least an InGaAsP active layer on a conductivity-type semiconductor substrate, and a step of stacking an n-conductivity type semiconductor layer including at least an InGaAsP active layer on a conductivity type semiconductor substrate, and a step of stacking an n-conductivity type semiconductor layer including at least an InGaAsP active layer, using a mask stripe from the epitaxial surface side to form at least a layer larger than the active layer. a step of forming a band-like mesa structure by performing deep mesa etching, and a second step of laminating a p-conductivity type current blocking layer covering the side surfaces of the band-shaped mesa structure and an n-conductivity type semiconductor layer on the current blocking layer.
an epitaxial growth step, a step of removing the mask stripe, and a third epitaxial growth step of forming at least one p-conductivity type semiconductor layer covering the surface of the band-shaped mesa structure. There is obtained a method for manufacturing a semiconductor light emitting device characterized by comprising:

Note that in the above, in the first epitaxial growth step, when the surface layer is a semiconductor layer laminated on the active layer and having a refractive index smaller than the refractive index of the active layer and larger than the refractive index of the semiconductor substrate; , that is, when the surface layer is a waveguide layer, a practically extremely effective BHLD is provided.

According to the above configuration, the active layer stripe width can be formed with a desired width with good reproducibility, the final epitaxial plane can be easily flattened, and the p-type
Although it is possible to increase the impurity concentration of the InGaAsP electrode formation layer, it requires two buried growth steps during the manufacturing process, so there is room for improvement.

In the present invention, we have further discovered a method in which the buried growth process can be completed in one step by properly oriented the surface of the substrate.

That is, according to the second aspect of the present invention, InP has a principal plane orientation of (001) and a cleavage plane orientation of (110).
A first epitaxial growth step in which a plurality of semiconductor layers including an n-conductivity buffer layer and an InGaAsP active layer thereon are laminated on an n-conductivity type semiconductor substrate composed of forming a band-like mesa structure by performing mesa etching at least deeper than the active layer using a stripe; removing the mask stripe; A second epitaxial growth step of laminating semiconductor layers both of n-conductivity type and then laminating a semiconductor layer of at least p-conductivity type to cover the surface of the band-shaped mesa structure. A method for manufacturing the device is obtained.

Note that in the above, in the first epitaxial growth step, when the surface layer is a semiconductor layer laminated on the active layer and having a refractive index smaller than the refractive index of the active layer and larger than the refractive index of the semiconductor substrate; , that is, when the surface layer is a waveguide layer,
In practice, a highly effective BHLD is provided.

According to the above manufacturing method, in addition to the first invention, the buried growth can be performed only once, so that an extremely excellent BHLD can be provided.

Next, a detailed description will be given with reference to the drawings.

FIG. 1 shows a perspective view of a BHLD produced by a conventional manufacturing method. This figure shows the configuration of the conventional device by Hirao et al. shown earlier.
is an n-type InP substrate whose main surface is (001), 2 is an n-type buffer layer, 3 is an InGaAsP active layer, and 4 is a p-type InP
Cladding layer, 5 is p-type InGaAsP cap layer, 6
is a p-type InGaAsP layer, 7 is an n-type InP current confinement layer,
8 is an n-type InGaAsP layer, 9 is a SiO ₂ film layer, 10 is a p-type
The side ohmic electrode and 10a indicate the n-side ohmic electrode layer, respectively. The orientation of the cleavage plane (front left in the figure) of this device is (110). This BHLD has an oscillation wavelength of 1.3 μm, a minimum oscillation threshold current of 20 mA, and can operate at temperatures of about 50°C, showing excellent characteristics.

However, in BHLD, there is generally a large difference in refractive index between the buried active layer 3 and the surrounding buffer layer 2, cladding layer 4, etc., and therefore high-order transverse modes are likely to be excited. In order to suppress the occurrence of this higher-order transverse mode, it is necessary to cut off the higher-order transverse mode by setting the stripe width of the active layer 3 to 1 to 2 μm, as described above. Hirao et al. used a special reverse mesa etching process to create an active layer with a width of 1 to 2 μm.
I am making InGaAsP BHLD, but the active layer 3
If the etching depth is several μm or more from the etched surface, mesa etching should be performed to accurately determine the stripe width of the active layer, which is also an optical waveguide, and to improve the linearity of the active layer stripe to reduce optical waveguide loss. Both are extremely difficult to do.

In addition, InGaAsP-based semiconductor lasers have poor temperature characteristics of the oscillation threshold current.
BHLD also introduces a p-type InP current blocking layer 6 to improve temperature characteristics. This p-type InP current blocking layer 6 needs to be epitaxially grown so that the surface of the blocking layer almost coincides with the active layer during buried growth, but a special epitaxial growth method is used to stack it on the side surface of the mesa shape. Therefore, it is difficult to control the thickness of the grown film.

As described above, BHLD is a light source suitable for optical fiber communication systems, but its drawback is that it is difficult to fabricate.

Next, we will explain the present invention, but before that, we will briefly explain the materials. InGaAsP-based materials are:
Compared to AlGaAs-based materials, Al is easily oxidized.
In, Ga, As, and P are not easily oxidized, and there are few cases of poor surface "wetting" caused by oxides or oxide films during epitaxial regrowth. Buried growth and selective epitaxial growth can be performed relatively easily, and even in the manufacture of buried heterostructure semiconductor lasers, the buried re-epitaxial growth process is no longer a factor that deteriorates the manufacturing yield. Therefore, the present invention improves the manufacturing yield of BHLD by first employing two buried growths.

Figure 2 shows InGaAsP/
This shows an example of the configuration of InP/BHLD. For components in FIG. 2 that are the same as in FIG. 1, the reference numerals in FIG. 1 plus 10 are used. Compared to the conventional BHLD shown in Figure 1,
There is no need to etch the p-type InP cladding layer 14 and the p-type InGaAsP cap layer 15 into an inverted mesa shape, and the epitaxial surface is similar to that shown in FIG.
It can be made flatter compared to BHLD.

FIG. 3 shows a diagram explaining the manufacturing method of the above-mentioned InGaAsP BHLD, and FIG.
N-type InP buffer layer 12 (Te doped, approximately 3μ thick)
The figure shows a state in which an InGaAsP active layer 13 (non-doped, approximately 0.2 μm thick) is laminated by ordinary liquid phase epitaxial growth (LPE) using a carbon slide board. The growth temperature of the active layer 13 is 630°C, and the cooling rate is 0.7°C/mm.
The composition of the active layer InGaAsP is adjusted so that the emission wavelength is 1.3 μm, and the lattice matching with the InP substrate 11 is Δa/a0.1%. Next, by CVD method
After depositing a SiO ₂ film with a thickness of approximately 3000 Å on the epitaxial growth surface, SiO ₂ stripes 21 with a width of 1 to 2 μm are formed using a conventional photolithography method.
form. Thereafter, mesa etching is performed to a depth of approximately 1 μm using Br-methyl alcohol. This state is shown in FIG. 3b.

Next, the first buried growth is performed. During buried growth, in order to avoid thermal etching of the substrate surface, approximately 100 ppm of PH ₃ gas was introduced into the H ₂ atmosphere to suppress thermal decomposition of InP on the substrate surface, and liquid phase epitaxial growth was performed. In the first buried growth, a p-type InP current blocking layer 16 (Zn-doped, about 1 μm thick near the active layer) and an n-type InP current confinement layer 17 (Sn-doped, about 1 μm thick near the active layer) were formed.
0.5 μm) are sequentially laminated. SiO ₂ stripe 21
acts as a mask, so p
The type InP layer 16 and the n-type InP layer 17 do not grow.
Further, the p-type InP layer 16 grows to completely cover the side surfaces of the mesa portion, and the n-type InP layer 17 grows to be higher than the active layer 13. This state is shown in FIG. 3c.

Next, before performing the second buried growth, SiO ₂
Stripe 21 is removed using a mixed buffer of HF and NH ₄ F. In the second buried growth, _PH3 gas was introduced and liquid phase epitaxial growth was performed to form a p-type
An InP cladding layer 14 (Zn doped, about 2 μm thick on the active layer) and a p-type InGaAsP cap layer 15 (Zn doped, about 0.5 μm thick) are laminated. The buried growth of these two layers completely smoothes the epitaxial growth surface. The above state is shown in FIG. 3d. After this, normal electrode formation processing is performed. That is, the third
As the p-side ohmic electrode 20 shown in the figure, Au-
Zn and Au- as the n-side ohmic electrode 20a.
Sn is heat-treated and alloyed in an H ₂ atmosphere to form an electrode.

In the above process, the active layer stripe width is completely determined by the width of the SiO ₂ stripe 21 and has good reproducibility, and recently, the manufacturing technology of high-density integrated circuits such as VLSI has progressed further.
It is relatively easy to form linear stripes with a width of about 1 to 2 μm, and this InGaAsP BHLD
Even by mesa-etching the active layer, good linear stripes with a width of 1 to 2 μm can be obtained. Also p
When growing the InP type blocking layer 16, the p-type
Since the InP film covers the side surfaces of the mesa part and is easy to grow epitaxially, the p-type InP blocking layer 1
It is easy to make the surface of No. 6 continuous with the surface of the active layer.

When fabricating the BHLD shown in FIG. 1, it is necessary to perform buried layer 8 and p-type InGaAsP cap layer 5 to a thickness that allows smooth connection between their surfaces, but in the process shown in FIG. is p-type
Since there is only an InGaAsP cap layer 15, the surface can be easily smoothed. Also p type
The InGaAsP cap layer 15 is a layer to facilitate the formation of an ohmic electrode, but unlike the BHLD manufacturing method shown in FIG.
Since the InGaAsP cap layer 15 is not kept at high temperature for a long time, the doped impurity Zn
Since there is little diffusion of Zn, the impurity concentration can be increased, and in particular, if Zn is diffused from the surface, it is possible to easily form an ohmic electrode without any other treatment.

Figure 4 shows the second BHLD produced by the manufacturing method of the present invention.
This is an example of the following. In the second example,
In addition to the first embodiment, it has a structure in which an optical waveguide layer 22 is laminated on the active layer 13, and everything else is the same as in the first embodiment. Optical waveguide layer 22
is smaller than the refractive index of the active layer 13, and the surrounding
Has a refractive index greater than that of InP
It is an InGaAsP semiconductor film. The thickness of the active layer 13
The thickness of the optical waveguide layer 22 is 0.3μ.
By making it about m, the light almost reaches the optical waveguide layer 22.
The waves are distributed within and guided. Therefore, the effective refractive index of the active layer becomes smaller, and the difference in refractive index between it and the surrounding InP becomes smaller, so the stripe width of the active layer for fundamental transverse mode oscillation can be made slightly wider, making manufacturing easier. becomes easier. Also, BHLD in Figure 4
Compared to the case of fabricating the BHLD shown in Figure 2, in the fabrication of BHLD, the surface of the active layer where carriers undergo radiative recombination is not exposed to the atmosphere during the fabrication process, so there is less risk of introducing defects. It has characteristics that can reduce this.

The above two examples each have their own characteristics, but as can be seen from the order of the steps, and as briefly mentioned at the beginning, they each have two buried growth steps. This leaves the drawback that the manufacturing process is complicated. Next, a manufacturing process to solve this problem will be described, but before describing an example, a brief explanation will be given of LPE growth when an InP film is epitaxially grown on an InP substrate with a plane orientation of (001).

Figure 5 shows an InP substrate with plane orientation (001) at a height of approximately
FIG. 3 is a diagram showing a case where InP is epitaxially grown on a 1.5 μm mask stripe formed using a cleavage plane (paper surface) with a plane orientation of (110).
For LPE growth, 60 mg of InP was added to 4 g of In at 650°C.
After being dissolved for a certain period of time, the temperature was lowered at a cooling rate of 0.7°C/min, and the substrate and solution were brought into contact with each other at 630°C to allow epitaxial growth for a predetermined period of time. growth in solution
This is a so-called two-phase solution method in which the InP crystals are not completely dissolved but float. Furthermore, in order to prevent thermal etching of the growth substrate, PH ₃ gas is introduced into the H ₂ atmosphere at a concentration of 100 ppm. In this case, as shown in FIG. 5, when the width of the mask stripe changes, the epitaxial growth pattern changes. When the stripe width is relatively wide, such as 50 μm, epitaxial growth occurs both at the periphery and above the mask stripe, regardless of the length of the growth time. However, if the stripe width is relatively narrow, such as 2 μm, epitaxial growth will not occur on the top of the mask stripe if the growth time is short. Only when the growth time is increased and the thickness of the InP epitaxial film at the periphery of the mask stripe becomes thick enough to exceed the height of the mask stripe will the top of the mask stripe be covered and the recess at the top of the mask stripe be formed. Epitaxial growth occurs as if embedding.

As described above, when embedding a mesa shape with a narrow stripe width, if the plane direction of the cleavage plane is (110), epitaxial growth will not occur on the upper part of the mask stripe, but will grow on the periphery and side surface of the mask stripe. In this example, by using such an epitaxial growth technique, it is possible to epitaxially grow an InP film without performing the two buried growth steps as in the first or second example. This makes it possible to complete the process with just one buried growth process. Needless to say, even if the cleavage plane has a (110) orientation, the SiO ₂ stripes 21 are provided and the buried growth is performed 2 times as in the first or second embodiment.
It may be divided into times.

Figure 6 shows In _1-x Ga _x As _1-y produced by the production method of the present invention.
This shows a third example of P _y /InP·BHLD. In this case, the plane orientation of the cleavage plane is selected to be (110). An n-type buffer layer 32 and an InGaAsP active layer 33 are formed on a substrate 31 with a plane orientation (001), and after this active layer 33 is mesa-etched with a stripe width of about 1.5 μm, a p-type InP current cladding layer is formed. 34, p-type InP current confinement blocking layer 3
6 and an n-type InP current confinement layer 37. Also, as the epitaxial final layer, a p-type In _1-x Ga _x As _1-y P _y electrode forming layer 35 is used.
are laminated to reduce the electrode resistance of the ohmic electrode 38 using Au--Zn. n-type
On the InP substrate side, an n-side ohmic electrode 39 is formed using Au-Sn.

Figure 7 shows the above In _1-x Ga _x As _1-y P _y /InP.
FIG. 3 is a diagram showing a method for manufacturing BHLD. Figure 7 a is n
InP type substrate 31 (Sn doped, plane orientation (001)),
n-type InP buffer layer 32 (Te doped, approximately 3μ thick)
The figure shows a state in which the active layer 33 (non-doped, about 0.2 μm thick) and In _{1-x Ga} x _{As 1-y} P _y is laminated by a normal liquid phase epitaxial growth method using a carbon slide board. There is. The growth temperature of the active layer 33 is 630°C, and the cooling rate is 0.7°C/mm. active layer
The composition of In _1-x Ga _x As _1-y P _y 33 has an emission wavelength of 1.3 μm
The lattice matching with the InP substrate is Δa/a0.1%. Next, a photoresist stripe 41 with a width of 1 to 2 μm is formed using the usual photolithography method, and then using this as a mask, Br-methyl alcohol is used to form a stripe 41 of photoresist.
Mesa-etch to a depth of 1 μm. This state is shown in FIG. 7b.

Next, the stripe 41 is removed and buried growth is performed. During buried growth, approximately _PH3 gas is added to the _H2 atmosphere to avoid thermal etching of the substrate surface.
100ppm was introduced. In embedded growth, In4g
After melting 60 mg of InP at 650°C for 1 hour, the temperature was lowered at a cooling rate of 0.7°C/mm, and from 630°C, the p-type InP block layer 36 (Zn doped, approximately
0.5 μm), n-type InP current confinement layer 37 (Te doped, approximately 1 μm thick), and p-type InP cladding layer 34
(Zn-doped, approximately 4 μm thick) is sequentially grown epitaxially. In the above, when growing the p-type InP current confinement layer 36 and the n-type InP current confinement layer 37, although the mesa stripe 41 has already been removed, the orientation of the cleavage plane is selected to be (110). Therefore, epitaxial growth is not performed on the upper part after that. However, at this time, it is unavoidable that some level of surface unevenness occurs, but by laminating the next p-type InP cladding layer 34 relatively thickly, the layers are stacked in a shape that almost completely fills the unevenness of the substrate. Finally, p-type In _1-x Ga _x As _1-y P _y electrode forming layer 3
5 (Zn-doped, approximately 0.5 μm thick) is laminated to complete the buried growth process. This state is shown in FIG. 7c. After the epitaxial growth process, a p-side ohmic electrode and an n-side ohmic electrode (not shown) are formed using normal electrode formation techniques, and each LD chip is cut out by cleaving to manufacture a buried heterostructure semiconductor laser. finish.

As described above, in the method for manufacturing a buried heterostructure semiconductor laser according to this embodiment, only one buried growth step is required.

Figure 8 shows In _1-x Ga _x As _1-y produced by the production method of the present invention.
This shows a fourth embodiment of P/InP BHLD. This fourth embodiment has a structure in which an optical waveguide layer 50 is laminated on an active layer 43. The optical waveguide layer 50 has a refractive index smaller than that of the active layer 43 and larger than that of the surrounding InP (n-type current confinement layer 37 and p-type cladding layer 34).
It is an In _1-x Ga _x As _1-y P _y semiconductor film. By reducing the thickness of the active layer 43 to about 0.05 μm and the thickness of the optical waveguide layer 50 to about 0.3 μm, light is substantially distributed and guided within the optical waveguide layer 50. Therefore, the effective refractive index of the active layer becomes smaller, and the difference in refractive index between it and the surrounding InP becomes smaller, so the stripe width of the active layer for fundamental transverse mode oscillation can be made slightly wider, which makes manufacturing easier. becomes easier. Furthermore, according to this method, the surface of the active layer where the carriers undergo radiative recombination is not exposed to the atmosphere during the manufacturing process, so that the introduction of defects can be reduced.

The present invention can be modified in several ways in addition to the basic embodiment described above. First, semiconductor materials
Not limited to InGaAsP system, Al _x Ga _1-x As system, Al _x Ga _1-x
As _1-y Sb _y may also be used. Further, the p-type InP current blocking layer may be a p-type InGaAsP layer having a lower refractive index than the active layer and the optical waveguide layer. or,
The n-type InP current confinement layer may be a semi-insulating InP layer as long as it has the effect of confining current flow.

Finally, to enumerate the features of the present invention, active layer stripes can be easily produced, p-type InP
The blocking layer can be easily grown on the side surface of the active layer, the final growth surface is flat, p
It is possible to increase the impurity concentration of the InGaAsP cap layer, and it is easy to form an ohmic electrode. Moreover, the embedding operation in the third and fourth embodiments only needs to be performed once, thereby further simplifying the manufacturing process.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of a BHLD in a conventional manufacturing method, Fig. 2 is a perspective view showing an example of the configuration of a BHLD in an embodiment of the present invention, and Fig. 3 is a method for manufacturing the device shown in Fig. 2. FIG. 4 is a perspective view showing an example of the configuration of BHLD in the second embodiment of the present invention.
FIG. 5 is a diagram showing a state in which epitaxial growth is performed on a mask stripe formed on an InP substrate, and FIG. 6 is a perspective view showing an example of the configuration of a BHLD in the third embodiment of the present invention. , FIG. 7 shows the steps a to c for forming the device shown in FIG.
FIG. 8 is a perspective view showing an example of a BHLD in a fourth embodiment of the present invention. Symbol explanation: 11 is n-type InP with plane orientation (001)
The substrate, 12 is an n-type InP buffer layer, 13 is
InGaAsP active layer, 14 is p-type InP cladding layer, 1
5 is a p-type InGaAsP cap layer, 16 is a p-type InP current blocking layer, 17 is an n-type InP current confinement layer, 2
0 represents a p-side ohmic electrode, 20a represents an n-side ohmic electrode, 21 represents an SiO ₂ stripe, and 22 represents an optical waveguide layer.

Claims (1)

[Claims] 1. A first epitaxial growth step in which an n-conductivity type semiconductor layer including at least an InGaAsP active layer is laminated on an n-conductivity type semiconductor substrate made of InP, and an epitaxial surface side forming a band-like mesa structure by performing mesa etching at least deeper than the active layer using a mask stripe;
a second layer comprising: a p-conductivity type current blocking layer covering the side surface of the band-shaped mesa structure; and an n-conductivity type semiconductor layer on the current blocking layer such that the n-conductivity type semiconductor layer does not come into contact with the semiconductor substrate. an epitaxial growth step, a step of removing the mask stripe, and a third epitaxial growth step of forming at least one p-conductivity type semiconductor layer covering the surface of the band-shaped mesa structure. A method of manufacturing a semiconductor light emitting device, comprising: 2 The orientation of the principal plane is (001) and the orientation of the cleavage plane is (1
10), an n-conductivity type buffer layer and an n-conductivity type buffer layer on the n-conductivity type semiconductor substrate made of InP.
a first epitaxial growth step of stacking a plurality of semiconductor layers including an InGaAsP active layer; and a step of performing mesa etching at least deeper than the active layer using a mask stripe from the epitaxial surface side to form a band-shaped mesa structure. , removing the mask stripes, and forming a P conductivity type current blocking layer on the current blocking layer covering the side surfaces of the band-shaped mesa structure without epitaxially growing at least on the surface of the band-shaped mesa structure. After stacking an n-conductivity type semiconductor layer so that the n-conductivity type semiconductor layer does not contact the semiconductor substrate, a semiconductor layer having at least a p-conductivity type is stacked to cover the surface of the band-shaped mesa structure. 2. A method for manufacturing a semiconductor light emitting device, comprising: 2. an epitaxial growth step.