JPS6248917B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multi-wavelength integrated semiconductor light emitting device in which a plurality of buried heterostructure semiconductor lasers having different emission wavelengths are integrated on the same substrate.

Recently, the OH content of silica glass optical fiber has been reduced, and the OH absorption loss peak in the wavelength band of 1.25 μm and 1.40 μm is no longer observed, and from the wavelength of 1.1 μm
It has become possible to obtain a low-loss optical fiber with a transmission loss of 0.5 dB/Km over a wide band of 1.6 μm. Along with this, the importance of optical fiber wavelength division multiplexing transmission systems, which can construct long-distance, large-capacity transmission systems by effectively utilizing the transmittable wavelength range, has become increasingly important. As a light source for an optical fiber wavelength division multiplexing transmission system, a multi-wavelength integrated semiconductor light emitting device, in which multiple semiconductor lasers with different emission wavelengths are configured on the same substrate, has a compact light source shape, low cost, stable performance, and reliability. It has advantages such as improved performance, and is a useful element for further improving the performance of wavelength division multiplexing transmission systems. The inventor of the present application has invented a multi-wavelength integrated semiconductor light emitting device as described in Japanese Patent Application No. 55-61671 and filed. As shown in FIG. 1, this multi-wavelength integrated semiconductor light emitting device includes a plurality of InGaAsP layers 3-1 to 3-3 with different forbidden bands.
is used as the active layer, and multiple semiconductor lasers with arbitrary wavelengths from 1.1 μm to 1.6 μm can be integrated.The structure of the semiconductor laser is a buried heterostructure, which allows room temperature CW oscillation at a low oscillation current threshold, and isotropic It has characteristics such as an output beam and stable single fundamental transverse mode oscillation. However, the manufacturing process of the multi-wavelength integrated semiconductor light emitting device shown in FIG. phase epitaxial growth (hereinafter referred to as
A total of three LPE processes are required: a second LPE process to form a current confinement layer after mesa etching, and a third LPE process to embed the entire structure. The process is long,
The disadvantage was that it required more man-hours.

The present invention provides a method for manufacturing a multi-wavelength integrated semiconductor light emitting device that eliminates the above drawbacks, reduces the number of liquid phase epitaxial steps, and shortens the overall manufacturing process.

The method for manufacturing a multi-wavelength integrated semiconductor light emitting device of the present invention includes epitaxially growing a plurality of semiconductor layers including at least two active layers having mutually different forbidden band widths and not in contact with each other on a semiconductor substrate. a first epitaxial growth step for forming a semiconductor stack; an etching step of forming a stepped semiconductor stack by sequentially etching at different depths in one direction, and etching a layer in a direction perpendicular to the one direction on the surface of each step of the stepped semiconductor stack; forming a stripe mask on the substrate and etching the surface portion of the at least two active layers from the surface portion where the stripe mask is not formed until portions corresponding to the surface portions of the at least two active layers are respectively removed to form at least two band-like mesa structures; a mesa etching step to form a semiconductor layer of the opposite conductivity type to the semiconductor substrate and a semiconductor layer of the same conductivity type as the semiconductor substrate except for the upper surfaces of the at least two band-shaped mesa stripes after removing the stripe mask. The method includes a second epitaxial growth step in which, after successive lamination, semiconductor layers of the opposite conductivity type to the semiconductor substrate are connected and laminated over the entire surface.

In the method for manufacturing a multi-wavelength integrated semiconductor light emitting device of the present invention, between the etching step of forming the stepped semiconductor laminate and the step of forming the stripe mask, the stepped surface portion is etched. The semiconductor substrate may be configured by adding an impurity diffusion step for inverting at least a portion above each active layer to a conductivity type opposite to that of the semiconductor substrate.

In the above two methods of manufacturing multi-wavelength integrated semiconductor light emitting devices, the semiconductor substrate has a plane orientation (001).
Using an InP substrate, the active layer is In _1-x GaxAsyP _1-y
It is preferable that a layer (0<x<1, 0<y≦1) is used, and the one direction is the <110> direction.

The basics of the present invention will be explained first, and then embodiments of the present invention will be explained.

First, the basics of the present invention will be explained by forming a mesa stripe extending in the <110> direction formed on an InP substrate with a plane orientation of (001) and filling it with an InP layer using a liquid phase epitaxial growth method to form a stacked layer shape. The case will be explained using FIGS. 2a to 2c as an example.

First, as shown in Figure 2a, the surface orientation (100)
A mesa stripe 13 having a mesa upper width of about 1.5 μm and a mesa depth of about 2 μm is formed on the InP substrate 12 .

Next, as shown in Figure 2b, InP polycrystalline In
Dissolution temperature into solution is 610℃, cooling rate is 0.7
The temperature is lowered at a rate of °C/min, and an InP layer is deposited on the mesa substrate in a two-phase solution state from a temperature of 600 °C. In this case, if the growth layer thickness is made relatively thin, each 0.6
P-type InP layer 14, n-type InP layer 1 with a film thickness of about μm
Even if two layers of No. 5 are laminated, they will not be laminated on the upper surface of the mesa. This is considered to be because the growth of the InP layer on the side surfaces of the mesa is rapid, and the P concentration in the In solution in contact with the substrate decreases around the side surfaces of the mesa, particularly on the top surface of the mesa.

As shown in Fig. 2c, if the thickness of the InP layer is increased, it will gradually be deposited on the upper surface of the mesa, and the whole will be almost flat with the p-type InP layer 16 having a thickness of about 3 μm in the flat areas other than the mesa area. buried in As will be described later, the buried shape shown in Figure 2c has a structure in which current flows concentrated only in the mesa portion, and a buried heterostructure semiconductor laser can be fabricated in one buried LPE process. It has a convenient shape that allows for The present invention utilizes the layer shape formed by LPE growth on the mesa substrate described above.

Next, examples of the present invention will be described.

FIGS. 3a to 3d are perspective views of the manufacturing process for explaining one embodiment of the present invention.

First, as shown in FIG.
(Te doped, about 5 μm thick) and InGaAsP first active layer 3-1 (λ=1.2 μm, non-doped, 0.2 μm thick)
μm), n-type InP first intermediate layer 4-1 (Te doped,
thickness 0.5 μm), InGaAsP second active layer 3-2 (λ=
1.3 μm, non-doped, 0.2 μm thick), n-type InP second intermediate layer 4-2 (Te doped, 0.5 μm thick),
A multilayer film wafer is formed by sequentially laminating InGaAsP third active layer 3-3 (λ=1.55 μm, non-doped, thickness 0.2 μm). Growth temperature is 630℃, cooling rate is
0.7℃/min. The lattice matching between each InGaAsP active layer and InP layer is Δa/a0.1%.

Next, as shown in FIG. 3b, the multilayer film wafer is coated with a photoresist mask so that each of the first to third active layers 3-1, 3-2, and 3-3 of InGaAsP is separated at intervals of 200 μm. , InGaAsP first active layer 3-
1. InGaAsP second active layer 3-2, InGaAsP third
The epitaxial surface is etched with a selective etching solution to repeatedly expose the surface of active layer 3-3. At this time, the direction perpendicular to the repetition direction is selected to be <110>.

Next, as shown in FIG.
was repeatedly exposed on the surface at intervals of 200 μm.
InGaAsP first to third active layers 3-1, 3-
2 and 3-3, and then using this as a mask, mesa etching is performed to a depth of about 2 μm using Br-methyl alcohol to form first, second and third mesa stripes 18-1. ,18-2,
A mesa substrate in which 18-3 is repeatedly formed is created.

Next, as shown in FIG. 3d, after the photoresist used as an etching mask is peeled off, a second LPE process is performed. This LPE process is the second
It is performed under the same conditions as the LPE growth shown in the figure. That is, p
InP type current blocking layer 5 (Zn doped, thickness at flat part 0.6 μm) and n type InP current confinement layer 6
(Te-doped, 0.6 μm thick at the flat part) is not laminated on the top surface of the mesa stripe, but is laminated continuously on the other parts, and then the p-type InP buried layer 7
(Zn-doped, 3 μm thick at the flat part) is continuously laminated over the entire surface, and finally an n-type InGaAsP electrode forming layer 8 (Te-doped, 0.5 μm thick) is laminated to create a multi-wavelength structure wafer. finish.

The above steps are the first example according to the present invention, and it can be seen that the number of LPE steps is two, which is fewer than the conventional three LPE steps.

FIG. 4 is a perspective view of a multi-wavelength integrated semiconductor light emitting device manufactured using the manufacturing method of the first embodiment.

The multi-wavelength structured wafer obtained by the manufacturing method of the first embodiment is coated with p-type film with a width of 10 μm using the SiO ₂ CVD film 10 as a selective diffusion mask.
First, second, and third selective Zn diffusion layers 9-1, 9-2, and 9-3 with a depth reaching the InP buried layer 7 are formed, and then an Au-Ge-Ni ohmic electrode is formed on the n side. 11a, on the p side, the first to third Au-Zn ohmic electrodes 11-1, 11-2, 11-3 are formed separately, and the (110) plane is a Fabry-Perot resonator. A multi-wavelength integrated semiconductor light emitting device is manufactured by cleaving it into a vessel surface.
From the left side of the paper in Figure 4, the emission wavelength is 1.2μm and 1.3μm.
It has a structure in which three buried heterostructure semiconductor lasers with a diameter of 1.5 μm and 1.5 μm are formed on the same substrate, and because the p-side electrodes are separated from each other, they can be driven independently. Emission wavelength 1.3
Taking a μm laser as an example, the second p-side electrode 11-
When a bias voltage is applied with 2 being positive and the n-side electrode 11a being negative, the portion of the InGaAsP second active layer 3-2 becomes
This is a forward bias of the pn junction, and radiative recombination occurs. Underneath the InGaAsP second active layer 3-2
Since no pn junction is formed in the InGaAsP first active layer 3-1, radiative recombination does not occur. In addition, the parts other than the InGaAsP second active layer 3-2 are
It is a pnpn junction, exhibiting negative resistance characteristics, and almost no current flows below the turn-on voltage. Therefore, the current flows concentratedly in the InGaAsP second active layer 3-2. Furthermore, since the InGaAsP second active layer 3-2 is surrounded by an InP layer with a large forbidden band width, there is little carrier leakage, and a low oscillation current threshold of about 20 mA at room temperature was obtained. Furthermore, the oscillation transverse mode is a single fundamental mode oscillation,
Even if the injection current is increased to about five times the threshold value, the shape of the transverse mode does not change. The current blocking layer 5 and the current confinement layer 6 are formed by forming the InGaAsP first active layer 3 at high temperature.
The increase in leakage current flowing through the InP pn junction around -1 is suppressed, and as a result, continuous oscillation is possible up to about 100°C. Emission wavelength 1.3μm, 1.5μm
The laser also exhibits characteristics similar to the above-mentioned laser with an emission wavelength of 1.2 μm.

FIGS. 5a to 5e are cross-sectional views showing main manufacturing steps for explaining the second embodiment of the present invention.

The difference from the first example is that the InGaAsP active layer formed in the first LPE process is not exposed to the surface.

As shown in FIG. 5a, an n-type InP third intermediate layer 4-3 (Te
A doped layer (0.5 μm thick) is deposited in the first LPE process to cover the InGaAsP active layer so as not to expose it.

Next, as shown in FIG. 5b, using a photoresist as a mask on this multilayer film wafer, the n-type InP first intermediate layer 4-1, the n-type InP second intermediate layer 4-1, and the n-type InP second
The epitaxial surface is etched using a selective etching solution so that the intermediate layer 4-2 and the n-type InP third intermediate layer 4-3 are repeatedly exposed. The orientation of the repetition is the same as in the first embodiment.

Next, as shown in FIG. 5c, the first to third intermediate layers 4-1, 4- of n-type InP exposed from the surface are
The conductivity types of layers 2 and 4-3 are inverted to first, second and third cladding layers 19-1, 19-2 and 19-3 of p-type InP.

Next, as shown in FIG. 5d, mesa etching is performed to form a mesa substrate.

Next, as shown in Figure 5e, the second LPE
A process is performed to fill the mesa substrate with an InP layer and form a multi-wavelength structured wafer.

The above steps are similar to those in the first embodiment, but by not exposing the InGaAsP active layer to the surface, there is a risk of mechanical or thermal damage to the InGaAsP active layer during the manufacturing process. 1st
This is smaller than in the case of the embodiment.

FIG. 6 is a perspective view of a multi-wavelength integrated semiconductor light emitting device manufactured using the manufacturing method of the second embodiment.

The difference from the multi-wavelength integrated semiconductor light emitting device in the first embodiment is that a 0.5 μm thick layer is formed on the first to third active layers 3-1, 3-2, and 3-3 of InGaAsP. InP type first to third cladding layers 19-
1, 19-2, and 19-3 are inserted, but the characteristics of each individual semiconductor laser are the same as in the first embodiment, and the oscillation current threshold is about 20 mA.
It also showed single-base transverse mode oscillation.

The present invention can be modified in several ways in addition to the two basic embodiments described above. First, the emission wavelength is
The wavelength is not limited to 1.2 μm, 1.3 μm, and 1.5 μm, and other wavelengths may be used. Next, the InGaAsP active layers are stacked in the order of emission wavelengths of 1.2 μm, 1.3 μm, and 1.5 μm, but the order is not limited to this. The n-type InP current confinement layer 6 allows the current to
It may be an n-type InGaAsP layer or a semi-insulating InP layer or InGaAsP layer, as long as it has the function of concentrating on the InGaAsP active layer. In addition, the material is not limited to InGaAsP, but also GaAlAs
It may be a compound semiconductor such as a type of semiconductor.

As explained in detail above, according to the present invention, the number of liquid phase epitaxial growth steps is reduced compared to the conventional method, and a multi-wavelength integrated semiconductor having excellent characteristics such as a low oscillation current threshold and single fundamental transverse mode oscillation is produced. The effect is great because a method for manufacturing a light emitting device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an example of a conventional multi-wavelength integrated semiconductor light emitting device, FIGS. 2 a to c are perspective views for explaining the basics of the present invention, and FIGS. FIG. 4 is a perspective view of a multi-wavelength integrated semiconductor light emitting device manufactured using the first example;
5a to 5e are perspective views of the manufacturing process for explaining the second embodiment of the present invention, and FIG. 6 is a perspective view of a multi-wavelength integrated semiconductor light emitting device manufactured using the second embodiment. It is. 1... n-type InP substrate, 2... n-type InP buffer layer, 3-1... InGaAsP first layer with emission wavelength of 1.2 μm
Active layer, 3-2... InGaAsP with emission wavelength of 1.3 μm
Second active layer, 3-3... InG- with emission wavelength of 1.5 μm
aAsP third active layer, 4-1... n-type InP first intermediate layer, 4-2... n-type InP second intermediate layer, 4-3...
n-type InP third intermediate layer, 5...p-type InP current blocking layer, 6...n-type InP current confinement layer, 7...p
InP type buried layer, 8... n-type InGaAsP electrode forming layer, 9-1, 9-2, 9-3... Zn diffusion region,
10...SiO ₂ CVD film, 11-1, 11-2, 1
1-3...Au-Zn ohmic electrode, 11a...
...Au-Ge-Ni ohmic electrode, 12...n type
InP substrate, 13... InP mesa stripe, 14...
...p-type InP layer, 15...n-type InP layer, 16...p
type InP layer, 17...photoresist stripe film, 18-1, 18-2, 18-3... mesa stripe including active layer 19-1, 19-2, 19-
3...p-type InP first, second, and third cladding layers.

Claims (1)

[Claims] 1. A first method of forming a semiconductor stack by epitaxially growing a plurality of semiconductor layers including at least two active layers having different forbidden band widths and not in contact with each other on a semiconductor substrate. an epitaxial growth step, and the semiconductor stack is sequentially grown in different directions in one direction so that at least the vicinity of the upper surface of each of the at least two active layers can be individually removed. an etching step of forming a stepped semiconductor stack by etching to a depth of 100 nm, and a step of forming a stripe mask in a direction perpendicular to the one on the surface of each step of the stepped semiconductor stack; , etching the stepped semiconductor laminate on which the stripe mask is formed from the surface portion where the stripe mask is not formed until portions corresponding to the surface portions of the at least two active layers are respectively removed; Tomo 2
a mesa etching step for forming two strip-shaped mesa structures, and after removing the stripe mask, a semiconductor layer having a conductivity type opposite to that of the semiconductor substrate and a semiconductor layer having the same conductivity type as the semiconductor substrate except for the upper surface of the at least two strip-shaped mesa stripes. A multi-wavelength integrated semiconductor light emitting device comprising: successively stacking semiconductor layers, and then a second epitaxial growth step of connecting and stacking semiconductor layers of the opposite conductivity type to the semiconductor substrate over the entire surface. Method of manufacturing the device. 2. A first epitaxial growth step of forming a semiconductor stack by epitaxially growing a plurality of semiconductor layers including at least two active layers having different forbidden band widths and not in contact with each other on a semiconductor substrate; , etching the semiconductor stack in one direction at different depths so that at least the vicinity of the upper surface of each of the at least two active layers can be individually removed; an etching step for forming a stepped semiconductor stack; and an impurity diffusion step for inverting at least a portion above each active layer corresponding to the stepped surface portion to a conductivity type opposite to that of the semiconductor substrate. , forming a stripe mask in a direction perpendicular to the one direction on the surface of each step of the stepped semiconductor stack; forming a stripe mask on the stepped semiconductor stack on which the stripe mask is formed; At least two etching steps are performed by etching at least two active layers from the unetched surface portions until respective portions of the at least two active layers corresponding to the surface portions are removed.
a mesa etching step for forming two strip-shaped mesa structures, and after removing the stripe mask, a semiconductor layer having a conductivity type opposite to that of the semiconductor substrate and a semiconductor layer having the same conductivity type as the semiconductor substrate except for the upper surface of the at least two strip-shaped mesa stripes. A multi-wavelength integrated semiconductor light emitting device comprising: successively stacking semiconductor layers, and then a second epitaxial growth step of connecting and stacking semiconductor layers of the opposite conductivity type to the semiconductor substrate over the entire surface. Method of manufacturing the device. 3. The semiconductor substrate is an InP substrate with plane orientation (001), and the active layer is In _1-x Ga _x As _y P _1-y (0<x
<1,0<y≦1) layer, and the one direction is <1
10. The method of manufacturing a multi-wavelength integrated semiconductor light emitting device according to claim 1, wherein the direction is 10>. 4. The semiconductor substrate is an InP substrate with plane orientation (001), and the active layer is In _1-X Ga _x As _y P _1-Y (0<x
<1,0<y≦1) layer, and the one direction is <1
3. The method of manufacturing a multi-wavelength integrated semiconductor light emitting device according to claim 2, wherein the direction is 10>.