JPH067639B2 - Method for manufacturing semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Use) The present invention relates to a method for manufacturing a semiconductor laser, and more particularly to G
The present invention relates to a method for manufacturing a semiconductor laser that oscillates in a vertical (axial) single mode of an aInAsP / InP system.

(Prior Art) FIGS. 2 (A) to 2 (D) are described in, for example, the literature (Electronics Letters 18 No.23 P.1006 to 10).
Conventional embedded DFB (Distibuted-fe) disclosed in 08)
FIG. 6 is a manufacturing process diagram of an edback) type semiconductor laser device.

In the conventional manufacturing method, first, the n-type InP buffer layer 13 is formed on the n-type InP substrate 11 by the first liquid phase epitaxial growth (hereinafter also referred to as LPE).
Then, the GaInAsP active layer 15 and the p-type GaInAsP optical waveguide layer 17 are sequentially grown. Subsequently, a resist pattern is formed on the upper side surface of the p-type GaInAsP optical transmission layer 17 by holographic lithography, and then an unnecessary portion of the optical waveguide layer 17 is etched by a chemical etching technique to obtain an optimum pitch and depth. Waveform (co
rrugation) 17a is formed on the n-type InP substrate 11 (FIG. 2 (A)). According to this document, the peak is 450
It has a depth of 0Å and a depth of 2000Å.

Next, by the second LPE, the p-type InP clad layer 1
9 and a p-type GaInAsP cap layer 19 are sequentially grown (FIG. 2 (B)).

Next, a cap layer 21, a clad layer 19, an optical waveguide layer 17, an active layer 15, and a buffer layer 13 are used by using a photoetching method similar to the manufacturing of a semiconductor laser having a normal buried structure.
Unnecessary portions of and are removed to form a laminated body 23 having an inverted mesa shape. (FIG. 2 (C)).

Next, the p-type InP current confinement layer is formed by the third LPE.
23 and an n-type InP current confinement layer 25 are sequentially grown on the substrate 11 to embed the mesa-shaped stack 23. (A cross section is shown in FIG. 2 (D)).

Further, although not shown, a negative electrode is provided on the lower side surface of the substrate 11 and a positive electrode is provided on the upper side surface of the cap layer 21 to configure this element.

When a predetermined bias is applied to such an element to operate it, the p-type InP current confinement layer 23 and the n-type InP current confinement layer are formed.
The interface with 25 is reverse biased, so that current is efficiently injected into the part of the active layer 15 that is forward biased. Therefore, it is possible to oscillate with a low threshold current.

Further, the light generated in the active layer 15 is guided in the optical waveguide layer 17,
The wave 17a provided on the surface of the optical waveguide layer causes Bragg reflection, and thus oscillates in a single longitudinal mode.

(Problems to be Solved by the Invention) However, in the method for manufacturing a semiconductor laser as described above, LPE (crystal growth step) is required three times during the manufacturing process, which increases the number of manufacturing steps. Due to this, there are problems that the yield is reduced and the manufacturing cost is increased.

In addition, there is a problem that the surface of the layer grown by the previous crystal growth is deteriorated during the subsequent crystal growth, which is different from the growth, so that the interface between the two growth layers is easily deteriorated. This phenomenon is the interface between the second and third crystal growth steps in the manufacturing process described above, that is, the n-type InP substrate 11 and the p-type In.
It is likely to occur at the pn junction at the interface of the P current constriction layer 25.

An object of the present invention is to manufacture a semiconductor laser which can solve the above-mentioned problems, reduce the number of crystal growth during the manufacturing process, and manufacture a semiconductor laser having characteristics similar to those of the conventional semiconductor laser. To provide a method.

(Means for Solving Problems) In order to achieve this object, according to the present invention, GaI
In manufacturing the nAsP / InP semiconductor laser using the liquid phase epitaxial growth method, from the (100) plane of the first conductivity type InP substrate to (111) A
A step of forming a stripe-shaped groove having a surface as a side surface, growth of a second-conductivity-type current confinement layer utilizing the plane orientation dependence of the growth rate on the grooved first-conductivity-type InP substrate, and the subsequent step A step of continuously performing the growth of the one conductivity type GaInAsP buffer layer, the first conductivity type InP lower cladding layer, the GaInAsP active layer and the second conductivity type GaInAsP optical waveguide layer by one liquid phase epitaxial growth; A step of processing the upper surface of the wave layer into a waveform having an appropriate pitch and depth according to the oscillation wavelength of the device, and the second conductivity type InP on the optical waveguide layer having the corrugated surface.
A step of performing the liquid phase epitaxial growth of the upper clad layer and the second conductivity type GaInAsP cap layer once, and the upper clad layer and the upper clad layer left in the upper part of the groove by etching the cap layer and And a step of forming a ridge portion formed of a cap layer portion.

(Operation) According to such a manufacturing method, the current confinement layer is formed by the first liquid phase epitaxial growth without growing the current confinement layer inside the groove due to the peculiar property of the plane orientation dependency,
The buffer layer, the lower clad layer, the active layer and the optical waveguide layer can be continuously grown on the substrate. Therefore,
The semiconductor laser obtained according to the present invention does not have a conventional interface that easily deteriorates.

Further, since the corrugation is provided on the surface of the optical waveguide layer opposite to the active layer, the light generated in the active layer is guided through the optical waveguide layer and Bragg-reflected by the corrugation on the surface of the optical waveguide layer. Therefore, it oscillates in the single longitudinal mode.

In addition, since the upper clad layer and the cap layer are sequentially and continuously grown by the second liquid phase epitaxial growth, the main part of the semiconductor laser (DFB type laser) is formed by performing the liquid phase epitaxial growth twice. Composed.

Further, since the clad layer and the cap layer are etched to have a structure in which the stripe-shaped ridge portion remains at least above the groove, the obtained semiconductor laser has a refractive index waveguide structure with a difference in refractive index. Therefore, stable transverse fundamental mode oscillation can be obtained.

Furthermore, since the internal current confinement layer is provided, the injection current efficiently flows into the active layer, and thus oscillates at a low threshold current.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. It should be noted that these drawings are only schematically shown to the extent that the present invention can be understood, and the shape, size, and arrangement relationship thereof are not limited to the illustrated examples. Further, in these drawings, the same constituent components are designated by the same reference numerals.

FIGS. 1A to 1D are process drawings showing a method for manufacturing a semiconductor laser device according to the present invention. 1 (B) and 1 (D) are shown as sectional views corresponding to the I-I section of FIG. 1 (A).

First, using a normal photo-etching technique, for example, a p-type InP substrate 31 (hereinafter, also referred to as a substrate) (100) surface as a first conductivity type InP substrate is <0
Stripes in the 1> direction and <011 of the substrate 31
An etching mask (not shown) made of, for example, SiO ₂ capable of exposing a partial region of the p-type InP substrate 31 with a predetermined width in the> direction is formed. Next, by etching the exposed portions of the substrate 31 with bromine in methanol, for example, a width (in FIG. 1, the dimension indicated by _{W A)} 1.5 [mu] m, depth 0.2μm
The stripe-shaped groove 33 is formed. Then, the etching mask is removed to obtain a wafer structure having a groove 33 as shown in FIG.

Next, by the first liquid phase epitaxial growth, for example, an n-type InP layer 35 as a second conductive InP layer functioning as a current confinement layer, for example a p-type GaInAsP layer 37 as a first conductive type buffer layer, and A substrate including a groove 33, for example, a p-type InP layer 39 as one conductivity type lower clad layer, for example, a GaInAsP layer 41 as an active layer, and an n-type GaInAsP layer 43 as a second conductivity type optical waveguide layer. The wafer structure shown in FIG. 1 (B) is obtained by sequentially and continuously forming on the substrate 31. Incidentally, the groove 33 formed in the p-type InP substrate 31.
Is a (111) A surface, and the lower surface of the groove 33 is curved. Here, if the n-type InP layer 35 is grown at a relatively low growth temperature of about 600 ° C. during the crystal growth step, the n-type InP layer is dependent on the plane orientation of the growth rate.
The layer 35 does not grow at all inside the groove 33 formed in the substrate 31,
It grows only on the substrate 31 other than 33. Also, this n-type InP
The p-type GaInAsP layer 37 grown on the layer 35 can also grow inside the groove 33. Therefore, this p-type GaInAsP layer 37 can be grown.
The p-type InP layer 39 and GaInAs formed on the sP layer 37
The P layer 41 and the n-type GaInAs layer 43 are grown on the entire surface of the substrate 31 (above the groove 33 and on the n-type InP layer 35. Such a growing method has been clarified by various experiments by the inventor of the present invention. The method and its details are disclosed in the literature (Technical Report of the Institute of Electronics and Communication Engineers OQE 84-52 P.17).

Therefore, when a predetermined bias (described later) is applied to the semiconductor laser of the present invention to operate it, the n-type InP layer 35 grown on the substrate 31 excluding the inside of the groove 33 and the p-type GaInAs are grown.
Between the portion of the P layer 37 grown on the n-type InP layer 35 (first
In the drawing, a portion indicated by xxx) becomes a reverse bias and functions as a current confinement layer, so that the current efficiently flows in the groove 33.

Next, a resist pattern is formed on the n-type GaInAs optical waveguide layer 43 by holographic lithography as in the case of manufacturing a conventional DFB laser, and then an unnecessary portion surface of the optical waveguide layer 43 is etched by a chemical etching technique. Then, a corrugation 43a having an appropriate pitch and depth according to the composition and thickness of the optical waveguide layer 43 is formed on the surface of the optical waveguide layer 43 (FIG. 1 (C)).

Next, the n-type InP layer 45 as the second conductivity type upper cladding layer, the n-type GaInAsP layer 47 as the second conductivity type cap layer, and the n-type GaInAsP optical waveguide layer 43 are formed by the second liquid phase epitaxial growth. Form on top. Then, in order to control the transverse mode oscillation of the semiconductor laser, at least a partial region of the n-type InP layer 45 and the n-type GaInAsP layer 47 facing the groove 33 is left as the ridge portion 49 by using a normal photoetching technique. These layers 45 and
The unnecessary portion of 47 is removed by etching to obtain a wafer as shown in FIG. Incidentally, the width of the ridge portion (the dimension in the same direction as the width of the groove 33, in FIG. 1 (D),
Dimensions shown in W _B) is set to an appropriate value depending on the composition and thickness of the n-type GaInAsP light waveguide layer 43.

Next, a p-electrode is formed on the lower surface of the substrate 31 (not shown) and the ridge
The semiconductor laser of the present invention can be obtained by forming n-electrodes on the upper surface of 49, respectively.

Therefore, according to the method of manufacturing a semiconductor laser of the present invention, it is possible to manufacture a DFB type laser by performing liquid phase epitaxial growth twice.

Although the above-described embodiments have described the method of manufacturing the semiconductor laser of the present invention with respect to the example using the p-type InP substrate, the manufacturing method of the present invention is used as a method of manufacturing the semiconductor laser using the n-type InP substrate. Is also suitable. In this case, it goes without saying that the conductivity type of each layer is changed corresponding to the n-type InP substrate.

(Effect of the Invention) As is clear from the above description, according to the method for manufacturing a semiconductor laser of the present invention, the current confinement layer is grown in the groove by utilizing the plane orientation dependence of the growth rate. Instead, the current confinement layer, the buffer layer, the lower clad layer, the active layer, and the optical waveguide layer are formed on the substrate by one-time liquid phase epitaxial growth. Then, a corrugation is formed on the surface of the optical waveguide layer opposite to the active layer. Next, the upper cladding layer and the cap layer are sequentially and continuously formed on the optical waveguide layer by the second liquid phase epitaxial growth. Further, a semiconductor laser is manufactured by removing unnecessary portions of these layers so that at least the partial regions of the upper clad layer and the cap layer facing the stripe-shaped grooves become ridge portions.

Therefore, the liquid phase epitaxial growth, which was conventionally required three times, can be performed twice, and the n-type InP current / current constriction layer and the p-type GaInAsP buffer layer plate can be continuously grown, so that each growth interface can be increased. Is unlikely to occur. Therefore, the yield, manufacturing cost and reliability can be improved as compared with the conventional case.

Further, the semiconductor laser of the present invention is capable of oscillating at a low threshold current by the internal current confinement layer, oscillates in the single longitudinal mode by the waveform provided in the optical waveguide layer, and further, the upper side facing the stripe-shaped groove. A clad layer and a cap layer are used as a ridge portion and a negative electrode is provided on this ridge portion to perform transverse fundamental mode oscillation.

For this reason, it is possible to reduce the number of times of crystal growth during the manufacturing process and to provide a manufacturing method capable of manufacturing a semiconductor laser having characteristics similar to the conventional one.

[Brief description of drawings]

FIGS. 1 (A) to (D) are manufacturing process diagrams for explaining the method for manufacturing a semiconductor laser of the present invention, and FIGS. 2 (A) to (D) are explanatory views showing a conventional method for manufacturing a semiconductor laser. is there. 31 ... p-type InP substrate 33 ... stripe-shaped groove 35 ... n-type InP current confinement layer 37 ... p-type GaInAsP buffer layer 39 ... p-type InP lower clad layer 41 ... GaInAsP active layer 43 ... n-type GaInAsP optical waveguide layer 43a ... Corrugation 45 ... n-type InP clad layer 47 ... n-type GaInAsP cap layer 49 ... ridge portion.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masato Kawahara 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) Reference JP-A-62-47182 (JP, A)

Claims (1)

[Claims] 1. When manufacturing a GaInAsP / InP semiconductor laser using a liquid phase epitaxial growth method, a (111) A film is formed from a (100) plane of a first conductivity type InP substrate.
A step of forming a stripe-shaped groove having a surface as a side surface, growth of a second-conductivity-type current constriction layer utilizing the plane orientation dependence of the growth rate on the grooved first-conductivity-type InP substrate, and the subsequent step A step of continuously performing the growth of the one conductivity type GaInAsP buffer layer, the first conductivity type InP lower cladding layer, the GaInAsP active layer, and the second conductivity type GaInAsP optical waveguide layer by one liquid phase epitaxial growth, and the optical waveguide A step of processing the upper surface of the layer into a corrugated shape, and a step of growing the second conductivity type InP upper cladding layer and the second conductivity type GaInAsP cap layer on the optical waveguide layer having the corrugated surface once by liquid phase epitaxial growth And the upper clad layer and the cap layer are etched to form a ridge portion composed of the upper clad layer and the cap layer remaining in the upper part of the groove. A method of manufacturing a semiconductor laser, comprising the steps of: