JPS62158387A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To form an active layer having desired thickness in a region corresponding to a groove section, and to oscillate the title laser by low threshold currents and at a transverse fundamental mode by shaping a first conduction type lower clad layer on a substrate so as to be brought to a flat (100) face. CONSTITUTION:An N-type InP layer is formed onto a P-type InP substrate 31 through liquid-phase epitaxial growth, etc., sections up to the substrate 31 from the surface of the semiconductor layer are removed through etching in predetermined width to a striped shape in parallel with the <011> direction of the substrate 31 to shape a striped groove 33, and an N-type InP current constriction layer 35 is formed. A P-type InP layer 37, a GaInAsP layer 39 and an N-type InP layer 41 are formed onto the substrate 31 containing the current constriction layer 35 and the groove 33 through liquid-phase epitaxial growth. The active layer 39 is changed into a striped active layer 39a, which can be oscillated at a transverse fundamental mode and has width WA, on a region corresponding to the groove 33 of the upper clad first layer 41 through a photolithographic technique. An N-type InP layer 43 and an N-type GaInAsP layer 45 are shaped in succession through a liquid-phase epitaxial growth method, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device that has a low threshold current and oscillates in a transverse fundamental mode.

(Prior art) Figures 2 (A) and CB) are shown in one document (II
Journal of Quantum Electronics (
IEEE Journal of Quantu+s E
electronicg), QE-18[10]
(1982) P, 1704-1711) for explaining the structure of a conventional semiconductor laser and its manufacturing process.

In FIG. 2(A), reference numeral 11 denotes an n-type InP substrate (hereinafter sometimes referred to as substrate 11). First, an n-type InP layer is formed on the substrate 11 (
Using 5i02 etc. as an etching mask, the stripe direction is formed on the <
oit> direction and perpendicular to the stripe direction, a groove 13 having a V-shaped cross section is formed by etching, and
A current confinement layer 15 is formed by the remaining n-type InP layer. The etchant used for this etching is HCfL.
If an H3PO4-based etchant is used, the inner side surface of the V-groove 13 becomes a (111) B plane.

Next, by liquid phase epitaxial growth, the n-type InP cladding layer 17, the GaI nAsP active layer 18, the p-type InP cladding layer 21, and the p-type GaI nASP cap layer 23 are grown on the inner surface of V@13 and the n-type InP They were sequentially formed on the surface of the current confinement layer 15 to obtain the wafer structure shown in FIG. 2(B).

In this wafer structure, a positive electrode is provided on the upper surface of the cap layer 23 and a negative electrode is provided on the lower surface of the substrate 11 to constitute a semiconductor laser, and when a predetermined bias is applied to this device and driven, the p-type InP The interface between the current confinement layer 15 and the n-type InP cladding layer 17 on the current confinement layer 15 is reverse biased. Therefore, the current flows through the V groove 13 (V
Since current is efficiently injected into the crescent-shaped active layer 19a formed in the V-groove 13, the semiconductor laser device can be oscillated with a low threshold current.

Further, according to the above-mentioned literature, in an element having such a structure, in g (FIG. 2 CB) of the active layer 19a within the V-groove 13,
The dimension indicated by W) is approximately 1.5 μm, and the thickness of the central portion of the region of the active layer 19a (d in FIG. 2(B)) is approximately 1.5 μm.
It has been reported that stable oscillation in the transverse fundamental mode can be obtained by setting the dimension (represented by ) to about 0.1 gm.

(Problems to be Solved by the Invention) However, in the structure of the conventional semiconductor laser device as described above, (1) the thickness d of the central portion of the active layer 19a in the groove 13 is set to about O, 1 gm or even more. The problem is that it is not possible to accurately form a semiconductor laser with a thin thickness for reasons described later, and therefore it is not possible to manufacture a semiconductor laser with a desired low threshold value and oscillation in the transverse fundamental mode with a high yield. was there.

The reason why the thickness of the active layer 19a cannot be precisely controlled will be explained below with reference to FIG.

In the above-described element, the plane within the V-groove is the (111) B plane, as described above. Therefore, the active layer 19a formed inside the groove grows on the surface of the n-type InP cladding layer 174 formed on the (111) 8 plane. or,
The active layer formed outside the groove is an n-type InP cladding layer 17b formed on the (100) plane of the current confinement layer 15.
will grow on the surface.

When growing an active layer on multiple surfaces with a complex structure and different crystal planes, as shown in FIG. This is more likely to occur as a nucleus than the solute in the solution in other parts, and therefore the concentration of the solute in the solution inside the groove and in the vicinity of the groove becomes thinner. Therefore, other parts (near the flat part 17b of the n-type InP lower cladding layer, etc.)
The melt 27 moves in the direction of the groove as shown by the arrow 28.

In this way, (1) nuclei are more likely to be generated inside the groove than in other parts, so that the growth rate of the active layer is faster inside the groove than outside the groove.

For this reason, even if the growth time of the active layer is set to about 1 second, for example, an active layer with a thickness of 0.21 Lm or more will grow inside the groove, and the active layer will not be as thin as desired. It was extremely difficult to control the size and precision.

An object of the present invention is to solve the above-mentioned problems, and to provide an active layer with a desired thickness in a region corresponding to the groove portion.
An object of the present invention is to provide a manufacturing method that can easily manufacture a semiconductor laser that oscillates in a transverse fundamental mode with a low threshold current.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, the second conductive type semiconductor layer formed on the (100) plane of the first conductive type InP substrate has a <011> direction. forming striped grooves and forming a current confinement layer using the remaining semiconductor layer;

A step of forming a first conductivity type lower cladding layer on the substrate including the current confinement layer so that the lower cladding layer has a flat (100) plane, and a step corresponding to the grooves in the lower cladding layer described above. on the area to
A process of forming an active layer having a stripe shape in the <Oll> direction and having a width suitable for controlling the lateral fundamental mode, and forming a second conductivity type upper cladding layer on the above-mentioned lower cladding layer including this active layer. It is characterized by including the step of.

(Function) According to the method for manufacturing a semiconductor laser of the present invention, when forming the first conductivity type lower cladding layer on the substrate including the current confinement layer, the second conductivity type semiconductor layer is used to form the current confinement layer. The stripe grooves formed by removing the cladding layer are buried and the lower cladding layer is formed to have a flat (100) plane, so the active layer formed on the lower cladding layer is a flat layer. becomes.

Therefore, it is possible to easily control the layer thickness of the active layer and pattern the active layer.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that these drawings are only schematic representations to enable understanding of the present invention, and the shapes, dimensions, and arrangement relationships thereof are not limited to the illustrated examples, and the same constituent components in these drawings are not limited to the illustrated examples. The same reference numerals are used for the same reference numerals.

FIGS. 1A to 1D are manufacturing process diagrams for explaining an example of the method for manufacturing a semiconductor laser of the present invention. In addition, FIG. 1 CB) to (D) are the I of the wafer shown in FIG. 1 (A).
It is a cross-sectional view corresponding to the -I cross section.

In each figure, 31 indicates, for example, a p-type InP substrate (hereinafter sometimes referred to as substrate 31) as a first conductivity type InP substrate.

First, on this substrate 31, for example, an n-type InP layer is formed as a second conductivity type semiconductor layer by a suitable method such as liquid phase epitaxial growth. Then, for example, S i
Using a normal photolithography method using 02 as an etching mask, this semiconductor layer is formed into stripes from the surface of the semiconductor layer to the substrate 31 in parallel to the 011> direction of the substrate 31, and in a predetermined direction orthogonal to the stripes. width (
The striped grooves 33 are formed by etching away the etching (dimensions indicated by W in FIG. 1A), and an n-type InP current confinement layer 35 is formed using the remaining semiconductor layer.
The wafer structure shown in Figure (A) is obtained.

Note that the width W of this groove 33 affects the oscillation threshold current. Therefore, in order to oscillate with a low threshold current, this @W is set to 1.54
The groove 33 is preferably formed by etching a part of the substrate 31 as shown in FIG. 1(A).
Since the purpose of forming this groove is to form a current confinement layer, it is of course possible to use this groove to remove only the n-type InP semiconductor layer mentioned above in a stripe pattern and expose the substrate surface without etching it. With such a groove, there is no need to perform the growth required to fill the groove in the substrate 31 portion when forming the lower cladding layer in the next step.

On the other hand, when a groove reaching the substrate 31 is formed as in this embodiment, if the etchant used to form the groove 33 is, for example, a hydrochloric acid/phosphoric acid etchant as in the conventional case, the inner side surface of the groove 33 is (111 ) B surface, and as the etching progresses, the shape of the groove 33 becomes a figure 7 in cross section/plane perpendicular to the stripe direction. When this etching time is set to an appropriate time and the etching is completed, the bottom surface of the groove becomes a flat surface as shown in FIG. 1(A). Incidentally, in order to shorten the growth time of the lower cladding layer performed in the next step, it is preferable that the depth of the groove formed in the substrate portion be as shallow as possible.

Next, as a second crystal growth, for example, by liquid phase epitaxial growth, a p-type InP layer 37 is formed as a first conductivity type lower cladding layer, and a GaInAs layer is formed as an active layer.
P layer 39 and n as the first layer of the 9th layer temperature 9 type upper cladding.
A type InP layer 41 is formed on the substrate 31 including the groove 33 and the current confinement layer 15.

In this crystal growth, when the lower cladding layer 37 is formed by normal liquid phase epitaxial growth, the grooves 33
Since the crystal growth rate inside the groove is faster than the growth rate outside the groove, the groove 33 is buried, and therefore, the entire surface of the lower cladding layer 37 grown on the groove 33 and the current confinement layer 15 is (100). It can be a flat surface. After the lower cladding layer 37 becomes a flat surface, the thickness of the lower cladding layer 37 (as shown in FIG. 1(B) , tl) is preferably thinner, so it is formed to have an appropriate thickness according to the design. In addition, when driving the device, the current confinement layer 35
Since the lower cladding layer portion on this current confinement layer 35 has a reverse bias, the layer thicknesses of these layers 35 and 37, shown as tl and tl in FIG. 1(B), have sufficient withstand voltage for the drive current. It is necessary to set it to the thickness that can be obtained. In this example, 1. is 0.5 g, thickness is m, and tl is 1. Ou
Although the thickness of Lm is assumed, these layer thicknesses can be changed depending on the characteristics required of the device.

Next, by a normal photolithography method, <011
For example, 5i02 has a stripe shape parallel to the direction of
An etching mask (not shown) is formed.

Thereafter, an unnecessary portion of the n-type InP upper rad first layer 41 is removed using a kM#-based etchant, and then an unnecessary portion of the GaInAsP active layer 39 is removed using a sulfuric acid-based etchant. In this process, the hydrochloric acid-based etchant selectively etches only InP. The acid-based etchant can selectively etch only GaInAsP. Therefore, the active layer 39 can be easily formed into a striped active layer 39a having @W^ of 1.5 pm or less and capable of oscillating in the transverse fundamental mode.

Next, by a suitable method such as a liquid phase epitaxial growth method, a second conductivity type upper cladding second layer, for example, an n-type I
An nP layer 43 and, for example, an n-type GaInAsP layer 45 as a second conductivity type cap layer are sequentially formed on the lower cladding R37 including the active layer 39a to obtain the wafer structure shown in FIG. 1CD). The remaining striped portions 41a of the first upper cladding layer constitute the upper cladding layer 47 together with the second upper cladding layer 45 formed thereon. A semiconductor laser can be obtained by providing a positive electrode on the lower surface of cap layer 31 and a negative electrode on the upper surface of cap layer 45, respectively.

When such a semiconductor laser is driven by applying a predetermined bias, current flows only near the groove 33 due to the current confinement layer 35 . Further, the lower cladding layer 3 is formed on both sides of the active layer 39a.
7 and the upper cladding layer 47, the current flows concentratedly in the active layer 39a, which has a smaller bandgap than this part, making it possible to oscillate with a low threshold current. Become.

Further, since @W^ of the active layer 3B is set to a width suitable for oscillation in the lateral fundamental mode, stable oscillation is achieved in the lateral fundamental mode.

In the above embodiment, in order to prevent the surface of the active layer from being exposed when the active layer 38 is processed into a stripe shape, the first upper crat layer 41 is provided on the active layer as a protective film on the surface of the active layer. This is explained using an example. However, if the surface of the active layer 39 can be protected without using the upper cladding first layer 41 and the active layer 39 can be formed into a striped active layer 39a, the upper cladding layer can be There is no need to form the two layers separately.

In addition, other suitable methods may be used for the groove forming method explained in the above-mentioned embodiments. The second conductivity type cap layer may be formed by other suitable methods such as molecular beam epitaxial growth.

Furthermore, in the above-described embodiments, a p-type InP substrate was used as the substrate. The reason for using a p-type substrate is that the withstand voltage of the current confinement layer is better when using a p-type substrate than when using an n-type substrate, so high output operation can be expected. .

However, in this invention, if the substrate is an n-type substrate, the conductivity type of each layer is inverted correspondingly, and the thickness of the current confinement layer is selected to be the optimum thickness, etc. Similar effects can be expected when used in the manufacture of semiconductor lasers using molded substrates.

(Effects of the Invention) As is clear from the above description, according to the method of manufacturing a semiconductor laser of the present invention, the stripe grooves formed by removing the second conductivity type semiconductor layer in order to form the current confinement layer. , the lower cladding layer is buried during crystal growth, and the lower cladding layer is formed to have a flat (Zoo) surface.

Next, since the active layer is grown on this flat lower cladding layer, the growth rate of the active layer is the same over the entire lower cladding layer.

Therefore, the thickness of the active layer can be controlled much more easily than in the past.

Furthermore, since a semiconductor laser is formed using a substrate on which a current confinement layer is formed, it oscillates with a low threshold current.

Furthermore, since the active layer can be selectively etched to easily control the width of the active layer to the optimum width for transverse fundamental mode oscillation, stable oscillation is achieved in the transverse fundamental mode.

Therefore, it is an object of the present invention to provide a manufacturing method that can easily manufacture a semiconductor laser that has an active layer of a desired thickness in a region corresponding to the groove portion and that oscillates in a transverse fundamental mode with a low threshold current. I can do it.

[Brief explanation of drawings]

FIGS. 1(A) to (D) are manufacturing process diagrams for explaining the manufacturing method of the semiconductor laser of the present invention, and FIG. 2 is (A) and (D).
B) is a manufacturing process diagram for explaining a conventional semiconductor laser manufacturing method, and FIG. 3 is a diagram for explaining the conventional technology. 31... p-type InP substrate 33... striped groove 35... n-type InP current confinement layer 37... p-type InP lower cladding layer 39--G a I n A s P active layer 39a
-G a I nA's P active layer 41... n-type In
P layer (upper cladding first layer) 41a... Remaining portion of upper cladding first layer 43... n-type InP layer (upper cladding second layer) 45... n-type GaInAsP cap+-/p layer 4
7...N-type InP upper rad layer. Patent applicant Oki Electric Industry Co., Ltd. J/: p'Hn
P curtain gL 35: n type 1nP? 'Flow 1f1 layer 33
Stripe: Ash 1st 37' p-type InP bottom! +1 Clad 13ri GaIn
AsP active/a layer 41 n-type 1nPk-conductor I class/nd first layer Manufacturing diagram of this early stage semiconductor layer Figure 1 3 (/cl: GaInAsP ?8 a, @4ft
l 1 flight 1 cladding first layer residual capital 43, n-type IFI
P-post! Craln 2nd Cold 45' 71
AsP side 47 'nf InPk side 7'
12 no 1i 15th period single ring 4 laser) similar engineering 1 diagram 1
Figure 2

Claims (1)

[Claims] (1) forming a striped groove in the <011> direction in the second conductivity type semiconductor layer formed on the (100) plane of the first conductivity type InP substrate and forming a current confinement layer with the remaining semiconductor layer; forming a first conductivity type lower cladding layer on the substrate including the current confinement layer so that the lower cladding layer has a flat (100) plane; and a step corresponding to the groove of the lower cladding layer. On the area, <01
a step of forming an active layer having a stripe shape in the 1> direction and having a width suitable for controlling the lateral fundamental mode; and a step of forming an upper cladding layer of a second conductivity type on the lower cladding layer including the active layer. A method for manufacturing a semiconductor laser, comprising: