JPH0983062A - Semiconductor optical element and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical element having a window part transparent to a waveguide light at the end part thereof and can be fabricated easily. SOLUTION: A recessed region 13 of substantially same length as a semiconductor optical element is made in the surface of a semiconductor substrate 11 having an edge at a protruding region 15 continuous to the recessed region 13 on the extension in the longitudinal direction. A waveguide structure 27 including a lower clad layer 17, an active layer 19 and an upper clad layer 21 is formed over the recessed region 13 of substrate 11 and the protruding region 15 on which the edge is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device having a window region transparent to guided light at the device end and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as an element of this kind, for example, a document I
(SPE Vol.1219, pp.117-125) has a disclosure. This device is provided with a blocking layer having two parallel ridges on a p-GaAs substrate as disclosed in, for example, FIG. 1 of Document I, and further, a lower clad layer and a guide layer are provided on this blocking layer. , An active layer, a confinement layer, a light emitting region composed of a buffer layer, an upper clad layer, and a contact layer in this order. However, the entire length of the light emitting region is shorter than the device length, and both ends thereof are covered with the upper clad layer. The upper clad layer portion covering both ends of this light emitting region functions as a window region (Fig. 3 of Reference I). Further, this semiconductor optical device is manufactured as follows. First, a blocking layer is formed on the GaAs substrate by the first crystal growth. Second
The lower clad layer, the guide layer, the active layer, the confinement layer, and the buffer layer are sequentially formed by the crystal growth for the second time. Then, each layer formed by the second crystal growth is etched so as to have the size of the light emitting region. Next, the upper clad layer and the contact layer are sequentially formed on the etched sample by the third crystal growth. After that, electrodes are attached to obtain an element.

[0003]

However, in the device of the above document, the light emitting region is formed by processing the lower clad layer, the guide layer, the active layer, the confinement layer, and the buffer layer so as to be shorter than the entire device length. And the upper cladding layer portion covering both ends of the light emitting region constitutes the window region,
There were the following problems.

(1) The number of times of crystal growth is large in manufacturing the element.

(2) The device manufacturing process is complicated.

(3) By the second crystal growth, the lower clad layer, the guide layer, the active layer, the confinement (confi
After forming the nement) layer and the buffer layer, it is necessary to perform etching processing on these so as to have the shape of the light emitting region, and therefore it is necessary to take out the sample from the growth chamber. Here, since the buffer layer is composed of the GaAlAs layer in this case, the easily oxidized GaAlAs is exposed to the atmosphere. Therefore, it is generally difficult to perform high-quality crystal growth in the third crystal growth.

[0007]

Therefore, according to the first invention of this application, in a semiconductor optical device having a window region transparent to guided light at an end portion of the device, the surface length of the semiconductor optical device is substantially equal to that of the semiconductor optical device. Substrate in which a concave region of the same length is formed, and an end face is formed in a convex region continuous with the concave region on the extension in the length direction, and on the concave region and the end face of the semiconductor substrate And a waveguide structure including an active layer, an upper clad layer, and a lower clad layer, which is formed as necessary, over the convex region portion.

According to the second invention of this application, in a semiconductor optical device having a window region transparent to guided light at the end of the device, the surface of the semiconductor optical device has substantially the same length as that of the semiconductor optical device. A semiconductor substrate in which a convex region is formed and an end face is formed in a concave region continuous with the convex region on the extension in the length direction, and a concave region portion on the convex region and the end face of the semiconductor substrate It is characterized by comprising a waveguide structure which is formed over the top and which includes an active layer and an upper clad layer and a lower clad layer which is formed as necessary.

Further, according to the third invention of this application, in a method of manufacturing a semiconductor optical device having a window region transparent to guided light at an end portion of the device, a semiconductor substrate has a device length substantially equal to that of the semiconductor optical device. A concave region having the same length or a convex region having a length substantially the same as the device length of the semiconductor optical device, and a lower side on the semiconductor substrate on which the concave region or the convex region is formed. A step of laminating a semiconductor layer including a clad layer, an active layer and an upper clad layer (provided that the lower clad layer is formed if necessary), And a step of dividing the region or the convex region outside by a predetermined dimension to obtain an end face.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. However,
Each drawing used in the description merely schematically shows the dimensions, shapes, and arrangement relationships of the respective constituents so that the present invention can be understood. In each figure, the same components are denoted by the same reference numerals.

1. Embodiments of First Invention and Manufacturing Example (Third Invention) Thereof First, embodiments of the first invention and the third invention will be described with reference to FIGS. 1 to 4. Each drawing is a process chart for explaining one mode of manufacturing the semiconductor optical device of the first invention by the manufacturing method of the third invention.

First, for example, n-Ga as a semiconductor substrate is used.
For example, a SiO ₂ film is vapor-deposited on the As substrate 11 (not shown), and this SiO ₂ film is processed by a photolithography technique and an etching technique so that the SiO ₂ film serves as a mask for forming a recessed region described later (FIG. (Not shown). Then, a portion of the n-GaAs substrate 11 exposed from the mask is etched by a predetermined amount to form a concave region 13 having a length substantially the same as the device length of the semiconductor optical device on the n-GaAs substrate 11. . FIGS. 1 (A) and 1 (B) are explanatory views of the recessed region 13 formed in this manner, particularly (A).
Is a perspective view showing a state of the whole substrate, and (B) is an enlarged perspective view of a part thereof (portion P in FIG. (A)).
In FIG. 1B, the length substantially equal to the element length in the concave region 13 is the length with L, and is about 500 μm, for example. The step d _e in the concave region 13 is set to 2 μm, for example. Note that the concave region 13 has a continuous concave portion in the direction orthogonal to the L direction (see FIG. 1A), but the present invention is not limited to this. Also, L
The convex regions 1 between the respective concave regions 13 arranged in the direction
The length M of 5 is about twice the length of the desired window region. Although details will be described later, by cleaving the wafer at the center of the convex region 15 later, individual optical elements and desired window regions in each element can be obtained.
In the case of this example, the length M of the convex region 15 is about 40 μm.

Next, the mask used for forming the concave region 13 is removed. Then, on this substrate, for example, using an MOCVD apparatus, the n-GaAlAs lower cladding layer 17 (for example, a thickness of 4 μm), the undoped GaAlAs active layer 19, p.
-GaAlAs upper cladding layer 21 (e.g.
m), and the p ⁺ -GaAs contact layer 23 (for example, 0.2 μm thick) is sequentially grown (FIG. 2A). In the case of this example, this corresponds to the case where the band gap energy of the GaAs substrate is smaller than the photon energy of the light (guided light) guided through the optical element (corresponding to the case where the substrate absorbs the guided light). Since the lower clad layer 17 is required, the lower clad layer is formed. The film thickness of each of the lower clad layer 17 and the upper clad layer 21 is any suitable film thickness (usually at least 1 μm if the basic design conditions are satisfied so that the waveguide structure is established).
Degree). However, in the first invention, the film thickness d _s of the lower clad layer 17 will be described later in detail, but the concave region 13
It is preferable to have a predetermined thickness (thickness satisfying the expression (1) described later) in consideration of the step d _e in the above step and the beam diameter d _w at the element end surface of the light guided through the optical element.

Next, using photolithography technology,
A stripe-shaped mask 25 made of, for example, SiO ₂ having a stripe direction of the length L and a width of about 2 μm is formed by p
^It is formed on the ⁺ -GaAs contact layer 23 (FIG. 2).
(B)).

Next, the unexposed GaAlAs active layer 1 is exposed from the stripe-shaped mask 25 by a dry etching method or a wet etching method.
9 is etched to form a waveguide stripe 27 (width of about 3 μm) as a waveguide structure (FIG. 3).
(A)).

Next, as shown in FIG. 3B, both sides of the waveguide stripe 27 are covered with an insulator 29 such as polyimide (however, only a part of the insulator is shown in FIG. 3B). ing.). Next, the upper ohmic contact electrode 31 and the upper bonding electrode 33 are formed by known methods.

Next, the back surface of the substrate 11 is polished to a thickness such that it can be cleaved, and then the lower ohmic contact electrode 35 and the lower bonding electrode 37 are formed on the polished surface by known methods.

Next, this sample is divided into the concave region 13 by a predetermined dimension outside in the direction of the element length L to obtain an end face. Here, the adjacent concave region 1
3 in the center of the lengthwise direction of the convex region 15 (see FIG. 3B).
Cleavage is performed at each of the portions marked with I-I lines therein to obtain an end face, and chips are formed.

Through the above steps, the semiconductor optical device 40 according to the first aspect of the invention is completed (FIG. 4A). That is, a concave region 13 having a length L substantially equal to the device length of the semiconductor optical device is formed on the surface, and a convex region 15 (here, the concave region 13 is continuous with the concave region 13 on the extension in the length direction). The lower clad layer is formed over the semiconductor substrate 11 having an end face formed on each of the convex regions on both sides of the region 13 and over the concave region 11 of the semiconductor substrate 11 and the convex region portion where the end face is formed. A semiconductor optical device 40 having a waveguide structure 27 including an active layer and an upper clad layer is obtained. In this semiconductor optical device 40, the convex region 15
A window region 41 is constructed on top.

Next, in order to deepen the understanding that the window region 41 is formed on the convex region 41, the operation of the semiconductor optical device 40 will be described. This description will be given with reference to FIGS. 4 (B) and 4 (C). Here, FIG. 4B is a cross-sectional view taken along line II-II in FIG. 4A, and FIG. 4C is FIG.
3 is a sectional view taken along line III-III in FIG.

In both FIG. 4B and FIG. 4C, the dotted line Q1 or Q2 in the figure indicates the approximate field distribution of the guided light. In this optical element 40, the upper side,
When a current is passed between the lower ohmic contact electrodes 31 and 35, AS is generated by the stimulated emission action in the active layer 19.
E (Amplified Spontaneous Emission) light is generated. Then, the concave region 13 of the optical element 40
In the upper part, since the refractive index confinement structure is in both the horizontal and vertical directions, the guided mode is the dotted line Q in FIG.
It is confined in the area surrounded by 2. On the other hand, since the refractive index confinement structure is not formed in the horizontal and vertical directions in the upper portion of the convex region 15 of the optical element 40, the guided light spreads as it propagates. This light is reflected back to the end face and returns, but further spreads, so that the component fed back to the active layer 17 is very small. Therefore, in this optical element 40, it can be seen that the window region 41 is formed on the convex region 15.

The step in the concave region 13 is d _e , the film thickness of the lower cladding layer 17 is d _s , and the convex region 15 is
Let d _w be the diameter of the beam at the element end face of the light propagating while spreading in (2).

D _s = 2 × de ≧ dw (1) In this way, the guided light does not substantially reach the substrate 11 in the window region 41 (the lower boundary of Q1 in FIG. 4B). And the substrate 11), the guided light is transmitted to the substrate 11
This is because it can be prevented from being absorbed by. Therefore, in the example of the optical element 40 described above, in general, the convex region 15
Is set to several tens of μm (about 20 μm in this example), and the spread of light at that time is about several μm to 10 μm. Therefore, if d _w is set to, for example, d _w = 4 μm (1) From the equation, it is preferable that d _s = 4 μm or more and de = 2 μm or more.

Of course, when the substrate 11 may absorb the guided light to some extent, the above d _s may be a little thinner within the range in which the basic waveguide structure is established.

If the bandgap energy of the semiconductor substrate is larger than the photon energy of the guided light (if the substrate does not absorb the guided light), the lower clad layer is not necessary in principle. I can say. For example, I
This example corresponds to a case where a semiconductor optical device is constructed using an nP substrate. In that case, it is preferable to determine the step d _e of the concave region 13 so as to satisfy the following expression (2). This is because the upper half of the guided light beam emitted from the end of the concave region 13 does not reach the active layer portion in the convex region 15. In this case, it can be seen that the step d _{e of the} concave region is half that in comparison with the case where GaAs is used as the semiconductor substrate.

D _e ≧ d _w / 2 (2) Of course, also in this case, the upper half of the beam of the guided light emitted from the end of the concave region 13 may reach the active layer portion in the convex region 15 to some extent. If so, the step d _e may be a little shallower within the range in which the object of the present invention that the window area is formed by using the step is obtained.

As is clear from the above description, according to the first invention and the manufacturing method thereof (third invention), the following effects can be obtained by providing the substrate with the uneven structure in advance.
(1). No special crystal growth step is needed to form the window structure. Therefore, the crystal growth process only needs to be performed once to obtain the waveguide structure. (2). Ga
Since the re-growth step on AlAs is not included, the problem of surface oxidation during the process is eliminated, and the process can be simplified, the yield can be improved, and the reliability can be improved.

2. Embodiments of Second Invention and Manufacturing Method Example (Third Invention) Next, embodiments of the second invention and the third invention will be described. The difference from the first invention of the second invention is that the first invention forms the window area on the convex area in the unevenness, whereas the second invention forms the window area in the concave area of the unevenness. is there. The differences will be mainly described below. This description will be given with reference to FIG. Here, FIG. 5 is a perspective view shown in the same notation as in FIG.

In this case, the n-GaAs substrate 11 has a convex region 51 having a length L substantially equal to the device length of the semiconductor optical device.
To form This length L is, for example, about 500 μm.
The level difference L _e of the convex region 51 is set to 2μm, for example.
Further, the length N of the concave region 53 between the large number of convex regions 51 continuous in the L direction is set to be about twice the length of the desired window region. The convex regions 51 are obtained by forming the concave regions 53 having a length N at the pitch L on the semiconductor substrate 11 by a known lithography technique and etching technique.
After that, growth of each semiconductor layer such as the lower clad layer (however, this is necessary), the active layer and the upper clad layer is performed in the same procedure as the procedure for manufacturing the semiconductor optical device 40 of the first invention. , Forming waveguide stripes, forming electrodes,
Cleavage (however, the cleaving position is the central portion of the concave region 53) may be performed. Thus, the semiconductor optical device 60 according to the second aspect of the invention is obtained (see FIG. 6A). That is, the convex region 51 having a length L substantially equal to the device length of the semiconductor optical device is formed on the surface, and the concave region 53 continuous with the convex region 51 on the extension in the length direction.
The semiconductor substrate 11 has an end face formed in each of the concave regions on both sides of the convex region 51, and is formed over the convex region 51 of the semiconductor substrate 11 and the convex region portion where the end face is formed, A semiconductor optical device 60 having a waveguide structure 27 including a lower clad layer, an active layer and an upper clad layer is obtained. In this semiconductor optical device 60, the window region 61 is formed on the concave region 53.

Next, in order to deepen the understanding that the window region 61 is formed on the concave region 53, the operation of the semiconductor optical device 60 will be described. This description will be given with reference to FIGS. 6 (B) and 6 (C). Here, FIG. 6B is a cross-sectional view taken along line IV-IV in FIG. 6A, and FIG. 6C is FIG. 6A.
5 is a sectional view taken along line VV in FIG.

In both FIGS. 6B and 6C, the dotted line Q1 or Q2 in the figure indicates the approximate field distribution of the guided light. In this optical element 60, the convex portion 5
In the part above 1, that is, the cross-sectional part of the line V-V, the dotted line Q
The guided mode is confined in the region surrounded by 2 (see FIG. 6C).

On the other hand, the concave region 53 of the optical element 60 is
In the part, that is, in the cross section of the IV-IV line, there is confinement in the horizontal direction, but there is no confinement in the vertical direction. Is obtained. Therefore, also in the second invention and the manufacturing method thereof, the same effect as that of the above-described embodiment of the first invention can be obtained.

In the case of the second invention as well, the lower clutch
Layer (if necessary) and upper cladding layer
The film thickness of each of the
Any suitable film thickness (usually small
At least about 1 μm). However, in this second invention
Is the film thickness d of the upper clad layer 21._s Of the upper clad layer
Thickness d_u , D in the convex region 51_e , Element end face
The diameter of the beam at d _w Then, the following equation (3) is
Good to meet. The beam will then be in the upper cladding layer 2
Since the light is guided in 1, the beam will come out to the air in the middle of the window area.
This is because it can be prevented (see FIG. 6B).

D _u −d _e ≧ d _w / 2 (3) 3. Other Embodiments The lengths of the concave region and the convex region, the substrate used, and the conductivity type of the substrate in each of the above-described embodiments are not limited to the above examples. Also,
By incorporating a grating structure in the element, DF
Each invention of this application is also effective for suppressing reflection at the end face by forming a B laser or DBR laser structure or by incorporating a DFB laser and a modulator. FIG. 7 shows a configuration example in which the DBR region 71 is further provided in series, which is a form of the first invention. As can be understood from the example of FIG. 7, in each invention of this application, the convex area continuous with the concave area (concave area continuous with the convex area) may be continuous with only one side of the concave area (convex area). Shall be included.

The inventions of this application are also applicable to the case where the both end surfaces of the element are AR-coated and are used as a semiconductor optical modulator or a semiconductor optical amplifier.

[0036]

As is apparent from the above description, according to the inventions of this application, the window region is formed by utilizing the steps in the predetermined concave region and convex region provided on the semiconductor substrate. It is possible to eliminate a special crystal growth process only for forming a structure. Therefore, the crystal growth process only needs to be performed once to obtain the waveguide structure. : GaAlA
Since the regrowth step on s is not included, the problem of surface oxidation during the process is eliminated, and the process can be simplified, the yield can be improved, and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of first and third inventions.

FIG. 2 is an explanatory diagram of the first and third embodiments of the present invention, following FIG.

FIG. 3 is an explanatory diagram of the first and third embodiments of the invention, following FIG.

FIG. 4 is an explanatory diagram of the embodiment of the first and third inventions following FIG.

FIG. 5 is an explanatory diagram of an embodiment of second and third inventions.

FIG. 6 is an explanatory diagram of the second and third embodiments of the invention, following FIG. 5;

FIG. 7 is an explanatory diagram of another embodiment.

[Explanation of symbols]

 11: Semiconductor substrate 13: Concave region of substantially the same length as the device length 15: Convex region 17: Lower clad layer 19: Active layer 21: Upper clad layer 23: Contact layer 27: Waveguide structure 40: No. Semiconductor optical device 41 of one embodiment of the invention 41: Window region 51: Convex region 53 of substantially the same length as the device length 53: Concave region 60: Semiconductor optical device of one embodiment of the second invention 61: Window region

Claims (6)

[Claims] 1. A semiconductor optical device having a window region transparent to guided light at an end of the device, wherein a concave region having a length substantially the same as the device length of the semiconductor optical device is formed on the surface, and A semiconductor substrate having an end face formed in a convex region continuous with the concave region in the extension of the length direction, and an active layer formed over the concave region of the semiconductor substrate and the convex region portion where the end face is formed. And a waveguide structure including an upper clad layer and a lower clad layer formed as needed, and a semiconductor optical device. 2. A semiconductor optical device according to claim 1, the thickness of the lower cladding layer d _s, the step of d _e between the concave region and a convex region, the beam diameter at the device end face of the guided light When d _w , respectively, the above d _s is satisfied so as to satisfy the following expression (1) or expression (2).
Alternatively, a semiconductor optical device characterized by setting d _e (where, the equation (1) is applied when the band gap energy of the semiconductor substrate is smaller than the photon energy of the guided light, and the equation (2) is Applicable when the bandgap energy of the semiconductor substrate is large relative to the photon energy of the guided light. d _s = 2 × d _e ≧ d _w (1) d _e ≧ d _w / 2 (2) 3. A semiconductor optical device having a window region transparent to guided light at an end of the device, wherein a convex region having a length substantially the same as the device length of the semiconductor optical device is formed on the surface, and A semiconductor substrate having an end face formed in a concave region continuous with the convex region in the extension of the length direction, and an active layer formed over the convex region and the concave region portion where the end face is formed of the semiconductor substrate. And a waveguide structure including an upper clad layer and a lower clad layer formed as needed, and a semiconductor optical device. The semiconductor optical device according to claim 3, the thickness d _u of the upper cladding layer, the step of d _e between the concave region and a convex region, the beam diameter at the light emitting end face of the guided light d _The semiconductor optical device is characterized in that the d _u is set so as to satisfy the following expression (3) when each is expressed as _w . d _u −d _e ≧ d _w / 2 (3) 5. A method of manufacturing a semiconductor optical device having a window region transparent to guided light at an end portion of the device, wherein a concave region having a length substantially the same as the device length of the semiconductor optical device is formed on a semiconductor substrate. A step of forming a convex region having substantially the same length as the device length of the semiconductor optical device, and a lower clad layer, an active layer and an upper clad layer on the semiconductor substrate on which the concave region or the convex region has been formed. A step of stacking a semiconductor layer including (wherein the lower clad layer is formed as necessary), and a sample on which the semiconductor layer has been stacked is subjected to a predetermined dimension with respect to the concave region or the convex region. And a step of obtaining an end face by dividing at the outside in the device length direction. 6. The method for manufacturing a semiconductor optical device according to claim 5, wherein (I). When forming the concave region on the semiconductor substrate, the thickness of the lower cladding layer d _s, when the step of d _e caused by the concave region, the beam diameter at the device end face of the guided light is respectively d _w , D _s or d _e is set so as to satisfy the following formula (1) or (2) (provided that formula (1) is used when the band gap energy of the semiconductor substrate is smaller than the photon energy of the guided light. (2) is applied when the band gap energy of the semiconductor substrate is larger than the photon energy of the guided light.), (II). The case of forming the convex region in the semiconductor substrate, the thickness of the upper cladding layer d _u, when step a d _e resulting from the convex area, the beam diameter at the light emitting end face of the guided light is respectively d _w, A method for manufacturing a semiconductor optical device, characterized in that the _du is set so as to satisfy the following expression (3). d _s = 2 × d _e ≧ d _w (1) d _e ≧ d _w / 2 (2) d _u −d _e ≧ d _w / 2 (3)