JP5140971B2 - Optical semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical semiconductor device that inputs and outputs light through an optical waveguide formed on a substrate through a window structure, and a manufacturing method thereof, and more particularly, to an optical semiconductor device that can easily form a window structure having a high upper surface and a manufacturing method thereof.

  In an optical semiconductor device using a striped optical waveguide, for example, an optical amplifier, an optical modulator, or a DFB laser, in order to operate stably, it is necessary to suppress reflection of light entering or exiting the optical waveguide at the element end face. is there. For example, in a semiconductor optical amplifier (SOA), if the reflection at the end face is large, ripples are generated in the gain spectrum, and the amplification characteristics such as gain vary with respect to the input wavelength. In addition, in a DFB laser in which a λ / 4 shift is introduced at the center of the diffraction grating, the operation may become unstable due to reflection at the end face.

  As a method for preventing reflection at the end face of the element, a method of providing a non-reflective coating film on the end face of the element or a method of arranging an optical waveguide inclined at the end face is widely known. Furthermore, in an optical semiconductor device that is greatly affected by end face reflection, a window structure is often employed in order to suppress reflection at the element end face. Hereinafter, a window structure used in a conventional optical semiconductor device will be described.

  FIG. 8 is a structural diagram of a conventional optical semiconductor device, showing an optical waveguide and a window structure. 8A is a plan view in the vicinity of the window structure, and FIG. 8B is a vertical cross section (plane perpendicular to the paper surface) passing through the center line of the optical waveguide in FIG. 8A.

  Referring to FIG. 8, in the conventional optical semiconductor device, mesa stripe 8 having both sides buried by buried layer 7 is formed on substrate 1, and substrate 1 near the end face of substrate 1, that is, the element end face. A window structure 5 made of a semiconductor layer not including an optical waveguide is provided on the upper surface. The mesa stripe 8 is composed of a multilayer structure of the optical waveguide 3 and a p-type upper cladding layer 3 and an n-type buffer layer 2 provided above and below the optical waveguide 3, respectively. The window structure 5 is composed of a semiconductor layer that is transparent to incoming and outgoing light, and is provided in contact with the end face (tip) of the optical waveguide 3.

  In this optical semiconductor device, the outgoing light 16 emitted from the optical waveguide to the window structure 5 travels while expanding in the window structure 5. For this reason, the reflected light reflected by the end surface 5-1 of the window structure 5 (which is also an end surface of the optical semiconductor device and forms the light input / output surface) further expands in the window structure 5 and travels in the direction of the optical waveguide 3. Therefore, the amount of reflected light that is input again into the optical waveguide 3 is very small, and a high reflection suppression effect can be realized.

  However, if the height of the window structure 5 is low, a part of the spread outgoing light 16 is reflected on the upper surface of the window structure 5 and travels downward again. For this reason, the intensity distribution of the light emitted through the end surface 5-1 of the window structure 5 is disturbed by reflection on the upper surface of the window structure 5, and the coupling efficiency with the optical fiber coupled at the end surface 5-1 is reduced. Let

  Therefore, the reflection of the emitted light 16 on the upper surface of the window structure 5 is avoided by forming the upper cladding layer 4 thick to increase the window structure 5 and increasing the distance from the waveguide 3 to the upper surface of the window structure 5. An optical semiconductor device has been devised.

  FIG. 9 is a structural view of a conventional improved semiconductor device (part 1), and shows a waveguide and a window structure of an optical semiconductor device in which the upper cladding layer 4 is thickened and the window structure 5 is increased. 9A is a plan view in the vicinity of the window structure, and FIG. 9B is a vertical sectional view passing through the center line of the optical waveguide in FIG. 9A.

  Referring to FIG. 9, in this optical semiconductor device, the upper cladding layer 4 is thickened in order to form the window structure 5 high. Outgoing light 16 that is emitted from the waveguide 3 to the window structure 5 and spreads, the light reflected on the upper surface of the window structure 5 is reduced to a negligible amount because the upper surface of the window structure 5 is high. For this reason, in this optical semiconductor device, the influence of the reflection of the end surface 5-1 can be made extremely small.

  However, in this optical semiconductor device, the upper clad layer 4 must be thicker than the required thickness required for the clad layer. As a result, the electric resistance of the upper clad layer 4 is increased, and the element characteristics are increased. It will deteriorate.

  A method of forming a high window structure 5 while avoiding an increase in electrical resistance of the upper cladding layer 4 has been devised.

FIG. 10 is a structural view of a conventional improved semiconductor device (part 2), showing a waveguide and a window structure of an optical semiconductor device in which a high window structure 5 is formed while avoiding an increase in electrical resistance of the upper cladding layer 4. ing. 10A is a plan view in the vicinity of the window structure, and FIG. 10B is a vertical sectional view passing through the center line of the optical waveguide in FIG. FIG. 10B shows a state where the masks 51 and 52 are removed. (For example, refer to Patent Document 1.)
Referring to FIG. 10, in this optical semiconductor device, upper clad layer 4 has the same thickness as upper clad layer 4 included in normal mesa stripe 8 shown in FIG. The upper surface of the stripe 8, that is, the upper surface of the upper cladding layer 4 is formed higher. Therefore, the electrical resistance of the upper cladding layer 4 is not increased, and the emitted light 16 is not reflected on the upper surface of the window structure 5.

The window structure 5 is manufactured by selective growth using a CVD method (chemical vapor deposition method). Referring to FIG. 10A, first, a lower layer of buffer layer 2, waveguide layer 3 and upper cladding layer 4 is deposited, and then SiO ₂ mask 52 and window structure 5 defining mesa stripe 8 are formed thereon. An SiO ₂ mask 51 having an opening that defines The mask 51 that defines the window structure 5 is provided closer to the end face of the substrate 1 than the end face of the substrate 1 and the end face of the waveguide 3, and has a width wider than the opening width of the mask 51.

Next, using these SiO ₂ 51 and 52 masks, the lower layer of the upper cladding layer 4, the waveguide layer 3 and the buffer layer 2 are patterned. As a result, a mesa stripe 8 is formed immediately below the mask 52, and A semiconductor layer having the same layer structure and the same height as the mesa stripe 8 is left immediately below the mask 51.

Next, the mesa stripe 8 and the semiconductor layer immediately below the mask 51 are buried with the buried layer 7 by the CVD method using the SiO ₂ masks 51 and 52. At this time, the buried layer 7 deposited in the opening of the wide mask 51 is deposited thicker than other portions. As a result, both sides of the mesa stripe 8 are filled with the buried layer 7 having almost the same height as the mesa stripe 8, and the buried layer 7 thicker than the mesa stripe 8 is formed in the opening of the wide mask 51.

  Next, the mask 52 and the mask 51 are removed, and the remaining layer which is the upper layer of the upper cladding layer 4 is formed on the entire surface of the substrate 1 to manufacture the optical semiconductor device.

  In the optical semiconductor device manufactured in this way, the window structure 5 is configured as a semiconductor layer composed of the buried layer 7 and the remaining layers of the upper cladding layer 4. Since the buried layer 7 deposited on the window structure 5 is deposited thicker than the mesa stripe 8, the upper surface of the window structure 5 is formed higher than the upper surface of the mesa stripe 8. Therefore, the window structure 5 having a high upper surface can be formed without increasing the thickness of the upper cladding layer 4.

  However, the method of depositing the buried layer 7 thick only in the region where the window structure 5 is formed using the mask 51 has a problem that it is difficult to form a sufficiently high window structure 5.

  This is because, in the growth method using the mask 51, in order to increase the thickness of the buried layer 7 deposited in the opening of the mask 51, the opening of the mask 51 must be narrowed. In that case, since the buried layer 7 is deposited thickly only in the narrow opening, the width of the opening necessary for the window structure 5 (the width parallel to the surface of the substrate 1 and perpendicular to the waveguide 3) is narrow. Limited by width. As a result, there arises a new problem that the emitted light spreading into the window structure 5 is reflected by the side surface of the window structure 5 (that is, the inner wall surface of the opening of the mask 51).

  For this reason, it is difficult to make the thickness of the buried layer 7 constituting the window structure 5 much higher than the thickness (height) of the mesa stripe 8. In the normal arrangement of the mesa stripe 8 and the window structure 5, it is necessary to suppress the thickness of the buried layer 7 of the window structure 5 to about three times that of the mesa stripe 8.

  FIG. 26 of Patent Document 1 shows the thickness of the window structure 5 for obtaining a sufficiently low reflectance. The distance from the optical waveguide 3 to the upper surface of the window structure 5 in the window structure 5 portion is the length of the window structure 5. This suggests that 4 μm or more is necessary when the thickness of the window structure 5 is 50 μm and 7 μm or more when the length of the window structure 5 is 50 μm. On the other hand, the height of the mesa stripe 8 is about 2.2 μm when the buffer layer is 0.5 μm, the optical waveguide 3 is 0.2 μm, and the upper cladding layer 4 is 0.5 μm. In order to avoid the adverse effect of the above, the thickness of the buried layer 7 in the window structure 5 part is three times as large as about 6.6 μm. For this reason, it is difficult to form the window structure 5 having a length of 50 μm or more by this method. Furthermore, if the upper cladding layer is made thinner to reduce the electrical resistance, the mesa stripe 8 becomes lower and it becomes more difficult to form the buried layer 7 of the thick window structure 5 part.

Further, it is difficult to apply selective growth using the mask 51 to the formation of a semi-insulating buried layer. This is because the semi-insulating buried layer is deposited by adding an organic chlorine compound in order to prevent abnormal growth occurring near the tip of the mesa stripe 8. However, in this case, the buried layer 7 can be deposited only up to the upper surface of the mesa stripe 8, and even if the wide SiO ₂ mask 51 is used, the buried layer 7 cannot be deposited thickly in the opening. For this reason, the buried layer 7 including the window structure 5 part cannot be formed by a single deposition. (See Patent Document 2.)
JP 2003-69149 A JP-A-2005-223300

  As described above, in a conventional optical semiconductor integrated device having a window structure having the same height as the upper cladding layer, the upper cladding layer must be thickened when the upper surface of the window structure is raised, and the electric resistance of the upper cladding layer is reduced. Increases and deteriorates characteristics. For this reason, it is not possible to sufficiently suppress an increase in reflectance due to reflection on the upper surface of the window structure by increasing the window structure.

  Further, in the conventional improved optical semiconductor device in which a thick buried layer is formed only in the window structure by selective growth using a mask, it is difficult to form a thick buried layer with a sufficient width for forming the window structure.

  If selective growth using this mask is used for depositing a semi-insulating buried layer, a thick buried layer of the window structure cannot be formed. For this reason, an optical semiconductor device in which a buried layer is formed only in the window structure cannot be manufactured for an optical semiconductor device in which the buried layer is semi-insulating.

  In addition, in the selective growth using the mask, a step of the semiconductor layer is generated in the mask portion, which may adversely affect the subsequent electrode formation process.

  An object of the present invention is to provide an optical semiconductor device that has a window structure made of a thick semiconductor layer on an end face of an optical waveguide and that can be easily manufactured, and a manufacturing method thereof.

  In order to solve the above problems, the optical semiconductor device having the first configuration of the present invention has a window structure forming region and an optical waveguide forming region defined on the upper surface of the substrate, and the window structure forming region is formed higher than the optical waveguide forming region. . And according to the level | step difference between a window structure formation area and an optical waveguide formation area, a window structure is formed higher than the upper clad layer formed on the optical waveguide.

  In this first configuration, the window structure forming region on the upper surface of the substrate is formed higher than the optical waveguide forming region on the upper surface of the substrate. Therefore, when a semiconductor layer is deposited to the same thickness on both the window structure forming region and the optical waveguide forming region, the upper surface of the semiconductor layer is higher than the optical waveguide forming region on the window structure forming region. It is formed higher by the minute.

  Therefore, the semiconductor layer on the optical waveguide forming region for forming the optical waveguide and the semiconductor layer on the window structure forming region constituting the window structure can be simultaneously deposited at the same deposition rate. That is, a semiconductor layer having a height substantially equal to that of the upper cladding layer is deposited on the optical waveguide forming region, and the semiconductor layer is simultaneously deposited on the window structure forming region with the same thickness, so that the window structure including the semiconductor layer is formed. Configure. At this time, the upper surface of the window structure is formed higher than the upper surface of the upper clad layer according to the level difference between the two regions.

  Thus, in this configuration, a window structure having an upper surface higher than that of the upper clad can be formed by depositing a semiconductor layer having the same thickness on both regions. At this time, a special process for forming the window structure is not required except for forming a step on the upper surface of the substrate.

  The height difference between the upper cladding layer and the window structure is determined by the height of the step on the upper surface of the substrate. Since this step can be easily controlled to a desired height by etching, the height of the window structure can be precisely controlled to an arbitrary height.

  Further, a deposition method having a deposition rate distribution is not required for the deposition of the semiconductor layer constituting the window structure. For this reason, since a wide buried layer is deposited in the lateral direction (parallel to the substrate surface and perpendicular to the optical waveguide), the buried layer is deposited to a sufficient height as the window structure while ensuring a sufficient width as the window structure. be able to.

  The second configuration of the present invention relates to an optical semiconductor device of the first configuration of the mesa stripe type that employs a current blocking structure with a pn junction. In the second configuration, the mesa stripe includes a buffer layer and an optical waveguide formed on the buffer layer, and the mesa stripe is embedded up to the upper surface of the optical waveguide by an embedded layer formed on the substrate. And it has the block layer opened on a mesa stripe, and the upper clad layer which extended the opening on the embedding block layer. These buried layer and block layer constitute a well-known current blocking structure with a pn junction.

  In this second configuration, the mesa stripe is embedded by the conductive embedded layer, and the embedded layer deposited on the window structure forming region is used as the semiconductor layer forming the window structure. Since the conductive buried layer is deposited on the substrate with a uniform thickness, the upper surface of the window structure including the buried layer is formed higher than the upper cladding layer by the level difference of the upper surface of the substrate. Accordingly, a window structure having a high upper surface can be formed simultaneously with the deposition of a semiconductor layer having a normal current blocking structure including a buried layer. This optical semiconductor device having the second configuration can form a window structure with a high upper surface only by forming a step on the upper surface of the substrate and without further increasing the number of steps.

  The third configuration of the present invention relates to a mesa stripe type first configuration optical semiconductor device employing an insulating buried structure. In the third configuration, a mesa stripe is formed on the optical waveguide formation region, and a dummy mesa stripe is formed on the window structure formation region. The mesa stripe includes an optical waveguide and an upper clad layer formed thereon. The dummy mesa stripe has the same structure as the mesa stripe and is provided on both sides of the extension line of the mesa stripe. That is, no dummy mesa stripe is formed on the extended line of the mesa stripe through which light passes. The side surfaces and end surfaces of the mesa stripe and the dummy mesa stripe are buried with a semi-insulating buried layer.

  In the third configuration, at least two dummy mesa stripes are provided on the window structure forming region, and the mesa stripe and the dummy mesa stripe are embedded by the semi-insulating embedded layer. Then, the buried layer deposited between the dummy mesa stripes formed on the window structure forming region is used as a semiconductor layer constituting the window structure. As is well known, the semi-insulating buried layer is deposited on the side and end surfaces of the mesa stripe at the same height as the mesa stripe. A buried layer is formed. Accordingly, a semi-insulating buried layer is deposited around the mesa stripe, and at the same time, a buried layer having the same height as the dummy mesa stripe is also deposited between the dummy mesa stripes. Since the dummy mesa stripe is formed on the upper surface of the substrate higher than the mesa stripe by a step, the buried layer deposited between the dummy mesa stripes is used as a semiconductor layer constituting the window structure, so that the buried layer and the mesa of the mesa stripe are formed. A window structure higher than the stripe can be formed by depositing the buried layer once. The dummy mesa stripe is formed simultaneously with the mesa stripe. Accordingly, in the manufacture of the optical semiconductor device having the third configuration, it is possible to form a window structure having a high upper surface without forming a step on the upper surface of the substrate without using a special manufacturing process. .

  According to the present invention, a window structure is formed by simply depositing a semiconductor layer having a uniform thickness on a substrate having a step, so that the window structure has an upper surface that is sufficiently wide and sufficiently higher than the upper surface of the upper cladding layer. Can be easily manufactured.

  The first embodiment of the present invention relates to a semiconductor optical amplifier, and more particularly to an optical semiconductor device having a mesa stripe type optical waveguide having a current blocking structure using a pn junction.

  FIG. 1 is a structural diagram of an optical semiconductor device according to a first embodiment of the present invention, showing a semiconductor optical amplifier having a mesa stripe type optical waveguide having a current block structure using a pn junction. 1A is a plan view, FIG. 1B is a sectional view taken along line AA ′ in FIG. 1A, and FIG. 1C is a sectional view taken along line BB ′ in FIG. .

  Referring to FIG. 1, in the optical semiconductor device of the first embodiment, mesa stripes 8 are formed on an optical waveguide forming region 1B provided at the center of the upper surface of the substrate 1, and both ends of the mesa stripe 8 on the upper surface of the substrate 1 are formed. The window structure 5 is formed on the window structure forming region 1A provided adjacent to the optical waveguide forming region 1B.

  The optical waveguide forming region 1B provided in the central portion of the substrate 1 is formed to have a lower upper surface than the window structure forming region 1A provided in the end surface portion of the substrate. The window structure forming region 1A has a flat surface 1a on the end surface side of the substrate 1, and has a slope 1b connecting the flat surface 1a and the optical waveguide forming region 1B. The window structure forming region 1A preferably includes a planar region 1d that is coplanar with the optical waveguide forming region 1B between the mesa stripe 8 and the inclined surface 1b. As described above, the semiconductor layer embedded in the mesa stripe 8 can be uniformly deposited by placing the plane region 1d between the mesa stripe 8 and the inclined surface 1b.

  The mesa stripe 8 has an n-type buffer layer 2 and an optical waveguide 3 formed thereon. The mesa stripe 8 is buried with the p-type buried layer 7 up to its upper surface (that is, the upper surface of the optical waveguide 3). The p-type buried layer 7 is formed with a substantially uniform thickness on the entire surface of the substrate 1 excluding the mesa stripe 8, and thus also on the window structure forming region 1A. As a result, the upper surface of the buried layer 7 inherits the same uneven shape as the upper surface of the substrate 1, and the step on the upper surface of the substrate 1 is inherited as it is to the upper surface of the buried layer 7.

  A block layer 6 made of an n-type semiconductor is formed on the buried layer 7. The n-type block layer 6 forms a pn junction in the opposite direction to the p-type buried layer 7 and blocks current from above to the buried layer 7. The block layer 6 is provided with an opening that exposes the upper surface of the optical waveguide 3, and this opening serves as a current path to the optical waveguide 3. The thickness of the block layer 6 is also uniform, and a step similar to the step on the upper surface of the substrate 1 is formed on the upper surface thereof.

  On this block layer 6, an opening of the block layer 6 is buried, and a p-type upper cladding layer 4 extending on the block layer 6 is provided. Further, a contact layer 11 is provided on the upper cladding layer 4. Since the upper clad layer 4 and the contact layer 11 are also uniform in thickness, a step similar to the step on the upper surface of the substrate 1 is formed on the upper surface thereof.

  The window structure 5 includes a semiconductor layer 5 </ b> A composed of a substrate 1 to an upper clad layer 4. Each layer constituting the semiconductor layer 5A has a uniform thickness. Therefore, the upper surface of each layer forms a step substantially equal to the step on the upper surface of the substrate 1. In other words, the upper surface of the window structure 5 has the same height as the upper cladding layer 4 formed on the optical waveguide formation region 1B according to the planar region 1d, the inclined surface 1b, and the flat surface 1a constituting the window structure formation region 1A. , A slope formed on the slope 1b, and a plane formed on the flat surface 1a.

  In this way, by making the step on the upper surface of the substrate 1 higher, the upper surface of the window structure 5 is made sufficiently higher than the upper surface of the upper cladding layer 4 formed on the optical waveguide forming region 1B. A semiconductor device is realized. This step can be easily formed by etching or the like. Further, since the semiconductor layer 5A constituting the window structure 5 is widely deposited in a direction perpendicular to the waveguide 3 and parallel to the substrate surface, the light intensity distribution in the lateral direction is not deteriorated. Therefore, an optical semiconductor device with little reflection can be easily manufactured.

  Further, a passivation insulating film 12 having an opening 12 a on the mesa stripe 8 is provided on the contact layer 11, and an upper electrode 13 for filling the opening is provided. A lower electrode is provided on the lower surface of the substrate 1.

  The manufacturing process of the optical semiconductor device of the first embodiment described above will be described below.

  FIG. 2 is a diagram (part 1) illustrating an optical semiconductor device manufacturing process according to the first embodiment of the present invention, and FIG. 3 is a diagram (part 2) illustrating an optical semiconductor device manufacturing process according to the first embodiment of the present invention. 2 (a), (c), (e) and (g) and FIGS. 3 (i), (k) and (m) are plan views, and FIGS. 2 (b), (d) and (f). And (h) and FIGS. 3 (j), (l) and (n) represent cross-sectional views.

First, referring to FIGS. 2A and 2B, an n-type (100) InP wafer in which a region to be the substrate 1 is defined by a scribe line is prepared, and an upper surface near both ends of the substrate 1 is prepared. A rectangular SiO ₂ mask 31 that defines the flat surface 1a of the window structure forming region 1A is formed by photolithography. Hereinafter, in order to simplify the description, in the description of this manufacturing process, in addition to the meaning of the individually separated substrates, the region defined by the scribe lines on the InP wafer, that is, the scribe lines. Is also used to mean the area of the wafer to be divided into individual substrates 1.

  Next, referring to FIGS. 2C and 2D, the upper surface of the substrate 1 is etched by 3.5 μm by wet etching using a hydrochloric acid-based etchant using the mask 31 as an etching mask. As a result, an optical waveguide forming region 1B having an upper surface that is 3.5 μm lower than the flat surface 1a covered with the mask 31 is formed on the upper surface of the substrate 1. At the same time, an inclined surface 1b is formed between the flat surface 1a and the optical waveguide forming region 1B.

  2E and 2F, after removing the mask 31, the buffer layer 3 made of n-type InP having a thickness of 0.5 μm is formed on the entire surface of the substrate 1 by CVD. An optical waveguide layer 3-1 having a thickness of 200 nm and a p-type InP upper cladding layer 4-1 having a thickness of 0.5 μm are deposited. The upper clad layer 4-1 constitutes a lower layer portion of the upper clad layer 4 with reference to FIG. The optical waveguide layer 3-1 is composed of an MQW structure active layer having a band gap wavelength of 1.55 μm and light confinement layers provided above and below it.

Next, with reference to FIGS. 2G and 2H, a SiO ₂ mask 32 that defines mesa stripes 8 extending in the <011> direction is formed on the optical waveguide forming region 1B by photolithography. Next, the upper cladding layer 4-1, the optical waveguide layer 3-1, and the buffer layer 3 are removed by etching to the upper surface of the substrate 1 using the mask 32, and the buffer layer 3 and the patterned optical waveguide layer 3-1. The mesa stripe 8 having the optical waveguide 3 and the upper cladding layer 4-1 is formed. The mesa stripe 8 is formed with a planar region 1d having a width of, for example, about 5 μm between the slope 1b so that both ends do not cover the slope 1b. The planar region 1d constitutes a window structure forming region 1A together with the inclined surface 1b and the flat surface 1a.

  Next, referring to FIGS. 3 (i) and 3 (j), a p-type InP buried layer 7 is deposited on the entire surface of the substrate 1 by CVD to bury the mesa stripe 8 up to the upper surface of the optical waveguide 3. Next, a block layer 6 made of n-type InP and an upper clad layer 4-2 made of p-type InP, which fill the remaining upper part of the mesa stripe 8, are deposited in this order by the CVD method. The buried layer 7, the n-type block layer 6, and the p-type upper cladding layer 4-2 are deposited on the substrate 1 with a uniform thickness. Further, the block layer 6 is not formed in the portion of the mesa stripe 8, and this portion becomes an opening of the block layer 6. Further, this opening is filled with the upper clad layer 4-1.

  As a result, the mesa stripe 8 is buried up to its upper surface with a semiconductor layer having a three-layer structure including the p-type buried layer 7 / n-type block layer 6 / p-type upper clad layer 4-2. The semiconductor layer having the three-layer structure is also formed on the window structure forming region 1A, and a step having the same shape as the window structure forming region 1A of the substrate 1 is formed on the upper surface thereof.

  Next, referring to FIGS. 3K and 3L, after removing the mask 32, an upper cladding layer 4-3 made of p-type InP having a thickness of 1.0 μm is formed on the entire surface of the substrate 1 by CVD. Then, a contact layer 11 having a two-layer structure made of InGaAsP / InGaAs is deposited thereon. The upper cladding layer 4-3 constitutes the upper cladding layer 4 together with the upper cladding layers 4-1 and 4-2. Further, the upper surface of the upper clad layer 4-3 and the contact layer 11 is also formed with a step having the same shape as the window structure forming region 1A of the substrate 1.

Next, with reference to FIGS. 3M and 3N, a passivation SiO ₂ insulating layer 12 having an opening for defining the upper electrode 13 is formed on the contact layer 11, and the opening is filled with Ti / An upper electrode 13 made of Pt / Au is formed. Further, a lower electrode 14 made of AuGe / Au is formed on the lower surface of the substrate 1.

  Next, the wafer is cut along the scribe line and divided into individual optical semiconductor devices. Thereafter, the antireflection film 15 is formed on the end face of the optical semiconductor device, and the optical semiconductor device according to the first embodiment is manufactured.

  In the optical semiconductor device of the first embodiment, the upper clad layer 4 on the optical waveguide 3 is composed of upper clad layers 4-1 and 4-3, and the thickness thereof is 1.5 μm. Accordingly, a sufficiently low resistance of the upper cladding layer 4 is realized while having a sufficient thickness as the upper cladding layer 4.

  The window structure 5 includes a buried layer 7, a block layer 6, upper clad layers 4-2 and 4-3 formed on the window structure formation region 1A, and an upper layer of the substrate 1 (the substrate 1 in the window region formation region 1A portion). ). The upper surface of the window structure 5 is the upper surface of the upper clad layer 4-3 on which a step is formed, and is formed as a step surface that is 3.5 μm higher than the upper surface of the upper clad layer 4-3 on the optical waveguide 3. The thickness of the cladding layer 4 on the optical waveguide 3 is 1.5 μm, and the upper surface of the window structure 5 is 3.5 μm higher than that. Accordingly, the upper surface of the window structure 5 is 5 μm higher than the upper surface of the optical waveguide 3. Thus, since the space | interval of the optical waveguide 3 and the window structure 5 upper surface is wide, the ratio with which the emitted light from the optical waveguide 3 is reflected on the upper surface of the window structure 5 is small, and a low reflectance is implement | achieved.

  In the manufacturing method of the optical semiconductor device according to the first embodiment described above, a step is formed on the substrate 1, and a window having a thin upper cladding layer 4 and a high upper surface is formed by a normal uniform semiconductor layer deposition process. Structure.

  The second embodiment of the present invention relates to a semiconductor optical amplifier, and more particularly to an optical semiconductor device having a mesa stripe optical waveguide in which a mesa stripe is embedded by a semi-insulating embedded layer.

  FIG. 4 is a structural diagram of an optical semiconductor device according to the second embodiment of the present invention, and shows a semiconductor optical amplifier having a mesa stripe type optical waveguide in which a mesa stripe is embedded by a semi-insulating embedded layer. 4A is a plan view, FIG. 4B is a CC ′ sectional view in FIG. 4A, and FIG. 4C is a DD ′ sectional view in FIG. 4A. .

  Referring to FIG. 4, the optical semiconductor device according to the second embodiment is the same except that it has dummy mesa stripe 22 and buried layer 21 in which mesa stripe 8 is embedded is formed of a semi-insulating semiconductor layer. This is almost the same as the optical semiconductor device of the first embodiment.

  First, a step is provided on the (001) InP substrate 1, and a window structure forming region 1A including a flat surface 1a forming the upper surface of the step, a slope 1b and a planar region 1d forming a part of the lower surface of the step on the upper surface of the substrate 1, and An optical waveguide forming region 1B forming the lower surface of the step is formed. A mesa stripe 8 extending in the <110> direction is formed in the optical waveguide forming region 1B. These are the same as in the first embodiment.

  The mesa stripe 8 includes a buffer layer 2 made of n-type InP having a thickness of 0.5 μm, an optical waveguide 3 having a thickness of 200 nm, an upper cladding layer 4 made of p-type InP having a thickness of 1.5 μm, and two layers of InPGaAsP / InGaAs. The contact layer 11 has a structure. The optical waveguide 3 has the same layer structure as that of the first embodiment.

  The dummy mesa stripe 22 has the same layer structure as the mesa stripe 8 and is provided in the window structure forming region 1A, for example, on the flat surface 1a, the flat surface 1a and the inclined surface 1b, or on the flat surface 1a, the inclined surface 1b and the flat region 1d. It is done. The dummy mesa stripe 22 is provided on both sides of the extended line of the mesa stripe 8, for example, in parallel with the mesa stripe 8. The dummy mesa stripes 22 can also be arranged non-parallel. Thereby, the upper surface of the window structure 5 can be inclined and the reflectance can be further reduced. Further, in an application where an increase in the manufacturing process is allowed, an arbitrary layer structure different from the mesa stripe 8 can be used.

  The mesa stripe 8 and the dummy mesa stripe 22 are buried with a semi-insulating InP buried layer 21. The buried layer 21 has a height substantially close to the upper surfaces of the mesa stripe 8 and the dummy mesa stripe 22 in the vicinity of the mesa stripe 8 and the dummy mesa stripe 22, that is, the upper surface of the contact layer 11, and is formed lower than this at a distant position. Is done. The low formation at this distant position is caused by the deposition method of the buried layer 21 as will be described later. If the deposition method allows, the height of the buried layer 21 is set to the mesa stripe 8 and the dummy mesa stripe 22. It can be almost the same as the top surface of the plate.

  The dummy mesa stripes 22 are arranged at a narrow interval so that the buried layer 21 deposited therebetween is deposited at substantially the same height as the dummy mesa stripes 22. The buried layer 21 deposited between the dummy mesa stripes 22 forms the window structure 5. Therefore, in the second embodiment, a window structure whose upper surface is higher than the height of the step formed on the upper surface of the substrate 1 can be formed by depositing the buried layer 21 once as in the first embodiment. An antireflection film 15 is coated on the end face of this window structure (end face of the optical semiconductor device).

  Further, a passivation insulating layer 12 having an opening is provided on the mesa stripe 8, an upper electrode 13 for embedding the opening is provided, and a lower electrode 14 is provided on the lower surface of the substrate 1.

  Next, a method for manufacturing the above-described optical semiconductor device (semiconductor optical amplifier) of the second embodiment will be described.

  FIGS. 5A and 5B are diagrams showing the optical semiconductor device manufacturing process according to the second embodiment of the present invention. FIGS. 5A, 5C, and 5E are plan views, and FIGS. FIG. 5F shows a vertical sectional view including the center line of the mesa stripe, and FIG. 5F shows an EE ′ vertical sectional view of FIG.

  In the method of manufacturing an optical semiconductor device according to the second embodiment of the present invention, a 3.5 μ step having a flat surface 1 a and a slope 1 b is formed on the upper surface of an n-type InP substrate 1 having (001) as a main surface. Until the window structure forming region 1A including the high surface and the optical waveguide forming region 1B including the low step surface are formed, the manufacturing process is the same as that of the first embodiment up to FIG.

  Next, referring to FIG. 5A, a buffer layer 2 made of n-type InP having a thickness of 0.5 μm, an optical waveguide layer 3-1 having a thickness of 200 nm, a thickness is formed on the upper surface of the substrate 1 using the CVD method. An upper clad layer 4 made of p-type InP having a thickness of 1.5 μm and a contact layer 11 made of two layers of InGaAsP / InGaAs are deposited in this order. These semiconductor layers are deposited on the upper surface of the substrate 1 with a substantially uniform thickness.

Next, referring to FIG. 5C, a SiO ₂ mask 23 that defines mesa stripe 8 and a SiO ₂ 23-1 mask that defines dummy mesa stripe 22 are formed on contact layer 11 by photolithography. . The dummy mesa stripe 22 is provided on the slope 1b and the flat surface 1a, for example. Further, the mesa stripe 8 and the dummy mesa stripe 22 extend in the <110> direction, for example.

  Next, referring to FIGS. 5C and 5D, the contact layer 11, the upper cladding layer 4, the optical waveguide layer 3-1, and the buffer layer 2 are formed by ion etching using the masks 23 and 23-1 as a mask. By removing, the mesa stripe 8 and the dummy mesa stripe 22 are formed. By this step, the contact layer 11, the upper cladding layer 4, the optical waveguide layer 3-1 and the buffer layer 2 are removed from the upper surface of the substrate 1 except for the layers constituting the mesa stripe 8 and the dummy mesa stripe 22. Note that the upper surface of the substrate 1 is exposed except for a region where the mesa stripe 8 and the dummy mesa stripe 22 are not formed.

  Next, by a CVD method using a source gas to which an organic chlorine compound such as 1,2-dichloroethane (C2H4Cl2), 1,2-dichloropropane (C3H6Cl2) or 1,2-dichloroethylene (C2H2Cl2) is added. Then, a buried layer 21 made of semi-insulating InP is deposited on the substrate 1 to bury the mesa stripe 8 and the dummy mesa stripe 22 up to the upper surface (upper surface of the contact layer 11). At this time, as the buried layer 21, an InP-based buried layer other than InP, for example, a buried layer made of InP, InGaP, or InGaAsP can be used.

  Referring to FIGS. 5E and 5F, the semi-insulating InP buried layer 21 deposited by the CVD method using a source gas containing an organochlorine compound is composed of (110) and (1-10). ) Are deposited on the side surfaces and the end surfaces of the mesa stripe 8 and the dummy mesa stripe 22 made of a plane so as not to crawl above the upper surfaces of the mesa stripe 8 and the dummy mesa stripe 22.

  As a result, the buried layer 21 is formed on both sides of the mesa stripe 8, between and outside the dummy mesa stripe 22, and between the mesa stripe 8 and the dummy mesa stripe 22. In addition, the dummy mesa stripe 22 is formed at the same height as that of the dummy mesa stripe 22 and is formed lower than that at the outer side.

  In the optical semiconductor device according to the second embodiment, the buried layer 21 (and the upper surface portion of the substrate 1) formed between the dummy mesa stripes 22 (a region on the extension line of the mesa stripe 8 from the tip of the mesa stripe 8) may be included. The window structure 5. The buried layer 21 constituting the window structure 5 has a flat upper surface, and its height is substantially equal to the height of the dummy mesa stripe 22. Therefore, the upper surface of the window structure 5 is formed higher than the upper surface of the mesa stripe 8 by the level difference of the substrate 1. Since the upper surface of the mesa stripe 8 is at least as thick as the contact layer 11 than the upper surface of the upper cladding layer 4, the upper surface of the window structure 5 is at least as thick as the upper cladding layer 4 with a thickness of 1.5 μm from the optical waveguide 3. It becomes higher by 5 μm, which is the sum of 3.5 μm. As described above, since the high window structure 5 can be formed while the upper cladding layer 4 is kept at the minimum necessary thickness, an optical semiconductor device having a low cladding layer resistance and a high antireflection effect is provided. Furthermore, the window structure 5 having a high upper surface of such an optical semiconductor device can be manufactured simply by adding a step forming process to the manufacturing process of a normal optical semiconductor device.

  Next, the masks 23 and 23-1 are removed, and further referring to FIGS. 3 (m) and 3 (n), the insulating film 12 having an opening on the mesa stripe 8, the upper electrode 13 filling the opening, and the substrate 1 Lower electrode 14 is formed on the lower surface. Thereafter, the wafer is divided into individual optical semiconductor devices, and an antireflection film 15 is coated on the end face of the optical semiconductor device to manufacture the optical semiconductor device (semiconductor optical amplifier) of the second embodiment. FIG. 6 is a plan view of a modification of the first embodiment of the present invention, and shows an optical semiconductor device having a current block structure using a pn junction.

  With reference to FIG. 6, in this modification, the mesa stripe 8 of the optical semiconductor device of the first embodiment is disposed obliquely with respect to the end face of the substrate 1, for example, by 10 degrees. The rest is the same as in the first embodiment. In such an arrangement, the light emitted from the optical waveguide 3 is incident on the end face of the substrate 1 at an angle, so that an optical semiconductor device that is less reflected by the end face of the substrate 1 and returning to the optical waveguide 3 is realized.

  FIG. 7 is a plan view of a modification of the second embodiment of the present invention, showing a mesa stripe type optical semiconductor device in which a mesa stripe is embedded by a semi-insulating buried layer.

  Referring to FIG. 7, in this modification, the mesa stripe 8 of the optical semiconductor device of the second embodiment is disposed obliquely with respect to the end surface of the substrate 1, for example, by 10 degrees. The rest is the same as in the second embodiment. In the optical semiconductor device having such an arrangement, similarly to the optical semiconductor device shown in FIG. 6, it is possible to reduce the light reflected by the end face of the substrate 1 and returning to the optical waveguide 3 again.

As described above, the present invention disclosed in the following supplementary notes is disclosed in this specification.
(Appendix 1) In an optical semiconductor device having an optical waveguide on a substrate and a window structure formed on an end face of the optical waveguide,
An optical waveguide forming region defined by the upper surface of the substrate in which the optical waveguide is formed;
A window structure forming region defined on the upper surface of the substrate and having an upper surface higher than the optical waveguide forming region, wherein the window structure is formed;
An upper cladding layer formed on the optical waveguide;
An optical semiconductor device comprising: a semiconductor layer that forms the window structure, and is formed above the upper surface of the upper cladding layer on the window structure forming region.
(Supplementary Note 2) A mesa stripe including the optical waveguide formed on the buffer layer of the first conductivity type and the puffer layer;
An embedded layer of a second conductivity type formed on the substrate and burying the side surface and end surface of the mesa stripe up to the upper surface of the optical waveguide;
A block layer of a first conductivity type formed on the buried layer and having an opening on the mesa stripe;
2. The optical semiconductor device according to claim 1, further comprising a second conductivity type upper cladding layer embedded in the opening and extending on the block layer.
(Supplementary Note 3) A mesa stripe including the optical waveguide and the upper clad;
Dummy mesa stripes formed on the window structure forming region along the extension lines on both sides of the extension lines of the mesa stripes;
A semi-insulating embedded layer that embeds side surfaces and end surfaces of the mesa stripe and the dummy mesa stripe; and
The optical semiconductor device according to claim 1, further comprising: an upper clad layer formed on the mesa stripe, the dummy mesa stripe, and the buried layer.
(Supplementary note 4) The optical semiconductor device according to supplementary note 3, wherein the dummy mesa stripe has the same structure as the mesa stripe.
(Supplementary note 5) The semiconductor device according to supplementary note 1, 2, 3 or 4, further comprising a non-reflective coating film on an outer end face of the window structure through which input / output light to the optical waveguide is transmitted.
(Additional remark 6) The said waveguide is arrange | positioned diagonally with respect to the outer side end surface of the said window structure, The semiconductor device of Additional remark 1, 2, 3, 4 or 5 characterized by the above-mentioned.
(Additional remark 7) In the manufacturing method of the optical semiconductor device which has an optical waveguide and the window structure formed in the end surface of the said optical waveguide on a board | substrate,
Leaving a window structure forming region near the end surface of the substrate surface, and forming an optical waveguide forming region formed of a recess on the substrate surface;
Forming a first conductivity type buffer layer and a mesa stripe including the optical waveguide formed on the buffer layer on the optical waveguide formation region;
Forming a second conductive type buried layer on the substrate to embed side and end faces of the mesa stripe; and forming a first conductive type block layer having an opening on the mesa stripe on the buried layer. Process,
And a step of forming a second conductivity type upper cladding layer filling the opening and extending on the block layer.
(Additional remark 8) In the manufacturing method of the optical semiconductor device which has an optical waveguide and the window structure formed in the end surface of the said optical waveguide on a board | substrate,
Leaving a window structure forming region near the end surface of the substrate surface, and forming an optical waveguide forming region formed of a recess on the substrate surface;
Forming a mesa stripe including the optical waveguide and an upper cladding layer formed on the optical waveguide on the optical waveguide formation region;
Forming dummy mesa stripes having the same structure as the mesa stripes on both sides of the extension line of the mesa stripes on the window structure forming region simultaneously with the mesa stripes;
Forming a semi-insulating buried layer on the substrate to bury side faces and end faces of the mesa stripe and the dummy mesa stripe.

  By applying the present invention to an optical semiconductor device having a buried mesa stripe type optical waveguide and a window structure, an optical semiconductor device with little return light and stable operation can be provided.

1 is a structural diagram of an optical semiconductor device according to a first embodiment of the present invention. The figure showing the optical semiconductor device manufacturing process of 1st Embodiment of this invention (the 1) The figure showing the optical semiconductor device manufacturing process of 1st Embodiment of this invention (the 2) Structure of optical semiconductor device according to second embodiment of the present invention The figure showing the optical semiconductor device manufacturing process of 2nd Embodiment of this invention. Modified plan view of the first embodiment of the present invention Modified plan view of the second embodiment of the present invention Conventional semiconductor device structure Conventionally Improved Semiconductor Device Structure (Part 1) Conventionally Improved Semiconductor Device Structure (Part 2)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 1A Window structure formation area 1B Optical waveguide formation area 1a Flat part 1b Slope 1d Plane area 2 Buffer layer 3 Optical waveguide 3-1 Optical waveguide layer 4, 4-1, 4-2 Upper cladding layer 5 Window structure 5-1 End face 5A Semiconductor layer forming window structure 6 Block layer 7, 21 Buried layer 8 Mesa stripe 11 Contact layer 12 Insulating layer 13 Upper electrode 14 Lower electrode 15 Antireflection film 16 Emission light 22 Dummy mesa stripe 23, 231, 32, 51 Mask 51, 52 Mask

Claims (2)

In an optical semiconductor device having an optical waveguide on a substrate and a window structure formed on an end face of the optical waveguide,
An optical waveguide forming region defined by the upper surface of the substrate in which the optical waveguide is formed;
A window structure forming region defined on the upper surface of the substrate and having an upper surface higher than the optical waveguide forming region, wherein the window structure is formed;
A mesa stripe formed on the optical waveguide forming region and including the optical waveguide and an upper cladding layer formed on the optical waveguide;
A dummy mesa stripe having the same height as the mesa stripe formed on the window structure forming region along the extension line on both sides of the extension line of the mesa stripe;
Semi- insulating embedding that is deposited at the same height as the mesa stripe and the dummy mesa stripe on the side surfaces and end faces of the mesa stripe and the dummy mesa stripe, and between the dummy mesa stripes is buried at the height of the dummy mesa stripe Layers,
An optical semiconductor device comprising: On a substrate, in an optical semiconductor device manufacturing method having an optical waveguide and a window structure formed on an end face of the optical waveguide,
Leaving a window structure forming region near the end surface of the substrate surface, and forming an optical waveguide forming region formed of a recess on the substrate surface;
Forming a mesa stripe including the optical waveguide and an upper cladding layer formed on the optical waveguide on the optical waveguide formation region;
Forming dummy mesa stripes having the same stacked structure as the mesa stripes on both sides of the extension lines of the mesa stripes on the window structure forming region simultaneously with the mesa stripes;
On the substrate, a semi-insulating embedded layer is formed on the side surfaces and end surfaces of the mesa stripe and the dummy mesa stripe, and is deposited at the same height as the mesa stripe and the dummy mesa stripe, and the gap between the dummy mesa stripes is formed. And a step of forming the buried layer buried at the height of the dummy mesa stripe.

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