JP5653270B2 - Light receiving element, manufacturing method thereof, and optical transmission / reception unit - Google Patents

Description

  Embodiments described herein relate generally to a light receiving element, a manufacturing method thereof, and an optical transmission / reception unit.

  In recent years, with the increase in integration density of LSI (Large Scale Integration), miniaturization of internal circuit patterns has progressed, and an optical wiring technique that replaces an electrical signal with an optical signal for miniaturization has attracted attention. Optical wiring technology is a method of transmitting signals using an optical waveguide instead of metal wiring, and does not increase the wiring resistance and inter-wiring capacitance due to the above-mentioned miniaturization, further increasing the operation speed Can be expected. As for a semiconductor laser (LD) used as a light source, a small microring LD using a microring resonator has begun to attract attention, and research and development has been activated.

  In order to realize optical wiring on an LSI chip, a light source element (transmission unit) and an optical waveguide (transmission unit) as well as a light receiving element (PD, reception unit) are compactly integrated on a chip on the same semiconductor substrate. It is necessary to form a transmission / reception unit. In particular, in the case of integration with a microring LD, it is strongly desired that the PD can be manufactured from a wafer having the same laminated structure from the viewpoint of cost reduction.

  However, in the wafer having the same structure as the LD, the absorption layer is composed of several layers of semiconductor quantum wells, the thickness of which is as thin as several tens of nanometers, and sufficient light absorption efficiency and sufficient light-electric conversion efficiency (according to this) Alternatively, it is very difficult to obtain a photocurrent.

  Therefore, it is expected to reduce the element size and increase the efficiency by connecting a waveguide to the ring-shaped light receiving part and circulating the input light inside the ring to increase the effective absorption length. . In fact, there is an example in which a ring-shaped light receiving element based on such a principle is proposed. However, it is not easy to obtain light by circulating light with low loss inside the ring and efficiently absorbing the light into the active medium to convert the light into carriers (electron-hole pairs). In particular, in a minute ring structure having a diameter of about 10 microns, light loss due to scattering and carrier loss due to surface recombination occur due to processing damage on the ring side wall, which causes a significant reduction in light-electric conversion efficiency. Further, in a ring or disk-shaped light receiving part, loss due to light emission or scattering is likely to occur, and as the size is reduced, the increase in these losses becomes more significant, making it difficult to increase efficiency.

US Pat. No. 6,978,067

  The problem to be solved by the invention is to obtain a small light receiving element and an optical transmission / reception unit that receive light with high efficiency.

A light receiving element according to an embodiment includes a thin wire optical waveguide having one end connected to a semiconductor light source and the other end formed in a spiral shape having at least one turn, and a semiconductor material provided on the other end of the thin wire optical waveguide. A lower clad layer formed on the lower clad layer and having a disk-like or ring-like shape, a light absorbing layer made of a semiconductor material, an upper clad layer made of a semiconductor material provided on the light absorbing layer, and the upper portion A first electrode opposed to the cladding layer via the first contact layer; and a second electrode opposed to the lower cladding layer via the second contact layer; The end has a tapered shape with a radius of curvature smaller than that of the one end and a width narrower than that of the one end, and the upper cladding layer is in contact with the first contact layer and the light absorption layer. A lower refractive index part having a lower refractive index than the other part of the upper cladding layer, or the lower cladding layer is in contact with the second contact layer and the light absorption layer. At least a portion of the side surface other than the portion has a low refractive index portion having a lower refractive index than other portions of the lower cladding layer, or both.

According to an embodiment of the present invention, there is provided a method of manufacturing the light receiving element, comprising: laminating a thin optical waveguide, a second contact layer, a lower cladding layer, a light absorbing layer, an upper cladding layer, and a first contact layer; And a step of oxidizing a part of a side surface of at least one of the upper cladding layers along an outer periphery, a step of forming a lower electrode in contact with the second contact layer, and an upper electrode in contact with the first contact layer. Forming.

An optical transceiver unit according to an embodiment includes a semiconductor light source, a thin optical waveguide having one end connected to the semiconductor light source and the other end formed in a spiral shape, and a semiconductor provided on the other end of the thin optical waveguide A lower clad layer made of a material, provided on the lower clad layer, in a disk shape or a ring shape, a light absorbing layer made of a semiconductor material, and an upper clad layer made of a semiconductor material provided on the light absorbing layer, A first electrode opposed to the upper cladding layer via a first contact layer; and a second electrode opposed to the lower cladding layer via a second contact layer; and The other end has a taper shape with a radius of curvature smaller than that of the one end and becomes narrower as it approaches the terminal end, and the upper cladding layer includes the first contact layer and the light absorption layer. A lower refractive index portion having a lower refractive index than other portions of the upper cladding layer is provided on at least a part of a side surface other than a portion in contact with the layer, or the lower cladding layer includes the second contact layer and the light absorption layer A light receiving element having at least a low refractive index portion having a lower refractive index than other portions of the lower clad layer, or both of them, on at least a part of a side surface other than a portion in contact with the lower cladding layer.

FIG. 3 is a top view and a bottom view showing a state before formation of an upper electrode and a lower electrode of a light receiving element according to a first embodiment. It is sectional drawing along the broken line II-II of the light receiving element shown in FIG. It is a figure which shows the simulation result of the absorption efficiency of a light receiving element. 6 is a cross-sectional view showing a manufacturing process of the light receiving element according to the first embodiment. FIG. It is a top view which shows the state before upper electrode and lower electrode formation of the light receiving element which concerns on 2nd Embodiment. FIG. 6 is a cross-sectional view taken along broken line VI-VI of the light receiving element shown in FIG. 5. It is a top view which shows the upper clad layer of the light receiving element which concerns on 3rd Embodiment, and the thin wire | line optical waveguide provided under it. It is a perspective view which shows the optical transmission / reception unit which concerns on 4th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.

  It should be noted that the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

(First embodiment)
FIG. 1 is a top view (A) and a bottom view (B) showing a state before formation of the upper electrode and the lower electrode of the light receiving element 100 of the first embodiment, and FIG. 2 is a broken line II-II shown in FIG. FIG. In FIG. 1, the light receiving element 100 shows a state before electrode formation. In FIGS. 1A and 1B, the left side is the upstream of the thin optical waveguide 20. In the light receiving element 100, the thin optical waveguide 20 is formed on a part of the dielectric layer 11 provided on the substrate 10. Yes. The downstream portion of the thin optical waveguide 20 is processed into a spiral shape of at least one round, and the terminal portion of the thin optical waveguide 20 merges with the outer periphery inside the spiral. FIG. 1B shows the position of the thin optical waveguide 20 on the substrate 10 and the dielectric layer 11 by a broken line. A lower cladding layer 30 is provided on the thin optical waveguide 20 via a bonding layer 35. A contact layer 80 is provided on the lower cladding layer 30. A light absorption layer 40 is provided on the contact layer 80 so as to cover the range of the thin optical waveguide 20. An upper cladding layer 50 is provided on the light absorption layer 40. On the upper cladding layer 50, a first contact layer 60 and an upper electrode 70 are laminated in this order. A lower electrode 90 is provided on the inner side surrounded by the light absorption layer 40 on the lower cladding layer 30.

  The bonding layer 35, the lower cladding layer 30, the second contact layer 80, the light absorption layer 40, the upper cladding layer 50, and the first contact layer 60 are each made of a semiconductor layer. Of the upper clad layer 50, the side surface portion 51 along the outer periphery between the first contact layer 60 and the light absorption layer 40 and the side surface portion 52 along the inner periphery surrounding the gap are the other parts of the upper clad layer 50. This is an oxide of the material constituting the portion 53. The side portions 51 and 52 of the upper cladding layer 50 have a lower refractive index than the other portions 53 of the upper cladding layer 50. In the lower clad layer 30, the side surface portion 31 along the outer periphery between the thin-line optical waveguide 20 and the light absorption layer 40 is an oxide of a material constituting the other portion of the lower clad layer 30. The side surface portion 31 of the lower cladding layer 30 has a lower refractive index than the other portion 32 of the lower cladding layer 30.

The substrate 10 is made of Si, for example. The dielectric layer 11 is made of, for example, SiO ₂ and has a thickness of 3 μm. The thin-line optical waveguide 20 is made of, for example, Si, has a thickness of 250 nm, and a width of the outer portion of the light receiving unit is 450 nm. The narrowest end has a width of 200 nm.

The bonding layer 35 is made of, for example, GaAs and has a thickness of 50 nm. The lower cladding layer 30 is made of, for example, AlGaAs except for the side surface portion 31, and the side surface portion 31 is made of Al ₂ O ₃ . The second contact layer 80 is made of, for example, p-type AlGaAs. The light absorption layer 40 includes, for example, two non-doped InGaAs optical confinement layers, and an InGaAs / GaAs multiple quantum well layer in which well layers and barrier layers provided therebetween are alternately stacked. The upper cladding layer 50 is made of, for example, AlGaAs except for the side portions 51 and 52, and the side portions 51 and 52 are made of Al ₂ O ₃ . The first contact layer 60 is made of, for example, n-type AlGaAs. The first electrode 70 and the second electrode 90 are made of, for example, an AuGe alloy and have a thickness of 20 nm.

  When the light that has entered and propagated into the thin-line optical waveguide 20 reaches the spiral end portion, the light penetrates into the ring-shaped light absorption layer 40 bonded to the upper surface thereof, and is combined and absorbed. When the thin-line optical waveguide 20 has a curved line, light oozes out of the waveguide more than in the case of a straight line. As a result, optical coupling and absorption to the light absorption layer 40 are enhanced.

  FIG. 3 is a simulation result of the absorption efficiency of the light receiving element 100 (diameter 10 μm). 95% or more of the light input to the thin optical waveguide 20 is absorbed within 2 picoseconds after entering.

  This enhancement effect of optical coupling and absorption increases as the radius of curvature of the thin-line optical waveguide decreases and as the cross-sectional size of the thin-line optical waveguide 20 decreases. For example, when a thin optical waveguide having a radius of curvature of 10 μm and a cross-sectional size of 450 nm × 250 nm is in contact with the lower surface of the semiconductor multilayer structure including the InGaAs / GaAs multiple quantum well layer, the absorption efficiency is the same as that of a linear thin optical waveguide. It increases about 1.5 times. In the spiral thin optical waveguide, the radius of curvature is further reduced toward the end, and further enhancement of coupling and absorption can be expected. Also, by adding a taper process so that the width of the thin optical waveguide becomes narrower as it approaches the end of the spiral, the light propagating through the thin optical waveguide shifts more quickly to the semiconductor multilayer structure side, and further coupled / Absorption can be enhanced.

  Furthermore, the side portions 51, 52, 31 of the upper cladding layer 50 and the lower cladding layer 30 are oxidized and constricted, so that the light coupled to the light absorption layer 40 leaks to the upper electrode 70 side and is absorbed and photocurrent. It is possible to suppress an increase in loss components that do not contribute to. Furthermore, since the light is confined inside the ring-shaped light absorption layer 40, it is possible to suppress light scattering loss due to the side wall and carrier loss in which carriers generated by absorption are lost due to surface recombination on the side wall. As described above, it is possible to realize an ultra-small and highly efficient light receiving element.

  In addition to the above, the shape of the thin-line optical waveguide 20 may be a disk-like shape without a cavity or a spiral shape, and the end portion may be terminated without joining the outer periphery. Yes.

  Even when the thin optical waveguide 20 having such a shape is used, the semiconductor layer above the light absorption layer 40 can be formed in a ring shape.

  In this embodiment, the case where the InGaAs / GaAs multiple quantum well on the GaAs substrate is used as the active layer has been described, but this may be replaced with, for example, an InGaAsP / InAlAs multiple quantum well on the InP substrate. In that case, the p-type InGaAs contact layer, the p-type InAlAs cladding layer, the non-doped InGaAsP optical confinement layer, the InGaAsP multiple quantum well active layer, the non-doped InGaAs optical confinement layer, the n-type InAlAs clad layer, and the n-type InP contact layer are arranged from the top. It ’s fine. Alternatively, these can be a semiconductor multilayer structure made of other materials.

  A method for manufacturing the light receiving element 100 shown in FIGS. 1 and 2 will be described below. FIG. 4 is a cross-sectional view showing a method for manufacturing the light receiving element 100.

  First, the Si thin-line optical waveguide 20 is formed on the substrate 10 having the dielectric layer 11 which is an SOI substrate, and the terminal portion thereof is processed into a spiral shape (FIG. 4A). A semiconductor multilayer structure including the light absorption layer 40 is bonded onto the spiral Si fine wire optical waveguide 20 (FIG. 4B). As the semiconductor multilayer structure, for example, a first contact layer 60 made of n-type AlGaAs formed on the GaAs substrate 1, an upper cladding layer 50 made of AlGaAs, a GaAs light confinement layer, an InGaAs / GaAs multiple quantum well layer, and GaAs light. The multilayer structure includes a light absorption layer 40 made of a confinement layer, a second contact layer 80 made of p-type AlGaAs, a lower cladding layer 30 made of AlGaAs, and a bonding layer 35 made of GaAs. As a bonding method, a direct wafer bonding method, a bonding method via an adhesive layer, or the like can be used. Thereafter, the substrate 1 is peeled off, and ring-shaped patterning is performed on the semiconductor multilayer structure (FIG. 4C). Here, the upper clad layer 50 and the lower clad layer 30 of the semiconductor multi-layer structure are formed by oxidizing the side portions 51, 52, and 31 into an insulating low refractive index oxide (FIG. 4D). In this oxidation treatment, the optical confinement layer and the multiple quantum well layer with a small Al composition hardly undergo oxidation, so that the semiconductor layer remains as it is.

  Thereafter, the upper electrode 70 and the lower electrode 90 are formed, and the light receiving element 100 is completed (FIG. 4E).

  The side surface portions 51 and 52 of the upper cladding layer 50 and the side surface portion 31 of the lower cladding layer 30 have a smaller lattice constant than AlGaAs forming the other portions 53 and 32 of the upper cladding layer 50 and the lower cladding layer 31, A tensile strain is applied to the InGaAs / GaAs multiple quantum well layer of the light absorption layer 40.

  By appropriately selecting the amount of selective oxidation, the amount of tensile strain applied to the InGaAs / GaAs multiple quantum well layer can be controlled, and the shift amount of the light absorption edge in the InGaAs / GaAs multiple quantum well layer can be controlled. Is possible. The oscillation wavelength of the semiconductor laser becomes longer due to the temperature rise in the surrounding environment and the heat generated by the semiconductor laser itself. For this reason, in a light receiving element having a layer structure common to the semiconductor laser, light on the further transparent region side of the base of the light absorption end is received, and the light receiving sensitivity may be greatly reduced. However, the shift amount of the light absorption edge can be adjusted by the amount of selective oxidation.

  According to the present embodiment, it is possible to form a light receiving element that is highly efficient in receiving light from a thin optical waveguide.

(Second Embodiment)
FIG. 5 is a top view showing a state before formation of the upper electrode 70 and the lower electrode 90 of the light receiving element 101 of the second embodiment, and FIG. 6 is a cross-sectional view taken along the broken line VI-VI shown in FIG. . In the present embodiment, in the semiconductor multilayer structure, a part of the upper cladding layer 50 close to the outer periphery is removed to form a groove. As shown in FIG. 5, when the semiconductor multilayer structure is viewed from the upper surface before the upper electrode 70 and the lower electrode 90 are formed, the nAlGaAs lower contact layer 80, the AlGaAs upper cladding layer 50, the light absorption are sequentially arranged from the center. Layer 40, AlGaAs upper cladding layer 50 can be seen.

  The side portions of the upper cladding layer 50 and the lower cladding layer 30 are selectively oxidized. In the upper clad layer 50, the side surface portion 51 along the outer periphery outside the groove, the side surface portion 52 along the inner periphery surrounding the gap, and the surface portion 54 inside the groove are low refractive index portions. In the lower cladding layer 30, the side surface portion 31 along the outer periphery is a low refractive index portion, as in the first embodiment.

  Since stress is applied to the light absorption layer 40 in the direction toward the center and in the direction toward the outer periphery, tensile strain can be applied more efficiently. In the present embodiment, the outermost periphery of the upper clad layer has a ring shape, but it goes without saying that it may have other shapes.

  According to the present embodiment, it is possible to form a light receiving element that is highly efficient in receiving light from a thin optical waveguide.

(Third embodiment)
FIG. 7 is a plan view showing the upper cladding layer 50 of the light receiving element 102 according to the third embodiment and the thin-line optical waveguide 20 provided therebelow. The present embodiment is characterized in that a protruding portion (strain-added portion) 55 is added to the outer periphery of the upper cladding layer 50. The protruding structure 55 is selectively oxidized along with the side surfaces along the outer periphery of the upper cladding layer 50. In this configuration, when the upper clad layer 50 and the lower clad layer 30 are selectively oxidized, the volume that is oxidized is increased as compared with the case where there is no projecting portion 55, so that stress due to deposition shrinkage due to oxidation is effectively absorbed by the light absorption region. To be applied. The shape of the protruding portion 55 here may be any shape. As shown in FIG. 7, a T-shaped projecting structure as viewed from above is desirable because oxidation proceeds uniformly and stress is applied to the light absorption layer 40 uniformly.

  In addition, the structure in which the T-shaped protrusion is added to the ring-shaped upper cladding layer of the present embodiment is the same as the case of forming the side surface portion 51 along the outer periphery outside the groove in the second embodiment. In this process, it can be easily formed using, for example, photolithography and dry etching.

  According to the present embodiment, it is possible to form a light receiving element that is highly efficient in receiving light from a thin optical waveguide.

(Fourth embodiment)
The light receiving element described above can have a common layer structure with the semiconductor laser. FIG. 8 is a perspective view showing the optical transceiver unit. The optical transmission / reception unit includes a semiconductor laser 110 formed on the dielectric layer 10, a light receiving element 100, and a thin-line optical waveguide 20 that connects them. The light receiving element is not limited to the light receiving element 100 of the first embodiment. Since the thin-line optical waveguide 20, the semiconductor laser 110, and the light receiving element 100 can be formed in a common process, it is possible to manufacture an optical transmission / reception unit at a low cost. At this time, the semiconductor laser 110 is preferably as small as possible, that is, a micro ring (or micro disk) laser.

  According to the present embodiment, it is possible to form an optical transmission / reception unit having a small light receiving element that is highly efficient in receiving light from a thin optical waveguide.

The embodiments of the present invention have been described above with reference to specific examples. However, embodiments of the present invention are not limited to these specific examples. The specific configuration of each element is included in the scope of the present invention as long as a person skilled in the art can appropriately perform the present invention by appropriately selecting from a known range and obtain the same effect.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.

  In addition, all display devices that can be implemented by a person skilled in the art based on the above-described display device as an embodiment of the present invention are included in the scope of the present invention as long as they include the gist of the present invention. .

  In addition, in the category of the idea of the present invention, those skilled in the art can conceive of various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

DESCRIPTION OF SYMBOLS 1 Substrate, 10 Substrate, 11 Dielectric layer, 20 Thin-line optical waveguide, 30 Lower clad layer, 31 Side part of lower clad layer, 32 Part other than lower clad layer side part, 35 Bonding layer, 40 Light absorption layer, 50 Upper part Cladding layer, 51 side surface portion of upper cladding layer, 52 side surface portion of upper cladding layer, 53 portion other than side surface portion of upper cladding layer, 54 part of upper cladding layer, 55 projecting portion, 60 first contact layer, 70 upper electrode, 80 cladding layer, 90 lower electrode, 100 light receiving element, 101 light receiving element, 102 light receiving element, 110 semiconductor laser

Claims (8)

One end is connected to a semiconductor light source and the other end is formed into a spiral shape having at least one turn,
A lower clad layer made of a semiconductor material provided on the other end of the thin-line optical waveguide;
A light absorption layer provided on the lower clad layer, in a disk shape or a ring shape, made of a semiconductor material;
An upper clad layer made of a semiconductor material provided on the light absorption layer;
A first electrode opposed to the upper cladding layer via a first contact layer;
A second electrode facing the lower cladding layer via a second contact layer;
With
The other end of the thin-line optical waveguide has a taper shape having a smaller radius of curvature than the one end and a width narrower than the one end,
The upper cladding layer has a low refractive index portion having a refractive index lower than that of other portions of the upper cladding layer on at least a part of the side surface other than the portion in contact with the first contact layer and the light absorption layer, or The lower clad layer has a low refractive index portion having a refractive index lower than that of other portions of the lower clad layer on at least a part of the side surface other than the portion in contact with the second contact layer and the light absorption layer, or both. A light receiving element. Wherein either the upper low refractive index portion of the cladding layer is smaller lattice constant than the other portions, or a low refractive index portion of the lower cladding layer lattice constant is smaller than other portions, according to claim 1 which is both The light receiving element described in 1. Light-receiving element according to claim 1 or 2, wherein the light-absorbing layer is characterized by the well layers and barrier layers are multiple quantum well layers are alternately laminated. The upper clad layer has a groove along an outer edge, and a surface on the inner side of the groove of the upper clad layer and a side surface along the outer periphery are low refractive index portions having a lower refractive index than other portions. Item 4. The light receiving element according to any one of Items 1 to 3 . The upper clad layer has a distortion adding portion, a light receiving device according to any one of claims 1 to 4. Low refractive index portion of the upper cladding layer and lower cladding layer, the upper clad layer or the lower clad layer is formed by oxidizing treatment, the light-receiving element according to any one of claims 1 to 5. Laminating a thin-line optical waveguide, a second contact layer, a lower cladding layer, a light absorbing layer, an upper cladding layer, and a first contact layer;
Oxidizing a part of a side surface along an outer periphery of at least one of the lower cladding layer and the upper cladding layer;
Forming a lower electrode in contact with the second contact layer;
Forming an upper electrode in contact with the first contact layer;
A method for manufacturing a light receiving element according to claim 1. A semiconductor light source;
One end is connected to the semiconductor light source, and the other end is formed in a spiral shape, a thin wire optical waveguide,
A lower cladding layer of semiconductor material provided on the other end of the wire waveguides, provided on the lower cladding layer, a disc-shaped or ring-shaped, a light absorbing layer of a semiconductor material, the light-absorbing An upper clad layer made of a semiconductor material provided on the layer; a first electrode opposed to the upper clad layer via the first contact layer; and a first electrode opposed to the lower clad layer via the second contact layer. The other end of the thin-line optical waveguide has a taper shape in which the radius of curvature is smaller than that of the one end and the width becomes narrower toward the end portion, and the upper clad layer At least a part of the side surface other than the portion in contact with the first contact layer and the light absorption layer has a low refractive index portion having a lower refractive index than other portions of the upper cladding layer, The pad layer has a low refractive index portion having a lower refractive index than other portions of the lower cladding layer at least in part of the side surface other than the portion in contact with the second contact layer and the light absorption layer, or both. A light receiving element,
An optical transceiver unit comprising:

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