JP6649869B2 - Photo detector - Google Patents

Description

  The present invention relates to a photodetector, and more particularly to a structure for providing a photodetector used in an optical communication system or an optical information processing system.

  With the spread of optical communication in recent years, cost reduction of optical communication devices has been demanded. As one of the solutions, there is a method of forming an optical circuit constituting an optical communication device on a large-diameter wafer such as a silicon wafer by using a micro optical circuit technology such as silicon photonics. As a result, the material cost per chip can be dramatically reduced, and the cost of the optical communication device can be reduced.

  As a typical photodetector formed on a silicon (Si) substrate using such a technique, there is a germanium photodetector (GePD) that can be monolithically integrated.

  FIG. 1 is a plan view schematically showing a structure of a conventional waveguide-coupled vertical germanium photodetector (GePD) 100 monolithically integrated on a silicon substrate.

  FIG. 2 is a cross-sectional view taken along the line II-II of the GePD 100 of FIG.

  The GePD 100 is formed on a SOI (Silicon On Insulator) substrate including a Si substrate, a Si oxide film, and a surface Si layer by using a lithography technique or the like. The GePD 100 shown in the cross-sectional view of FIG. 2 includes a silicon (Si) substrate 101, a lower cladding layer 102 made of a Si oxide film on a Si substrate, a silicon (Si) core layer 110 for guiding signal light, and a A germanium (Ge) layer 114 for absorbing light, an upper cladding layer 103 formed on the core layer 110 and the Ge layer 114, and electrodes 116 to 118.

  In FIG. 1 and subsequent figures, a portion surrounded by a square of the GePD 100 indicates a functional region corresponding to the GePD, and does not necessarily indicate a boundary such as a physical chip structure. In order to make the structure easy to understand, in the plan view of FIG. 1, lines showing the internal shapes of the cladding layer 103 and the electrodes 116 to 118 shown in FIG. 2 are omitted, and the shapes of the electrodes 116 to 118 on the surface of the cladding layer 103 are changed. This is indicated by a solid line in a rectangular area. In addition, the boundaries between the p ++ Si electrode portions 112 and 113 and the n-type Ge region 115 inside the substrate are indicated by dotted lines.

  As can be seen from FIG. 1, the Si core layer 110 is divided into a waveguide 1101 and a Si slab 1102, and light to be detected enters from the left end of the waveguide 1101 and reaches the Si slab 1102.

  As shown in the cross-sectional view of FIG. 2, the Si core layer 110 of the Si slab 1102 includes a p-type Si slab 111 (silicon region) doped with impurity ions of the first conductivity type (for example, p-type), and p Type impurities are doped at a high concentration, and p ++ silicon (Si) electrode portions 112 and 113 functioning as electrodes are formed. The Ge layer 114 is stacked on the p-type Si slab 111 by epitaxial growth, and an n-type Ge region 115 (germanium region) doped with a second conductivity type (for example, n-type) impurity is formed thereon, It constitutes a photodiode. Further, electrodes 116 to 118 are provided on p ++ Si electrode portions 112 and 113 and n-type Ge region 115 so as to be in contact therewith.

  When light is incident on the Si core layer 110 and the light is absorbed by the Ge layer 114, a photocurrent flows between the electrode 117 and the electrodes 116 and 118, so that the GePD 100 detects the current to generate light. To detect.

Japanese Patent No. 5370857

  The GePD 100 shown in FIG. 2 has a problem that it cannot withstand high-power optical input.

  FIG. 3 shows a thermal analysis result of a general GePD. FIG. 3A is a cross-sectional view of a thermal analysis model 200 in which the bottom surface of the Ge layer 114 of GePD is a heat source 202, and FIG. 3B is a diagram illustrating a Ge layer when the power of the heat source 202 is changed. 14 is a graph in which the temperature of the plot 114 is plotted. In order to simplify the calculation, the structures of the p-type Si slab 111, the p ++ Si electrode portions 112 and 113, the n-type Ge region 115, and the electrodes 116 and 118 in FIG. 2 have been removed. The remaining structure is equivalent to FIG.

  The optical input power may be directly translated into the heat source 202 in FIG. Experiments show that germanium grown on silicon melts at about 600 to 800 ° C. and loses its function as a photodiode. In particular, in the waveguide type GePD 100 as shown in FIGS. 1 and 2, a portion near the waveguide in the Ge layer 114 absorbs light intensively, so that the vicinity of the region 119 in FIG. 1 is melted. At 201 in FIG. 3, germanium reaches the melting temperature with an input of about 75 to 100 mW. On the other hand, the receiver of the metro network may receive the optical input power in the above range.

  If a GePD that cannot withstand high-power optical input is to be incorporated into an optical communication system, a variable attenuator or an optical switch for attenuating or switching power is required, which increases the manufacturing cost.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a GePD which does not require an additional optical component such as an attenuator or a switch and can withstand a high power input. is there.

In order to solve the above problems, the present invention is a photodetector, a silicon substrate, a lower cladding layer formed on the silicon substrate, formed on the lower cladding layer, a first impurity A silicon core layer including a slab region including a silicon region doped with ions and a waveguide region connected to the slab region; and a germanium region formed on the silicon core layer and doped with a second impurity ion. And a slab region including the silicon region of the silicon core layer, an upper cladding layer formed on the waveguide region and the germanium layer, and a germanium layer separated from the silicon region and the germanium region, respectively. a plurality of electrodes formed Te, formed in addition between the plurality of electrodes on the front Symbol slab region of said silicon core layer Comprising a metal layer, wherein the metal layer is characterized by radiating heat generated in the germanium layer.

  According to a second aspect of the present invention, in the photodetector according to the first aspect, the metal layer is insulated from the electrode.

  The invention according to claim 3 is the photodetector according to claim 2, wherein the metal layer is also formed on the upper cladding layer near the germanium region on the waveguide region side. And

  The invention according to claim 4 is the photodetector according to claim 1, wherein the metal layer is in contact with the electrode.

  The invention according to claim 5 is the photodetector according to any one of claims 1 to 4, wherein the metal layer is also in contact with the silicon substrate and the lower cladding layer.

  The present invention suppresses a temperature rise of the Ge layer by expanding a Si core layer having a high thermal conductivity in contact with the Ge layer and forming a metal layer for heat dissipation, thereby reducing input power without additional optical components. It has the effect of improving resistance.

It is a top view which shows typically the structure of the waveguide coupling type | mold vertical GePD100 monolithically integrated on the conventional silicon substrate. FIG. 2 is a cross-sectional view taken along the line II-II of the GePD 100 in FIG. 1. (A) is a cross-sectional view of a thermal analysis model 200 using the bottom surface of the Ge layer 114 of GePD as a heat source 202, and (b) plots the temperature of the Ge layer 114 when the power of the heat source 202 is changed. It is a graph. FIG. 2 is a plan view schematically showing the structure of the GePD 100 according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view taken along a line VV of the GePD 100 in FIG. 4. (A) is a diagram showing a temperature change when the same heat source is applied immediately below the Ge layer 114 in the II-II cross section of the conventional GePD of FIG. 1, and (b) is a diagram of the GePD of the present invention of FIG. FIG. 5 is a diagram showing a temperature change when the same heat source is applied immediately below a Ge layer 114 in a VV cross section. FIG. 5 is a cross-sectional view schematically illustrating a structure of a GePD 100 according to a second embodiment of the present invention. FIG. 10 is a plan view schematically showing a structure of a GePD 100 according to Embodiment 3 of the present invention. 9 is a cross-sectional view of the IX-IX portion of the GePD 100 in FIG. It is a top view showing typically the structure of GePD100 concerning Embodiment 4 of the present invention. It is sectional drawing of the XI-XI part of GePD100 of FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

  The present invention is characterized by having the following configuration in order to achieve such an object.

(Embodiment 1)
FIG. 4 is a plan view schematically showing the structure of the GePD 100 according to the first embodiment of the present invention. FIG. 5 is a cross section taken along the line VV of the GePD 100 in FIG.

  As shown in the cross-sectional view of FIG. 5, the GePD 100 of the first embodiment includes a silicon (Si) substrate 101, a lower cladding layer 102 made of a Si oxide film on a Si substrate, and a silicon (Si) core for guiding signal light. It includes a layer 110, a germanium (Ge) layer 114 formed on the core layer 110 for absorbing light, an upper cladding layer 103 formed on the core layer 110 and the Ge layer 114, and electrodes 116 to 118. Further, as shown in FIGS. 4 and 5, metal layers 121 and 122 are arranged on the Si core layer 110 so as to surround the electrodes 116 and 118. As shown in FIG. 5, the metal layers 121 and 122 have a thickness corresponding to the height of the upper cladding 103 and are in contact with the Si core layer 110.

  In order to make the structure easy to understand, in the plan view of FIG. 4, similarly to FIG. 1, lines showing the internal shapes of the cladding layer 103 and the electrodes 116 to 118 shown in FIG. The shapes of 116 to 118 are indicated by solid lines in a rectangular area. In addition, the boundaries between the p ++ Si electrode portions 112 and 113 and the n-type Ge region 115 inside the substrate are indicated by dotted lines.

  The metal layers 121 and 122 and the Si core layer 110 have significantly higher thermal conductivity than the lower cladding layer 102 and the upper cladding layer 103. Therefore, the heat generated in the Ge layer 114 is diffused along the Si core layer 110 in the vertical and horizontal directions of FIG. The diffused heat is gradually radiated through the metal layers 121 and 122, the lower cladding layer 102, and the Si substrate layer 101.

  Although the Si slab 1102 of the Si core layer 110 in the conventional GePD 100 is slightly larger than the p-type Si slab 111, in the present invention, the Si slab 1102 portion of the Si core layer 110 is divided into the waveguide 1101 and the waveguide 1101. It is spread on the lower cladding layer 102 so as not to be in contact with other than the emission end and to be separated from the waveguide 1101 so as not to optically interfere. Metal layers 121 and 122 are formed on the enlarged Si core layer 110 so as not to contact the electrodes 116 to 118. The metal layers 121 and 122 are not formed between the electrodes 116 to 118 so that the electrodes 116 and 118 and the electrode 117 are not short-circuited.

  The larger the Si core layer 110 and the metal layers 121 and 122 are, the higher the heat radiation effect is. Therefore, the Si core layer 110 may be formed as wide as possible as long as it does not optically interfere with the waveguide 1101. The metal layers 121 and 122 may be formed so as to cover a region of the Si core layer 110 where there is no major structure of GePD, that is, a region that does not interfere with the waveguide 1101 and the p-type Si slab 111 of the Si core layer 110. .

  If the electrodes 116 and 118 are connected to the metal layers 121 and 122, high-frequency signals may not be transmitted depending on the design. Therefore, in the first embodiment, the electrode 116 and the metal layer 121 are insulated.

  FIG. 6A shows a temperature change when the same heat source is applied immediately below the Ge layer 114 in the II-II cross section of the conventional GePD of FIG. 1, and FIG. 6B shows the present invention of FIG. 3 shows a temperature change when the same heat source is applied immediately below the Ge layer 114 in the VV cross section of the GePD. In the conventional GePD 100 of FIG. 6A, the Ge layer 114 is heated to about 600 ° C. by the heat source, but the temperature of the Ge layer 114 of the GePD 100 of the present invention shown in FIG.

  From the temperature drop and the graph of FIG. 3B, it can be seen that the input power of the present invention has been improved by about 13 mW. That is, as compared with the conventional vertical GePD, the structure of the GePD of the present invention is a GePD that can withstand even higher power input.

(Embodiment 2)
FIG. 7 is a sectional view schematically showing the structure of the GePD 100 according to the second embodiment of the present invention.

  The GePD 100 according to the second embodiment is different from the GePD 100 according to the first embodiment in that the via penetrates the Si core layer 110 and the lower cladding layer 102 and a part of the Si substrate 101 is etched to form a via. Is filled in.

  Since the metal layers 121 and 122 reach the Si substrate layer 101 through the lower heat-insulating lower cladding layer 102, heat is easily diffused to the Si substrate layer 101 through the metal layers 121 and 122.

(Embodiment 3)
FIG. 8 is a plan view schematically showing the structure of the GePD 100 according to Embodiment 3 of the present invention. FIG. 9 is a cross section of the IX-IX portion of the GePD 100 of FIG.

  The GePD 100 according to the third embodiment has a configuration in which the electrodes 116 and 118 of the GePD 100 according to the first embodiment are connected to metal layers 121 and 122 for heat radiation. Since the insulating upper clad layer 103 between the electrodes 116 and 118 and the heat dissipating metal layers 121 and 122 is eliminated, the thermal conductivity to the metal layers 121 and 122 is higher than in the first embodiment.

  On the other hand, in order for the GePD 100 to receive a high-speed signal, the electrodes 116 and 118 are limited to a size of about 1/10 to 1/20 of the wavelength that can be handled lumpedly.

  In the third embodiment, as in the second embodiment, a via that reaches the Si substrate layer 101 is formed, the vias are filled with the metal layers 121 and 122, and the metal layers 121 and 122 are in contact with the Si substrate layer 101. Can also.

(Embodiment 4)
FIG. 10 is a plan view schematically showing the structure of the GePD 100 according to Embodiment 4 of the present invention. FIG. 11 is a cross section of the XI-XI portion of the GePD 100 of FIG.

  The GePD 100 according to the fourth embodiment is different from the GePD 100 according to the first embodiment in that the metal layers 121 and 122 are formed by forming upper metal layers 121 and 122 near the connection between the waveguide 1101 and the Si slab 1102, that is, near the waveguide 1101 of the Ge layer 114. In this structure, the layers are connected by a metal layer 123 on the layer 103. The metal layer 123 is thinner than the metal layers 121 and 123, is formed on the upper cladding layer 103, and is arranged so as not to contact the electrodes 116 to 118. When the metal layers 121 to 123 are insulated from the electrodes 116 to 118 as described above, the size of the metal layers 121 to 123 is arbitrary.

  Since the metal layer 123 having high heat conductivity is located near the region 119 where heat is concentrated, heat conductivity and heat dissipation to the metal layers 121 and 122 are improved.

  In the fourth embodiment, as in the second embodiment, a via that reaches the Si substrate layer 101 may be formed, the vias may be filled with the metal layers 121 and 122, and the metal layers 121 and 122 may be in contact with the Si substrate layer 101. it can.

  Further, the fourth embodiment may have a configuration in which the electrodes 116 and 118 are connected to the metal layers 121 and 122 for heat dissipation as in the third embodiment. However, in order to receive a high-speed signal with the GePD 100, the electrodes 116 and 118 and the metal layers 121 and 122 need to be about 1/10 to 1/20 of the wavelength that can be treated as a lumped constant, as in the third embodiment. Limited to the size of

100 GePD
DESCRIPTION OF SYMBOLS 101 Si substrate 102 Lower cladding layer 103 Upper cladding layer 110 Si core layer 111 p-type Si slab 112, 113 p ++ Si electrode part 114 Ge layer 115 n-type Ge region 116-118 electrode 121, 122 metal layer 1101 waveguide 1102 Si slab

Claims (5)

A silicon substrate,
A lower cladding layer formed on the silicon substrate,
A silicon core layer formed on the lower cladding layer and including a slab region including a silicon region doped with a first impurity ion and a waveguide region connected to the slab region;
A germanium layer formed on the silicon core layer and including a germanium region doped with a second impurity ion;
An upper cladding layer formed on the slab region including the silicon region of the silicon core layer, the waveguide region and the germanium layer;
A plurality of electrodes formed separately on the silicon region and the germanium region,
And a metal layer formed in addition between the plurality of electrodes before SL on the slab region of the silicon core layer,
The metal layer dissipates heat generated in the germanium layer
A photodetector for said and this.   The photodetector according to claim 1, wherein the metal layer is insulated from the electrode.   The photodetector according to claim 2, wherein the metal layer is also formed on the upper cladding layer near the germanium region on the waveguide region side.   The photodetector according to claim 1, wherein the metal layer is in contact with the electrode.   The photodetector according to claim 1, wherein the metal layer is also in contact with the silicon substrate and the lower clad layer.