Light detector

Abstract

The present invention aims to provide a photodetector that can prevent damage caused by electrostatic discharge and is expected to improve the withstand voltage of 100V or more. The photodetector of the present invention is characterized in that a Zener diode composed of germanium and silicon is connected to a germanium photodiode (GePD). The photodetector shares the silicon substrate, lower cladding layer, silicon core layer, and upper cladding layer of the photodiode and the Zener diode.

Description

Technical Field

[0001] The present invention relates to a photodetector used in an optical communication system or an optical information processing system, and more particularly to a structure for providing a photodetector having excellent resistance to electrostatic discharge. Background Art

[0002] With the popularization of optical communication in recent years, there is a demand for low-cost optical communication devices. As one of the solutions, there is a method of using micro-optical circuit technology such as silicon photonics technology to form an optical circuit constituting an optical communication device on a large-diameter wafer such as a silicon wafer. This can significantly reduce the material cost of each chip, thereby seeking to reduce the cost of optical communication devices.

[0003] As a typical photodetector formed on a silicon (Si) substrate using such a technology, there is a monolithically integrated germanium photodetector (Germanium photodetector; GePD). Figure 1 This is a diagram schematically showing the structure of a conventional waveguide-coupled vertical GePD. Figure 2 yes Figure 1 It should be noted that in order to facilitate the understanding of the structure, Figure 1 Omitted Figure 2 The upper cladding layer 103 and electrodes 116 to 118 are shown. For the electrodes 116 to 118, only the positions where they are connected to the p++ silicon electrode portion 112, the p++ silicon electrode portion 113, and the n-type Ge region 115 are shown by quadrilaterals. The quadrilaterals show the connection surfaces of the electrodes 116 to 118. The p++ silicon electrode portion 112 is also called a p++Si electrode portion or a p-type silicon electrode portion.

[0004] The GePD is formed on a SOI (Silicon On Insulator) substrate including a Si substrate, a Si oxide film, and a surface Si layer using a photolithography technique or the like. Figure 2 The GePD100 shown comprises a Si substrate 101, a lower cladding layer 102 comprising a Si oxide film on the Si substrate, a core layer 110, a waveguide (waveguide layer) 109 for guiding signal light, a germanium (Ge) layer 114 for absorbing light formed on the core layer 110, and an upper cladding layer 103 formed on the core layer 110 and the Ge layer 114.

[0005] The core layer 110 is formed with a p-type silicon (Si) plate 111a doped with p-type impurity ions, and p++ silicon electrode portions 112 and 113 doped with p-type impurities at a high concentration and functioning as electrodes. The Ge layer 114 is formed with an n-type Ge region 115 stacked by epitaxial growth and doped with n-type impurities on its upper portion. In addition, electrodes 116 to 118 are provided on the p++ silicon electrode portion 112, the p++ silicon electrode portion 113, and the n-type Ge region 115 so that they are in contact with each other.

[0006] When light is incident on the core layer 110 and absorbed by the Ge layer 114 , a photocurrent flows between the electrode 117 and the electrodes 116 and 118 . Therefore, the GePD detects the light by detecting the current.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 5370857 Summary of the invention

[0010] Problems to be solved by the invention

[0011] Figure 1 , Figure 2 The general GePD shown has the problem of weak anti-electrostatic discharge capability. Electrostatic discharge is a phenomenon in which a high voltage pulse is applied to a device instantaneously. As general electrostatic discharge specification models, there are charged device models, machine models, and human models. For example, a general GePD has a withstand voltage of about 50V to 150V in the human model. The withstand voltage in the human model required by general devices is about 250V to 500V, and the withstand voltage of GePD is insufficient. As a general method to improve the withstand voltage of electrostatic discharge, there are adding capacitors in parallel, adding resistors in series, adding varistors and Zener diodes in parallel, etc., but there is a problem that the addition of resistors and capacitors reduces the high-speed characteristics of GePD. General varistors and Zener diodes have the following problems: the action threshold for proper protection cannot be shown, and the capacitance of the varistors and Zener diodes themselves becomes the main reason for reducing the high-speed characteristics of GePD, and it becomes an external component that is not easy to be integrated on a silicon substrate, so the circuit scale increases.

[0012] The present invention has been made in view of the above problems, and an object of the present invention is to provide a photodetector which can prevent destruction due to electrostatic discharge and is expected to have a withstand voltage of 100 V or more.

[0013] Solutions for solving problems

[0014] The present invention is used to solve such a problem, and is a photodetector with a Zener diode that can be monolithically integrated using silicon photonics technology on a general GePD. The Zener diode provided in the present invention has extremely low capacitance and low series resistance, and protects the GePD with a low threshold voltage of -7V while covering the operating voltage of 0.5V to -7V and the general operating voltage of GePD, which is 0V to 3V. Therefore, the high-speed characteristics of the GePD will not be degraded, and the increase in the circuit scale and the number of steps in the manufacturing process can be suppressed by monolithic integration.

[0015] The photodetector of the present invention is characterized by having the following structure. Figure 3 As shown in FIG. 1 , a Zener diode 301 composed of germanium and silicon is connected in parallel to a general GePD 300. The Zener diode connected in the present invention is set to Figure 4 Such a cross-sectional structure.

[0016] In order to achieve the above-mentioned purpose, the first scheme of the present invention is a photodetector having a photodiode and a Zener diode, characterized in that the photodiode has an anode electrode and a cathode electrode, and the Zener diode has: a silicon substrate; a lower cladding layer on the silicon substrate; a core layer on the lower cladding layer, having a first-type silicon region doped with first-type impurity ions and a second-type silicon region doped with second-type impurity ions; a waveguide layer connected to the core layer; a germanium layer on the core layer; an upper cladding layer on the germanium layer; and an anode electrode and a cathode electrode, respectively connected to any one of the first-type silicon region and the second-type silicon region, the anode electrode of the Zener diode is connected to the anode electrode of the photodiode, and the cathode electrode of the Zener diode is connected to the cathode electrode of the photodiode.

[0017] In addition, the second scheme of the present invention is characterized in that, in the photodetector of the first scheme, in the Zener diode, the second type silicon region is located directly below the germanium layer, the intrinsic silicon region is located between the bottom surface of the germanium layer and the first type silicon region, and the intrinsic silicon region is located between the first type silicon region and the second type silicon region.

[0018] In addition, the third scheme of the present invention is characterized in that, in the photodetector of the first scheme or the second scheme, the photodiode comprises: a silicon substrate; a lower cladding layer on the silicon substrate; a core layer on the lower cladding layer, having a first-type silicon plate doped with first-type impurity ions; a waveguide layer connected to the core layer; a germanium layer on the core layer, comprising a second-type germanium region doped with second-type impurities; an upper cladding layer on the core layer and the germanium layer; and electrodes, respectively connected to the first-type silicon plate and the second-type germanium region.

[0019] Furthermore, a fourth aspect of the present invention is characterized in that, in the photodetector according to the third aspect, the silicon substrate, the lower cladding layer, the core layer, and the upper cladding layer included in the photodiode and the Zener diode are commonly used.

[0020] Furthermore, a fifth aspect of the present invention is the photodetector according to the fourth aspect, wherein the photodiode and the Zener diode are arranged in an incident direction of light passing through the waveguide layer provided in the photodiode.

[0021] Furthermore, a sixth aspect of the present invention is the photodetector according to the fourth aspect, wherein the photodiode and the Zener diode are arranged in a direction perpendicular to an incident direction of light passing through the waveguide layer provided in the photodiode.

[0022] Furthermore, a seventh aspect of the present invention is the photodetector according to any one of the first to sixth aspects, wherein a plurality of the Zener diodes are connected to the photodiode.

[0023] Furthermore, an eighth aspect of the present invention is characterized in that, in the photodetector described in any one of the first to seventh aspects, the first type impurity ions are p-type impurity ions, and the second type impurity ions are n-type impurity ions.

[0024] Effects of the Invention

[0025] In the photodetector of the present invention, the voltage applied to the GePD is constant before the Zener diode is destroyed, thereby being protected, thereby preventing destruction caused by electrostatic discharge. In addition, the photodetector of the present invention is expected to increase the withstand voltage by more than 100V compared to the general GePD, so it can achieve the withstand voltage generally required in the human-type model. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram showing a conventional vertical GePD.

[0027] Figure 2 Yes means Figure 1 Figure 2. The cross-sectional structure of the GePD.

[0028] Figure 3 It is a diagram showing the structure of the photodetector of the present invention.

[0029] Figure 4 It is a diagram showing a cross-sectional structure of a Zener diode included in the photodetector of the present invention.

[0030] Figure 5 It is a diagram showing current-voltage curves of the photodetector of the present invention, a general vertical GePD, and a Zener diode included in the photodetector of the present invention.

[0031] Figure 6 This is a diagram showing a voltage-resistance curve of a Zener diode included in the photodetector of the present invention.

[0032] Figure 7 It is a diagram showing a voltage-capacitance curve of a Zener diode included in the photodetector of the present invention.

[0033] Figure 8 It is a diagram showing a photodetector according to Example 2 of the present invention. DETAILED DESCRIPTION

[0034] Hereinafter, the optical modulator of the present invention will be described in detail using examples and drawings. It should be noted that in the drawings, parts having the same function are marked with the same reference numerals to clarify the description. However, the present invention is not limited to the contents of the embodiments shown below, and it is obvious to those skilled in the art that various changes can be made to the methods and details without departing from the gist of the invention disclosed in this specification and the like.

[0035] (Example 1)

[0036] Figure 3 The structure of the photodetector of the present invention is shown in FIG. Figure 1 In this embodiment, when viewed from the waveguide 109 , the GePD 300 and the Zener diode 301 are arranged in a straight line, and are arranged in the incident direction of light from the waveguide 109 . Figure 3 The cross-sectional view at the dotted line II-II' and the cross-sectional view at the dotted line IV-IV' correspond to Figure 2 and Figure 4 .

[0037] Figure 3 The Zener diode 301 is formed on a core layer 110 (also referred to as a core layer) including silicon, and includes a p-type silicon plate 111a doped with p-type impurity ions, a p++ silicon electrode portion 112 doped with p-type impurities at a high concentration and functioning as an electrode, an n-type silicon plate 119 doped with n-type impurity ions, and an n++ silicon electrode portion 120 doped with n-type impurities at a high concentration and functioning as an electrode. The n-type silicon plate is also referred to as an n-type Si plate or an n-type silicon region. The n++ silicon electrode portion is also referred to as an n-portion silicon electrode portion or an n-type electrode portion. The Ge layer 114 is stacked by epitaxial growth. In addition, electrodes 116 and 117 are provided on the p++ silicon electrode portion 112 and the n++ silicon electrode portion 120 so that they are in contact with each other. The electrodes 116 and 117 are connected to the electrodes of the GePD 300.

[0038] The Ge layer 114 is formed on the n-type silicon plate 119, but not on the p-type silicon (Si) region 111b. There is a gap between the p-type silicon region 111b and the n-type silicon plate 119, and an intrinsic silicon region 125 is provided. The threshold of the reverse bias side of the Zener diode is determined by the size of the gap.

[0039] An anode electrode of the Zener diode 301 is connected to an anode electrode of the GePD 300 , and a cathode electrode of the Zener diode 301 is connected to a cathode electrode of the GePD 300 .

[0040] When the electrode 116 functions as an anode electrode, the electrodes 117 and 118 function as cathode electrodes. When the electrode 116 functions as a cathode electrode, the electrodes 117 and 118 function as anode electrodes.

[0041] Figure 4 It is a cross-sectional view of the Zener diode 301 of the present invention at IV-IV'. The p-type silicon region 111b on the core layer 110 is not located directly below the Ge layer 114, and the n-type silicon plate 119 is located below the Ge layer 114. The p++ silicon electrode portion 112 is located on the p-type silicon region 111b, and the n++ silicon electrode portion 120 is located on the n-type silicon plate 119, and the p++ silicon electrode portion 112 is connected to the electrode 116. In addition, the n++ silicon electrode portion 120 is connected to the electrode 117. There is an intrinsic silicon region 125 that is not injected between the p-type silicon region 111b and the n-type silicon plate 119. The action threshold of the Zener diode is determined by the size of the intrinsic silicon region 125 and the doping concentration of the p-type silicon region 111b and the n-type silicon plate 119. In order to adjust the action threshold, the intrinsic silicon region 125 can also be removed to make the p-type silicon region 111b and the n-type silicon plate 119 contact. At this time, the p-type silicon region 111 b may enter directly below the Ge layer 114 .

[0042] In this embodiment, use Figure 5 The relationship between the current and voltage of the photodetector of the present invention, a general vertical GePD, and a Zener diode included in the photodetector of the present invention will be described.

[0043] The Zener diode provided in the photodetector of the present invention exhibits Figure 5 The current-voltage characteristics as in (1). Figure 5 (2) is the current-voltage characteristic of a general GePD. In addition, Figure 5 (3) is a method in which a Zener diode is provided in the GePD having the structure of the first embodiment. Figure 3 The current-voltage characteristics of the photodetector constructed by .

[0044] like Figure 5As shown in (1), the Zener diode of the present invention increases the current from about -7V on the reverse bias side, and increases the current from about 0.5V on the forward bias side. Moreover, the current flowing between 0.5V and -7V is about several nA, which is a typical Zener diode operation. When observing Figure 5 The current-voltage characteristics of the photodetector of the present invention in (3) are as follows: Figure 5 The current-voltage characteristics of a conventional GePD are different from those of (2), and the current increases suddenly from about -7V. Figure 5 (1) The current-voltage characteristics of the Zener diode overlap. When there is an instantaneous voltage rise caused by electrostatic discharge, the rapid current increase of the Zener diode plays a role in maintaining the voltage in the GePD at around -7V. Therefore, the voltage applied to the GePD is constant before the Zener diode is destroyed, thereby being protected, thereby preventing destruction caused by electrostatic discharge. The photodetector of the present invention is expected to increase the withstand voltage by more than 100V compared to the general GePD, so it can achieve the withstand voltage generally required in the human-type model.

[0045] Figure 6 The figure shows the change in resistance when a forward bias is applied to the Zener diode of the present invention, showing that the diode is saturated at about 30Ω, and the series resistance component of the Zener diode is about 30Ω.

[0046] Figure 7 The figure shows the change in capacitance of the Zener diode of the present invention with respect to the reverse bias voltage, which varies from about 8fF to 15fF.

[0047] It can be seen that according to Figure 6 , Figure 7 The CR time constant calculated from the capacitance and resistance of the GePD exceeds 100 GHz, and the high-speed operation characteristics of the GePD will not be reduced by adding a Zener diode. Figure 1 , Figure 2 The vertical GePD in the image can also be changed to other photodiodes made using silicon photonics technology.

[0048] Figure 4It is a cross-sectional view of the Zener diode 301 of the present invention at IV-IV'. The p-type silicon region 111b in the core layer 110 is not located directly below the Ge layer 114, and the n-type silicon plate 119 is located below the Ge layer 114. The p++ silicon electrode portion 112 is located on the p-type silicon region 111b, and the n++ silicon electrode portion 120 is located on the n-type silicon plate 119, and the p++ silicon electrode portion 112 is connected to the electrode 116. In addition, the n++ silicon electrode portion 120 is connected to the electrode 117. There is an intrinsic silicon region 125 that is not injected between the p-type silicon region 111b and the n-type silicon plate 119. The action threshold of the Zener diode is determined by the size of the intrinsic silicon region 125 and the doping concentration of the p-type silicon region 111b and the n-type silicon plate 119. In order to adjust the action threshold, the intrinsic silicon region 125 can also be removed to make the p-type silicon region 111b and the n-type silicon plate 119 contact. At this time, the p-type silicon region 111 b may enter directly below the Ge layer 114 .

[0049] (Example 2)

[0050] Figure 8 This is an example in which the Zener diode 301 of the present invention is arranged near the GePD 300. Figure 3 In the first embodiment of the present invention, when viewed from the waveguide 109, the GePD 300 and the Zener diode 301 are arranged in a straight line, but Figure 8 In the second embodiment, when viewed from the waveguide 109, the GePD 300 and the Zener diode 301 are not arranged in a straight line, but are arranged in a direction perpendicular to the incident direction of light from the waveguide 109. The long dimension direction of the Ge layer 114 of the GePD 300 and the long dimension direction of the Ge layer 114 of the Zener diode 301 are approximately parallel. Figure 8 The cross-sectional view at the dotted line II-II' and the cross-sectional view at the dotted line IV-IV' correspond to Figure 2 and Figure 4 .

[0051] exist Figure 8 In the configuration, since the light traveling straight from the waveguide 109 does not enter the Zener diode 301, the Zener diode does not detect a photocurrent.

[0052] In addition, Figure 8 In the embodiment, one Zener diode 301 is connected to the GePD 300, but a plurality of Zener diodes 301 may be connected. In this case, although the high-speed operation characteristics of the GePD are affected, a higher resistance to electrostatic discharge can be obtained.

[0053] Industrial Applicability

[0054] The present invention relates to a photodetector used in an optical communication system or an optical information processing system, and in particular can be applied to a photodetector having excellent resistance to electrostatic discharge.

[0055] Description of reference numerals:

[0056] 100, 300...GePD;

[0057] 101...Si substrate;

[0058] 102...lower cladding;

[0059] 103...upper cladding;

[0060] 109... waveguide;

[0061] 110... core layer;

[0062] 111a……p-type silicon plate;

[0063] 111b……p-type silicon region;

[0064] 112……p++ silicon electrode part;

[0065] 113……p++ silicon electrode part;

[0066] 114...Each level;

[0067] 115……n-type Ge region;

[0068] 116~118……Electrode;

[0069] 119……n-type silicon plate;

[0070] 120...n++ silicon electrode part;

[0071] 125…Intrinsic silicon region;

[0072] 301...Zener diode.

Claims

1. A photodetector comprising a photodiode and a Zener diode, wherein: The photodiode comprises an anode electrode and a cathode electrode. The Zener diode has: Silicon substrate; A lower cladding layer on the silicon substrate; The core layer on the lower cladding layer has a first-type silicon region doped with first-type impurity ions and a second-type silicon region doped with second-type impurity ions; a germanium layer on the core layer; an upper cladding layer on the germanium layer; as well as The anode electrode and the cathode electrode are an anode electrode connected to the first type silicon region and a cathode electrode connected to the second type silicon region, or a cathode electrode connected to the first type silicon region and an anode electrode connected to the second type silicon region. The anode electrode of the Zener diode is connected to the anode electrode of the photodiode, The cathode electrode of the Zener diode is connected to the cathode electrode of the photodiode, The photodiode has: the silicon substrate; the lower cladding layer on the silicon substrate; The core layer on the lower cladding layer has a first-type silicon plate doped with first-type impurity ions; a waveguide layer connected to the core layer; The germanium layer on the core layer includes a second-type germanium region doped with second-type impurities; the upper cladding layer on the core layer and the germanium layer including the second-type germanium region; as well as electrodes, connected to the first-type silicon plate and the second-type germanium region, respectively, The silicon substrate, the lower cladding layer, the core layer, and the upper cladding layer included in the photodiode and the Zener diode are common. The photodiode and the Zener diode are arranged in a direction perpendicular to an incident direction of light that passes through the waveguide layer provided in the photodiode and enters the core layer.

2. The optical detector according to claim 1, characterized in that In the Zener diode, The second type silicon region is located directly below the germanium layer, The intrinsic silicon region is between the bottom surface of the germanium layer and the first type silicon region, The intrinsic silicon region is located between the first type silicon region and the second type silicon region.

3. The photodetector according to claim 1 or 2, characterized in that A plurality of the Zener diodes are connected to the photodiode.

4. The photodetector according to claim 1 or 2, characterized in that: The first-type impurity ions are p-type impurity ions, and the second-type impurity ions are n-type impurity ions.

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