Photodetector

Abstract

This photodetector is provided with a photodiode (300) and a protection diode (301), and is characterized in that the photodiode (300) and the protection diode (301) are integrated on the same semiconductor substrate, and the photodiode (300) is provided with: a semiconductor section comprising at least one semiconductor material; an anode electrode; and a cathode electrode. The protection diode (301) is provided with: a core layer; a semiconductor part including a first-type semiconductor region doped with first-type impurity ions and a second-type semiconductor region doped with second-type impurity ions, which are provided in the core layer; an anode electrode; and a cathode electrode, the semiconductor part of the protection diode (301) is composed of only one semiconductor material used in the semiconductor part of the photodiode (300), and the anode electrode of the protection diode (301) is connected to the anode electrode of the photodiode (300). The cathode electrode of the protection diode (301) is connected with the cathode electrode of the photodiode (300).

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 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 on a large-diameter wafer such as a silicon wafer to form an optical circuit constituting an optical communication device. This can reduce the material cost of each chip and seek low-cost optical communication devices.

[0003] As a representative photodetector formed on a silicon (Si) substrate using such a technology, there is a monolithically integrated germanium photodetector (hereinafter also referred to as GePD) (Patent Document 1). However, this photodetector does not have a protection circuit, and therefore has a problem of weak resistance to electrostatic discharge.

[0004] On the other hand, a photodetector provided with a protection circuit (protection Zener diode) is disclosed in Patent Document 2. The protection Zener diode of the photodetector is formed using both a Ge layer and a Si layer.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application No. 5370857

[0008] Patent Document 2: Japanese Patent Application No. 6981365 Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, the photodetector with a protective Zener diode of Patent Document 2 performs ion implantation (doping process) using a mask to form the Ge layer and the Si layer separately. At this time, due to manufacturing errors, the Zener diode for the protection circuit sometimes has a positional shift between the p-type semiconductor part, the n-type semiconductor part (pn junction), or the p-type semiconductor part, the intrinsic semiconductor part, and the n-type semiconductor part (pin junction) on the Si core layer and the light absorption layer (Ge layer). In addition, this positional shift has a problem of affecting the rectification characteristics of the photodetector.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a photodetector capable of eliminating the influence on rectification characteristics caused by positional deviation in a protective Zener diode.

[0012] Solutions for solving problems

[0013] In order to achieve the above-mentioned purpose, the photodetector of the first scheme of the present invention comprises a photodiode and a protection diode, and is characterized in that the photodiode and the protection diode are integrated on the same semiconductor substrate, the photodiode comprises: a semiconductor portion, which is composed of at least one semiconductor material; an anode electrode; and a cathode electrode, and the protection diode comprises: a core layer; a semiconductor portion, including a first-type semiconductor region doped with first-type impurity ions and a second-type semiconductor region doped with second-type impurity ions possessed by the core layer; an anode electrode; and a cathode electrode, the semiconductor portion of the protection diode is composed of only one of the semiconductor materials used in the semiconductor portion of the photodiode, the anode electrode of the protection diode is connected to the anode electrode of the photodiode, and the cathode electrode of the protection diode is connected to the cathode electrode of the photodiode.

[0014] Effects of the Invention

[0015] The photodetector of the present invention can eliminate the influence on the rectification characteristics caused by the positional deviation in the protective Zener diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a diagram showing a top view of Embodiment 1 of the present invention.

[0017] Figure 2 It is a diagram showing a cross-sectional structure of a Zener diode included in the photodetector according to Embodiment 1 of the present invention.

[0018] Figure 3 This is a diagram showing the upper surface of a photodetector according to Embodiment 2 of the present invention.

[0019] Figure 4 It is a diagram showing a top view of a photodetector according to a comparative example.

[0020] Figure 5 It is a diagram showing a cross-sectional structure of a Zener diode included in a photodetector of a comparative example. DETAILED DESCRIPTION

[0021] Hereinafter, the method of the photodetector of the present invention will be described in detail using the embodiments and the accompanying drawings. It should be noted that in the accompanying drawings, the same numbers are given to parts having the same functions 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 method and details without departing from the gist of the invention disclosed in this specification, etc.

[0022] (Implementation Method 1)

[0023] Figure 1 It is a plan view showing the structure of a photodetector according to one embodiment of the present invention.

[0024] The photodetector according to one embodiment of the present invention is configured by electrically connecting a GePD 300 and a protective Zener diode 301 in parallel.

[0025] The GePD 300 includes a core layer 110 doped with a first type impurity (n-type impurity), a (optical) waveguide 109 connected to the core layer 110, a light absorption layer (Ge layer) 114 doped with a second type impurity on the core layer 110, and a lower cladding layer 102 (see Figure 2 ), the semiconductor substrate 101 under the lower cladding layer 102 (refer to Figure 2 ), and the upper cladding layer 103 on the core layer 110 and the light absorbing layer (refer to Figure 2 ). A p-type silicon plate 111a and p++ silicon contact regions 112 and 113 are formed in the core layer 110. In addition, an n-type Ge region 115 is formed in the light absorption layer 114. Moreover, the p++ silicon contact regions 112 and 113 and the n-type Ge region 115 are provided with electrodes 116, 117 and 118 connected thereto, respectively. In the GePD 300, when light is incident on the core layer 110 and absorbed by the light absorption layer 114, a current flows between the electrode 117 and the electrodes 116 and 118, and light can be detected by detecting the current.

[0026] In the present embodiment, the GePD 300 and the Zener diode 301 are arranged in a straight line when viewed from the waveguide 109 , and are arranged in the incident direction of light from the waveguide 109 .

[0027] The Zener diode 301 is formed in a core layer 110 continuous from GePD300, and includes: a p-type silicon plate (region) 111b doped with p-type impurity ions and a p++ silicon contact region 112 doped with p-type impurities at a high concentration and serving as an ohmic contact with an electrode 116; and an n-type silicon plate 119 doped with n-type impurity ions and an n++ silicon contact region 120 doped with n-type impurities at a high concentration and serving as an ohmic contact with an electrode 117. The n-type silicon plate 119 is also referred to as an n-type Si plate or an n-type silicon region. The n++ silicon contact region is also referred to as an n-portion silicon contact region or an n-type electrode portion. Similarly, an upper cladding layer 103 (see FIG. 1 ) continuous from GePD300 is formed on the p++ silicon contact region 112 and the n++ silicon contact region 120. Figure 2), electrodes 116 and 117 are formed respectively in a manner of contacting the p++ silicon contact region 112 and the n++ silicon contact region 120 via a plurality of openings formed in the upper cladding layer 103. The electrodes 116 and 117 are connected to the electrodes 116 and 117 of the GePD 300.

[0028] Figure 2 1 is a cross-sectional view of the Zener diode 301 at II-II'. In the core layer 110, the p++ silicon contact region 112 is located on the p-type silicon region 111b, and the n++ silicon contact region 120 is located on the n-type silicon plate 119. In addition, the p++ silicon contact region 112 is connected to the electrode 116, and the n++ silicon contact region 120 is connected to the electrode 117. There is an intrinsic silicon region 125 without ion implantation between the p-type silicon region 111b and the n-type silicon plate 119. Figure 2 In the figure, the action threshold of the Zener diode is determined by the size of the intrinsic silicon region 125 indicated by the arrow 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 may be removed so that the p-type silicon region 111b and the n-type silicon plate 119 are in contact to form a PN junction.

[0029] The upper cladding layer 103 is formed directly on the p-type semiconductor portion (p-type silicon region 111b and p++ silicon contact region 112), the I-type semiconductor portion (intrinsic silicon region 125), and the p-type semiconductor portion (n-type silicon plate 119 and n++ silicon contact region 120). Figure 4 , Figure 5 As will be described later in the comparison of the comparative example shown, a Ge layer in contact with the core layer 110 is not formed. That is, in the photodetector of the present embodiment, an upper cladding layer 103 is formed directly on the p-type semiconductor part and the n-type semiconductor part, and only the upper cladding layer is between the electrodes connected to the p-type semiconductor part and the n-type semiconductor part. The semiconductor part of the protection diode is composed of only one of the semiconductor materials used in the semiconductor part of the photodiode. As a result, there is no room for positional deviation between the pn junction composed of the p-type semiconductor part and the n-type semiconductor part and the light absorbing layer (Ge layer), and as a result, it is possible to prevent the rectification characteristics of the photodiode from being affected.

[0030] The applicant presumes that the reason why the photodetector of the present embodiment can be driven is because the impurity doping concentration is set so that the Zener breakdown voltage of the protection diode is lower than the avalanche breakdown voltage of the photodetector body.

[0031] 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 .

[0032] 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. Between the electrodes 117 and 118, only the upper cladding layer 103 exists.

[0033] The core layer 110 of the GePD 300 and the semiconductor portion (the n-type silicon plate 119 and the n++ silicon contact region 120 ) of the protection diode 301 are made of the same material.

[0034] As described above, the core layer 110 of the GePD 300 is the same layer as the semiconductor portion (the n-type silicon plate 119 and the n++ silicon contact region 120 ) of the protection diode 301 .

[0035] In the present embodiment, Ge is used as the main material of the light absorbing layer 114 , but other semiconductor materials such as GeSn, InGaAs, and InGaAsP may also be used.

[0036] exist Figure 2 In the embodiment, GePD 300 and protection diode 301 are located on a continuous core layer 110, but this is not necessarily the case, and they can also be made on separate Si plates. The height and material of the layer used as the Si plate are roughly the same as those of the core layer 110, but they can also be separated.

[0037] In this embodiment, Si is used as the main material of the core layer 110, but other semiconductor materials such as InP and SiC may also be used. In addition, the position of the p-type semiconductor portion and the position of the n-type semiconductor portion may also be opposite. As described above, the protection diode 301 may adopt a pin junction or a pn junction. Moreover, as described above, the protection diode 301 may be a single one or multiple ones may be installed in parallel.

[0038] (Implementation Method 2)

[0039] like Figure 3 As shown, the photodetector according to one embodiment of the present invention is configured by electrically connecting a GePD 300 and a Zener diode 301 as a protection circuit in series.

[0040] For GePD300, Figure 1 In the first embodiment of the present invention, the GePD 300 and the Zener diode 301 are arranged in a straight line when viewed from the waveguide 109, but Figure 3In the second embodiment, GePD 300 and Zener diode 301 are not arranged in a straight line when viewed from waveguide 109, but are arranged in a direction perpendicular to the incident direction of light from waveguide 109. The length direction of Ge layer 114 of GePD 300 is approximately parallel to the length directions of p++ silicon contact region 112 and n++ silicon contact region 120 of Zener diode 301. Figure 3 The cross-sectional view of the dotted line II-II' is Figure 2 correspond.

[0041] exist Figure 3 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.

[0042] In the present embodiment, the semiconductor portion of the protection diode 301 is also composed of only one of the semiconductor materials used in the semiconductor portion of the photodiode 300. Therefore, in terms of the rectification characteristics of the photodetector of the present embodiment, it is possible to provide a photodetector having a protection circuit that is not affected by the pn junction composed of the p-type semiconductor portion and the n-type semiconductor portion or the positional shift of the p-type semiconductor portion, the I-type semiconductor portion, the n-type semiconductor portion (pin junction) and the light absorption layer (Ge layer).

[0043] In addition, Figure 3 In FIG. 1 , one Zener diode (protection 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, high resistance to electrostatic discharge can be obtained.

[0044] (Comparative Example)

[0045] Figure 4 , Figure 5 The structure of the photodetector of the comparative example is shown. The GePD 300 has the same structure as the GePD 300 of Embodiments 1 and 2. In the comparative example, the GePD 300 and the Zener diode 401 are arranged in a straight line when viewed from the waveguide 109 , and are arranged in the incident direction of the light from the waveguide 109 . Figure 4 The V-V' cross-section diagram is Figure 5 correspond.

[0046] The Zener diode 401 of this comparative example is different from the Zener diode 301 of the above-mentioned embodiments 1 and 2 in that the Zener diode for the protection circuit has a Ge layer 114. There is a problem that sometimes a positional offset occurs between the Ge layer and the p-type semiconductor part, n-type semiconductor part (pn junction), or the p-type semiconductor part, intrinsic semiconductor part, and n-type semiconductor part (pin junction) on the Si core layer, and this positional offset affects the rectification characteristics of the photodetector.

[0047] Figure 5 This is a cross-sectional view of the Zener diode 401 of the present invention taken along the line V-V'. The Ge layer 114 is formed on the n-type silicon plate 119 and is not formed on the p-type silicon (Si) region 111b. In addition, the Ge layer 114 is present between the electrodes 117 and 118.

[0048] There is no p-type silicon region 111b of the core layer 110 directly below the Ge layer 114, and there is an n-type silicon plate 119 below the Ge layer 114. In addition, the p-type silicon region 111b may also enter directly below the Ge layer 114.

[0049] There is a problem that since the Ge layer 114 is formed by injecting Ge material using a mask during the manufacturing process, a PN junction corresponding to the p-type semiconductor part and the n-type semiconductor part or a positional shift of the p-type semiconductor part, the i-type semiconductor part, and the n-type semiconductor part (pin junction) may occur, and this positional shift affects the rectification characteristics of the photodetector. Figure 1 to Figure 3 In the detector of the embodiment of the present invention described above, there is no Ge layer under the upper cladding 103, so there is no room for positional deviation, and the influence on the rectification characteristics of the optical detector can be eliminated. In addition, the detector of the embodiment of the present invention has the following advantages: it can eliminate the problems caused when the Ge layer 114 exists. Specifically, the interface between Ge and Si becomes a leakage current path, which becomes a cause of the deviation of the reverse current when the alignment accuracy between the PN junction and the Ge layer 114 is not good, but the detector of the embodiment of the present invention can suppress this deviation.

[0050] Industrial Applicability

[0051] The present invention relates to a photodetector used in an optical communication system or an optical information processing system, and is particularly applicable to a photodetector having resistance to electrostatic discharge.

[0052] Description of reference numerals:

[0053] 101: semiconductor substrate; 102: lower cladding; 103: upper cladding; 109: waveguide; 110: core layer; 111a: p-type silicon plate; 111b: p-type silicon plate (region); 112: silicon contact region; 113: p++ silicon contact region; 114: light absorption layer (Ge layer); 115: n-type Ge region; 116: electrode; 117: electrode; 118: electrode; 119: n-type silicon plate; 120: silicon contact region; 125: intrinsic silicon region; 300: GePD; 301: protection (Zener) diode; 401: protection (Zener) diode.

Claims

1. A photodetector comprising a photodiode and a protection diode, characterized in that: The photodiode and the protection diode are integrated on the same semiconductor substrate. The photodiode has: The semiconductor part is composed of at least one semiconductor material; an anode electrode; and cathode electrode, The protection diode has: Core layer; The semiconductor portion includes a first-type semiconductor region doped with first-type impurity ions and a second-type semiconductor region doped with second-type impurity ions included in the core layer; Anode electrode; as well as cathode electrode, The semiconductor portion of the protection diode is composed of only one of the semiconductor materials used in the semiconductor portion of the photodiode, The anode electrode of the protection diode is connected to the anode electrode of the photodiode, A cathode electrode of the protection diode is connected to a cathode electrode of the photodiode.

2. The optical detector according to claim 1, characterized in that The semiconductor portion of the photodiode includes: The core layer is doped with type I impurities; an optical waveguide connected to the core layer; a light absorbing layer doped with second type impurities on the core layer; A lower cladding layer below the core layer; an upper cladding layer on the core layer and the light absorbing layer; as well as The electrodes are connected to the core layer and the light absorbing layer respectively.

3. The light detector according to claim 2, characterized in that The core layer of the photodiode and the semiconductor portion of the protection diode are made of the same material.

4. The light detector according to claim 2 or 3, characterized in that A core layer of the photodiode and a semiconductor portion of the protection diode share the same layer.

5. The light detector according to claim 2, wherein The main material of the core layer of the photodiode is silicon, and the main material of the light absorption layer is germanium.

6. The photodetector according to claim 1 or 2, characterized in that: The photodiode and the protection diode are arranged in an incident direction of light that has passed through a silicon waveguide layer included in the photodiode.

7. The photodetector according to claim 1 or 2, characterized in that: The photodiode and the protection diode are arranged in a direction perpendicular to an incident direction of light passing through a silicon waveguide layer included in the photodiode.

8. The photodetector according to claim 1 or 2, characterized in that: The photodiode is connected to a plurality of protection diodes.

9. The photodetector according to claim 1 or 2, characterized in that: Only an upper cladding layer is formed in contact with the semiconductor portion of the protection diode and between the electrodes of the protection diode.

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