Photodetector

Abstract

A photodetector according to the present invention is a photodetector including a photodiode (300) and a protection diode (301), wherein the photodiode (300) and the protection diode (301) are integrated on the same semiconductor substrate, the photodiode (300) includes a semiconductor portion made of at least one type of semiconductor material, an anode electrode, and a cathode electrode, the protection diode (301) includes 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 provided in the core layer, an anode electrode, and a cathode electrode, the semiconductor portion of the protection diode (301) is made of only one type of material among semiconductor materials used for the semiconductor portion of the photodiode (300), the anode electrode of the protection diode (301) and the anode electrode of the photodiode (300) are connected, and the cathode electrode of the protection diode (301) and the cathode electrode of the photodiode (300) are connected.

Description

Technical Field

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

Background Art

[0002] With the recent spread of optical communication, 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 using a micro-optical circuit technology such as silicon photonics. Thereby, the material cost per chip can be reduced, and the cost of the optical communication device can be reduced.

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

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the photodetector equipped with a protective Zener diode described in Patent Document 2 performs ion implantation (doping process) using a mask to form the Ge layer and Si layer, respectively. During this process, due to manufacturing errors, the Zener diode for the protective circuit may consist of a p-type semiconductor portion, an n-type semiconductor portion (pn junction), or a p-type semiconductor portion, an intrinsic semiconductor portion, and an n-type semiconductor portion on the Si core layer. A misalignment can occur between the body (pin junction) and the absorption layer (Ge layer). This misalignment has the problem of affecting the rectification characteristics of the photodetector.

[0007] The present invention has been made in view of these problems, and its objective is to provide a photodetector that can eliminate the influence on rectification characteristics caused by misalignment in the protective Zener diode. [Means for solving the problem]

[0008] To achieve the above objective, a first aspect of the present invention provides a photodetector comprising a photodiode and a protection diode, wherein the photodiode and the protection diode are integrated on the same semiconductor substrate, the photodiode comprises a semiconductor portion made of at least one type of semiconductor material, an anode electrode, and a cathode electrode, the protection diode comprises a core layer, a semiconductor portion including a type first semiconductor region doped with type first impurity ions and a type second semiconductor region doped with type second impurity ions provided in the core layer, an anode electrode, and a cathode electrode, the semiconductor portion of the protection diode is composed of only one type of semiconductor material 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. [Effects of the Invention]

[0009] The photodetector of the present invention makes it possible to eliminate the influence on rectification characteristics caused by misalignment in the protective Zener diode. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a top view according to Embodiment 1 of the present invention. [Figure 2] This figure shows the cross-sectional structure of a Zener diode provided in a photodetector according to Embodiment 1 of the present invention. [Figure 3] This figure shows a top view of a photodetector according to Embodiment 2 of the present invention. [Figure 4] This figure shows a top view of the photodetector in the comparative example. [Figure 5] This figure shows the cross-sectional structure of the Zener diode in the comparative example's photodetector. [Modes for carrying out the invention]

[0011] The embodiments of the photodetector of the present invention will be described in detail below with reference to embodiments and drawings. In the drawings, parts having the same function are numbered the same to clarify the explanation. However, it will be obvious to those skilled in the art that the present invention is not limited to the embodiments described below, and that the form and details can be changed in various ways without departing from the spirit of the invention disclosed herein.

[0012] (Embodiment 1) Figure 1 is a top view showing the configuration of a photodetector according to one embodiment of the present invention.

[0013] A photodetector according to one embodiment of the present invention is configured by electrically connecting a GePD300 and a protective Zener diode 301 in parallel.

[0014] The GePD300 comprises a core layer 110 doped with type I impurities (n-type impurities), an (optical) waveguide 109 connected to the core layer 110, an absorption layer (Ge layer) 114 doped with type II impurities on the core layer 110, a lower cladding layer 102 below the core layer 110 (see Figure 2), a semiconductor substrate 101 below the lower cladding layer 102 (see Figure 2), and an upper cladding layer 103 on the core layer 110 and the absorption layer (see Figure 2). The core layer 110 has a p-type silicon slab 111a and p++ silicon contact regions 112 and 113 formed thereon. The absorption layer 114 has an n-type Ge region 115 formed thereon. The p++ silicon contact regions 112 and 113 and the n-type Ge region 115 are provided with electrodes 116, 117, and 118 connected to them, respectively. In the GePD300, when light is incident on the core layer 110 and absorbed by the absorption layer 114, a current flows between electrode 117 and electrodes 116 and 118, and light can be detected by detecting this current.

[0015] In this embodiment, the GePD300 and Zener diode 301 are arranged in a straight line when viewed from the waveguide 109, and are arranged in the direction of incidence of light from the waveguide 109.

[0016] The Zener diode 301 has a core layer 110 that is continuous with the GePD 300, and includes a p-type silicon slab (region) 111b doped with p-type impurity ions, a p++ silicon contact region 112 that is highly doped with p-type impurities and plays a role in ohmic contact with electrode 116, an n-type silicon slab 119 doped with n-type impurity ions, and an n++ silicon contact region 120 that is highly doped with n-type impurities and plays a role in ohmic contact with electrode 117. The n-type silicon slab 119 is also called an n-type Si slab or n-type silicon region. The n++ silicon contact region is n typeThis is also referred to as the silicon contact region or the n-type electrode portion. On the p++ silicon contact region 112 and the n++ silicon contact region 120, an upper cladding layer 103 (see FIG. 2) that is also continuous from GePD300 is formed. Electrodes 116 and 117 are respectively formed so as to contact the p++ silicon contact region 112 and the n++ silicon contact region 120 through a plurality of openings formed in the upper cladding layer 103. These electrodes 116 and 117 are continuous with the electrodes 116 and 117 of GePD300.

[0017] FIG. 2 is a cross-sectional view taken along the line II-II' of the Zener diode 301. 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 slab 119. 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. An intrinsic silicon region 125 without ion implantation exists between the p-type silicon region 111b and the n-type silicon slab 119. In FIG. 2, the operating threshold of the Zener diode is determined by the size of the intrinsic silicon region 125 indicated by the arrow and the doping concentrations of the p-type silicon region 111b and the n-type silicon slab 119. To adjust the operating threshold, the intrinsic silicon region 125 may be eliminated and the p-type silicon region 111b and the n-type silicon slab 119 may be brought into contact to form a PN junction.

[0018] The upper cladding layer 103 includes a p-type semiconductor portion (p-type silicon region 111b and p++ silicon contact region 112), an I-type semiconductor portion (intrinsic silicon region 125), and nIt is formed directly on the type semiconductor part (n-type silicon slab 119 and n++ silicon contact region 120). As will be described later in comparison with the comparative example shown in FIGS. 4 and 5, a Ge layer in contact with the core layer 110 is not formed. That is, in the photodetector of the present embodiment, the 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 kind of the semiconductor materials used for the semiconductor part of the photodiode. Thus, there is no room for misalignment between the pn junction composed of the p-type semiconductor Department reference and the n-type semiconductor part and the absorption layer (Ge layer), and as a result, it is possible to eliminate the influence on the rectifying characteristics of the photodiode.

[0019] The applicant speculates that the reason why the photodetector of the present embodiment can be driven is that the impurity doping concentration is set such that the voltage of the Zener breakdown of the protection diode is smaller than the avalanche breakdown of the photodetector body.

[0020] The anode electrode of the Zener diode 301 is connected to the anode electrode of the GePD300, and the cathode electrode of the Zener diode 301 is connected to the cathode electrode of the GePD300.

[0021] 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 116 , 117 there is only the upper cladding layer 103.

[0022] The core layer 110 of the GePD300 and the semiconductor part (n-type silicon slab 119 and n++ silicon contact region 120) of the protection diode 301 are made of the same material.

[0023] As described above, the core layer 110 of the GePD300 is the same layer as the semiconductor portion of the protection diode 301 (n-type silicon slab 119 and n++ silicon contact region 120).

[0024] In this embodiment, Ge was used as the main material for the absorption layer 114, but other semiconductor materials such as GeSn, InGaAs, and InGaAsP may also be used.

[0025] In Figure 2, the GePD300 and protection diode 301 are located on a continuous core layer 110, but this is not necessarily required; they may be fabricated on separate Si slabs. The height and material of the layers used as Si slabs are approximately the same as those of the core layer 110, but they may be separated.

[0026] In this embodiment, Si is used as the main material for the core layer 110, but other semiconductor materials such as InP and SiC may be used. Also, the positions of the p-type semiconductor portion and the n-type semiconductor portion may be reversed. As described above, the protection diode 301 may employ a pin junction or a pn junction. Furthermore, as described above, the protection diode 301 may be a single unit or multiple units may be mounted in parallel.

[0027] (Embodiment 2) As shown in Figure 3, a photodetector according to one embodiment of the present invention is configured by electrically connecting a GePD300 and a Zener diode 301 as a protection circuit in series.

[0028] In Embodiment 1 of Figure 1, the GePD300 and the Zener diode 301 are aligned in a straight line when viewed from the waveguide 109. However, in Embodiment 2 of Figure 3, the GePD300 and the Zener diode 301 are not aligned in a straight line when viewed from the waveguide 109, but are arranged in a direction perpendicular to the direction of incidence of light from the waveguide 109. The longitudinal direction of the Ge layer 114 of the GePD300 and the longitudinal directions of the p++ silicon contact region 112 and n++ silicon contact region 120 of the Zener diode 301 are roughly parallel. The cross-sectional view along the dashed line II-II' in Figure 3 corresponds to Figure 2.

[0029] In the configuration shown in Figure 3, light traveling straight from waveguide 109 does not enter Zener diode 301, and therefore the Zener diode does not detect photocurrent.

[0030] In this embodiment as well, the semiconductor portion of the protection diode 301 is composed of only one type of semiconductor material used in the semiconductor portion of the photodiode 300. Therefore, this embodiment provides a photodetector with a protection circuit whose rectification characteristics are not affected by misalignment between a pn junction consisting of a p-type semiconductor portion and an n-type semiconductor portion, or a p-type semiconductor portion, an I-type semiconductor portion, an n-type semiconductor portion (pin junction), and an absorption layer (Ge layer).

[0031] Furthermore, although Figure 3 shows one Zener diode (protection diode) 301 connected to the GePD 300, multiple Zener diodes 301 can also be connected. In that case, although it will affect the high-speed operating characteristics of the GePD, high resistance to electrostatic discharge can be obtained.

[0032] (Comparative example) Figures 4 and 5 show the configuration of the photodetector in the comparative example. The GePD300 has the same configuration as the GePD300 in Embodiments 1 and 2. In the comparative example, the GePD300 and Zener diode 401 are arranged in a straight line when viewed from the waveguide 109, and are arranged in the direction of light incidence from the waveguide 109. The cross-sectional view at V-V' in Figure 4 corresponds to Figure 5.

[0033] The difference between the Zener diode 401 of this comparative example and the Zener diode 301 of embodiments 1 and 2 is that the Zener diode for the protection circuit has a Ge layer 114. This Ge layer is connected to the p-type semiconductor portion, n-type semiconductor portion (pn junction), or p-type semiconductor portion on the Si core layer. A misalignment can occur between the semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion (pin junction), and this misalignment can affect the rectification characteristics of the photodetector.

[0034] Figure 5 is Comparative Example This is a cross-sectional view of the Zener diode 401 at V-V'. The Ge layer 114 is formed on the n-type silicon slab 119 and not on the p-type silicon (Si) region 111b. Also, the electrodes 116 , 117 There is a Ge layer 114 in between.

[0035] The p-type silicon region 111b, which is located over the core layer 110, is not directly beneath the Ge layer 114, and the n-type silicon slab 119 is located beneath the Ge layer 114. Alternatively, the p-type silicon region 111b may be located directly beneath the Ge layer 114.

[0036] Because the Ge layer 114 is formed by implanting Ge material using a mask during the manufacturing process, misalignment may occur between the PN junction corresponding to the p-type semiconductor portion and the n-type semiconductor portion, or between the p-type semiconductor portion, i-type semiconductor portion, and n-type semiconductor portion (pin junction), and this misalignment may affect the photodetector. There is a problem that this affects the rectification characteristics. In contrast, the detector according to the embodiment of the present invention described in Figures 1 to 3 does not have a Ge layer under the upper cladding layer 103, so there is no room for misalignment, and this eliminates the effect on the rectification characteristics of the photodetector. Furthermore, the detector according to the embodiment of the present invention has the advantage of resolving the problems that occurred when the Ge layer 114 was present. Specifically, the interface between Ge and Si became a leakage current path, and when the alignment accuracy between the PN junction and the Ge layer 114 was not good, it caused variations in the reverse current, but the detector according to the embodiment of the present invention can suppress this variation. [Industrial applicability]

[0037] The present invention relates to a photodetector used in optical communication systems and optical information processing systems, and can be applied in particular to a photodetector resistant to electrostatic discharge. [Explanation of Symbols]

[0038] 101 Semiconductor substrate, 102 Lower cladding layer, 103 Upper cladding layer, 109 Waveguide, 110 Core layer, 111a p-type silicon slab, 111b p-type silicon slab (region), 112 Silicon contact region, 113 p++ silicon contact region, 114 Absorbance layer (Ge layer), 115 n-type Ge region, 116 electrode, 117 electrode, 118 electrode, 119 n-type silicon slab, 120 silicon contact region, 125 intrinsic silicon region, 3 00 GePD, 301 Zener diode, 401 Zener diode

Claims

1. In a photodetector comprising a photodiode and a protection diode, The photodiode and the protection diode are integrated on the same semiconductor substrate. The aforementioned photodiode is A semiconductor part consisting of at least one type of semiconductor material, Anode electrode and It comprises a cathode electrode, The aforementioned protection diode is The core layer, The semiconductor portion includes a type I semiconductor region doped with type I impurity ions, a type II semiconductor region doped with type II impurity ions, and an intrinsic semiconductor region provided in the core layer, Anode electrode and It comprises a cathode electrode, The semiconductor portion of the protection diode is composed of only one type of semiconductor material used in the semiconductor portion of the photodiode. The upper cladding layer is formed in contact with the semiconductor portion of the protection diode, and only the upper cladding layer is formed between the anode electrode and the cathode electrode of the protection diode. The anode electrode of the protection diode and the anode electrode of the photodiode are connected. A photodetector characterized in that the cathode electrode of the protection diode and the cathode electrode of the photodiode are connected.

2. The semiconductor portion of the aforementioned photodiode is A core layer doped with type 1 impurities, An optical waveguide connected to the core layer, The core layer is doped with a type II impurity, and The lower cladding layer below the core layer, The core layer and the upper cladding layer on the light-absorbing layer, The anode electrode and cathode electrode of the photodiode are connected to the core layer and the absorption layer, respectively. The photodetector according to claim 1, characterized by comprising:

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

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

6. The photodetector according to claim 1 or 2, characterized in that the photodiode and the protection diode are aligned in the direction of incidence of light passing through the silicon waveguide layer provided by the photodiode.

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

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

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