Semiconductor light receiving element

Abstract

A current amplification factor equivalent to that of the APD is obtained by applying a bias of a drive voltage 3 to 5V of a general PIN-PD or bipolar transistor.SOLUTION: On a supporting substrate are provided an input waveguide, a photodiode unit having a first conductivity type region and a second conductivity type region, which absorbs signal light introduced via the input waveguide and outputs a photocurrent, and a bipolar transistor unit having a first conductivity type region as a base region, into which the photocurrent is input, and which amplifies and outputs the photocurrent, wherein the first conductivity type region of the photodiode unit and the base region of the bipolar transistor unit are integrally configured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor light-receiving element. [Background technology]

[0002] PIN photodiodes (PIN-PDs) are widely used as light-detecting devices. PIN-PDs have an insulating i-type semiconductor region between p-type and n-type semiconductor regions. PIN-PDs operate at low power supply voltages and have a high frequency response.

[0003] In addition to PIN-PDs, avalanche photodiodes (APDs) and phototransistors (PTs) are known as devices for detecting particularly weak light.

[0004] Although APDs have the advantage of higher light-receiving sensitivity due to the internal amplification effect compared to PIN-PDs, they have the disadvantage of requiring a higher power supply voltage than PIN-PDs.For this reason, a structure has been proposed in which the germanium (Ge) that forms the light absorption region is made thinner, thereby increasing the internal electric field of Ge even at low voltages.

[0005] In APDs, thinning the Ge that forms the light absorption region makes it easier for avalanche breakdown to occur inside the Ge, thereby achieving the internal amplification effect that is unique to APDs even at a power supply voltage of -3 V. However, by thinning the Ge that forms the light absorption region, the wavelengths at which significant light receiving sensitivity can be obtained are limited to the O band (original band), represented by 1310 nm, and sufficient light receiving sensitivity cannot be obtained in the C band (conventional band), represented by the wavelength of 1550 nm that is currently used in subscriber optical communications.

[0006] Furthermore, although PTs have the advantage of high light-receiving sensitivity due to the internal amplification effect at a low power supply voltage equivalent to that of PIN-PDs, they have the disadvantage of having inferior frequency response characteristics compared to PIN-PDs and APDs.

[0007] Therefore, a device has been proposed that integrates a bipolar transistor into a PIN-PD to have a high frequency response at a low power supply voltage equivalent to that of a PIN-PD, while adding the amplification effect of the bipolar transistor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 9-223785 Summary of the Invention [Problem to be solved by the invention]

[0009] In the PD integrated with a bipolar transistor disclosed in Patent Document 1, the PD and bipolar transistor are arranged and integrated adjacent to each other. However, the structure is such that photocarriers (electrons and holes) generated in the PD are input to the bipolar transistor through the PD's pillar electrode, metal electrode layer, and pillar electrode of the bipolar transistor. This results in a problem in that the photocarriers have to travel a long distance, making it difficult to obtain sufficient frequency response.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor photodetector that can obtain a current gain equivalent to that of an APD by applying a bias voltage of 3 to 5 V, which is a drive voltage for a general PIN-PD or bipolar transistor. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the semiconductor light-receiving element of the present invention comprises, on a support substrate, a photodiode portion having an input waveguide, a first conductivity type region, and a second conductivity type region, which absorbs signal light introduced through the input waveguide and outputs a photocurrent, and a bipolar transistor portion having a first conductivity type region as a base region, which receives the photocurrent, amplifies the photocurrent, and outputs the amplified photocurrent, and the first conductivity type region of the photodiode portion and the base region of the bipolar transistor portion are integrally configured.

[0012] According to a preferred embodiment of the semiconductor light-receiving element of the present invention, the bipolar transistor portion includes a collector region and an emitter region, each of which has a second conductivity type, and the collector region and the emitter region are disposed adjacent to the base region and sandwiching the base region therebetween.

[0013] According to a further preferred embodiment of the semiconductor light-receiving element of the present invention, the width of the first conductivity type region of the photodiode section and the width of the base region of the bipolar transistor section are different from each other.

[0014] According to another preferred embodiment of the semiconductor light-receiving element of the present invention, the carrier concentration of the first conductivity type region of the photodiode section and the carrier concentration of the base region of the bipolar transistor section are different from each other.

[0015] According to another preferred embodiment of the semiconductor light-receiving element of the present invention, the width of the first conductivity type region of the photodiode portion and the width of the base region of the bipolar transistor portion are different from each other, and the carrier concentration of the first conductivity type region of the photodiode portion and the carrier concentration of the base region of the bipolar transistor portion are different from each other.

[0016] According to another preferred embodiment of the semiconductor photodetector of the present invention, the bipolar transistor portion comprises one or more collector regions and one or more emitter regions, which are second conductivity type regions, and the collector regions and the emitter regions are contained within the base region.

[0017] According to a further preferred embodiment of the semiconductor photodetector of the present invention, the input waveguide is composed of a silicon waveguide core and a silicon dioxide clad, and the first conductivity type region of the photodiode section and the base region of the bipolar transistor section are regions of first conductivity type silicon. [Effects of the Invention]

[0018] According to the semiconductor light receiving element of the present invention, a current amplification factor equivalent to that of an APD can be obtained by applying a bias voltage of 3 to 5 V, which is the drive voltage of a typical PIN-PD or bipolar transistor. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 3 is a schematic diagram for explaining a first light receiving element. [Figure 2] 5A and 5B are schematic diagrams for explaining the operation of the first light receiving element. [Figure 3] FIG. 4 is a schematic diagram for explaining a second light receiving element. [Figure 4] FIG. 10 is a schematic diagram for explaining a third light receiving element. [Figure 5] FIG. 10 is a schematic diagram illustrating a fourth light receiving element. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and positional relationship of each component are merely shown in a schematic manner to enable understanding of the present invention. Furthermore, preferred configuration examples of the present invention will be described below. However, the materials and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many modifications and variations that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention. Note that, although some hatching is applied in the plan view, it should be understood that this does not represent a cross section, but is added to facilitate understanding of the invention.

[0021] (first light receiving element) An example of the configuration of a semiconductor light-receiving element (hereinafter also referred to as a first light-receiving element) according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram for explaining the first light-receiving element. Fig. 1(A) is a schematic plan view of the first element. In Fig. 1(A), some components such as cladding are omitted. Figs. 1(B) to 1(D) show cross sections taken along lines AA, BB, and CC, respectively, in Fig. 1(A).

[0022] The first light receiving element is configured to include an input waveguide, a photodiode (PD) section, and a bipolar transistor (BT) section on a support substrate.

[0023] The support substrate 10 is, for example, a Si substrate with a thickness of 775 μm. A lower clad 22 is provided on the support substrate 10. The lower clad 22 is formed by depositing, for example, silicon dioxide (SiO2) over the entire upper surface of the support substrate 10 to a thickness of 3 μm.

[0024] A Si wire waveguide 32 and a Si slab waveguide 34 are formed with a thickness of 220 nm using, for example, Si as a material on the lower cladding 22. A photodiode section 100 and a bipolar transistor section 200 are formed in the Si slab waveguide 34.

[0025] A PD-p-Si region 110 of a first conductivity type, here p-type, and a PD-n-Si region 120 of a second conductivity type, here n-type, which is the opposite conductivity type to the first conductivity type, are formed in the Si slab waveguide 34 of the photodiode section 100. The PD-p-Si region 110 and the PD-n-Si region 120 are each formed to the same depth as the thickness of the Si slab waveguide 34. The PD-p-Si region 110 and the PD-n-Si region 120 are arranged side by side in the horizontal direction, sandwiching a PD-i-Si region 130, which is an insulating intrinsic semiconductor.

[0026] The PD-p-Si region 110 is formed by adding a trivalent element, such as boron (B) or aluminum (Al), to an intrinsic semiconductor of tetravalent silicon. The PD-n-Si region 120 is formed by adding a pentavalent element, such as phosphorus (P) or arsenic (As), to an intrinsic semiconductor of silicon. The carrier concentrations of both the PD-p-Si region 110 and the PD-n-Si region 120 are, for example, 1×10 17 cm -3 is.

[0027] In addition, inside the PD-n-Si region 120, a PD-n + The -Si region 150 is formed as a contact region. + The -Si region 130 is formed to a depth equal to or shallower than the thickness of the Si slab waveguide 34. + An Al electrode 190 is formed on the -Si region 150 to a thickness of, for example, 1 μm. + The carrier concentration of the -Si region 150 is set to obtain ohmic contact with the Al electrode 190, for example, 1×10 20 cm -3 is.

[0028] Furthermore, on the PD-p-Si region 110, the PD-i-Si region 130, and the PD-n-Si region 120, a PD-i-Ge region 140, which is a region of an intrinsic semiconductor of Ge, is formed to a thickness of, for example, 500 nm.

[0029] With the above-described configuration, a PIN-PD is formed in the photodiode section 100 of the first light receiving element.

[0030] The Si slab waveguide 34 of the bipolar transistor section 200 is configured to include a BT-p-Si region 210 of a first conductivity type, here p-type, and a first BT-n-Si region 221 and a second BT-n-Si region 222 of a second conductivity type, here n-type, which are arranged side by side in the horizontal direction on both sides of the BT-p-Si region 210 and adjacent to the BT-p-Si region 210. The carrier concentrations of the first BT-n-Si region 221 and the second BT-n-Si region 222 are each, for example, 1×10 16 cm -3 and 1×10 19 cm -3 is.

[0031] Inside the first BT-n-Si region 221 and inside the second BT-n-Si region 222, The first BT-n-Si region 221 and the second BT-n-Si region 222 have higher carrier concentrations than the first BT-n-Si region 221 and the second BT-n-Si region 222, respectively. + -Si region 231 and the second BT-n + The -Si region 232 is formed as a contact region at a depth equal to or shallower than the thickness of the Si slab waveguide .

[0032] First BT-n + -Si region 231 and the second BT-n + A first Al electrode 291 and a second Al electrode 292 are formed on the -Si region 232 to a thickness of, for example, 1 μm. + -Si region 231 and the second BT-n + The carrier concentration of the -Si region 232 is set to obtain ohmic contact with the Al electrodes 291 and 292, and is, for example, 1×10 20 cm -3 is.

[0033] With the above-described configuration, an npn-type bipolar transistor is configured in the bipolar transistor section. In this case, the BT-p-Si region 210 serves as the base region, the first BT-n-Si region 221 with a lower carrier concentration serves as the collector region, and the second BT-n-Si region 222 with a higher carrier concentration serves as the emitter region.

[0034] Here, the PD-p-Si region 110 of the photodiode section 100 and the BT-p-Si region 210, which is the base region of the bipolar transistor section 200, are directly connected. In other words, the PD-p-Si region 110 and the PD-p-Si region 210 are integrally configured.

[0035] In this way, a part of the p-type Si region is the PD-p-Si region 110, and another part is the BT-p-Si region 210. As a result, one p-type Si region serves as both the PD-p-Si region 110 and the BT-p-Si region 210.

[0036] Furthermore, upper cladding 24 made of SiO is formed on lower cladding 22 to a thickness of 1 μm, covering Si wire waveguide 32, photodiode section 100, and bipolar transistor section 200. Si wire waveguide 32 and the portion of cladding 20 made of upper cladding 24 and lower cladding 22 surrounding the Si wire waveguide form a so-called input waveguide. Furthermore, Al electrodes 190, 291, and 292 are provided so as to be exposed on the upper surface of cladding 20.

[0037] The operation of the first light receiving element will be described with reference to Fig. 2. Fig. 2 is a schematic diagram for explaining the operation of the first light receiving element. The second BT-n-Si region 222, which becomes the emitter region (E) of the bipolar transistor section 200, is grounded, and a positive bias V BE is applied to the first BT-n-Si region 221, which will be the collector region (C) of the bipolar transistor section 200, and a positive bias V CE is applied.

[0038] In this case, a reverse bias is applied to the pin structure formed by the PD-p-Si region 110, the PD-i-Si region 130, and the PD-n-Si region 120. Also, a forward bias is applied to the collector region (C) of the bipolar transistor section 200.

[0039] When input light is introduced into the photodiode section 100 from an input waveguide including a Si wire waveguide 32, the input light propagates from the Si wire waveguide 32 to the Si slab waveguide 34, and then transitions from the Si slab waveguide 34 to the PD-i-Ge region 140, which has a refractive index higher than that of Si.

[0040] The input light that has transitioned to the PD-i-Ge region 140 is absorbed by the PD-i-Ge region 140, generating electrons and holes that serve as photocarriers. The electrons and holes generated in the PD-i-Ge region 140 are affected by an electric field due to the reverse bias applied to the pin structure of the photodiode section 100. As a result, the electrons drift to the PD-n-Si region 120, and the holes drift to the PD-p-Si region 110, resulting in a photocurrent.

[0041] On the other hand, in the bipolar transistor section 200, the second BT-n-Si region 222, which becomes the emitter region (E), is grounded, so that the bipolar transistor section 200 operates as a grounded-emitter bipolar transistor.

[0042] In the first light receiving element, the PD-p-Si region 110 also serves as the base region (B) 210 of the bipolar transistor section, so that the photocurrent of the photodiode section 100 is the base current I B If the grounded emitter current amplification factor is β0, the collector current I C is given by the following equation (1).

[0043]

number

[0044] At this time, the emitter current I E is given by the following equation (2).

[0045]

number

[0046] It is generally known that the grounded emitter current amplification factor β0 can be calculated by the following equation (3).

[0047]

number

[0048] Here, W is the depletion layer width, and Lp is the hole diffusion length. B =1×10 17 cm -3 , the carrier concentration in the emitter region N E =1×10 19 cm -3 In this case, the hole diffusion length Lp is 0.29 μm and the depletion layer width W is 0.05 μm, so the grounded emitter current amplification factor β0 is expected to be 68.

[0049] As described above, the first photodetector is a semiconductor photodetector that can be easily manufactured based on silicon photonics technology, and since the PT-p-Si region also serves as the base region of the bipolar transistor section, it is possible to obtain a current amplification factor equivalent to that of an APD by applying a bias voltage of 3 to 5 V, which is the driving voltage of a typical PIN-PD or bipolar transistor.

[0050] (Second light receiving element) With reference to Fig. 3, an example of the configuration of a semiconductor light-receiving element (hereinafter also referred to as a second light-receiving element) according to a second embodiment of the present invention will be described. Fig. 3 is a schematic diagram for explaining the second light-receiving element. Fig. 3(A) is a schematic plan view of the second light-receiving element. In Fig. 3(A), some components such as cladding are omitted. Figs. 3(B) to 3(D) show cross sections taken along lines AA, BB, and CC in Fig. 3(A), respectively.

[0051] The second light receiving element has the same basic structure as the first light receiving element. The width W of the PD-p-Si region 110 and the width W of the BT-p-Si region 211 of the bipolar transistor section 201, i.e., the base region, are T and are different from each other. In this example, the width W of the base region T The width W of the PD-p-Si region 110 is P The difference from the first light receiving element is that it is narrower than the first light receiving element. Other configurations are the same as those of the first light receiving element, so redundant explanations will be omitted.

[0052] As with the first light receiving element, the second light receiving element can obtain a current gain equivalent to that of an APD by applying a bias voltage of 3 to 5 V, which is a drive voltage of a typical PIN-PD or bipolar transistor. P Therefore, the base region width W of the bipolar transistor section 201 T Since the gap between the collector and base regions of the bipolar transistor section 201 is narrower, the probability that holes that diffuse from the collector region to the base region of the bipolar transistor section 201 will recombine with electrons in the base region and disappear is reduced. As a result, holes can reach the emitter region more easily in the second light-receiving element than in the first light-receiving element. Therefore, the second light-receiving element can obtain a grounded-emitter current gain that is closer to the theoretical value.

[0053] (Third light receiving element) Referring to Fig. 4, a configuration example of a semiconductor light receiving element (hereinafter also referred to as a third light receiving element) according to a third embodiment of the present invention will be described. Fig. 4 is a schematic diagram for explaining the third light receiving element. Fig. 4(A) is a schematic plan view of the third light receiving element. In Fig. 4(A), some components such as cladding are omitted. Figs. 4(B) to 4(D) show cross sections taken along lines AA, BB, and CC in Fig. 4(A), respectively.

[0054] The third light receiving element has the same basic structure as the first light receiving element. The only difference is that the carrier concentration of the PD-p-Si region 112 of the photodiode section 102 is different from the carrier concentration of the BT-p-Si region 212, i.e., the base region, of the bipolar transistor section 202. Other configurations are the same as those of the first light receiving element, so redundant explanations will be omitted.

[0055] By setting the carrier concentration of the PD-p-Si region 112 of the photodiode section 102 of the third light receiving element to a carrier concentration that reduces the internal resistance of the photodiode and is expected to result in high light receiving sensitivity and high-speed response, and by setting the carrier concentration of the base region of the bipolar transistor section 202 to a carrier concentration that is expected to result in a high current amplification factor, a semiconductor light receiving element is obtained that exhibits higher light receiving sensitivity and higher current amplification factor than the first light receiving element.

[0056] Those skilled in the art can appropriately set the carrier concentration of the PD-p-Si region 112 according to the desired characteristics of the photodiode, and the carrier concentration of the base region according to the desired characteristics of the bipolar transistor.

[0057] Furthermore, here we have shown an example of only two types of carrier concentration in the p-Si region: the PD-p-Si region and the base region of the bipolar transistor section, but the carrier concentration is not limited to two types, and the same effect can be obtained even if the configuration has three or more types of values.

[0058] (fourth light receiving element) An example of the configuration of a semiconductor light-receiving element (hereinafter also referred to as a fourth light-receiving element) according to a fourth embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a schematic diagram for explaining the fourth light-receiving element, and is a schematic plan view of the fourth light-receiving element. In Fig. 5, some components such as cladding are omitted.

[0059] In the fourth light-receiving element, the collector region and the emitter region are contained in the base region. The other configurations are the same as those of the first light-receiving element, so a duplicated description will be omitted.

[0060] 5, the collector region 251 is divided into two or more regions, and photocarriers pass between the divided collector regions 251, and holes pass through the fourth light-receiving element and drift to the emitter region 260. These holes drifting to the emitter region 260 are the base current that serves as the input current of the bipolar transistor section 203.

[0061] Meanwhile, minority carriers, or holes, diffuse from the collector region 251 and flow into the base region of the bipolar transistor section 203, forming the collector current. Therefore, the addition of the collector current to the base current produces an amplification effect. In particular, in the case of the fourth light-receiving element, the emitter region 260 and the collector region 251 are contained within the base region 213, so the distance from the i-Ge region 143, which generates photocarriers in the photodiode section 103, to the emitter region 260 can be made shorter than in the first light-receiving element. Therefore, a faster photoelectric conversion response can be expected.

[0062] Here, an example is shown in which the collector region 251 is divided and the emitter region 260 is integrated into the BT-p-Si region, but the collector region does not have to be divided, and the emitter region may be divided.

[0063] (Other embodiments) Although the first to fourth light receiving elements described above are examples of semiconductor light receiving elements based on silicon photonics technology, the same effect can be obtained by using a compound semiconductor such as InP.

[0064] In addition, in the second light-receiving element, an example is shown in which the width of the base region of the bipolar transistor is narrower than the width of the PD-p-Si region, and in the third light-receiving element, an example is shown in which the carrier concentrations of the PD-p-Si region and the base region of the bipolar transistor are different.However, the same effect can be achieved by combining the second light-receiving element and the third light-receiving element to have a configuration in which the width of the base region of the bipolar transistor is narrower than the width of the PD-p-Si region and the carrier concentrations of the PD-p-Si region and the base region of the bipolar transistor are different.

[0065] In addition, although an example has been shown here in which the pin configuration of the photodiode section is horizontal, with p-Si, i-Si, i-Ge, and n-Si aligned horizontally relative to the surface of the support substrate 10, the same effect can also be obtained when the pin configuration of the photodiode is configured in such a way that p-Si, i-Ge, and n-Ge are arranged vertically relative to the surface of the support substrate 10.

[0066] Also, here, an example has been shown in which SiO2 is used for the lower clad and upper clad, and Al is used for the electrode material, but the lower clad, upper clad, and electrode materials are not limited to this.

[0067] Also, here, the contact area, p + -Si region and n + -Si region carrier concentration is 1×10 20 cm -3 , and the carrier concentration of the PD-n-Si region and the PD-p-Si region is 1×10 17 cm -3 , the carrier concentrations in the collector, base, and emitter regions of the bipolar transistor are 1×10 16 cm -3 , 1×10 17 cm -3 , 1×1019 cm -3 However, the carrier concentration of each region is not limited to this example.

[0068] Here, the configuration has been shown in which the p-type region of the photodiode also serves as the base region of the bipolar transistor, and the bipolar transistor is of the npn type, but the configuration of the semiconductor light-receiving element of the present invention is not limited to this. The same effect can be obtained with a configuration in which the n-type region of the photodiode also serves as the base region of the bipolar transistor, and the bipolar transistor is of the pnp type. [Explanation of symbols]

[0069] 10 Support substrate 20 Clad 22 Lower Cladding 24 Upper Cladding 32 Si wire waveguide 34 Si slab waveguide 100, 102, 103 Photodiode section 110 PD-p-Si region 120 PD-n-Si area 130 PD-i-Si area 140, 143 PD-i-Ge region 150 PD-n + -Si area 190, 291, 292 Al electrode 200, 201, 202, 203 Bipolar transistor section 210 BT-p-Si region 221, 222 BT-n-Si region 231, 232 BT-n + -Si area 251 Collector Region 260 emitter area

Claims

1. an input waveguide; a photodiode section having a first conductivity type region and a second conductivity type region, absorbing signal light introduced through the input waveguide and outputting a photocurrent; a bipolar transistor section having a first conductivity type region as a base region, receiving the photocurrent, amplifying the photocurrent, and outputting the amplified photocurrent; on a support substrate, The first conductivity type region of the photodiode section and the base region of the bipolar transistor section are integrally formed. Semiconductor photodetector.

2. the bipolar transistor portion includes a collector region and an emitter region, and a second conductivity type region; The collector region and the emitter region are disposed adjacent to the base region and sandwich the base region therebetween.

2. The semiconductor light-receiving element according to claim 1.

3. The width of the first conductivity type region of the photodiode section and the width of the base region of the bipolar transistor section are different from each other.

3. The semiconductor light-receiving element according to claim 2.

4. The carrier concentration of the first conductivity type region of the photodiode section and the carrier concentration of the base region of the bipolar transistor section are different from each other.

3. The semiconductor light-receiving element according to claim 2.

5. a width of a first conductivity type region of the photodiode section and a width of a base region of the bipolar transistor section are different from each other, The carrier concentration of the first conductivity type region of the photodiode section and the carrier concentration of the base region of the bipolar transistor section are different from each other.

3. The semiconductor light-receiving element according to claim 2.

6. the bipolar transistor section includes one or more collector regions and one or more emitter regions of a second conductivity type; The collector region and the emitter region are contained within the base region.

2. The semiconductor light-receiving element according to claim 1.

7. the input waveguide is composed of a Si wire waveguide and a silicon dioxide clad; The first conductivity type region of the photodiode section and the base region of the bipolar transistor section are regions of first conductivity type silicon. The semiconductor light-receiving element according to any one of claims 1 to 6.

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