Light detection device and range finding device

Abstract

Provided is a light detection device comprising: a waveguide; a lateral PIN-type photodiode that comprises a P-type layer, an i layer, and an N-type layer lined up along the width direction of the waveguide; and a reflection structure that traps light from the waveguide in the i layer positioned on the waveguide.

Description

Light detection and ranging devices

[0001] The present disclosure relates to a light detection device and a distance measurement device.

[0002] LiDAR (Light Detection and Ranging) is a distance measurement technology that uses scattered light from laser irradiation and is applied to various applications including autonomous driving. One of the LiDAR measurement methods is the Frequency Modulated Continuation Wave (FMCW) method, which transmits a frequency-modulated continuous wave and determines distance from the frequency difference (beat frequency) between the transmitted wave and the reflected wave. A PIN-type germanium photodiode, for example, is used as a photodetector for detecting light in such a distance measurement device using LiDAR.

[0003] The PIN type germanium photodiode has a P-type layer in which germanium is doped with P-type impurities, an i-layer of germanium that is not doped with impurities, and an N-type layer in which germanium is doped with N-type impurities.

[0004] International Publication No. 2023 / 062949

[0005] In a PIN-type germanium photodiode (photodetector), carriers (electrons) generated by photoelectric conversion in the i-layer are detected as photocurrent. On the other hand, carriers generated by photoelectric conversion in the P-type and N-type layers are difficult to detect as photocurrent because they recombine with majority carriers present in each layer. Therefore, in a PIN-type germanium photodiode, carriers generated outside the i-layer are lost, which has limited the ability to improve the quantum efficiency of the PIN-type germanium photodiode.

[0006] Therefore, the present disclosure proposes a photodetector and a distance measuring device that can improve quantum efficiency by suppressing the loss of carriers caused by photoelectric conversion.

[0007] According to the present disclosure, there is provided a photodetector device comprising a waveguide, a lateral PIN photodiode consisting of a P-type layer, an i-layer, and an N-type layer aligned along the width direction of the waveguide, and a reflective structure that confines light from the waveguide to the i-layer located on the waveguide.

[0008] Furthermore, according to the present disclosure, there is provided a distance measuring device including a photodetector, the photodetector having a waveguide, a lateral PIN photodiode consisting of a P-type layer, an i-layer, and an N-type layer arranged along the width direction of the waveguide, and a reflective structure that confines light from the waveguide to the i-layer located on the waveguide.

[0009] FIG. 1 is a block diagram showing an example configuration of a distance measuring device to which a balanced photodiode according to an embodiment of the present disclosure can be applied. FIG. 2 is a plan view of a photodetector according to a comparative example. FIG. 3 is a cross-sectional view of a photodetector according to a comparative example. FIG. 4 is a schematic view of a germanium PIN photodiode. FIG. 5 is an explanatory view for explaining a photodetector according to a comparative example. FIG. 6 is a schematic view of a photonic crystal. FIG. 7 is a schematic view of a distributed Bragg reflector. FIG. 8 is a plan view of a photodetector according to a first embodiment of the present disclosure. FIG. 9 is a cross-sectional view of a photodetector according to the first embodiment of the present disclosure. FIG. 10 is an explanatory view showing a manufacturing process of a photodetector according to the first embodiment of the present disclosure. FIG. 11 is a plan view of a photodetector according to a second embodiment of the present disclosure. FIG. 12 is a cross-sectional view of a photodetector according to a third embodiment of the present disclosure. FIG. 13 is an explanatory view showing a manufacturing process of a photodetector according to the third embodiment of the present disclosure. FIG. 14 is a cross-sectional view of a photodetector according to a fourth embodiment of the present disclosure. FIG. 15 is an explanatory view showing a manufacturing process of a photodetector according to the fourth embodiment of the present disclosure. FIG. 16 is a cross-sectional view of a photodetector according to a fifth embodiment of the present disclosure. FIG. 17 is an explanatory view showing a manufacturing process of a photodetector according to the fifth embodiment of the present disclosure. FIG. 2 is an explanatory diagram showing an example of the installation positions of an outside-vehicle information detection unit and an imaging unit.

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted. Furthermore, in this specification and the drawings, multiple components having substantially the same or similar functional configurations may be distinguished by adding different letters after the same reference numeral. However, when there is no particular need to distinguish between multiple components having substantially the same or similar functional configurations, only the same reference numerals will be used.

[0011] The drawings referenced in the following description are intended to facilitate the description and understanding of the embodiments of the present disclosure. For clarity, the shapes, dimensions, ratios, etc. shown in the drawings may differ from the actual shapes. Furthermore, descriptions of specific shapes in the following description do not only refer to the geometrically identical shape, but also include shapes similar to the shape with allowable variations (errors and distortions) in manufacturing and use. For example, the term "substantially circular" in the following description does not necessarily refer to a perfect circle, but also to shapes similar to a perfect circle, such as an ellipse. Furthermore, the design of the devices shown in the drawings can be modified as appropriate, taking into account the following description and known technologies.

[0012] The description will be given in the following order: 1. Background leading to the creation of the embodiments of the present disclosure 1.1 Range finding device 1.2 Comparative example 1.3 Background 2. First embodiment 2.1 Detailed configuration 2.2 Manufacturing method 3. Second embodiment 4. Third embodiment 4.1 Detailed configuration 4.2 Manufacturing method 5. Fourth embodiment 5.1 Detailed configuration 5.2 Manufacturing method 6. Fifth embodiment 6.1 Detailed configuration 6.2 Manufacturing method 7. Sixth embodiment 8. Seventh embodiment 9. Summary 10. Application example 11. Supplementary information

[0013] <<1. Background to the Creation of the Embodiments of the Present Disclosure>> First, the background to the creation of the embodiments of the present disclosure by the inventors will be described.

[0014] 1.1 Distance Measuring Device First, a distance measuring device 1 to which a light detection device (photodiode) 100 according to an embodiment of the present disclosure can be applied will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example configuration of a distance measuring device 1 to which a light detection device 100 according to an embodiment of the present disclosure can be applied. The distance measuring device 1 is, for example, an FMCW type distance measuring device.

[0015] 1, the distance measuring device 1 mainly includes a laser light source 10, a modulator 20, a splitter 30, a circulator 40, a scanner 60, a coupler 90, a photodetector 100, an ADC (Analog-to-Digital Converter) 120, and an FFT (Fast Fourier Transform) calculation circuit 130. For example, some or all of the multiple elements constituting the distance measuring device 1 may be provided on a single semiconductor chip (not shown). Alternatively, for example, some or all of the multiple elements constituting the distance measuring device 1 may be provided on multiple semiconductor chips (not shown) that are stacked on top of each other. Each element constituting the distance measuring device 1 will be described below in order.

[0016] The laser light source 10, modulator 20, splitter 30, circulator 40, scanner 60, coupler 90, and photodetector 100 are configured, for example, as photonic circuits and are connected to each other by a waveguide that guides the laser light. On the other hand, the ADC 120 and FFT calculation circuit 130 are electronic circuits and are electrically connected to each other by wiring.

[0017] The laser light source 10 is capable of emitting laser light by receiving power supply from a dedicated power supply network or the like.

[0018] The modulator 20 modulates the phase or frequency of the laser light from the laser light source 10 and outputs the modulated light to the splitter 30, which will be described later.

[0019] The splitter 30 splits the light from the modulator 20 into two. The split ratio may be 1:1 or any other ratio. One of the split light is guided to the circulator 40 via a waveguide. The other split light is guided to the coupler 90 via another waveguide.

[0020] The circulator 40 transfers light input from a first end of the circulator 40 to a second end on the scanner 60 side.

[0021] The scanner 60 can two-dimensionally output the light distributed from the circulator 40 and two-dimensionally receive the light reflected by the object 2. For example, the scanner 60 has a configuration in which a plurality of waveguides extending in the X direction are arranged in the Y direction. Furthermore, each waveguide has a grating extending in the Y direction. This allows the scanner 60 to two-dimensionally emit light in the Z direction from the XY plane.

[0022] Furthermore, the reflected light incident on the scanner 60 is collected by the circulator 40. The circulator 40 can receive the collected reflected light from a second end thereof and output it from a third end on the coupler 90 side. That is, the circulator 40 is configured to emit light incident from a first end on the laser light source 10 side to the second end, and to output reflected light incident from the second end to the third end.

[0023] The coupler 90 receives the light split by the splitter 30 and the reflected light from the circulator 40 , combines these two lights, and outputs the combined wave to the photodetector 100 .

[0024] The photodetector 100 is configured with a photodiode such as a PIN-type germanium photodiode, and can photoelectrically convert the composite wave combined by the coupler 90 into an electrical signal. The photodetector 100 outputs the electrical signal obtained by the conversion to an ADC 120, which will be described later. The photodetector 100 may also be a balanced photodiode in which two photodiodes are connected in series, and in this case, the composite wave combined by the coupler 90 may be input to each of the photodiodes. An amplifier (TIA) that amplifies the electrical signal may also be provided downstream of the photodiodes.

[0025] The ADC 120 can convert the electrical signal from the photodetector 100 into a digital signal, and outputs the digital signal obtained by the conversion to the FFT calculation circuit 130, which will be described later.

[0026] The FFT calculation circuit 130 performs FFT processing on the digital signal from the ADC 120 and calculates the peak frequency of the difference frequency of the composite wave. The difference frequency of the composite wave depends on the distance from the distance measuring device 1 to the object 2. The distance from the distance measuring device 1 to the object 2 is proportional to the difference frequency between the emitted light from the distance measuring device 1 and the reflected light from the object 2. For example, if the distance from the distance measuring device 1 to the object 2 is relatively short, the difference frequency is small. On the other hand, if the distance from the distance measuring device 1 to the object 2 is relatively long, the difference frequency is large. The peak frequency of the difference frequency is output from the FFT calculation circuit 130 to the outside of the distance measuring device 1 as depth data indicating the distance from the distance measuring device 1 to the object 2 and relative velocity data indicating the relative velocity.

[0027] The photodetector according to the embodiment of the present disclosure described below can be applied to, for example, the photodetector 100 of the distance measuring device 1. In the embodiment of the present disclosure, the distance measuring device 1 is not limited to the form shown in Fig. 1 and can be modified into various forms.

[0028] 1.2 Comparative Example Next, in order to understand the background that led the inventors to create the embodiments of the present disclosure, a detailed configuration of a photodetector 100a according to a comparative example will be described with reference to FIGS. 2A and 2B. FIG. 2A is a plan view of the photodetector 100a according to the comparative example. FIG. 2B is a cross-sectional view of the photodetector 100a according to the comparative example. Specifically, the upper diagram is a cross-sectional view of the photodetector 100a taken along line A-A' in FIG. 2A, and the lower diagram is a cross-sectional view of the photodetector 100a taken along line B-B' in FIG. 2A. Note that the comparative example here refers to the photodetector 100a that the inventors studied before creating the embodiments of the present disclosure.

[0029] The above-described FMCW ranging device (LiDAR) 1 uses light with a wavelength of 1550 nm (=0.8 eV) from the viewpoint of eye safety to prevent transmission loss and eye damage. Because light with such a wavelength is not absorbed by silicon (Si), which has a bandgap of 1.12 eV, a photodiode made of germanium (Ge), which has a smaller bandgap of 0.66 eV, is used as the photodetector 100a.

[0030] As shown in FIGS. 2A and 2B, in the photodetector 100a according to the comparative example, silicon oxide (SiO ２ A waveguide 300 made of silicon or the like is provided on a layer 200 made of a material such as silicon dioxide. Furthermore, a lateral PIN germanium photodiode 400 is provided on the waveguide 300. The lateral PIN germanium photodiode 400 has an N-type layer 402, an i-layer 404, and a P-type layer 406 aligned along the width direction of the waveguide 300. As shown in the upper part of FIG. 2B , light guided by the waveguide 300 is incident on the lateral PIN germanium photodiode 400. Furthermore, the lateral PIN germanium photodiode 400 generates carriers (electrons) by photoelectric conversion and detects the generated carriers as a photocurrent.

[0031] Here, the P-type layer 406 is a layer of germanium doped with P-type impurities. The i-layer 404 is a layer of germanium that is not doped with impurities. The N-type layer 402 is a layer of germanium doped with N-type impurities. The photodiode 400 thus configured with the P-type layer 406, i-layer 404, and N-type layer 402 is called a PIN photodiode.

[0032] 2A and 2B, a photodiode 400 having an N-type layer 402, an i-type layer 404, and a P-type layer 406 arranged laterally on a substrate such as the waveguide 300 is called a lateral PIN photodiode. The advantages of the lateral PIN germanium photodiode 400 will be described later.

[0033] 1.3 Background Next, the background that led the inventors to create the embodiments of the present disclosure will be described with reference to Figures 3 and 4. Figure 3 is a schematic diagram of PIN-type germanium photodiodes 400, 400a. Figure 4 is an explanatory diagram for explaining a photodetector device 100a according to a comparative example, and in detail is an enlarged view of region C shown in the lower part of Figure 2B.

[0034] As PIN photodiodes 400 made of germanium, there are two photodiodes 400, 400a as shown in FIG. 3. The left side of FIG. 3 shows a vertical PIN germanium photodiode 400a. Specifically, the vertical PIN germanium photodiode 400a has a P-type layer 406a provided on a silicon substrate 300a, an i-layer 404 provided on the P-type layer 406a via a buffer layer made of silicon-germanium, and an N-type layer 402 provided on the i-layer 404. The right side of FIG. 3 also shows a lateral PIN germanium photodiode 400. The lateral PIN germanium photodiode 400 has an N-type layer 402, an i-layer 404, and a P-type layer 406 arranged along the width direction of the silicon substrate 300a (specifically, on the silicon substrate 300a via a buffer layer made of silicon-germanium). Here, the P-type layer 406a is a layer in which silicon is doped with P-type impurities.

[0035] Generally, crystal defects are likely to occur between crystal layers made of different materials. Specifically, as shown on the right side of FIG. 3 , in the vertical PIN germanium photodiode 400a, crystal defects are likely to occur near the interface between the P-type layer 406a and the i-layer 404. These crystal defects become carrier conduction paths, making it easy for dark current to occur. Also, as shown on the left side of FIG. 3 , in the lateral PIN germanium photodiode 400, crystal defects occur near the interfaces between the silicon substrate 300a and the P-type layer 406, the i-layer 404, and the N-type layer 402. However, because the crystal defects occur between the silicon substrate 300a and the interface, the crystal defects are unlikely to become carrier conduction paths. Therefore, the lateral PIN germanium photodiode 400 is less likely to generate dark current than the vertical PIN germanium photodiode 400a. Therefore, from the viewpoint of such dark current characteristics, it is preferable to use the lateral PIN type germanium photodiode 400 as the photodetector 100 a of the distance measuring device 1 .

[0036] In the lateral PIN germanium photodiode 400, as shown in Figure 4, carriers (electrons) generated by photoelectric conversion in the i-layer 404 can be detected as photocurrent. On the other hand, in the P-type layer 406 and the N-type layer 402, carriers generated by photoelectric conversion recombine with majority carriers present in each layer, making it difficult to detect them as photocurrent. Therefore, in the lateral PIN germanium photodiode 400, carriers generated in areas other than the i-layer 404 end up as losses.

[0037] In view of these circumstances, the present inventors have conducted extensive research to suppress the loss of carriers caused by photoelectric conversion and improve the quantum efficiency of the photodetector 100. Through their research, the present inventors have come up with an embodiment of the present disclosure that can suppress the loss of carriers caused by photoelectric conversion and improve the quantum efficiency of the photodetector 100 by confining light in the i-layer 404 using a reflection structure made of a photonic crystal or a distributed Bragg reflector.

[0038] FIG. 5 is a schematic diagram of a photonic crystal 500. The photonic crystal 500 has a structure in which, for example, a plurality of holes 502 having a diameter smaller than the wavelength of light are periodically arranged, thereby confining, reflecting, or transmitting light within a small region. Therefore, in an embodiment of the present disclosure, applying such a photonic crystal 500 to the photodetector 100 reflects light toward the i-layer 404, thereby confining the light within the i-layer 404. In this manner, according to the embodiment of the present disclosure, much of the light is photoelectrically converted in the i-layer 404 and detected as a photocurrent, thereby suppressing carrier loss caused by photoelectric conversion and improving the quantum efficiency of the photodetector 100.

[0039] 6 is a schematic diagram of a distributed Bragg reflector (DBR mirror) 510. The distributed Bragg reflector 510 is a reflecting mirror configured by alternately stacking layers 512 and 514 with different refractive indices. Therefore, in an embodiment of the present disclosure, the distributed Bragg reflector 510 is applied to the photodetector 100, thereby reflecting light toward the i-layer 404 and confining the light in the i-layer 404. In this manner, according to an embodiment of the present disclosure, much of the light is photoelectrically converted in the i-layer 404 and detected as a photocurrent, thereby suppressing carrier loss caused by photoelectric conversion and improving the quantum efficiency of the photodetector 100.

[0040] Hereinafter, details of each embodiment of the present disclosure created by the inventors will be described in order.

[0041] 7A and 7B , a detailed configuration of the photodetector 100 according to the first embodiment of the present disclosure will be described. Fig. 7A is a plan view of the photodetector 100 according to this embodiment. Fig. 7B is a cross-sectional view of the photodetector 100 according to this embodiment, specifically, a cross-sectional view of the photodetector 100 taken along line BB' shown in Fig. 7A .

[0042] 7A and 7B , in the photodetector 100 according to this embodiment, as in the comparative example, a waveguide 300 made of, for example, silicon is provided on a layer 200 made of, for example, silicon oxide. Furthermore, in this embodiment, a lateral PIN germanium photodiode 400 is provided on the waveguide 300. The lateral PIN germanium photodiode 400 has an N-type layer 402 made of germanium, an i-layer 404 made of germanium, and a P-type layer 406 made of germanium, which are provided on the waveguide 300 and aligned along the width direction of the waveguide 300. Although not shown, a buffer layer made of silicon-germanium may be provided between the waveguide 300 and the lateral PIN germanium photodiode 400.

[0043] Furthermore, in the photodetector 100 according to this embodiment, a photonic crystal 500 is provided as an example of a reflective structure that confines the light from the waveguide 300 in the i-layer 404 .

[0044] 7A and 7B , in this embodiment, a plurality of holes 502, each having a diameter smaller than the wavelength of light, are periodically arranged in the photonic crystal 500, penetrating the photodiode 400 and the waveguide 300 in their film thickness direction. As described above, the photonic crystal 500 has a structure that can reflect light by periodically arranging a plurality of holes 502, each having a diameter smaller than the wavelength of light.

[0045] In detail, the plurality of holes 502 provided as the photonic crystal 500 includes, for example, two types of holes, as shown in Figures 7A and 7B. The plurality of holes (first holes) 502a are provided near the interface between the P-type layer 406 or the N-type layer 402 and the i-layer 404, so as to penetrate the i-layer 404 and the waveguide 300. The plurality of holes 502a reflect light toward region D (waveguide 300) shown in Figure 7B, thereby suppressing the light from spreading in the waveguide 300. Then, the light guided to the center of the waveguide 300 is incident on the i-layer 404 provided thereon.

[0046] Furthermore, a plurality of holes (second holes) 502b are provided near the interface between the i-layer 404 and the P-type layer 406 or the N-type layer 402, so as to penetrate the P-type layer 406 or the N-type layer 402 and the waveguide 300. The plurality of holes 502b reflect light toward region E (i-layer 404) shown in FIG. 7B , thereby confining the light in the i-layer 404.

[0047] In this embodiment, light guided to the center of the waveguide 300 by the hole 502a enters the i-layer 404 provided thereon. Furthermore, in this embodiment, light incident on the P-type layer 406 or the N-type layer 402 is also reflected by the hole 502b and confined in the i-layer 404. Therefore, in this embodiment, more light is confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. In other words, in this embodiment, the amount of light photoelectrically converted in the P-type layer 406 and the N-type layer 402 can be reduced, thereby suppressing recombination between carriers generated in these layers and majority carriers present in these layers, thereby reducing carrier loss. As a result, this embodiment suppresses carrier loss caused by photoelectric conversion and improves the quantum efficiency of the photodetector 100.

[0048] Furthermore, although the holes 502a and 502b have the same function of reflecting light, the combinations of materials (refractive indexes) that make up their interfaces are different, and therefore the diameters (sizes) and spacing of the holes 502a and 502b are adjusted accordingly. Therefore, in this embodiment, at least one of the diameters (sizes) and spacing of the holes 502a and 502b is different from each other.

[0049] 7A, the cross sections of the holes 502a and 502b are not limited to being substantially circular, but may be, for example, substantially polygonal. For the same reasons as above, the cross sections of the holes 502a and 502b may be different from each other in this embodiment.

[0050] Furthermore, the inside of the holes 502a and 502b is filled with, for example, silicon oxide or silicon nitride (Si ３ N ４) can be embedded. In this embodiment, since silicon oxide and silicon nitride have different refractive indices, it is preferable to adjust the diameter (size) and spacing of the holes 502a and holes 502b accordingly. Furthermore, for the same reason as above, in this embodiment, the materials embedded in the holes 502a and holes 502b (the materials inside the holes 502a and 502b) may be different from each other.

[0051] The inside of the holes 502a and 502b may be hollow.

[0052] As described above, in this embodiment, the plurality of holes 502a reflect light toward the center of the waveguide 300, thereby suppressing the spread of light in the waveguide 300. The light guided to the center of the waveguide 300 is then incident on the i-layer 404 provided thereon. In addition, in this embodiment, the plurality of holes 502b reflect light toward the i-layer 404, thereby confining the light in the i-layer 404. Therefore, according to this embodiment, since more light is confined in the i-layer 404, much of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. As a result, according to this embodiment, the loss of carriers generated by photoelectric conversion is suppressed, and the quantum efficiency of the photodetector 100 can be improved.

[0053] 7A and 7B, the holes 502a and 502b are provided so as to penetrate both the lateral PIN germanium photodiode 400 and the waveguide 300. However, this embodiment is not limited to this configuration. For example, the hole 502a may be provided so as to penetrate only the waveguide 300, i.e., only the waveguide 300 located below the i-layer 404 near the interface between the P-type layer 406 or the N-type layer 402 and the i-layer 404. The hole 502b may be provided so as to penetrate only the PIN germanium photodiode 400, i.e., only the P-type layer 406 or the N-type layer 402 near the interface between the P-type layer 406 or the N-type layer 402 and the i-layer 404.

[0054] In this embodiment, when the holes 502a and 502b penetrate both the photodiode 400 and the waveguide 300, the diameter (size) of the holes and the material inside the holes may be changed depending on the layers they penetrate.

[0055] The photodetector 100 according to this embodiment is not limited to the configuration shown in FIGS. 7A and 7B, but can be modified into various other configurations.

[0056] Furthermore, in this embodiment, the photonic crystal 500 may have any structure that is periodically arranged at the nano-size level, which is shorter than the wavelength of light, and may be, for example, periodic steps or periodically arranged dots (spheres), and is not limited to the form described above.

[0057] 2.2 Manufacturing Method Next, an example of a manufacturing method for the photodetector 100 according to this embodiment will be described with reference to Fig. 8. Fig. 8 is an explanatory diagram showing the manufacturing process of the photodetector 100 according to this embodiment, and is a cross-sectional view corresponding to Fig. 7B in each manufacturing process.

[0058] 8, a layer 200 made of, for example, silicon oxide is formed on one surface of a silicon substrate that will become the waveguide 300. A silicon oxide film 202 is formed on the other surface of the silicon substrate that will become the waveguide 300 so as to cover the entire surface except for the region where the photodiode 400 is to be provided.

[0059] 8, an i-layer 404 made of germanium that is not doped with impurities is formed on the silicon substrate (waveguide 300) exposed from silicon oxide film 202. Furthermore, a plurality of openings 504a (corresponding to holes 502a) and openings 504b (corresponding to holes 502b) having predetermined diameters (sizes) and penetrating the i-layer and silicon substrate (waveguide 300) are formed at predetermined positions in i-layer 404.

[0060] 8, N-type impurities are then implanted into predetermined positions in the i-layer 404 to form the N-type layer 402, and P-type impurities are then implanted to form the P-type layer 406. Furthermore, holes 502a and 502b are formed by filling the multiple openings 504a and 504b with, for example, silicon oxide. In this manner, the photodetector 100 according to this embodiment can be formed.

[0061] <<3. Second Embodiment>> Next, a detailed configuration of a photodetector 100 according to a second embodiment of the present disclosure will be described with reference to Fig. 9. In this embodiment, the photonic crystal 500 of the first embodiment is replaced with a distributed Bragg reflector 510. Fig. 9 is a plan view of the photodetector 100 according to this embodiment. Note that the cross-sectional view of the photodetector 100 according to this embodiment corresponds to Fig. 7B, and in this cross-sectional view, the hole 502 is replaced with the distributed Bragg reflector 510.

[0062] 9 and 7B, in the photodetector 100 according to this embodiment, as in the first embodiment, a lateral PIN germanium photodiode 400 is provided on a waveguide 300 on a layer 200. Note that in this embodiment as well, a buffer layer made of silicon-germanium may be provided between the waveguide 300 and the lateral PIN germanium photodiode 400.

[0063] In the photodetector 100 according to this embodiment, a distributed Bragg reflector 510 is provided as a reflecting structure that confines the light from the waveguide 300 in the i-layer 404 .

[0064] In this embodiment, a plurality of distributed Bragg reflectors 510 are periodically arranged, penetrating the photodiode 400 and the waveguide 300 in the film thickness direction. As described with reference to FIG. 6 , the distributed Bragg reflector 510 is a reflector configured by alternately stacking layers 512 and 514 having different refractive indices.

[0065] 9, the plurality of distributed Bragg reflectors 510 includes two types of reflectors. The plurality of distributed Bragg reflectors (first reflectors) 510a are provided near the interface between the p-type layer 406 or the n-type layer 402 and the i-layer 404, so as to penetrate the i-layer 404 and the waveguide 300. The plurality of distributed Bragg reflectors 510a reflect light toward the center of the waveguide 300, thereby suppressing the light from spreading in the waveguide 300. The light guided to the center of the waveguide 300 is then incident on the i-layer 404 provided above it.

[0066] Furthermore, a plurality of distributed Bragg reflectors (second reflectors) 510b are provided near the interface between the i-layer 404 and the P-type layer 406 or the N-type layer 402, so as to penetrate the P-type layer 406 or the N-type layer 402 and the waveguide 300. The plurality of distributed Bragg reflectors 510b reflect light toward the i-layer 404, thereby confining the light in the i-layer 404.

[0067] In this embodiment, too, light guided to the center of the waveguide 300 by the distributed Bragg reflector 510a is incident on the i-layer 404 provided thereon. Furthermore, in this embodiment, light incident on the P-type layer 406 or the N-type layer 402 is also reflected by the distributed Bragg reflector 510b and confined in the i-layer 404. Therefore, according to this embodiment, more light is confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. In other words, in this embodiment, the amount of light photoelectrically converted in the P-type layer 406 and the N-type layer 402 can be reduced, thereby suppressing recombination between carriers generated in these layers and majority carriers present in these layers, thereby reducing carrier loss. As a result, according to this embodiment, carrier loss caused by photoelectric conversion can be suppressed, and the quantum efficiency of the photodetector 100 can be improved.

[0068] Furthermore, in this embodiment as well, although the function of reflecting light is the same, the combination of materials (refractive indexes) constituting the interface is different, and therefore distributed Bragg reflectors 510a and 510b are adjusted accordingly in terms of surface area (size), spacing, material (substance of material), and number of stacked layers constituting each distributed Bragg reflector 510. Therefore, in this embodiment as well, distributed Bragg reflectors 510a and 510b are different from each other in at least one of surface area, spacing, material, and number of stacked layers constituting each distributed Bragg reflector 510.

[0069] Furthermore, the cross sections of distributed Bragg reflectors 510a and 510b can be, for example, substantially rectangular as shown in Fig. 9. Note that in this embodiment, the cross sections of distributed Bragg reflectors 510a and 510b are not limited to being substantially rectangular.

[0070] Furthermore, distributed Bragg reflectors 510a and 510b may be formed from, for example, silicon oxide, silicon nitride, or a combination thereof.

[0071] As described above, in this embodiment as well, the multiple distributed Bragg reflectors 510a reflect light toward the center of the waveguide 300, thereby suppressing the spread of light in the waveguide 300. The light guided to the center of the waveguide 300 is then incident on the i-layer 404 provided thereon. In addition, in this embodiment, the multiple distributed Bragg reflectors 510b reflect light toward the i-layer 404, thereby confining the light in the i-layer 404. Therefore, according to this embodiment, more light is confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. As a result, according to this embodiment, the loss of carriers caused by photoelectric conversion is suppressed, and the quantum efficiency of the photodetector 100 can be improved.

[0072] From the viewpoint of ease of manufacture, in this embodiment as well, distributed Bragg reflectors 510a and 510b are provided so as to penetrate both lateral PIN germanium photodiode 400 and waveguide 300. However, this embodiment is not limited to this configuration. For example, distributed Bragg reflector 510a may be provided so as to penetrate only waveguide 300, i.e., only the waveguide 300 located below i-layer 404 near the interface between p-type layer 406 or n-type layer 402 and i-layer 404. Furthermore, distributed Bragg reflector 510b may be provided so as to penetrate only PIN germanium photodiode 400, i.e., only the p-type layer 406 or n-type layer 402 near the interface between p-type layer 406 or n-type layer 402 and i-layer 404.

[0073] Furthermore, the photodetector 100 according to this embodiment is not limited to the configurations shown in FIGS. 9 and 7B, and can be modified into various other configurations.

[0074] Furthermore, the method for manufacturing the photodetector 100 according to this embodiment is the same as that of the first embodiment, and therefore a description thereof will be omitted here.

[0075] <<4. Third Embodiment>> <4.1 Detailed Configuration> Next, a detailed configuration of a photodetector 100 according to a third embodiment of the present disclosure will be described with reference to Fig. 10. Fig. 10 is a cross-sectional view of the photodetector 100 according to this embodiment.

[0076] In this embodiment, as shown in Fig. 10 , a protruding portion 300c having a substantially rectangular cross section and protruding upward is provided at the center of a substrate made of, for example, silicon, which forms a waveguide. The protruding portion 300c functions as a waveguide that guides light and extends along a perpendicular line that intersects perpendicularly with the plane of Fig. 10 . In this embodiment, the upper and side surfaces of the protruding portion 300c are covered with an i-layer 404, so that light leaking laterally from the waveguide 300 is also absorbed by the i-layer 304, as shown in the enlarged view of region F on the right side of Fig. 10 . Therefore, in this embodiment, much of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent.

[0077] In this embodiment, the cross section of the protrusion 300c is not limited to being substantially rectangular, and may be, for example, substantially circular or substantially polygonal, as long as the surface of the protrusion 300c is covered with the i layer 404. Furthermore, in this embodiment, as long as the surface of the protrusion 300c is covered with the i layer 404, multiple protrusions 300c may be provided.

[0078] 10 , the i-layer 404 covering the protruding portion 300c has a cross-sectional shape resembling an upside-down letter T, i.e., has a protruding region in the center. In this embodiment, a P-type layer 406 and an N-type layer 402 made of germanium are provided on either side of the protruding region of the i-layer 404. In other words, the PIN-type germanium photodiode 400 has the N-type layer 402, the protruding region of the i-layer 404, and the P-type layer 406 aligned in a row along the width direction of the waveguide 300.

[0079] Furthermore, in the photodetector 100 according to this embodiment, as in the first embodiment described above, a photonic crystal 500 is provided as an example of a reflective structure that confines light from the waveguide 300 in the i-layer 404.

[0080] 10 , a plurality of holes 502 provided as a photonic crystal 500 are provided so as to penetrate the P-type layer 406 or the N-type layer 402 and a portion of the waveguide 300. In this embodiment, the plurality of holes 502 reflect light toward the i-layer 404, thereby confining the light in the i-layer 404. Therefore, according to this embodiment, more light can be confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. As a result, according to this embodiment, loss of carriers caused by photoelectric conversion can be suppressed, and the quantum efficiency of the photodetector 100 can be improved.

[0081] In this embodiment, similarly to the second embodiment, a plurality of distributed Bragg reflectors 510 may be provided in place of the photonic crystal 500 .

[0082] Furthermore, the photodetector 100 according to this embodiment is not limited to the configuration shown in FIG. 10, but can be modified into various other configurations.

[0083] 4.2 Manufacturing Method Next, a manufacturing method of the photodetector 100 according to this embodiment will be described with reference to Fig. 11. Fig. 11 is an explanatory diagram showing the manufacturing process of the photodetector 100 according to this embodiment, and is a cross-sectional view corresponding to Fig. 10 in each manufacturing process.

[0084] 11, a layer 200 made of silicon oxide is formed on one surface of a silicon substrate that will become the waveguide 300. Then, on the other surface of the silicon substrate that will become the waveguide 300, a central portion (corresponding to the protruding portion 300c) of an area where the photodiode 400 will be provided is left unremoved, and the other area is dug out.

[0085] 11, an i-layer 404 made of undoped germanium is formed on the silicon substrate (waveguide 300). Furthermore, N-type impurities are implanted into predetermined positions of the i-layer 404 to form N-type layers 402, and P-type impurities are implanted to form P-type layers 406.

[0086] 11 , a plurality of openings having a predetermined diameter (size) are formed at predetermined positions in the N-type layer 402 and the P-type layer 406, penetrating the N-type layer 402, the P-type layer 406, and the silicon substrate (waveguide 300). Furthermore, holes 502 are formed by filling the openings with, for example, silicon oxide. In this manner, the photodetector 100 according to this embodiment can be formed.

[0087] <<5. Fourth Embodiment>> <5.1 Detailed Configuration> Next, a detailed configuration of a photodetector 100 according to a fourth embodiment of the present disclosure will be described with reference to Fig. 12. Fig. 12 is a cross-sectional view of the photodetector 100 according to this embodiment.

[0088] In this embodiment, as shown in FIG. 12 , a trench 302 is formed by digging into the center of a thick silicon substrate that will become the waveguide 300, and an i-layer 404 of a lateral PIN photodiode 400 is provided in the trench 302. Specifically, a substantially rectangular trench 302 extending along the length of the waveguide 300 is formed in the thick silicon substrate. In this embodiment, the i-layer 404 is provided so as to be located within the trench 302. Furthermore, in this embodiment, an N-type layer 402a made of silicon doped with N-type impurities and a P-type layer 406a made of silicon doped with P-type impurities are provided so as to sandwich the i-layer 404. That is, in this embodiment, the PIN germanium photodiode 400 has the N-type layer 402a made of silicon, the i-layer 404 made of germanium, and the P-type layer 406 made of silicon, which are aligned in a row along the width direction of the waveguide 300. Furthermore, in this embodiment, unlike the fifth embodiment described later, it is preferable that the top surfaces of the N-type layer 402a made of silicon, the i-layer 404 made of germanium, and the P-type layer 406 made of silicon are flush with each other. According to this embodiment, by forming the lateral PIN photodiode 400 in this manner, the photodetector 100 can be easily manufactured.

[0089] Also in this embodiment, similarly to the first embodiment described above, a photonic crystal 500 is provided as an example of a reflective structure that confines light from the waveguide 300 in the i-layer 404 .

[0090] 12 , a plurality of holes 502 provided as a photonic crystal 500 are provided so as to penetrate the P-type layer 406 a or the N-type layer 402 a and the waveguide 300. In this embodiment, the plurality of holes 502 reflect light toward the i-layer 404, thereby confining the light in the i-layer 404. Therefore, according to this embodiment, more light can be confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. As a result, according to this embodiment, loss of carriers caused by photoelectric conversion can be suppressed, and the quantum efficiency of the photodetector 100 can be improved.

[0091] In this embodiment, similarly to the second embodiment, a plurality of distributed Bragg reflectors 510 may be provided in place of the photonic crystal 500 .

[0092] Furthermore, the photodetector 100 according to this embodiment is not limited to the configuration shown in FIG. 12, but can be modified into various other configurations.

[0093] 5.2 Manufacturing Method Next, a manufacturing method of the photodetector 100 according to this embodiment will be described with reference to Fig. 13. Fig. 13 is an explanatory diagram showing the manufacturing process of the photodetector 100 according to this embodiment, and is a cross-sectional view corresponding to Fig. 12 at each manufacturing step.

[0094] 13, a layer 200 made of silicon oxide is formed on one surface of a thick silicon substrate that will become the waveguide 300. A region where the i-layer of the PIN photodiode 400 will be provided is dug into the other surface of the silicon substrate that will become the waveguide 300. In this way, a trench 302 is formed in the center.

[0095] 13, N-type impurities are implanted into predetermined positions of the silicon substrate (waveguide 300) to form N-type layers 402a, and P-type impurities are implanted into predetermined positions of the silicon substrate (waveguide 300) to form P-type layers 406a. Furthermore, a plurality of openings 504 having a predetermined diameter (size) are formed at predetermined positions of the N-type layer 402 and the P-type layer 406, penetrating the N-type layer 402, the P-type layer 406, and the silicon substrate.

[0096] 13, holes 502 are formed by filling the openings 504 with, for example, silicon oxide. Furthermore, an i-layer 404 made of germanium that is not doped with impurities is formed in the trench 302. In this manner, the photodetector 100 according to this embodiment can be formed.

[0097] <<6. Fifth Embodiment>> <6.1 Detailed Configuration> Next, a detailed configuration of a photodetector 100 according to a fifth embodiment of the present disclosure will be described with reference to Fig. 14. Fig. 14 is a cross-sectional view of the photodetector 100 according to this embodiment.

[0098] In this embodiment, as shown in FIG. 14 , an i-layer 404 of a lateral PIN diode 400 is provided on a waveguide 300. Furthermore, in this embodiment, an N-type layer 402a made of silicon doped with N-type impurities and a P-type layer 406a made of silicon doped with P-type impurities are provided on either side of the waveguide 300. Also, in this embodiment, the width of the i-layer 404 is made wider than the width of the waveguide 300. In this manner, the i-layer 404 comes into contact with the N-type layer 402a and the P-type layer 406a, and the lateral PIN diode 400 can be configured by the P-type layer 406a, i-layer 404, and N-type layer 402a. That is, in this embodiment, the photodetector 100 has an N-type layer 402a made of silicon, the waveguide 300, and a P-type layer 406 made of silicon, which are aligned in a line along the width direction of the waveguide 300, and an i-layer 404 made of germanium provided on the waveguide 300. Furthermore, in this embodiment, unlike the above-mentioned fourth embodiment, it is preferable that the top surfaces of the N-type layer 402a made of silicon, the waveguide 300, and the P-type layer 406 made of silicon are flush with each other.

[0099] In this embodiment, similarly to the first embodiment described above, a photonic crystal 500 is provided as an example of a reflective structure that confines the light from the waveguide 300 in the i-layer 404 .

[0100] In this embodiment, as shown in FIG. 14 , the plurality of holes 502 provided as the photonic crystal 500 are provided so as to penetrate the P-type layer 406 a or the N-type layer 402 a. In this embodiment, the plurality of holes 502 reflect light toward the waveguide 300, and the light guided into the waveguide 300 is incident on the i-layer 404 provided thereon. Therefore, according to this embodiment, more light can be confined in the i-layer 404, and most of the light is photoelectrically converted in the i-layer 404 to generate a photocurrent. As a result, according to this embodiment, carrier loss caused by photoelectric conversion can be suppressed, and the quantum efficiency of the photodetector 100 can be improved. Furthermore, according to this embodiment, the plurality of holes 502 may be of the same type (having the same size, arrangement, etc.), which facilitates the manufacture of the photodetector 100.

[0101] In this embodiment, similarly to the second embodiment, a plurality of distributed Bragg reflectors 510 may be provided in place of the photonic crystal 500 .

[0102] Furthermore, the photodetector 100 according to this embodiment is not limited to the configuration shown in FIG. 14, but can be modified into various other configurations.

[0103] 6.2 Manufacturing Method Next, a manufacturing method of the photodetector 100 according to this embodiment will be described with reference to Fig. 15. Fig. 15 is an explanatory diagram showing the manufacturing process of the photodetector 100 according to this embodiment, and is a cross-sectional view corresponding to Fig. 14 at each manufacturing step.

[0104] First, as shown in the upper part of FIG. 15, a thick silicon layer that will become a waveguide 300 is formed on a layer 200 made of silicon oxide.

[0105] 15 , N-type impurities are implanted into a pair of regions of the silicon layer sandwiching the central portion (corresponding to the waveguide 300) to form N-type layers 402a, and P-type impurities are implanted into the pair of regions to form P-type layers 406a. Furthermore, a plurality of openings 504 having a predetermined diameter (size) are formed at predetermined positions in the N-type layer 402 and the P-type layer 406, penetrating the N-type layer 402 and the P-type layer 406.

[0106] 15, holes 502 are formed by filling the openings 504 with, for example, silicon oxide. Furthermore, an i-layer 404 made of undoped germanium is formed on the center of the silicon layer that will become the waveguide 300. In this manner, the photodetector 100 according to this embodiment can be formed.

[0107] 7. Sixth Embodiment Next, a detailed configuration of a photodetector 100 according to a sixth embodiment of the present disclosure will be described with reference to Fig. 16. Fig. 16 is a plan view of the photodetector 100 according to this embodiment. This embodiment assumes an embodiment in which the photodetector 100 uses a balanced photodiode in which two lateral PIN photodiodes 400 are connected in series.

[0108] For example, in the embodiment shown on the left side of Fig. 16 , two PIN photodiodes 400 share a P-type layer 406, thereby reducing the space occupied by the photodetector device 100. Furthermore, for example, in the embodiment shown on the right side of Fig. 16 , two PIN photodiodes 400 share an N-type layer 402, thereby reducing the space occupied by the photodetector device 100. Note that in this embodiment as well, the lateral PIN photodiodes 400 according to the embodiments of the present disclosure described above can be applied to the two lateral PIN photodiodes 400.

[0109] The photodetector 100 according to this embodiment is not limited to the form shown in FIG. 16, but can be modified into various forms, such as arranging two or more lateral PIN photodiodes 400 side by side.

[0110] <<8. Seventh Embodiment>> The photodetector 100 according to an embodiment of the present disclosure is not limited to being applied to the distance measuring device 1 described above, and can be applied to, for example, a light receiving device for optical communication. Therefore, a configuration example of a light receiving device 600 according to a seventh embodiment of the present disclosure will be described with reference to Fig. 17. Fig. 17 is a block diagram showing the configuration example of the light receiving device 600 according to this embodiment.

[0111] For example, as shown in FIG. 17, a light receiving device 600 mainly includes a waveguide 602, a light detecting device 100, a signal detecting section 604, and a signal processing section 606.

[0112] For example, the photodetector 100 can acquire an optical signal guided to a waveguide 602 in the photodetector 600 via an optical fiber 610 or the like connected to the photodetector 600. The photodetector 100 then performs photoelectric conversion on the guided optical signal to generate an electrical signal as a photocurrent. The photodetector 100 then outputs the generated electrical signal to a signal detector 604. The photodetector 100 according to the embodiment of the present disclosure described above can be applied to the photodetector 100.

[0113] Next, the signal detection unit 604 amplifies the input electrical signal and converts it into a digital signal, and outputs the processed digital signal to the signal processing unit 606. Furthermore, the signal processing unit 606 processes the digital signal and outputs the processing result to, for example, a network device 620 connected to the light receiving device 600.

[0114] The light receiving device 600 according to this embodiment is not limited to a specific type as long as it is optical communication. The light receiving device 600 according to this embodiment is not limited to the configuration shown in Fig. 17, but can be modified into various other configurations.

[0115] <<9. Summary>> As described above, in each embodiment of the present disclosure, by confining light in the i-layer 404 using a reflection structure made of a photonic crystal or a distributed Bragg reflector, it is possible to suppress the loss of carriers caused by photoelectric conversion and improve the quantum efficiency of the photodetector 100.

[0116] In the above description, the lateral PIN diode 400 is described as including germanium, but the embodiments of the present disclosure are not limited to this, and the lateral PIN diode 400 may include other semiconductor materials such as indium gallium arsenide (InGaAs).

[0117] Furthermore, in this embodiment, it is possible to manufacture the semiconductor device by using the method, apparatus, and conditions that are used in the manufacture of a general semiconductor device, i.e., in this embodiment, it is possible to use the existing semiconductor device manufacturing process.

[0118] Examples of the above-mentioned method include a PVD (Physical Vapor Deposition) method, a CVD (Chemical Vapor Deposition) method, and an ALD (Atomic Layer Deposition) method. Examples of PVD methods include vacuum deposition, EB (electron beam) deposition, various sputtering methods (magnetron sputtering, RF (radio frequency)-DC (direct current) combined bias sputtering, ECR (electron cyclotron resonance) sputtering, facing target sputtering, high frequency sputtering, etc.), ion plating, laser ablation, molecular beam epitaxy (MBE), and laser transfer. Examples of CVD methods include plasma CVD, thermal CVD, metal organic (MO) CVD, and photo CVD. Other methods include electroplating, electroless plating, spin coating, dipping, casting, microcontact printing, drop casting, various printing methods such as screen printing, inkjet printing, offset printing, gravure printing, and flexographic printing, stamping, spraying, and various coating methods such as air doctor coater, blade coater, rod coater, knife coater, squeeze coater, reverse roll coater, transfer roll coater, gravure coater, kiss coater, cast coater, spray coater, slit orifice coater, and calendar coater. Furthermore, patterning methods include chemical etching such as shadow mask, laser transfer, and photolithography, and physical etching using ultraviolet light or laser. Additionally, planarization techniques include CMP (Chemical Mechanical Polishing), laser planarization, and reflow.

[0119] <<10. Application Examples>> The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, or a robot.

[0120] FIG. 18 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied.

[0121] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 18, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also shown as functional components of the integrated control unit 12050 are a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (Interface) 12053.

[0122] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force of the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle.

[0123] The body system control unit 12020 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 12020. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0124] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture images outside the vehicle and receives the captured images. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, characters on the road surface, etc. based on the received images.

[0125] The imaging unit 12031 is an optical sensor that receives light and outputs an electrical signal corresponding to the amount of light received. The imaging unit 12031 can output the electrical signal as an image or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0126] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

[0127] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, steering mechanism, or braking device based on the information inside and outside the vehicle acquired by the outside-vehicle information detection unit 12030 or the inside-vehicle information detection unit 12040, and output control commands to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing the functions of an ADAS (Advanced Driver Assistance System), including vehicle collision avoidance or impact mitigation, following driving based on the inter-vehicle distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc.

[0128] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle obtained by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0129] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12030 based on the information outside the vehicle acquired by the outside information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside information detection unit 12030, and perform cooperative control aimed at preventing glare, such as switching from high beams to low beams.

[0130] The audio / video output unit 12052 transmits at least one of audio and video output signals to an output device capable of visually or audibly notifying the passengers of the vehicle or the outside of the vehicle of information. In the example of Fig. 18, the output devices are exemplified by an audio speaker 12061, a display unit 12062, and an instrument panel 12063. The display unit 12062 may include, for example, at least one of an on-board display and a head-up display.

[0131] FIG. 19 is a diagram showing an example of the installation position of the imaging unit 12031.

[0132] In FIG. 19, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0133] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at positions such as the front nose, side mirrors, rear bumper, back door, and the top of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided on the front nose and the imaging unit 12105 provided on the top of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided on the top of the windshield inside the vehicle cabin is mainly used to detect preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0134] 19 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 12101 to 12104, an overhead image of the vehicle 12100 viewed from above can be obtained.

[0135] At least one of the image capturing units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the image capturing units 12101 to 12104 may be a stereo camera made up of multiple image capturing elements, or may be an image capturing element having pixels for phase difference detection.

[0136] For example, based on the distance information obtained from the imaging units 12101 to 12104, the microcomputer 12051 can calculate the distance to each three-dimensional object within the imaging ranges 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100), thereby extracting as a preceding vehicle, in particular, the three-dimensional object that is the closest three-dimensional object on the path of the vehicle 12100 and traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or higher). Furthermore, the microcomputer 12051 can set a vehicle-to-vehicle distance to be maintained in advance in front of the preceding vehicle, and perform automatic braking control (including follow-up stop control), automatic acceleration control (including follow-up start control), etc. In this way, cooperative control can be performed for the purpose of autonomous driving, which runs autonomously without relying on driver operation.

[0137] For example, the microcomputer 12051 classifies and extracts three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 then determines a collision risk that indicates the risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

[0138] At least one of the image capturing units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether a pedestrian is present in the images captured by the image capturing units 12101 to 12104. Such pedestrian recognition is performed, for example, by extracting feature points from the images captured by the image capturing units 12101 to 12104 as infrared cameras and performing pattern matching on a series of feature points that indicate the outline of an object to determine whether the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the image capturing units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular outline on the recognized pedestrian for emphasis. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating the pedestrian at a desired position.

[0139] The above describes an example of a vehicle control system to which the technology according to the present disclosure can be applied. The technology according to the present disclosure can be applied to the image capturing unit 12031.

[0140] <<11. Supplementary Information>> Although preferred embodiments of the present disclosure have been described above in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified examples, alterations, or combinations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0141] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0142] The present technology can also be configured as follows: (1) A photodetector comprising: a waveguide; a lateral PIN photodiode composed of a P-type layer, an i-layer, and an N-type layer aligned along the width direction of the waveguide; and a reflective structure that confines light from the waveguide in the i-layer located on the waveguide. (2) The photodetector according to (1), wherein the reflective structure is made of a photonic crystal composed of a plurality of periodically arranged holes. (3) The photodetector according to (2) above, wherein the P-type layer, the i-layer, and the N-type layer are provided on the waveguide, and the plurality of holes include a plurality of first holes that suppress diffusion of the light in the waveguide, and a plurality of second holes that reflect the light toward the i-layer, and the plurality of first holes are provided so as to penetrate the waveguide located below the i-layer near an interface between the P-type layer or the N-type layer and the i-layer, and the plurality of second holes are provided so as to penetrate the P-type layer or the N-type layer near the interface. (4) The photodetector according to (3) above, wherein the plurality of first holes are provided so as to penetrate the i-layer near the interface, and the plurality of second holes are provided so as to penetrate the waveguide below the P-type layer or the N-type layer near the interface. (5) The photodetector according to (3) or (4), wherein the plurality of first holes and the plurality of second holes differ in size, arrangement interval, shape, or internal material. (6) The photodetector according to (2), wherein the plurality of holes are provided so as to penetrate part of the P-type layer and the N-type layer along the film thickness direction. (7) The photodetector according to (6), wherein the N-type layer and the P-type layer are provided so as to sandwich the waveguide. (8) The photodetector according to (7), wherein the upper surfaces of the N-type layer and the P-type layer are flush with the upper surface of the waveguide. (9) The photodetector according to (6), wherein the i-layer is provided so as to cover the upper surface and side surfaces of the waveguide. (10) The photodetector according to any one of (2) to (8), wherein silicon oxide or silicon nitride is embedded in each of the holes.(11) The photodetector according to (1), wherein the reflection structure is composed of a plurality of periodically arranged distributed Bragg reflectors. (12) The photodetector according to (1), wherein the P-type layer, the i-layer, and the N-type layer are provided on the waveguide, and the plurality of distributed Bragg reflectors include a plurality of first reflectors that suppress spreading of the light in the waveguide, and a plurality of second reflectors that reflect the light toward the i-layer, and the plurality of first reflectors are provided to penetrate the waveguide located below the i-layer near an interface between the P-type layer or the N-type layer and the i-layer, and the plurality of second reflectors are provided to penetrate the P-type layer or the N-type layer near the interface. (13) The photodetector according to (12) above, wherein the plurality of first reflecting mirrors are provided so as to penetrate the i-layer near the interface, and the plurality of second reflecting mirrors are provided so as to penetrate the waveguide below the P-type layer or the N-type layer near the interface. (14) The photodetector according to (12) above, wherein the plurality of first reflecting mirrors and the plurality of second reflecting mirrors are different in size, arrangement interval, number of layers constituting the first and second reflecting mirrors, or material. (15) The photodetector according to (11) above, wherein the plurality of distributed Bragg reflectors are provided so as to penetrate part of the P-type layer and the N-type layer along the film thickness direction. (16) The photodetector according to (15) above, wherein the N-type layer and the P-type layer are provided so as to sandwich the waveguide. (17) The photodetector according to (15) above, wherein the i-layer is provided so as to cover the top and side surfaces of the waveguide. (18) The photodetector according to any one of (1) to (17), wherein the i-layer is made of germanium, and the P-type layer and the N-type layer are made of germanium or silicon. (19) The photodetector according to any one of (1) to (18), wherein the waveguide is made of silicon.(20) A distance measuring device including a photodetector, the photodetector having: a waveguide; a lateral PIN photodiode consisting of a P-type layer, an i-layer, and an N-type layer aligned along the width direction of the waveguide; and a reflection structure that confines light from the waveguide to the i-layer located on the waveguide.

[0143] REFERENCE SIGNS LIST 1 Range finding device 2 Object 10 Laser light source 20 Modulator 30 Splitter 40 Circulator 60 Scanner 90 Coupler 100, 100a Photodetector 120 ADC 130 FFT calculation circuit 200, 512, 514 Layer 202 Silicon oxide film 300, 602 Waveguide 300a Silicon substrate 300c Protrusion 302 Trench 400, 400a Photodiode 402, 402a N-type layer 404 i-layer 406, 406a P-type layer 500 Photonic crystal 502, 502a, 502b Hole 504, 504a, 504b Opening 510, 510a, 510b Distributed Bragg reflector 600 Light receiving device 604 Signal detection unit 606 Signal processing unit 610 Optical fiber 620 Network device

Claims

1. A photodetector comprising: a waveguide; a lateral PIN photodiode consisting of a P-type layer, an i-layer, and an N-type layer aligned along the width direction of the waveguide; and a reflective structure that confines light from the waveguide to the i-layer located on the waveguide.

2. The optical detection device according to claim 1, wherein the reflecting structure is made of a photonic crystal having a plurality of periodically arranged holes.

3. The photodetector device of claim 2, wherein the P-type layer, the i-layer and the N-type layer are provided on the waveguide, and the plurality of holes include a plurality of first holes that suppress the light from spreading in the waveguide, and a plurality of second holes that reflect the light toward the i-layer, and the plurality of first holes are provided so as to penetrate the waveguide located below the i-layer in the vicinity of an interface between the P-type layer or the N-type layer and the i-layer, and the plurality of second holes are provided so as to penetrate the P-type layer or the N-type layer in the vicinity of the interface.

4. The optical detection device described in claim 3, wherein the plurality of first holes are provided so as to penetrate the i-layer near the interface, and the plurality of second holes are provided so as to penetrate the waveguide below the P-type layer or the N-type layer near the interface.

5. The optical detection device according to claim 3, wherein the plurality of first holes and the plurality of second holes are different in size, arrangement interval, shape, or internal material.

6. The photodetector according to claim 2, wherein the plurality of holes are provided so as to penetrate a portion of the P-type layer and the N-type layer in a film thickness direction.

7. The photodetector according to claim 6, wherein the N-type layer and the P-type layer are provided so as to sandwich the waveguide.

8. The photodetector device according to claim 7, wherein upper surfaces of the N-type layer and the P-type layer are flush with an upper surface of the waveguide.

9. The photodetector according to claim 6, wherein the i-layer is provided so as to cover an upper surface and a side surface of the waveguide.

10. The photodetector according to claim 2, wherein each of said holes is filled with silicon oxide or silicon nitride.

11. The optical detection device according to claim 1, wherein the reflecting structure comprises a plurality of periodically arranged distributed Bragg reflectors.

12. The optical detection device described in claim 11, wherein the P-type layer, the i-layer and the N-type layer are provided on the waveguide, and the plurality of distributed Bragg reflectors include a plurality of first reflectors that suppress the light from spreading in the waveguide, and a plurality of second reflectors that reflect the light toward the i-layer, and the plurality of first reflectors are provided to penetrate the waveguide located below the i-layer in the vicinity of an interface between the P-type layer or the N-type layer and the i-layer, and the plurality of second reflectors are provided to penetrate the P-type layer or the N-type layer in the vicinity of the interface.

13. The optical detection device described in claim 12, wherein the plurality of first reflectors are arranged to penetrate the i-layer near the interface, and the plurality of second reflectors are arranged to penetrate the waveguide below the P-type layer or the N-type layer near the interface.

14. The optical detection device according to claim 12, wherein the plurality of first reflecting mirrors and the plurality of second reflecting mirrors are different in size, spacing, number of layers constituting the first and second reflecting mirrors, or material.

15. The photodetector according to claim 11, wherein the plurality of distributed Bragg reflectors are provided so as to penetrate part of the P-type layer and the N-type layer in the film thickness direction.

16. The photodetector according to claim 15, wherein the N-type layer and the P-type layer are disposed so as to sandwich the waveguide.

17. The photodetector according to claim 15, wherein the i-layer is provided so as to cover an upper surface and a side surface of the waveguide.

18. The photodetector device according to claim 1, wherein the i-layer is made of germanium, and the P-type layer and the N-type layer are made of germanium or silicon.

19. The optical detection device of claim 1, wherein the waveguide is made of silicon.

20. A distance measuring device equipped with a photodetector, the photodetector having: a waveguide; a lateral PIN photodiode consisting of a P-type layer, an i-layer, and an N-type layer aligned along the width direction of the waveguide; and a reflection structure that confines light from the waveguide to the i-layer located on the waveguide.

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