JP6534888B2 - Planar light detector - Google Patents

Description

  The present invention relates to a surface light detector.

  In recent years, for speeding up communication between server racks in a data center, and speeding up communication between CPUs or between a CPU and a memory in a server board on which a plurality of CPUs (central processing units) are mounted. Optical communication has come to be used. These short distance optical communications are called optical interconnects and are distinguished from long distance optical communications. In communication equipment for long distance communication, high transmission speed is regarded as the most important in order to support a large amount of communication demand, but in communication equipment for optical interconnects, it is inexpensive while providing some communication speed Is required.

  In order to meet such requirements for optical interconnect communication devices, development of silicon photonics optical transmitters and optical receivers has been activated. Silicon photonics is a technology for forming an optical integrated circuit on a silicon (Si) substrate by utilizing the already matured CMOS LSI (complementary metal oxide semiconductor large scale integrated circuit) manufacturing technology. Unlike single optical device manufacturing technology using III-V group compound semiconductors etc., silicon photonics has a relatively high optical processing accuracy and mass productivity of CMOS technology, and it is relatively large in optical integrated circuit where multiple optical functional devices are integrated. It aims at manufacturing cheaply.

  However, since silicon is an indirect transition semiconductor, efficient light source technology has not been established yet. Therefore, to construct an optical transmitter using silicon photonics, for example, a laser chip for a light source using a direct transition type III-V compound semiconductor is mounted on a silicon chip on which an optical modulator is formed. Is often done.

  On the other hand, in the case of an optical receiver, a photodetector that converts received light into an electrical signal is the main optical device, and germanium (Ge) epitaxially grown on silicon is used as a photoelectric conversion medium for the photodetector. Is the mainstream. Germanium is low in efficiency as a light emitting medium for a light source, but if the wavelength is properly selected, high efficiency can be shown as a light absorbing medium for a photodetector. Germanium has a band gap energy of 0.66 eV and absorbs light of a wavelength of about 1880 nm or less to convert it into electrons. However, since germanium is an indirect transition semiconductor like silicon, it has a small light absorption coefficient. However, when light having energy of about 0.8 eV or more, that is, light having a wavelength in vacuum of 1550 nm or less is incident, absorption due to direct transition occurs simultaneously with indirect transition, and thus a high absorption coefficient is exhibited. Therefore, the efficiency is achieved by using germanium grown on silicon, especially in the case of receiving light of a communication wavelength band called the O (o) band whose wavelength is sufficiently shorter than 1550 nm, that is, the wavelength range 1260 to 1360 nm. Light signal can be received.

  There are roughly two types of photodetectors: waveguide type and surface type. The waveguide type can easily obtain sufficient light receiving sensitivity by lengthening the waveguide for light absorption. Instead, to optically couple with the optical fiber, a spot size converter must be attached to convert the different mode diameters of the waveguide and the optical fiber, and the light loss caused by the spot size converter substantially Light reception sensitivity may decrease. On the other hand, the surface light detector is capable of direct light coupling with an optical fiber because the light receiving surface can be easily enlarged. However, in order to obtain the required light reception sensitivity, it is necessary to make the light absorbing medium sufficiently thick.

  Most optical circuit chips based on silicon photonics in recent years are manufactured using a silicon-on-insulator wafer. Therefore, it is also required to design a germanium photodetector on the premise of using an SOI wafer. FIG. 1 is a schematic view of a basic layer structure of a surface light detector in which germanium is stacked on an SOI wafer. The original SOI wafer before processing consists of a silicon substrate 4, a buried oxide film layer (BOX layer) 3 made of silicon dioxide, and an SOI layer 2 which is silicon. Then, a germanium layer 1 which is an absorption medium layer is epitaxially grown on the SOI layer 2, and an oxide film layer 5 made of silicon dioxide for surface protection is further deposited on the germanium layer 1 to constitute a surface type photodetector. Be done.

  If the germanium layer 1 can be made sufficiently thick, most of the light incident on the germanium layer 1 from above through the oxide film layer 5 is absorbed by the germanium layer 1 and converted into electrons once it enters the germanium layer 1 Be done. In this case, the main loss generation factor of the photodetector is the light reflection loss at the incident side interface 15 of the germanium layer 1. Therefore, in the prior art, when the germanium layer 1 can be made sufficiently thick, the formation of an antireflective film on the germanium layer 1 is performed.

Japanese Patent Application Publication No. 2013-532902

  However, when the germanium layer is thickened and further an antireflective film is laminated, the total thickness of the germanium layer and the antireflective film layer becomes about several μm. As a result, if only the photodetector becomes thick in the optical circuit in which a plurality of optical functional devices are integrated at the same time, the height of the surface of the photodetector and that of the surrounding devices will be largely different. The problem arises that the lithography process and the wiring formation process that require a certain level of flatness on the surface become difficult.

  Further, even when considering the germanium layer as the light absorbing medium alone, there is also a problem that the response speed is lowered if the germanium layer is too thick. Electrons and holes generated when light is absorbed travel to the front side and the back side of the germanium layer, but the traveling time becomes longer in proportion to the thickness of the germanium layer. As a result, the response speed is reduced, and the ability to convert a high-speed optical signal into current accurately is reduced. If the photosensitivity may be sacrificed to some extent, thinning the germanium layer of the light absorbing medium is considered as a countermeasure. However, if the germanium layer is simply thinned, part of the light that can not be absorbed by the germanium layer is reflected by the lower surface of the germanium layer and returned to the incident side, and then returned to the transmitter, There is a risk of destabilizing the operation of the emitting optical transmitter.

  The present invention has been made in view of the above-described point, and one of its objects is to provide a highly sensitive photodetector which has a thin germanium layer, does not require an anti-reflection film, and hardly reflects incident light. It is to do.

  In order to solve the problems described above, one aspect of the present invention is a light absorption layer, and at least one pair layer of a silicon rich layer and a germanium rich layer located under the light absorption layer, and the pair Planar light detection comprising a first silicon layer located below the layer, an oxide layer located below the first silicon layer, and a second silicon layer located below the oxide layer The light absorbing layer is a germanium or silicon-germanium compound having a composition ratio of silicon of 0 to 0.1, and the silicon rich layer is a silicon of silicon having a composition ratio of 0.9 to 1. A germanium compound or silicon, and the germanium rich layer is a germanium or silicon-germanium compound having a composition ratio of silicon of 0 to 0.1, and a thickness of the light absorption layer is The material is in the range of (m / 4 ± 1/8) times (m is a positive integer) times the wavelength of light in the material forming the light absorbing layer, and the thickness of the silicon rich layer is the material forming the silicon rich layer And the thickness of the germanium-rich layer is in the material forming the germanium-rich layer. The wavelength of light is within the range of ((2s-1) / 4 ± 1/8) times (s is a positive integer), and the thickness of the first silicon layer is / 2 ± 1/8 times (p is a positive integer), and the thickness of the oxide film layer is ((2q-1) / 4) of the wavelength of light in the material forming the oxide film layer. The surface light detector is characterized in that it is within a range of ± 1/8 times (q is a positive integer).

  Further, according to another aspect of the present invention, in the above-mentioned one aspect, the paired layers are stacked in an odd number, and m is an even number.

  Moreover, the other one aspect of this invention is a planar type | mold photodetector characterized by the lamination | stacking number of the said pair layer being 1 and m being 8 or 10 or 12 in the said one aspect.

  Another embodiment of the present invention is the surface type photodetector according to the above-mentioned embodiment, characterized in that the paired layers are stacked in even layers, and m is an odd number.

  In addition, according to another aspect of the present invention, in the above-mentioned one aspect, the number of stacked layers of the pair layer is 2, and m is 7 or 9 or 11.

  Moreover, the other one aspect of this invention is further provided with the cap layer located on the said light absorption layer in the said one aspect, and the said cap layer is a silicon-germanium with a composition ratio of 0.9-1 of silicon. The thickness of the cap layer is in the range of (f / 4 ± 1/8) times (f is 0 or a positive integer) times the wavelength of light in the material forming the cap layer; It is a surface-type light detector characterized in that.

  Another aspect of the present invention is the planar light detector characterized in that f is 0 or an even number in the above one aspect.

  Another aspect of the present invention is the planar light detector characterized in that f is 0 or 2 in the above one aspect.

  Another embodiment of the present invention is the surface type photodetector characterized in that f is an odd number in the above one embodiment.

  According to the present invention, it is possible to provide a highly sensitive photodetector which has a thin germanium layer, which does not require an antireflective film, and which hardly reflects incident light.

It is a schematic diagram of the basic layer structure of the conventional surface type photodetector. FIG. 1 is a schematic cross-sectional view showing the configuration of a surface light detector 20 according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of a surface light detector 30 according to the first embodiment. It is a typical sectional view showing the composition of surface type photodetector 40 by a 2nd embodiment. It is a figure which shows the FDTD simulation result of the time change of the power transmission factor of the light which injected into the layer structure of the planar light detector 40, and a power reflectivity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a schematic cross-sectional view showing the configuration of the surface light detector 20 according to the first embodiment of the present invention. As shown in FIG. 2, the surface light detector 20 of this embodiment includes the light absorption layer 21, the silicon rich layer 28 thereunder, the germanium rich layer 27 thereunder, and the first silicon therebelow It comprises a layer 22, an underlying oxide layer 23, and a second silicon layer 24 underneath. The second silicon layer 24, the oxide film layer 23, and the first silicon layer 22 form a layer structure of a so-called SOI wafer. The surface light detector 20 may include an upper cladding layer 25 on the light absorption layer 21.

  The material forming the light absorption layer 21 is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1. The material of the silicon rich layer 28 is a silicon-germanium compound having a composition ratio of silicon of 0.9 to 1, or silicon. The material of the germanium rich layer 27 is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1. The material of the oxide film layer 23 is silicon dioxide.

The thickness t ₂₁ of the light absorption layer 21 is in the range of (m / 4 ± 1/8) times (m is a positive integer) the wavelength of light in the material forming the light absorption layer 21. The thickness _{t 28} of the silicon-rich layer 28 is in the range of wavelengths of light in the material constituting the silicon-rich layer 28 ((2r-1) / 4 ± 1/8) times (r is a positive integer). The thickness t ₂₇ of the germanium rich layer 27 is in the range of ((2 s −1) / 4 ± 1/8) times (s is a positive integer) the wavelength of light in the material forming the germanium rich layer 27. The thickness t ₂₂ of the first silicon layer 22 is in the range of (p / 2 ± 1/8) times (p is a positive integer) the wavelength of light in the first silicon layer 22. The thickness _{t 23} of the oxide layer 23 is in the range of wavelengths of light in the material constituting the oxide film layer 23 ((2q-1) / 4 ± 1/8) times (q is a positive integer). However, “within the range of a ± b” means a numerical range larger than a−b and smaller than a + b.

  The operation of the surface light detector 20 according to the first embodiment is as follows.

The silicon rich layer 28, the germanium rich layer 27, the first silicon layer 22, and the oxide film layer 23 have a high reflection film with respect to light propagating toward the second silicon layer 24 from the light absorption layer 21. To work. The material of the silicon rich layer 28 is silicon, the material of the germanium rich layer 27 is germanium, and the thickness of each layer has an error in each of the above formulas. In this case, the power reflectivity of light is 0.69, in the case of taking a value of exactly one that does not include the (± 1/8) -fold term that is the represented term. The silicon rich layer 28 and the germanium rich layer 27 are layers newly introduced in the present invention. Assuming that the wavelength of light in vacuum is 1310 nm, the refractive indices of silicon and germanium at that wavelength are 3.505 and 4.3, respectively, and r = 1 and s = 1, under the conditions that give the above-mentioned maximum reflectance. in each thickness _{t 27} of the thickness _{t 28} and germanium-rich layer 27 of silicon-rich layer 28 is 93 nm, a 76nm, the combined thickness of both _(t 28 _{+ t 27)} is the sum of 170 nm (93 nm and 76nm The difference from 169 nm is due to rounding operation). Since the power reflectivity when the silicon rich layer 28 and the germanium rich layer 27 are not provided is 0.57, the reflectivity is improved by 0.12.

  Thus, by introducing the silicon rich layer 28 and the germanium rich layer 27, the reflectance on the back surface of the light absorption layer 21 (that is, the interface between the light absorption layer 21 and the silicon rich layer 28) can be improved. it can. The improvement of the back surface reflectance has an effect of reducing the light which is lost through the back surface side of the light absorption layer 21. In addition, the back surface reflectance can be further improved by increasing the number of silicon rich layer and germanium rich layer pairs (hereinafter referred to as “reflective layer pair”). However, it should be noted that the combined thickness of the silicon rich layer and the germanium rich layer increases by the number of pairs. If only one pair is added, it will increase by 170 nm of the sum of the thicknesses of the two layers.

By increasing the reflectance on the back surface side of the light absorption layer 21 in this way, the loss due to the back surface transmission light is reduced, but just by reducing the back surface transmission light, light is reflected by the back surface of the light absorption layer 21 and absorbed. Light returning through the layer 21 will pass through to the incident side (ie, the side of the upper cladding layer 25). Therefore, the phase of the light that has passed through is opposite to the phase of the light that is reflected by the surface of the light absorption layer 21 (that is, the interface between the light absorption layer 21 and the upper cladding layer 25) and returns to the incident side. The thickness t ₂₁ of the light absorption layer ₂₁ is set to By making the phases of the two reflected return lights from the back surface and the surface of the light absorption layer 21 opposite to each other, destructive interference occurs between them and the final return from the surface of the light absorption layer 21 to the incident side Reflected light is reduced. Although the final reflected light from the surface of the light absorption layer 21 is minimized when the intensities of the two reflected return lights that cause destructive interference are equal, it means that the front and back surfaces of the light absorption layer 21 are the same. And the absorption coefficient of the light absorbing medium (i.e., germanium or silicon-germanium compound) forming the light absorbing layer 21.

As a result of theoretical analysis and finite difference time domain (FDTD) electromagnetic field simulation conducted that the upper cladding layer 25 is silicon dioxide, when the wavelength of light in vacuum is 1310 nm, the thickness t ₂₁ of the light absorption layer ₂₁ is It has been found that good results can be obtained as an optical receiver when the integer m in the above equation represents an even number, in particular m = 8, 10, 12. Since the refractive index of germanium at a wavelength of 1310 nm is 4.3, and hence the wavelength of light in the light absorption layer 21 is 305 nm, the thickness t ₂₁ of the light absorption layer 21 corresponding to m / 4 times the wavelength is , M = 8, 10, 12 are calculated to be 609 nm, 762 nm, 914 nm, respectively. The thickness t ₂₁ of the light absorbing layer 21, as represented by the aforementioned formula, the deviation of ± 76 nm, which corresponds to 1/8 of the wavelength relative to the thickness corresponding to m / 4 times the wavelength Yes You may

  In addition, as a result of simulation, the final reflection loss on the surface of the light absorption layer 21 was 0.2% at the minimum when m = 8, but the transmission loss was 25%. The loss was about 25%. On the other hand, when m = 12, the reflection loss is 1.9%, which is about 10 times that in the case of m = 8, but the transmission loss is reduced to 17%, and the total light loss is about 19%, The total light loss was 6% lower than in the case of m = 8. Therefore, in order to minimize reflected light, it is better to select m = 8, and when resistance to reflected return light of the optical transmitter is high, selecting m = 12 as an optical receiver The light reception sensitivity of the

As described above, the thickness t ₂₈ of the silicon rich layer 28 is 93 nm, the thickness t ₂₇ of the germanium rich layer ₂₇ is 76 nm, and the thickness t _{21 of the} light absorbing layer 21 (germanium layer) in the case of m = 8. Is 609 nm, the total thickness (t ₂₁ + t ₂₇ + t ₂₈ ) of these three layers is 778 nm. In the case of m = 10 and 12, the thicknesses of the light absorption layer 21 are 762 nm and 914 nm, respectively, so the total thickness of these three layers is 931 nm and 1083 nm, respectively.

  The reflective layer pair of the silicon rich layer 28 and the germanium rich layer 27 may be not only one but two or more. However, when the number of reflective layer pairs is an even number, the final reflected light from the surface of the light absorption layer 21 is reduced when m is an odd number, as confirmed by theoretical analysis and FDTD simulation. I understood. When the reflective layer pair is two pairs and m = 7, the reflection loss and the transmission loss are 0.2% and 25%, respectively, and the total loss of them is about 25%, and two pairs of reflective layers The total thickness of the pair and the light absorption layer 21 was 871 nm. Similarly, in the case of m = 9, the reflection loss and the transmission loss are 0.7% and 20%, respectively, and the total combined loss is about 21%, and the two reflective layer pairs and the light absorbing layer The total thickness of 21 was 1023 nm. Furthermore, in the case of m = 11, the reflection loss and the transmission loss are 1.9% and 17%, respectively, and the total loss is about 19%, and the total thickness of the two reflective layer pairs and the light absorbing layer 21 is It was 1176 nm.

  The material of the upper cladding layer 25 is not limited to silicon dioxide, but may be silicon nitride, silicon oxynitride, or another material, and should be appropriately selected according to the film forming apparatus that can be used.

  Next, with reference to FIG. 3, a method of manufacturing the planar light detector 30, which is a specific example to which the layer structure according to the first embodiment is applied, will be described. FIG. 3 shows the cross-sectional structure of the completed planar light detector 30. As shown in FIG. In FIG. 3, the basic laminated structure of the planar light detector 30 is the same as the laminated structure of the planar light detector 20 shown in FIG. 2, but the planar light detector 30 is a planar light detector. In addition to the twenty configurations, p electrodes (31a, 31b) and n electrodes (32a, 32b) are further provided.

  As a wafer for producing the planar light detector 30, an SOI wafer comprising a first silicon layer (SOI layer) 32, an oxide film layer (BOX layer) 33 and a second silicon layer 34 was used. The thickness of each layer of the SOI wafer was set to 2942 nm for the oxide film layer 33 and 187 nm for the first silicon layer 32. In the manufacturing step, first, p-type ion implantation is performed on a partial region of the SOI layer 32 (a region where a multilayer film of germanium and silicon is to be selectively epitaxially grown in the next step), and activation annealing is performed. Next, an oxide film (not shown) having a thickness of 100 nm is deposited on the SOI wafer, and a mask pattern (not shown) having holes opened only in the partial region is formed on the oxide film by lithography. An etching process was performed to make holes in the oxide film using the pattern. Next, a germanium-and-silicon multilayer film is selectively epitaxially grown on the SOI layer 32 in the hole portion of the oxide film, thereby sequentially forming the germanium-rich layer 37, the silicon-rich layer 38, and the light absorption layer 31. Next, n-type ion implantation was performed in the region of the epitaxial growth layer, and activation annealing was performed. Next, the upper cladding layer 35 made of silicon dioxide was deposited so as to cover the SOI layer 32 and the epitaxial growth layer (germanium rich layer 37, silicon rich layer 38, and light absorption layer 31). Next, contact holes (not shown) were formed in the outer periphery on the inner side of the epitaxial growth layer and in the vicinity of the outer side, and aluminum electrodes (31a, 31b, 32a, 32b) were formed inside the contact holes. Finally, an oxide film 35 was deposited as a protective film.

  In the first embodiment, an oxide film is deposited directly on the light absorption layer germanium. However, some CMOS production lines do not create a situation where silicon is grown continuously from epitaxial growth of germanium in order to prevent contamination of germanium with production equipment other than germanium growth equipment, and germanium is directly exposed to the outside. You may be asked to Next, another embodiment capable of solving the problem that the light receiving sensitivity of the light receiver decreases in such a case will be described below.

  FIG. 4 is a schematic cross-sectional view showing the configuration of a surface light detector 40 according to a second embodiment of the present invention. As shown in FIG. 4, the layer structure of the surface light detector 40 of the present embodiment is almost the same as the layer structure of the surface light detector 20 shown in FIG. 2. That is, the light absorption layer 41, the silicon rich layer 48, the germanium rich layer 47, the first silicon layer 42, the oxide film layer 43, the second silicon layer 44, and the upper cladding layer 45 in FIG. The light absorption layer 21, the silicon rich layer 28, the germanium rich layer 27, the first silicon layer 22, the oxide film layer 23, the second silicon layer 24, and the upper cladding layer 25 correspond to each other. In addition to the configuration of the planar light detector 20, the planar light detector 40 of the present embodiment further includes a cap layer 46 on the light absorption layer 41. The material forming the cap layer 46 is a silicon-germanium compound having a composition ratio of silicon of 0.9 to 1, or silicon. If the cap layer 46 is intended to prevent direct exposure of the germanium that is the constituent material of the light absorbing layer 41, it is desirable that the cap layer 46 be silicon.

The thickness t ₄₆ of the cap layer 46 is in the range of (f / 4 ± 1/8) times (f is 0 or a positive integer) the wavelength of light in the material forming the cap layer 46. As a result of theoretical analysis and FDTD simulation, it was confirmed that when f is 0 or an even number, the cap layer 46 hardly affects the reflectance and transmittance of the planar light detector 40 (light absorption layer 41). . Here, it is desirable that f is 0 or 2 in consideration of the fact that the silicon forming the cap layer 46 does not contribute to light absorption. For example, assuming that the wavelength of light in vacuum is 1310 nm, the refractive index of silicon at that wavelength is 3.505, and hence the wavelength of light in the cap layer 46 is 374 nm. Because of the error term of (1/8) times the wavelength in the above equation, the cap layer 46 has a thickness of at most 47 nm. Also, in the case of f = 2, the cap layer 46 has a thickness of between 140 and 234 nm.

  On the other hand, it was found from theoretical analysis and FDTD simulation that if f is an odd number, the overall light loss can be reduced as compared with the structure without the cap layer 46. Assuming that the material of cap layer 46 is silicon and f = 1, cap layer 46 has a thickness of 93 nm. FIG. 5 shows an FDTD simulation result of the time change of the power transmittance and the power reflectance of light incident on the layer structure of the planar light detector 40 in this case. As shown, after a sufficient time, the reflectance of incident light was 0.2%, the transmission was 12%, and the total light loss dropped to about 12%. However, the thickness of the light absorption layer 41 was 1588 nm (m = 17), and the total thickness of the light absorption layer 41 and the pair of reflective layers was a little as 1757 nm. Nevertheless, this surface light detector 40 has the advantage of not having to worry about the influence on other optical function elements, since it is not necessary to further stack an antireflective film.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible in the range which does not deviate from the summary.

20, 30, 40 planar photodetectors 21, 31, 41 light absorbing layers 22, 32, 42 first silicon layers 23, 33, 43 oxide film layers 24, 34, 44 second silicon layers 25, 35, 45 upper cladding layer 27, 37, 47 germanium rich layer 28, 38, 48 silicon rich layer 31a, 31b p electrode 32a, 32b n electrode 46 cap layer

Claims (6)

A light absorbing layer, at least one pair of layers located under the light absorbing layer and comprising a silicon rich layer and a germanium rich layer, a first silicon layer located under the pair layer, and A surface light detector comprising an oxide film layer located under the silicon layer of the second layer and a second silicon layer located under the oxide film layer,
The light absorbing layer is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1,
The silicon rich layer is a silicon-germanium compound having a composition ratio of silicon of 0.9 to 1, or silicon.
The germanium rich layer is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1,
The thickness of the light absorbing layer is in the range of (m / 4 ± 1/8) times (m is a positive integer) the wavelength of light in the material forming the light absorbing layer,
The thickness of the silicon rich layer is in the range of ((2r-1) / 4 ± 1/8) times (r is a positive integer) the wavelength of light in the material forming the silicon rich layer,
The thickness of the germanium rich layer is in the range of ((2s-1) / 4 ± 1/8) times (s is a positive integer) the wavelength of light in the material forming the germanium rich layer,
The thickness of the first silicon layer is in the range of (p / 2 ± 1/8) times (p is a positive integer) times the wavelength of light in silicon,
The thickness of the oxide layer, Ri range der of the wavelength of light in the material constituting the oxide film layer ((2q-1) / 4 ± 1/8) times (q is a positive integer),
The paired layers are stacked in odd layers, and m is 8 or 10 or 12.
A planar light detector characterized by A light absorbing layer, at least one pair of layers located under the light absorbing layer and comprising a silicon rich layer and a germanium rich layer, a first silicon layer located under the pair layer, and A surface light detector comprising an oxide film layer located under the silicon layer of the second layer and a second silicon layer located under the oxide film layer,
The light absorbing layer is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1,
The silicon rich layer is a silicon-germanium compound having a composition ratio of silicon of 0.9 to 1, or silicon.
The germanium rich layer is germanium or a silicon-germanium compound having a composition ratio of silicon of 0 to 0.1,
The thickness of the light absorbing layer is in the range of (m / 4 ± 1/8) times (m is a positive integer) the wavelength of light in the material forming the light absorbing layer,
The thickness of the silicon rich layer is in the range of ((2r-1) / 4 ± 1/8) times (r is a positive integer) the wavelength of light in the material forming the silicon rich layer,
The thickness of the germanium rich layer is in the range of ((2s-1) / 4 ± 1/8) times (s is a positive integer) the wavelength of light in the material forming the germanium rich layer,
The thickness of the first silicon layer is in the range of (p / 2 ± 1/8) times (p is a positive integer) times the wavelength of light in silicon,
The thickness of the oxide film layer is in the range of ((2q-1) / 4 ± 1/8) times (q is a positive integer) the wavelength of light in the material forming the oxide film layer,
The paired layers are stacked in even layers, and m is 7 or 9 or 11,
A planar light detector characterized by Further comprising a cap layer located on the light absorbing layer,
The cap layer is a silicon-germanium compound or silicon having a composition ratio of silicon of 0.9 to 1,
The thickness of the cap layer is in the range of (f / 4 ± 1/8) times (f is 0 or a positive integer) the wavelength of light in the material forming the cap layer.
The planar light detector according to claim 1 or 2 , wherein 4. The surface light detector according to claim 3 , wherein f is 0 or an even number. 5. The surface light detector according to claim 4 , wherein f is 0 or 2. 4. The surface light detector according to claim 3 , wherein f is an odd number.

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