InGaAs single-photon avalanche detector and preparation method thereof

Abstract

The invention discloses an InGaAs single-photon avalanche detector and a preparation method thereof. The InGaAs single-photon avalanche detector comprises an InP substrate, an InP buffer layer, an i-In < x > Ga < 1-x > As buffer layer, an i-In < 0.53 > Ga < 0.47 > As absorption layer, an i-In < 0.59 > GAsP transition layer, an In < x > GaAsP electric field smooth transition layer, an InP charge layer and an i-InP diffusion layer which grow from bottom to top. A dielectric film is arranged on the upper surface of the i-InP diffusion layer, surface-doped diffusion holes are formed in the dielectric film, and Al2O3 / HfO2 passivation layers are formed on the upper surfaces of the dielectric film and the diffusion holes; according to the invention, tunneling electric leakage can be reduced, surface electric leakage can be suppressed, dark current of the device is reduced, dark counting of the device is reduced, the detection rate of the device is improved, weak light detection with a high signal-to-noise ratio is realized, secondary diffusion is not needed, and the difficulty and cost of a chip preparation process are greatly reduced.

Description

Technical Field

[0001] This invention relates to the technical field of single-photon avalanche detectors, and in particular to an InGaAs single-photon avalanche detector and its fabrication method. Background Technology

[0002] Currently, most commonly used lidar systems utilize silicon-based photodetectors with a detection wavelength of 905nm. These detectors have weak resistance to weather interference and poor penetration in adverse weather conditions such as rain and fog. Furthermore, the 905nm band is considered dangerous for the human eye, necessitating power limitation to reduce eye damage. InGaAs, a typical III-V group semiconductor material, possesses high quantum efficiency and high electron mobility. Its operating wavelength is 1550nm, falling within the eye-safe band. Moreover, it exhibits high contrast in low-visibility environments such as fog and haze, demonstrating excellent penetration and significantly extended detection range. In recent years, research on InGaAs single-photon detectors has increased considerably.

[0003] However, InGaAs / InP materials have many internal defects. Defects and impurities during the epitaxial layer growth process can lead to an increase in dark current caused by GR current. At the same time, the shunt current related to surface passivation can also increase the dark current, which in turn leads to a significant increase in the dark count of the device. This affects the detector rate and the probability of back pulses. The detector rate and dark count are directly related to the performance of the InGaAs single-photon detector chip itself. Therefore, it is very important to reduce the dark current of the device, thereby reducing the dark count caused by avalanche triggered by charge carriers in the dark current, and improving the detector rate of the device. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing an InGaAs single-photon avalanche detector and its fabrication method, based on intrinsic InGaAs... 0.59 A further gradient of weakly doped In is added to the GaAsP transition layer. x The GaAsP transition layer features a synchronously varying In composition and doping concentration to optimize the electric field distribution of the device and reduce tunneling leakage current. Simultaneously, an Al2O3 / HfO2 bilayer passivation is employed to reduce surface dangling bonds and suppress surface leakage current. The aim is to further reduce the tunneling and surface leakage current of the device, thereby reducing the probability of carrier-triggered avalanche in the dark current, reducing the device's dark count, improving the device's detectivity, and achieving high signal-to-noise ratio weak light detection.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: an InGaAs single-photon avalanche detector, comprising an InP substrate, an n-type InP buffer layer grown from bottom to top on the InP substrate, and a slightly negative mismatched i-In... x Ga 1- x As buffer layer, i-In0.53 Ga 0.47 As absorption layer, i-In 0.59 GAsP transition layer, In x The GaAsP electric field smoothing transition layer, the n-type InP charge layer, and the i-InP diffusion layer; wherein, the In... x The GaAsP electric field smoothing transition layer consists of several layers of gradually weakened doped n-type In. x A GaAsP monolayer is provided with a SiO2 / SiN dielectric film on the upper surface of the i-InP diffusion layer. Several surface Zn-doped diffusion holes are formed on the SiO2 / SiN dielectric film. An Al2O3 / HfO2 passivation layer is formed on the upper surface of the SiO2 / SiN dielectric film and the diffusion holes. A P electrode and an N electrode and an AR reflective layer are formed on the lower surface of the InP substrate. Before growing the AR reflective layer, the InP substrate is thinned and polished. An InP micro / nano light-trapping structure grating is fabricated in the region corresponding to the photosensitive region of the InP substrate using electron beam lithography.

[0006] Furthermore, in the slightly negative mismatched i-In x Ga 1-x In the As buffer layer, the value of X ranges from 0.53 to 0.58, and is used to reduce i-In. 0.53 Ga 0.47 Defects in the As absorption layer reduce dark counts caused by nonradiative recombination, while also lowering the probability of afterpulse caused by defect recombination.

[0007] Furthermore, the In x The GaAsP electric field smoothing transition layer consists of 1-5 layers of gradually weakened doped n-type In. x GaAsP monolayers are used to smooth the electric field and reduce tunneling leakage current under high voltage.

[0008] Furthermore, the thickness of the SiO2 / SiN dielectric film is 100-1000 nm; the pore size of the diffusion pore is 15-60 μm.

[0009] Furthermore, the InP micro-nano light-trapping structure grating is a rectangular array with a side length of 120-200nm, and the spacing between individual grating units is 120-200nm. The grating period is filled according to the size of the photosensitive region to improve the light absorption rate.

[0010] A method for fabricating an InGaAs single-photon avalanche detector according to the above-mentioned method includes the following steps:

[0011] S1. An n-type InP buffer layer is grown on an InP substrate using MOCVD or MBE technology. The thickness of the buffer layer is 200-800 nm.

[0012] S2, Growing slightly negatively mismatched i-In on the buffer layer x Ga 1-x As a buffer layer;

[0013] S3, in i-In x Ga 1-x An intrinsic i-In0.53Ga0.47As absorber layer with a thickness of 1.5-2.5 μm is grown on the As buffer layer;

[0014] S4, in i-In 0.53 Ga 0.47 Intrinsic i-In grows on the As absorption layer 0.59 GaAsP transition layer with a thickness of 50–200 nm;

[0015] S5, in i-In 0.59 Several layers of gradually weakly doped In are grown on the GaAsP transition layer. x GaAsP electric field smoothing transition layer, with a total thickness of 150-300nm;

[0016] S6, In x A lightly doped n-type InP charge layer with a thickness of 200–600 nm is grown on a GaAsP electric field smoothing transition layer.

[0017] S7. An intrinsically undoped InP diffusion layer with a thickness of 2.5–4.5 μm is grown on the n-type InP charge layer.

[0018] S8. A high-temperature resistant SiO2 or SiN dielectric film with a thickness of 100-1000 nm is grown on the surface of the intrinsic InP layer. Diffusion holes are formed by photolithography and etching technology, and then Zn element is doped by MOCVD technology to form the P region.

[0019] S9. After diffusion is complete, without removing the dielectric film, ALD growth of double-layer passivated Al2O3 / HfO2 is carried out directly with thicknesses of 70nm / 50nm.

[0020] After the S10 and passivation dielectric layers are grown, the contact holes are opened using photolithography and etching processes. Then, the P / N electrodes and AR reflective layers are fabricated by EB evaporation to complete the fabrication of the InGaAs single-photon avalanche detector. Before growing the AR reflective layer, the substrate needs to be thinned and polished. Then, InP micro / nano light-trapping gratings are fabricated on the photosensitive substrate using electron beam lithography to improve the light absorption rate.

[0021] Furthermore, step S2 includes:

[0022] Growing slightly mismatched i-In on the buffer layer x Ga 1-x As a buffer layer, where the value of X ranges from 0.53 to X < 0.58, and the thickness is 10-50 nm, the purpose of which is to reduce defects in the absorption layer.

[0023] Furthermore, step S5 includes:

[0024] In x The GaAsP electric field smoothing transition layer consists of 1-5 layers of gradually weakly doped n-type In. x GaAsP monolayer.

[0025] Furthermore, step S8 includes:

[0026] A high-temperature resistant SiO2 or SiN dielectric film with a thickness of 300–700 nm is grown on the surface of the intrinsic InP layer. The SiO2 growth temperature is 280 °C, the pressure is 0.83 Pa, the ICP power is 450 W, and the SiH4 to O2 flow ratio is approximately 10.1:1. The SiN growth temperature is 230 °C, the pressure is 7 Pa, the ICP power is 350 W, the SiH4 to O2 flow ratio is approximately 13:1, and the refractive index is 2.12. Based on the above epitaxial structure, the InGaAs single-photon detector only requires one diffusion, and the diffusion mask is retained and does not need to be removed. After diffusion, double-layer passivation is performed directly. The diffusion aperture is 15–60 μm; the Zn diffusion temperature is 510–560 °C, the diffusion pressure is 60–150 Tor, the diffusion time is 1500–2000 s, and the diffusion flow rate is 60–150 cc.

[0027] Furthermore, step S10 includes:

[0028] After the passivation dielectric layer is grown, the contact holes are opened using photolithography and etching processes. Then, the P / N electrodes and AR reflective layer are fabricated by EB evaporation to complete the fabrication of the InGaAs single-photon avalanche detector. Before growing the AR reflective layer, the InP substrate is thinned and polished. Then, InP micro-nano light-trapping structure gratings are fabricated in the region corresponding to the photosensitive area of ​​the InP substrate using electron beam lithography. The grating size is a rectangular array with a side length of 120-200 nm, and the spacing between individual grating units is 120-200 nm. The grating period is filled according to the size of the photosensitive area to improve the light absorption rate.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] This invention further adds a gradient weakly doped InxGaAsP transition layer on top of the i-In0.59GaAsP transition layer. The In composition and doping concentration are synchronously gradiented, causing the bandgap to gradually change from 0.74 eV to 1.2 eV, optimizing the electric field distribution of the device and reducing tunneling leakage current. Simultaneously, a SiO2 / SiN dielectric film with a thickness of 100-1000 nm is used, and diffusion holes with a diameter of 15-60 μm are formed through photolithography and etching techniques, ultimately forming an Al2O3 / HfO2 double-layer passivation. This reduces surface dangling bonds, suppresses surface leakage current, and further reduces the dark current of the device. This, in turn, reduces the probability of carrier-triggered avalanche in the dark current, lowers the dark count, and improves the detector rate, achieving high signal-to-noise ratio weak light detection. Furthermore, this invention only requires one Zn diffusion, eliminating the need for secondary diffusion, significantly reducing the difficulty and cost of chip fabrication. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the present invention.

[0032] Figure 2 This is a comparison diagram of the dark current of the present invention and the prior art.

[0033] Figure 3 This is a comparison diagram of the PDE of the present invention and the prior art. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] See Figure 1 As shown, the InGaAs single-photon avalanche detector provided in this embodiment includes an InP substrate 1, an n-type InP buffer layer 2 grown from bottom to top on the InP substrate 1, and a slightly negative mismatched i-In x Ga 1-x As buffer layer 3, i-In 0.53 Ga 0.47 As absorption layer 4, i-In 0.59 GAsP transition layer 5, In x GaAsP electric field smoothing transition layer 6, n-type InP charge layer 7, and i-InP diffusion layer 8.

[0036] A buffer layer 2 of n-type InP with a thickness of 200–800 nm is grown on an InP substrate 1 using MOCVD or MBE technology; a slightly negative mismatched i-InP layer is then formed. x Ga 1-x In buffer layer 3 (As), the value of X ranges from 0.53 to 0.58, which is used to reduce i-In. 0.53 Ga 0.47Defects in the As absorption layer 4 are reduced to decrease dark counts caused by nonradiative recombination, while also lowering the afterpulse probability due to defect recombination; then intrinsic i-In is grown. 0.53 Ga 0.47 As absorber layer 4, with a thickness of 1.5–2.5 μm; intrinsically i-In grown. 0.59 GaAsP transition layer 5, with a thickness of 50–200 nm; In x The GaAsP electric field smoothing transition layer 6 includes 1-5 layers of gradually weakened doped n-type In. x A GaAsP monolayer is preferred to smooth the electric field and reduce tunneling leakage current under high voltage. A three-layer gradient weakly doped n-type In is also preferred. x GaAsP electric field smoothing transition layer 6 has In composition of 0.59 / 0.73 / 0.92, doping concentration of 1E17 / 2E17 / 2E17, and thickness of 20-60 nm / 20-60 nm / 80-150 nm, respectively; followed by a low-doped n-type InP charge layer 7 with a thickness of 200-600 nm; and an intrinsically undoped i-InP diffusion layer 8 with a thickness of 2.5-4.5 μm.

[0037] A high-temperature resistant SiO2 dielectric film 12 with a thickness of 300–700 nm is grown on the surface of the intrinsic i-InP diffusion layer 8. Diffusion pores are formed by photolithography and etching. Then, Zn is doped by MOCVD to form a P region 13 with a diffusion pore diameter of 15–60 μm, a Zn diffusion temperature of 510–560 °C, a diffusion pressure of 60–150 Tor, a diffusion time of 1500–2000 s, and a diffusion flow rate of 60–150 cc.

[0038] After diffusion is complete, there is no need to remove the diffusion mask medium layer. ALD growth of Al2O3 / HfO2 passivation layer 14 is performed directly with thicknesses of 70nm / 50nm.

[0039] After the passivation dielectric layer is grown, semiconductor technologies such as photolithography and etching are used to open the contact holes. Then, P / N electrodes 9 and 10 and the AR reflective layer 11 are fabricated using EB evaporation. P electrode 9 is formed inside the diffusion hole, and N electrode 10 and AR reflective layer 11 are formed on the lower surface of InP substrate 1. Before growing the AR reflective layer, the substrate needs to be thinned and polished. Then, InP micro / nano light-trapping gratings are fabricated in the region corresponding to the photosensitive area of ​​the substrate using electron beam lithography. The gratings are square arrays with a width of 120-200 nm and a spacing of 120-200 nm. The grating period is filled according to the size of the photosensitive area to improve the light absorption rate.

[0040] The fabricated single-photon detector was packaged and tested. Test results showed that the new structure exhibited a dark current as low as 0.3 pA, a dark count of only 13 kHz, and a detectivity of 28% at a test temperature of -40°C. (See also...) Figure 2 and Figure 3 The figure shown is a comparison diagram of dark current and PDE between the present invention and the prior art.

[0041] A method for fabricating an InGaAs single-photon avalanche detector according to the above-described method includes the following steps:

[0042] S1. Use MOCVD or MBE technology to grow an n-type InP buffer layer on an InP substrate. The thickness of the buffer layer is 200-800 nm.

[0043] S2, Growing slightly negatively mismatched i-In on the buffer layer x Ga 1-x As a buffer layer, where the value of X ranges from 0.53 to X < 0.58, and the thickness is 10-50 nm, to reduce defects in the absorption layer;

[0044] S3, in i-In x Ga 1-x An intrinsic i-In0.53Ga0.47As absorber layer with a thickness of 1.5-2.5 μm is grown on the As buffer layer;

[0045] S4, in i-In 0.53 Ga 0.47 Intrinsic i-In grows on the As absorption layer 0.59 GaAsP transition layer with a thickness of 50–200 nm;

[0046] S5, in i-In 0.59 Gradually weakened In doping grown on the GaAsP transition layer x The GaAsP electric field smoothing transition layer has a total thickness of 150-300 nm; the In x The GaAsP electric field smoothing transition layer consists of 1-5 layers of gradually weakened doped n-type In. x A GaAsP monolayer, preferably a three-layer gradually weakly doped In. x The GaAsP electric field smoothing transition layer has an In composition of 0.59 / 0.73 / 0.92, a doping concentration of 1E17 / 2E17 / 2E17, and a thickness of 20–60 nm / 20–60 nm / 80–150 nm.

[0047] S6, In x A lightly doped n-type InP charge layer with a thickness of 200–600 nm is grown on a GaAsP electric field smoothing transition layer.

[0048] S7. An intrinsically undoped InP diffusion layer with a thickness of 2.5–4.5 μm is grown on the n-type InP charge layer.

[0049] S8. A high-temperature resistant SiO2 or SiN dielectric film with a thickness of 100–1000 nm is grown on the surface of the intrinsic InP layer. Diffusion holes are formed using photolithography and etching techniques, followed by Zn doping using MOCVD technology to form the P-region. Specifically, a high-temperature resistant SiO2 or SiN dielectric film with a thickness of 300–700 nm is grown on the surface of the intrinsic InP layer. The SiO2 growth temperature is 280℃, the pressure is 0.83 Pa, the ICP power is 450 W, and the SiH4 to O2 flow ratio is approximately 10.1:1. The SiN... The growth temperature is 230℃, the pressure is 7Pa, the ICP power is 350W, the SiH4 to O2 flow ratio is approximately 13:1, and the refractive index is 2.12. Based on the above epitaxial structure, the InGaAs single-photon detector only requires one diffusion, and the diffusion mask is retained and does not need to be removed. After diffusion, double-layer passivation is performed directly. The diffusion aperture is 15-60μm; the Zn diffusion temperature is 510-560℃, the diffusion pressure is 60-150Tor, the diffusion time is 1500-2000s, and the diffusion flow rate is 60-150cc.

[0050] S9. After diffusion is complete, without removing the dielectric film, ALD growth of double-layer passivated Al2O3 / HfO2 is carried out directly with thicknesses of 70nm / 50nm.

[0051] After the S10 and passivation dielectric layers are grown, the contact holes are opened using photolithography and etching processes. Then, the P / N electrodes and AR reflective layer are fabricated by EB evaporation to complete the fabrication of the InGaAs single-photon avalanche detector. Before growing the AR reflective layer, the InP substrate is thinned and polished. Then, InP micro-nano light-trapping gratings are fabricated in the region corresponding to the photosensitive area of ​​the InP substrate using electron beam lithography. The grating size is a rectangular array with a side length of 120-200 nm, and the spacing between individual grating units is 120-200 nm. The grating period is filled according to the size of the photosensitive area to improve the light absorption rate.

[0052] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any changes made in accordance with the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. An InGaAs single-photon avalanche detector, comprising an InP substrate, characterized in that: Includes a buffer layer of n-type InP grown from bottom to top on an InP substrate, and slightly negative mismatched i-In x Ga 1-x As buffer layer, i-In 0.53 Ga 0.47 As absorption layer, i-In 0.59 GAsP transition layer, In x The GaAsP electric field smoothing transition layer, the n-type InP charge layer, and the i-InP diffusion layer; wherein, the In... x The GaAsP electric field smoothing transition layer consists of several layers of gradually weakened doped n-type In. x A GaAsP monolayer is provided with a SiO2 / SiN dielectric film on the upper surface of the i-InP diffusion layer. Several surface Zn-doped diffusion holes are formed on the SiO2 / SiN dielectric film. An Al2O3 / HfO2 passivation layer is formed on the upper surface of the SiO2 / SiN dielectric film and the diffusion holes. A P electrode and an N electrode and an AR reflective layer are formed on the lower surface of the InP substrate. Before growing the AR reflective layer, the InP substrate is thinned and polished. An InP micro / nano light-trapping structure grating is fabricated in the region corresponding to the photosensitive region of the InP substrate using electron beam lithography.

2. The InGaAs single-photon avalanche detector according to claim 1, characterized in that: In the slight negative mismatch of i-In x Ga 1-x In the As buffer layer, the value of X ranges from 0.53 to 0.58, and is used to reduce i-In. 0.53 Ga 0.47 Defects in the As absorption layer reduce dark counts caused by nonradiative recombination, while also lowering the probability of afterpulse caused by defect recombination.

3. The InGaAs single-photon avalanche detector according to claim 1, characterized in that: The In x The GaAsP electric field smoothing transition layer consists of 1-5 layers of gradually weakened doped n-type In. x GaAsP monolayers are used to smooth the electric field and reduce tunneling leakage current under high voltage.

4. The InGaAs single-photon avalanche detector according to claim 1, characterized in that: The thickness of the SiO2 / SiN dielectric film is 100-1000 nm; the pore size of the diffusion pore is 15-60 μm.

5. An InGaAs single-photon avalanche detector according to claim 1, characterized in that: The InP micro-nano light-trapping structure grating is a rectangular array with a side length of 120-200nm. The spacing between individual grating units is 120-200nm, and the grating period is filled according to the size of the photosensitive region to improve the light absorption rate.

6. A method for fabricating an InGaAs single-photon avalanche detector according to any one of claims 1-5, characterized in that, Includes the following steps: S1. An n-type InP buffer layer is grown on an InP substrate using MOCVD or MBE technology. The thickness of the buffer layer is 200-800 nm. S2, Growing slightly negatively mismatched i-In on the buffer layer x Ga 1-x As a buffer layer; S3, in i-In x Ga 1-x An intrinsic i-In0.53Ga0.47As absorber layer with a thickness of 1.5-2.5 μm is grown on the As buffer layer; S4, in i-In 0.53 Ga 0.47 Intrinsic i-In grows on the As absorption layer 0.59 GaAsP transition layer with a thickness of 50–200 nm; S5, in i-In 0.59 Several layers of gradually weakly doped In are grown on the GaAsP transition layer. x GaAsP electric field smoothing transition layer, with a total thickness of 150-300nm; S6, In x A lightly doped n-type InP charge layer with a thickness of 200–600 nm is grown on a GaAsP electric field smoothing transition layer. S7. An intrinsically undoped InP diffusion layer with a thickness of 2.5–4.5 μm is grown on the n-type InP charge layer. S8. A high-temperature resistant SiO2 or SiN dielectric film with a thickness of 100-1000 nm is grown on the surface of the intrinsic InP layer. Diffusion holes are formed by photolithography and etching technology, and then Zn element is doped by MOCVD technology to form the P region. S9. After diffusion is complete, without removing the dielectric film, ALD growth of double-layer passivated Al2O3 / HfO2 is carried out directly with thicknesses of 70nm / 50nm. After the S10 and passivation dielectric layers are grown, the contact holes are opened using photolithography and etching processes. Then, the P / N electrodes and AR reflective layers are fabricated by EB evaporation to complete the fabrication of the InGaAs single-photon avalanche detector. Before growing the AR reflective layer, the substrate needs to be thinned and polished. Then, InP micro / nano light-trapping gratings are fabricated on the photosensitive substrate using electron beam lithography to improve the light absorption rate.

7. The method for fabricating an InGaAs single-photon avalanche detector according to claim 6, characterized in that, Step S2 includes: Growing slightly mismatched i-In on the buffer layer x Ga 1-x As a buffer layer, where the value of X ranges from 0.53 to X < 0.58, and the thickness is 10-50 nm, to reduce defects in the absorption layer.

8. The method for fabricating an InGaAs single-photon avalanche detector according to claim 6, characterized in that, Step S5 includes: In x The GaAsP electric field smoothing transition layer consists of 1-5 layers of gradually weakly doped n-type In. x GaAsP monolayer.

9. The method for fabricating an InGaAs single-photon avalanche detector according to claim 6, characterized in that, Step S8 includes: A high-temperature resistant SiO2 or SiN dielectric film with a thickness of 300–700 nm is grown on the surface of the intrinsic InP layer. The SiO2 growth temperature is 280 °C, the pressure is 0.83 Pa, the ICP power is 450 W, and the SiH4 to O2 flow ratio is approximately 10.1:

1. The SiN growth temperature is 230 °C, the pressure is 7 Pa, the ICP power is 350 W, the SiH4 to O2 flow ratio is approximately 13:1, and the refractive index is 2.

12. Based on the above epitaxial structure, the InGaAs single-photon detector only requires one diffusion, and the diffusion mask is retained and does not need to be removed. After diffusion, double-layer passivation is performed directly. The diffusion aperture is 15–60 μm; the Zn diffusion temperature is 510–560 °C, the diffusion pressure is 60–150 Tor, the diffusion time is 1500–2000 s, and the diffusion flow rate is 60–150 cc.

10. The method for fabricating an InGaAs single-photon avalanche detector according to claim 9, characterized in that, Step S10 includes: After the passivation dielectric layer is grown, the contact holes are opened using photolithography and etching processes. Then, the P / N electrodes and AR reflective layer are fabricated by EB evaporation to complete the fabrication of the InGaAs single-photon avalanche detector. Before growing the AR reflective layer, the InP substrate is thinned and polished. Then, InP micro-nano light-trapping structure gratings are fabricated in the region corresponding to the photosensitive area of ​​the InP substrate using electron beam lithography. The grating size is a rectangular array with a side length of 120-200 nm, and the spacing between individual grating units is 120-200 nm. The grating period is filled according to the size of the photosensitive area to improve the light absorption rate.

Images