Epitaxial structure of vertical profile receiving high-speed photodiode and preparation method thereof

Abstract

The invention relates to the technical field of optical communication equipment, in particular to an epitaxial structure of a vertical profile receiving high-speed photodiode and a preparation method of the epitaxial structure. The avalanche multiplication layer of the epitaxial structure of the vertical profile receiving high-speed photodiode is an iAlAs < 0.56 > Sb < 0.44 > material layer or an iAlGa < x > As < 0.56 > Sb < 0.44 > material layer, and x is 0.1-0.2. According to the epitaxial structure, the AlAsSb material or the AlGaAsSb material is used as the avalanche multiplication layer, and the i AlAs < 0.56 > Sb < 0.44 > material or the i AlGaxAs < 0.56 > Sb < 0.44 > material is mainly used for electron ionization, so that the light absorption efficiency of the epitaxial structure of the vertical surface receiving high-speed photodiode is improved, and the excess noise is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication equipment, and in particular to an epitaxial structure of a vertical surface receiving high-speed photodiode and a preparation method thereof. Background Art

[0002] Photodiodes (APDs) are core components of optical communication systems, with the advantages of low dark current and high responsiveness. As the demand for information transmission speed in optical communication networks continues to increase, high-speed optical modules in optical communication systems have also put forward higher requirements for the detection speed of APD detectors, especially for 50GPON products that need to use high-speed APDs above 25G as light receiving devices. Traditional APD detectors include contact layers, absorption layers, charge layers, and avalanche multiplication layers. Due to the demand for high responsiveness of APDs, the photosensitive surface is usually large in area and the absorption layer is relatively thick, resulting in the application rate of APDs being limited to less than 10G, which cannot meet the product requirements of high-speed optical modules. Although waveguide APDs can take into account the needs of miniaturization and high speed, their application in optical modules is very limited due to the difficulty and loss of optical coupling, as well as special requirements for packaging.

[0003] The patent application number is CN101271935A, which discloses a high-speed planar avalanche photodiode. The structure uses InP as the avalanche multiplication layer material, and because the hole ionization coefficient of the InP material is greater than the electron ionization coefficient, the avalanche photodiode made on the n-type substrate has a large excess noise, which affects the further improvement of the receiving sensitivity. Summary of the invention

[0004] In view of the above-mentioned deficiencies of the prior art, the present invention provides an epitaxial structure of a vertical surface receiving high-speed photodiode and a preparation method thereof. The epitaxial structure of the vertical surface receiving high-speed photodiode adopts an AlAsSb material layer or an AlGaAsSb material layer as an avalanche multiplication layer. 0.56 Sb 0.44 Material layer or i AlGa x As 0.56 Sb 0.44 The material layer is mainly electron ionized, so that the epitaxial structure of the vertical surface receiving high-speed photodiode obtained improves the light absorption efficiency and reduces the excess noise, overcomes the technical defects of the existing high-speed planar avalanche photodiode with large excess noise, and improves the receiving sensitivity.

[0005] The present invention is achieved through the following technical solutions:

[0006] The epitaxial structure of a vertical surface receiving high-speed photodiode includes a substrate, a lower contact layer, a buffer layer, an avalanche multiplication layer, a charge layer, a lower gradient layer, a light absorption layer, an upper gradient layer, a diffusion barrier layer, an upper contact layer and an upper electrode layer arranged in sequence from bottom to top, wherein a lower electrode layer is deposited on the lower contact layer.

[0007] The avalanche multiplication layer is iAlAs 0.56 Sb 0.44 Material layer or i AlGa x As 0.56 Sb 0.44 Material layer, x is 0.1-0.2, Ga element varies between 0.1-0.2 according to actual needs, the present invention mainly designs the material of the avalanche multiplication layer to overcome the problem of large excess noise in the prior art using InP as the avalanche multiplication layer material.

[0008] Preferably, the buffer layer is silicon-doped n+AlAs 0.56 Sb 0.44 Material layer, doping amount of silicon element ≥1×10 19 / cm 3 ; The thickness of the buffer layer is 40-60nm.

[0009] Preferably, the thickness of the avalanche multiplication layer is 200-300 nm.

[0010] Preferably, the charge layer is beryllium-doped pAlAs 0.56 Sb 0.44 Material layer or pAlGa x As 0.56 Sb 0.44 , x is 0.1-0.2, and the doping amount of beryllium is 1×10 17 / cm 3 ~1×10 18 / cm 3 ; The thickness of the charge layer is 50-100nm.

[0011] Preferably, the diffusion barrier layer is p+AlAs doped with beryllium 0.56 Sb 0.44 Material layer, beryllium doping amount ≥ 1×10 19 / cm 3 ; The thickness of the diffusion barrier layer is 40-60nm.

[0012] Preferably, the lower contact layer is n+In doped with silicon. 0.53 Ga 0.47 As material layer, silicon doping amount ≥ 1×10 19 / cm 3 .

[0013] The lower gradient layer is i In 0.52 Al 0.23 Ga 0.25 As material layer.

[0014] The light absorbing layer is i In 0.53 Ga 0.47 As material layer.

[0015] The upper gradient layer is i In 0.52 Al 0.23 Ga 0.25 As material layer.

[0016] The upper contact layer is p+In doped with beryllium 0.53 Ga 0.47 As material layer, beryllium doping amount ≥ 1×10 19 / cm 3 .

[0017] Preferably, the thickness of the lower contact layer, the lower gradient layer, the upper gradient layer and the upper contact layer are all 50-100 nm; and the thickness of the light absorption layer is 500-1000 nm.

[0018] Preferably, the charge layer and the lower gradient layer constitute a charge layer-gradient layer unit, and there are one or two charge layer-gradient layer units.

[0019] The present invention also protects a method for preparing the epitaxial structure of the vertical surface receiving high-speed photodiode, which comprises the following steps:

[0020] The lower contact layer, the buffer layer, the avalanche multiplication layer, the heavily doped charge layer, the lower gradient layer, the light absorption layer, the upper gradient layer, the diffusion barrier layer and the upper contact layer are grown in sequence on the substrate by molecular beam epitaxy.

[0021] The buffer layer, the avalanche multiplication layer, the heavily doped charge layer, the lower gradient layer, the light absorption layer, the upper gradient layer, the diffusion barrier layer and the upper contact layer edge are etched to obtain a cylinder.

[0022] After etching, a photosensitive surface is formed on the top surface of the upper contact layer, and a titanium-gold alloy is deposited on the surface of the photosensitive surface by vacuum evaporation to obtain the upper electrode layer.

[0023] A titanium-gold alloy is deposited on the surface of the lower contact layer by vacuum evaporation to obtain the lower electrode layer, and the lower electrode layer and the upper electrode layer are located on the same side.

[0024] Preferably, the diameter of the photosensitive surface is 20-40 μm.

[0025] The lower electrode layer is an arc-shaped electrode layer, and the lower electrode layer surrounds the photosensitive surface, which helps to evenly distribute the electric field inside the diode.

[0026] Preferably, the upper electrode layer is an annular electrode layer, the inner diameter of the upper electrode layer is 10 μm, and the width between the inner diameter and the outer diameter of the annular electrode layer is 2 μm.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention uses i AlAs 0.56 Sb 0.44 Material layer or i AlGa 0.1-0.2 As 0.56 Sb 0.44 The material layer is used as an avalanche multiplying layer material. The material is mainly electron ionized, has lower avalanche excess noise, and a wider bandgap. Compared with the existing photodiode using InP as the avalanche multiplying layer material, it can obtain lower dark current and higher bandwidth, can be used in higher-speed optical transmission systems, and has better receiving sensitivity.

[0029] 2. The epitaxial structure of the vertical surface receiving high-speed photodiode of the present invention is a vertical surface receiving structure. Compared with the waveguide structure, it reduces the light loss caused by optical via coupling between different layers in integrated photonics, and the light coupling method is simple, achieving a good compromise in the speed and responsiveness performance of the photodiode. It is also easy to package as a discrete device, and the packaging form is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the epitaxial structure of a vertical surface receiving high-speed photodiode.

[0031] Figure 2 This is a top view of the photosensitive surface.

[0032] Figure 3 Schematic diagram of the electric field distribution of the epitaxial structure of the vertical surface receiving high-speed photodiode of Example 1.

[0033] Figure 4 Schematic diagram of the electric field distribution of the epitaxial structure of the vertical surface receiving high-speed photodiode of Example 2.

[0034] Figure 5 Schematic diagram of the epitaxial structure of the vertical surface receiving high-speed photodiode of Example 3.

[0035] Figure 6The photoelectric multiplication factor gain and excess noise diagram of the epitaxial structure of the vertical surface receiving high-speed photodiode of Example 1.

[0036] Description of reference numerals:

[0037] 1. Substrate; 2. Lower contact layer; 3. Buffer layer; 4. Avalanche multiplication layer; 5. Charge layer; 6. Lower gradient layer; 7. Light absorption layer; 8. Upper gradient layer; 9. Diffusion barrier layer; 10. Upper contact layer; 11. Upper electrode layer; 12. Lower electrode layer; 13. Photosensitive surface. DETAILED DESCRIPTION

[0038] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0039] In the present invention, Figure 1-Figure 2 As shown, the substrate material is n-type or semi-insulating InP material, and the contact layer is divided into an upper contact layer 10 and a lower contact layer 2. The upper contact layer 10 is heavily doped p+In 0.53 Ga 0.47 As material layer, doped with beryllium, lower contact layer 2 heavily doped with n+In 0.53 Ga 0.47 As material layer, the doping element is silicon, and the doping amount of the upper contact layer 10 and the lower contact layer 2 is 1×10 19 / cm 3 The upper electrode layer 11 is deposited on the photosensitive surface 13. The titanium-gold alloy after the deposition of the upper electrode layer 11 is a ring structure. The upper contact layer 10 is heavily doped with beryllium. In order to form a rapid bending of the energy band at the interface between the upper contact layer 10 and the upper electrode layer 11, the carriers form an ohmic contact with the titanium-gold alloy of the upper electrode layer 11 through the tunnel effect, thereby reducing the series resistance effect of the epitaxial structure of the vertical surface receiving high-speed photodiode during use, which helps to improve the bandwidth.

[0040] Avalanche multiplication layer 4 uses iAlAs 0.56 Sb 0.44 Material layer or i AlGa x As 0.56 Sb 0.44 The material layer is selected according to the specific process requirements. Compared with the existing technology using InP material as the avalanche multiplication layer, the hole ionization coefficient of InP material is greater than the electron ionization coefficient, that is, it is mainly based on hole ionization. The hole ionization coefficient is relatively low and it is easy to cause large noise, thus affecting the final sensitivity.0.56 Sb 0.44 Material layer or i AlGa x As 0.56 Sb 0.44 The material layer is mainly electron ionized, and has a higher electron-hole ionization coefficient ratio than InP materials, which makes the avalanche noise lower when there is gain. In order to achieve the purpose of high-speed communication, the thickness of the avalanche multiplication layer is controlled at 200-300nm, that is, controlled below 300nm, to limit the carrier transit time and achieve higher bandwidth.

[0041] Charge layer 5 is pAlAs 0.56 Sb 0.44 Material layer or pAlGa x As 0.56 Sb 0.44 Material layer, thickness is 50-100nm, doping amount is 1×10 17 / cm 3 ~1×10 18 / cm 3 . Figure 3 and Figure 4 Schematic diagram showing the electric field distribution in the epitaxial structure of the vertical receiving high-speed photodiode. Due to the electric field modulation effect of the charge layer 5, the electric field strength of the avalanche multiplication layer 4 can reach 1×10 5 V / cm or more, and the electric field in the light absorbing layer 7 is limited to 1×10 4 V / cm or less, so that carriers drift to the avalanche multiplication layer 4 under the action of the electric field without avalanche ionization in the light absorption layer 7, and ionization occurs after entering the avalanche multiplication layer 4.

[0042] The charge layer 5 and the adjacent lower gradient layer 6 constitute a charge layer-gradient layer unit. There are one or two charge layer-gradient layer units. In actual situations, the number of charge layer-gradient layer units can be adjusted accordingly according to needs, such as Figure 5 As shown, in the case of relatively high avalanche gain, if the electric field in the absorption layer 5 is still too high, the carriers will be avalanche ionized in the absorption layer 5, causing the dark current and the avalanche noise of the photodiode to increase. The charge layer 5 and the adjacent lower gradient layer 6 can be expanded into two units, such as Figure 5 As shown in the numbers (1) and (2) in the figure, such a design can increase the difference in electric field intensity between the avalanche multiplication layer 4 and the light absorption layer 7, and also make the optical gain change relatively smoothly with voltage. Since the operating voltage of the photodiode is close to the avalanche breakdown voltage during use, and the breakdown voltage is temperature sensitive, the change of the breakdown voltage with temperature will bring about a huge change in the optical gain during use. Therefore, the change of the optical gain with voltage is relatively smooth, which can avoid the above problems and make the photodiode more reliable.

[0043] The lower gradient layer 6 is located between the light absorption layer 7 and the charge layer 5, and the upper gradient layer 8 is located between the light absorption layer 7 and the diffusion barrier layer 9. The lower gradient layer 6 and the upper gradient layer 8 are both i In 0.52 Al 0.23 Ga 0.25 As material layer, thickness is 50-100nm, by controlling the composition of each element to adjust the bandwidth of the lower gradient layer 6 and the upper gradient layer 8 between In 0.53 Ga 0.47 As material layer and AlAs 0.56 Sb 0.44 The bandgap width of the material layer is due to In 0.53 Ga 0.47 As material layer and AlAs 0.56 Sb 0.44 The bandgap width difference of the material layers reaches 0.8 eV. The carriers need to overcome a large energy band difference during transport. The lower gradient layer 6 and the upper gradient layer 8 can form an energy band ladder, which is beneficial to the drift transport of carriers in the device structure.

[0044] The light absorbing layer 7 is an intrinsic i In 0.53 Ga 0.47 As material layer, lattice matching with InP material, and the band gap width is only 0.74eV, so i In 0.53 Ga 0.47 The As material layer has light absorption in a wide wavelength range from visible light to near infrared, and is widely used as a light absorption layer in photodiodes. In the present invention, the thickness of the absorption layer 7 is 500-1000nm. Due to the demand for working speed, the thickness of the light absorption layer 7 needs to be precisely controlled. When the thickness is 1000nm, the photodiode can completely absorb light at 1.55μm, and when the thickness of the light absorption layer 7 is 500nm, the light absorption rate can reach 80% when the surface of the light absorption layer 7 is coated with an anti-reflection layer.

[0045] The diffusion barrier layer 9 is p+AlAs with a high bandgap width. 0.56 Sb 0.44 Material layer, since the upper contact layer 10 is a narrow bandgap p+In 0.53 Ga 0.47 As material layer, in order to reduce the dark current, a high bandgap semiconductor diffusion barrier layer 9 is grown below the narrow bandgap upper contact layer 10 in the electron incident direction, which can block the electrons that form the dark current, thereby ensuring the photocurrent while reducing the dark current, and improving the performance of the epitaxial structure of the vertical surface receiving high-speed photodiode.

[0046] After etching the edges of the buffer layer 3, avalanche multiplication layer 4, heavily doped charge layer 5, lower gradient layer 6, light absorption layer 7, upper gradient layer 8, diffusion barrier layer 9 and upper contact layer 10, a cylinder is obtained. At this time, a photosensitive surface 13 is formed on the upper surface of the upper contact layer 10, and the diameter of the photosensitive surface 13 is 20-40μm.

[0047] After etching, titanium-gold alloy is deposited on the photosensitive surface 13 by vacuum evaporation to obtain the upper electrode layer 11, and titanium-gold alloy is deposited on the surface of the lower contact layer 2 by vacuum evaporation to obtain the lower electrode layer 12, thereby obtaining an epitaxial structure of a vertical surface receiving high-speed photodiode.

[0048] On the epitaxial structure of the vertical surface receiving high-speed photodiode, silicon nitride or benzocyclobutene is covered by a plasma enhanced chemical vapor deposition process to form a passivation layer. After the passivation layer is formed, through holes are etched at the positions of the upper electrode layer 11 and the lower electrode layer 12.

[0049] An anti-radiation anti-reflection layer is covered on the photosensitive surface 13 and above the passivation layer to increase light absorption efficiency.

[0050] The technical solution of the present invention is further explained by using embodiments below, which are specifically as follows:

[0051] Example 1

[0052] A method for preparing an epitaxial structure of a vertical surface receiving high-speed photodiode, such as Figure 3 As shown, the following steps are included:

[0053] S1. Use molecular beam epitaxy to grow n+In on n-type InP substrate 0.53 Ga 0.47 As material layer, doped with Si element, doping amount is 1×10 19 / cm 3 , forming a lower contact layer 2; the method is: Si source, In source, Ga source and As source are mixed, and then n+In is grown on an n-type InP substrate at 420°C. 0.53 Ga 0.47 As material layer, n+In 0.53 Ga 0.47 The thickness of the As material layer is 100 nm.

[0054] S2, using molecular beam epitaxy to grow n+AlAs on the lower contact layer 2 0.56 Sb 0.44 Material layer, doped with Si element, doping amount is 1×10 19 / cm 3, forming a buffer layer 3 by mixing Si source, Al source, As source and Sb source, and then growing n+AlAs on the lower contact layer 2 at 420°C 0.56 Sb 0.44 Material layer, n+AlAs 0.56 Sb 0.44 The thickness of the material layer is 50 nm.

[0055] S3, using molecular beam epitaxy to grow i AlAs on buffer layer 3 0.56 Sb 0.44 The avalanche multiplication layer 4 is formed by mixing Al source, As source and Sb source, and then growing i AlAs on the buffer layer 3 at 420°C. 0.56 Sb 0.44 Material layer, i AlAs 0.56 Sb 0.44 The thickness of the material layer is 200 nm.

[0056] S4, using molecular beam epitaxy to grow p AlAs on the avalanche multiplication layer 4 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 17 / cm 3 , forming the charge layer 5 by mixing Be source, Al source, As source and Sb source, and then growing pAlAs on the avalanche multiplication layer 4 at 420°C 0.56 Sb 0.44 Material layer, pAlAs 0.56 Sb 0.44 The thickness of the material layer is 50 nm.

[0057] S5, using molecular beam epitaxy to grow i In on the charge layer 5 0.52 Al 0.23 Ga 0.25 As material layer, forming the lower gradient layer 6, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the charge layer 5 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 50 nm.

[0058] S6, using molecular beam epitaxy to grow i In on the lower gradient layer 6 0.53 Ga 0.47As material layer, forming the light absorption layer 7, the method is: In source, Ga source and As source are mixed, and then i In is grown on the lower gradient layer 6 at 420°C. 0.53 Ga 0.47 As material layer, i In 0.53 Ga 0.47 The thickness of the As material layer is 500 nm.

[0059] S7, using molecular beam epitaxy to grow i In on the light absorption layer 7 0.52 Al 0.23 Ga 0.25 As material layer, forming the upper gradient layer 8, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the light absorption layer 7 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 100 nm.

[0060] S8, using molecular beam epitaxy to grow p+AlAs on the gradient layer 8 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming a diffusion barrier layer 9 by mixing a Be source, an Al source, an As source and a Sb source, and then growing p+AlAs on the graded layer 8 at 420°C 0.56 Sb 0.44 Material layer, p+AlAs 0.56 Sb 0.44 The thickness of the material layer is 50 nm.

[0061] S9, using molecular beam epitaxy to grow p+In on the diffusion barrier layer 9 0.53 Ga 0.47 As material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming the upper contact layer 10 by mixing Be source, In source, Ga source and As source, and then growing p+In on the diffusion barrier layer 9 at 420°C. 0.53 Ga 0.47 As material layer, p+In 0.53 Ga 0.47 The thickness of the As material layer is 100 nm.

[0062] S10. Use dry etching to etch the buffer layer 3, avalanche multiplication layer 4, heavily doped charge layer 5, lower gradient layer 6, light absorption layer 7, upper gradient layer 8, diffusion barrier layer 9 and the edge of the upper contact layer 10 through a photolithography mask to obtain a cylinder; at this time, a photosensitive surface 13 is formed on the upper surface of the upper contact layer 10, and the diameter of the photosensitive surface 13 is 20μm.

[0063] S11, depositing titanium-gold alloy on the photosensitive surface 13 by vacuum evaporation to obtain an upper electrode layer 11, and depositing titanium-gold alloy on the surface of the lower contact layer 2 by vacuum evaporation to obtain a lower electrode layer 12.

[0064] S12, on the epitaxial structure of the vertical surface receiving high-speed photodiode, covering silicon nitride through a plasma enhanced chemical vapor deposition process to form a passivation layer.

[0065] S13, covering the photosensitive surface 13 and above the passivation layer with an anti-radiation anti-reflection layer to improve the absorption rate of incident light, thereby increasing the final responsiveness of the epitaxial structure of the vertical surface receiving high-speed photodiode.

[0066] Example 2

[0067] A method for preparing an epitaxial structure of a vertical surface receiving high-speed photodiode, such as Figure 4 As shown, the following steps are included:

[0068] S1. Use molecular beam epitaxy to grow n+In on n-type InP substrate 0.53 Ga 0.47 As material layer, doped with Si element, doping amount is 1×10 19 / cm 3 , forming a lower contact layer 2; the method is: Si source, In source, Ga source and As source are mixed, and then n+In is grown on an n-type InP substrate at 420°C. 0.53 Ga 0.47 As material layer, n+In 0.53 Ga 0.47 The thickness of the As material layer is 80 nm.

[0069] S2, using molecular beam epitaxy to grow n+AlAs on the lower contact layer 2 0.56 Sb 0.44 Material layer, doped with Si element, doping amount is 1×10 19 / cm 3 , forming a buffer layer 3 by mixing Si source, Al source, As source and Sb source, and then growing n+AlAs on the lower contact layer 2 at 420°C 0.56 Sb 0.44 Material layer, n+AlAs 0.56 Sb0.44 The thickness of the material layer is 40 nm.

[0070] S3, using molecular beam epitaxy to grow i AlGa on buffer layer 3 0.2 As 0.56 Sb 0.44 The avalanche multiplication layer 4 is formed by mixing Al source, Ga source, As source and Sb source, and then growing iAlGa on the buffer layer 3 at 420°C. 0.2 As 0.56 Sb 0.44 Material layer, i AlGa 0.2 As 0.56 Sb 0.44 The thickness of the material layer is 250 nm.

[0071] S4, using molecular beam epitaxy to grow pAlGa on the avalanche multiplication layer 4 0.1 As 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 18 / cm 3 , forming the charge layer 5 by mixing Be source, Al source, Ga source, As source and Sb source, and then growing p AlGa on the avalanche multiplication layer 4 at 420°C. 0.1 As 0.56 Sb 0.44 Material layer, pAlGa 0.1 As 0.56 Sb 0.44 The thickness of the material layer is 100 nm.

[0072] S5, using molecular beam epitaxy to grow i In on the charge layer 5 0.52 Al 0.23 Ga 0.25 As material layer, forming the lower gradient layer 6, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the charge layer 5 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 70 nm.

[0073] S6, using molecular beam epitaxy to grow i In on the lower gradient layer 6 0.53 Ga 0.47 As material layer, forming the light absorption layer 7, the method is: In source, Ga source and As source are mixed, and then i In is grown on the lower gradient layer 6 at 420°C.0.53 Ga 0.47 As material layer, i In 0.53 Ga 0.47 The thickness of the As material layer is 800 nm.

[0074] S7, using molecular beam epitaxy to grow i In on the light absorption layer 7 0.52 Al 0.23 Ga 0.25 As material layer, forming the upper gradient layer 8, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the light absorption layer 7 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 50 nm.

[0075] S8, using molecular beam epitaxy to grow p+AlAs on the gradient layer 8 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming a diffusion barrier layer 9 by mixing a Be source, an Al source, an As source and a Sb source, and then growing p+AlAs on the graded layer 8 at 420°C 0.56 Sb 0.44 Material layer, p+AlAs 0.56 Sb 0.44 The thickness of the material layer is 60 nm.

[0076] S9, using molecular beam epitaxy to grow p+In on the diffusion barrier layer 9 0.53 Ga 0.47 As material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming the upper contact layer 10 by mixing Be source, In source, Ga source and As source, and then growing p+In on the diffusion barrier layer 9 at 420°C. 0.53 Ga 0.47 As material layer, p+In 0.53 Ga 0.47 The thickness of the As material layer is 50 nm.

[0077] S10. Use dry etching to etch the buffer layer 3, avalanche multiplication layer 4, heavily doped charge layer 5, lower gradient layer 6, light absorption layer 7, upper gradient layer 8, diffusion barrier layer 9 and the edge of the upper contact layer 10 through a photolithography mask to obtain a cylinder; at this time, a photosensitive surface 13 is formed on the upper surface of the upper contact layer 10, and the diameter of the photosensitive surface 13 is 30μm.

[0078] S11, depositing titanium-gold alloy on the photosensitive surface 13 by vacuum evaporation to obtain an upper electrode layer 11, and depositing titanium-gold alloy on the surface of the lower contact layer 2 by vacuum evaporation to obtain a lower electrode layer 12.

[0079] S12, on the epitaxial structure of the vertical surface receiving high-speed photodiode, covering silicon nitride through a plasma enhanced chemical vapor deposition process to form a passivation layer.

[0080] S13, covering the photosensitive surface 13 and above the passivation layer with an anti-radiation anti-reflection layer to improve the absorption rate of incident light, thereby increasing the final responsiveness of the epitaxial structure of the vertical surface receiving high-speed photodiode.

[0081] Example 3

[0082] A method for preparing an epitaxial structure of a vertical surface receiving high-speed photodiode, such as Figure 5 As shown, the following steps are included:

[0083] S1. Use molecular beam epitaxy to grow n+In on n-type InP substrate 0.53 Ga 0.47 As material layer, doped with Si element, doping amount is 1×10 19 / cm 3 , forming a lower contact layer 2; the method is: Si source, In source, Ga source and As source are mixed, and then n+In is grown on an n-type InP substrate at 420°C. 0.53 Ga 0.47 As material layer, n+In 0.53 Ga 0.47 The thickness of the As material layer is 50 nm.

[0084] S2, using molecular beam epitaxy to grow n+AlAs on the lower contact layer 2 0.56 Sb 0.44 Material layer, doped with Si element, doping amount is 1×10 19 / cm 3 , forming a buffer layer 3 by mixing Si source, Al source, As source and Sb source, and then growing n+AlAs on the lower contact layer 2 at 420°C 0.56 Sb 0.44 Material layer, n+AlAs 0.56 Sb0.44 The thickness of the material layer is 60 nm.

[0085] S3, using molecular beam epitaxy to grow i AlAs on buffer layer 3 0.56 Sb 0.44 The avalanche multiplication layer 4 is formed by mixing Al source, As source and Sb source, and then growing i AlAs on the buffer layer 3 at 420°C. 0.56 Sb 0.44 Material layer, i AlAs 0.56 Sb 0.44 The thickness of the material layer is 300 nm.

[0086] S4, using molecular beam epitaxy to grow p AlAs on the avalanche multiplication layer 4 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 17 / cm 3 , forming the charge layer 5 by mixing Be source, Al source, As source and Sb source, and then growing pAlAs on the avalanche multiplication layer 4 at 420°C 0.56 Sb 0.44 Material layer, pAlAs 0.56 Sb 0.44 The thickness of the material layer is 80 nm.

[0087] S5, using molecular beam epitaxy to grow i In on the charge layer 5 0.52 Al 0.23 Ga 0.25 As material layer, forming the lower gradient layer 6, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the charge layer 5 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 80 nm.

[0088] S6, the charge layer 5 and its adjacent lower gradient layer 6 constitute a charge layer-gradient layer unit. In this embodiment, there are two charge layer-gradient layer units, that is, repeat steps S4 and S5, and continue to deposit the charge layer-gradient layer unit on the charge layer-gradient layer unit.

[0089] S7, using molecular beam epitaxy to grow i In on the lower gradient layer 6 0.53 Ga 0.47As material layer, forming the light absorption layer 7, the method is: In source, Ga source and As source are mixed, and then i In is grown on the lower gradient layer 6 at 420°C. 0.53 Ga 0.47 As material layer, i In 0.53 Ga 0.47 The thickness of the As material layer is 1000 nm.

[0090] S8, using molecular beam epitaxy to grow i In on the light absorption layer 7 0.52 Al 0.23 Ga 0.25 As material layer, forming the upper gradient layer 8, the method is: In source, Al source, Ga source and As source are mixed, and then iIn is grown on the light absorption layer 7 at 420°C. 0.52 Al 0.23 Ga 0.25 As material layer, i In 0.52 Al 0.23 Ga 0.25 The thickness of the As material layer is 70 nm.

[0091] S9, using molecular beam epitaxy to grow p+AlAs on the gradient layer 8 0.56 Sb 0.44 Material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming a diffusion barrier layer 9 by mixing a Be source, an Al source, an As source and a Sb source, and then growing p+AlAs on the graded layer 8 at 420°C 0.56 Sb 0.44 Material layer, p+AlAs 0.56 Sb 0.44 The thickness of the material layer is 40 nm.

[0092] S10, using molecular beam epitaxy to grow p+In on the diffusion barrier layer 9 0.53 Ga 0.47 As material layer, doped with Be element, doping amount is 1×10 19 / cm 3 , forming the upper contact layer 10 by mixing Be source, In source, Ga source and As source, and then growing p+In on the diffusion barrier layer 9 at 420°C. 0.53 Ga 0.47 As material layer, p+In 0.53 Ga 0.47 The thickness of the As material layer is 50 nm.

[0093] S11. Use dry etching to etch the buffer layer 3, avalanche multiplication layer 4, heavily doped charge layer 5, lower gradient layer 6, light absorption layer 7, upper gradient layer 8, diffusion barrier layer 9 and the edge of the upper contact layer 10 through a photolithography mask to obtain a cylinder; at this time, a photosensitive surface 13 is formed on the upper surface of the upper contact layer 10, and the diameter of the photosensitive surface 13 is 40μm.

[0094] S12, depositing titanium-gold alloy on the photosensitive surface 13 by vacuum evaporation to obtain the upper electrode layer 11, and depositing titanium-gold alloy on the surface of the lower contact layer 2 by vacuum evaporation to obtain the lower electrode layer 12.

[0095] S13, on the epitaxial structure of the vertical surface receiving high-speed photodiode, silicon nitride is covered by a plasma enhanced chemical vapor deposition process to form a passivation layer.

[0096] S14, covering the photosensitive surface 13 and above the passivation layer with an anti-radiation anti-reflection layer to improve the absorption rate of incident light, thereby increasing the final responsivity of the epitaxial structure of the vertical surface receiving high-speed photodiode.

[0097] The following study is conducted by taking the epitaxial structure of the vertical surface receiving high-speed photodiode obtained in Example 1 as an example. The research method and results are as follows:

[0098] The photodiode according to the present invention has extremely low excess noise due to the AlAsSb material. The excess noise of the epitaxial structure of the vertical surface receiving high-speed photodiode in Example 1 is as follows: Figure 6 As shown, the solid line is the theoretical value based on the McIntyre model, and the green dot is the relationship between the excess noise and photomultiplier gain of the epitaxial structure of the vertical surface receiving high-speed photodiode based on AlAsSb material. The results show that the k value is close to 0.12, while the excess noise k value of the vertical surface receiving high-speed photodiode based on InP material is as high as 0.4. The results show that AlAsSb material is more beneficial than InP material in preparing the avalanche multiplication layer of high-speed photodiode to reduce excess noise and thus obtain high sensitivity.

[0099] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, they are also intended to be included.

Claims

1. An epitaxial structure of a vertical surface receiving high-speed photodiode, comprising a substrate (1), a lower contact layer (2), a buffer layer (3), an avalanche multiplication layer (4), a charge layer (5), a lower gradient layer (6), a light absorption layer (7), an upper gradient layer (8), a diffusion barrier layer (9), an upper contact layer (10) and an upper electrode layer (11) arranged in sequence from bottom to top, wherein a lower electrode layer (12) is deposited on the lower contact layer (2), characterized in that: The avalanche multiplication layer (4) is iAlAs 0.56 Sb 0.44 Material layer or i AlGa x As 0.56 Sb 0.44 Material layer, x is 0.1-0.

2.

2. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 1, characterized in that: The thickness of the avalanche multiplication layer (4) is 200-300 nm.

3. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 1, characterized in that: The charge layer (5) is pAlAs doped with beryllium 0.56 Sb 0.44 Material layer or p AlGa x As 0.56 Sb 0.44 Material layer, x is 0.1-0.2, and the doping amount of beryllium is 1×10 17 / cm 3 ~1×10 18 / cm 3 , the thickness of the charge layer (5) is 50-100 nm.

4. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 1, characterized in that: The buffer layer (3) is n+AlAs doped with silicon. 0.56 Sb 0.44 Material layer, silicon doping amount ≥ 1×10 19 / cm 3 , the thickness of the buffer layer (3) is 40-60nm.

5. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 1, characterized in that: The diffusion barrier layer (9) is p+AlAs doped with beryllium 0.56 Sb 0.44 Material layer, beryllium doping amount ≥ 1×10 19 / cm 3 , the thickness of the diffusion barrier layer (9) is 40-60nm.

6. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 1, characterized in that: The lower contact layer (2) is n+In doped with silicon. 0.53 Ga 0.47 As material layer, silicon doping amount ≥ 1×10 19 / cm 3 ; The lower gradient layer (6) is i In 0.52 Al 0.23 Ga 0.25 As material layer; The light absorbing layer (7) is i In 0.53 Ga 0.47 As material layer; The upper gradient layer (8) is i In 0.52 Al 0.23 Ga 0.25 As material layer; The upper contact layer (10) is p+In doped with beryllium 0.53 Ga 0.47 As material layer, beryllium doping amount ≥ 1×10 19 / cm 3 .

7. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 6, characterized in that: The thickness of the lower contact layer (2), the lower gradient layer (6), the upper gradient layer (8) and the upper contact layer (10) are all 50-100 nm; the thickness of the light absorption layer (7) is 500-1000 nm.

8. A method for preparing an epitaxial structure of a vertical surface receiving high-speed photodiode according to any one of claims 1 to 7, characterized in that: The steps include: The lower contact layer (2), the buffer layer (3), the avalanche multiplication layer (4), the heavily doped charge layer (5), the lower gradient layer (6), the light absorption layer (7), the upper gradient layer (8), the diffusion barrier layer (9) and the upper contact layer (10) are sequentially grown on the substrate (1) by molecular beam epitaxy; Etching the edges of the buffer layer (3), the avalanche multiplication layer (4), the heavily doped charge layer (5), the lower gradient layer (6), the light absorption layer (7), the upper gradient layer (8), the diffusion barrier layer (9) and the upper contact layer (10) to obtain a cylinder; After etching, a photosensitive surface (13) is formed on the top surface of the upper contact layer (10), and a titanium-gold alloy is deposited on the surface of the photosensitive surface (13) by vacuum evaporation to obtain the upper electrode layer (11); A titanium-gold alloy is deposited on the surface of the lower contact layer (2) by vacuum evaporation to obtain the lower electrode layer (12), wherein the lower electrode layer (12) and the upper electrode layer (11) are located on the same side.

9. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 8, characterized in that: The diameter of the photosensitive surface (13) is 20-40 μm; The lower electrode layer (12) is an arc-shaped electrode layer, and the lower electrode layer (12) surrounds the photosensitive surface (13).

10. The epitaxial structure of the vertical surface receiving high-speed photodiode according to claim 8, characterized in that: The upper electrode layer (11) is an annular electrode layer, the inner diameter of the upper electrode layer (11) is 10 μm, and the width between the inner diameter and the outer diameter of the annular electrode layer is 2 μm.

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