Preparation method of external absorption inhibition structure of avalanche region of indium gallium arsenide Geiger avalanche photodetector

Abstract

The application discloses a preparation method of an avalanche region external absorption inhibition structure of an indium gallium arsenide Geiger avalanche detector, and is based on an absorption multiplication separation Geiger avalanche diode structure, uses indium gallium arsenide as an absorption layer material, uses indium aluminum arsenide as a band gradual change material, and uses indium phosphide as a multiplication layer material. A new type of PN junction preparation method of a Zn protection ring doped region combined with a groove diffusion main junction is adopted to relieve the siphoning effect of an avalanche electric field on external absorption carriers of an avalanche region in traditional twice diffusion main junctions without a protection ring, solve an internal and external electric field control problem of the avalanche region, combine strong absorption of 1.06 mu m and 1.55 mu m wavelength incident photons outside the avalanche region by a thick aluminum film, effectively shield incident light outside the avalanche region, solve the problem that external absorption carriers of the avalanche region diffuse to the avalanche region, and solve the problem that the light-generated current is in response to tailing caused by carrier absorption and diffusion outside the avalanche region from two aspects of a light-generated carrier diffusion path and a photon absorption path.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device technology, and relates to an indium gallium arsenide Geiger avalanche detector, specifically a method for preparing an avalanche region external absorption suppression structure for an indium gallium arsenide Geiger avalanche detector. Background Technology

[0002] A Geiger avalanche detector is a semiconductor optoelectronic device with single-photon sensitivity based on a Geiger avalanche diode structure. It is primarily used for single-photon laser ranging and weak light photon counting, and has wide applications in ultra-long-distance deep-space laser ranging, space-to-ground quantum communication, and solar spectral irradiance calibration. The basic principle of a Geiger avalanche detector is to utilize the ultra-high gain obtained by periodically operating under high electric field conditions in a breakdown state. This allows a single photon to undergo collisional ionization, generating a chain reaction of avalanche amplification, which triggers a large avalanche current, thus achieving single-photon detection.

[0003] Indium gallium arsenide (IGAA) Geiger avalanche detectors primarily meet the requirements for single-photon detection in the near-infrared band of 1000nm–1700nm. However, compared to silicon-based Geiger avalanche detectors, IGAA, being a group III-V compound material, is mainly obtained through heteroepitaxial growth on an indium phosphide substrate. Consequently, it has lower purity and more defects, making it more prone to carrier trapping by material trap centers under high electric field conditions. This results in a certain probability that the optical signal received in the previous detection cycle will be delayed in conversion into an electrical signal, potentially affecting the operation of the next detection cycle. This is known as a significant after-pulse effect. Since the electrical signal arrives significantly later than the optical signal, it ultimately manifests as a response tailing phenomenon. Compared to the sub-ns pulse width of the optical signal, the optical signal can even tail for more than 100ns, reducing the signal detection accuracy.

[0004] The main reasons for the response tailing phenomenon in current InGaAsP Geiger avalanche detectors are as follows: First, the avalanche electric field of the traditional unprotected, double-diffused main junction exhibits a gradually increasing trend from the periphery to the center. Therefore, the avalanche region has a siphon effect on carriers absorbed outside the avalanche region, collecting carriers from the outer edges into the avalanche region. Due to the longer path length of carriers at the periphery, this leads to response lag. Second, the traditional InGaAsP transition layer generally adopts a three-layer bandgap structure. Due to discontinuities, carrier accumulation can still occur, leading to response lag. Third, if the incident light cannot be completely concentrated in the avalanche region, some of it will still be absorbed outside the avalanche region, also causing response lag. Therefore, addressing these factors is crucial to effectively solve the problem of response tailing caused by the absorption and diffusion of carriers outside the avalanche region. Summary of the Invention

[0005] (I) Purpose of the Invention

[0006] The purpose of this invention is to provide a method for fabricating an avalanche region absorption suppression structure for an indium gallium arsenide Geiger avalanche detector, thereby solving the response tailing phenomenon caused by the diffusion of charge carriers absorbed outside the avalanche region into the avalanche region in current indium gallium arsenide Geiger avalanche detectors, and achieving low dark count rate and low afterpulse rate single-photon laser detection at wavelengths of 1.06 μm and 1.55 μm.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention is based on an absorption-multiplying split Geiger avalanche diode structure. It uses indium gallium arsenide (IGAA) as the absorption layer material, indium aluminum arsenide (IAA) as the bandgap material, and indium phosphide (IP) as the multiplication layer material. A novel PN junction fabrication method combining a Zn guard ring doped region with a groove-diffused main junction is employed. This method alleviates the siphon effect of the avalanche electric field on carriers absorbed outside the avalanche region, present in traditional double-diffused main junctions without a guard ring. It solves the problem of electric field control inside and outside the avalanche region. Combined with the strong absorption of 1.06 μm and 1.55 μm wavelength incident photons outside the avalanche region by a thick aluminum film, it effectively shields incident light outside the avalanche region, solving the problem of carriers absorbed outside the avalanche region diffusing into the avalanche region. From both the photogenerated carrier diffusion path and the photon absorption path, it addresses the problem of photocurrent response tailing caused by carrier absorption and diffusion outside the avalanche region.

[0009] The method for fabricating the avalanche region outside absorption suppression structure of the indium gallium arsenide Geiger avalanche detector of the present invention includes the following steps:

[0010] The first step involves using a heteroepitaxial growth process to sequentially epitaxially grow an n+ type InP buffer layer 2, an i-type InGaAs absorber layer 3, an i-type InAlAs bandgap layer 4, an n+ type InP charge layer 5, and an i-type InP top layer 6 on an n+ type InP substrate 1. The InAlAs bandgap layer 4 is made of InAlAs material with tunable composition and bandgap characteristics.

[0011] The second step involves using photolithography and etching processes to fabricate diffusion-doped grooves 7 on the i-type InP top layer 6.

[0012] The third step involves using a diffusion process to prepare a diffusion-doped groove 7 on the i-type InP top layer 6 to form a p+ type Zn main junction doped region 8.

[0013] Step 4: Prepare a p+ type Zn guard ring doped region 9 with a greater doping depth around the p+ type Zn main junction doped region 8. The depth of the p+ type Zn guard ring doped region 9 is greater than the depth of the p+ type Zn main junction doped region 8.

[0014] Step 5: Using a dielectric film deposition process, a passivation layer 10 is deposited on the surface of the i-type InP top layer 6.

[0015] Step 6: Using a metal film deposition process, a titanium-platinum p electrode 11 is prepared and forms an ohmic contact with the p+ type Zn main junction doped region 8.

[0016] Step 7: Using a metal film deposition process, gold germanium nickel n electrode 12 and thick aluminum film 13 are prepared on n+ type InP substrate 1. The thick aluminum film 13 serves as an outer shielding layer for the avalanche zone.

[0017] Step 8: At the position corresponding to the p+ type Zn main junction doped region 8, a light-entry hole 14 is prepared by photolithography etching process.

[0018] Step 9: Deposit an antireflection film 15 on the surface of the n+ type InP substrate 1 in the light inlet aperture.

[0019] (III) Beneficial Effects

[0020] The above-mentioned technical solution provides a method for fabricating an avalanche region absorption suppression structure for an indium gallium arsenide (IGAA) Geiger avalanche detector. It employs a groove-diffused main junction with a deep Zn guard ring doped region to alleviate the siphon effect of the avalanche electric field on carriers absorbed outside the avalanche region, as present in traditional double-diffused main junctions without guard rings, thus solving the problem of electric field control inside and outside the avalanche region. It uses an InAlAs bandgap layer to reduce the potential barrier between the InGaAs absorption layer and the InP charge layer, accelerating carrier transit and avoiding hysteresis caused by accumulation at the interface. It uses a thick aluminum film to effectively shield incident light outside the avalanche region, solving the problem of carriers absorbed outside the avalanche region diffusing into the avalanche region. From both the photogenerated carrier diffusion path and the photon absorption path, it solves the problem of photocurrent response tailing caused by carrier absorption and diffusion outside the avalanche region. Attached Figure Description

[0021] Figures 1 to 4 These are schematic diagrams illustrating the process of the method of the present invention. Detailed Implementation

[0022] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0023] According to the avalanche region absorption suppression structure design method of the indium gallium arsenide Geiger avalanche detector described in this invention, an indium gallium arsenide / indium phosphorus heteroepitaxial material with an absorption multiplication separation structure was prepared based on a 2-inch InP wafer, and an indium gallium arsenide Geiger avalanche detector was prepared accordingly, as an embodiment of this invention.

[0024] The first step involves using an MOCVD deposition system to deposit materials with a thickness of 350 μm and a doping concentration of 3–8E18 cm⁻¹. -3 On an n+ type InP substrate 1, epitaxial growth was performed sequentially to create layers with a thickness of 0.5 μm and a doping concentration of 1E18 cm⁻¹. -31. An n+ type InP buffer layer; 2. A 2 μm thick unintentionally doped i-type InGaAs absorber layer; 3. A 0.1 μm thick unintentionally doped i-type InAlAs bandgap layer; 4. A 0.4 μm thick layer with a doping concentration of 8E16cm⁻¹. -3 5. An n+ type InP charge layer with a thickness of 4 μm and an unintentionally doped i-type InP top layer, see appendix. Figure 1 .

[0025] The second step involves using photolithography and ICP etching equipment to fabricate circular diffusion-doped grooves 7 with a depth of 0.5 μm and a diameter of 20 μm on the i-type InP top layer 6. (See attached image.) Figure 2 .

[0026] The third step involves using a high-temperature diffusion doping apparatus to prepare a circular p+ type Zn main junction doped region 8, concentric with the diffusion doping groove 7, with a depth of 3 μm and a diameter of 25 μm. (See attached diagram.) Figure 3 .

[0027] The fourth step involves using a high-temperature diffusion doping apparatus to prepare a concentric annular p+ type Zn protective ring doped region 9 around the p+ type Zn main junction doped region 8. The annular region 9 has a depth of 3.5 μm, an inner diameter of 30 μm, and an outer diameter of 35 μm. (See attached diagram.) Figure 3 .

[0028] Fifth, using a PECVD device, a silicon nitride passivation layer 10 with a thickness of 0.4 μm was deposited (see attached image). Figure 4 .

[0029] Step 6: Using photolithography and electron beam evaporation equipment, a 1μm thick titanium-platinum p-electrode 11 is fabricated on the front side of the chip. An ohmic contact is then formed using a vacuum alloying furnace. (See attached diagram) Figure 4 .

[0030] Step 7: Using magnetron sputtering equipment, gold-germanium-nickel n-electrode 12 and a thick aluminum film 13 are fabricated on the n+ type InP substrate 1 on the back side of the chip, as shown in the appendix. Figure 4 .

[0031] Step 8: Using photolithography and ICP etching equipment, a light-gathering hole 14 with a diameter of 18 μm was fabricated at the position corresponding to the p+ type Zn main junction doped region 8. (See attached image) Figure 4 .

[0032] Step 9: Using a PECVD device, a silicon nitride antireflection film 15 is deposited on the surface of the n+ type InP substrate 1 in the light-entry aperture, as shown in the appendix. Figure 4 .

[0033] According to the test and evaluation, the indium gallium arsenide Geiger avalanche detector prepared according to the avalanche region external absorption suppression structure design method of the present invention achieves a dark count rate of less than 5kHz and an afterpulse probability of less than 10%@1μs dead time, which is superior to the performance of traditional devices.

[0034] As can be seen from the above technical solution, the present invention has the following significant features:

[0035] (1) Based on the absorption multiplication separation Geiger avalanche diode structure, this invention uses indium gallium arsenide as the absorption layer material, indium aluminum arsenide as the band gradient material, and indium phosphide as the multiplication layer material. It proposes a novel PN junction preparation method that combines a Zn protection ring doped region with a groove diffusion main junction. Combined with the strong absorption of incident photons at wavelengths of 1.06μm and 1.55μm outside the avalanche region by a thick aluminum film, effective measures are taken from both the photogenerated carrier diffusion path and the photon absorption path to solve the problem of photogenerated current response tailing caused by carrier absorption and diffusion outside the avalanche region, thereby improving device performance and applicability.

[0036] (2) Based on MBE or MOCVD heteroepitaxial technology, this invention uses a groove diffusion main junction with a deep Zn guard ring doped region to alleviate the siphon effect of the avalanche electric field on the carriers absorbed outside the avalanche region in the traditional two-diffusion main junction without a guard ring, thus solving the problem of electric field control inside and outside the avalanche region. An InAlAs band gradient layer is used to reduce the potential barrier between the InGaAs absorption layer and the InP charge layer, accelerating the carrier transit and avoiding the hysteresis problem caused by accumulation at the interface. A thick aluminum film is used to effectively shield the incident light outside the avalanche region, solving the problem of carriers absorbed outside the avalanche region diffusing into the avalanche region. Therefore, it can achieve absorption suppression outside the avalanche region and effectively solve the response tailing phenomenon.

[0037] (3) This invention innovatively proposes to use a groove diffusion main junction with a deep Zn protective ring doped region combined with an InAlAs band gradient layer, and to use a thick aluminum film to shield the incident light outside the avalanche region, thereby achieving absorption suppression outside the avalanche region.

[0038] (4) This invention can provide a reference for the design and fabrication of indium gallium arsenide Geiger avalanche detectors. The indium gallium arsenide Geiger avalanche detector fabricated according to this invention achieves single-photon detection with low dark count and low afterpulse at wavelengths of 1.06 μm and 1.55 μm. This method is practical.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating an avalanche region out-of-absorption suppression structure for an indium gallium arsenide Geiger avalanche detector, characterized in that, Includes the following steps: Step 1: Using heteroepitaxial growth process, on an n+ type InP substrate (1), an n+ type InP buffer layer (2), an i type InGaAs absorber layer (3), an i type InAlAs band gradient layer (4), an n+ type InP charge layer (5), and an i type InP top layer (6) are epitaxially grown sequentially. The second step is to use photolithography and etching processes to prepare a diffusion doping groove (7) on the i-type InP top layer (6). The third step is to use a diffusion process to form a p+ type Zn main junction doped region (8) in the diffusion doping groove (7) on the i-type InP top layer (6). Step 4: Prepare a p+ type Zn protective ring doped region (9) around the p+ type Zn main junction doped region (8); Step 5: Using a dielectric film deposition process, a passivation layer (10) is deposited on the surface of the i-type InP top layer (6). Step 6: A titanium-platinum p electrode (11) is prepared using a metal film deposition process and forms an ohmic contact with the p+ type Zn main junction doped region (8); Step 7: Using metal film deposition process, gold germanium nickel n electrode (12) and thick aluminum film (13) are prepared on n+ type InP substrate (1). The thick aluminum film (13) serves as an outer shielding layer for the avalanche zone. Step 8: At the position corresponding to the p+ type Zn main junction doped region (8), a light-entry hole (14) is prepared by photolithography etching process. Step 9: Deposit an antireflection film (15) on the surface of the n+ type InP substrate (1) in the light inlet hole.

2. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 1, characterized in that, In the first step, the n+ type InP substrate (1) has a thickness of 350 μm and a doping concentration of 3~8E18cm. -3 .

3. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 2, characterized in that, In the first step, on the n+ type InP substrate (1), a doping layer with a thickness of 0.5 μm and a doping concentration of 1E18 cm⁻¹ is sequentially epitaxially grown. -3 The n+ type InP buffer layer (2), the unintentionally doped i-type InGaAs absorber layer with a thickness of 2 μm (3), the unintentionally doped i-type InAlAs band gradient layer with a thickness of 0.1 μm (4), and the doped layer with a thickness of 0.4 μm and a doping concentration of 8E16cm -3 The n+ type InP charge layer (5) and the unintentionally doped i-type InP top layer with a thickness of 4 μm (6).

4. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 3, characterized in that, In the second step, a circular diffusion doping groove (7) with a depth of 0.5 μm and a diameter of 20 μm is prepared on the i-type InP top layer (6).

5. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 4, characterized in that, In the third step, the p+ type Zn main junction doped region (8) is circular, concentric with the diffusion doping groove (7), with a depth of 3μm and a diameter of 25μm.

6. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 5, characterized in that, In the fourth step, a concentric annular p+ type Zn protective ring doped region (9) with a depth of 3.5 μm, an inner diameter of 30 μm, and an outer diameter of 35 μm is prepared around the p+ type Zn main junction doped region (8).

7. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 6, characterized in that, In the fourth step, the depth of the p+ type Zn guard ring doped region (9) is greater than the depth of the p+ type Zn main junction doped region (8).

8. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 7, characterized in that, In the fifth step, the silicon nitride passivation layer (10) has a thickness of 0.4 μm.

9. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 8, characterized in that, In step 6, the titanium platinum p electrode (11) has a thickness of 1 μm.

10. The method for fabricating the avalanche region external absorption suppression structure of the indium gallium arsenide Geiger avalanche detector as described in claim 9, characterized in that, In step 8, the diameter of the light inlet aperture (14) is 18 μm.

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