Single Photon Detector with Improved Photon Detection Efficiency

Abstract

A single-photon detector with improved photon detection efficiency is disclosed. According to one aspect of the present embodiment, a single photon detection device is provided in which a buffer layer, a light absorption layer, a grading layer, an electric field control layer, and a window layer are sequentially stacked on a substrate, wherein the single photon detection device comprises an active region formed within the window layer, an anode electrode formed on the upper part of the active region to supply power to the active region, a quenching resistor directly bonded onto the window layer on which the active region is formed, and a metal electrode formed on the quenching resistor.

Description

Technology Field

[0001] This embodiment relates to a single-photon detection device that improves the detection efficiency of photons. Background Technology

[0002] The content described in this section merely provides background information regarding the present embodiment and does not constitute prior art.

[0003] With the development of information and communication technology, the importance of single photon detectors capable of detecting single photons in quantum cryptography is emerging.

[0004] Single photon detectors are suitable for long-distance communication wavelength bands of 1.3 µm to 1.5 µm, and are particularly effective for detecting optical signals of weak intensity, such as single photons. These single photon detectors mainly use an InGaAs / InP type APD (Avalanche Photo Diode) as a photodetector.

[0005] An APD operates at a voltage above its breakdown voltage to detect a single photon, which is called Geiger mode. In Geiger mode, a large reverse voltage is applied to the PN junction of the APD, which forms a large electric field in the junction. At this time, electron-hole pairs are generated in the junction by photons incident on the junction. Electron-hole pairs that gain energy from the strong electric field applied to the junction are accelerated in sequence, generating new electron-hole pairs. The cumulative occurrence of this phenomenon is called the avalanche phenomenon.

[0006] However, there are cases where photons are detected as having entered even though they have not. This phenomenon is called dark current. In a semiconductor pn junction, dark current is generated as electrons in the valence band transition to the conduction band due to thermal energy, and it has the characteristic of increasing or decreasing exponentially with respect to the magnitude of the band gap energy[∝ In addition, electronic states that are not bonded to the semiconductor surface are called dangling bonds. Since the energy state of the electron is located at the center of the band gap, the dark current caused by tunneling through the energy state of the dangling bond can increase significantly.

[0007] This dark current decreases as the temperature is lowered. However, while the frequency of dark current generation decreases as the temperature drops, it may no longer decrease or may even increase once the temperature falls below a certain level (e.g., -40°C). This phenomenon, known as the "After Pulse" effect, refers to the fact that as the temperature decreases, the number of thermally generated charges (electron-hole pairs) diminishes, but their lifetime lengthens, increasing the probability of them entering the SPAD active region. As such, dark current and the After Pulse effect have a conflicting relationship with respect to temperature; accordingly, it is desirable for SPADs to operate at sub-zero temperatures.

[0008] Meanwhile, when a photon is detected, an avalanche signal is generated in the photodiode; however, additional photons may be incident on the photodiode while the avalanche signal is being generated. If additional photons are incident during the generation of the avalanche signal, it becomes unclear whether the avalanche signal generated by the photodiode is due to the previously incident photons or the additionally incident photons, which may lead to inaccurate detection results. To prevent this problem, a quenching resistor is additionally placed in the avalanche photodiode. The quenching resistor rapidly reduces the avalanche signal caused by photon detection and stabilizes the avalanche photodiode.

[0009] However, in conventional avalanche photodiodes, flip-chip bonding using solder is performed when a quenching resistor is connected. Since solder has a size of several micrometers (μm), a problem arises where reliability at the solder joint is reduced. As a result, the capacitance at the joint increases, degrading the performance of the single-photon detector and causing stress due to the difference in the coefficient of thermal expansion between the solder and the bonding material. In addition, when the soldering process is performed, the photodiode is exposed to temperatures above a certain level, which has an adverse effect on the photodiode. The problem to be solved

[0010] One embodiment of the present invention has the objective of providing a single-photon detector that improves reliability and photon detection efficiency by directly integrating a quenching resistor into the device. means of solving the problem

[0011] According to one aspect of the present embodiment, a single photon detection device is provided in which a buffer layer, a light absorption layer, a grading layer, an electric field control layer, and a window layer are sequentially stacked on a substrate, wherein the single photon detection device comprises an active region formed within the window layer, an anode electrode formed on the upper part of the active region to supply power to the active region, a quenching resistor directly bonded onto the window layer on which the active region is formed, and a metal electrode formed on the quenching resistor.

[0012] According to one aspect of the present embodiment, the single photon detection device further comprises an ohmic contact layer stacked on a window layer in which the active region is formed.

[0013] According to one aspect of the present embodiment, the ohmic contact layer is characterized by electrically connecting the active region and the window layer.

[0014] According to one aspect of the present embodiment, the quenching resistance is characterized by comprising a first bonding layer, a second bonding layer, and a resistance material.

[0015] According to one aspect of the present embodiment, the first bonding layer is disposed on the ohmic contact layer to make ohmic contact between the ohmic contact layer and the resistive material.

[0016] According to one aspect of the present embodiment, the second bonding layer is disposed on the resistive material to make ohmic contact between the resistive material and the metal electrode.

[0017] According to one aspect of the present embodiment, the metal electrode is characterized by operating as an anode electrode. Effects of the invention

[0018] As explained above, according to one aspect of the present embodiment, there is an advantage in that the precision of the inspection can be structurally improved without having an excessively long inspection time. Brief explanation of the drawing

[0019] FIG. 1 is a circuit diagram of a single-photon detection system according to one embodiment of the present invention. FIG. 2 is a diagram illustrating the configuration of a single-photon detection system according to one embodiment of the present invention. FIG. 3 is a cross-sectional view of a single-photon detection device according to one embodiment of the present invention. FIG. 4 is a diagram illustrating the structure of a quenching resistor according to one embodiment of the present invention. Specific details for implementing the invention

[0020] The present invention is susceptible to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing.

[0021] Terms such as first, second, A, B, etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0022] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0023] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" should be understood as not precluding the existence or addition of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification.

[0024] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains.

[0025] Terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0026] In addition, each component, process, procedure, or method included in each embodiment of the present invention may be shared within a scope that is not technically contradictory to one another.

[0027] FIG. 1 is a circuit diagram of a single-photon detection system according to one embodiment of the present invention, and FIG. 2 is a diagram illustrating the configuration of a single-photon detection system according to one embodiment of the present invention.

[0028] Referring to FIGS. 1 and 2, a single photon detection system (100) according to one embodiment of the present invention includes a single photon detection device (110), a quenching resistor (120), and a metal electrode (130).

[0029] A single photon detector (110) detects incoming photons by receiving power. The single photon detector (110) includes a cathode terminal (C) that receives power, a photodiode that receives photons and generates an avalanche signal (photocurrent), and an anode terminal (A) from which the avalanche signal generated from the photodiode is output.

[0030] The cathode terminal (C) is provided at one end of the single-photon detection device and receives a gate signal (GS) generated from the gate signal generator (110) and transmits it to the single-photon detection device.

[0031] The single-photon detector (110) may be implemented as an InGaAs / InP type APD (Avalanche Photo Diode, or avalanche photo diode), but is not necessarily limited thereto. The single-photon detector (110) receives a DC power supply or a DC power supply and a gate signal (gate power supply) at the cathode terminal (C), thereby breaking down the breakdown voltage (V B Reverse bias voltage (V) greater than ) gh It operates in Geiger mode, which performs light detection at ). Here, in Geiger mode, the single-photon detector (110) operates at a breakdown voltage (V B Reverse bias condition greater than ) (V gh or V g2It refers to an operation that performs photodetection in ). That is, the single-photon detector (110) operates in Geiger mode by the gate signal (GS), and as it receives photons from the outside, an avalanche phenomenon (or amplification) occurs within the single-photon detector (110) in which carriers are amplified. To explain more specifically, when the single-photon detector (110) is biased in the reverse direction by the gate signal (GS), the bias voltage (V) of the applied gate signal (GS) gh or V g2 A high electric field is formed at the PN junction surface of the single-photon detector (110) by means of ). At this time, when carriers generated by the absorption of photons are injected into the amplification layer of the single-photon detector (110), an electron avalanche breakdown occurs within the single-photon detector (110) through continuous avalanche impact ionization, which amplifies the current. Accordingly, the single-photon detector (110) outputs an avalanche signal (photocurrent).

[0032] The anode (A) is provided at the other end of the single-photon detector (110) and transmits the avalanche signal generated from the single-photon detector (110) to the outside.

[0033] As mentioned in the background technology of the invention, the quenching resistor (120) is placed at the cathode terminal (C) of the single-photon detector (110) to rapidly reduce the avalanche signal caused by photon detection and stabilize the single-photon detector (110).

[0034] The metal electrode (130) can operate as the aforementioned anode electrode and transmits the avalanche signal generated from the single-photon detector (110) to the outside. The metal electrode (130) can be implemented as a p-type electrode.

[0035] A negative voltage V is used with a single photon detector (110). biasWhen applied, the single-photon detector (110) outputs a response signal due to capacitance. A voltage (V) that enables the single-photon detector (110) to detect a single photon. gh ) is the breakdown voltage (V) of the single-photon detector (110). B ) and overvoltage (V vover It is equal to the sum of ). That is, the breakdown voltage (V) of the single photon detector (110) of the single photon detector (110). B ) and overvoltage (V vover When a voltage of the combined magnitude of ) is applied, a single photon can be detected.

[0036] Meanwhile, if no photon is introduced into the single-photon detector (110), no current flows through the quenching resistor (120). Therefore, since no voltage drop occurs in the quenching resistor, the voltage (V) applied across the single-photon detector (101) D ) is voltage (V gh It becomes the same as ).

[0037] When a photon is absorbed, the avalanche current generated in the single-photon detector (110) begins to flow along the quenching resistor (120). Accordingly, a voltage drop (V) in the quenching resistor (120) occurs by an amount corresponding to the product of the magnitude of the quenching resistor (120) and the magnitude of the avalanche current. R ) occurs. When the voltage drop in the quenching resistor (120) exceeds the magnitude of the excess voltage, the voltage (V) applied to both ends of the single-photon detector (101) D ) is the breakdown voltage (V) of the single-photon detector (110). B It becomes smaller than ). As a result, passive quenching can be performed in the single photon detector (110), and the generation of avalanche current is stopped.

[0038] At this time, the (re)operation speed of the single photon detector (110) is determined by the speed at which a detectable output signal is generated, the time required to quench the single photon detector (110), the time for the captured carrier to remove and avoid the after pulse, and the time required for the single photon detector (110) to re-operate. Since the single photon detector (110) uses a signal to generate an output signal or passive quenching, the quenching speed is considerably fast. Meanwhile, the time required for the single photon detector (110) to re-operate is determined by a time constant represented by the product of resistance (R) and capacitance (C). Therefore, the (re)operation speed of the single photon detector (110) becomes faster as the after pulse and the time constant, more specifically the capacitance (C), are reduced. As the single photon detector (110) has the structure shown in FIG. 3, it can reduce the capacitance (C) that occurs and improve the (re)operation speed.

[0039] FIG. 3 is a cross-sectional view of a single-photon detection device according to one embodiment of the present invention.

[0040] Referring to FIG. 3, a single photon detection device (110) according to one embodiment of the present invention comprises a substrate (310), a buffer layer (315), a light absorption layer (320), a grading layer (325), an electric field control layer (330), a window layer (335), an n-type ohmic contact layer (340a) formed in an area not diffused or ion-implanted, a p-type ohmic contact layer (340b) converted to p-type, an active region (350) formed by converting to p-type through p-type impurity diffusion or implantation on an epitaxial wafer composed of the ohmic contact layer (340), a guard ring (355) formed by diffusion or ion implantation into the active region p-type, an insulating film (360), a blocking film (365), a light transmission part (370), and an amplification layer (390).

[0041] The active region (350) consists of a central region where the penetration depth of p-type impurities is formed deeply and a peripheral region where p-type impurities penetrate to a relatively shallow depth. The penetration depth of p-type impurities in the center of the active region (350) is characterized by being formed within the window layer (335). The penetration depth of p-type impurities in the barrier junction (360) can be formed up to a part of the window layer (335) or the light absorption layer (320).

[0042] The substrate (310) allows a buffer layer (315), etc., to be laminated on top. The substrate (310) is n + It can be implemented as InP semiconductor material or SI (Semi Insulating)-InP semiconductor material.

[0043] The buffer layer (315) is laminated on the upper surface of the substrate (310) and can perform the function of grid matching. The buffer layer (315) is n + It can be composed of semiconductor materials of InP.

[0044] The light absorption layer (320) is laminated on the upper surface of the buffer layer (315) and converts photons incident on the light transmission part (370) into carriers. The light absorption layer (320) has a bandgap smaller than that of the substrate (310) and the buffer layer (315). - It is composed of InGaAs and converts photons incident on the light transmission part (370) and passed through the substrate (310) and buffer layer (315) into carriers.

[0045] The grading layer (325) is laminated on the upper surface of the light absorption layer (320) and allows carriers generated in the light absorption layer (320) to be rapidly transferred to the amplification layer (390) at the bottom of the active region (350). The grading layer (3325) must be composed of a material having an intermediate value between the energy bandgap of the light absorption layer (320) and the energy bandgap of the electric field control layer (330) so that carriers generated in the light absorption layer (320) can be rapidly and effectively transferred to the bottom of the active region (350). Accordingly, the grading layer (325) n -It can be configured in a stacked form with multiple layers composed of InGaAsP. The multiple n-InGaAsP layers have different bandgap energies and are configured such that the bandgap energy increases from the InGaAs absorption layer to the InP electric field control layer (330).

[0046] The electric field control layer (330) is laminated on the upper surface of the grading layer (325) and controls the electric field of the amplification layer (390) at the bottom of the active region (350). The electric field control layer (330) may be composed of an n-type InP semiconductor material for controlling the electric field.

[0047] The window layer (335) is laminated on the upper surface of the electric field control layer (330). The window layer (335) is n - It is composed of InP so that an active region (350, 360) is formed inside, or an amplification layer (390) can be formed at the bottom of the active region (350).

[0048] The n-type ohmic contact layer (340a) is formed at a position (a position further from the active area than the guard ring) at a predetermined distance from the guard ring (355) on the upper surface of the window layer, thereby electrically connecting the window layer (335) to the cathode electrode layer (345).

[0049] The p-type ohmic contact layer (340b) is formed on the active region (350) converted to p-type among the window layers, and electrically connects the active region (350) to the metal electrode (130).

[0050] The cathode electrode layer (345) is laminated on the upper surface of the n-type ohmic contact layer (340a) to supply power.

[0051] The active region (350) is an area within the window layer (335) where a diffusion source is implanted or diffused. The diffusion source that is implanted or diffused may be a p-type impurity such as zinc, and as the diffusion source is implanted or diffused, the active region (350) has p-type InP characteristics. The active region (350) is formed vertically above the light transmission section (370) through which photons from the outside enter the single photon detector (110). An amplification layer (390) for inducing an avalanche phenomenon is formed at the bottom of the active region (350), so that the active region (350) transmits an electrical signal resulting from the incoming photons to the metal electrode (120). Since an amplification layer (390) for inducing an avalanche phenomenon must be formed at the bottom of the active region (350), the diffusion source into the active region (350) is implanted only up to a portion of the window layer (335).

[0052] When a bias voltage is applied to the metal electrode (120) and the cathode electrode layer (345), power is supplied to the active region (350). Accordingly, the active region (350) forms equipotential lines (380a, 380b, 380c) according to each potential. Since an electric field is formed in the direction perpendicular to the equipotential lines (380) formed in this way, carriers formed by photons in the direction perpendicular to the equipotential lines are attracted to the amplification layer (390).

[0053] The guard ring (355) may be configured in the form of a closed curve or ring that surrounds the active area (350) on the outer edge of the active area (350), and reduces the peak of the electric field formed on the outer edge of the active area (350).

[0054] The insulating film (360) is laminated on the window layer (335) and serves as an anti-reflective coating layer while protecting the components of the single-photon detector from the outside.

[0055] A blocking film (365) is formed on the lower part of the substrate (310) to allow photons to be incident only on the light-transmitting portion (370). The blocking film (365) is formed on the lower part of the substrate (310) excluding the light-transmitting portion (370) to prevent photons from being incident on areas other than the light-transmitting portion (370).

[0056] The light-transmitting portion (370) is a portion of the lower part of the substrate (310) where the electrode (345) is not formed, allowing photons provided from the outside to be incident thereon. Since reflection loss of photons may occur due to the difference in refractive index between air and the semiconductor, an anti-reflective film (370) is formed to minimize this. To allow photons to be incident on the active region (350), the light-transmitting portion (370) is formed vertically below the active region (350) and may have a width equal to the width of the active region (350).

[0057] Meanwhile, the quenching resistor (120) has a structure as shown in FIG. 4, so that it is not flip-chip bonded onto the p-type ohmic contact layer (340b) but is directly bonded to perform the aforementioned operation.

[0058] FIG. 4 is a diagram illustrating the structure of a quenching resistor according to one embodiment of the present invention.

[0059] Referring to FIG. 4, a quenching resistor (120) according to one embodiment of the present invention is implemented with a bonding layer (410a, 410b) and a resistive material (420).

[0060] A bonding layer (410a) is disposed on a p-type ohmic contact layer (340b) to make ohmic contact between the p-type ohmic contact layer (340b) and the resistive material (420). As the bonding layer (410a) is implemented with amorphous silicon, it bonds the two (340b, 420).

[0061] A resistive material (420) is placed on the junction layer (410a) and performs the function of a quenching resistor. The resistive material (420) can be implemented as silicon-rich silicon dioxide (SiO2). Accordingly, the resistive material (420) rapidly lowers the avalanche signal as a quenching resistor. The resistive material (420) can have a thickness of 40 nm to 2 µm and a resistance value of 10 kΩ to 10 MΩ.

[0062] A bonding layer (410b) is placed on a resistive material (420) to make ohmic contact between the resistive material (420) and the metal electrode (130). By making ohmic contact between the two (420, 130), the bonding layer (410b) allows the metal electrode (130) to be electrically connected to the active region (350) via the quenching resistor (120) as an anode electrode.

[0063] In order for the resistive material (420) to function as a quenching resistor, it must be implemented with the aforementioned material. However, if the resistive material (420) is implemented with the aforementioned material and placed on the p-type ohmic contact layer (340b), the two (340b, 420) cannot smoothly perform ohmic contact and instead perform Schottky contact. However, if they are joined by Schottky contact, it causes a problem where the quenching speed of the quenching resistor drops significantly. Accordingly, joining layers (410a, 410b) are placed at both ends of the resistive material (420) to make ohmic contact between each component (340b and 420, 420 and 130). Additionally, if only the resistive material is placed on the p-type ohmic contact layer (340b) as in the conventional method, the thickness or shape of the resistive material is fixed so that the resistive material has a specific resistance value. That is, if the resistive material is arranged as in the conventional manner, structural constraints arise in the arrangement of the quenching resistor. On the other hand, if bonding layers (410a, 410b) are arranged at both ends of the resistive material (420), the structure or arrangement of the resistive material (420) can be made free by the bonding layers (410a, 410b). Accordingly, the structure of the quenching resistor (120) can be made free, so that constraints on the shape or thickness of the single photon detector (110) can be minimized.

[0064] As the quenching resistor (120) has such a structure, the metal electrode (130) can be bonded to the active region (350) through ohmic contact. When the two (130, 350) are in ohmic contact, the problems that may occur when flip-chip bonding as in the conventional method can be fundamentally eliminated. In addition, when the two (130, 350) are in contact by flip-chip bonding as in the conventional method, solder is present between the two, which causes the physical distance between the two (130, 350) to increase. An increase in the physical distance between the two (130, 350) leads to a problem in that it increases the size of parasitic capacitance, thereby increasing the capacitance (C) of the single-photon detector (110). As described above, if the capacitance (C) of the single photon detector (110) increases, the time constant increases, causing a problem in improving the re-operation speed of the single photon detector (110).

[0065] The quenching resistor (120) has the aforementioned structure, and by reducing the physical distance between the two (130, 350) compared to the conventional technology, the problem that may occur with the presence of solder can be resolved.

[0066] The above description is merely an illustrative explanation of the technical concept of the present embodiment, and a person skilled in the art to which the present embodiment belongs would be able to make various modifications and variations within the scope of the essential characteristics of the present embodiment. Accordingly, the present embodiments are intended to explain, not limit, the technical concept of the present embodiment, and the scope of the technical concept of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present embodiment. Explanation of the symbols

[0067] 100: Single-photon detection system 110: Single-photon detector 120: Quenching resistance 130: Metal electrode 310: Substrate 315: Buffer layer 320: Light absorption layer 325: Grading layer 330: Electric field control layer 335: Window layer 340: Ohmic contact layer 345: Electrode 350: Active area 355: Guard Ring 360: Insulating film 370: Light-transmitting part 380: Equipotential lines 390: Amplification layer 410: Bonding layer 420: Resistance material

Claims

Claim 1 A single-photon detection device comprising a buffer layer, a light absorption layer, a grading layer, an electric field control layer, and a window layer sequentially stacked on a substrate, wherein the device comprises: an active region formed within the window layer and formed by injecting or diffusing a diffusion source which is a p-type impurity; an ohmic contact layer stacked on the window layer on which the active region is formed; an anode electrode formed on the upper portion of the active region to supply power to the active region; a quenching resistor directly bonded onto the window layer on which the active region is formed; and a metal electrode formed on the quenching resistor to operate as an anode electrode and transmit an avalanche signal to the outside, wherein the quenching resistor is implemented with silicon dioxide, has a thickness of 40 nm to 2 μm and a resistance value of 10 kΩ to 10 MΩ, and performs operation as a quenching resistor; and a first junction layer disposed on the ohmic contact layer to make ohmic contact between the ohmic contact layer and the resistive material. A single-photon detection device characterized by including a second junction layer disposed on the resistive material and ohmic contacting the resistive material and the metal electrode. Claim 2 delete Claim 3 A single-photon detection device according to claim 1, wherein the ohmic contact layer electrically connects the active region and the window layer. Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete

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