Light receiving element

Abstract

Provided is a light-receiving element that makes it possible to maintain high-speed and high-sensitivity properties while omitting a step for flip-chip assembly when mounting to an optical receiver. This light-receiving element (300) comprises: a first electrode metal (307) formed on the upper surface of a substrate (301); a semiconductor layer (302) bonded to the upper surface of the first electrode metal (307); and a second electrode metal (306a) formed on the upper surface of the semiconductor layer (302). The semiconductor layer (302) has a first semiconductor contact layer (303), a second semiconductor contact layer (305), and a semiconductor absorption layer (303) between the first semiconductor contact layer (303) and the second semiconductor contact layer (305). The first electrode metal (307) includes an extraction path for propagating signals to an anode electrode or a cathode electrode.

Description

[Technical Field]

[0001] The present disclosure relates to a light receiving element, and more particularly to a light receiving element that can maintain high speed and high sensitivity while eliminating the step of flip-chip mounting when mounting on an optical receiver. [Background technology]

[0002] Semiconductor photodetectors are used in a variety of applications, including optical communications and various sensors. In particular, semiconductor photodetectors for optical communications applications require increased light-receiving sensitivity to extend the transmission distance of optical communications, and increased bandwidth to achieve higher communication capacity. Photodetectors also play an important role in Radio-over-fiber (RoF) technology, which uses a photodetector to photoelectrically convert analog signals in the optical domain transmitted through an optical fiber and then emit them as wireless signals in the electrical domain. In addition to a broadband capability sufficient to emit the carrier frequency of the wireless signal, photodetectors are also required to have high incidence tolerance and current output, because the output current from the photodetector is related to the strength of the wireless signal transmitted via the antenna (see, for example, Non-Patent Document 1).

[0003] Photodetectors used in optical communications are typically integrated into a package to form an optical receiver, which includes a photodetector, a transimpedance amplifier, an optical fiber, a lens that focuses the incident light from the optical fiber onto the photodetector, and a waveguide. In this case, it is important in designing an optical receiver to make the photodetector as easy to optically and electrically mount as possible. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A. Beling et al., “High-power, high-linearity photodiodes”, Optica, Vol. 3, Issue 3, pp.328-338, (2016) [Non-patent document 2] E. Higurashi et al., “Au-Au Surface-Activated Bonding and Its Application to Optical Microsensors With 3-D Structure”, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 15, Issue 5, (2009) Summary of the Invention

[0005] However, mounting a photodetector on an optical receiver has the following problems. The present disclosure has been made in view of these problems, and an object of the present disclosure is to provide a photodetector that can maintain high speed and high sensitivity while eliminating the flip-chip mounting process when mounting on an optical receiver.

[0006] To achieve this objective, one embodiment of a light-receiving element of the present disclosure comprises a substrate, a first electrode metal formed on an upper surface of the substrate, a semiconductor layer bonded to the upper surface of the first electrode metal, and a second electrode metal formed on the upper surface of the semiconductor layer, the semiconductor layer having a first semiconductor contact layer in contact with the first electrode metal, a second semiconductor contact layer in contact with the second electrode metal, and a semiconductor absorption layer between the first semiconductor contact layer and the second semiconductor contact layer, and the first electrode metal includes an extraction path for propagating a signal to an anode electrode or a cathode electrode.

[0007] According to this configuration, it is possible to provide a light receiving element that can omit the flip-chip mounting process when mounting on an optical receiver and that can maintain high speed and high sensitivity. [Brief explanation of the drawings]

[0008] [Figure 1] 1(a) and 1(b) are diagrams illustrating a typical example of mounting a light receiving element on an optical receiver. [Figure 2]2(a) and 2(b) are side views showing a schematic configuration of an optical receiver in which light is incident from the back surface of the light receiving element using a flip-chip substrate separate from the mounting substrate. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of the light receiving element of this embodiment, where FIG. 3(a) is a cross-sectional view and FIG. 3(b) is a top view. [Figure 4] FIG. 4 is a diagram illustrating a method for manufacturing a light-receiving element according to an embodiment of the present disclosure. [Figure 5] 5A and 5B are diagrams showing a schematic configuration of a light-receiving element according to an embodiment of the present disclosure, where FIG. 5A is a cross-sectional view and FIG. 5B is a top view. [Figure 6] 6A and 6B are diagrams showing a schematic configuration of a light-receiving element according to an embodiment of the present disclosure, where FIG. 6A is a cross-sectional view and FIG. 6B is a top view. [Figure 7] 7A and 7B are diagrams showing a schematic configuration of a light-receiving element according to an embodiment of the present disclosure, where FIG. 7A is a cross-sectional view and FIG. 7B is a top view. [Figure 8] 8A and 8B are diagrams showing a schematic configuration of a light-receiving element according to an embodiment of the present disclosure, where FIG. 8A is a cross-sectional view and FIG. 8B is a top view. DETAILED DESCRIPTION OF THE INVENTION

[0009] Various embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference numerals in the drawings indicate the same or similar elements, and redundant explanations may be omitted. The values ​​and materials used in the following description are examples, and other values ​​and materials may be used for the light-receiving element according to the embodiments without departing from the spirit of the present disclosure.

[0010] Before describing various embodiments of the light-receiving element of the present disclosure, a typical example of mounting the light-receiving element in an optical receiver will be described with reference to FIGS.

[0011] FIG. 1(a) is a diagram illustrating a typical example of mounting the above-described light-receiving element on an optical receiver, and is a side view showing a schematic configuration of an optical receiver in a form in which light is incident from the front surface of the light-receiving element (hereinafter referred to as a surface-mount form). The optical receiver 100a shown in FIG. 1(a) includes a substrate 101a, a light-receiving element 102, and an amplifier 103. As shown in the figure, the light-receiving element 102 and the amplifier 103 are mounted on one of the two main surfaces of the substrate 101a (hereinafter referred to as the mounting surface). The light-receiving element 102 is connected to an external terminal (not shown) and the amplifier 103 via wiring 104a.

[0012] The light receiving element 102 is configured to receive a voltage from a voltage source connected to an external terminal (not shown) via wiring 104a, and is configured to output an electrical signal obtained by photoelectric conversion to the amplifier 103 via wiring 104a.

[0013] The amplifier 103 amplifies the electrical signal from the light receiving element 102 and outputs it to an external terminal via a wiring 104a. The signal is configured to be output to a processor or the like (not shown) connected to a child (not shown).

[0014] As shown in FIG. 1(a), by designing the optical receiver 100a so that light is incident on the surface of the light receiving element 102, a simple configuration can be achieved in which the light receiving element 102 is simply placed on the mounting surface of the substrate 101a.

[0015] 1(b) is a diagram illustrating another typical example of the surface mounting of the light receiving element on the optical receiver. The optical receiver 100b shown in FIG. 1(b) is characterized in that it includes wiring 104b provided on the mounting surface of the substrate 101a, and the light receiving element 102 is mounted in contact with the surface of the wiring 104b. 1 This differs from the configuration in (a) in that the connection position of the wiring 104a for applying a voltage to the light receiving element 102 can be moved from the upper surface of the light receiving element 102 to the upper surface of the wiring 104b provided on the surface of the substrate 101a.

[0016] However, increasing the speed and sensitivity of a photodetector makes surface mounting difficult. A photodetector must have a light-receiving window and electrodes on its surface. If the diameter of the photodetector is reduced to increase its speed, the incident light will interfere with the electrodes, reducing its sensitivity. Furthermore, surface mounting makes it difficult to form a reflective mirror on the substrate. A photodetector that does not have a reflective mirror on the surface opposite the light-receiving surface has a "one-pass structure," in which the incident light passes through the light-absorbing layer inside the photodetector only once. With a "one-pass structure," reducing the thickness of the light-absorbing layer significantly reduces sensitivity. To solve these problems, flip-chip mounting is available.

[0017] 2(a) and 2(b) are side views showing a schematic configuration of an optical receiver in a configuration in which light is incident from the backside of a light-receiving element using a flip-chip substrate separate from the mounting substrate (hereinafter referred to as a flip-chip mounting configuration). The optical receiver 100c shown in FIG. 2(a) differs from the configurations shown in FIGS. 1(a) and 1(b) in that a flip-chip substrate 201 is provided between a substrate 101a and a light-receiving element 102, and the front side of the light-receiving element 102 is mounted so that it faces the upper surface of the flip-chip substrate 201. In the optical receiver 100c, the light-receiving element 102 is configured to output an electrical signal, which is photoelectrically converted from light incident from the backside, to an amplifier 103 via wiring 104a.

[0018] The optical receiver 100d shown in FIG. 2(b) includes a transparent semiconductor substrate 101b, a light-receiving element 102 formed on the mounting surface of the semiconductor substrate 101b, a mirror 202 formed on the front side of the light-receiving element 102 (the lower side of the figure), and a flip-chip substrate 201 facing the mounting surface of the semiconductor substrate 101b. The mounting surface of the semiconductor substrate 101b and the main surface of the flip-chip substrate 201 are connected via stacked pads 203a, 203b, and 203c. The semiconductor substrate 101b is transparent to incident light. In the optical receiver 100d, the light-receiving element 102 is configured to output an electrical signal photoelectrically converted from light incident from the back side through the semiconductor substrate 101b and light reflected by the mirror 202 provided on the front side.

[0019] 2(a) and (b), incident light is incident from the back surface of the light-receiving element, so interference from electrodes can be avoided, and furthermore, a mirror can be formed on the top surface of the element in the normal light-receiving element process, so it is easy to achieve a "two-path structure" in which incident light passes through the absorption layer twice. However, in the case of the flip-chip mounted optical receiver 100c shown in Figure 2(a), the light-receiving element 102 is diced once to form individual elements, and then mounted on the main surface of the flip-chip substrate 201, and then the flip-chip substrate 201 is mounted on the main surface of the substrate 101a, which presents an issue in terms of the complexity of the mounting process.

[0020] Here, we will discuss the perspective of increasing the input and output resistance of photodetectors. As mentioned above, in optical wireless applications such as RoF, photodetectors are required to receive optical signals with as high an intensity as possible and output a high current. However, the output current of a photodetector is not necessarily linear with respect to the optical input intensity. One of the reasons for this is the rise in junction temperature within the element, which depends on the current density.

[0021] When light is incident on a photodetector, a large number of photocarriers (electron-hole pairs generated by photoexcitation) are generated within the photodetector. When the incident light intensity is low, the generated electrons move immediately toward the n-type electrode, and the holes move toward the p-type electrode, depending on the applied voltage. However, when the incident light intensity is high, heat generation due to Joule heat, which is determined by the voltage applied to the photodetector and the current flowing through it, becomes significant. In general, the saturation speed of electrons and holes decreases as the temperature rises, so when Joule heat is significant, the output current value is limited. In other words, from the perspective of application to optical wireless systems such as RoF, suppressing heat generation in photodetectors is an issue.

[0022] As mentioned above, when applying photodetectors to optical communications, ease of mounting the photodetector onto an optical receiver is important, along with high speed and high sensitivity. While flip-chip mounting can ensure high speed and high sensitivity, it poses a challenge in terms of the mounting process, as it requires an additional step, making the mounting process itself more complex and requiring more steps. Furthermore, when applying it to optical wireless systems such as RoF, there is an issue that the linearity of the output current relative to the incident light intensity is impaired due to Joule heat when the incident light intensity is high.

[0023] The present disclosure provides a photodetector structure that eliminates the need for a flip-chip mounting process when mounting a photodetector on an optical receiver, while maintaining high speed and high sensitivity, and improving the linearity of the output current when the incident light intensity is high.

[0024] [First embodiment] A first embodiment of a light-receiving element according to the present disclosure will be described with reference to Figures 3 and 4. This embodiment is a basic structure of various light-receiving elements according to the present disclosure. The following description will be given taking a light-receiving element made of a compound semiconductor as an example.

[0025] Fig. 3 is a diagram showing a schematic configuration of the light receiving element of this embodiment, Fig. 3(a) is a cross-sectional view and Fig. 3(b) is a top view, Fig. 4 is a diagram showing a method for manufacturing the light receiving element of this embodiment.

[0026] 3 includes a host substrate 301, an electrode 307 formed on the main surface of the host substrate 301, a semiconductor layer 302, and an electrode 306 formed on the upper surface of the semiconductor layer 302. The light-receiving element 300 further includes an interlayer insulating film 310, and electrode pads 308 and 309.

[0027] The semiconductor layer 302 includes an n-type contact layer 303, a light absorbing layer 304, and a p-type contact layer 305, which are stacked in this order.

[0028] The electrode 307 includes a bonding portion 307a and an extraction portion 307b, and the lower surface of the semiconductor layer 302 is bonded to the host substrate 301 via the bonding portion 307a. The electrode 307 is also called a bonding electrode because it is an electrode that bonds the semiconductor layer 302 to the host substrate 301.

[0029] The interlayer insulating film 310 is formed in contact with the upper surface of the host substrate 301 or the electrode 307 and the side surface of the semiconductor layer 302. The position of the upper surface of the interlayer insulating film 310 is the same as the position of the upper surface of the semiconductor layer. The material of the interlayer insulating film 310 can be polyimide.

[0030] The electrode 306 is formed on a plane including the upper surface of the interlayer insulating film 310 and the upper surface of the semiconductor layer. The electrode 306 includes an annular portion 306a and an extraction portion 306b that are electrically coupled to each other. The annular portion 306a is formed along the edge of the upper surface of the p-type contact layer 305, and the extraction portion 306b is 6 b is formed on the upper surface of the interlayer insulating film 310. Light enters from the p-type contact layer of the semiconductor layer 302 through the opening in the annular portion 306a of the electrode 306.

[0031] The electrode pad 308 is formed on the upper surface of the interlayer insulating film 310 so as to contact the lead portion 306 b of the electrode 306 .

[0032] The electrode pad 309 is formed on the upper surface of the host substrate 301 so as to contact the lead portion 307 b of the electrode 307 .

[0033] In the light-receiving element 300, the material of the host substrate 301 may be Si, the material of the electrodes 306 and 307 may be Au, and the semiconductor layer 302 may be an epitaxial layer including an InGaAs absorption layer.

[0034] The n-type contact layer 303, the light absorption layer 304, and the p-type contact layer 305 constituting the semiconductor layer 302 can be an n-type InP contact layer, an InGaAs absorption layer, and a p-type InP contact layer, respectively.

[0035] The manufacturing method of this embodiment will be described with reference to Fig. 4. As shown in Fig. 4(a), an epitaxial substrate that will become the semiconductor layer 302 and a Si substrate that will become the host substrate 301 are prepared. The epitaxial substrate that will become the semiconductor layer 302 may be formed by growing an n-type contact layer 303, a light absorption layer 304, and a p-type contact layer 305 on an InP substrate 401 using MOCVD. To enable the n-type contact layer 303 to be bonded to the host substrate 301 by subsequent wafer bonding, the p-type contact layer 305, the light absorption layer 304, and the n-type contact layer 303 are crystal-grown in this order on the surface of the InP substrate 401.

[0036] 4(b), Au, which will become electrode 307, is deposited on the surface of host substrate 301 in a vacuum chamber, and then wafer bonding is performed with the epitaxial substrate, which will become semiconductor layer 302, facing down. The Au film formed in the vacuum chamber can easily bond host substrate 301 and a compound semiconductor substrate according to the mechanism of surface activation or atomic diffusion (see, for example, Non-Patent Document 2).

[0037] 4(c), the InP substrate 401 is peeled off from the epitaxial layer by using a grinder and wet etching. When a p-type InP substrate is used as the InP substrate 401, the remaining part of the p-type InP after peeling off a part of the p-type InP from the epitaxial layer functions as the p-type contact layer 305.

[0038] Next, as shown in Figure 4(d), the annular portion 306a of the electrode 306 that contacts the upper surface of the p-type contact layer 305 is formed by EB evaporation. An electrode of any ring shape can be formed using a conventional resist, exposure and development process using a stepper, and a lift-off process. In addition, to improve the accuracy of the subsequent process, an alignment mark (not shown) may be formed in the same process.

[0039] Subsequently, as shown in FIG. 4( e ), a mesa of an n-type contact layer 303 , a light absorption layer 304 , and a p-type contact layer 305 is formed by resist exposure and development and wet etching processes to form a semiconductor layer 302 .

[0040] 4(f), the Au metal film formed on the surface of the host substrate 301 is patterned using resist exposure and development and dry etching to form an electrode 307. The Au film is patterned to have the shapes of an extraction portion 307b extending from a bonding portion 307a bonded to the lower surface of the n-type contact layer 303 and an electrode pad 309.

[0041] Subsequently, as shown in FIG. 4(g), an interlayer insulating film 310 is formed using polyimide, which is a photosensitive polymer.

[0042] Finally, as shown in FIG. 4(h), resist exposure and development and metal plating processes are used to form an extraction portion 306b connected to the annular portion 306a of the electrode 306 formed on the upper surface of the p-type contact layer 305, an electrode pad 308, and an electrode pad 309 on the extraction portion 307b connected to the junction portion 307a of the electrode 307 joined to the n-type contact layer 303.

[0043] Here, the operating principle of the photodetector of the present disclosure will be explained. According to the photodetector of the present disclosure, the ring-shaped electrode formed on the top of the photodetector allows light to be incident from above. In other words, the optical receiver can be surface-mounted. Light incident from above the photodetector is reflected by the junction 307a of the electrode 307, which is formed by depositing an Au film and bonding it to the n-type contact layer, and then passes through the light-absorbing layer 304 again. In other words, a "two-pass structure" can be achieved in which light passes through the light-absorbing layer 304 twice, even in a surface-incident configuration. However, if the Au film thickness is extremely thin, there is a concern that the incident light will pass through the Au. If the Au film thickness is 30 nm or more, 95% or more of the incident light can be reflected and pass through the light-absorbing layer 304 again.

[0044] Furthermore, in the case of III-V semiconductors, such as InGaAs absorption layers, the Joule heat generated at high light inputs is mainly inhibited from dissipating by the InP substrate, which has low thermal conductivity. However, in the photodetector of the present disclosure, the host substrate 301 that constitutes the photodetector is made of Si, which has excellent thermal conductivity at the time of completion of the device. This significantly improves the efficiency of Joule heat dissipation, enabling high current output even at high inputs.

[0045] As described above, according to this embodiment, a two-path structure can be realized in a front-side incident state without flip-chip mounting for a high-speed, high-sensitivity photodetector, which previously required flip-chip mounting. This achieves both ease of mounting and high speed and high sensitivity. Furthermore, the improved heat dissipation of the substrate also makes it possible to simultaneously achieve linearity of the output current with respect to the optical input intensity.

[0046] [Second embodiment] A second embodiment of the light-receiving element of the present disclosure will be described with reference to Fig. 5. Fig. 5 is a diagram showing a schematic configuration of the light-receiving element of this embodiment, with Fig. 5(a) being a cross-sectional view and Fig. 5(b) being a top view.

[0047] The light receiving element 500 of this embodiment differs from the light receiving element 300 of the first embodiment in that it includes a dielectric multilayer film 501 .

[0048] 5, the dielectric multilayer film 501 is formed on the upper surface of the light receiving element 500 excluding the upper surfaces of the electrode pads 308 and 309, and protects the upper surface of the light receiving element 500. The dielectric multilayer film 501 is configured to minimize the reflectance at the wavelength of light incident on the semiconductor layer 302, and also functions as an anti-reflection film.

[0049] In the manufacturing method of the light-receiving element 500 of this embodiment, as shown in FIG. 4(h), after forming the lead portion 306b of the electrode 306, the electrode pad 308, the lead portion 307b of the electrode 307, and the electrode pad 309, a multilayer film of TiO2 and SiO2 is formed over the entire wafer by sputtering. The thickness of each of these two types of film is individually designed taking into account the expected wavelength of incident light. After forming the dielectric multilayer film 501, through holes are formed only on the top surfaces of the electrode pads 308 and 309 using a standard photolithography process.

[0050] The light receiving element 500 of this embodiment: 1st Implementation In a positive manner In addition to the ease of mounting, high speed, and high sensitivity shown above, as well as the improved linearity of the output current relative to the optical input intensity, it is possible to simultaneously achieve even higher sensitivity with the anti-reflection coating and improved environmental reliability with the surface insulating film.

[0051] [Third embodiment] A third embodiment of the light-receiving element of the present disclosure will be described with reference to Fig. 6. Fig. 6 is a diagram showing a schematic configuration of the light-receiving element of this embodiment, with Fig. 6(a) being a cross-sectional view and Fig. 6(b) being a top view.

[0052] 6, in the light-receiving element 600 of this embodiment, the distance between the upper surfaces of the electrode pads 308 and 309 and the upper surface of the host substrate 301 is smaller than the distance between the upper surface of the p-type contact layer 305 and the upper surface of the host substrate 301. The light-receiving element 600 differs from the light-receiving element 500 of the second embodiment in that the heights of both the electrode pads 308 and 309 are formed at positions lower than the p-type contact layer 305 located at the top of the semiconductor layer 302, thereby matching the heights of the anode and cathode.

[0053] When evaluating the optical response characteristics of a fabricated photodetector, an RF probe that guarantees signal transmission up to several tens of GHz is often used. These RF probes are mostly a combination of a two-terminal probe with a GS configuration or a three-terminal probe with a GSG configuration, and therefore, if the heights of the anode and cathode are not aligned, it is not uncommon for probing to be difficult.

[0054] In the light receiving element 600 of this embodiment, the electrode pads 308 and 309 are positioned at the same height for the above-mentioned probe evaluation.

[0055] In the manufacturing method of the photodetector 600 of this embodiment, in the process of forming the polyimide interlayer insulating film 310 (FIG. 4(g)) in the manufacturing method of the photodetector 500 shown in FIG. 5, the pattern of the interlayer insulating film 310 is designed in advance so as not to overlap the electrode pads 308 and 309. After forming the polyimide interlayer insulating film 310, in the process of forming the electrode pad 309 (FIG. 4(h)), Au is patterned from the upper surface of the interlayer insulating film 310 to the upper surface of the host substrate 301 using photolithography and plating processes to form the lead portion 306b of the electrode 306. Then, the electrode pad 309 is formed on the lead portion 307b of the electrode 307, and the electrode pad 308 is formed on the lead portion 306b of the electrode 306 on the surface of the host substrate 301. After that, a multilayer film of TiO2 and SiO2 is formed over the entire wafer by sputtering. The thicknesses of these two types of films are individually designed taking into account the expected wavelength of incident light. After the dielectric multilayer film 501 is formed, through holes are formed only on the upper surfaces of the electrode pads 308 and 309 using a normal photolithography process.

[0056] The photodetector 600 of this embodiment can also achieve ease of mounting, high speed and high sensitivity, and improved linearity of the output current relative to the optical input intensity, similar to the photodetector 500 shown in Fig. 5. Furthermore, the photodetector 600 of this embodiment can simultaneously achieve even higher sensitivity due to the anti-reflection coating and improved environmental reliability due to the insulating film on the surface, while also achieving ease of probing in photoresponse measurement.

[0057] [Fourth embodiment] A fourth embodiment of the light-receiving element of the present disclosure will be described with reference to Fig. 7. Fig. 7 is a diagram showing a schematic configuration of the light-receiving element of this embodiment, with Fig. 7(a) being a cross-sectional view and Fig. 7(b) being a top view.

[0058] 7, in the light-receiving element 700 of this embodiment, the distance between the lower surfaces of the electrode pads 308 and 309 and the upper surface of the host substrate 301 is larger than the distance between the upper surface of the p-type contact layer 305 and the upper surface of the host substrate 301. The light-receiving element 700 differs from the light-receiving element 500 of the second embodiment in that the heights of both the electrode pads 308 and 309 are formed at positions higher than the p-type contact layer 305 located at the top of the semiconductor layer 302, thereby matching the heights of the anode and cathode.

[0059] Furthermore, the photodetector 700 of this embodiment differs from the photodetector 500 of the second embodiment in that the n-type contact layer 303 of the semiconductor layer 302 joined to the junction 307a of the electrode 307 on the host substrate 301 includes a selectively doped doped region 303b and an undoped region 303a.

[0060] 6, when evaluating the photoresponse characteristics of an actually fabricated photodetector, it is desirable that the heights of the electrode pads 308 and 309 be equal for the anode and cathode. In the photodetector 700 of this embodiment, the electrode pads 308 and 309 are positioned higher than the upper surface of the p-type contact layer at the top of the semiconductor layer 302.

[0061] Furthermore, in photodetectors such as avalanche photodiodes (APDs), which reduce the electric field on the surface to achieve low dark current and high reliability, the above objectives are achieved by confining the electric field inside the element and mitigating the electric field on the side of the element.

[0062] The photodetector 700 of this embodiment achieves electric field confinement by selectively doping the n-type contact layer 303 of the epitaxial layer, for example, in the process of preparing an epitaxial substrate (FIG. 4(a)) before the process of bonding the host substrate 301 to a wafer having a semiconductor layer 302 (FIG. 4(b)).

[0063] The method for manufacturing the photodetector 700 of this embodiment is the same as the method for manufacturing the photodetector 500 shown in FIG. 5 . For example, in the step of preparing an epitaxial substrate ( FIG. 4( a) ), the epitaxial wafer on the semiconductor layer 302 side used in wafer bonding is selectively doped by Si ion implantation to form a doped region 302b in the n-type contact layer 303, which is the top surface layer. The n-type contact layer 303, which is the top surface layer, should have as low an impurity concentration as possible to improve the field confinement effect. Typically, it should be undoped InP. Furthermore, mesas are formed by wet etching the n-type contact layer 303, the light absorption layer 304, and the p-type contact layer 305. In the step of forming the semiconductor layer 302 ( FIG. 4( e) ), the semiconductor layer 302 is left, along with the portions where the electrode pads 308 and 309 will be formed (mesas are also formed on the right and left sides of the semiconductor layer 302). After forming the polyimide interlayer insulating film 310 (FIG. 4(g)), in the process of forming the electrode pad 309 (FIG. 4(h)), Au is patterned by photolithography and plating processes from the top surface of the interlayer insulating film 310 to the top surface of the left epitaxial layer remaining together with the semiconductor layer 302 (including the side surfaces of the interlayer insulating film 310 and the surface of the host substrate 301) to form the lead portion 306b of the electrode 306. At the same time, Au is patterned from the top surface of the lead portion 307b of the electrode 307 to the top surface of the right epitaxial layer remaining together with the semiconductor layer 302 (including the side surfaces of the interlayer insulating film 310 and the surface of the host substrate 301) to form the lead portion 307c of the electrode 307. An electrode pad 308 is formed on the lead portion 306b, and an electrode pad 309 is formed on the lead portion 307c. Then, a multilayer film of TiO2 and SiO2 is formed over the entire surface of the wafer by sputtering. The thickness of each of these two types of film is individually designed taking into consideration the wavelength of the expected incident light. After the dielectric multilayer film is formed, a through hole is formed only in the pad portion using a normal photolithography process.

[0064] Like the photodetector 600 shown in FIG. 6, the photodetector 700 of this embodiment also achieves ease of mounting, high speed and high sensitivity, improved linearity of output current with respect to optical input intensity, ease of probing, low dark current, and high reliability.

[0065] [Fifth embodiment] A fifth embodiment of the light-receiving element of the present disclosure will be described with reference to Fig. 8. Fig. 8 is a diagram showing a schematic configuration of the light-receiving element of this embodiment, with Fig. 8(a) being a cross-sectional view and Fig. 8(b) being a top view.

[0066] As shown in Fig. 8, the photodetector 800 of this embodiment is realized by etching the structure for electric field confinement described in relation to the photodetector 700 in Fig. 7. As shown in Fig. 8, the active region of the photodetector 800 in its operating state is defined by reducing the diameter of the p-type contact layer 305 of the semiconductor layer 302, so that no electric field is generated on the side surfaces of the other layers including the light absorption layer 304, or the electric field strength is weaker than that in the center.

[0067] A specific manufacturing method for the photodetector 800 of this embodiment is the same as the manufacturing method for the photodetector 600 shown in FIG. 6 , except that mesas for the n-type contact layer 303, the light absorption layer 304, and the p-type contact layer 305 are formed by wet etching. In the step of forming the semiconductor layer 302 ( FIG. 4( e)), portions for forming the electrode pads 308 and 309 are also left (mesas are also formed on the right and left sides of the semiconductor layer 302). Furthermore, a separate photomask is used to process the p-type contact layer 305 so that its diameter is smaller than those of the light absorption layer 304 and the n-type contact layer. After forming the polyimide interlayer insulating film 310 ( FIG. 4( g)), in the step of forming the electrode pad 309 ( FIG. 4( h)), the lead portion 306b of the electrode 306 and the lead portion 307c of the electrode 307 are formed, and the electrode pad 309 is then formed on the lead portion 307c. Electrode pad 308 is formed on lead-out portion 306b, and electrode pad 309 is formed on lead-out portion 307c. Then, a multilayer film of TiO2 and SiO2 is formed over the entire wafer surface by sputtering. The thickness of each of these two films is individually designed taking into account the expected wavelength of incident light. After the dielectric multilayer film is formed, through-holes are formed only in the pad areas using a standard photolithography process.

[0068] The photodetector 800 of this embodiment, like the photodetectors 600 and 700 described above, can achieve ease of mounting, high speed and high sensitivity, and improved linearity of the output current relative to the optical input intensity, as well as ease of probing, low dark current, and high reliability.

[0069] In the above description of various embodiments of the light-receiving element, a substrate using Si has been exemplified as the host substrate 301, but a substrate using other materials may be used instead of Si as long as the material has high mechanical strength and excellent heat dissipation properties. Examples of other materials that may be used include SiC.

[0070] In addition, in the description of various embodiments of the photodetector, a PIN structure having an InGaAs absorption layer has been exemplified as the epitaxial layer structure of the semiconductor layer 302, but for example, a UTC-PD structure having a p-type absorption layer or an APD structure having a multiplication layer and an electric field control layer may also be used.

[0071] In addition, in the description of various embodiments of the light-receiving element, polyimide is used as the interlayer insulating film 310, but there are no restrictions on the material as long as it is a commonly used interlayer insulating film such as BCB. Furthermore, the dielectric multilayer film 501 functioning as an anti-reflection film is not limited to SiO2 / TiO2, and may be made of Ta2O5 or SiN.

[0072] In addition, in the explanation of various embodiments of the light receiving element, a single layer of Au is used as the electrode 307, which is a bonding metal, but a metal multilayer film such as Ti / Au may also be used to improve adhesion. [Industrial Applicability]

[0073] It is possible to provide a light-receiving element that can maintain high speed and high sensitivity while omitting the flip-chip mounting process when mounting it on an optical receiver.

Claims

1. A substrate; a first electrode metal formed on an upper surface of the substrate; a semiconductor layer bonded to an upper surface of the first electrode metal; a second electrode metal formed on the upper surface of the semiconductor layer; Equipped with The semiconductor layer is a first semiconductor contact layer in contact with the first electrode metal; a second semiconductor contact layer in contact with the second electrode metal; a semiconductor absorption layer between the first semiconductor contact layer and the second semiconductor contact layer; the first electrode metal includes a lead-out path for transmitting a signal to an anode electrode or a cathode electrode; a first electrode pad connected to the first electrode metal; a second electrode pad connected to the second electrode metal; Furthermore, a light-receiving element, wherein the first electrode pad and the second electrode pad are formed at the same height and at a position where the distance between the upper surfaces of the first electrode pad and the second electrode pad and the upper surface of the substrate is smaller than the distance between the upper surface of the second semiconductor contact layer and the upper surface of the substrate.

2. A substrate; a first electrode metal formed on an upper surface of the substrate; a semiconductor layer bonded to an upper surface of the first electrode metal; a second electrode metal formed on the upper surface of the semiconductor layer; Equipped with The semiconductor layer is a first semiconductor contact layer in contact with the first electrode metal; a second semiconductor contact layer in contact with the second electrode metal; a semiconductor absorption layer between the first semiconductor contact layer and the second semiconductor contact layer; the first electrode metal includes a lead-out path for transmitting a signal to an anode electrode or a cathode electrode; a first electrode pad connected to the first electrode metal; a second electrode pad connected to the second electrode metal; Furthermore, A light-receiving element, wherein the first electrode pad and the second electrode pad are of the same height and are formed at a position where the distance between the lower surfaces of the first electrode pad and the second electrode pad and the upper surface of the substrate is greater than the distance between the upper surface of the second semiconductor contact layer and the upper surface of the substrate.

3. A photodetector as described in claim 1 or 2, further comprising an anti-reflection film formed on the second semiconductor contact layer.

4. 3. The light-receiving element according to claim 1, wherein the first electrode metal comprises gold having a thickness of at least 30 nm.

5. 3. The photodiode according to claim 1, wherein the first semiconductor contact layer includes a selectively doped region.

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