Light-receiving device

Abstract

The purpose of the present invention is to provide a light-receiving device that is capable of eliminating a "trade-off between operation speed and sensitivity" and is easy to manufacture, and a method for manufacturing said device.　A light-receiving device according to the present invention is characterized by comprising: a pn junction structure in which a p-type semiconductor layer (12A, 13) and an n-type semiconductor layer (12B, 14) sandwich a light absorption layer (11); a half mirror layer (17) on one side of the pn junction structure, the half mirror layer (17) transmitting light from the outside to the pn junction structure and reflecting light from the light-absorption-layer side to the light-absorption-layer side; and a highly reflective layer (15) on the other side of the pn junction structure, the highly reflective layer (15) reflecting the light from the light-absorption-layer side to the light-absorption-layer side, the light-receiving device furthermore being characterized in that the thickness W1 between the highly reflective layer and the light absorption layer, the thickness W2 between the half mirror layer and the light absorption layer, and the thickness Wabs of the light absorption layer are set to any combination having a maximum value in quantum efficiency in the light absorption layer at the wavelength of the light.

Description

Light receiving device

[0001] The present disclosure relates to a light-receiving device in which semiconductor layers are stacked.

[0002] Semiconductor photodetector devices are widely used in various fields that handle optical signals, and are essential devices for applications such as optical communication, optical measurement, optical spectroscopy, optical imaging, etc. Furthermore, if a semiconductor photodetector device has the property of being able to increase its electrical saturation output, it can ensure a sufficient S / N ratio in direct OE conversion from an optical signal to an electrical signal (typically a THz wave) even when an electrical amplifier does not exist or cannot be used.

[0003] Here, the conversion efficiency of the optical receiving device is an important indicator of the overall system performance. This is because as the frequency of the electrical signal handled after OE conversion increases, the optical receiving device is constrained by the "trade-off between operating speed and sensitivity," meaning that increasing operating speed reduces sensitivity. If the optical signal input is constant, a decrease in optical receiving sensitivity will reduce the electrical signal output.

[0004] For example, as of 2024, digital optical communication systems based on 50 to 100 Gbaud will use photodiodes (PDs) and avalanche photodiodes (APDs) as light-receiving devices for long wavelength bands (O-band, C-band, L-band, etc.). However, they are now facing a situation where the "trade-off between operating speed and sensitivity," which was not an issue in previous systems, has become a problem. Specifically, in order to reduce the delay time of carrier travel inside PD and APD elements, it is necessary to thin the light absorption layer, i.e., to reduce sensitivity while ensuring operating speed.

[0005] Furthermore, in the field of "THz wireless communication," in which signals are transmitted by modulating a THz wave carrier using a laser light source, the trade-off between operating speed and sensitivity is more severely restricted than in the case of optical modulation of so-called base-band signals, because the frequency of the THz wave carrier is high.

[0006] Efforts to increase the electrical output of high-speed PDs and APDs have been underway since the 1980s in the fields of measurement technology and optical microwave technology, which require ultrafast optical-to-electrical conversion. Typical technologies include distributed traveling-wave PDs (see, for example, Non-Patent Document 1) and waveguide PDs (see, for example, Non-Patent Document 2). However, practical application of optical receiving devices using these technologies remains difficult. One reason for this is that, even though the carrier response speed of these optical receiving devices has been improved, they have issues such as large junction capacitance and difficulty in matching the speed of light and electrical signals, so their structures are not necessarily advantageous for higher speeds (100 GHz or higher to the THz range). "Improving sensitivity" to increase the output level for a limited optical input remains a continuing challenge.

[0007] Here, an ultrafast PD will be described using FIGS. 1 to 3. FIG. 1 is a cross-sectional view illustrating a typical bottom-illuminated, 300 GHz-band planar PD. This PD has a wide bandgap layer (32A) and a wide bandgap semiconductor anode layer (33) on the anode side, and a wide bandgap layer (32B) and a wide bandgap semiconductor cathode layer (34) on the cathode side, sandwiching an optical absorption layer (31) with a thickness on the order of 0.1 to 0.15 μm. This PD is placed on a semi-insulating InP substrate (38) so that the semiconductor cathode layer (34) is in contact with the semi-insulating InP substrate (38). An anode electrode (35) and a cathode electrode (36) are formed in ohmic contact with the wide bandgap semiconductor anode layer (33) and the wide bandgap semiconductor cathode layer (34), respectively.

[0008] The light is incident from the InP substrate 38 side. Since there is little light absorption in the one-way light propagation, the anode electrode 35 is used as a metal reflective film to utilize the light reflected from the anode side.

[0009] 2 is a diagram illustrating the light receiving sensitivity of the PD in FIG. 1. The thickness W of the light absorption layer (31) ａｂｓ When the thickness is 0.155 μm, 0.135 μm, and 0.10 μm, the distance W from the light absorption layer (31) to the anode electrode (35) (the total thickness of the wide band gap layer (32A) and the wide band gap semiconductor anode layer (33))１ The change in the light receiving sensitivity (A / W) is calculated based on the anode electrode (35) assumed to be made of Ti.

[0010] The reason why the light receiving sensitivity is wavy is because it follows the optical standing wave (optical power) inside the element, and it does not mean that resonance absorption is occurring. ａｂｓ Since the distance is short, W ａｂｓ The position of W １ The wave changes in sensitivity occur due to the change in W. ａｂｓ W = 0.135 μm, which is near the peak of the waveform １ = 0.19 μm, the light receiving sensitivity is calculated to be about 0.22 A / W.

[0011] However, W ａｂｓ Determine the position of W １ Because of the risk of position control, W1 is often set to about 0.04 to 0.06 μm, and the light receiving sensitivity is actually about 0.15 A / W. [Supplementary information] The above has the following meaning. Film thickness W １ The wide band gap layer (32A) and the wide band gap semiconductor anode layer (33) that constitute the W are formed by epitaxial growth, but when attempting to form a thick film, it becomes difficult to control the film thickness. １ If the film is thick, such as W = 0.19 μm, the film thickness deviates from the design value, making it difficult to match the peak of the light receiving sensitivity. １ The thickness of the film is often controlled by thin film.

[0012] Figure 3 is W ａｂｓ and W １ This is a mapping of the light receiving sensitivity with two parameters. ａｂｓ and W １ The change in light receiving sensitivity to W is periodic. ａｂｓ As the value of W increases, the light receiving sensitivity tends to increase. ａｂｓ = 0.135 μm, W １This is the region near the peak of the waveform at 0.19 μm.

[0013] On the other hand, structures that increase the light receiving sensitivity by incorporating a resonant cavity function into the PD structure have also been reported (see, for example, Non-Patent Documents 3, 4, and 5). However, most of these structures operate at a low response speed, use a quarter-wave multilayer film (e.g., a Distributed Bragg Reflector (DBR)) incorporated into the semiconductor during growth as a highly reflective film, or have a small resonant absorption effect. In principle, these structures can increase the light receiving sensitivity. However, because DBRs are thick films, there are issues with controllability during epitaxial growth and heat dissipation methods for the element, making them difficult to realize.

[0014] Looking back at history, in the 100 GHz and higher frequency range, various attempts have been made, but the reality is that PDs that have normal light incidence from the backside or that have an overhanging PD chip with effective backside incidence due to refraction from the side are used in products. The latter PD structure requires a large junction area, so PDs with normal light incidence from the backside are advantageous in terms of speed.

[0015] Ultimately, what is required is to increase the speed and sensitivity of PD elements, while at the same time raising the saturation point of output, and to achieve a higher electrical output level while improving the trade-off between speed and sensitivity.

[0016] G. Rangel-Sharp et al., "Traveling-Wave Photodetectors: A Review," The Radio Science Bulletin No 311 (December, 2004). Efthymios Rouvalis et al., "Traveling-wave Uni-Traveling Carrier Photodiodes for continuous wave THz generation," Optics Express Vol. 18, Issue 11, pp. 11105-11110 (2010). Ravi Kuchibhotla et al., "Low-Voltage High-Gain Resonant-Cavity Avalanche Photodiode," IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 3, NO. 4, APRIL 1991. Albert Chin and T.Y. Chang, "Enhancement of Quantum Efficiency in Thin Photodiodes Through Absorptive Resonance," JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL 9, NO. 3, MARCH 1991. P. Latzel et al., "Generation of mW level in the 300-GHz band using resonant-cavity-enhanced uni-traveling carrier photodiodes," IEEE Trans. Terahertz Sci. and Technol., vol. 7, no. 6, pp. 800-807, 2017.

[0017] A planar PD with perpendicular light incidence on the light absorption layer of the light receiving device is the most advantageous in terms of reducing junction capacitance. However, due to the "trade-off between operating speed and sensitivity" mentioned above, PDs designed with a thin light absorption layer (for example, for applications with operating frequencies of 100 GHz or higher, a thickness of about 5000 Å from the optical wavelength within the crystal) have the problem that light receiving sensitivity is not necessarily sufficient, and a larger optical input power is required to obtain a certain output.

[0018] Therefore, in order to solve the above problems, an object of the present invention is to provide a light-receiving device and a method for manufacturing the same that can alleviate the "trade-off between operating speed and sensitivity," i.e., that minimizes deterioration in sensitivity even when the operating speed is increased, and that is easy to manufacture.

[0019] In order to achieve the above object, the light-receiving device of the present invention has a pn junction structure including a light absorption layer sandwiched between a highly reflective layer and a half mirror layer that allows light to enter, thereby adding a resonant cavity function.

[0020] Specifically, the light receiving device according to the present invention comprises a pn junction structure in which a light absorbing layer is sandwiched between a p-type semiconductor layer and an n-type semiconductor layer, a half mirror layer on one side of the pn junction structure that transmits external light to the pn junction structure and reflects light from the light absorbing layer side toward the light absorbing layer side, and a highly reflective layer on the other side of the pn junction structure that reflects the light from the light absorbing layer side toward the light absorbing layer side, wherein a thickness W between the highly reflective layer and the light absorbing layer is １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ are set to any of the combinations that give a maximum quantum efficiency in the light absorption layer at the wavelength of the light.

[0021] A method for manufacturing a light-receiving device according to the present invention is a method for manufacturing a light-receiving device having a pn junction structure in which a p-type semiconductor layer and an n-type semiconductor layer sandwich a light-absorbing layer, the method comprising: forming, on one side of the pn junction structure, a half mirror layer that transmits external light to the pn junction structure and reflects light from the light-absorbing layer side toward the light-absorbing layer side; forming, on the other side of the pn junction structure, a highly reflective layer that reflects the light from the light-absorbing layer side toward the light-absorbing layer side; and forming a thickness W between the highly reflective layer and the light-absorbing layer. １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ is set to any of the combinations that give a maximum quantum efficiency in the light absorption layer at the wavelength of the light.

[0022] This photodetector device has an optically highly reflective layer on one side of the semiconductor layer (pn junction structure) that forms the PD, and an optical half-mirror layer on the other side. Here, in this photodetector device, the optical half-mirror layer is stably disposed between the semiconductor layer and the host substrate (reference numeral 17 in Figure 4 ), rather than being incorporated into the semiconductor layer as in the past. Alternatively, this photodetector device may have a properly designed half-mirror layer or a protective film that is sufficiently thinner than the wavelength formed between the air layer and the semiconductor layer (reference numeral 27 in Figure 7 ).

[0023] Even if the light absorption layer is thinned to increase speed, the light receiving sensitivity can be increased by absorbing light in the resonant cavity using the high-reflection layer and half mirror layer.In addition, since the resonant cavity function is not configured using a DBR as in conventional devices, manufacturing is easy and the heat dissipation of the device can be improved.

[0024] Therefore, the present invention can alleviate the "trade-off between operating speed and sensitivity," i.e., it can provide a light-receiving device and a method for manufacturing the same that can increase the operating speed without deteriorating the sensitivity as much as possible and that is easy to manufacture.

[0025] Here, it is preferable that the highly reflective layer also functions as an electrode.

[0026] The device may be a back-illuminated type in which the half mirror layer is formed on the host substrate side, and the highly reflective layer also functions as an electrode, or may be a front-illuminated type in which the highly reflective layer is formed on the host substrate side, and the highly reflective layer also functions as an electrode.

[0027] For example, the highly reflective layer is a metal layer, and the half mirror layer is a dielectric layer.

[0028] The above inventions can be combined as much as possible.

[0029] By using the "resonant cavity absorption" technology of the photodiode (PD) of this application, it is possible to increase the light receiving sensitivity of PD, which was previously limited by the "trade-off between operating speed and sensitivity" constraint of conventional technology. In other words, it is possible to increase the electrical output under constant optical input conditions. Since the electrical output is equal to the square of (current sensitivity A / W), the greater the change in sensitivity, the greater the effect of increasing output.

[0030] The present invention can provide a light-receiving device and a method for manufacturing the same that can alleviate the "trade-off between operating speed and sensitivity," that is, can increase the operating speed without deteriorating the sensitivity as much as possible and is easy to manufacture.

[0031] FIG. 1 is a diagram for explaining the structure of a related light-receiving device. FIG. 2 is a diagram for explaining the light sensitivity characteristics of a related light-receiving device. FIG. 3 is a diagram for explaining the light sensitivity characteristics of a related light-receiving device. FIG. 4 is a diagram for explaining the structure of a light-receiving device according to the present invention. FIG. 5 is a diagram for explaining the light sensitivity characteristics of a light-receiving device according to the present invention. FIG. 6 is a diagram for explaining the light sensitivity characteristics of a light-receiving device according to the present invention. FIG. 7 is a diagram for explaining the structure of a light-receiving device according to the present invention. FIG. 8 is a diagram for explaining the light sensitivity characteristics of a light-receiving device according to the present invention.

[0032] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0033] 4 is a cross-sectional view illustrating a light-receiving device of this embodiment. The light-receiving device includes a pn junction structure in which a light-absorbing layer (11) is sandwiched between p-type semiconductor layers (12A, 13) and n-type semiconductor layers (12B, 14), a half mirror layer (17) on one side of the pn junction structure that transmits external light to the pn junction structure and reflects light from the light-absorbing layer side toward the light-absorbing layer side, and a highly reflective layer (15) on the other side of the pn junction structure that reflects the light from the light-absorbing layer side toward the light-absorbing layer side, and a thickness W between the highly reflective layer and the light-absorbing layer. １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ are set to any of the combinations that give a maximum quantum efficiency in the light absorption layer at the wavelength of the light.

[0034] This light-receiving device is a back-illuminated type in which the half mirror layer (17) is formed on the host substrate (18) side, and the highly reflective layer (15) also functions as an electrode. The host substrate (18) is, for example, SiC. Figure 5 is a diagram illustrating the light-receiving sensitivity of this light-receiving device.

[0035] The light-receiving device has a basic structure of a so-called p-up type, with the p-side (anode side) being the upper surface. ａｂｓ The upper layer of the pn junction is a wide bandgap layer (12A) and a wide bandgap semiconductor anode layer (13), and the lower layer is a wide bandgap layer (12B) and a wide bandgap semiconductor cathode layer (14). The pn junction structure up to this point is not significantly different from the conventional high-speed PD structure.

[0036] This photodetector device connects an anode electrode (15) made of a refractory metal, such as Mo, which can also function as an optically highly reflective layer, to the wide bandgap semiconductor anode layer (13). The reflectivity of refractory Mo is slightly better than that of the conventionally used Ti. The reason for using a refractory metal is to suppress reaction between the metal and the semiconductor electrode layer and ensure stable and reliable operation. While the reflection loss is somewhat greater than that of an electrode mainly made of Au, it is on the order of about 5%, which is not a major problem for ultra-high speed applications.

[0037] A Si layer is placed between the bottom of the wide bandgap semiconductor cathode layer (14) and the host substrate (18). ３ N ４ A half-mirror dielectric layer (17) such as a silicon dioxide film is disposed. Compared with a semiconductor DBR (Distributed Bragg Reflector) layer used as a conventional reflective layer, a Si ３ N ４ Although the reflectance of the combination with the SiC / Si film remains low, the effect as a half mirror is recognized. ３ N ４ When the reflectance is calculated when the film is combined with InGaAsP (Eg=0.90 eV), it is found to be as small as R=15%, and a strong resonance absorption effect cannot be expected.

[0038] However, in the case of an ultra-high speed PD with a thin light absorption layer, the maximum light receiving sensitivity (responsivity) is improved to 0.42 A / W (W as shown in FIG. 5) compared to 0.22 A / W (FIG. 2) when the absorption layer thickness is W abs = 0.135 μm in the conventional PD structure. ２ The thickness is constant at 0.66 μm, which is the condition that gives the maximum value of light receiving sensitivity).

[0039] The important point is that the same W ａｂｓ , W ２ If it is a combination of １ Even if the value changes, the operating speed does not change, so in order to improve the operating speed, ａｂｓ The advantage of this is that it is possible to increase the light receiving sensitivity even when the substrate is thin, thereby mitigating the "trade-off between operating speed and sensitivity."

[0040] The thickness of the wide bandgap layer (12A) plus the wide bandgap semiconductor anode layer (13) = W １ , and the thickness of the light absorbing layer (11) = W ａｂｓ This changes the positional relationship of the light absorption layer (11) from the anode electrode (15), which also functions as an optically highly reflective layer. The interface of the optically highly reflective layer becomes a "node" of the optical field amplitude of the incident light, generating a standing wave, and the light receiving sensitivity is determined by the position and thickness of the light absorption layer (11) relative to the standing wave. On the other hand, the thickness of the wide band gap layer (12B) plus the wide band gap semiconductor cathode layer (14) = W ２ is used to adjust the length of the optical cavity of the PD, and W １ and W ａｂｓ This parameter determines the light receiving sensitivity by changing the state of the standing wave while being related to the

[0041] FIG. 5 shows the W ２ When fixed, W １ The sensitivity change to three W ａｂｓ Value (W ａｂｓ = 0.10, 0.135, 0.155 μm). ａｂｓ and W １ This is a mapping of the light receiving sensitivity with two parameters. １ and W ａｂｓ The area A in FIG. 6 has a clear periodic structure with respect to the W ａｂｓ = 0.135 μm, W １ This is the region near the peak of the waveform at 0.19 μm.

[0042] 5 and 6, the quantum efficiency QE, which is the light receiving sensitivity, is １ , W ａｂｓ , W ２ There are periodic peaks (extremes) for It is as follows.

[0043] (Embodiment 2) Fig. 7 is a cross-sectional view illustrating a light-receiving device of this embodiment. The pn junction structure is the same as the pn junction structure described in embodiment 1 (Fig. 4). This light-receiving device comprises a pn junction structure in which a light-absorbing layer (21) is sandwiched between p-type semiconductor layers (22B, 24) and n-type semiconductor layers (22A, 23), a half mirror layer (27) on one side of the pn junction structure that transmits external light to the pn junction structure and reflects light from the light-absorbing layer side toward the light-absorbing layer side, and a highly reflective layer (26) on the other side of the pn junction structure that reflects the light from the light-absorbing layer side toward the light-absorbing layer side, and a thickness W between the highly reflective layer and the light-absorbing layer. １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ are set to any of the combinations that give a maximum quantum efficiency in the light absorption layer at the wavelength of the light.

[0044] This light-receiving device is a front-illuminated type in which the highly reflective layer (26) is formed on the host substrate (28) side, and the highly reflective layer (26) also functions as an electrode. The host substrate (28) is, for example, SiC. FIG. 8 is a diagram illustrating the light-receiving sensitivity of this light-receiving device.

[0045] This light-receiving device is a so-called n-up type with the cathode side facing up. ａｂｓ The upper layer of the pn junction is a wide bandgap layer (22A) and a wide bandgap semiconductor cathode layer (23), and the lower layer is a wide bandgap layer (22B) and a wide bandgap semiconductor anode layer (24). The pn junction structure up to this point is not significantly different from the conventional high-speed PD structure.

[0046] The present light-receiving device is characterized by the insertion of an anode electrode layer (26) made of a refractory metal, such as Mo, which can also function as an optically highly reflective layer, between a host substrate (28) such as SiC and a wide bandgap semiconductor anode layer (24). This light-receiving device is completely different from the structure of the light-receiving device shown in Figure 4, in which the semiconductor electrode layer (wide bandgap semiconductor cathode layer (14)) is pulled out to the side and then contacts the cathode electrode (16). Since the anode electrode layer (26) is in vertical contact with the wide bandgap semiconductor anode layer (24), the series resistance can be reduced.

[0047] The half mirror layer (27) is a thin dielectric protective film. Alternatively, the half mirror layer (27) may be a protective layer formed between the air and the semiconductor layer that is sufficiently thinner than the wavelength of light. Even though it is a thin film, the reflectance R is 31%, and the Si ３ N ４ This is significantly larger than the reflectance R of the film, which is 15%. A ring-shaped cathode electrode (25) is disposed around the half mirror layer (27) and is in contact with the pn junction structure.

[0048] FIG. 8 shows the W ２ When fixed, W １ The sensitivity change to three W ａｂｓ Value (W ａｂｓ For example, when the thickness of the light absorption layer is W ａｂｓ = 0.135 μm, W １ When the absorption layer thickness is adjusted to 0.2 μm, the peak value of the light receiving sensitivity rises to 0.53 A / W. This is a 2.4-fold improvement over the 0.22 A / W (Figure 2) obtained when the absorption layer thickness is W = 0.135 μm in the conventional PD structure, and corresponds to an approximately 6-fold improvement in the electrical output for the same optical input intensity.

[0049] As explained in the first embodiment, the important point is that the same W ａｂｓ , W ２ If it is a combination of １ Even if the value changes, the operating speed does not change, so in order to improve the operating speed, ａｂｓThe advantage of this embodiment is that the light receiving sensitivity can be increased even if the thickness of the light absorbing layer 21 is thin, thereby eliminating the trade-off between operating speed and sensitivity. As in the first embodiment, the change in light receiving sensitivity is determined by the relative position of the light absorbing layer 21 with respect to the standing wave of the optical cavity that the PD constitutes.

[0050] Figure 9 is W ａｂｓ and W １ This is a mapping of the light receiving sensitivity with two parameters. １ and W ａｂｓ The width of the light sensitivity contour line is narrower than in the case of Figure 3, and the light sensitivity W １ The area A in FIG. 9 corresponds to the above-mentioned W ａｂｓ = 0.135 μm, W １ This is the region near the peak of the waveform at 0.19 μm.

[0051] 8 and 9, the quantum efficiency QE, which is the light receiving sensitivity, is １ , W ａｂｓ , W ２ There are periodic peaks (extremes) for It is as follows.

[0052] Achieving high photosensitivity also means that the thickness of the semiconductor layer can be more tightly controlled. The photosensitive device of this embodiment has the advantage that the photosensitivity can be brought close to its maximum value at the desired light wavelength by monitoring the photosensitivity in a nearly completed state of the device and thinning the wide bandgap semiconductor cathode layer (23) by etching or adjusting the thickness of the dielectric protection film (half mirror layer (27)).

[0053] Other Embodiments In the light-receiving devices of Embodiments 1 and 2, the semiconductor layer on the cathode side is described as being n-type and the semiconductor layer on the anode side is described as being p-type, but the present invention is not limited to this configuration. That is, the light-receiving device according to the present invention may have a configuration in which the semiconductor layer on the cathode side is replaced with a p-type and the semiconductor layer on the anode side is replaced with an n-type.

[0054] (Note) This disclosure relates to ultrafast optical signal reception, terahertz wave generation and photoelectric signal conversion using optical signals, and more specifically, to the structure of semiconductor photodetector devices used therein, and provides technology for more efficiently achieving high-speed, high-frequency operation. In other words, the objective of this invention is to improve the photodetector sensitivity in order to increase the output of PDs. More directly, it aims to easily realize resonant cavity absorption, which has previously been difficult to fabricate due to its complex structure.

[0055] The means for solving the above problems according to the present invention are as follows.

[0056] [Configuration 1] A pn ​​junction diode including, as components, a semiconductor laminated structure including a light absorbing layer, two wide band gap layers stacked above and below this layer, and a wide band gap semiconductor anode layer and wide band gap semiconductor cathode layer arranged adjacent to the outer sides thereof, and an anode electrode and a cathode electrode for electrically connecting the wide band gap anode layer and the wide band gap cathode layer, respectively, wherein the pn junction diode has an optically highly reflective layer arranged on one side and an optical half mirror layer arranged adjacent to the upper and lower outer sides of the wide band gap semiconductor anode layer and the wide band gap semiconductor cathode layer, and the pn junction diode has an optical configuration in which an incident light signal is introduced from the half mirror layer side, and further wherein the total thickness of the wide band gap layer arranged between the optically highly reflective layer and the light absorbing layer is W １ , the thickness of the light absorbing layer is W ａｂｓ , the total thickness of the wide band gap layer between the light absorption layer and the half mirror layer is W ２ When this is done, the quantum efficiency QE of the optical absorption at the wavelength of the predetermined optical input signal is set to have a maximum value, that is, To satisfy the conditions of W １ , W ａｂｓ , W ２ a pn junction diode having a layer structure in which a set of the above-mentioned optically highly reflective layer is a layer made of a refractory metal, and also serves as a function for electrically connecting to a semiconductor anode layer or a semiconductor cathode layer.

[0057] [Configuration 2] A semiconductor light-receiving device according to configuration 1, characterized in that the half mirror layer side is bonded to a host substrate that is optically transparent and has mechanical strength and high thermal conductivity, and the light reflectance and transmittance are determined by the combination of the host substrate, the half mirror layer, and a semiconductor layer adjacent to the half mirror layer.

[0058] [Configuration 3] A semiconductor light-receiving device according to Configuration 1, characterized in that the optically highly reflective layer side made of a metal layer is bonded to a host substrate having mechanical strength and high thermal conductivity, and the optical reflectance and transmittance are determined by a combination of an air layer, the half mirror layer, and a semiconductor layer adjacent to the half mirror layer.

[0059] [Effects] The photodiode (PD) structure of the present invention can significantly increase the light receiving sensitivity of PDs by using the technology of "resonant cavity absorption." In high-speed PD structures, sensitivity is sacrificed to ensure operating speed when the frequency increases (e.g., 300 GHz operation), but this technology is one solution for improving this. The calculated current sensitivity for a 300 GHz structure is 2.4 times higher, which is equivalent to six times the electrical output. Since the electrical output can be significantly increased under limited optical input conditions, this has great practical advantages.

[0060] 11, 21, 31: Light absorption layer 12A, 22A, 32A: Wide band gap layer 12B, 22B, 32B: Wide band gap layer 13, 24, 33: Wide band gap semiconductor anode layer 14, 23, 34: Wide band gap semiconductor cathode layer 15: Anode electrode (highly reflective layer) 16: Cathode electrode 17, 27: Dielectric layer (half mirror layer) 18, 28, 38: Host substrate 25: Cathode electrode 26: Anode electrode (highly reflective layer)

Claims

1. A pn ​​junction structure in which a light absorbing layer is sandwiched between a p-type semiconductor layer and an n-type semiconductor layer; a half mirror layer on one side of the pn junction structure that transmits external light to the pn junction structure and reflects light from the light absorbing layer side toward the light absorbing layer side; and a highly reflective layer on the other side of the pn junction structure that reflects the light from the light absorbing layer side toward the light absorbing layer side, wherein a thickness W between the highly reflective layer and the light absorbing layer is １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ and the combination of the light absorbing layer and the light receiving layer is set to any one of the combinations that gives a maximum quantum efficiency at the wavelength of the light.

2. The light-receiving device according to claim 1, wherein the highly reflective layer also functions as an electrode.

3. The light-receiving device according to claim 1, characterized in that it is a back-illuminated type in which the half mirror layer is formed on the host substrate side, and the highly reflective layer also functions as an electrode.

4. The light-receiving device according to claim 1, which is a front-illuminated type in which the highly reflective layer is formed on the host substrate side, and the highly reflective layer also functions as an electrode.

5. The light-receiving device according to claim 1, wherein the highly reflective layer is a metal layer, and the half mirror layer is a dielectric layer.

6. A method for manufacturing a light-receiving device having a pn junction structure in which a p-type semiconductor layer and an n-type semiconductor layer sandwich a light-absorbing layer, comprising: forming a half-mirror layer on one side of the pn junction structure that transmits external light to the pn junction structure and reflects light from the light-absorbing layer side toward the light-absorbing layer side; forming a highly reflective layer on the other side of the pn junction structure that reflects the light from the light-absorbing layer side toward the light-absorbing layer side; and forming a thickness W between the highly reflective layer and the light-absorbing layer. １ , the thickness W between the half mirror layer and the light absorbing layer ２ and the thickness W of the light absorbing layer ａｂｓ and setting the light receiving layer to any of the combinations that give a maximum quantum efficiency in the light absorption layer at the wavelength of the light.

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